Vegetation Cover and Elevation in Long-Term Experimental Nutrient-Enrichment Plots in Great Sippewissett Salt Marsh, Cape Cod, Massachusetts: Implications for Eutrophication and Sea Level rise

Abstract

Nitrogen inputs restructure ecosystems and can interact with other agents of ecological change and potentially intensify them. To examine the effects of nitrogen combined with those of elevation and competition, in 2005 we mapped vegetation and elevation within experimental plots that have been fertilized since 1970 in Great Sippewissett salt marsh, Cape Cod, MA, USA and compared the resulting effects on marsh vegetation. Decadal-scale chronic nutrient enrichment forced changes in cover and spatial distribution of different species. With increasing enrichment, there was a shift in species cover primarily involving loss of Spartina alterniflora and an increase in Distichlis spicata. Percent cover of near monocultures increased with nitrogen fertilization, owing mainly to the proliferation of D. spicata. The experimental fertilization prompted a shift from the short form of S. alterniflora to taller forms, hence increasing above-ground biomass, where this species managed to remain. Chronic enrichment increased upper and lower limits of the elevation range within which certain species occurred. The shift to increased cover of D. spicata was also associated with faster accretion of the marsh surface where this species was dominant, but not where S. alterniflora was dominant. Interactions among nutrient supply, elevation, and competition altered the direction of competitive success among different species of marsh plants, and forced changes in the spatial distribution and composition of the salt marsh plant communities. The results imply that there will be parallel changes in New England salt marshes owing to the widespread eutrophication of coastal waters and the increasing sea level rise. Knowing the mechanisms structuring marsh vegetative cover, and their role in modification of salt marsh accretion, may provide background with which to manage maintenance of affected coastal wetlands.

Microbially mediated nitrogen retention and loss in a salt marsh soil

“…Plant species can affect microbially mediated processes by directly altering soil redox (Windham and Lathrop 1999). Over long time scales, faster marsh accretion under particular species can affect sediment redox by increasing marsh elevation relative to sea level (Reed 1995, Fox et al 2012.…”

“…Global change factors such as sea level rise, warming, and eutrophication can lead to the loss of plant diversity and even the development of monocultures in salt marshes (Bertness et al 2002, Silliman and Bertness 2004, Gedan and Bertness 2009, Gedan et al 2011, Fox et al 2012. Sea level rise may increase the dominance of forbs in some coastal ecosystems (Warren and Niering 1993) whereas N inputs may allow graminoids to outcompete forbs (Bowman et al 1993, De Schrijver et al 2011.…”

Differential bait preference and rate of attraction by Argentine ants (Linepithema humileMayr) at freshwater and saltwater marsh sites in southern California

“…Plants grow tall (max. height 1-3 m) and dense in the lower marsh along tidal creeks where nutrients and dissolved oxygen are more available (Fox et al 2012). Shorter plants (max.…”

“…Shorter plants (max. height <1 m) persist in backwater areas of the high marsh that are relatively nutrient depleted and lack efficient drainage (Fox et al 2012). Typically, there is an abrupt transition between the height classes less than 5 m from creek channels.…”

Shifting Restoration Policy to Address Landscape Change, Novel Ecosystems, and Monitoring

“…Where rural and urban surfaces are impervious, nitrogen moves downstream in runoff, accumulates in wetlands, and drives changes in vegetation. Nitrogen affects native plants directly and indirectly by enhancing distributions of aggressive weeds that displace native species (Bobbink et al 2010, Stohlgren et al 2011, Fox et al 2012). In the United States, several invasive clonal graminoids expand vegetatively and displace desired native species (Drexler andBedford 2002, Frieswyk et al 2007).…”