Structure and Function of a Freshwater Tidal-Marsh Ecosystem Pvincipal investigator^: Dennis F. Whigharn, Chesapeake Bay Center for Environ- mental Studies, Smithsonian Institution, Edgewater, Mary- land; and Robert L. Simpson, Rider College, Lawrenceville, New Jersey. Grant No. 1313: For a study of the structure and hnction of a freshwater tidal-marsh ecosystem (Hamilton Marshes, Delaware River). ' In 1973 we began a series of investigations of ecological characteristics of a Delaware River freshwater tidal marsh. At that time, there had been few studies of freshwater tidal marshes (McCormick, Grant, and Patrick, 1970; McCormick, 1970; McCormick and Ashbaugh, 1972; Walton and Patrick, 1973) even though they are widespread in tidal portions of eastern North American rivers. Initially our studies were centered on the floristics,of the marsh vegetation. Our primary objectives were to determine which species occurred in tidally influenced freshwater marshes and how the species segre- gated into community types. Additionally we wanted to determine whether or not freshwater tidal marshes were as productive as estuarine brackish marshes. Based on preliminary data, Walton and Patrick (1970) had suggest- ed that freshwater tidal marshes were efficient nutrient processors. Therefore, a second phase of our work centered on the patterns of nutrient movement through and within the marshes by analyzing seasonal patterns of selected water quality parameters, particularly nitrogen and phosphorus. The research was conducted in the 500-hectare Hamilton Marshes (fig. l), which are the northernmost tidal marshes in the Delaware River. In addi- tion to the marshes, located near Trenton, New Jersey, there are lowland for- ests, tidally influenced shrub forests, and a few shallow impoundments (Whigham, 1974). Table 1 summarizes the coverage and production data for the major marsh vegetation types. In addition to the National Geographic Society, we extend our thanks to the Hamilton Township Environmenral Commission for its financial support and to the following students whose work on the project was supported by the Society's grant: Paula Bozowski, Herbert Grover, Barie Kline, Thomas Leslie, and David West. National Geographic Society TABLE 1. Aerial Extent and Total Aboveground Production Estimates for Dominant Vegetation Associations of the Hamilton Marshes -- - Mixed Cattail Giant ragweed Arrow arum Spiked loosestrife Wildrice Yellow waterlily TOTALS *t = ton. ha= hectare. Structurally the marsh consists of several distinct habitats, including stream banks, high marsh, and pondlike areas. The most extensive habitat is the high marsh, which is usually flooded to a depth of half a meter or less only during 3 hours of a 12-hour tide cycle. There are several recognizable commu- nity types in this habitat even though most species are widespread and occur throughout the high marsh. The most common high-marsh community con- sists of sweetflag (Acorzs calamw), arrow arum (Peltandra virginica), tear- thumb (Polygonzlm arifolizlm), bur marigold (Bidens laevir), touch-me-not (lm- patiens capensis), wildrice (Zizania aqwtica), and arrowhead (Sagittaria latifo- ha). Phenologically, sweetflag and arrow arum dominate the marsh landscape in the early part of the growing season, but they are eventually overtopped by wildrice, which dominates in July and August, and finally by bur marigold, which dominates until the end of the growing season. Several additional spe- cies, including giant ragweed (Ambrosia trifida), cattail (Typha angustifoolia and T. lat$olia), and purple loosestrife (Lythrzm salicaria), become dominant in other high-marsh communities (Whigham et al., 1978). Stream-bank communities are dominated by waterlily (Naphar advena), pickerelweed (Pontederia cordata), waterhemp (Acnida cannabina), smartweed (Polygonurn punctatzm), and wildrice (Zizania aqzatica). One large marsh area (site 4B in fig. 1) is pondlike and flooded to a depth of 1 meter at high tide and drained only at low tide. Waterlily, arrow arum, wildrice, cattail, smart- weed, and pickerelweed dominate in this habitat. In areas adjacent to upland habitats, the open marsh is replaced by a shrub forest, which is inundated at high tide. All the herbaceous species found in Reseurch Reports o 1974 Projects TRENTON SCALE 1:2400 1WO 0 3OW 7000 F1. 1 m-- - L - 9 KM. L 1 .I 0 D E L . R I V E R FIG. 1. Schematic diagram of the Hamilton Marshes. The pattern of water move- ment into and out of the marsh is shown at the lower right. the open marsh plus several woody shrubs, the most common being arrow- wood (Viburnum dentatum), red maple (Acer rubrumkalder (Alnus serrukata), and buttonbush (Cephalantbus occcidentdis), occur in this transition zone. Compared to salt marshes, the outstanding floristic characteristics of freshwater tidal marshes are high diversity and abundance, and, in some cases dominance, of annuals. The latter are virtually excluded from salt marshes, National Geographic Society and whereas species richness is normally approximately 30 vascular plants in Delaware River sa l t marshes, there may be more t h a n 60 species in freshwater TABLE 2. Summary of Production Values for Marsh Plants Aboveground Commzlnity type net production (domtnant) (g/m2/yr) Locale Refermce Wildrice (Zizania aquatics) Giant Ragweed (Ambrosia tuifda) Yellow Waterlily (Ntlphar advena) Cattail (Typha SP . ) Mixed (Bidens laevis) Primrose willow (Jusiaea repens) Arrowhead (Sagittarin sp. ) Arrow arum (Peltandra uirginica) Sweetflag (Acmus calmuj) Loosestrifr (Lythrum salicaria) Waterhemp (Acnida cannabina) (1) Freshwater Tidal Marshes Pa. N.J. N.J. Pa. N.J. Pa. N. J. N. J. Va. Pa. N.J. N. J. Va . Pa. N. J. Pa. Pa. Pa. N.J. N. J. Pa. N.J. Pa. McCormick, 1970 Present study McCormick and Ashbaugh, 1972 McCormick, 1970 Present study McCormick, 1970 McCormick acd Ashbaugh, 1972 Present study Wass and Wright, 1969 McCormick, 1970 McCormick and Ashbaugh, 1972 Present study Wass and Wright, 1969 McCormick, 1970 Present study McCormick, 1970 McCormick, 1970 McCormick, 1970 Present study Present study McCormick, 1970 Present study McCormick, 1970 (2) Salt Marshes between New York and Virginia Saltwater cordgrass 1332 Va. Wass and Wright, 1969 (Spartind altwnifora) 4/15 Del. M. H . Morgan, 1961 300 N.J. Good, 1965 Salt-meadow grass 805 Va. Wass and Wright, 1969 (spartinu patem) Spike grass 360 Va. Wass and Wright, 1969 (Ftmbristylij sp.) i Research Reports o 1974 Projects FIG. 2. Changes in dissolved oxygen (D.O.) at sites 2, 8, 5 , and 5A in the Hamilton Marshes between May 1974 and July 1975. Solid lines represent high slack water (HSW) and dashed lines low slack water (LSW). Refer to figure 1 for location of sam- pling stations. tidal marshes. Most likely the higher level of species richness is due to the lack of salt stress that is a normal feature in salt-marsh environments. Table 2 shows biomass data for Delaware and Chesapeake Bay salt marshes and freshwater tidal marshes along the Delaware River from south of Philadelphia (Tinicum Marshes) to the Hamilton Marshes. It is apparent that, compared to saline marshes, a great number of community types occur in the freshwater tidal marshes. Even though the biomass data given for the fresh- water marshes in table 2 represent underestimates of net production because of the seasonal changes in dominance (Whigham et al., 1978), it is obvious that freshwater tidal marshes are extremely productive and that they are probably more productive than salt marshes at the same latitude. Me estimated a mean production of 950 g/m2/yr in the Hamilton Marshes. Purple-loosestrife com- munities were the most productive (2100 g/m2), while waterlily-dominated areas were the least productive (450 g/m2). The marshes are metabolically active throughout the year (Simpson et al., 1978), as shown in figures 2 and 3. Flood-tide waters from the Delaware Riv- er are consistently higher in oxygen and lower in carbon dioxide than waters ,----_---- I ; ~ -.__- ---- 35 site a 30 FIG. 3 . Changes in carbon-dioxide content at sites 2, 8, 5 , and 5A in the Hamilton Marshes between May 1974 and July 1975. Solid lines represent high slack water (HSW) and dashed lines low slack water (LSW). Refer to figure 1 for location of sam- pling stations. leaving the marsh at low slack water (compare site 2 of figs. 2 and 3). The highest carbon-dioxide levels occur in October (site 5 and 5A, fig. 3), corre- sponding with the fall dieback ofvascular plants in the marsh, suggesting that heterotrophic activity is most pronounced at that time. High levels ofproductivity should be indicative of efficient nutrient utili- zation. Our water-quality studies (Simpson and Whigham, 1975; Simpson et al., 1978) demonstrated that nitrogen and phosphorus are assimilated by all marsh habitats during the growing season. Figures4 and 5 demonstrate the seasonal pattern of nitrogen and phosphorus for high-marsh site 5A (fig. 1). During the summer nitrate and ammonia nitrogen and inorganic phosphate are assimilated, whereas during the winter they are exported. The pondlike areas (site 4B) were interesting because they appeared to assimilate nitrogen and phosphorus during the entire year (figs. 4, 5). Nutrient assimilation in the summer months is performed primarily by vascular plants in both habi- tats. In the pondlike areas filamentous algae appear to be the assimilators dur- ing the winter months. It is obvious that this riverine freshwater marsh ecosystem is capable of assimilating nutrients, especially during the summer months when eutrophication is a problem, and that they play an important role in the over-all nutrient budgets of the Delaware River (Whigham and Simpson, 1978). Research Reports o 1 974 Projects Site 5A FIG. 4. Changes in nitrate nitro- gen at sites 5A and 4B in the Hamilton Marshes. Refer to fig- ure 1 for locations of sampling stations. Water samples were collected at high slack water (HSW) and low slack water (LSW) from May 1974 until July 1975. FIG. 5. Changes in inorganic phosphate at sites 5A and 4B in the Hamilton Marshes. Refer to figure 1 for locations of sam- pling stations. Water samples ---- -- were collected at high slack wa- 1 r ..______- \ ,' ter (HSW) and low slack water 5He 4~ (LSW) from May 1974 until July 1975. REFERENCES GOOD, RALPH E. 1965. Salt marsh vegetation, Cape May, N.J. Bull. New Jersey Acad. Sci., vol. 10, pp. 1-11. MC~ORMILK, JACK , 1970. The natural features of Tinicum Marsh, with particular emphasis on the vegetation. Pp. 1-104 in "Two Studies of Tinicum Marsh, Delaware and Philadelphia Counties, Pa. ," J. F. McCormick, R. R. Grant, Jr., and R. Patrick, eds. Conservation Foundation, Washington, D. C. National Geogrdphic Society MCCORMICK, JACK, and ASHBAUGH, T. 1972. Vegetation of a section of Oldmans Creek tidal marsh and related areas in Salem and Gloucester Counties, New Jersey. Bull. New Jersey Aca& Sci., vol. 17, pp. 31-37. MCCORMICK, JACK; GRANT, R. R. , JR. ; and PATRICK, R. 1970. Two studies of Tinicum Marsh, Delaware and Philadelphia Counties, Pa., 123 pp. conservation Foundation, Washington, D. C. SIMPSON, ROBERT L., and WHIGHAM, DENNIS F. 1976. Seasonal distribution of selected water chemical parameters in a Dela- ware River freshwater tidal marsh. American Society of Limnology and Oceanography, Savannah, Georgla. (Abstract.) SIMPSON, ROBERT L.; WHIGHAM, DENNIS F.; and WALKER, R. 1978. Seasonal patterns of nutrient movemcnt in a freshwater tidal marsh. Pp. 242-258 in "Freshwater Wetlands: Ecological Process and Potential," R. E. Good, D. F. Whigham, and R. L. Simpson, eds. Academic Press, New York. WALTON, T., and PATRICK, R. 197 3. Delaware River estuarine marsh survey. In "Delaware Estuary System: Environmental Impacts and Socio-economic Effects," 177 pp. A report prepared for the National Science Foundation (RUN). Academy of Natural Sciences of Philadelphia. WASS, MARVIN L., and WRIGHT, THOMAS D. 1969. Coastal wetlands of Virginia. Interim report to the Governor and Gener- al Assembly. Virginia Insr. Mar. Sci. Spec. Rpt. in Appl. Mar. Sci. and Ocean Eng., no. 10, 154 pp. WHIGHAM, DENNIS F. 1974. Preliminary ecological studies of the Hamilton Marshes: Progress report for the period ending Januacy 1974, 66 pp. Rider College, Lawrence- ville, New Jersey. WHIGHAM, DENNIS F.; MCCORMICK, JACK; GOOD, RALPH E.; and SIMPSON, ROB- ERT L. 1978. Biomass and primary production in freshwater tidal wetlands of the Mid- dle Atlantic Coast. Pp. 1-20 in "Freshwater Wetlands: Ecological Pro- cess and Management Potential," R. E. Good, D. F. Whigham, and R. L. Simpson, eds. Academic Press, New York. WHIGHAM, DENNIS F.. and SIMPSON. ROBERT L. Ecological studies of the Hamilton Marshes: Progress report for the peri- od June, 1974-January, 1975, 185 pp. Rider College, Lawrenceville, New Jersey. The potential use of freshwater tidal marshes in the management of wa- rer quality in the Delaware River. Pp. 173-186 in "Biological Control of Water," Joachim Tourbier and Robert W . Pierson, Jr., eds. Uni- versity of Pennsylvania Press. Nitrogen and phosphorus movement in a freshwater tidal wetland re- ceiving sewage effluent. Pp. 2089-2203 in "Coastal 78: Symposium on Technical, Environmental, Socioeconomic, and Regulatory Aspects of Coastal Zone Management." American Society of Civil Engineers, Minneapolis, Minnesota. DENNIS F. WHIGHAM