Table 2. - Historical and Recent Data on Nitrogen Concentrations in the Mississippi River

Basin (Results in milligrams per liter as N).

Number

of aba Nauta
Location Samples Toul DON! PON! Nitate-N NHg-N DIN Total N2
Lower Minois River
1897-1902 weekly 101 059 042 1.25 O38 163 2.66
1990-98 189 122 045 060 409 O14 423 5.46
Upper Mississippi River near Grafton (below Illinois R. & above Missouri R.)
1899-1900 70 110 048 062 059 O13 0.72 1.82
1980-98 120 127 O8t 063 263 O11 2.74 4.01
Lower Missouri River
1899-1900 63 183 030 153 O51 006 O57 240
1980-98 186 103 OS! «069 «(123 OOS 1.28 224
Lower Mississippi
1905-06 $2 11 040° 0.76 056 O19 066 182
1980-98 104 092 052 038 145 006 151 240

|DON and PON not analyzed on all samples in 1980-98, thus DON + PON does not equal total

organic N for this time period.

2Toual N calculated as the sum of total organic N + DIN.
Calculated as the sum of DON + PON.

Estimated from DON concentrations in upper Mississippi River and Lower Missouri River.
Estimated as 2 times the average 1980-98 PON concentration.

BREGEREREGERE

mated from NH4 concentrations in the upper Mississippi and Lower Missouri River.

Pristine w-a 6-08
1, Nitzogen Concentrations in Lower iilinats River

i



Table 1. — Estimates of Nitrogen Concentrations in the Mississippi River Basin prior to
European Settlement (Pristine conditions).

Nitrogen species mg/L Reference of source

Nitrate 0.10 Maybeck (1982). Ave. for unpolluted major
world rivers

0.09 Clark, et al., (in press) median for 82 relatively
undeveloped U.S. watersheds

Ammonium 001s Maybeck (1982)

Dissolved inorganic N 0.115 Calculated from Maybeck (1982)

Total dissolved N 0.375 Maybeck (1982)

Dissolved organic N 0.26 Calculated (from Maybeck, 1982)

Particulate organic N 0.86 Calculated from estimated pre-development
sediment flux of 400 x 106 t/y (Meade, 1995); N
content of sediment of 0.15%; 1980-96 mean
annual streamflow of 21,990 m/s,

Total organic N 112 Calculated from dissolved and particulate
organic N

Total N 1.24 Calculated from total dissolved N and particulate
organic N

Other estimates of totalN 0.93 Howarth et al., 1996 (from Maybeck 1982)

0,08-1.15 Howarth et al., 1996 (from Lewis, 1986)

0.79 Howarth et al., (1998) for mean discharge=17,313
m/s; basin area=3.23 x 106 km?

0.26 Clark, et al. (in press); small watersheds

throughout the United States


; ud af

i i
th tH
H i

339939a89a893938 $3339339399389939393



U.S. Geological Survey
Mail Stop 406, DFC

Lakewood, CO 80225
December 16, 1999

Gulf of Mexico Hypoxia Working Group

National Atmospheric and Oceanic Administration
National Centers for Coastal Ocean Science

Room 9127, East West Highway

Silver Spring, MD 20910

Colleagues:

The following material is being submitted in response to public comments suggesting that total
nitrogen concentrations in the lower Mississippi River were higher at the beginning of this
century than they are today. This response is based largely on published data presented in

by Palmer (ca. 1903), Leighton (1907), Dole et al.(1909), Goolsby et al (1999), Howarth et al.
(1996, 1998), and Maybeck (1982).

To provide a basis for determining long-term changes in nitrogen concentrations in the
Mississippi Basin, an estimate of mean nitrogen concentrations in the basin before European
settlement (“pristine” conditions) was developed for all major nitrogen species. This estimate is
given in table ! at the end of this document. The mean dissolved inorganic nitrogen (DIN)
concentration, nitrate + nitrite + ammonium, was estimated to be about 0.115 mg/L, and the mean
total dissolved nitrogen (organic + DIN) was estimated to be 0.375 mg/L (Maybeck, 1982). From
these estimates the mean dissolved organic nitrogen (DON) was calculated to be about 0.26
mg/L. Particulate organic nitrogen (PON) concentration was calculated from the pre-development
annual sediment flux from the Mississippi-Atchafalaya Basin to the Gulf (400 million metric tons
per year; Meade, 1995), the estimated N content of the sediment (0.15%), and a mean annual
streamflow of 21,990 cubic meters per second (table 2,2 in Goolsby et al,, 1999). From this
calculation, the PON concentration was estimated to be 0.86 mg/L. The pre-development total
nitrogen (TN) concentration was then calculated from the sum of the DIN + DON + PON to be
1.24 mg/L. Other TN estimates from the literature range from 0.79 to 1.15 mg/L (see table 1).
‘Thus, our TN estimate of 1,24 mg/l may be a little high.

Published data were used to develop estimates of mean annual concentrations of all major
nitrogen species during the period 1897-1906 for 4 locations in the Mississippi Basin. The
locations are 1) the Lower Illinois River, 2) Mississippi River near Grafton, IL (below Illinois
River and above Missouri River), 3) Lower Missouri River, and 4) Lower Mississippi River.
‘These estimates, based on data published in Palmer (ca. 1903), Leighton (1907), and Dole,
(1909), are shown in table 2, Mean nitrogen concentrations at these 4 sites for 1980-98 (Goolsby,
et al., 1999) are also shown in table 2 for comparison.

‘The concentrations of DIN, DON, and PON are shown in graphic form in figures 1-4 for the four
locations, Estimates are shown for three periods in the history of the basin~ pristine, 1897-1906,
and the present (1980-98).

Results presented in tables 1-2 and figures 1-4 show that concentrations of total nitrogen



=

I
ih
if

i

S48393884883333
1GUN td SRIYUOTTUN ‘NaDOLLLIN



increased significantly at 3 of the 4 sites during the past 100 years. Essentially all of the increase
can be attributed to nitrate, which has increased 2 to more than 5 fold. The exception to this is the
lower Missouri River where total N decreased slightly, even though the DIN concentration more
than doubled. All of the decrease in total N in the Missouri River cam be attributed to a large
reduction in the suspended sediment and PON flux from the Missouri Basin. Sediment discharge
from the Missouri River has decreased more than 50% since the 1950s due to construction of
several large reservoirs. The reservoirs trap large amounts of sediment and particulate forms of
nitrogen (PON) and other nutrients. The sediment flux from the Mississippi Basin to the Gulf of
Mexico has also decreased by about 50% since the 1950s (Meade, 1995). As a result, the PON.
flux to the Gulf has also decreased by about 50%.

In summary, we found no data that would indicate the total nitrogen flux to the Gulf was higher
in the past than it is at the present time. PON flux to the Gulf was higher before construction of
the Missouri River reservoirs than it is today. However, the decrease in PON flux has been more
than offset by an increase in nitrate and DIN flux.

References

Clark, G.M., Mueller, D.K., and Mast, M.A., in press, Concentrations and yields of
nitrogen and phosphorus in streams draining relatively undeveloped basins of the
United States, 1990-95, Jour. Am. Water Res. Assoc,

Dole, R.B. 1909. The quality of surface waters in the United States: Part L. -- Analysis of
waters cast of the one hundredth meridian. U.S. Geological Survey Water-Supply
Paper 236. Washington, DC: Government Printing Office. 123 p.

Goolsby, D.A., Battaglin, W.A., Lawrence, G.B., Artz, R.S., Aulenbach, B.T., Hooper,
RP., Keeney, D.R., and Stensland, GJ., 1999. Flux and Sources of Nutrients in the
Mississippi-Atchafalaya River Basin: Topic 3 Report for the integrated Assessment
on Hypoxia in the Gulf of Mexico. NOAA Coastal Ocean Program Decision
Analysis Series No. 17. NOWA Cosstal Qostia Office; altvyr Spring, MD, 129 p.
Also available at URL:

Howarth, R.W., G. Billen, D, Swaney, A. Townsend, N, Jaworski, K, Lajtha, J.A.
Downing, R. Elmgren, N Caraco, T. Jordan, F. Berendse, J. Freney, V. Kudeyarov, P.
Murdoch, and Z. Zhao-Liang. 1996. Regional nitrogen budgets and riverine N & P
pes Oe Oe Sees ee ee ae Natural and human influences.
Biogeochemistry 35:75-139.

Howarth, R.W, 1998. An assessment of human influences on fluxes of nitrogen from the
terrestrial landscape to the estuaries and continental shelves of the North Adantic

Ocean. Nutrient Cycling in Agroecosystems p. 213-223.

Leighton, M.O., 1907, Pollution of the Illinois River by Chicago Sewage, U.S, Geological
Survey WSP 194, 369 p. (this report cites data presented in the Palmer report and other sources).



Lewis, W.M., 1986, Nitrogen and phosphorus runoff losses from nutrient-poor tropical forest.
Ecology v67, p127$-1282. °

Maybeck, Michael, 1982, Carbon, Nitrogen, and Phosphorus Transport by World Rivers.
American Journal of Science, v282, April, 1982, p 401-300.

Meade, R-H. 1995. Contaminants in the Mississippi River. U.S, Geological Survey
Circular 1133. 140 p.

Palmer, Arthar W., ca, 1903, Chemical Survey of the Waters of Illinois: Report for the years
1897-1902, University of Illinois, 254 p.

len abel Heber

US. Geological Survey