‘A: Nelsen et al. examined several sediment cores from the hypoxia region for the mineral
glauconite (a mineral that is formed under reducing conditions caused by hypoxia/anoxia). These
data indicate that there has been an increase in the duration of hypoxia in recent years.

As the research into areas of hypoxia and carbon flux on the Louisiana-Texas Continental Shelf
only go back to the 1970's, it is difficult to determine the long term trends in riverine loading,
phytoplankton production, and temporal and spatial extents of hypoxia. In order to assess
changes in these parameters, researchers have used sedimentary evidence to infer the past state of
the Louisiana-Texas Continental Shelf ecosystem. The main thrusts of this research have been to
provide corollary evidence that 1) primary production has increased and 2) hypoxic events have
increased in duration and severity.

Historical evidence for increased phytoplankton production is from studies of sediment biogenic
silica concentrations (Turner and Rabalais, 1994) and sediment organic carbon concentrations
and isotope abundance (Eadie et al., 1994). Turner and Rabalais (1994) found sediment biogenic
silica from diatom frustules had a constant concentration from 1900 to 1960 but increased
dramatically from 1960 to the present. They concluded that diatom production in the plume and
diatom surface to bottom flux beneath the Mississippi River plume have increased during this
century. However, the possibility that dissolution of biogenic silica is at least: partly responsible
for these differences cannot be overlooked. :

Eadie et al. (1994) found the 8-"C of the sediment organic carbon became lighter with
increasing age of the sediments. The &-“C of terrigenous POC in the Mississippi River is —
25,5%e and the 8-'3C of phytoplankton POC is —19.5%o. Thus, this trend indicates that the
contribution of phytoplankton-derived organic matter in the sediments has increased during the
past century. However, as mentioned above, this trend could also be influenced by the
contribution of POC from terrestrial C, plants (Gofii et al., 1997).

Historical evidence for an increase in the frequency of hypoxia is provided by Nelsen et al.
(1994) and Sen Gupta et al. (1996). Nelsen et al. (1994) found that the mineral glauconite
increased in abundance from the past to the present. This mineral is known to form under
reducing conditions such as found in the hypoxic regions of the Northen Gulf of Mexico. The
sediment core in this study that showed increased glauconite abundance is located in the
Mississippi River Bight, an area known to experience persistent seasonal hypoxia (Rabalais et
al., 1994; Rabalais et al., 1996). Glauconite’s presence downcore indicates that hypoxia has
occurred historically. The increase in glauconite upcore was interpreted by Nelsen et al. (1994) to
represent an increase in the frequency and duration of hypoxic bottom water at this location.
Cores taken from outside known hypoxic areas do not have glauconite present.

Nelsen et al. (1994) and Sen Gupta et al. (1996) also examined the composition of benthic
foraminifera tests in the sediment cores. Benthic foraminifera can be identified by species by the
morphology of their tests (shells). Benthic foraminifera species diversity decreased upcore in a
core taken from an area known to experience seasonal hypoxia presently (Nelsen et al. 1994).
There was also a shift of dominant species upcore. Species unable to tolerate low bottom water
oxygen concentrations were more abundant downcore while upcore the dominant species were
species known to tolerate low oxygen concentrations (Nelsen et al., 1994; Sen Gupta et al.,
1996). Benthic foraminifera in cores taken outside of the region of hypoxia did not have shifts in



causes a reduction of 1 million metric tons of nitrogen at the Gulf.” The use of the words
“seasonable assumption” and “conceivably” point out that this is far less than a totally scientific
exercise. We congratulate the authors for being candid on the point and hope that readers
understand that much of the information presented in the other five topic reports are of a similar
vein, although couched in highly positive, scientific-type statements that may mislead readers.

On the next page (page 93) the authors talk about system delay and buffering. “There are two
factors in the Mississippi River Basin that confound the idea that a reduction of nutrients well up
in the watershed will have an impact in the Gulf of Mexico. First there is a delay between the
time that fertilizer is applied and the time that it appears in streams and rivers. Second, there is a
considerable delay between the discharge of a kilogram of nitrogen in the upper basin and its
appearance in the Gulf of Mexico. On its way, it has perhaps spiraled through the nitrogen cycle
several times and is also subject to in-stream retention. On the other hand, if all sources of
nitrogen were eliminated in the upper basin of the basin, there would still be in-stream release of
nitrogen chemicals from storages in the sediments of streams and rivers and from allochthonous
sources along the streams, e.g., litterfall from riparian forests. It is almost impossible to estimate
how important this buffering effect of in-stream processes would be.”

On the next page (page 94), the authors make another important observation about nutrients.
* ‘The increase in nitrate-nitrogen observed in the Mississippi River near the Gulf over the past 50
_ years has not been a one-variable experiment. Sediment, phosphorus, and silicate loads have also
changed as a result of pollution, dam building, and land use change in the Basin. Although _
significant literature implicates nitrogen as the limiting factor in coastal waters around the world,
there are confounding factors involved in determining if the reduction of a known amount of
nitrogen will reduce the area of hypoxia. There is the question as to whether other chemicals,
particularly phosphorus and silicate, are now co-! imiting factors in the Gulf. As the amount of
nitrogen has continued to rise in the Mississippi River, the N/P and N/Si ratios have increased to
the point that phosphorus and silicate could be seasonally limiting.” (We would add to this
organic carbon, an issue that has already been discussed under Topic L)

‘The authors go on to state in their conclusions and recommendations (page 100) “Nevertheless,
we conclude that a significant >50% reduction of nitrogen loading to the Gulf of Mexico is
possible through the implementation of a number of proven techniques working in concert. The
suite of techniques includes: 1) modification of farm practices to make the use of nitrogen from
fertilizer, soil, and manure more effective and efficient, 2) the creation and restoration of
wetlands and riparian ecosystems between farmland and streams and rivers, but particularly in
those areas where concentrations of subsurface nitrate-nitrogen is highest, 3) the reflooding of
former wetlands that are not contributing excessive loadings of nitrate-nitrogen due to their
drainage, 4) the implementation of nitrogen contro] on domestic wastewater treatment plants and
on significant industrial sources, 5) flood contro! in the Upper Mississippi that involves retention
of floodwaters rather than preventing flood waters from leaving the major river channel, and 6)
the diversion of floodwaters to backwaters of the Mississippi River delta and coastal wetlands.
Several of these recommendations need to be implemented in concert if a major reduction in
nitrogen loading to the Gulf of Mexico is expected. If policies are devised to implement only
one or two of these recommended approaches, then improvement in the Gulf of Mexico is not as
likely.”

20


However, by looking at the graph in Figure 6, it is difficult to rationalize the authors’
conclusions. First, the stated average flow translates into 494,340 cfs annual flow. Not even the
dry decades of the 1930's or the 1950's fall below that average. The period 1991-1997 averaged
41% higher flow than Topic 1’s statement of the average, and: that has to have some effect,
especially ever since 1977, when a full 30% of the Mississippi River flow was diverted into the
Atchafalaya. Topic 1 even states that, “An effect likely to occur in the offshore region as a result
of increased flow through the Atchafalaya delta is an increase in stratification west of
Atchafalaya Bay and further westward into Texas.” Furthermore, the yearly average for the flood
of 1993 was nearly twice as large as the long-term average stated by Topic 1, and the spring and
summer flows were HUGE compared to normal. Topic 1 doesn’t say so, but an important point
to note is that hypoxia cannot occur without stratification, regardless of the nutrient load.
Also, no mention is made of whether conditions from December of 1992 through December of
1993 were more or less favorable for mixing the ocean water with the fresh water. If there was
less mixing, there would be a greater tendency to stratify larger areas of the Gulf than-normal.

ne


incentive based programs to improve water quality will yield real gains for the Mississippi River,
the Mississippi River Basin and the Gulf of Mexico without damaging the most productive
farming in the world.

What is needed are additional resources better targeted to impaired watersheds and directed at
on-the-ground activities and practices that will result in further water quality improvements.
Agricultural research, improved water quality monitoring, technical assistance and conservation
initiatives are keys to water quality and continued agricultural abundance.

It is critical that adequate federal resources be allocated to address water quality challenges.
Over $100 billion has been spent over 26 years to deal with urban point sources of water
pollution. With the increasing emphasis on nonpoint sources, resources should shift as well.
The State Revolving Loan Fund should have more impact on rural areas and additional funding
should be allocated to improving water quality monitoring, technical assistance and cost-share
programs rather than new regulatory programs at the federal level. The Environmental Quality
Incentives Program (EQIP) , and the buffer component of the Conservation Reserve Program
(CRP) all are farmer supported, voluntary programs with important water quality benefits that
must be fully funded to meet growing needs. Additional research and pilot projects are needed to
determine how farmers can most effectively use wetlands as a tool to reduce nutrient loss to
waters. Additional funding is also needed for state directed technical assistance and financial
incentives for farmers and assistance in the development of nutrient, management plans.
Research funding that focuses on nitrogen utilization, efficiency and loss reduction technology in
impaired watersheds is critical for long term solutions to nutrient loss.

The Natural Resources Conservation Service (NRCS) must be funded to support its primary
mission of being the lead agency in the federal system that works with and assists farmers to
improve water quality. Fully funded and supported programs that work with farmers to improve
water quality through cost sharing and nutrient management that also supports the economics of
the particular farm business is the most effective method of reducing nutrients to waters in the
Mississippi River Basin.

Terry Francl
Jim Porterfield


Also at times the flux of zooplankton fecal pellets and phytoplankton cells constitutes an
insignificant contribution to the vertical TOC flux (Figure 29). Qureshi’s data showed that direct
flux of terrestrial organic carbon (sinking of terrestrial particulate organic carbon) to depth varies
seasonally; at times it represents a significant fraction of the organic carbon flux to the benthos.
‘Trefry et al.’s (1994) results (Figure 30) showed that at depth particulate terrestrial organic
carbon concentrations from the river can be similar to particulate marine organic carbon
concentrations. Although the type of non-fecal pellet/non-phytoplankton organic carbon in the
sediment traps is not described, a possible source for the organic carbon’s origin is from the
river. With the above data in mind it is difficult to accept the hypothesis that nutrient enriched
phytoplankton production is the primary mechanism fueling the observed variability in bottom
water oxygen concentrations.

Q: Is phytoplankton carbon the major proportion of fecal pellet carbon?

A: No, our calculations suggest that phytoplankton carbon constitutes less than half of the fecal
pellet carbon produced. : :

An analysis of data concerning organic carbon flux to depth and food web dynamics on the
Louisiana-Texas Shelf suggests that phytoplankton organic carbon supplies less than half of the

organic carbon deposited by fecal pellets (Appendix 3). Though these are admittedly crude -..:

calculations, they lead to an important question: What is the source of the missing carbon and -.,
why has it been overlooked? Terrigenous organic carbon has previously been considered too
recalcitrant to be of use as an energy source. However, Ittekott’s (1988) and Amon and Benner’s
(1996) work suggest that organic carbon from rivers can be more labile than previously thought -
and bacteria can readily utilize this carbon for energy. Further, terrigenous organic carbon as an
organic carbon source for the Northern Gulf of Mexico food chain invokes the microbial food
web as an important aspect of energy transfer to higher trophic levels.

Even though the concepts of energy transfer to higher trophic levels by the microbial food web
have been in place for 25 years (Pomeroy, 1974), the importance of energy transfer from organic
carbon to bacteria to higher trophic levels is not easily quantified in marine ecosystems. Recent
studies by limnologists (Laybourn-Parry et al., 1994) in Loch Ness indicate the microbial food
web can subsist almost entirely on allochthonous carbon sources: (carbon produced outside of the
system). Studies like this and evidence that zooplankton can exploit detrital organic carbon
(Bowen, 1984), bacteria (Porter et al., 1983) and protozoans (Gifford and Dagg, 1991) as carbon
sources point to the quantitative significance of terrigenous organic carbon and the microbial
food web as an energy conduit to higher trophic levels in ecosystems with high extemal organic
carbon loading rates. Based on these considerations and our calculations (Appendix 3),
terrigenous organic carbon in the plume and on the shelf may be a significant source of carbon
input into the coastal food chain via the transfer of organic carbon through the microbial loop to
higher trophic levels.


Nutrient Enhanced Coastal Ocean Productivity Workshop. Publ. No. TAMU-SG-92-109,
Texas Sea Grant College Program, Texas A&M University, College Station, Texas.

Dortch, Q., D. Milsted, N. N. Rabalais, S. E. Lohrenz, D. G. Redalje, M. J. Dagg, R. E. Turner,
and T. E. Whitledge. 1992b. Role of silicate availability in phytoplankton species composition
and fate of carbon, p.76-83, In: Proceedings, Nutrient Enhanced Coastal Ocean Productivity
Workshop. Publ. No. TAMU-SG-92-109, Texas Sea Grant College Program, Texas A&M
University, College Station, Texas

Dortch, Q., and T. E. Whitledge. 1992. Does nitrogen or silicon limit phytoplankton production
in the Mississippi River plume and nearby regions? Contin. Shelf Res. 12:1293-1309.

Eadie, B. J., B. A. McKee, M. B. Lansing, J. A. Robbins, S. Metz and J. H. Trefry. 1994.
Records of nutrient-enhanced coastal ocean productivity in sediments from the Louisiana
continental shelf. Estuaries. 17:754-765.

Fahnenstiel, G. L., M. H. Marcovitz, M. J. McCormick, D. G. Redalje, S. E. Lohrenz, H. J.
Carrick, and M. J. Dagg. 1992. High growth and microzooplankton-grazing loss rates for
phytoplankton populations from the Mississippi River plume, p. 111-116, In: Proceedings,
Nutrient Enhanced Coastal Ocean Productivity Workshop. Publ. No. TAMU-SG-92-109,
Texas Sea Grant College Program, Texas A&M University, College Station, Texas

Fahnenstiel, G. L., M. J. McCormick, G. A. Lang, D. G. Redalje, S. E. Lohrenz, M. Markowitz,
B. Wagoner, and H. J. Carrick. 1995. Taxon-specific growth and loss rates for dominant
phytoplankton populations from the northern Gulf of Mexico. Mar. Ecol. Prog. Ser. 117:229-
239. ,

Fucik, K. W. 1974. The effect of petroleum operations on the phytoplankton ecology of the
Louisiana coastal waters. M. S. thesis. Texas A&M University, College Station, Texas.

Gearing, P., F. E. Plucker, and P. L. Parker. 1977. Organic carbon stable isotope ratios of
continental sediments. Mar. Chem. 5:251-266.

Gifford, D. J., and M. J. Dagg. 1991. The microzooplankton-mesozooplankton link: consumption
of planktonic protozoa by the calanoid copepods Acartia tonsa Dana and Neocalanus
plumchrus Marukawa. Mar. Microb. Food Webs 5:161-177.

Gofti, M. A., K. C. Ruttenberg, and T. L Eglinton. 1997. Sources and contributions of terrigenous
organic carbon to surface sediments in the Gulf of Mexico. Nature. 389:275-278.

Gofii, M. A., K. C. Ruttenberg, and T. L Eglinton. 1998. A reassessment of the sources and
importance of land-derived organic matter in surface sediments from the Gulf of Mexico.
Geochim. Cosmochim. Acta. 62(18):3055-3075.

Hedges, J. I. and P. L. Parker. 1976. Land-derived organic matter in surface sediments from the
Gulf of Mexico. Geochim. Cosmochim. Acta. 40:1019-1029.

Hopkinson, C. S., L Buffam, J. Hobbie, J. Vallino, M. Perdue, B. Eversmeyer, F. Prahl, J.
Covert, R. Hodson, M. A. Moran, E. Smith, J. Baross, B. Crump, S. Findlay and K. Foreman.
1998. Terrestrial inputs of organic matter to coastal ecosystems: An intercomparison of
chemical characteristics and bioavailability, Biogeochem. 43:211-234.


Topic 5
‘Wetland Percentages Vastly Understate Real Impacts

Topic 5 proposes to restore or create 24 million acres of wetlands or 3.4 % of the Mississippi
River Basin. However, the authors fail to point out that most of these restored acres would, by
necessity, have to be located in six states MN, IL, IA, IN, OH and MO because that’s where the
nitrate flux is supposedly coming from. There were 83.5 million acres of corn and soybeans in
these six states in 1997. Most of the suggested 24 million restored wetland acres would have to
come out of existing corm and soybean acreages and that would be a whopping 29% of the
productive land area, and that is a far different set of circumstances and impacts than using just
3.4 percent of the total land area in the basin as Topic 5 suggests. Two states, LA and IL would be
forced to reduce cor and soybean acreages by 19 percent, assuming that Topic 3 has accurately
identified that 35% of the nitrate flux is from these two states. That would cost farmers in those
two states about $2.6 billion dollars of gross income or about $15,000 of lost income per farmer
and that would come right off the top of their profits.

Even taking only 5 million acres out of production for wetlands, as recommended in Topic 6,
would affect 6 percent of the productive land of the Midwest and that would have at least 8 times
more impact on crop production than the reader would be led to believe by distributing the
acreage randomly throughout the basin as Topic 5 implies. : .

On page 101 the authors drop the bomb shell in this report. “This would require approximately a
20% reduction in fertilizer/nitrogen application in addition to other best management practices
such: as optimum timing of fertilizer application, use of alternative crops, such as perennials,
wider spacing of tile drains, and better management of livestock waste whether stored or applied
to the land.”

‘While there is much discussion about the use of nitrogen in this report, it fails to demonstrate the
link between a 20% reduction in nitrogen fertilizer application and whether there would be a
reduction in nitrate levels in the Gulf of Mexico. And, if so, how much and when. While we
acknowledge that two of the seven authors are professional agronomists, there appears to bea
real disconnect in regard to this recommendation and the data or research necessary to back up
the recommendation.

This issue becomes even more important in view of the possibility that nitrogen may not be the
only factor involved in creating the hypoxic zone in the Gulf of Mexico. If organic carbon is
determined to be another important variable in the hypoxic equation, then these actions must be
judged in that context. It might be that some of these recommended actions would have a
detrimental impact on the hypoxic zone, causing more organic carbon and thus a further
imbalance.

While we appreciate the time and effort put forth by the contributing authors to this report, we
have a number of questions and several concerns about the economic analysis.

First, and foremost, we would like to call attention to the underlying premise of an economic
analysis, that is some type of cost-benefit analysis. Please note the following quote from Section


increasing the mass of nutrient) not necessarily by approaching the Redfield ratio. However, a
changing Si:N ratio will affect diatom production.

Page xvi. The authors state that “Although the Mississippi and Atchafalya Rivers discharge
organic matter to the shelf, the principal source of carbon reaching the bottom waters in the
northern Gulf influenced by the river effluent and characterized by hypoxia is from in situ
phytoplankton production.” This point is debatable (see the attached excerpt from Carey et al.
1999)

Page xvi. The authors state that there is no evidence for century long changes in freshwater
discharge. We do not understand why they state this as they later discuss how the Atchafalaya
River has increased from 15% of the total flow in 1900 to 30% of the total flow in the present.
Further, Carey et al. (1999) determined that total discharge from the river system has increased
by 11% since 1967. The increase in streamflow was also noted in the Topic 3 report.
“Streamflow in the Mississippi River also increased about 30% during 1970-83 as a result of
increased precipitation. The increase in nitrate flux to the Gulf is attributed to both an increase in
nitrate concentration and an increase in streamflow.” (Topic 3, page 13)

The authors state that “The maps of mid-summer extent of hypoxia provide a benchmark for
year-to-year comparisons, albeit they are minimal estimates of the total amount of seabed
subjected to hypoxia and not necessarily representative of conditions through the summer.”(Page
22) This point is very important for 2 reasons, first, the temporal resolution of these data is poor
and more monitoring cruises are needed to temporally describe the extent of hypoxia and,
second, these data maps are insufficient to adequately describe a year-to-year trend.

Page 32. There is a strong statistical correlation between river flow and the area of mid-summer
hypoxia for the years prior to the flood of 1993. After the flood this relationship does not hold
and the authors suggest that organic carbon burial in the sediments during the flood of 1993
contributed to the extensive area of hypoxia seen in 1994. The authors do not indicate whether
they believe this carbon is of marine or terrestrial origin. However, as organic carbon of marine
origin (phytoplankton) is generally a very labile source of carbon one would expect that this
carbon would be respired quickly by the microbes. If this is indeed the case then terrestrial
organic carbon would be the primary form stored in the sediments. Further, the flood of 1993
carried Jarge loads of both nutrients and organic carbon. USGS data from Alton/Grafton,
Missouri from 1993 show that total organic carbon flux at this station was 7x higher than the
average for the previous five years (Carey et al. 1999). Respiration of this terrestrial organic
carbon in addition to marine organic carbon produced in 1994 may have contributed to the more
extensive hypoxia seen in 1994 under lower flow conditions. These results indicate the difficulty
in determining cause and effect relationships for hypoxia in this system.

Page 35-43. The authors sum up this section well with the closing sentence on p.43. As oxygen
dynamics are a function of both physical and biological processes more integrated studies of the
type the authors have been involved in in the past (e.g. NECOP and LATEX) are needed. More
work is needed to describe inter-annual variation in the development of the secondary pycnocline


Nitrate Loading in Mississippi River vs
Efficiency of N-Fertilizer Use on Com in the U.S.

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As Figure 5 shows, there is a significant downward trend in the five-year running average for the

_ amount of nitrogen applied to produce a bushel of corn. That trend almost exactly parallels the
downward trend in the flux of nitrate-nitrogen moving into the Gulf. Voluntary actions and the
marketplace were primarily responsible for these trends... -

Atmospheric Deposition is Understated

Atmospheric deposition appears to be greatly underestimated in terms of its contribution to the
total load of nitrate-nitrogen in the river. Topic 3 minimizes the atmospheric contribution
stating, “These inputs are small relative to the other nitrogen inputs to most of the Mississippi-
Atchafalaya River Basin.” Inputs such as fertilizer which are buried in the soil, must take a much
more convoluted route to get to a stream than does the nitrate in rainfall, much of which moves
as surface runoff directly to the streams. The concentrations of nitrate in surface runoff almost
always exceed the concentration of nitrate in the rainfall that created the runoff. Therefore, it is
conservative to assume that the concentration in the rain can be multiplied by the volume of
precipitation and the percentage of precipitation that ends up as gaged streamflow to determine
the flux of nitrate-nitrogen due to wet deposition of nitrate from the atmosphere. Using the ratio
of wet NO3 to dry NO; from Table 5.1 of Topic 3 and multiplying it times the large basin totals
for wet and dry atmospheric deposition from Table 5.2 and further multiplying by the percentage
of precipitation that shows up as streamflow in each basin (calculated from 1997 NADP precip.
maps) we show that 250,734 tons of NOs-N or 28 percent of the Mississippi River’s load of
887,000 metric tons of nitrate nitrogen could be coming directly from atmospheric deposition.
And this does not count any of the dry deposition of NOs nor the NH.. Taking the wet and dry

ar


species diversity (Nelsen et al., 1994). This type of evidence does indicate that hypoxia has
increased in duration but does not explain the cause of this hypoxia.

Appendix 3. Analysis of Fecal Pellet Carbon Origin Based on Food Web
Dynamics
If we suppose that phytoplankton production on the Louisiana-Texas Continental Shelf is 290 g
Cm’ yr’ (Sklar and Turner, 1981) and also that 82% of that amount of production is ingested by
the microzooplankton community (Fahnenstiel et al., 1992; 1995) then
290 g C m” x 0.82 = 238 g Cm” yr"

passes through the microzooplankton community.
If the microzooplankton community has a growth gross efficiency of 30% (Straile, 1997), then
the microzooplankton community retains

238 g Cm’ yr x 0.30=71 gC m* yr"
which is of phytoplankton origin. The remainder of the organic carbon ingested by the
microzooplankton is respired as CO, or is released as POC and DOC. The POC released by the

microzooplankton will not be a major source of organic carbon flux because these units are not
packaged into a pellet like the POC released by the macrozooplankton.

Based on Qureshi’s (1995) phytoplankton flux measurements and Sklar and Turner’s (1981)

annual shelf phytoplankton production estimate, approximately 4% of the annual phytoplankton
production is lost to sedimentation. This leaves 14% [100 - (82 sraepuinm + 4 ntmearsin) Of the 290 g :
Cm’ yr’ annual phytoplankton production available for consumption by the macrozooplankton.

If all of this remaining 14% of phytoplankton production is available for consumption by the
macrozooptankton, then

290 g Cm’ yr" x 0.14=41 gC m’ yr"
of phytoplankton carbon is ingested by the macrozooplankton.

Zooplankton are known to have decreasing assimilation efficiencies with increasing food.
concentration (Landry et al., 1984; Straile, 1997). If we take the low value of the range of
zooplankton assimilation efficiencies determined by Landry et al. (1984), then approximately
70% of the ingested carbon is assimilated and the remaining 30% is excreted as fecal pellets. If
the Louisiana continental shelf macrozooplankton consume all of the microzooptankton and all
the remaining 14% of the phytoplankton, then the macrozooplankton community ingests

TgCm’+41 gCm‘*yr'=112gCm* yr"
Of that 112 g Cm’ yr’, 70% is assimilated and 30% or

112 g Cm? yr" x 0.30= 34 gC m’ yr’

goes to fecal pellet production.

During four cruises between July 1990 and May 1992, Redalje et al. (1994) found that the
average TOC flux was 1.015 g C m?d’ in the plume and 0.296 g C m*d" on the shelf (Table 7).


Ward, C. H., M. E. Bender, and D. J. Reish (eds.). 1979. The Offshore Ecology Investigation.
Effects of oil drilling and production in a coastal environment. Rice University Studies 65:1-

589.


These daily flux rates, when converted to yearly flux rates, yield an annual plume TOC flux rate
of 370 g Cm” yr" and an annual shelf TOC flux rate of 108 g C m’ yr’.

Qureshi estimated that fecal pellet flux constituted 55% of the TOC flux. Thus, the fecal pellet
flux in the plume is

370 gC m’ yr' x 0.55 =204 gC m* yr"
and the fecal pellet flux on the shelf is
109 g Cm” yr'x 0.55 = 59 gC m’ yr"

The fecal pellet flux of 34 g C m® yr" derived from phytoplankton carbon is much less than the
total fecal pellet carbon flux.

For mass balance, the total fecal pellet organic carbon and the remaining fecal pellet carbon flux
must be derived from terrestrial organic carbon delivered by the river and other sources of marine -
organic carbon.

Although this modeling exercise is based on parameters estimated from a small number of
observations, the results suggest allochthonous organic carbon in the fecal pellet flux and the
direct flux of particles of terrestrial origin are both important components of total POC flux to
bottom waters.

References Cited

Amon, R. M., and R. Benner. 1996. Bacterial utilization of different size classes of dissolved
organic matter. Limnol. Oceanogr. 41:41-51.

Banse, K. 1982. Cell volumes, maximal growth rates of unicellular algae and ciliates, and the
role of ciliates in the marine pelagial. Limnology and Oceanography. 27:1059-1071.

Barber, L. B. and J.H. Writer. 1998. Impact of the 1993 flood on the distribution of organic
contaminants in bed sediments of the upper Mississippi River. Environ. Sci. Technol.
32:2077-2083.

Benner, R., G. Chin-leo, W. Gardner, B. Eadie, and J. Cotner. 1992. The fates and effects of
riverine and shelf-derived DOM on Mississippi River plume/Gulf shelf processes, p. 84-94,
In: Proceedings, Nutrient Enhanced Coastal Ocean Productivity Workshop. Publ. No. TAMU-
SG-92-109, Texas Sea Grant College Program, Texas A&M University, College Station,
Texas.

Bowen, S. H. 1984. Evidence of a detritus food chain based on consumption of organic
precipitates. Bull. Mar. Sci. 35:440-448.

Dagg, M. J. 1995. Copepod grazing and the fate of phytoplankton in the northern Gulf of
Mexico. Contin. Shelf Res.

Dortch, Q., A. Bode, R. R. Twilley. 1992a. Nitrogen uptake and regeneration in surface waters of
the Louisiana continental shelf influenced by the Mississippi River, p. 52-56. In: Proceedings,

W


deposition together from Table 5.2 increases the estimated contribution to 425,000 metric tons of
nitrogen as N. This could be as much as 48% of the 887,000 metric tons average load of nitrate-
nitrogen estimated for 1995-97 which is significantly higher than Topic 3’s estimate of 23
percent. Of the atmospheric loading, the Lower Mississippi River Basin contributes the largest
amount at 20 %. This could be expected with large amounts of precipitation and a high
percentage of it showing up as stream flow.

% of 250,734 metric tons of
Atmospheric Nitrate Wet
deposition which shows up as
NO;-N Flux in MS. River. ( by
River Basin )
18%|Upper Ohio
18%|Lower Ohio
3%|Upper Missouri
8%|Lower Missouri
9%|Upper Mississippi
13%|Middie Mississippi
5%|Arkansas
20%|Lower Mississippi i
7%|Red & Ouachita

Point Source Contributions

On page 15 of Topic 3 it is stated that municipal and industrial point sources contribute about 11 .
percent to the total nitrogen flux. This number seems low because dividing their 287,000 metric

tons contribution by the MAR’s 1,567,000 metric tons discharge from Table 6.1 equals 18.3

percent. Since most of the output of these point sources is now showing up as nitrate, instead of

ammonia, it could equal as much as 32 percent of the 887,000 metric tons of nitrate-nitrogen

being discharged by the river.

Also, Topic 5 states that point sources of nitrate nitrogen appear to be of little consequence
(<5% of the overall Mississippi River Basin load. However, Topic 3 states that point sources
contribute 11% of the nitrogen flux. Which is it, 5% or 11%?

Minimizing Event-Driven Freshwater Contributions to Stratification vs. Maximizing
Perception of Volume of Nitrate as the Culprit. In Topic 1, page xv, it is stated that flow rate
in the “...Mississippi River at Vicksburg is remarkably stable near 14,000 m ?/s despite
significant interannual variability and some decadal trends.” Topic 1 tends to minimize the effect
of increased flow by downplaying the effect of river flow by calling it remarkably stable, saying
that the slight increase in discharge is accounted for by the September through December time
frame and that this is a “much less important” time for the ocean than spring and summer. The
authors also conclude that long-term effects on the offshore ecosystem are not due to the amount
of freshwater discharge or alterations in delivery.

aa


plant (com and grasses) organic matter in these sediments. They also conclude that this material
is old, highly degraded and has been cycled through the soil several times.

Gofii et al. (1998) considered the possibility of marsh-derived organic matter as a source of the
terrigenous organic matter they observe in Gulf of Mexico sediments. They find this explanation
unlikely because of the subsidence of the deltaic plain and surrounding lands which is

This means that the delta should be a sink, not a source, of sediments. In addition, marsh
sediments would be younger in '*C-age than the old sediments they observe on the shelf and
slope.

The ultimate fate of riverine-bome terrigenous component is unknown. However, the work of
Keil et al. (1997) has shown that much of the POC entering the delta regions of large rivers like
the Amazon is not buried there, but is “lost.” Whether this lost POC (~70% in the case of the
Amazon) is decomposed directly or is transported seaward in a dissolved form, is unclear In
either case, mineralization (i.c., decomposition and the concomitant consumption of some
electron donor, like O2) must occur in relatively short times (Keil et al, 1997). Sediment cores
do, however, indicate an increase of organic matter accumulation from about 1925 to the present
adie et al., 1994). This increased preservation may be duc to increased burial rates (Eadie et
al., 1994). This needs to be reconciled with the observed decrease of the riverine input of
particulate matter and allochthonous organic matter documented over this time Petiod (Meade
and Milliman, 1983; Mayer- et al., 1998).

How important could this allochthonous carbon flux be for benthic. metabolism and O2
consumption in the nearshore and shelf region of the Gulf of Mexico? To answer this question,
we have performed a rather simple-minded calculation. We have used Dortch et al.’s (1994) total
benthic respiration rate from the tiypoxic zone obtained in 1991 (range of 160 to 800 mg O; m?
a). We have taken the estimated area of the hypoxic zone for that year and multiplied the
equivalent amount of carbon respired by the measured benthic respiration rate (Dortch et al.,
1994) cited above, to produce an estimate of total benthic respiration in the bh rypoxic zone. This
yields a carbon respiration or organic carbon consumption of 2.4 to 11.8x10" moles of carbon
annually. This value is quite similar both to that of Trefry et al. (1994) and the mean USGS flux
discussed above, even if we assume that only 35% (Ittekott, 1988) of the total organic carbon is
labile or oxidizable (17x10"° moles C and 9.2x10'° moles C, respectively). The respiration of
terrestrially-produced organic carbon is a complex phenomenon which varies both with flow and
source (Sun et al., 1997; Hopkinson et al., 1998). Gofii er al. (1998) pointed out that much of the
organic matter found in the surface sediments of the shelf is highly degraded and refractory, and
thus is unavailable for respiration. However, even if only 10% of the total organic carbon flux
could be metabolized within the bottom waters or at the sediment-water int&rface, this could
account for a significant portion of O2 loss.

Recent work by Mayer et al. (1998) has indicated that although the dissolved inorganic nitrogen
(DIN) concentrations of the Mississippi River have increased over time from 1950-52 until 1973-
82, the amount of “labile” or bioavailable particulate nitrogen (LPN) has decreased. They
attributed the increase of DIN to fertilizer usage increase, but they attributed the LPN decrease to
decreased particle fluxes resulting from engineered structures along the river (Mayer eft al.,
1998). If one argues, as Mayer and colleagues have, that this LPN can be rapidly solubilized and
utilized by coastal phytoplankton, the actual bioavailable N introduced to the shelf from the

17


preferred by grazers and thus would be less likely to be incorporated in fecal pellet flux (a major
[source of organic input to the sediments on the shelf).

3

Nitrate-N (pg atom -1)

250
200 3

150

Silicate-Si (ug atom 11)
3
ae
. be)

Re

An | 4

cv — - ——
1900 1925, 1950 “1975 2000
Year

Total P (ug atorn 1)

Figure 12. Nitrate, silicate and phosphorus concentrations measured at New Orleans
(open circles) and St. Francisville (shaded circles). +/-1 standard error bars are
indicated for the annual average of monthly means. Figure adapted from Tumer and
Rabalais (1991)


Figure 4.

Average Monthly Flow of Mississippi River at Vicksburg for
December 1992-December 1993 vs. Average of Monthly Flows
for 65 year period from 1931 to 1995

Average Monthty Flow (cts)

>
s
<

HUGE Flows All Year in 1993 Increase Volume and Area of Gulf Likely to Stratify.

An important point to note that is missing from all the executive summaries (and
presumably from all the rest of the reports) is that hypoxia cannot occur without stratification,
regardless of the nutrient load. Stratification occurs when lighter freshwater from the river
floats over heavier salt water and there is not enough current or wind to mix the two. It is
obvious from the graph in Figure 4 that above-average flow occurred for 13 consecutive months
starting in December of 1992. The shallow Atchafalaya bay and adjacent coastal area received


Topic 3

The reports contain contradictory statements, and above all, a fundamental intellectual and
scientific bias of proposing reductions in nitrogen even after a complete and utter failure of Topic
2 to discover any benefit at all of doing so.

Total Nitrogen Declining in Latter Half of Century. Topic 3 states that nitrate concentration
in the Mississippi River has increased 2- to 5- fold in the last century. However, while Topic 3
notes that total nitrogen concentration was about 2.26 mg/L for 1980-96, it fails to note that data
from Leighton (1907) could be interpreted to indicate that the concentration of total nitrogen in
the Mississippi River has gone down in the last century from 2.5 to 3.0 mg/L in the early 1900's
and its high point of the 3.0 mg/L of the 1950s.

Report € 3 falls to mention that the Total Nitrogen Concentration in
Mississippi River has been Descreasing In the latter hatf of the century.

» Bef

Total Nitrogen mg/L
Pr -_ a

1905-06 1955-65 1980-1996

Nitrate vs Total Nitrogen. Topic 3 states that flux of total nitrogen from the Mississippi-
Atchafalaya River Basin to the Gulf is about 1.6 million metric tons per year, while Topic 1
states that the yearly flux is 1.6 x 10° t/yr nitrate. There is a huge difference between “nitrate” and
“total nitrogen.” This inconsistent use of terminology between reports is confusing at best, and,
at worst, will result in policy being set totally differently depending upon which terminology is
used. These discrepancies should have been caught and corrected in the peer review process.

Nitrate-N Flux Trending Down Despite What Topic 3 Says. Topic 3 states that nitrate flux
has averaged nearly 1 million metric tons per year since 1980. On page 30-31 the report further
states that “There is no statistically significant trend, upward or downward in nitrate flux since
1980, even if the flood year of 1993 is removed.” While mathematically true, the authors chose
to ignore that things changed in 1983. Furthermore, they ignored all the data that existed before


which is thought to control the morphology of the hypoxia region (Wiseman et al. 1997).
Without an understanding of this variation it will be extremely difficult to predict the
magnitude of hypoxia based on river discharge or nutrient and organic carbon loading.

Page 45. Peak flow occurs in March, April, and May. So the delivery of solutes and particulates
associated with peak flow coincides with warming of surface waters and concomitant increases
in microbial activity associated with increasing temperature. Trefry et al (1994) documented that
80% of the annual total organic carbon flux occurs between December and June. These data
along with N flux data, discussed on page 55 of this report, indicate that both organic carbon flux
and N flux are primarily a function of discharge. Stratification, which is the ultimate driver of
hypoxia, is also a function of discharge. As area of hypoxia, nutrient concentrations, and -
organic carbon concentrations all covary with discharge it is difficult establish statistical
correlations among these variables.

Page 51. The authors report that average nitrate concentrations have doubled from the time
period 1955-1970 to 1980-1996. Most of this change occurred between 1970-1983 and the mean
annual N flux has not changed since the early 1980's. However, the authors chose to ignore that
the N flux is declining as illustrated in Figure 2. :

Page 53. Table 1 in the report documents a significant increase in dissolved inorganic nitrogen
concentration from the early 1960s to the middle 1980s. :

Page 63. “Although the Mississippi River discharges organic matter and decomposition of some
of this organic matter could consume oxygen in the coastal ecosystem, the principal source of

ic matter reaching he bottom waters of the northem Gulf of Mexico influenced by the
Mississippi River effluent and characterized by hypoxia is from in site phytoplankton production
(Rabalais et al. 1992b, Turner and Rabalais 1994a, Eadie et al. 1994, Justic’ et al. 1996, 1997).”
See the attached excerpt from Carey et al. (1999) for a rebuttal to this arguement.

Page 63-64. Regarding the last two sentences from the bottom continuing to the top of p. 64:
‘We do not understand this arguement nor do we agree with it if they mean what they appear to
say. They say that the C:N ratio of marine phytoplankton is higher than the C:N ratio of
Mississippi River flux and thus sedimenting phytoplankton cells would contribute much more
carbon to hypoxic zones than riverine organic matter. However, this is not a correct comparison
as they compare the C:N ratio of phytoplankton (9.5-9.9:1) to the total-C:total-N ratio of the river
which includes both the dissolved and particulate fractions. If you look only at the particulate
organic matter fraction in the river (which is a more appropriate comparison to the phytoplankton
C:N) the C:N ratio averages 8.5:1 (Trefry et al. 1994). Further, sedimenting phytoplankton cells
are a small fraction of the vertical organic carbon flux (Qureshi 1995, Figure 55 on page 82 of
the report). Even so, the C:N ratio of the organic matter is not an appropriate number for
justifying the importance of marine vs. terrestrial organic carbon vertical flux. =;

Page 63. “The amount of organic loading in the Mississippi River is not large enough to account
for the observed decline in oxygen over such a large area and volume (Tumer and Allen
1982b).”. We agree with this statement. Surely, oxygen depletion is due to microbial respiration
of both phytoplankton organic carbon and riverine organic carbon. There is too much uncertainty
about the ultimate fate of terrestrial organic carbon to discount it completely.


Accept or

# of Degrees of Years Avera
Location Regression ; ' an) Reject Null ge
eg Observations freedom fyootnesis analyzed cone, mg/L
Mississippi River

Clinton, iowa (1986) NOS vs time 46 48 0.0254 -0.1686 accept Sept 79 to Sept 86 1.241
Clinton, lows (1991 on} NO3 vs time 76 78 0.2044 -1.8079 accept Apr 91 to Sept 93 2.263
Royaiton NO3 vs time 89 87 0.1007 0.9444 accep! Sept 79 to Mar 95 0.200
Minnesota R. NOS vs time 161 159 0.2157 2.7849 Reject Jan 73 to Mar 95

St Paul NOS vs time 0.917
Nininger NOS vs time 69 67 0.2540. 2.1492 Reject Nov 79 to Mar 8S 2.459
Winona NOS vs time 46 43° 0.1727 1.1486 accept dan 73 to Aug 86 1.441
Wisconsin R. NOS vs time vit 109 0.1526 1.6116

Clinton NOS vs time Reject Sept 79 to Sept 93 1.921
Keokuk NOS vs time 47 45 0.0133 0.0892 accept Oct 79 to Aug 86 2.359
Wttinois A. NOS vs time

Alton/Gratton NOS vs time 129 128 0.0312 -0.3616 accept Sept 79 to Sept 94 2.678
Missour A. NOS vs time .

Ohio Fiver NOS v6 time

Memphis NOG vs time 79 78 0.0016 -0.0136 accept Oct 78 to Aug o4 1,520
Arkansas City NOS vs time 74 72 0.0432 -0.3669 accept Nov 74 to Feb 92 1.366
Vicksburg NOS ve time B5 B4 0.0846 -0.7732 accept Oct 79 to Aug 04 1,480
Belle Chasse NOS vs time 122 121 «0.0189 0.2074 accept Sept 79 to June 9S 1.420
litinols River

Vatiey City, ill NOS ve time 104 102 0,1082 1.0694 accept Sept 79 to Sept 93 3.837
Wisconsin River

Muscode, Wise NOS vs time mw 409 0,1626 1.6916 accept Sept 79 to May 95 0.525
Minnesota River

Jordan, Minn NOS vs time 50 48 0.3312 -2,4321 Reject Jan 73 to Aug 77 0.917
Ohio River :

‘Wheoling, W. Va. NOG ve time 103 102 0.0113 0.1135 accept Aug 79 to Aug 95 0.923
Warsaw, Ky NO2 vs time 43 42 0.0554 0.3555 accept Sept 79 to Aug 86 1.166
Grand Chain, fil NOS vs time 170 160 0.0881 -1,1461 accept Sept 79 to June 95 1,002

Table 5. Results of trend analysis of dissolved nitrate in the Mississippl River and its tributaries. Date from usGs,



Mississippi River may have actually decreased from 1950-52 to 1973-82 (Figure 31). Clearly,

180 @lAverage DIN (microM)
1604 GLabile PN in suspended matter
s (microM in river}
E140 Total Labile N (microM in river)
12074
roo
Zz
2 80
a
2 60 i
= 604
g 404 ty
> oy A
H yp
* 20 by Yj
A Ly
LBZ Yi

1950-1952 1953-1972 1973-1982
Years

31. A Miss
eer vaio ais horn Mayor ora eee Inorganic nitrogen, particulate nitrogen and

labile N is “lost” from particulate material in the river either before or after deposition, but before
burial on the shelf (Mayer et al., 1998). This loss of particulate N may support the notion that a
percentage of the terrestrial organic matter is labile and rapidly lost from the riverine and shelf
system via respiration.

Smith and Hollibaugh (1993) suggest net heterotrophy occurs in the coastal ocean, based on
terrigenous inputs of carbon. The amount of carbon input into the Northern Gulf of Mexico by
the Mississippi/Atchafalaya River System suggests this fraction could contribute significantly to
coastal ecosystem metabolism. This is similar to the conclusion reached by Trefry et ai (1994).
Thus, this source of organic carbon, plus the measurements indicating high ammonium
regeneration rates (Dortch et al., 1992a), and the bacterial utilization of a large portion of
phytoplankton produced carbon (Benner et al., 1992) suggest the Louisiana-Texas Continental
Shelf may be net heterotrophic.

Sediment Evidence for Increased Phytoplankton Production
and Hypoxia

Q: What do sediment data tell us about long-term patterns of hypoxia on the Louisiana shelf?



Excerpts from

Carey, A.E., J.R. Pennock, J.C. Lehrter, W.B. Lyons, and J.-C. Bonzongo (1999). The Role of
the Mississippi River in Gulf of Mexico Hypoxia. Final Technical Report. Environmental
Institute Publication Number 70. Prepared for the Fertilizer Institute by The University of
Alabama, Tuscaloosa, Alabama. 119 pp.

Q: What are the patterns for inorganic nutrient ratios and why are these ratios important?

A: The ratios between the major ions (nitrogen, silicate and phosphorus) have been shown to
have significant influence on phytoplankton species composition in aquatic systems. Tumer and
Rabalais have shown that the nitrogen:silicate ratio in the lower Mississippi River has
approached 1:1 in recent years and suggested that this might have a major impact on
phytoplankton species composition and hypoxia.

Some studies (Dortch and Whitledge, 1992; Justic et al., 1995a) suggested silicate limitation of
phytoplankton production at salinities less than 30% on the Louisiana shelf. These studies were
based on stoichiometric relationships of Si:N:P. Phytoplankton cells should have Si:N:P ratios
close to the Redfield ratio of Si:N:P of 16:16:1. If the Si:N ratio drops below 1:1 (16:16) diatom
production will become Si limited because the ratio of cellular demand for Si is greater than that
available in the water column. This analysis assumes that all other macro- and micronutrients
required for growth are available in excess. Generally, it is difficult.to assess nutrient limitation
based solely on Si:N:P ratios because standing stock nutrient concentrations do not adequately
represent uptake and regeneration rates. For example, Smith and Hitchcock (1994). determined
the tumover time of the inorganic dissolved P pool in the Mississippi River plume surface waters
during a summer high flow event was less than 10 minutes. Furthermore, Si is utilized only by
diatoms and thus does not limit production by the non-diatom phytoplankton community.

Silicate is important however in determining the species composition of the phytoplankton
assemblage (e., if silicate is present, diatoms are present). Corollary evidence for potential
silicate limitation is that NO3 concentrations in the Mississippi River have doubled while silicate
(Si) concentrations decreased by half during the past century (Turner and Rabalais, 1991). As a
result of these changes, the Si:N ratio in the Mississippi River changed from 4:1 to 1:1. This
change resulted in the current Si:N:P ratio equal to the Redfield ratio of 16:16:1 (Figure 12). The
trend of nutrient concentrations moving towards the Redfield ratio indicates that the Northern
Gulf of Mexico phytoplankton are growing under ideal nutrient concentrations and thus their
production has increased over time Qustic et al., 199Sa; Rabalais et al., 1996).

Q: Have changes in phytoplankton species composition occurred and is this significant to the
hypoxia issue?

A: There is some evidence that phytoplankton species composition has changed in favor of
lightly silicified and non-diatom species during certain periods of the year. Some authors have
argued that this shift may increase the input of phytoplankton-derived organic matter to the
sediments on the Louisiana Shelf. However, lightly silicified diatoms and flagellates would
probably be less likely to sink than more heavily silicified diatoms. Similarly, flagellates are less



Ittekkot. V. 1988. Global trends in the nature of organic matter in river suspensions. Nature
332:436-438.

Justic, D., N. N., Rabalais, and R. E. Tumer. 199Sa. Stoichiometric nutrient balance and origin of
coastal eutrophication. Mar. Pollution Bull. 30:41-46.

Justic, D., N. N. Rabalais, R. E. Turner, and Q. Dortch. 1995b. Changes in nutrient structure of
river-dominated coastal waters: Stoichiometric nutrient balance and its consequences. Est.
Coast. Shelf Sci. 40:339-356.

Justic, D., N. N. Rabalais, R. E. Tuer, and W. J. Wiseman. 1993. Seasonal coupling between
riverbome nutrients, net productivity, and hypoxia. Mar. Pollution Bull. 26:184-189.

Keil, R. G., L. M. Mayer, P. D. Quay, J. E. Richey and J. I. Hedges. 1997. Loss of organic matter
from riverine particles in deltas. Geochim. Cosmochim. Acta. 61:1507-1511.

Landry, M.R., R. P. Hassett, V. L. Fagemess, J. Downs, and C. J. Lorenzen. 1984. Effect of
food acclimation on assimilation efficiency of Calanus pacificus. Limonl. Oceanger. 29:361-
364.

Laybourn-Parry, J., M. Walton, J. Young, R. L Jones, and A. Shine. 1994. Protozooplankton and
bacterioplankton in a large oligotrophic lake-Loch Ness, Scotland. J. Plankton Res. 16:1655-
1670.

Ludwig, W., P. Amiotte-Suchet, and J.-L. Probst. 1996. River discharges of carbon to the world’s.
oceans: determining local inputs of alkalinity and of dissolved and particulate organic carbon.
C. R. Acad. Sci. Paris, t. 323, series Ha, p. 1007-1114.

Mayer, L. M., R. G. Keil, S. A. Macko, S. B. Joye, K. C. Ruttenberg and R. C. Aller. 1998.
Importance of suspended particulates in riverine delivery of bioavailable nitrogen to coastal
zones. Global Biogeochem. Cycles. 12(4):573-579.

Meade, R. H. and J. D. Milliman. 1983. World-wide delivery of river sediment to the oceans. J.
Geol. 91:1-21.

Nelsen, T. A., P. Blackwelder, T. Hood, B. McKee, N., Romer, C. Alvarez-Zarikian, and S.
Metz. 1994. Time-based correlation of biogenic, lithogenic and authigenic sediment
components with anthropogenic inputs in the Gulf of Mexico NECOP study area. Estuaries.
17:873-885.

Officer, C. B., and J. H. Ryther, 1980, The possible importance of silicon in marine
eutrophication, Mar. Ecol. Progr. Ser. 3, 83-91.
Pomeroy, L. R. 1974. The ocean’s food web, a changing paradigm. BioScience. 24:499-504.

Porter, K. G., Y. S. Feig, and E. F. Vetter. 1983. Morphology, flow regimes and filtering rates of
Daphnia, Ceriodaphnia and Bosmina fed on natural bacteria. Oecologia (Berlin). 58:156-163.

Qureshi, N. A. 1995. The role of fecal pellets in the flux of carbon to the sea floor on a river
influenced continental shelf subject to hypoxia. Ph.D. Dissertation, Louisiana State University,
Baton Rouge, Louisiana.


Kentucky Farm Bureau Federation

9201 Bunsen Parkway « P.O. Box 20700 « Louisville, KY 40250-0700
Telephone (502) 495-5000 + Fax ($02) 495-5114 « E-mail info@kyfb.com

SAM MOORE
President

MARSHALL COYLE,
First Vice President

MARK HANEY
‘Second Vice President

DAVID S. BECK
Executive Vice President

August 9, 1999

Gulf of Mexico Hypoxia Working Group
National Centers for Coastal Ocean Science
WS 13446 SSMC4

1305 East-West Hwy.

Silver Springs, MD 20910

RE: Assessment on the Causes of Hypoxia in the Gulf of Mexico
To Whom It May Concern:

The Kentucky Farm Bureau and its over 400,000 member families, support and submit for
review the enclosed comments in response to the Gulf of Mexico Hypoxia Working Group’s
assessment on the causes of Hypoxia in the Gulf of Mexico. The American Farm Bureau

. Federation prepared these technical comments at the request of and on behalf of its member state
Farm Bureaus

Kentucky Farm Bureau urges the Gulf of Mexico Hypoxia Working Group to thoroughly review
this document. We very strongly believe that our comments and suggestions are well-formulated
scientific principles for the protection of United States coastal waters. Our membership expects
that the Gulf of Mexico Hypoxia Working Group and the National Centers for Coastal Ocean
Science will use extreme care in assessing the potential causes of Hypoxia and in making any
formal recommendations that adversely affect agricultural activities. Thank you for your
consideration of our comments.

Sincerely,

Sam More

Sam Moore

President

SMirtf

Enclosures 1

cc: Kentucky Congressional Delegation; Ira Linville; John Mark Hack

“Yoice of Kentucky Agriculture ”’-



As discussed above, the onset of hypoxia is dependent on both stratification and the presence of
organic matter to fuel respiration. Research in the Northem Gulf of Mexico has implicated the
vertical flux of organic matter derived from phytoplankton production as the primary source of
organic matter fueling respiration below the pycnocline (Tumer and Rabalais, 1991; Rabalais et
al, 1996). The mechanisms they proposed for vertical transport of phytoplankton-derived
organic matter were the direct sinking of phytoplankton cells or indirect sinking of organic matter
of phytoplankton origin as zooplankton fecal pellets.

The distinction between these two types of phytoplankton sinking is important. The
sedimentation rate of phytoplankton cells could be altered by changes in the phytoplankton
species assemblage caused by shifts in nutrient stoichiometries and concentrations. For diatoms, .
sedimentation is a significant loss term, especially for large colonial diatoms like Thalassiosira
rotula and Skeletonema costatum. These two species had sinking rates of greater than 20 m day?
and 4-13 m day", respectively (Fahnenstiel et ai., 1995). Sedimentation of diatoms was also
much higher in the spring when maximal sedimentation represented a 200% loss compared to the
summer when sedimentation represented a 20% loss (Fahnenstiel et al., 1995). Sedimentation
can represent a large loss term for diatoms but for non-diatoms this loss term is less than 1%
(Fahnenstiel et al., 1995). For the phytoplankton community as a whole, sedimentation is not a
significant loss term. Redalje et al. (1994) determined that the less than 8 pm portion of the
phytoplankton community (non-diatoms) accounts for most of the total primary production
(Figure 28). In addition, sinking of phytoplankton cells composed only a small percent of the
_ total organic carbon flux to depth, averaging 4% of the vertical TOC flux (Qureshi, 1995). -

Qureshi’s (1995) sediment trap data indicate that zooplankton fecal pellet production by the

macrozooplankton (zooplankton >200 j1m) is the primary mechanism for the flux of organic

matter to depth. Zooplankton fecal pellet sedimentation accounts for an average’ of 55% of the |
TOC flux but at times fecal pellet organic carbon flux is greater than 95% of the TOC flux

(Figure 29). Turner and Rabalais (1991) and Rabalais et al. (1996) hypothesized that vertical flux

of phytoplankton-derived organic material was the cause of hypoxia and that the mechanism for

this flux is zooplankton fecal pellet production by the macrozooplankton community.

However, this hypothesis is problematic because macrozooplankton are not the dominant
herbivores, neither in the Mississippi River plume (Dagg, 1995) nor away from the plume
(Fahnenstiel et al. 1995). Measured macrozooplankton community ingestion rates in the
Mississippi River plume in September 1991 accounted for 14-62% of the daily phytoplankton
production while in May 1992, macrozooplankton community ingestion rates accounted for only
4-5% of the daily phytoplankton production (Dagg, 1995). Alternatively, Fahnenstiel et al.
(1995) found that the primary fate of small, non-diatom phytoplankton (responsible for the
majority of phytoplankton production) is to be grazed upon by the microzooplankton community
(zooplankton <200 pm). Microzooplankton grazing accounted for an average of 82% of the
production of the non-diatoms.

Dagg (1995) suggested that macrozooplankton do not become important herbivores until they are
able to respond numerically to increased phytoplankton concentrations. Both the
microzooplankton grazing rates obtained by Fahnenstiel (1992; 1995) and the observation that


Another possible consequence of the change in nutrient stoichiometry and possible silicate
limitation is that more non-diatom blooms may occur. This could lead to an increase in the
number of non diatom harmful algal blooms (Justic et al., 1995b). Farther, Rabalais et al. (1996)
postulated that the change in Si:N has altered the species composition of the phytoplankton
assemblage. In such a scenario, a shift from palatable diatoms to less palatable flagellates could
exacerbate organic carbon sedimentation in the form of phytoplankton cells. The increased
magnitude of phytoplankton cell sedimentation would result from decreased grazing by the
zooplankton community (Officer and Ryther, 1980). Thus, a shift from diatoms to flagellates
would exacerbate hypoxia with more organic carbon input to depth.

Direct comparisons of published phytoplankton species surveys from the past with those of the
present are difficult as a result of different sampling techniques, sample locations, and seasons
sampled. Rabalais et al. (1996) grouped phytoplankton species data from 1955-57, close to the
delta (Simmons and Thomas, 1962) along with 1972-73 data from 80 km west of the delta
(Fucik, 1974; Ward et al., 1979) and compared these data to 1990-93 data collected near the delta
and south of Terrebonne Bay in 20m deep waters. Rabalais et al. (1996) acknowledged that early
phytoplankton species studies probably did not include small phytoflagellates and cyanobacteria.
Thus, no data are available to determine if small phytoplankton cells, which typically dominate
current samples, have increased in numbers as a result of silicate limitation. Rabalais et al.
(1996) reported a decrease in the presence and dominance of heavily silicified diatoms and an
increase in the presence and dominance of lightly silicified diatoms. Rabalais et al. (1996) also
found that some harmful algal species were present which in the past either had been absent or
were present in much smaller populations. Pseudonitzchia pseudodelicatissima (a sometimes
toxic form of Nitzchia pungens) causes amnesic shellfish poisoning. Its concentration has
increased from the 1950's to the present, with some bloom concentrations exceeding 1x10° cells
L’ (Rabalais et al., 1996). Dinophysis caudata (a dinoflagellate which may cause diarrhetic
shellfish poisoning) was not present in the early studies but has recently been found at
concentrations sometimes exceeding 1x10° cells L" (Rabalais et al., 1996).

‘The discussed shift in phytoplankton species assemblage since the 1950's could affect hypoxia in
two different ways. First, the shift from heavily silicified diatoms to more lightly silicified
diatoms may have decreased the sedimentation of diatom cells (Dortch et al., 1992b). Second,
the shift from palatable diatoms to unpalatable flagellates may have increased the flux of organic
material through sinking of ungrazed phytoplankton cells (Officer and Ryther, 1980). This
hypothesis, however, precludes the increased awareness of the microbial loop and the importance
of microzooplankton in the removal of phytoplankton cells.

Organic Matter Vertical Flux and the Fate of Phytoplankton

Q: What is the role of fecal pellet flux in the deposition of phytoplankton carbon on the
sediments of the Louisiana shelf? .

A: The packaging of phytoplankton into zooplankton fecal pellets is an important mechanism by
which phytoplankton carbon can be transported to the sediments. Sediment traps on the
Louisiana shelf often show fecal pellets to be a high percentage of the total material collected in
these traps.

10


Section 5.2 (page 46) - “Along with the potential and direct agricultural benefits from hypoxia,
reduced nutrient loadage from agriculture would also be expected to lead to reduced
contamination of surface- and aquifer-based drinking water supplies, and thus benefits in the
form of reduced costs to obtain portable drinking water.” Again, we are not aware that this is a
major problem in the Mississippi River Basin. And to the extent that it is a problem, it is more
often related to point source pollution rather than to non-point pollution. Furthermore, the Avery
report on infantile methemoglobinemia (blue baby syndrome) suggests that the drinking water
standard for nitrate could be raised to 15 or 20 ppm nitrate-N which would eliminate the “nitrate
problem” in drinking water in the vast majority of cases.

Table 4.2.1 — 2, (page 109) — Percentage Change in Crop Prices. Just as an example of how this
model is not related to the real world, we point out the change in corn vs. sorghum chart shown
in this table. According to the table, a 20% reduction in nitrogen would result in a 9.4% increase
in corn prices and a 19.3% increase in sorghum prices. However, com and sorghum are direct
substitutes with sorghum priced at approximately at 95% of the value of com. The idea that
sorghum prices would increase at twice the rate of cor prices is simply not possible in today’s
world. While this is a relatively small matter, it does point out how models can quickly stray
from real world realities.

‘The issues of excess or “insurance” nitrogen application.

For decades, there has been an ongoing discussion about what the optimal rate of nitrogen
fertilizer application should be. Some agronomists suggest that farmers apply too much nitrogen.
Yet, when you look at other recommendations from the various state land grant universities,

_ there is some variance between states. Moreover, while there are some articles in the journals
about this issue, they are relatively few.

The reality is that the optimal nitrogen fertilization application rate depends upon.a number of
variables, such as soil type, weather and the management skills of the operator. Farmers
determine nitrogen and other fertilizer rates based on some predetermined yield goal and normal
weather. The fertilizer is usually applied preplanted with some farmers side dressing additional
amounts early on in the growing season. If the weather cooperates and the yield goal is achieved,
all the fertilizer is utilized, at least in theory. But if the weather does not cooperate and yields
slip, according to the agronomist, the farmer has applied too much fertilizer.

While there may be some farmers who apply more nitrogen than necessary for optimal yield, we
would argue that this practice is much less frequent than suggested in this report. There is
evidence to support this position as reflected in nitrogen utilized per bushel of com. As indicated
in the Porterfield article, the nitrogen fertilizer utilized per bushel of com has declined steadily
since the mid-eighties.

If farmers were ever utilizing excess nitrogen, there are much fewer today. There are many
farmers that are probably very close, +/-10%, to the rates recommended by agronomist at land
grant universities, probably the majority. A mandated across-the-board, 20% reduction in
fertilizer nitrogen application rates could have a devastating impact of yields, much greater than
the 2% to 6% reduction indicated in these reports. Moreover, mandated application rates may
preclude the higher rates of application necessary for future yield improvements. Com yields
increase approximately one bushel per year over time. The advent of genetic manipulation may
accelerate this trend. :

ay


Figure 3.

1955

1960 jee

Nitrate-N Flux per cfs

8 6 §&

1980 tee

1985 +

1990 +

1995


1980 and chose not to use the more robust statistical analysis that they could have used with the
43 years of data that were available to them. Statistical textbooks state that 30 data points are
needed to do proper trend analysis; why then, did the authors of Topic 3 choose to only use 17
data points to make their statement of “no statistically significant trend”? Our analysis of the 43
years of available data shows that there was a statistically significant trend since 1983 and that
trend was downward at the rate of 17,000 metric tons per year, Figure 2. The r-square for this

analysis is 0.82.

Figure 2.

Nitrate Loading in Mississippi River
Has Been Declining Since 1983

1.6
is
812
s
o
= S rawntate
trend
£0. G _osters
5
£0.
E
z°
»
go.

°
1955
1960 |
1965

5

1975
1980
1985
1990
1995

Figure 3 is another graph indicating that the downward trend is real, as it shows nitrate nitrogen
flux normalized for flow. Since 1982, both the highs and lows have been declining. Topic 1
states that, “There is no dobugt [doubt} that the concentration and flux of nitrogen (per unit
volume discharge) has increased from the 1950s to 1960s, especially in the spring.” However,
Figure 3 clearly contradicts that statement by showing that, with the exception of 1969, Nitrate-N
flux was lower in the 1960s than the 1950s, and in fact, it was not until 1975 where the Nitrate-N
flux reached a level that was consistently higher than what it was in 1955.


Page 71. The authors state that there is no clear relationship between bottom water chlorophyll
concentration (surrogate for phytoplankton concentration) and hypoxia. This result again
suggests the difficulty in determining cause and effect relationships for hypoxia.

Page 78. Second paragraph. The authors state that the spatial and temporal switching of the
primary nutrient (N, P, or Si) limiting phytoplankton production is poorly understood. This will
make it extremely difficult to implement effective TMDL management plans aimed at reducing
phytoplankton production rates. This is an area of research that requires a Jot more work.

Page 82. Figure 55 shows the total organic carbon flux to depth split into three fractions: fecal
pellets, phytoplankton, and other material. While zooplankton fecal pellets (which may or may
not contain a large fraction of phytoplankton carbon depending on location and time of year)
make up 55% of the vertical organic carbon flux to the bottom, it is also apparent from figure 55
that the other material is the dominant fraction collected in the surface sediment traps and is often
the dominant fraction in the bottom traps. These results also show that often the other material is
the dominant fraction in the surface traps but is greatly reduced in the bottom traps suggesting
that this material is rapidly respired as it sinks through the water column and thus makes :a
significant contribution to oxygen utilization rates in the water column. The authors state that
this other material consists of molts, dead zooplankton, marine snow (particle aggregates
colonized by bacteria), and particles with adsorbed organic carbon but do not discuss the
percentage contribution of each fraction within the other material category.

Page 86. Section 6.8. We think this is one of the strongest portions of the report and contains
good theory and convincing data that changing Si:N affects the vertical transport of
phytoplankton organic carbon to depth. -

Page 91. We do not follow their calculations at the top of this page. They calculate that if N
fluxes were 50% lower then this flux would support a daily production rate of 0.29 g C m? d?.
They then say that this translates to an annual production rate that would not exceed 25 g C m?
yt', We do not know how they catculated this number as converting this number to a yearly rate
yields 0.29 x 365 = 105.85 gC m” yr! They then use an annual production value of 35 g C m?
yr to make further calculations. We are confused about where they got this number as well.

Page 104. Figure 66. The 5!°C data used to determine the marine or terrestrial signal of sediment
organic carbon should be reevaluated in light of the recent work by Gofii et al. (1997). See
attached excerpt from Carey et al. (1999).

Page 112. Figure 72. This figure showing geological (glauconite abundance) and biological
(diversity indices) data in relation to fertilizer use from 1900-1990 suggests that hypoxia has
increased in duration and intensity as fertilizer use increased throughout the century. However, a
coorelation in these numbers does not necessarily mean there is causation.


“Cruise “Plume Region “Shelf Region
“July-August 1990 . .

POC flux 0.29 (0.02; n=3) 0.18 (0.01; n=4)
PON flux 0.06 (0.003; n=6) 0.03 (0.02; n=8)
"March 1991 . oo.

POC flux 0.95 (0.01; n=3) 0.32 (9.02; n=3)
PON flux 0.16 (0.009; n=6) 0.05 (0.002; n=6)
“Sept 1991 . ;

POC flux 0.69 (0.02; n=12) 0.19 (0.01; n=6)
PON flux 0.12 (0.003; n=12) 0.03 (0.001; n=6)
“May 1992 . .

POC flux 1.80 (0.04; n=8) 0.40 (0.02; n=10)
PON flux 0.27 (0.008; n=16) 0.07 (0.004; n=10)

“Table 7. Vertical fluxes of POC and PON out of the photic zone. Units are grams of C
or grams of N per square meter per day.
Values in parentheses indicate the standard error and the number of replicates.

Data from Redalje (1994).


sentence simply states that, ‘The estimated extent was 12,500 km? in mid-summer of 1998.” The
number for 1998 is mentioned briefly again on pages 1 and 5, but it is buried in the text and the
word “decrease” is never used to talk about what happened in 1998. In the 1,000+ pages of the
six reports these are the only mentions that we can find of what happened in 1998. None of the
graphs in any of the six reports show the decrease in the extent of the hypoxic area in 1998.
Clearly, the bias of these reports is to show a big increase and to obscure any mention of fact that
might detract from the predetermined outcome.

With respect to Topic 5, we remain puzzled about how the authors developed their
recommendations for a 20% reduction in fertilizer application in addition to other fertilizer best
management practices. Another recommendation was “ A major effort to restore or create 5
million acres (0.7% of the Mississippi River Basin) of wetlands and 19 million acres of riparian
forests (2.7% of the Mississippi River Basin) or some combination of these two approaches to
cause a combined 40% reduction of nitrogen loading in the Gulf-—.” a :

The question we have is what is the quantifiably/identifiable link to these practices and a
reduction in nitrate concentration levels at the mouth of the Mississippi River Basin? . As noted
in our comments on Topic 5, until researchers can give some notion of what cause and effect of
these various actions may be, it is difficult to understand why they would recommend their
implementation.

According to the authors, the main focus of this report would be to identify and evaluate methods
to reduce nutrient loads to surface water and ground water in the Gulf of Mexico. While the
authors were true to their task, one nagging question remains. - If nitrate levels in wafer are
reduced in the Upper Basin of the Mississippi Watershed, what impact will that haye on the
hypoxic zone in the Gulf of Mexico. In other words, what is the link between the two, the cause
and effect?

Topic 4

In the original posting of Topic 4 in section 3.2.3.3, the last sentence of the second paragraph

read as follows:
"Concentrations of 1.5 mg/L for total N and 0.075 mg/L for total P were proposed as
approximate boundaries separating mesotrophic and eutrophic conditions in these flowing
waters (Dodds et al, 1998).”

Compare the sentence above, to the second sentence of the last paragraph of the same section
3.2.3.3 which reads as follows:

“The mean TP concentration of water reported by Smith et al. (1987) for 381 riverine
sites in the continental United States is 130 g/L, a value greatly in excess of the
mesotrophic-eutrophic boundary of 75 g/L proposed by Dodds et al. (1998)."

One of these two sentences appears to be off by 6 orders of magnitude. Which is correct- 0.075
mg/L or 75 g/L? In fairness to the authors, it apparently was a glitch in transferring from one
type of computer to another and it was fixed once the error was pointed out. However, the fact of
the matter is that the error was posted on the web site in the first place, indicating another

aq


example of lack of quality control. With these kinds of factual errors distributed throughout the
reports, it calls into question all the rest of the numbers in the reports. :

The Topic 5 report touches on many important issues with regard to the hypoxic question. For
example, on page 69 they point out that “From the 1930s until the present, there has been a
dramatic loss of wetlands in the Mississippi delta with estimates as high as 100 km? per year —.”
‘They go on to say that “An understanding of the causes of this land loss is important not only that
effective management plans can be developed deal with the land loss but also to understand the
relationships among land loss, water quality and offshore hypoxia.”

“A number of factors have been linked to land loss including elimination of riverine input to
most of the coastal zone due to construction of flood control levees along the Mississippi River,
altered wetland hydrology mostly due to canal construction, salt water intrusion, wave erosion
along exposed shorelines, high subsidence rates, and sea level rise —-. Most have concluded that
land loss is a complex interaction of these factors acting at different spatial and temporal scales .”

The authors go on subsequent pages to substantiate the potential reductions in nitrogen based on
various measurements and experiences. They go on to conclude (page 79) that “The

- effectiveness of these large-scale diversions on significant uptake of nitrate-nitrogen has been
controversial and is not universally accepted (Turner, 1998) so there needs to be additional study
to determine the actual discharge rates of diversion, the area of wetlands needed, the potential .
and actual nitrogen reductions and the linkages between riverine input and offshore response. A.
10-15% reduction of NOs loading during the spring flood might had significant and official
impacts on offshore production in hypoxia.” :

One statement, (page 87) should be retracted “High concentrations in drinking water cause a
disease called “methemoglominemia” or “blue baby.” It should be noted that recent research has
refuted the link between nitrogen and blue baby syndrome. “— The evidence suggests that
diarrhea and/or gastrointestinal infection/inflammation, not ingested nitrates, are the principle
causative factor in infantile methemoglobinemia;—“

“Given the estimated 1-2.4% of water sources contaminated with nitrate levels exceeding 10 ppm
nitrate-N and a dearth of infantile methemogtobinemia cases connected to such water sources,
there is little indication that relaxing the drinking water standard for nitrate (not nitrite) to 15 or
20 ppm nitrate-N would increase the health risk to infants (27).” Environmental Health
Perspectives, Volume 107, Number 7, July 1999.

The authors go on to discuss river diversions in Louisiana (page 91). “Removing 50,000 metric
tons per year would require about 500,000 hectares and a diversion of about 13% of the river
flow. Removal of about 100,000 metric tons would require about 1,000,000 hectares and
diversion of about 26% of the river flow. Because nitrate removal can take place in marshes,
swamps or shallow open water, these areas can be compared to the areas of these habitats in the
coastal zone.

One of our concerns with these reports are statements such as the following. (page 92) “A
“reasonable assumption” is that most of this nitrogen that leaves a farm field does reach the Gulf
as Goolsby et al. (1999) point out that there appears to be little in stream loss of nitrogen once it
reaches the streams and rivers. Reducing 1 million tons of nitrogen in a wetland “conceivably”


Review of Hydroqual proposal
‘THE NEXT STEP TO PURSUE ON THE ORGANIC CARBON ISSUE

‘There is a company called Hydroqual that has developed a carbon model that could probably be
utilized to explore the organic carbon issue in detail. We recommend that the CENR approach
Hydroqual to explore the use of their model regarding this issue. The unknowns pertaining to
organic carbon are 1) the role of terrestrial carbon as energy in the trophic food web (this relates
directly to determining the source of carbon in zooplankton fecal pellets), 2) the lability of
terrestrial carbon (i.e. how much is being respired by the microbes vs. how much is buried in the
sediments), 3) determining seasonal variation in the isotopic signal of terrestrial carbon so that
you can point to the fallacy of using a simple two-member mixing model to determine the
contribution of terrestrial vs marine carbon, and 4) determining the oxygen utilization rates of
particulate terrestrial organic carbon and dissolved organic carbon derived from the breakdown
of the particulate fraction. None of these unknowns will be easy to measure and it will not be
inexpensive to do this work.

um


from the surface to the bottom where it is decomposed primarily by bacteria. The bacteria utilize
oxygen during the decomposition process and if the water column is stratified, i.e. no mixing of
oxygen from the atmosphere to the bottom waters, this microbial respiration may reduce oxygen
concentrations to levels of hypoxia or anoxia (zero oxygen concentration). An important point
is that hypoxia cannot occur without stratification, regardless of the nutrient load.

In the northern Gulf of Mexico the Mississippi/Atchafalaya River system delivers an average of
580 km? of freshwater per year to the northern Gulf of Mexico. This freshwater disperses over
the denser Gulf of Mexico salt water causing water-column stratification. During the late fall,
winter, and early spring the frequent passage of storms impart sufficient energy to disrupt this
stratification and mix the water column. During the summer, however, storms are infrequent and
stratification may persist for months at a time. During this period of stratification, hypoxic
bottom waters form as a result of microbial respiration of organic matter and lack of surface and
bottom water mixing. Once the passage of strong storms resume, stratification is disrupted and
hypoxic conditions cease. Further exacerbating the duration of stratification is the low tidal
mixing energy in the Gulf of Mexico. Thus, physical factors make this region highly susceptible
to water-column stratification and subsequently the onset and maintenance of hypoxia.

‘The other ingredient needed for the onset of hypoxia is a sufficient amount of organic carbon in
the bottom waters and sediments so that respiration of this carbon reduces oxygen concentrations
to levels of hypoxia. In the eutrophication paradigm, this excess of organic carbon is derived
from primary production sinking from the surface waters. This is based on work primarily in
lakes and coastal regions receiving high nutrient loads, but not receiving high rates of organic
carbon loading from the watershed. The Mississippi River, however, carries a large load of both
nutrients and organic carbon that are input directly to the region where hypoxia forms. Thus, it
is difficult to determine whether it is nutrients and the eutrophication paradigm, river-
borne organic carbon, or more likely a combination of both marine and terrestrial organic
carbon that fuels the decline in bottom water oxygen concentration.

This question would be much easier to answer if long term Mississippi River nutrient and
organic flux data, long-term records of hypoxia, and a better understanding of the mechanisms
regulating the vertical flux of both marine and terrestrial organic carbon to bottom waters were in
place. As determining the source of organic carbon fueling hypoxia is critical for management
decisions we will focus our remarks on this issue for the majority of the review of Topic 1.

Review Comments

Page. xv. The report indicates that nitrate concentrations have doubled or tripled since the 1950s
to 1960s. The authors admit that nitrate concentrations have stabilized but that trends are
masked because of high variability. Carey et al. (1999) determined that there has not been a
statistically significant increase in nitrate concentration during the period from 1979-1995. Table
5 (attached) from Carey et al. (1999) shows that almost all stations with data over this period
show no trend in nitrate concentration (Le. accept null hypothesis of no change). This is an
important result as it is argued by the CENR authors that the size of the hypoxia region has
increased over this time period. .

Page xv. The authors state that a stoichiometric nutrient ratio approaching the Redfield ratio has
increased offshore primary production. This is not necessarily the case as production is defined
as biomass/time. Thus, increased production occurs by increasing nutrient concentrations (i.e.


Agriculture Accused of 2.5 to 3 times more pollution than even EPA’s National Water Quality
Inventory Indicates. Serious factual errors were made on page 5 of the revised Topic 6 dated
April 15, 1999, and were posted to the web site.

The report read as follows:
“A 1994 report to Congress (EPA, 1994) indicated that 23% of rivers surveyed, 43% of
lakes and 47% of estuaries were impaired by nutrient enrichment.”
These are serious factual errors overstating agricultural pollution by 2-1/2 to 3 times. This
should have been caught in the peer review process. The numbers in this sentence should be 8%,
17% and 17% respectively, and even these numbers can be shown to be suspect on the high side!.
‘The source for these numbers is the National Water Quality Inventory 1994 Report to Congress,
Appendix pages A-15, B-14, and C-14. See attachment “Spring Cleaning Time for EPA’s Black
Hole of Data,” Public Policy Digest, Volume 6, No. 2, May 1999, for details about how the
National Water Quality Inventory lacks scientific process and lacks solid numbers from water
quality monitoring data.

Topic 6 continued with the next sentence:
“Two years later, the 1996 National Water Quality Inventory, reported even higher levels
of nutrient impairment, 40% of. surveyed rivers, 51% of surveyed lakes, and 57% of
estuaries.”
Again, these are serious factual errors that overstate the issue by nearly 3 times. The actual
numbers ate 14%, 20% and 22%, respectively. (See Appendix of the National Water Quality
Inventory 1996 Report to Congress, Tables A-4, B-4. and C-4.) These are the kinds of errors that
the peer review process should have filtered out.

Summary and Recommendations

The CENR reports ignore many crucial issues which affect hypoxia including the reduction in
fertilizer use by farmers and the impact of changes in the flow. of the Mississippi River. U.S.
Geological Survey data show that the nitrate load in the river has been declining. At the same
time, the flow of the river has been changing. Rainfall has increased in the Mississippi River
Basin over the last thirty years and engineering changes for flood control have added to the flow.

The CENR reports focused on nutrients from agriculture as the cause of hypoxia and predictably
offered nutrient based solutions, including reduced nitrogen use and wetlands creation. The
reports find no economic damage to the commercial fishery from hypoxia, no threat to human
health, do not examine important factors about the complexity of the Mississippi River system,
yet suggest fixing one of the alleged causes by increased regulation of agriculture.

‘The better approach would be to acknowledge and work to understand the tremendous
complexities of the issue. Farmers today are producing more crops with less fertilizer, meaning
they are more efficient and are leaving Jess nitrogen in the environment. Voluntary, cooperative,

1 AN the numbers contained in the EPA National Water Quality Inventory report are suspect on the high side as
noted in, By the Numbers A Review af EPA’s National Water Quality Inventory A Crisis in the Making. American
Farm Bureau Federation, and Murky Waters Official Water Quality Reports Are All Wet, An Inside Look at EPA's
Implementation of the Clean Water Act. May 1999, PEER White Paper.

Ar


+1

Fecal pellet carbon and phytoplankton cell

Gontribution in Bottom Trap 1991 ‘ Fecal peltet carbon Contribution In Top Trap 1992
100 100
80 80
60 + ro MFPCPOC) 60
40 "enim Pool: POC)
40
20 20
° 0
Fecal pellet carbon and phytoplankton cell Fecal pellet carbon in Bottom Trap 1992
100 Contribution in Tan Trap 1991 100
80 80
60 —e—xrecroc) — 60
—w— *iPoett: POC)
40 Bw
20 20
SeRfaRRaESREGERE °
gargs a
Sggeeed esses ees PePEaSERRE REE
ne . ea F 8 8 8 e §

Figure 29, Fecal pellet carbon flux percent contribution to total POG flux % (FPC:POC) and phytoplanklon
carbon flux percent contribution to total POC flux % (Peat:POC). Organic carbon flux was determined from
sedimentation to the surface (5-6 m depth) and bottom (15 m depth) water sediment traps at stations C6B

which is located about 20 km south of Terrebonne Bay. Figure adapted from Qureshi (1995).



particulate organic carbon (POC) and 34% was dissolved organic carbon (DOC). Trefry et ai.
(1994) estimated that 80% of the annual TOC flux from the Mississippi/ Atchafalaya River
System to the Northern Gulf of Mexico occurred from December to June. They also showed that
the POC flux was linearly related to the total suspended matter of the lower Mississippi River,
indicating that POC flux was linearly related with Mississippi River discharge. The %POC in
Mississippi River particles also varied with total suspended matter. At total suspended matter
concentrations greater than 5O mg L" the fraction as POC averaged 1.8% but when the total
suspended matter was below 50 mg L" the fraction of POC increased dramatically to as high as
7.1% (Trefiry et al., 1994).

Ludwig et al. (1996) suggested that 5-10x10" g of terrestrial organic carbon (dissolved plus
particulate) is introduced into the Gulf of Mexico annually in the region that encompasses the
Mississippi delta. These data are similar to those of Trefry et al. (1994) discussed above. Using
the mean instantancous flux of organic carbon of 102 kg per second calculated from USGS data
at St. Francisville, Louisiana over the period 1973 through 1995, we have determined a mean
flux of 2x10" grams of carbon per year. Clearly, all three calculations yield fluxes of 10'? to 10"
grams carbon per year. In fact, additional calculations (using USGS data) show that the total
organic carbon flux at Alton/Grafton, Missouri in 1993 was 85x10" g, approximately 7x greater
than that of the average of the 5 previous years. Although these data are well upstream from the
Gulf of Mexico, they might suggest that during flood years even higher fluxes of organic carbon
from the river onto the shelf could occur. :

Carbon isotopic studies of Gulf of Mexico continental shelf sediments, up until 1997, had
concluded that 50% or more of surficial organic matter derived from marine or phytodetrital
sources (Hedges and Parker, 1976; Gearing et al., 1977; Eadie et al., 1994). However, this idea
came into doubt when Gofii et al. (1997) pointed out that the “C “ages” of surface (0-2 cm)
sediments are very old (~2600 to 6800 years).

This recent work (Gofii et al., 1997) on stable carbon isotopes (8-"C) in organic compounds of
the continental shelf sediments has distinguished between organic carbon whose source was
terrestrial detritus and that of marine production. These authors concluded that many previous
studies have underestimated the amount of organic matter in marine sediments which originated
as terrestrial plant detritus, particularly from Cy, grasses which have stable isotope signatures
similar to that of marine organic carbon. Gofii et al.’s compound-specific stable isotopic analyses
of Gulf of Mexico sediments suggest that organic matter in nearshore Gulf sediments originates
from C; plants from forests and swamps, but that the offshore compounds derive from grasses
(C4 plants) originating from the Mississippi River basin. They state that “quantitative
assessments of terrigenous organic matter inputs using bulk &-"C,, are difficult to accomplish
and may have led to an underestimation of allochthonous contributions.” In fact, no simple
mixing model, using only one terrestrial and one marine endmember, can explain the bulk 6- 5c
data (Ruttenberg and Gofii, 1997). In addition, the organic carbon in suspended matter in the
Lower Mississippi and Atchafalaya Rivers yielded 8-"°C values of the -19% to -24% observed
in surface sediment on the shelf (Onstad et al., in review, as quoted by Gofii et al, 1998).
Ruttenberg and Goiii (1997) also observed that at stations in shallow water depths on the shelf
(<600 m) have C:P and C:N ratios higher than Redfield ratios, which indicates a strong terrestrial
signat (Ruttenberg and Gofii, 1997). Using Gulf of Mexico shelf and slope sediment cores
collected in 1987, Gofii et al. (1998) have recently shown the importance of land-derived C,


into the Gulf of Mexico in 1967. From 1967 to 1995, the mean flow discharge that’s measured at
Vicksburg was 11% greater than the mean flow prior to that time. (page 33-Figure 18).
However, Report 3 states that streamflow in the Mississippi River increased about 30% during
1970-83. There are a number of possible physical reasons for the increase in the Mississippi
River discharge. They range from an increase in the precipitation in the watershed to changes in
the river flow as a result of engineering changes along the river. Ixrespective of the cause, there
is widespread evidence that the flow has increased.

On the other hand, the nitrate concentration levels in the water have stabilized, if not actually
declined in recent years, it is to the extent that the nitrate flux has increased in recent years that is
due to solely to the increase in the flow of water to the Gulf of Mexico.

Another important issue is the question of which nutrients play a role in the hypoxia zone. In the
Topic 1 Report, authors focus almost exclusively on the role of nitrogen. This overlooks another
important nutrient source, organic carbon. Organic carbon is necessary for the onset of hypoxia
in the bottom waters and sediments so that respiration of this carbon reduces oxygen
concentrations to the levels that are hypoxic. It is difficult to determine whether nutrients and the
eutrophication paradigm, river-bome organic carbon, or more likely a combination of both
marine and terrestrial organic carbon that fuels the decline in bottom water oxygen concentration.
(See attached review of this issue.)

Unfortunately, the authors of Topic 1 have focused almost exclusively on the nitrogen issue.
Other researchers are of the opinion that determining the source of organic carbon fueling
hypoxia is critical for management decisions related to the hypoxic zone. This issue must be
thoroughly researched and reviewed prior to taking any precipitous action regarding nitrogen.
Topic 1

This report is a significant contribution to the body of knowledge regarding hypoxia on the
Louisiana/Texas continental shelf. In this review we will provide an overview of the report and
discuss the strengths and weaknesses of the data. Alternate interpretations of the data, especially
as regards the role of terrestrial organic carbon, will draw heavily from a recently published
report on the issue at the University of Alabama (Carey et al. 1999).

Statement of the Problem

World-wide, nutrient over-enrichment (eutrophication) is a critical management issue in coastal
environments as a result of the negative effect that it has on water quality parameters such as
bottom water oxygen concentrations and light attenuation, as well as commercial fishery harvest
and the recreational and aesthetic value of these ecosystems. Changes in the magnitude and
timing of nutrient loading, primarily nitrogen (N), caused by watershed land-use alterations and
combustion of fossil fuels are likely to have a significant impact on coastal ecosystem health as a
result of their effects on biogeochemical processes and food web dynamics in these ecosystems
(Rabalais et al. 1996; Vitousek et al. 1997).

The hypoxia issue in the northem Gulf of Mexico and hence management issues concerning
nutrient runoff are rooted in the “eutrophication paradigm”. The paradigm is a simple sequence
of processes that occur in aquatic and marine ecosystems that are experiencing elevated rates of
nutrient, nitrogen or phosphorus, loading. Incoming nutrient enhances rates of primary
production which is equivalent to organic carbon production. The organic carbon then sinks


Average Annual Flow in Mississippi River at Vickburg by
10-year Interval vs. Avg. Flow for 1820-1992

1000000 5 |e now 932885
Flow .

900000 7 aon240 cls

800000

4931-40 1941-50 1951-60 1961-70 1971-80 1981-90 1991-97 1993

Figure 6.

On page xv of Topic 1 the average flow of the Mississippi River at Vicksburg is stated as 14,000
mi/s which is equal to a total volume of 442 km’ per year of freshwater per year flowing into the
Gulf. However, in the same paragraph on the preceding page (xiv) the authors state that the .
Mississippi River delivers an average of 580 km’ per year to the Gulf, which is a volume that is
31% greater than the volume that would be discharged based on the long-term flow rate of
14,000 m?/s. The difference in total volume is 138 km’ which is enough to cover three average-
size counties in Iowa 100 feet deep. The authors of Topic 1 first use a high number (580 km’)
for volume that is almost exactly equivalent to the average flow rate of 648,783 cfs that occurred
in the decade of 1981-1990 (see Figure 6.), but in the next breath use a low number 14,000 m’/s
(494,340cfs), to describe long-term rate of flow. By using the slight-of-hand of comparing a low
flow rate with a much higher volume in the same paragraph, the authors essentially minimize the
perception of flow rate as a significant long-term agent of change in the Gulf and maximize the
perception that large volumes of nutrients in the short-term are the chief culprit.

Downplaying and Omissions of Key Information

Topic 3 uses data only through 1997 to describe the size of the hypoxic zone even though 1998
data was readily available in mid-1998. Topic 1 leads with a sentence on page xiv about how the
extent of the hypoxic waters “increased” to 16,000 to 18,000 km2 in 1993-1997. The next

26


Rabalais, N. N., W. J. Wiseman, Jr., and R. E. Tuer. 1994. Comparison of continuous records
of near-bottom dissolved oxygen from the hypoxia zone along the Louisiana coast. Estuaries.
17:850-861.

Rabalais, N. N., W. J. Wiseman, Jr., R. E. Turner, D. Justic, B. K. Sen-Gupta, and Q. Dortch.
1996. Nutrient changes in the Mississippi River and system responses on the adjacent
continental shelf. Estuaries 19:386-407.

Redalje, D. G., S. E. Lohrenz, and G. L. Fahnenstiel. 1994. The relationship between primary
production and the vertical export of particulate organic matter in a river-impacted coastal
ecosystem. Estuaries. 17:829-838.

Riley, G. C. 1937. The significance of the Mississippi River drainage for biological conditions in
the northern Gulf of Mexico. J. Mar. Res. 1(1):60-74.

Ruttenberg, K. C. and M. A. Gofii , 1997. Phosphorus distribution, C:N:P ratios, and 8°C in
arctic, temperate and tropical coastal sediments: Tools for characterizing bulk sedimentary
organic matter. Marine Geology, 139:123-145.

Sklar, F. H., and R. E. Tumer. 1981. Characteristics of phytoplankton production off Barataria
Bay in an area influenced by the Mississippi River. Contrib. Mar. Sci. 24:93-106.

Smith, S. M., and G. L. Hitchcock. 1994. Nutrient enrichments and phytoplankton growth i in the
surface. waters of the Louisiana Bight. Estuaries. 17:740-753.

Smith, S. V., and J. T: Hollibaugh. 1993. Coastal metabolism and the oceanic carbon balance.
Rev. Geophys. 31:75-89.

Straile, D. 1997. Gross growth efficiencies of protozoan and metazoan zooplankton and their
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Oceanogr. 42:1375-1385.

Sun, L., E. M. Perdue, J. L. Meyer and J. Weis. 1997. Use of elemental composition to predict
bioavailability of dissolved organic matter in a Georgia river. Limnol. Oceanogr. 42(4):714-
721.

Trefry, J. H., S. Metz, T. A. Nelsen, R. P. Trocine, and B. J. Eadie. 1994. Transport of particulate
organic carbon by the Mississippi River and its fate in the Gulf of Mexico. Estuaries 17:839-
849.

Tumer, R. E. 1984. Zooplankton feeding ecology: contents of fecal pellets of the copepods
Eucalanus pilaetus and Paracalanus quasimodo from continental shelf waters of the Gulf of
Mexico. Mar. Ecol. Prog. Ser. 15:27-46.

Tumer, R. E., and N. N. Rabalais. 1991. Changes in Mississippi River water quality this century:
Implications for coastal foodwebs. BioScience. 41:140-147.

Tumer, R. E., and N. N. Rabalais. 1994. Coastal eutrophication near the Mississippi river delta.
Nature. 368:619-621.

Vitousek, P. M., J. D. Aber, R. W. Howarth, G. E. Likens, P. A. Matson, D. W. Schindler, W. H.
Schlesinger and D. G. Tilman. 1997. Human alteration of the global nitrogen cycle: Sources
and consequences. Ecol. Application. 7:737-750.


Gulf of Mexico Hypoxia Working Group

National Centers for Coastal Ocean Science
WS 13446SSMC4

1305 East-West Highway

Silver Spring, MD 20910

A significant number of the American Farm Bureau Federation's five million members live and
farm within the Mississippi River Basin. We appreciate the opportunity to respond to the six
topical scientific reports requested by the National Science and Technology Council’s Committee
On Environment and Natural Resources (CENR) for an assessment on the causes of hypoxia in
the Gulf of Mexico. Any policies promulgated, as a result of this report will have an immediate,
and possibly profound, impact on the majority of our members.,

Attached are a number of specific responses related to the six topic reports. First, we will make
some overall comments about the CENR reports and the recommendations submitted. Then we
will go back and go over the reports starting with Topic 1.

While there has been a significant amount of work by the scientists who prepared these reports,
the reports themselves raise as many questions as they provide answers.

The first and perhaps overriding issue is the impact of the hypoxic zone on the fisheries of the
Gulf of Mexico. According to Topic 2:
“1) There is no discernable, measurable, or documentable “detrimental
ecological and economic effects” to the Gulf environment or its
fisheries from hypoxia. (Topic 2, p. 52);

2) _. Even during the recent unprecedented extremes in hypoxic conditions (1993-97),
Louisiana’s coastal fisheries flourished, maintaining “energy flow to productive
fisheries (crabs and shrimps) that depend on the bottom.” (Topic 2, p. 9 );

3) Such ecosystem disturbances in the shallow continental shelf
as can be documented are as likely to be the result of trawling
or “other sources of stress.” (Topic 2, p. 50).”

These quotes reflects the very challenging aspect of the Gulf of Mexico hypoxia issue. The
question remains of whether hypoxic zone will ever have any measurable impact on the people
and the economies of the areas in and surrounding the Gulf of Mexico? The indication from this
exhaustive research is that it has not had an impact in the past which means it most likely will not ,
have an impact in the foreseeable future. While some would stop at this point and suggest it is
not necessary to pursue this issue further, we believe that there are other important questions that
need to be addressed.

Tuming next to Topic #1. There are several important issues that need more research and
explanation. For example, Carey notes that there was an upward shift in the mean water flow


an average of over 300,000 cfs from the Mississippi River during the entire month of August of
1993, which is nearly 3 times more flow than it normally would receive from the Mississippi
diversion in August. Assuming 30% average diversion of Mississippi River water for the entire
year of 1993 would amount to an average of 280,000 cfs which is enough to cover 5.5 average-
sized Midwest counties to a depth of 100 feet. While this fact is alluded to as, “episodic event
such as the 1993 flood,” in Topic 3, consideration of the fresh water volume itself is minimized
in favor of extended discussion on nitrate. The magnitude of the volume of the fresh water itself
and the stratification that it would cause at the warmest time of the year, whether it contained any
nitrate at all, would probably have been significant enough to set up hypoxic conditions over
much broader areas of the Gulf than normal. What role the fresh water stratification, nitrate and
organic carbon carried by these flood waters had in prolonging the expanded hypoxic zone in the
years after 1993 is not examined to any degree by the reports.

Are Inputs and Outputs Increasing or Leveling Off? The summary of Topic 3 states that the
annual nitrogen flux has become highly variable since about 1980 due in part to increased
(emphasis added) annual nitrogen inputs into the basin. However, on page 65, Topic 3 states that,
“The leveling off (emphasis added) of fertilizer input, crop outputs and the N residuals may
indicate that a new steady state condition was established about 1980.” The latter statement
contradicts the first statement with regard to nitrogen fertilizer inputs. Furthermore, to say that
crop output has leveled off is erroneous since the national five-year running average yield for
com was 96 bushels per acre in 1980 and has climbed steadily to128 bushels per acre in 1998. _

Market Signals and Voluntary Actions are Surprisingly Effective. On page 78.0f Topic 3 the .
authors state that, “At present no programs or mechanisms are in place to determine if changes in |; ;
nutrient flux in streams occur as a result of voluntary actions and new policies.” While no formal
wide-scale program is in place, there is some long-term data to show that voluntary actions do
make a difference and have slowly and steadily been making a difference since 1983.

Figure 5.


3.5.1 (page 24) of the report. “It is worth emphasizing, as did Topic 2, that failure to identify
hypoxic effects in the commercial fisheries data does not mean that they do not exist. But, if
hypoxic effects do exist, their magnitude must be small in relation to the other sources of
-variability of the data.”

What follows is over 100 pages of text, charts and tables, and references for a cost-benefit
analysis. If there is no identifiable cost, or if it is so small in relation to other variables that it is
not identifiable, why go through the process of months of analysis?

‘The report goes on to say “nonetheless, given the lack of measurable economic benefits from
reduced hypoxia, the Economic Analysis undertaken below was restricted to a cost-effectiveness
analysis that sought to identify least-cost policies for attaining a representative reduction in non-
point nitrogen runoff to the Gulf of Mexico. The fixed target level of nitrogen loss reduction
20%, was suggested by topic Group 5 as a reasonable level that could be attained given the
current technology that would have the potential to decrease incidences of hypoxia in the Gulf.”

If we understand correctly, what the authors are saying is irrespective of the fact that there is no
identifiable cost associated with hypoxia, that they are going to go ahead and fix a target level of
nitrogen loss reduction of 20% as a reasonable level that has some “unquantifiable potential” to
decrease incidences of hypoxia in the Gulf. The logic of this bold position and the following
analysis simply escapes us.

Section 4.2.1 (page 32) “However, transaction costs (developing site-specific plans honoring alt
* producers’ activity) would almost certainly outweigh the benefits. In addition, the results of a
model such as USMP are not detailed enough for a real application of the results to the ground.
Instead, policy must be designed around a few factors that are easy to observe and that are closely
related to nitrogen loss. We determined that a combination of nitrogen fertilizer use reduction
and land retirement were most responsible. To.achieve the 20% N-loss reduction goal, fertilizer
use appeared to be the most important factor.’ We pointed out these statements as an
indication of the hypothetical and subjective nature of the entire Topic 6 report.

Section 4.1 (page 27) the USMP model was developed by the Economic Research Service,
USDA to analyze the effects of government commodity programs, environmental policies on the
US. Ag. sector on the environment.” There is some concern among agricultural economists
about the USMP model. For example, this model has never been available for public scrutiny
and comment. Second, many agricultural economists are of the opinion that this model is
relatively outdated and impracticable for the type of analysis necessary for this situation.

One of the obvious shortcomings in the model is that it shows that when fertilizer applications
are reduced and crop production declines, higher crop prices ensue and offset much of the decline
in income. However, in the internationally competitive environment of the real world, this could
happen only for a very short time period. in an internationally competitive environment. As
soon as U.S. crop prices increase, international competitors ranging from Argentina to Thailand
to China will increase their production and replace the United States in the corn export market.
Consequently, the increase in prices in very transitionary, lasting only briefly unti} other countries
increase their production. The ultimate loss of export markets is much greater as is the loss of
farm income.

AL


Topic 2

Moving briefly on to Topic 2, one quick point needs to be made with regard to the comparison of
the hypoxic zone in the Gulf of Mexico with other parts of the world. “So, in this respect the
northern Gulf of Mexico is not unique. Interestingly, the degree of obvious ecological and
economic effects related to the hypoxia varies from system to system. The most serious
ecological and economic effects of the combined problems of eutrophication and hypoxia are
seen in the Black Sea and Baltic Sea where demersal trawl fisheries have either been eliminated
or severely stressed (Mee 1992, Elmgren 1984). A comparison of effects from three similar
coastal hypoxic zones within the Gulf. indicates that, at least for now significant declines in
fishery production attributable to hypoxia have not been documented for the Gulf of Mexico
(Table 3.1).” (Page 26 — Topic 2)

‘What the authors failed to acknowledge is that the Gulf of Mexico is an open, highly dynamic
system compared to other water bodies such as the Black Sea and the Baltic Sea. Specifically,
the circulation of the Black Sea is very slow, it takes over 10 years to renew the waters in this
body. Moreover, these bodies are surrounded by heavily populated human areas and industrial
systems that have severely polluted their waters. In contrast, the Gulf of Mexico is a very open
and dynamic system. The waters flow in a counterclockwise within the Gulf, with the Atlantic
Ocean constantly recharging or mixing the area. While the Gulf of Mexico hypoxic zone stays in
the same general area along the Coast, it does move and change in formation from year-to-year. ..
Moreover, the hypoxic zone and the Gulf of Mexico is temporal, sting not much more than 90...
days in any given year.

With this in mind, it is difficult to understand why researchers seem to imply by comparison that
the fisheries experience in the Black Sea and Baltic Sea will eventually occur in the Gulf of
Mexico. They simply are not comparable. There has not been a measurable decline in the Gulf
of Mexico fishery production in the past and there is unlikely to be a measurable decline in the
Gulf of Mexico fisheries in the future. .

Contradictions in Basic Hypoxia Theory

Page xvii of Topic 2 states that, “Models that link Mississippi River discharge with Gulf of
Mexico hypoxia demonstrate a worsening hypoxia in bottom waters with increased freshwater
discharge...” However, on page xv of Topic 1 the authors state that the long-term effects in the
offshore ecosystem are not the result of the amount of freshwater discharge or alterations in its
delivery. Since even the authors of the reports are not in agreement about the fundamental
rudiments of how hypoxic conditions arise, it raises a serious question of how can there be clear
direction of what, if anything, needs to be done?

Contradictions in Basic Hypoxia Theory: Page xvii of Topic 2 states that “Models that link
Mississippi River discharge with Gulf of Mexico hypoxia demonstrate a worsening hypoxia in
bottom waters with increased freshwater discharge...” However, on page xv of Topic 1 the
authors state that the long-term effects in the offshore ecosystem are not the result of the amount
of freshwater discharge or alterations in its delivery. Since even the authors of the reports are not
in agreement about the fundamental rudiments of how hypoxic conditions arise, it raises a serious
question of how can there be clear direction of what, if anything, needs to be done?

7


o<tme

Proqucion, mg Pruducton, myC
J = e 4 a x
te i oom

PO owz Opye

Utypunde —agha

Figure 28. Size-fractioned phytplankton production for phytoplankton < 81m and phytoplankton
> 8m in size.
Figure adapted from Redalje et al. (1994)

microzooplankton often grow at rates equal to or greater than phytoplankton and thus can
numerically respond in kind to increases in phytoplankton abundance (Banse, 1982) suggest that
the macrozooplankton are not the dominant herbivores on the Louisiana-Texas Continental Shelf.
This suggests the possibility that the primary source of carbon contributing to macrozooplankton
fecal pellet deposition may not be directly of phytoplankton origin.

It is likely that the macrozooplankton community subsist primarily on microzooplankton (Gifford
and Dagg, 1991). In addition, particles in the Mississippi River plume may serve as a minor
carbon source. These particles have been found in fecal pellets from copepods collected near the
Mississippi River plume (Turner, 1984). If, as indicated, macrozcoplankton are not the dominant
herbivores, then the primary mechanism for vertical carbon flux in the plume is not the transfer
of nutrients to phytoplankton to zooplankton to organic flux. Herbivory by the microzooplankton
community and the transfer of organic carbon through microbial communities to higher trophic
levels have not been considered.

wn


ANA (Feb-Mar 91) ANT (ubAug 90)
POC, micromoles per Ror y ES . POC, micromeles per er

tz (Febrater 81) Ate (dabhug 01)
: POC, micromoles per Ber POC, micromoles par er
bs 10 20 cS 40 50 ° 0 20 30 40 so
1 --* : “
“—— -
fr Ws {" a
~AL oh /
fe > 2 {* /
7 teE i ?
I~ | [EN —_

“Figure 20. Marine and tentgeous particulate organic carbon concentrations measured by Trafrey at al (1994).
Co vant i just west of Souttwest Pass. Station AN-2 is approximataly 20 kam west of AN-1.

Q: How does organic carbon transport in the river affect hypoxia in the Gulf?

A: There is a significant amount of evidence that there is a large export of organic carbon from
terrigenous sources to the Louisiana Shelf, particularly during major flooding events. Recent
papers contradict earlier stable isotope analyses and suggest that a larger portion of the organic
carbon in the sediments is from terrestrial sources than previously thought. Insufficient
information is available to assess the ultimate sink for this material.

It is easy to understand why the terrigenous organic carbon has been overlooked as a source of
organic carbon to the Northern Gulf of Mexico ecosystem. One major gap in determining the role
of terrestrial organic carbon in Gulf hypoxia is that it has been unclear exactly how much organic
carbon actually is introduced onto the continental margin from the river and what percentage of
organic carbon on the shelf was actually allochthonous. Early investigations of organic carbon
transport in the Mississippi River included work performed by Riley (1937). Ratios of organic
matter to chlorophyll suggested to Riley that the river carried “large quantities of organic
detritus.” More recent studies, before and after the 1993 flood, suggested that riverine
sedimentary organic matter can be transported long distances downstream during such events
Garber and Writer, 1998).

Trefry et al. (1994) estimated the.total organic carbon (TOC) flux from the Mississippi River and
Atchafalaya River to be 5.76x10'? g yr’. Of this total, they reported 66% of the TOC flux was

1