APPENDIX 1

LITERATURE CITED AND SUGGESTED REFERENCES

Freshwater Inflow and Effects of Alteration

Armitage, P.D. 1978, Downstream changes in the composition,
numbers, and biomass of fauna in the Tees below Cow Green
Reservoir and in an unregulated tributary, Maize Beck, in
the first five years after.impoundment. Hydrobiologia
58(2):145-156.

Baxter, R.M. 1977. Environmental effects of dams and impoundments.
Ann. Rev. Ecol. Syst. 8:255-283.

Benson, N.G. 1981. The freshwater-inflow-to estuaries issue.
Fisheries 6(5):8-10. .

Pandian, T.J. 1980. Impact of dam-building on marine life.
Helgol. Meeresunters. 33:415-421.

Peters, J.C. 1982. Effects of river and streamflow alteration.
on fishery resources. Fisheries.7(2):20-22.

Vannote, R.L., G.W. Minshall, K.W. Cummins, J.R. Sedell, and C.E.
Cushing. 1980. The river continuum concept. Can. J. Fish.
Aquat. Sci. 37(1):130-137.

The Contribution of Wetland and Estuarine Habitats to Fishery
Production .

Adams, S.M. 1976. The ecology of eelgrass Zostera marina fish
communities. II. Functional analysis. J. Exp. Mar. Biol.
Ecol. 22:293-311.

Bahr, Jr., L.M., J.W. Day, Jr. and J.H. Stone. 1982. Energy
cost accounting of Louisiana fishery production. Estuaries
5(3):209-215.

Blaber, S.J. and T.G. Blaber. 1980. Factors affecting the
distribution of juvenile estuarine and inshore fish. J.
Fish. Biol. 17:143-162,

Bozeman, E.L. and J.M. Dean. 1980. The abundance of estuarine
larval juvenile fish in a South Carolina creek. Estuaries
3389-97.

Chao, L.N. and J.A. Musick. 1977. Life history, feeding habits,

and functional morphology of juvenile sciaenid fishes in the
York River estuary, Virginia. Fish. Bull. 75(4):657-702.

16


Changes in freshwater inflow/salinity alter the amount of
habitat. For example, more estuarine area is available during
periods of high river flow and may represent increased habitat
availability (Deegan and Day, 1984). Salinity may also interact
with temperature to alter the areal extent of habitat. available
for an individual species.

Estuarine hydrodynamics relating to salinity is altered
by the influx of lower temperature river flow. Mihursky et al.
(1981) identified correlations between year class strength of
striped bass (Morone saxatilis) in the Potomac River estuary and
above average spring freshwater runoff and colder than normal
winters. Polgar et al. (1985) similarly identified positive
correlations between climatic factors and the catch per unit
effort of Potomac River striped bass and American shad over
a long-term period. (1929-1976), indicating freshwater inputs
strongly influence survival of these species through critical
periods in development. Survival rate of juvenile chinook salmon
(Oncorhynchus tshawytscha) in the Sacramento-San Joaquin estuary
and the numbers of fry and juvenile salmon are increased through
releases of additional inflow at appropriate seasonal periods
(Kjelson et al., 1981).

Freshwater discharge is also important to anadromous fishes
which make use of rheotaxis in locating the mouth of their natal
river or spawning stream. However, coinciding physical changes
in salinity, temperature, and seston make identification of
cause-and-effect relationships of these migrations difficult.

In summary, salinity is likely one of many physicochemical
and biological factors regulating the amount of habitat available
for fish production, although salinity tolerance limits may be
the key mechanism needed to manage freshwater inflow to estuaries
as previously suggested by Darnell (1981).

The Role of Freshwater Inflows in Estuarine Nutrient Cycling

Estuarine productivity is a result of maintenance of
high nutrient levels in bottom sediments and the water column.
However, controversy remains concerning the extent to. which
freshwater inflows contribute nutrients to estuarine waters.
Nixon (1981) identified five major hypotheses that have been
presented to account for estuarine production: (1) nutrient
enrichment via freshwater inflow; (2) advection of nutrients
from offshore waters; (3) nutrient entrapment in estuarine
circulation; (4) outwelling of nutrients from saltmarshes and
wetlands; and (5) recycling of nutrients within the estuary.
Of these hypotheses, the author concluded that recycling and
remineralization of nutrients and coupling of heterotrophic
and autotrophic processes provide the greater contribution to
estuarine productivity than does the contribution of nutrients
derived from frehwater influx, although nutrients associated
with freshwater inflows may be more influential over estuarine

10


Wandschneider, P. 1984. Control and management of the Columbia-
Snake River system. Agric. Res. Center Publ., Wash. State
Univ. Sea Grant Prog. XB0937.

Biotic Changes Attributed to Altered Salinity Regimes

Adams, D.A. 1963. Factors influencing vascular plant zonation
in North Carolina salt marshes. Ecology 44:445-456,.

Andrews, J.D. and J.L. Wood. 1967, Oyster mortality studies
in Virginia. VI. History and distribution of Minchinia
nelsoni, a pathogen of oysters in Virginia. Ches. Sci.
8(1):1-13.

Blaber, S.J. and T.G. Blaber. 1980. Factors affecting the
distribution of juvenile estuarine and inshore fish. J.
Fish. Biol. 17:143-162.

Bowler, M.W. and A.J. Seidenberg. 1971. Salinity tolerance
of the prawns, Palaemonetes vulgaris and BP. pugio, and
its relationship to the distribution of these species in
nature. Va. J. Sci. 22:94.

Cain, T.D. 1975. Reproduction and recruitment of the brackish
water clam, Rangia cuneata in the James River, Virginia.
Fish. Bull. 73(2):412-417.

Castagna, M. and P. Chanley. 1973. Salinity tolerances of some
marine bivalves from inshore and estuarine environments in
Virginia waters from the mid-Atlantic coast. Malacologia
12:47-96.

Copeland, B.J. 1966. Effects of decreased river flow on
estuarine ecology. J. Water Pollut. Control Fed.
38(11):1831-1839,

Darnell, R.M. 1981. Strategies for the management of;
estuaries. In: Proceedings of the National Symposium
on Freshwater | Inflow to Estuaries. Vol. II. R.D. Cross
and D.L. Williams (eds.). pp. 434-447.

Davis, H.C. 1958. Survival and growth of clam and oyster larvae
at different salinities. Biol. Bull. 114(3):296-307.

Deegan, L.A. and J.W. Day, Jr. 1984. Estuarine fishery habitat
requirements. In: Research for Managing the Nation's
Estuaries. Conf. Proc. in Raleigh, North Carolina.

B.J. Copeland, K. Hart, N. Davis, and S. Friday (eds.).
pp. 315-336. Univ. North Carolina Sea Grant Publ.
UNC-SG-84-08.

20



Introduction

Coastal waters, estuaries, wetlands, and rivers are
important spawning, nursery, and forage habitats for many
fish and shellfish species harvested in U.S. commercial and
recreational fisheries. Many human activities adversely affect
these fishery-related habitats. For example, between the 1950's
and 1970's, an average 18,000 acres of estuarine wetlands were
lost annually in the United States (Tiner, 1984). Although
coastal marsh losses were attributed primarily to subsidence in
the Gulf of Mexico, elsewhere urban development involving dredge
and fill activities significantly contributed to the loss of
wetlands.

The National Marine Fisheries Service (NMFS) recognizes
the significance of both tidal and non-tidal wetlands and other
riverine, estuarine, and coastal habitats as a basis for survival
and health of some living marine resources. These habitats
are interrelated in a complex ecological continuum, so each
contributes an integral role in fishery resource production.
Hence, an ecosystem approach is essential in the assessment
of impacts of human activities on fishery resources and
associated habitats.

The NMFS has primary responsibility for the conservation,
Management, and development of living marine resources and the
protection of certain marine mammals and endangered species.
NMFS also recognizes its responsibility to conserve, restore,
and enhance productive marine, estuarine, coastal, and riverine
habitats that contribute to sustaining the living marine
resources of national interest. In 1983, the NMFS implemented
the Habitat Conservation Policy (48 Federal Register 53142) to
address the agency objective to conserve fishery habitats and
biological communities, and to define the role of the NMFS in
addressing habitat conservation activities through federal
legislative mandates. Under the Fish and Wildlife Coordination
Act (16 U.S.C. 661 et seq.), for example, the NMFS provides an
essential consultative service on regulatory and construction
actions under purview of other federal agencies... The
participation by NMFS in the federal regulatory reform process
is essential to help ensure that regulators fully consider
habitat issues in their decisions. Integral to this concept is
the early involvement of all participants in the decision-making
process, to minimize habitat alteration.

In estuarine and riverine environments, the NMFS is
particularly concerned with alterations of freshwater inflows
which have adverse effects on wetland and open-water habitats and
fish stocks. Instream flow modifications causing environmental
problems include changes in water quality and quantity, creation
of physical barriers, and reductions in flows. Changes in
quantity include modification in total volumes, seasonal
discharges, and rates or timing of flows. The introduction


Conner, J.W. and F.M. Truesdale. 1973. Ecological implications
of a freshwater impoundment in a low-salinity marsh. In:
Coastal Marsh and Estuarine Management. Procs. of the
Coastal and Estuary Management Symposium. R.H. Chabreck
(ed.). pp.- 259-276. a .

Correll, D.L. 1978. Estuarine productivity. BioScience 28:646-
650.

Darnell, R.M. 1961. Trophic spectrum of an estuarine community
based on studies of Lake Pontchartrain, Louisiana. Ecology
42(3):553-568.

Deegan, L.A. and J.W. Day, Jr. 1984. Estuarine fishery habitat
requirements. In: Research for Managing the Nation's
Estuaries. Conf. Proc. in Raleigh, North Carolina.

B.J. Copeland, K. Hart, N. Davis, and S. Friday (eds.).
pp. 315-336. Univ. North Carolina Sea Grant Publ.
UNC-SG-84-08. :

Gunter, G. 1967. Some relationships of estuaries to fisheries
of the Gulf of Mexico. In: Estuaries. G.H. Lauff (ed.).
Amer. Assoc. Adv. Sci. Publ. No. 83. pp. 621-637.

Haines, F.B. and C.L. Montegue. 1979. Food sources of estuarine
invertebrates analyzed using 13C/12C ratios. Ecology
60: 48-56.

Heck, K.L. and R.J. Orth. 1980. Sea grass habitats: the role of
habitat complexity, competition and predation in structuring
associated fish and motile invertebrate assemblages. In:
Estuarine Perspectives. V.S. Kennedy (ed.). pp. 449-464.
Academic Press, N.Y.

Hyatt, K.D. 1979. Feeding strategy. In: Biogenetics and
Growth. Vol. XI. W.S. Hoar, D.J. Randell, and J.R. Brett
(eds.). pp. 71-119. Academic Press, N.Y.

Lewis, V.P. and D.S. Peters. 1984. Menhaden - A single step
from vascular plant to fishery harvest. J. Exp. Mar. Biol.
Ecol. 84:95-100.

McHugh, J.L. 1966. Management of estuarine fisheries. In:
A Symposium on Estuarine Fisheries. R.F. Smith, A.H.
Schwartz, and W.H. Massmann (eds.). Amer. Fish. Soc.

Spec. Publ. 3. pp. 133-154. Wash., D.C.

Estuarine Processes. Vol. I. pp. 15-27. M. Wiley (ed.)
Academic Press, NY.

McHugh, J.L. 1976. Estuarine fisheries: Are they doomed? In:

Nixon, S.W. 1982. Nutrient dynamics, primary production and
fishery yields of lagoons. Oceanologia Acta. Proc.
International Symposium on Coastal Lagoons.

17


Stevenson, J.C. and N.M. Confer. 1978. Summary of available
information on Chesapeake Bay submerged vegetation.
Contract No. FWS 14-16-0008-2138. FWS/OBS-78/66. August
1978. 335 pp.

Stewart, R.E. 1962. Waterfowl populations in the upper
Chesapeake region. U.S. Fish Wildl. Serv. Spec. Sci.
Rep.-Wildl. 65. 208 pp.

U.S. Army Corps of Engineers. 1984. Chesapeake Bay low
freshwater inflow study. Main rep. 74 pp.

Weinstein, M.P. and H.A. Brooks. 1983. Comparative ecology of
nekton residing in a tidal creek and adjacent sea grass
Meadow: community composition and structure. Mar. Ecol.
Prog. Ser. 12:15-27.

Weinstein, M.P. and M.P. Walters. 1981. Growth, survival and
production in young-of-year populations of Leiostomus
xanthurus Lacepede residing in tidal creeks. Estuaries
4:185-197.

The Role of Freshwater Inflows in Estuarine Nutrient Cycling

Anderson, G.F., and B.J. Neilson. 1985. Trapping efficiency
of a small irrigation impoundment on the Eastern Shore of
Virginia. A Report to Virginia State Water Control Board.

Armstrong, N.E. 1982. Responses of Texas estuaries to
freshwater inflows. In: Estuarine Comparisons. V.S.
Kennedy (ed.). Academic Press, N.Y.

Axelrad, D.M., K.A. Moore, and M.E. Bender. 1976. Nitrogen,
phosphorus, and carbon flux in Chesapeake Bay marshes.
Virginia Water Resources Research Center Bull. 79.
VPI-VWRRC-BULL 79. 57 pp.

Borman, F.H., G.E. Likens, J.G. Siccama, R.S. Pierce, and J.S.
Eaton. 1974. The export of nutrients and recovery of
stable conditions following deforestation at Hubbard
Brook. Ecol. Monogr. 44:255-277.

Bowden, W.B. 1984. Nitrogen and phosphorus in the sediments of
a tidal freshwater marsh in Massachusetts. Estuaries 8(2):
108-118.

Copeland, B.J., H.T. Odum, and D.C. Cooper. 1972. Water
quantity for preservation of estuarine ecology. In:
Conflicts in Water Resources Planning. . Water Resources
Symposium No. 5. E.F. Gloyna and W.S. Butcher (eds.).

23


Tiner, Jr., R.W. 1984. Wetlands of the United States: Current
status and recent trends. U.S. Fish and Wildlife Service,
March 1984. Wash., D.C. vii + 59 pp.

Turner, R.E. 1977. Intertidal vegetation and commercial yields
of penaeid shrimp. Trans. Amer. Fish. Soc. 106:411-416,

U.S. Dept. of Commerce. 1985. Fisheries of the United States,
1984. Current fishery statistics No. 8360.

Weinstein, M.P. 1979. Shallow marsh habitats as primary
nurseries for fish and shellfish, Cape Fear, North
Carolina. Fish. Bull. 77:339-357.

Weinstein, M.P. and H.A. Brooks. 1983. Comparative ecology of
nekton residing in a tidal creek and adjacent sea grass
meadow: community composition and structure. Mar. Ecol.
Prog. Ser. 12:15-27.

Weinstein, M.P. and M.F. Walters. 1981. Growth, survival and
production in young-of~-year populations of Leiostomus
xanthurus, Lacepede residing in tidal creeks. Estuaries
4:184-197,

Whitaker, R.H. and G.E. Likens. 1975. ‘The biosphere and man.
In: Primary Productivity of the Biosphere. H. Leith and
R.H. Whitaker (eds.). pp. 305-328. Springer-Verlag, N.Y.

Zedler, J.B., T. Winfield, and P. Williams. 1980. Salt marsh
productivity with natural and altered tidal circulation.
Oecologia 44:236-240.

Case Studies of Altered Freshwater Inflows

Aleem, A.A. 1972. Effect of river outflow management on marine
life. Mar. Biol. 15:200-208.

Johns, G. 1981. Freshwater inflow and water management in
California. In: Proceedings of the National Symposium on
Freshwater Inflow to Estuaries. Vol. II. R.D. Cross and
D.L. Williams (eds.). pp. 84-87. U.S. Fish Wildl. Serv.
Biol. Serv. Prog., Wash., D.C. FWS/OBS-81/04.

Kjerfve, B. 1976. The Santee-Cooper: a study of estuarine
manipulations. In: Estuarine Processes. Vol. I. M.L.

Wiley (ed.). pp. 44-56. Academic Press, N.Y.

Texas Department of Water Resources. 1981. The influence of
freshwater inflows upon the major bays and estuaries of
the Texas Gulf Coast. Executive Summary. LP-115.

U.S. Army Corps of Engineers. 1984. Chesapeake Bay low
freshwater inflow study. Main rep. 74 pp.

19


regeneration rates are significantly affected by physical and
chemical parameters of the overlying water column (Edwards,
1981). Hence, freshwater inflow can result in salinity
transitions to create changes in nutrient regeneration rates
controlled by complex biological and physicochemical processes.

Seasonally high freshwater inflows transport organic matter
from saltmarshes to estuarine waters. Some Spartina marshes
provide significant quantities of detritus to estuaries (Teal,
1962), although few organisms are able to digest and directly
utilize the material (Pomeroy et al., 1976). Consequently,
microorganisms must convert plant detritus to soluble compounds
utilized by detritivores. River flows. provide a detrital
transport mechanism allowing plant debris to reach decomposers
at the sediment-water interface, and thus, contribute to overall
estuarine productivity. Further, freshwater inflows transport
algae, protozoa, fungi, and bacteria, thereby providing energy
sources for detritivores (Odum, 1980). -

Zedler et al. (1980) studied the influence of river inflow
on saltmarsh productivity and concluded that higher productivity
values were attributed to river inflow which physically altered
an embayment area. In turn, alteration decreased soil salinity
and retained nutrients in the marsh. Linthurst (1980)
demonstrated that an increase in substrate salinity (from 15 ppt
to 45 ppt) decreased S. alterniflora biomass by 66 percent,
although the presence of N and aeration of the substrate reduced
the effects of high salinity. Hence, freshwater flows also
provide a circulatory mechanism that stimulates increased
saltmarsh production.

Summary and Conclusions

Freshwater inflows draining terrestrial ecosystems transport
sediments, nutrients, detritus, and dissolved inorganic materials
to the marine environment and. influence physicochemical estuarine
conditions. Flowing waters link diverse physical gradients and
associated biotic influences, thus providing energy-transfer
pathways and an ecological continuum. Consequently, freshwaters
moving from uplands thru bottomland hardwood swamps and vegetated
and non-vegetated tidal and non-tidal wetlands to estuaries
replenish, exchange, and transport matter and energy to sustain
a balance throughout the ecosystem.

Estuaries and associated wetlands are valuable spawning,
nursery, and feeding habitats for many commercially and
recreationally important fishery resources and essential forage
species. The quantity of freshwater inflow to estuaries affects
the composition, abundance, and productivity of estuarine
communities because life history strategies, migratory patterns,
and feeding habits are keyed to salinity shifts and flushing
patterns. Nutrients, sediments, detritus, toxins, and pathogens
alter the quality of freshwater inflows ultimately influencing
fishery resource Production.

14


Analyses produced over 115 statistically significant
multiple regression harvest equations. Major seasonal response
differences were noted among the species, particularly between
fisheries populations inhabitating the upper: (high rainfall)
coast versus lower (low rainfall) coast of Texas. Overall, 86
percent of harvest correlations were positively linked to spring
inflows, while 57 and 76 percent were rélated positively to early
and late fall inflows, respectively.

The U.S. Army Corps of Engineers (1984) evaluated the
effects of reduced freshwater inflow on environmental and
socioeconomic values of the Chesapeake Bay. Major objectives
of the study were to assess existing physicochemical, biological,
and environmental conditions of Chesapeake Bay and to project
future water resource needs to the year 2020. Utilizing life
history information on 57 Chesapeake Bay ‘species, hydraulic
modelling identified potential short- and long-term spatial
impacts attributed to salinity changes on the biota and
commercial fisheries of the Bay.

San Francisco Bay and the Sacramento-San Joaquin Delta
have been adversely affected by water diversions from the tidal
basin. Since 1951, freshwater flow entering the Bay via the
San Joaquin and Sacramento Rivers has been reduced by 50 percent
as federal and state projects have diverted river water to
irrigate agricultural lands (Johns, 1981). Populations of
spawning salmon in the Sacramento River have declined by more
than 50 percent between 1960 and 1979. In addition, freshwater
diversion projects have contributed to the large decline in
numbers of striped bass in the San Francisco estuary, and have
significantly altered the salinity balance in the estuarine
zone of the Sacramento-San Joaquin Delta (Orlob, 1976).

Dam construction and altered instream flows have contributed
to significant declines or elimination of many salmon runs in
the Pacific Northwest (Pacific Fishery Management Council,
1979). The Columbia-Snake River System has 39 federal, 19 non-
federal, and 3 international treaty dams in operation or under
construction (Wandschneider, 1984). Dam construction, the
primary factor in the decline of the Pacific Northwest's
anadromous fish resources, has altered seasonal and annual
river flow regimes, created delays in migration, and increased
mortalities in juvenile fish as they pass through turbines and
over spillways.

Prior to 1941, the Santee River in South Carolina had the
fourth largest river discharge of any East Coast river. However,
increased energy needs resulted in hydroelectric development
which diverted approximately 88 percent of the Santee River's
flow ‘to the nearby Cooper River ' (Kjerfve, 1976). As a result
salinity regimes, sediment deposition and érosion patterns,
flooding characteristics, and floral and faunal communities were
drastically altered. A hard clam fishery and extensive seed
oyster beds in the lower Santee River were eliminated by the
effects of the diversion project.



Simpson, R.L., D.F. Whigham, and R. Walker. 1978. Seasonal
patterns of nutrient movement in a freshwater tidal marsh.
In: Freshwater Wetlands: Ecological Processes and Management
Potential. R.F. Good, D.F. Whigham, and R.L. Simpson
(eds.). pp. 243-257. Academic Press, N.Y.

Simpson, R.L., R.E. Good, M.A. Leck, and D.F. Whigham. 1983,
The ecology of freshwater tidal wetlands. BioScience
33:255-259,

Stevenson, J.C., D.R. Heinle, D.A. Flemer, R.J. Small, R.A.
Ronland, and J.F. Ustach. 1977. Nutrient exchanges between
brackish water marshes and the estuary. In: Estuarine
Processes. Vol. II. M. Wiley (ed.). pp. 219-240.

Academic Press, N.Y.

Teal, J.M. 1962. Energy flow in a salt marsh ecosystem of
Georgia. Ecology 43:614-624,.

Valiela, I. and J.M. Teal. 1979. The nitrogen budget of a salt
marsh ecosystem. Nature 280:652-656.

Ward, G.H., J.M. Wiersema, and N.E. Armstrong. 1982. Matagorda
Bay: a Management plan. Report to the National Coastal
Ecosystems Team, U.S. Fish and Wildlife Service, Wash.,
D.C. Contract No. 14-16-009-78-066.

Wharton, C.H., W.M. Kitchens, E.C. Pendelton, and T.W. Sipe.
1982. The Ecology of Bottomland Hardwood Swamps of the
Southeast: A Community Profile. U.S. Fish and Wildlife
Service, Wash., D.C. FWS/OBS-81/37. 133 pp.

Wilcox, D.P. and W.M. Childress. 1981. Nutrient flux between
the Nueces deltaic marsh and the Nueces Estuary on the Texas
Gulf coast. In: Proceedings of the National Symposium

Freshwater Inflow to Estuaries. Vol. I. R.D. Cross and
D.L. Williams (ed.). pp. 472-488.

Zedler, J.B., T. Winfield, and P. Williams, 1980. Salt marsh
productivity with natural and altered tidal circulation.
Oecologia 44:236-240.

Ay, S$, GOVERNMENT PRINTING OFFICE: 1987--701-817--60033

26



waters. This holistic approach, including linkages between
streams and their terrestrial setting, and identifying biotic
interactions and integration of ecological principles, helps to
identify cause-and-effect relationships between freshwater inflow
and estuarine productivity. The NMFS believes that holistic
research would document such relationships.

We have reviewed pertinent technical literature and provide
reference lists regarding the following: (1) the contribution of
wetland and estuarine habitats to fishery production; (2) case
studies of altered freshwater inflows; (3) biotic changes
attributed to altered salinity regimes; and (4) the role of
freshwater inflows in estuarine nutrient cycling (Appendix 1).

In addition we provide a brief summary of the references in the
following narrative.

Each section summarizes the available information,
although discussion is generally limited to site-specific studies
relevant to the contribution of freshwater inflows to estuarine
productivity and fishery resource production. We provide this
compilation for consideration by all regulatory agencies having
authority over projects that would result in modified freshwater
flows to marine and estuarine ecosystems. We recommend that the
reader consult additional reviews addressing the issue of altered
freshwater inflows (e.g., Copeland (1966), Baxter (1977),
Armitage (1978), Pandian (1980), Benson (1981), and Peters
(1982)).

Literature Reviews

The Contribution of Wetland and Estuarine Habitats to Fishery
Production

Estuaries are semi-enclosed bodies of water. with an opening
to the sea measurably diluted with freshwater derived from
land drainage (Pritchard, 1967). Rivers draining terrestrial
ecosystems transport freshwater, sediments, organic detritus,
dissolved organic and inorganic materials, and pollutants to
the marine environment. Thus, riverine, estuarine, and coastal
waters are integrally linked to terrestrial ecosystems via
freshwater inflows.

Estuaries are among the most biologically productive
ecosystems in the world (Odum, 1971), possessing mean annual
primary proguction rates of 1500 grams (dry matter) per square
metet (om/m ) as compared with values of 125, 360,400, and
650 gm/m* for open ocean, continental shelf water, lakes and
cultivated land, respectively (Whitaker and Likens, 1975).
Estuarine production results from five types of autotrophs:
emergent vegetation, phytoplankton, benthic algae, periphyton,
and submerged aquatic vegetation (Correll, 1978). Biomass
and energy produced by these autotrophs is then. consumed by

3


of contaminants including toxic organic compounds, heavy metals,
and pathogens, and alterations in fluxes of nutrients and
sediments contribute to changes in water quality. Water quality
degradation could also occur as diminished freshwater inflow
exacerbates pollution by reducing the amount of dilution in
estuarine waters. In addition, alterations in water quality
include reductions in the amount of dissolved and particulate
(detrital) material in the freshwaters entering estuaries via
non-tidal wetlands and other floodplain ecosystems. Physical
barriers reduce downstream flow of food material and sediments
necessary to nourish marshes, submerged aquatic vegetation and
other estuarine species, and prevent or impede the upstream
spawning migration of anadromous fish resources.

Activities including water diversion projects for
agricultural irrigation under federal purview of the Bureau
of Reclamation; dam construction for water supply and flood
control under permit authority of the Army Corps of Engineers;
and hydroelectric development under authority of the Federal
Energy Regulatory Commission have contributed to alterations of
freshwater inflow to estuaries. Although large projects such as
hydropower dams on the Pacific Northwest's Columbia River and
water diversion projects within the Colorado River Basin have
adversely affected living marine resources, the NMFS is also
concerned that projects of lesser magnitude similarly alter
instream flows within smaller watersheds. These activities
have equally adverse impacts on fishery resources and the marine
ecosystem when considered cumulatively. Consequently, effective
freshwater inflow planning requires that all human activities
modifying the water quality, quantity, or seasonal flow regimes
entering the ocean be adequately assessed to determine )
synergistic effects and cumulative impacts on fishery-related
habitats.

An example of this approach occurs in the Pacific Northwest,
where the NMFS interacts with other agencies and organizations
through legislative mandate of the Pacific Northwest Electric
Power Planning and Conservation Act (16 U.S.C. 839 et seq.)
to ensure full consideration of habitat conservation in
hydroelectric development. The law includes specific provisions
for adequate water flows and fish passage facilities prior to
construction, as well as the assurance that fish protection
and mitigation measures are operational at the time of initial
Project operation. The NMFS advocates the need for early
involvement by all participants in regulatory processes to
ensure that impacts to fishery-related habitats are minimized.

Although the influence of freshwater inflows on estuarine
productivity has been documented, the NMFS believes that further
research is necessary to identify cumulative impacts to the
marine ecosystem. The River Continuum Concept (Vannote et al.,
1980), conceptualizing the entire fluvial system as an integrated
series of physical gradients and associated biotic adjustments,
is the current paradigm addressing the ecology of flowing °

2


Many human activities have altered freshwater inflows.
Consumptive uses decrease overall freshwater availability to
estuaries while non-consumptive uses restrict natural flow
of matter to estuaries. Dam and levee construction, stream
channelization, navigational channel dredging, deforestation,
and agricultural diversions modify total volumes, seasonal
discharges, and rates or timing of flows. Additionally, these
projects affect water quality and create physical barriers that
ultimately influence fishery resource yield.

The.NMFS is conducting comparative studies relating species
(both vertebrate and invertebrate) composition, abundance,
size, and food intake to water depth and salinity in estuaries
influenced by both unaltered and altered freshwater inflows.

In addition, the NMFS funds research projects addressing
freshwater inflow issues through the Saltonstall-Kennedy
Fisheries Development Grant Program, the Commercial Fisheries
Research and Development Act (P.L. 88-309), and the Anadromous
Fish Conservation Act (P.L. 89-304), while the National Oceanic
and Atmospheric Administration supports additional projects
through the Sea Grant Program. -The NMFS recognizes research
activities by the other federal agencies and recommends that
both environmental and regulatory agencies continue to conduct
or support research which aids in identifying cause-and-effect
relationships between freshwater inflows and fishery resource
production, and ultimately influences management decisions to
conserve fishery-related habitats.

The NMFS believes that all federal and state agencies
regulating projects which alter freshwater inflows should
consider the cumulative effects to estuarine production in their
decision-making processes. Permits and licenses issued must
contain provisions for withdrawal, discharge, and the return
of water that minimize adverse effects to the environment.
Management decisions should be directed to meet societal. needs
while still maintaining adequate freshwater inflows that sustain
estuarine and fishery resource production.

Acknowledgments
We are grateful to Robert L. Lippson and several anonymous
reviewers at the Northeast Fisheries Center who contributed
helpful criticism and suggestions to the draft document.
The authors are especially grateful to Anne Bergman for her

patience and good nature in word processing the many revisions
of the manuscript.

15


and indirectly, for estuarine fishes (Darnell, 1961; Odum and
Heald, 1975; Lewis and Peters, 1984). Conversely, Haines and
Monteque (1979) identified phytoplankton, rather than marsh
grass, as the major factor in shellfish production in a Georgia
estuary. In fact, estuarine food webs are likely a mixture of
detrital- and phytoplankton-based pathways, with the source and
extent of primary production highly variable among estuaries
(Deegan and Day, 1984).

Case Studies of Altered Freshwater Inflows

Numerous studies have correlated freshwater inflows and
fishery resource production. Aleem (1972) described the impacts
on coastal life near the Nile Delta from construction of the
Aswan Dam in Egypt. The disappearance of nearshore phytoplankton
blooms was attributed to a reduced net annual loss of 35 billion
cubic meters of freshwater to the Mediterranean, reducing catches
in the Sardinella fishery along the delta coast from 4600 metric
tons (mt) in 1965 to 544 mt in 1966.

Sutcliffe (1972) identified positive relationships
between the flux of particulate nitrogen and carbon material to
St. Margaret's Bay, Nova Scotia (a large estuary located in the
St. Lawrence River drainage) and the catch of four commercially
important fish species in the Gulf of St. Lawrence. In another
study (Sutcliffe, 1973), river discharge was positively
correlated with local landings of the American lobster (Homarus
americanus) and the Atlantic halibut (Hippoglossus hippoglossus)
in the Gulf of St. Lawrence.

Seven major and several smaller estuarine systems along
370 miles of Texas coastline have been affected by significant
reductions in freshwater inflow due to upstream water diversion
projects (Texas Department of Water Resources, 1981).
Consequently, regulations were passed (Texas Water Codes,
Sections 11.147 and 16.051, as amended), requiring the Texas
Department of Water Resources to base management decisions upon
the cumulative impacts of upstream water resource developments
and the probable impacts of all new applications for water right
permits on the fishery resources and associated habitats of the
Texas bays and estuaries.

Models were also developed to evaluate the effects of
freshwater inflow on fish production and habitats in the seven
Texas estuaries: (1) the Sabine-Neches system, (2) the Trinity-
San Jacinto system, (3) the Lavaca-Tres Palacios system, (4) the
Guadalupe estuary, (5) the Mission-Aransas system, (6) the Nueces
system, and (7) the Laguna Madre system. Technical analyses
quantified the annual and seasonal inflow needs in relation ito
nutrient supplies, habitat maintenance, and production of fishery
resources in an effort to maintain the fisheries that generate an
estimated $153 million (1980$) in annual personal income in Texas
(Texas Department of Water Resources, 1981).

5


Diener, R.A. 1975. Cooperative Gulf of Mexico Estuarine
Inventory and Study - Texas: Area Description. Natl. Mar.
Fish. Serv. Circ. 393. 129 pp.

Gunter, G. 1961. Some relationships of estuarine organisms to
salinity. Limnol. Oceanogr. 6:182-190.

Gunter, G., B.S. Ballard, and A. Venkataramaish. 1973. Salinity
problems of organisms in coastal areas subject to the effect
of engineering works. Contract Rep. H-73-3. Dept. of the
Army, Corps of Engineers. 176 pp.

Heck, K.L. and R.J. Orth. 1980. Sea grass habitats: the role of
habitat complexity, competition and predation in structuring
associated fish and motile invertebrate assemblages. In:
Estuarine Perspectives. V.S. Kennedy (ed.). pp. 449-464.
Academic Press, N.Y.

Holland, A.F. 1985. Long-term variation of macrobenthos in a
mesohaline region of Chesapeake Bay. Estuaries 3(2A):93-
113.

Hopkins, S.H. 1973. Annotated bibliography on effects of
salinity and salinity changes on life in coastal waters.
Texas A&M Univ. Res. Found, College Station, Texas.

411 pp.

Hughes, D.A. 1968. Responses to Salinity change as a tidal
transport mechanism of pink shrimp, Penaeus duorarum.
Biol. Bull. 136:43-53.

Joseph, E.B. 1973. Analysis of nursery ground. In: Proceedings
of a Workshop on Egg, Larval and Juvenile Stages of Fish in
Atlantic Coast Estuaries. A.L. Pacheco (ed.). pp. 118-121.

Kalke, R.D. 1981. The effects of freshwater inflow on salinity
and zooplankton populations at four stations in the Nueces-
Corpus Christi and Copano-Aransas Bay systems, Texas from
October 1972-May 1975. In: Proceedings of the National
Symposium on Freshwater Inflow to Estuaries. Vol. I.

R.D. Cross and D.L. Williams (eds.). pp. 454-471.

Kinne, 0. 1967. Physiology of estuarine organisms with special
reference to salinity and temperature: general aspects. In:
Estuaries. G.H. Lauff (ed.). pp. 525-540.

Kjelson, M.A., P.F. Raguel, and F.W. Fisher. 1981. Life
history of fall-run juvenile chinook salmon (Oncorhynchus
tshawytscha), in the Sacramento-San Joaquin estuary,
California. In: Estuarine Comparisons. V.S. Kennedy
(ed.). Vol. II. pp. 393-411. Academic Press, N.Y.

21


This TM series is used for documentation and timely communication of
preliminary results, interim reports, or special-purpose information, and
has not received complete formal review, editorial control, or detailed
editing.

Influence of Freshwater Inflows
on Estuarine Productivity

James G. Turek’, Timothy E. Goodger', Thomas E. Bigford2, and John S. Nichols?

‘Northeast Regional Office, National Marine Fisheries Serv., Oxford, MD 21654
?Northeast Regional Office, National Marine Fisheries Serv., 2 State Fish Pier, Gloucester, MA 01930

U.S. DEPARTMENT OF COMMERCE

Matcolm Baldrige, Secretary

National Oceanic and Atmospheric Administration
Anthony J. Calio/ Administrator

National Marine Fisheries Sérvice
William E. Evans, Assistant Administrator for Fisheries

Northeast Fisheries Center
Woods Hole, Massachusetts
May 1987 \

Semen Los ice
| Sena



Species may increase or decline in abundance, become
extinct, or migrate to other suitable estuarine areas in response
to salinity changes. Shifts in abundance or distribution imply
new trophic relationships that may alter estuarine primary
production. Phytoplankton production may be significantly
altered by changes in freshwater influx. If inflow is decreased,
the most dominant group in the phytoplankton community will shift
towards a more marine form. The amount of freshwater influx
also dictates estuarine salinity gradients that influence
phytoplankton distribution. Modelling of the lower Hudson
estuary by Malone et al. (1980) and Neale et al. (1981) indicated
that peaks in netplankton biomass occur between pulses in
freshwater flow. During peaks of high river flow, estuarine
circulation and the pycnocline (boundary layer of sharp vertical
density change) are altered as denser marine bottom water moves
up into estuarine surface waters. Consequently, diatoms
entrained in the boundary layer are advected into the upper
water column of the estuary. Hence, biomass fluxes in terms of
chlorophyll a are dominated by boundary inputs during high flow,
and by growth and grazing by more euryhaline plankton species
during low flow.

Herbivorous zooplankton which consume a major portion of
phytoplankton are a key link in energy transfer to higher trophic
levels. The calanoid copepod, Acartia tonsa, is a widespread,
seasonally dominant zooplankton species in Chesapeake Bay, and
is estimated to consume approximately half of the phytoplankton
production in the Patuxent River, Maryland during the summer
months (U.S. Army Corps of Engineers, 1984). Estuarine
zooplankton populations are sensitive to salinity and temperature
changes such that optimal conditions for growth and survival
occur at different times during the year for each species. In
the Nueces-Corpus Christi and Copano-Aransas estuarine systems
in Texas, freshwater inflows resulted in replacement of estuarine
species with oligotrophic species. Consequently, populations of
A. tonsa were lowest during maximum inflow but sharply increased
following salinity increases by as little as 1 to 3 ppt (Kalke,
1981). In addition, estuarine zooplankton composition and
abundance are also influenced by development rates versus
flushing time (Perkins, 1974).

Adult benthic organisms have limited motility; thus,
biomass, distribution, and diversity fluctuations are strongly
correlated with salinity variability. Benthic species
distribution may be determined primarily by the rate and
magnitude of salinity change rather than the salinity gradient.
Hence, a species would have a greater salinity tolerance in
an estuary with a smaller rate of salinity change. Further,
sediment salinity is likely the more critical factor limiting
species distribution than water column salinity, because most
benthic organisms live in rather than on the sediment surface
(Sanders et al., 1965).



Biotic Changes Attributed to Altered Salinity Regimes

Salinity is a primary ecological factor regulating the
distribution and survival of marine organisms (Gunter, 1967).
Gunter (1961) and Hopkins (1973) reviewed the relationships of
salinity to all organisms living in coastal waters with emphasis
on Gulf and Atlantic coast estuaries, particularly those
influenced by water diversion projects which alter salinity
regimes. -

The amount of freshwater entering an estuary determines
physicochemical variables (e.g., salinity, temperature, and
turbidity) directly affecting physiological processes in
organisms. Previous studies on freshwater inflow alterations
to estuaries identified effects on physicochemical processes
(Orlob, 1976; Schroeder, 1978), and also on the physiological
effects on estuarine organisms (Kinne, 1967). Estuarine fauna
must’, adjust to fluctuating osmotic conditions either by
tolerating considerable variation in blood concentration or
by efficient osmoregulation. Hence, the lower salinity limit
of an organism is primarily a physiological response; the upper
salinity limit is either ecological or behavioral rather than
physiological. The increase of predator/competitor species and
disease with increasing salinity is one reason why many animals
are not found in higher salinities which the species can,
otherwise, physiologically tolerate (Gunter et al., 1973).

Salinity is a primary factor regulating estuarine primary
production. Adams (1963), for example, found that salinity
is a major factor in the zonation of vascular plants in
saltmarshes. Direct effects of freshwater inflow/salinity
fluctuations are primarily physiological, affecting seed
germination, plant growth, and biomass, and these responses are
ultimately reflected in the competitive balance among emergent
plant species and the presence of plant zonation in marshes
(Nestler, 1977; Smart and Barko, 1978).

Submerged aquatic vegetation (SAV) species, providing
valuable habitats to marine organisms, reducing shoreline erosion
by trapping sediments and dissipating wave energy, and acting
as important sources of primary production, are limited in
distribution by salinity regimes (Dierner, 1975). Aquatic
vegetation such as coontail (Ceratophyllum dermersum), sago
pondweed (Potamogeton pectinatus), and redhead grass (P. |
perfoliatus) have upper salinity tolerances of 7, 13, and
12 parts per thousand (ppt), respectively (Stevenson and Confer,
1978). Stewart (1962) documented a dramatic increase inthe
number of SAV species from higher to lower salinity regimes in
Chesapeake Bay estuaries. Hence, distributional patterns of
seagrasses are at least partially related to the. species-specific
salinity tolerances, and freshwater inflow reductions could be
detrimental to species growing near upper salinity limits.



herbivores and other secondary producers. Adult Atlantic
menhaden (Brevoortia tyrannus) populations in Atlantic and Gulf
of Mexico waters consume large quantities of phytoplankton and
benthic algae (Peters and Schaaf, 1981), although vascular plant
detritus was identified as the primary constituent in the diet of
juvenile B. tyrannus (Lewis and Peters, 1984). Hence, there is

a direct link from primary production to fishery utilization.

McHugh (1966, 1976) estimated that more than 69 percent of
the total U.S. commercial and recreational fin- and shellfish
landings (in weight) are estuarine-dependent. In the Gulf
of Mexico, approximately 98 percent of the fish species of
commercial value utilize estuaries during one or more of their
life stages (Gunter, 1967). The 1984 U.S. commercial landings
of estuarine-dependent shrimp, menhaden, and blue crabs, for
example, were valued at $488 million, $117 million, and $56
million, respectively (U.S. Dept. of Commerce, 1985). Commercial
landings of wetland-dependent species had an ex-vessel Price
exceeding $700 million in 1976, while recreational fishermen
spent $13.1 billion on fishery activities directed toward
wetland-associated fishes (Peters et al., 1978).

Empirical studies on the abundance of larval and juvenile
fishes have identified that shallow tidal creeks and marsh shoals
Support dense populations of juvenile marine species such as
flounder, menhaden, croaker, seatrout and spot (Conner and
Truesdale, 1973; Chao and Musick, 1977; Shenker and Dean, 1979;
Bozeman and Dean, 1980; Weinstein and Brooks, 1983). Statistical
relationships indicated that in some Texas estuaries at least
60 kg of penaeid shrimp are harvested per acre of intertidal
marsh (Turner, 1977). In addition, estuaries also contain
habitats such as seagrass (e.g., Zostera, Ruppia spp.) meadows
that enhance nursery habitat for both fin- and shellfish species
(Adams, 1976; Heck and Orth, 1980).

Estuarine and coastal waters serving as nursery habitats
have a direct relationship with primary production. Nixon (1982)
identified a statistically significant positive correlation
between estuarine fisheries yield per unit area with the primary
production per unit area of the estuary, while Bahr et al.
(1982) quantified a positive correlation between gross primary
production and secondary fish production. Other studies have
revealed that food supplies to fish species are limited in
estuaries (Peters and Kjelson, 1975; Weinstein, 1979), and may
be a cause of mortality in juvenile fishes. Polgar (1982), for
example, identified food availability as the primary cause of
differential mortality in the striped bass (Morone saxatilis)
in the Potomac River.

There is a question as to what degree fishery production and
composition are limited by estuarine food sources. Some believe
that production within an ecosystem is primarily based on
detrital flux-or phytoplankton production. Studies have shown
that wetlands detritus is a primary food source, both directly

4


Odum, E.P. 1971. Fundamentals of Ecology. W.B. Saunders Co.,
Philadelphia. .

Odum, W.E. and E.J. Heald. 1975. The detritus-based food web of
an estuarine mangrove community. In: Estuarine Research.
Vol. I. L.E. Cronin (ed.). pp. 265-286. Academic Press,
N.Y.

Perkins, E.J. 1974. The Biology of Estuaries and Coastal
Waters. Academic Press, N.Y.

Peters, D.S. and M.A. Kjelson. 1975. Consumption and
utilization of food by various postlarval and juvenile
fishes of North Carolina estuaries. In: Estuarine
Research. Vol. I. L.E. Cronin (ed.). pp. 448-472.
Academic Press, N.Y.

Peters, D.S. and W.E. Schaaf. 1981. Food requirements and
sources for juvenile Atlantic menhaden. Trans. Amer. Fish.
Soc. 110:317-324.

Peters, D.S., D.W. Ahrenholz, and T.R. Rice. 1978. Harvest and
value of wetland associated fish and shellfish. In: Wetland

Functions and Values: The State of Our Understanding. P.E.
Greeson, J.R. Clark, and J.E. Clark (eds.).. pp. 606-617.

Polgar, T.T. 1982. Factors affecting recruitment of Potomac
River striped bass and resulting implications for
Management. In: Estuarine Comparisons. V.S. Kennedy
(ed.). pp. 427-442. Academic Press, N.Y. a

Pritchard, D. 1967. What is an estuary: physical viewpoint. 1
In: Estuaries. G.H. Lauff (ed.). Amer. Assoc. Adv. Sci.
Publ. No. 83. pp. 3-5. Wash., D.C.

Shenker, J.M. and J.M. Dean. 1979... The utilization of
intertidal salt marsh creek by larval and juvenile fishes:
abundance, diversity and temporal variation. Estuaries
2:154-163.

Smith, P.F., A.H. Schwartz, and W.H. Massmann (eds.). 1966.
A symposium on estuarine fisheries. Amer. Fish. Soc. Spec.
Publ. 3. 154 pp. Wash., D.C..

Sutcliffe, Jr., W.H. 1972. Some relations of land drainage,
nutrients, particulate material and fish catch in two
eastern Canadian bays. J. Fish. Res. Board Can. 29:357-362.

Sutcliffe, Jr., W.H. 1973. Correlations between seasonal river
discharge and local landings of American lobster (Homarus
americanus) and Atlantic halibut (Hippoglossus hippoglossus)
in the Gulf of St. Lawrence. J. Fish. Res. Board Can.
30:856-859.

18



Corliss, J. and L. Trent. 1971. Comparison of phytoplankton
production between natural and altered areas in West Bay,
Texas. Fish. Bull. 69(4):829-832.

Correll, D.L. 1978. Estuarine productivity. BioScience 28:646-
650.

Day, Jr., J.W., T.J. Butler, and U.H. Conner. 1977. Production
and nutrient export studies in a cypress swamp and lake
system in Louisiana. In: Estuarine Processes. Vol. II.

M. Wiley (ed.). pp. 255-269. Academic Press. N.Y.

Edwards, R.E. 1981. The influence of salinity transition
on benthic nutrient regeneration in estuaries. In:
Proceedings of the National Symposium on Freshwater Inflow
to Estuaries. Vol. II. R.D. Cross and D.L. Williams
(eds.). pp. 2-16.

Gosselink, J.E. and R.E. Turner. 1978. The role of hydrology
in freshwater wetland ecosystems. In: Freshwater
Wetlands. Ecological Processes and Management Potential.
R.E. Good, D.F. Whigham, R.L. Simpson and C.G. Jackson Jr.
(eds.). pp. 63-78. Academic Press, N.Y.

Haines, E.B. 1977. The origins of detritus in Georgia salt
marsh estuaries. Oikos 29:254-260.

Haines, E., A. Chambers, R. Hanson, and B. Sherr. 1976.
Nitrogen pools and fluxes in a Georgia saltmarsh. In:

Estuarine Processes. Vol. II. M. Wiley (ed.). pp. 241-
254,

Jordan, T.E., D.L. Correll, and D.F. Whingham. 1983. Nutrient
flux in the Rhode River: tidal exchange of nutrients by
brackish marshes. Estuarine Coastal Shelf Sci. 17:651-667.

Kadlec, R.H. and J.A. Kadlec. 1979. Wetlands and water
quality. In: Wetlands Functions and Values: The State
of Our Understanding. R.E. Geerson, J.R. Clark, and J.E.
Clark (eds.). Amer. Water Res. Assoc.

Klopatek, J.M. 1978. Nutrient dynamics of freshwater riverine
Marshes and the role of emergent macrophytes. In:
Freshwater Wetlands. R.E. Good, D.F. Whigham, and R.L.
Simpson (eds.). pp. 195-215. Academic Press, N.Y.

Linthurst, R.A. 1980. An evaluation of aeration, nitrogen, pH,
and salinity as factors affecting Spartina alterniflora
growth: a summary. In: Estuarine Perspectives. V.S.
Kennedy (ed.) pp. 235-247. Academic Press, N.Y.

24




productivity in the long term. Armstrong (1982) calculated that
less than 5 percent of the total external nutrient inputs to six
major estuarine systems in Texas were derived from adjacent,
upstream saltmarshes. Similarly, Ward et al. (1982) calculated
that freshwater inflows accounted for only 2 and 5 percent of

the total nitrogen (N) and phosphorus (P) (respectively) fixed by
primary producers in Matagorda Bay, Texas, concluding that most
of the nutrients were derived from recycling through the pelagic
and benthic systems. Conversely, Correll (1978) suggested that a
combination of the nutrient sources is responsible for estuarine
productivity.

It is. inferred that freshwater inflows provide at least
some of the nutrients utilized in estuarine food webs, although
great variability exists between estuarine systems. The amount
of dissolved organic and inorganic nutrients and particulate
detrital material transported to estuarine waters is related to
a host of factors including hydrology, types of soil, vegetation
and wetlands of the drainage basin, seasonality, and human
intervention (Odum, 1985). Reduced freshwater inflows result
in a decreased quantity of organics and inorganics imported
to the estuary from the drainage basin, and productivity of
estuarine food webs dependent on this source is thus limited
(Copeland et. al., 1972). Nutrients supplied by freshwater
inflow support both detritus-based (Odum and Heald, 1975) and
plankton/algae-based (Haines, 1977; Correll, 1978) estuarine
food webs. However, excessive nutrient levels in estuaries
exacerbated by reduced water exchange may limit phytoplankton
production (Corliss and Trent, 1971). Thus, freshwater inflows
influenced by upriver nutrient load, urban and agricultural
runoff, wastewater discharges, and biochemical and chemical
processes may enhance or limit overall estuarine productivity.

Wetlands have the ability to intercept and retain nutrients
from the water which flows through and over them, although
seasonal uptake. pattern and length of time which the nutrients
are retained vary greatly between wetland sites and types
(Odum, 1985). The coupling of tidal and non-tidal wetlands
form a vegetatively diverse continuum which influences nutrient
cycling and transport from rivers to estuaries.

Bottomland hardwood swamps undergo cyclic wet/dry periods,
creating a unique chemical environment which affects nutrient
cycling. Flooding regulates chemical properties of floodplain
soils by replenishing minerals, providing anaerobic soil
conditions, importing particulate and dissolved organic matter,
and exporting decomposing leaf litter and other detritus (Wharton
et al., 1982)... Livingston et al. (1976) demonstrated that the
productivity of Apalachicola Bay, Florida was strongly influenced
by the organic detrital source via bottomland hardwoods. Day
et al. (1977) also found that a Louisiana hardwood swamp provided
pulses of carbon, N, and P to Barataria Bay. Hence, large
quantities of organic matter contributed by bottomland hardwood
swamps may be transported to estuaries although dam construction

ll


ecosystems directly control nutrient loads transported to
estuarine ecosystems (Gosselink and Turner, 1978).

Estuarine marshes act as nutrient (N and P) transformers,
and function either as sources or sinks depending on a number
of factors (Axelrad et al., 1976; Valiela and Teal, 1979;
Nixon, 1980). Generally, coastal wetlands have a net import of
nutrients at the beginning and during the plant growth period,
whereas these marshes have a net export in the fall and winter.
Stevenson et al. (1977) identified factors determining whether
a marsh is importing materials or exporting nutrients to the
estuary. Factors include: (1) successional stage of the marsh,
(2) salinity and redox characteristics, (3) nutrients released
from point sources, (4) nutrients released from non-point
sources, (5) tidal energy input, and (6) stability and magnitude
of the nutrient flux of the estuary to which the marsh is
coupled.

Study results of a tidal marsh in the Choptank River,
Maryland indicated that the wetland exported inorganic N and P
to the estuary in the winter, while in the spring there was a
net import of inorganic N and P to the marsh (Stevenson et al.,
1977). Results also demonstrated that another tidal marsh
located in the Patuxent River, Maryland imported dissolved
inorganic N between May and July, although there was a net N
flow to the estuary when dissolved organic N was included.
Wilcox and Childress (1981) found that virtually.all nutrient
forms were directed out of a tidal marsh in Nueces Estuary,
Texas during the fall and winter, but were directed into the
marsh during the spring; thus, the wetland also acted as a
nutrient sink. Axelrad et al. (1976) found that, in both a
Spartina cynosuroides dominated marsh (Ware Creek) and S.
alterniflora dominated marsh (Carter Creek), net dissolved
inorganic and organic P were exported to the York River estuary,
Virginia, while net particulate P was imported to both marshes.
There was a net annual export of dissolved organic N from
both marshes and a net import of particulate N into the S.
alterniflora dominated marsh. A study by Jordan et al. (1983)
indicated that a Typha angustifolia dominated brackish marsh
retained only small amounts of N and P. The authors suggested
that the marsh acts more as a nutrient transformer, while the
adjacent mudflat functions as a sink for the nutrients.

_Saltmarshes have the ability to intercept and retain
nutrients from incoming freshwaters. Haines et al. (1976)
suggested that river water is the primary source of inorganic N
in some unpolluted estuaries. Conversely, Nixon (1981) reasoned
that freshwater inflow is a minor nutrient source to saltmarshes
in comparison to the contribution attained from recycling,
remineralization, and complex interactions between autotrophic
and heterotrophic processes in estuarine waters. Rather,
freshwater inflows likely provide a long-term contribution as
a nutrient source by replenishing nutrients lost in benthic
regeneration and complex biological processes. In addition,

13


a
~~» 3 CONTENTS ©

Bio ot ole L Cok ob Rose ne a

Literature REVIEWS. cee e cece eee e ee cee eee e ce eeeecee recess eessesed

ed
*The Contribution of Wetland and Estuarine Habitats
to Fishery Productions. .c eee c cece eee cece erence eee eee r ened

ere)

“- Case Studies of Altered Freshwater Inflows’......

Biotic Changes Attributed to Altered Salinity Regimes......7

“The Role of Freshwater Inflows in Estuarine Nutrient
CYCLING. deveesereseseeereceseeesesteeeesesetetereseee cease LO

Summary and ConclusSionsS...... cece cece cece cece cece eee eeee ee ld
AcknowledgmentS... ccc ccc ccc cece eee eects ee eee lS
Literature Cited and Suggested ReferenceS....ceceeeecceercceee el

Freshwater Inflow and Effects of Alteration............+--16

The Contribution of Wetland and Estuarine Habitats
to Fishery Production. ccc eee cece cece ececeseel&

Case Studies of Altered Freshwater Inflows.......+.++e++--19
Biotic Changes Attributed to Altered Salinity Regimes.....20

The Role of Freshwater Inflows in Estuarine Nutrient

(0'Zo8 Oh oe ee 2

OT
Preceding Page Blank


Malone, T.C., P.J. Neale, and D. Boardman. 1980. Influence of
estuarine circulation on the distribution and biomass of
phytoplankton size fractions. In: Estuarine Perspectives.
V.S. Kennedy (ed.). pp. 249-262. Academic Press, N.Y.

Manzi, J.J. 1970. Combined effects of salinity and temperature
on the feeding, reproduction, and survival rates of Eupleura
caudata (Say) and Urosalpinx cinerea (Say) (Prosobranchia:
Muricidae). Biol. Bull. 138:35-46.

Mihursky, J.A., W.R. Boynton, E.M. Setzler-Hamilton, and K.V.
Wood. 1981. Freshwater influences on striped bass
population dynamics. In: Proceedings of the National
Symposium on Freshwater Inflow to Estuaries. Vol. I.
R.D. Cross and D.L. Williams (ed.). pp. 149-167.

Neale, P.J., T.C. Malone, and D.C. Boardman. 1981. Effects
of frehwater flow on salinity and phytoplankton biomass in
the lower Hudson estuary. In: Proceesings of the National
Symposium on Freshwater Inflow to Estuaries. Vol. I.
R.D. Cross and D.L. Williams (ed.). pp. 168-184.

Nestler, J. 1977. Interstitial salinity as a cause of ecophenic
variation in Spartina alterniflora. Estuarine Coastal Mar.
Sci. 5:707-714.

Orlob, G.T. 1976. Impact of upstream storage and diversions on
salinity balance in estuaries. In: Estuarine Processes.
Vol. II. M. Wiley (ed.). pp. 3-17. Academic Press, N.Y.

Pearson, J.C. 1948. Fluctuations in the abundance of the blue
crab in Chesapeake Bay. U.S. Fish Wildl. Serv. Res. Rep.
14. 26 pp.

Polgar, T.T., J.K. Summers, R.A. Cummins, K.A. Rose, and D.G.
Heimbuch. 1985. Investigation of relationships among
pollutant loadings and fish stock levels in northeastern
estuaries. Estuaries 8(2A):125-135.

Sanders, H.L., P.C. Mangelsdorf, Jr., and G.R. Hampson. 1965.
Salinity and faunal distribution in the Pocasset River,
Massachusetts. Limnol. Oceanogr. 10 (Suppl.): R216-R229.

Schroeder, W.W. 1978. Riverine influence on estuaries: a case
study. In: Estuarine Interaction. M. Wiley (ed.). pp.
347-364, Academic Press, N.Y.

Smart, R.M. and J.W. Barko. 1978. Influence of sediment
salinity and nutrients on the physiological ecology of
selected salt marsh plants. Estuarine Coastal Mar. Sci.
7:487-495.

22




Livingston, R.J., R.L. Iverson, and D.C. White. 1976. Energy
relationships and the productivity of Apalachicola Bay.
Final Res. Rep. to Florida Sea Grant College. 437 pp.

Nixon, S.W. 1980. Between coastal marshes and coastal waters -
a review of twenty years of speculation and research on
the role of salt marshes in estuarine productivity and
water chemistry. In: Estuarine and Wetlands Processes.
P. Hamilton and K.B. MacDonald (eds.). pp. 437-525.

Nixon, S.W. 1981. Freshwater inputs and estuarine
productivity. In: Proceedings of the National Symposium
on Freshwater Inflow to Estuaries. -R.D. Cross and D.L.
Williams (eds.). pp. 31-57.

Odum, E.P. 1980. The status of three ecosystem-level
hypotheses regarding salt marsh estuaries: tidal subsidy,
outwelling, and detritus-based food chains. In: Estuarine
Perspectives. V.S. Kennedy (ed.). pp. 485-495. Academic
Press, N.Y.

Odum, W.E. 1985. The role of non-tidal and tidal freshwater
marshes in reducing nutrient inputs to Chesapeake Bay. In:
Wetlands of the Chesapeake. Protecting the Future of the
Bay. Conf. Proc. H.A. Groman, T.R. Henderson, E.J. Meyers,
D.M. Burke, and J.A. Kusler (eds.). pp. 76-83.

Odum, W.E. and E.J. Heald. 1975. The detritus-based food web of
an estuarine mangrove community. In: Estuarine Research.
Vol. I.  L.E. Cronin (ed.). pp. 265-286. Academic Press,
N.Y.

Odum, W.E., S.J. Fisher, and J.C. Pickral. 1979. Factors
controlling the flux of particulate organic from estuarine
wetlands. In: Ecological Processes in Coastal and Marine
Systems. pp. 69-80. Plenum Press, N.Y.

Odum, W.E., T.d. Smith III, J.K. Hoover, and C.C. McIvor.
1984, The Ecology of Tidal Freshwater Marshes of the United
States East Coast: A Community Profile. U.S. Fish and
Wildlife Service, Wash., D.C. FWS/OBS-83/17. 177 pp.

Pomeroy, L.R., K. Bancroft, J. Breed, R.R. Christian, D.
Frankenberg, J.R. Hall, L.G. Maurer, W.J. Wiebe, R.G.
Wiegert, and R.L. Wetzel. 1976. Flux of organic matter
through a salt marsh. In: Estuarine Processes. Vol. II.
M. Wiley (ed.). pp. 270-279. Academic Press, N.Y.

Richardson, C.J., D.L. Tilton, J.A. Kadlec, J.P. Chamie, and
W.A. Wentz. 1978. Nutrient dynamics of northern wetland
ecosystems. In: Freshwater Wetlands. R.E. Good, D.F.
Whigham, and R.L. Simpson (eds.). pp. 217-241. Academic
Press, N.Y.

25


Holland (1985) identified salinity as a primary factor
regulating macrobenthic recruitment in a mesohaline region of
Chesapeake Bay, as the early developmental stages of macrobenthic
species have narrower tolerances to environmental conditions,
particularly salinity. Castagna and Chanley (1973) identified
salinity tolerances of the bivalves endemic. to mid-Atlantic
coastal waters. Cain (1975) found that salinity has a
controlling effect on the spawning and recruitment of brackish
water clam (Rangia cuneata) populations in the James River,
Virginia. A seasonal salinity change from fresh. to 5 ppt induced
spawning in upstream populations of R. cuneata. The American
oyster (Crassostrea virginica) flourishes in a wide range
of salinities, although survival and growth of larvae are
physiologically (Davis, 1958) and ecologically (Manzi, 1970)
controlled by salinity. For example, the distribution of some
oyster predators, such as drills (Eupleura caudata and Urosalpinx
cinerea), and pathogens, including MSX (Minchinia nelsoni), are
limited to higher salinities in Chesapeake Bay (Andrews and Wood,
1967).

Pluctuations in salinity affect growth and recruitment
of other benthic invertebrates. Pearson (1948) identified a
positive correlation between low river discharge, salinity
and survival and recruitment of the blue crab (Callinectes
sapidus). Bowler and Seidenberg (1971) found the grass shrimp
(Palaemonetes vulgaris) to be less tolerant of low salinities
(less than 3 ppt), but more tolerant of high salinities (36
and 40 ppt) than its cogener, P. pugio. Corresponding to this
relationship, the composition of the Palaemonetes population
made up by P. vulgaris decreased markedly with decreased salinity
in the York River, Virginia. Further, salinity change is a
mechanism contributing to tidal transport of post larvae and
juvenile pink shrimp (Penaeus duorarum) from inshore nursery
areas to offshore waters of the Gulf of Mexico (Hughes, 1968).
Copeland (1966) detailed the effects of decreased river flow and
salinity on oyster, shrimp, and blue crab production in several
major estuaries.

Finfish production, growth, recruitment, and distribution
in estuaries are controlled by altered freshwater inflows and
salinity. Primary effects of inflow/salinity on finfish
production are physiological and play an important role in
survival of early life stages, metabolic stress of adult
populations, and adaptability rates by juveniles. Distribution
of juvenile fishes within primary nursery ‘areas has been
correlated with salinity (Gunter, 1961). In addition, salinity‘
governs fish distribution by secondarily restricting predator
distribution (Joseph, 1973; Blaber and Blaber, 1980). Extreme
temperature and salinity fluctuations in shallow.embayments and
creeks may exclude large adult predators, but not juvenile
fishes (Hyatt, 1979). Weinstein and Walters (1981) identified
salinity as the primary factor controlling mortality of the
spot (Leiostomus xanthurus) by limiting stenohaline predator
distribution.



or other modifications to floodplain swamps can significantly
change mineral and detrital fluxes and seasonal flooding, and
consequently, alter downstream nutrient movement (Wharton et al.,
1982).

Tidal freshwater wetlands contribute detritus (Odum et al.,
1984), serve as sinks for nutrients (Kadlec and Kadlec, 1979),
and provide mineral nutrients to estuaries (Simpson et al.,
1983). These systems also function as nutrient transformers by
importing dissolved oxidized forms of WN (i.e., nitrite, nitrate)
and P (i.e., phosphate) and exporting dissolved and particulate
reduced forms (i.e., ammonium and organic forms) (Bowden,

1984). Overall, tidal freshwater wetlands act as either
nutrient sinks or sources depending on local conditions such

as hydrological variables (e.g., circulation, tidal range,
precipitation), geomorphological characteristics (e.g., drainage
area, elevation gradient), and the age of the wetland (Odum

et al., 1979).

Nutrient and particulate fluxes in tidal freshwater
wetlands result from the complex interaction of chemical,
physical, and biological processes similar to processes occurring
in saltmarshes (Nixon, 1980). Diurnal fluctuations act as
additional nutrient flux mechanisms. Phosphorus may be removed
from overlying water either by plant uptake or absorption into
particulate matter and subsequently buried (Klopatek, 1978).
Nitrogen imported into freshwater tidal wetlands may be retained,
converted from nitrate to nitrite through denitrification, or
exported. Tidal freshwater marshes have distinct seasonal
nutrient exchange processes. Studies demonstrated that after
dieback of plant vegetation in the fall and early winter, 80
percent or more of the N and P of standing dead litter may be
lost within one to two months and exported out of some marsh
systems (Richardson et al., 1978; Simpson et al., 1978).

Because of an almost total lack of litter cover at the onset
of the growing season, there is a net import of N and P into
the system. Organic N and P occur in plant tissues during peak
vegetative growth, while there is an export of reduced N and P
following plant decomposition (Odum et al., 1984). .

The volume of river flow has often been correlated
positively with the presence of particulate organic material
(Borman et al., 1974). Maximum organic matter concentrations
are typically associated with high discharges related directly or
indirectly to precipitation. Hence, the creation of impoundments
in tidal freshwater wetlands can interrupt flux of organic matter
and nutrients to the downstream estuary. For example, Anderson
and Neilson (1985) identified that impounding some tidal
freshwater wetlands on the Eastern Shore of Virginia had a
trapping efficiency of 46.7 percent of the total P moving through
a small drainage. Hence, even small dam construction may alter
the nutrient flux from tidal and non-tidal freshwater wetlands to
the marine environment. Overall, the source, velocity, renewal
rate, and seasonal quantity of water in freshwater wetland

12