title: Salt marsh as a coastal filter for the oceans: changes in function with experimental increases in nitrogen loading and sea-level rise.
abstract: Coastal salt marshes are among Earth's most productive ecosystems and provide a number of ecosystem services, including interception of watershed-derived nitrogen (N) before it reaches nearshore oceans. Nitrogen pollution and climate change are two dominant drivers of global-change impacts on ecosystems, yet their interacting effects at the land-sea interface are poorly understood. We addressed how sea-level rise and anthropogenic N additions affect the salt marsh ecosystem process of nitrogen uptake using a field-based, manipulative experiment. We crossed simulated sea-level change and ammonium-nitrate (NH(4)NO(3))-addition treatments in a fully factorial design to examine their potentially interacting effects on emergent marsh plants in a central California estuary. We measured above- and belowground biomass and tissue nutrient concentrations seasonally and found that N-addition had a significant, positive effect on a) aboveground biomass, b) plant tissue N concentrations, c) N stock sequestered in plants, and d) shoot:root ratios in summer. Relative sea-level rise did not significantly affect biomass, with the exception of the most extreme sea-level-rise simulation, in which all plants died by the summer of the second year. Although there was a strong response to N-addition treatments, salt marsh responses varied by season. Our results suggest that in our site at Coyote Marsh, Elkhorn Slough, coastal salt marsh plants serve as a robust N trap and coastal filter; this function is not saturated by high background annual N inputs from upstream agriculture. However, if the marsh is drowned by rising seas, as in our most extreme sea-level rise treatment, marsh plants will no longer provide the ecosystem service of buffering the coastal ocean from eutrophication.
authors.affiliation: Environmental Studies Department, University of California Santa Cruz, Santa Cruz, California, United States of America. jnelson@stanfordalumni.org
authors.forename: Joanna L
authors.initials: JL
authors.lastname: Nelson
authors.forename: Erika S
authors.initials: ES
authors.lastname: Zavaleta
mesh_terms: D018533:Biomass; D002140:California; D017753:Ecosystem; D005843:Geography; D009584:Nitrogen / Q000378:metabolism / Q000494:pharmacology*; D009792:Oceans and Seas; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development; D018520:Plant Shoots / Q000187:drug effects / Q000254:growth & development; D055051:Salt-Tolerant Plants / Q000187:drug effects; D012621:Seasons; D012623:Seawater / Q000032:analysis*; D012965:Sodium Chloride / Q000737:chemistry*; D014872:Water Movements; D053833:Wetlands
chemical_list: D012965:Sodium Chloride; D009584:Nitrogen