Abstract: Tidal freshwater wetlands (TFWs) occur along the Gulf of Mexico, Atlantic, and Pacific coasts of the continental United States and Canada. Latitudinal patterns may be a response to climate gradients along the Atlantic coast and precipitation gradients along the Pacific coast. In this chapter, we limit our discussion to (1) the extent of TFW in the east along the Atlantic coast from the Canadian border (St. Lawrence River) to the northern Gulf of Mexico and in the west along the Pacific coast from Washington state south to California (Fig. 1).
They are best developed in the east along the Atlantic coast from New Jersey to Georgia and along the northern Gulf of Mexico coast and in the west in Alaska (Chapters 13-16). Characteristic plant species of tidal freshwater marshes along the Atlantic and Gulf of Mexico coasts. An interesting feature of TFW along the Gulf of Mexico is the imperceptible change from low marsh to high marsh and random appearance of plant associations (see: Chapter 15).
Long-term variation
Field and Phillip (2000) reported that the overall percentage of low marsh habitats along the Delaware River
On the Pacific coast, interannual variation in annuals and minor perennials may reflect habitat disturbances such as woody detritus in the Pacific Northwest (Maser &. Species richness was found in marsh meadows exposed to four hydrologic treatment regimes in Plotted values are means ± SE of counts plant species in the experimental units throughout the duration of the study.
Effect of date and date x hydrological regime was not significant (P>0.05) (Van Baldwin et al. 2001; reproduced with permission).
SPATIAL VEGETATION PATTERNS AND FACTORS
Local vegetation patterns
Smaller species respond quickly and increase in frequency and abundance over the next few years (M. Vasey, L. Schile, V. Parker & J. Callaway pers. obs.). Most germination and seedling establishment occurs in the spring and several factors control the transition from seed in the seed bank to seedling establishment (Leck 1996). In contrast, species with small seeds that require light and varying temperatures for germination were persistent in the seed bank (Bidens laevis).
In raised bogs, seedlings are often found in slightly elevated microhabitats, eg, at the bases of perennial plants or where litter has accumulated (M. Leck & R. Simpson pers. obs.). Also in the field, perennials did not persist through the growing season, and in the greenhouse germination of Sagittaria latifolia was 1–1.5 months later than most other species (Parker & Leck 1985, M. Leck pers. obs.). In a study of oligohaline wetlands in the Mississippi Delta, Baldwin et al. 1996) found that salinity did not affect seed viability but inhibited germination.
Regional (estuarine) patterns
The observed changes in the intertidal landscape in the marshes may have resulted from periodic pulses of saltwater downstream of the freshwater intertidal zone, which stunted trees and shrubs and created a high-light environment that could support a well-developed herbaceous understory and subsequent seed bank. Other within-estuary effects have been observed in changes in species distribution in the Delaware Estuary. However, in the absence of competition, the 10 test species grew best in the lowest salinity wetlands.
The influence of salinity in systems where freshwater flow is regulated by dams can be seen in the distribution of certain salt-tolerant species (i.e., Distichlis spicata, Spartina patens) across a salinity gradient (Crain et al. 2004). Similarly, where earlier wetlands had been reclaimed for agriculture, levee breaches in the California Delta island system diverted additional freshwater flow patterns and brought brackish water further inland. For example, a breach of the Jones Track levee in June 2004 resulted in a 5 ppt salinity increase in the western Delta, a normally freshwater region (S. Siegel pers. comm.). 2004) notes a paradox - the highest species richness occurs where competition is greatest.
Geographic effects
In estuaries, TFW in the oligohaline transition boundary may experience periodic saltwater pulses during storms and, over a longer period, during periods of low water flow (e.g., late summer and early fall). In the Columbia River estuary, TFW can be found as far as 164 km from the mouth of the river and is mainly dominated by Carex lyngbyei, S. Away from the Pacific Maritime climate influence in the San Francisco Bay Delta, TFW is dominated by Schoenoplectus acutus and S.
The prevalence of freshwater marshes in the east appears to be related to geomorphology and to the presence of coastal plains in southern New Jersey. Also in the east (New Jersey), certain species (Aeschynomene virginica) occur in the coastal Pine Barrens rivers (Maurice River), but not along the Delaware River; Another floristic study of TFW species (Ferren. & Schuyler 1980) found the Delaware and Raritan River systems to be similar but distinct from the Mullica and Great Egg Harbor River systems, which originate in the Pine Barrens and looked alike. .
SPECIES OF SPECIAL INTEREST (ANNUALS, RARE, AND INVASIVE
Interestingly, relatively more salt tolerant species such as Carex lyngbyei dominate low marshes rather than high marshes along the Pacific coast. However, as Mediterranean climatic conditions intensify southward along the California coast, freshwater species such as Schoenoplectus acutus and Phragmites australis dominate the lower marshes, where more tidal action occurs, while more halophytic species such as Distichlis spicata and Jaumea carnosa dominate above the higher areas of the marshes, which are less frequently flooded and accumulate salt (4-10 ppt). TFWs in Washington and Oregon are often dominated by Carex lyngbyei, Eleocharis palustris, Schoenoplectus americanus, and S.
As in the Atlantic coast areas, few complete species lists are available for most of the Pacific coast, making it difficult to compare floristic patterns. Other species, including dominants, are either restricted to the Pacific coast (eg Potentilla anserina spp. pacifica) or even more locally restricted (Lilaeopsis masonii) (Mason 1957, Hickman 1993). The Delaware and Raritan systems had affinities with the Hudson system to the north and the Chesapeake system to the south.
SPECIES)
Typha species (T. angustifolia, T. latifolia et hybrida) frequentes sunt etiam in locis intertidal aquis fluvialibus, ut Phragmites australis. Praeterea litus Pacificum TFW multas alias species late diffusas continet, inter quas Calystegia sepium, Epilobium ciliatum, Juncus balticus, Lythrum californicum, Mimulus guttatus, Oenanthe sarmentosa et Polygonum punctatum. Condiciones leves novales, additis speciebus includunt Distichla spicata, Euthamia occidentalis, Pluchea odorata et Potentilla anserina ssp.
The Delta region of California is reported to have more than 90 native wetland species, while more than 130 have been found on Browns Island, an oligohaline ancient wetland located at the confluence of the San Joaquin and Sacramento Rivers (Knight species are listed in Mason 1957). Pacific Coast marshes are present, although their extent is more limited and located primarily in Oregon and Washington, reflecting rainfall patterns. However, brackish species were collected in both groups, indicating the importance of salinity in distribution patterns.
Annuals
Rare species
Invasive species
In addition, Lythrum salicaria and Phragmites australis and Butomus umbellatus are not important in the TFW of the Sv. Lawrence, especially in the lower reaches of the river, probably due to high-amplitude tides and species-poor but dense populations of native species that resist invasion (Lavoie et al. 2003). Invasive species are a major problem in many wetlands along the Pacific coast, especially in Oregon and Washington.
Although these species also occur further south in the San Francisco Bay-Delta region (Raven & Thomas 1970, Knight 1980, Grossinger et al. 1998), they are not yet a problem. In addition, the San Francisco Bay-Delta estuary has been considered one of the most invaded estuaries in the world (Cohen & Carlton 1998), the majority of the invasive species being invertebrates and fish. Invasive vascular plants such as Lepidium latifolium, and to a lesser extent, Arundo donax and Eichhornia crassipes, commonly invade and pose a long-term problem for restoration and management (Young et al. 1997, Grossinger et al. 1998, Renz 2002).
CONCLUSIONS AND FUTURE STUDIES
In contrast to and despite its reputation, Lythrum salicaria in a Delaware River constructed wetland had no long-term effect on richness (Leck 2003, Leck & Leck 2005). Amorpha fruticosa, Iris pseudacorus, Lythrum salicaria and Phalaris arundinacea are considered noxious weeds and invade disturbed as well as undisturbed wetlands (Apfelbaum & Sams 1987, Christy & Putera 1992, Glad & . Halse 1991). The responses of Pacific coastal wetlands, which may be older than Atlantic coastal wetlands (1000 vs. 500 years), to sea-level rise and other disturbances merit study.
Finally, the context for future research will inevitably incorporate the changes in global climate (e.g. Day et al. 2005, Osborn & Briffa 2006) and the subsequent rapid rise in sea level (Rignot & Kanagaratnam 2006), which will have an ongoing impact on all intertidal ecosystems. Future studies need to establish careful baseline information on all aspects of their system to control for or directly study such influences. Unfortunately, we are just beginning to investigate TFW at a time when global climate and sea level changes are causing background manipulation of processes before a general understanding of these systems is possible.
ACKNOWLEDGEMENTS
Cox T (2008) Primary oxygen and plankton production in freshwater tidal streams of the Schelde estuary. Field RT & Phillip KR (2000) Vegetation changes in freshwater tidal marshes of the Delaware Estuary. Findlay SEG, Pace ML & Fischer DT (1996) Spatial and temporal variability in the lower food web of the freshwater tidal Hudson River.
Gerkens M & Thiel R (2001) Habitat use of 0-year-old shad (Alosa fallax Lacepede, 1803) in the tidal freshwater area of the River Elbe, Germany. Meanley B (1965) Early fall food and habitat of the sora in the Patuxent River Marsh, Maryland. Sousa R, Guilhermino L & Antunes C (2005) Molluscan fauna in the freshwater tidal area of the Minho River estuary, NW.
Vader W (1977) Habitat and distribution of Perforatella rubiginosa (Gastropoda, Pulmonata) in the freshwater intertidal zone of the Scheldt estuary, Belgium. Winogrond HG & Kiviat E (1997) Invasion of Phragmites australis in tidal wetlands of the Hudson River.
