The Pace of Ecosystem Development of Constructed Spartina Alterniflora Marshes

Abstract

Abstract. Ecological attributes were measured along a chronosequence of 1-to 28-yrold, constructed Spartina alternifIora marshes to identify trajectories and rates of ecosystem development of wetland structure and function. Attributes related to biological productivity and diversity (Spartina, epiphytic and sediment algae, benthic invertebrates), soil development (sediment deposition, organic C, N, P, organic matter quality), and microbial processes (C mineralization) were compared among e i a t constructed marshes and eight paired natural reference marshes. Most ecological attributes developed in a predictable manner over time, and most achieved equivalence to natural marshes 5-15 yr after marsh construction. An exception was soil organic C and N pools (0-30 cm) that, after 28 yr, were significantly lower in constructed marshes. Development of habitat structure (Spartina stem height and density) and biodiversity (algae and invertebrates) developed concurrently with functional characteristics such as biomass, chlorophyll a, and invertebrate density. Processes related to hydrology, sediment deposition and soil C and N accumulation, developed almost instantaneously with the establishment of Spartina, and young (1-to 3-yr-old), constructed marshes trapped sediment and sequestered N at higher rates than comparable reference marshes. Development of heterotrophic activity (C mineralization, invertebrate density) was strongly linked to surface (0-10 cm) soil organic C content. Ecosystem development of constructed (and natural) salt marshes depended on a minimum of 100 g Nlm2 (0.05-0.1% N) to support emergent vegetation and 1000 g Clm2 (0.5-1% C) to sustain the heterotrophic community.

Detrital Decomposition As a Measure of Ecosystem Function in Created Wetlands

“…~c c o m~a n~i n g changes in the rate of detritus processing provide plausible measures of ecosystem function. A number of studies have confirmed that benthic organic matter accumulates, at least initially, in some created wetlands, and that natural wetland substrate has a higher organic content and a lower density than that of young created wetlands (Craft et al 1999and 2003, Zedler and Callaway 1999, Nair et al 2001. Further, there is evidence that the rates of detritus decomposition (Atkinson and Cairns 2001) and carbon mineralization (Craft et al 2003) increase with age in created wetlands.…”

“…A number of studies have confirmed that benthic organic matter accumulates, at least initially, in some created wetlands, and that natural wetland substrate has a higher organic content and a lower density than that of young created wetlands (Craft et al 1999and 2003, Zedler and Callaway 1999, Nair et al 2001. Further, there is evidence that the rates of detritus decomposition (Atkinson and Cairns 2001) and carbon mineralization (Craft et al 2003) increase with age in created wetlands. Decomposition dynamics have important associations with wetland soil development, seed germination, faunal colonization, and hydrologic regime Callaway 1999, Taylor andMiddleton 2004), and as such they may be suitable tools for assessing the evolution of ecosystem function.…”

“…In another approach, Simenstad and Thom (1996) assessed wetland function by considering changes in ecosystem structure and composition over a seven-year period. Analyses of wetland function less frequently have included direct measurement of system processes, such as flow and sequestration of energy or material and biogeochemical transformation (Richardson 1994, Craft et al 2003. Process-based functional analysis is centered on the ideas that ecosystem attributes change over successional time (Odum 1969) and that these changes express "the multifaceted nature of ecosystems" (Brinson and Rheinhardt 1996).…”

Human Land-Use and Soil Change

“…Coastal marshes have been managed for forage and grazing for centuries (Gedan et al 2009), and they are increasingly under heavy pressure from human development including pollution, introduced species, altered hydrology (including nutrient and sediment loadings), and climate change (Adam 2002;Scavia et al 2002;Kirwan and Megonigal 2013). Many have been degraded and even destroyed by direct and indirect human management on the Atlantic (Coverdale et al 2014;Kearney et al 2002), Gulf (Turner 2011), and Pacific coasts (Craft et al 2003;Kennish 2001). Kirwan et al (2010) summarized the stability of coastal marshes as the balance between accretion and submergence where biological and physical factors interact to modify the marsh environment.…”

A five year study of floristic succession in a restored urban wetland

“…We refrain from calling the SWAMP a fully restored wetland since reverting to the original state (Bradshaw, 1996) is an unattainable goal after only a few years (Craft et al, 2003). Instead, the SWAMP is a designed wetland complex that includes riverine, palustrine, and lacustrine wetlands to maximize habitat for biota as well as improve water quality.…”