Ecosystem Functions of Tidal Fresh, Brackish, and Salt Marshes on the Georgia CoastAbstractIntroductionMethodsField and Laboratory MethodsStatistical AnalysisResultsDiscussionReferencesEcosystem Functions of Tidal Fresh, Brackish,and Salt Marshes on the Georgia CoastKazimierz Więski & Hongyu Guo &Christopher B. Craft & Steven C. PenningsReceived: 6 November 2008 / Revised: 1 February 2009 / Accepted: 1 October 2009 / Published online: 15 October 2009#Coastal and Estuarine Research Federation 2009Abstract We examined patterns of habitat function (plantspecies richness), productivity (plant aboveground biomassand total C), and nutrient stocks (N and P in abovegroundplant biomass and soil) in tidal marshes of the Satilla,Altamaha, and Ogeechee Estuaries in Georgia, USA. Wework ed at two sites within each salinity zone (fresh,brackish, and saline) in each estuary, sampling a transectfrom the creekbank to the marsh platform. In total, 110plant species were found. Site-scale and plot-scale speciesrichness decreased from fresh to saline sites. Standing cropbiomass and total carbon stocks were greatest at brackishsites, followed by freshwater then saline sites. Nitrogenstocks in plants and soil decreased across sites as salinityincreased, while phosphorus stocks did not differ betweenfresh and brackish sites but were lowest at salty sites. Theseresults generally support past speculation about ecosystemchange across the estuarine gradient, emphasizing thatecosystem function in tidal wetlands changes sharply acrossthe relatively short horizontal distance of the estuary.Changes in plant distribution patterns driven by globalchanges such as sea level rise, changing climates, or freshwater withdrawal are likely to have strong impacts on avariety of wetland functions and services.Keywords Ecosystem services.Salinity.Sea level rise.Soils.Macrophytes.Biodiversity.Carbon.Nitrogen.Phosphorus.Tidal marshes.Wetland functionsIntroductionEcological communities differ in their structural attributesand hence in ecosystem functions. Since some of thesefunctions provide in a direct or indirect way goods andservices satisfying human needs (de Groot et al. 2002),there have been attempts to assess their value (Farber et al.2002; Costanza et al. 2008). For example, tidal marshes areestimated to provide services to th e society of about$10,000 ha−1year−1(in 1994 dollars; Costanza et al.1997) in the form of habitat (e.g., diversity), regulation(e.g., denitrification and nutrient retention), and productivity(e.g., biomass) functions. Given a total acreage of approx-imately 16,000 km2in North America (Greenberg et al.2006), this translates into a total value of $16 billion yearly.All tidal marshes, however, are not the same, and manydo not provide the same levels of ecosystem functions. Forexample, within a riverine estuary, variation in salinity maylead to marked differences in the functioning of tidal marshplant communities (Odum 1988). Odum argued thatsalinity-driven stress should reduce plant diversity in tidalsalt marshes compared to tidal freshwater marshes, whilethe lower salinity stress in the tidal freshwater systemsshould incre ase decomposition rates, net primary produc-tion of vascular plants, and ultimately organic matteraccumulation. Craft (2007) showed that soil organic mattercontent and accumulation differed mark edly among tidalfresh, brackish, and salt marsh sites, but we are unaware ofany studies that have compared plant community functionsat replicated sites across the estuarine salinity gradient.Electronic supplementary material The online version of this article(doi:10.1007/s12237-009-9230-4) contains supplementary material,which is available to authorized users.K. Więski:H. Guo:S. C. Pennings (*)Department of Biology and Biochemistry, University of Houston,Houston, TX 77204, USAe-mail: [email protected]. B. CraftSchool of Public and Environmental Affairs, Indiana University,Bloomington, IN 47405, USAEstuaries and Coasts (2010) 33:161–169DOI 10.1007/s12237-009-9230-4To test the hypothesis that the productivity and nutrientretention functions of tidal marshes would increase fromsalt to fresh marshes, we examined patterns of habitat (plantdiversity), production (plant biomass and total C), andregulation (sto cks of N and P in aboveground plant biomassand soil) functions in tidal salt, brackish, and freshwatermarshes of the Satilla, Altamaha, and Ogeechee estuaries inGeorgia.MethodsField and Laboratory MethodsVascular plant diversity, biomass, and nutrient retentionwere measured at replicate sites along the salinity gradient.We studied two sites within each of three salinity zones(fresh, brackish, and saline) in each of three riverineestuaries along the Georgia coast (Fig. 1,ElectronicSupporting Material, Appendix 1). Salinity zones wereinitially determined based on the dominant vegetation andposition along the estuary. Down-estuary sites dominatedby Spartina alterniflora were selected as saline; mid-estuary sites dominated by mixtures of S. alterniflora,Spartina cynosuroides,andJuncus roemerianu s wereselected as brackish; and up-estuary sites dominated bymixtures of S. cynosuroides, Schoenoplectus tabernaemon-tani,andZizaniopsis miliacea were selected as fresh.Salinity records from the water column near theAltamaha River sites during 2006 showed that we hadidentified three distinct salinity regions in this estuary(Fig. 2). Water column salinities increased from springthrough the summer due to reduced river discharge andfluctuated due to the spring-neap tide cycle. The highestsalinities (up to 35 PSU) were observed at saline sites,followed by brackish (up to 21 PSU) and fresh sites(usually less than 1 but occasionally up to 2 PSU). Wemeasured water column salinities in the other two estuariesonce a month in July, August, and October 2006 and in July2008 when we visited the sites, and these limited valueswere broadly consistent with the more frequent recordsfrom the Altamaha River except that the fresh and brackishsites were somewhat saltier than on the Altamaha River(Satilla: fresh: 6.7 (1.5), brackish: 23.7 (1.3), saline: 30.8(0.71); Ogeechee: fresh: 12.2 (1.4), brackish: 23.6 (1.9),saline: 28.9 (0.4); PSU (standard error )), in part becausethey represented summer and fall seasons when riverdischarge in Georgia is generally lower and salinities higher(e.g., Fig. 2). Although there appeared to be some variationamong rivers in the exact salinity values, the sitesrepresented a clea r