Journal Article

Coastal eutrophication as a driver of salt marsh loss

Fleeger, John W., Wollheim, Wilfred M., Deegan, Linda A., Warren, R. Scott, Fagherazzi, Sergio, Peterson, Bruce J., Johnson, David Samuel

2012

Overview

A nine-year whole-ecosystem experiment demonstrates that nutrient enrichment, a global problem in coastal ecosystems, can be a driver of salt-marsh loss. Excess nutrients threaten salt marshes Salt marshes provide important ecosystem services such as storm protection for coastal cities, nutrient removal and carbon sequestration, but despite protective measures these ecosystems are in decline. Nine years of data from a whole-ecosystem nutrient-enrichment experiment now demonstrate that current levels of coastal nutrient loading can alter key salt-marsh-ecosystem properties, leading to the collapse of creek banks and, ultimately, the conversion of salt marsh into mudflat. The potential deterioration of coastal marshes owing to eutrophication adds another dimension to the challenge of managing nitrogen while meeting food-production demands in the twenty-first century. Salt marshes are highly productive coastal wetlands that provide important ecosystem services such as storm protection for coastal cities, nutrient removal and carbon sequestration. Despite protective measures, however, worldwide losses of these ecosystems have accelerated in recent decades 1 . Here we present data from a nine-year whole-ecosystem nutrient-enrichment experiment. Our study demonstrates that nutrient enrichment, a global problem for coastal ecosystems 2 , 3 , 4 , can be a driver of salt marsh loss. We show that nutrient levels commonly associated with coastal eutrophication increased above-ground leaf biomass, decreased the dense, below-ground biomass of bank-stabilizing roots, and increased microbial decomposition of organic matter. Alterations in these key ecosystem properties reduced geomorphic stability, resulting in creek-bank collapse with significant areas of creek-bank marsh converted to unvegetated mud. This pattern of marsh loss parallels observations for anthropogenically nutrient-enriched marshes worldwide, with creek-edge and bay-edge marsh evolving into mudflats and wider creeks 5 , 6 , 7 . Our work suggests that current nutrient loading rates to many coastal ecosystems have overwhelmed the capacity of marshes to remove nitrogen without deleterious effects. Projected increases in nitrogen flux to the coast, related to increased fertilizer use required to feed an expanding human population, may rapidly result in a coastal landscape with less marsh, which would reduce the capacity of coastal regions to provide important ecological and economic services.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 704/158/2458 / Animal and plant ecology / Animal, plant and microbial ecology / Animals / Anthropogenic factors / Applied ecology / Banks / Biological and medical sciences / Biomass / Brackish water ecosystems / Carbon Sequestration / Coastal ecosystems / Coastal zone / Conservation, protection and management of environment and wildlife / Creeks / Creeks & streams / Decomposition / Ecosystem services / Ecotoxicology, biological effects of pollution / Environmental aspects / Environmental degradation: ecosystems survey and restoration / Eutrophication / Eutrophication - physiology / Fertilizers / Food / Food Supply / Fundamental and applied biological sciences. Psychology / Global positioning systems / GPS / Human populations / Humanities and Social Sciences / letter / Mud flats / multidisciplinary / Nitrates / Nitrogen / Nitrogen - metabolism / Nitrogen Cycle / Nutrient loading / Nutrient loss / Nutrient removal / Organic matter / Salt marshes / Salts / Science / Shear strength / Soil erosion / Synecology / Terrestrial environment, soil, air / Tidal marshes / Wetlands