Coastal eutrophication as a driver of salt marsh loss

Abstract

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. 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, 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. 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.

Ecological succession reveals potential signatures of marine–terrestrial transition in salt marsh fungal communities

“…We addressed the relatedness between the observed temporal changes and the shifting environmental conditions, aiming to understand how fungal communities establish in the chronosequence and may affect local ecological processes such as C transformations. As salt marshes are important C sinks, understanding the distribution and drivers of fungal communities in these threatened areas are of critical importance (Deegan et al, 2012;Kirwan and Mudd, 2012). Thus, the results of this study may directly affect ecological models that aim to predict ecosystem responses to climate change and direct anthropogenic perturbations (see Bardgett et al, 2008;Chapin et al, 2009).…”

An overlooked nitrogen loss linked to anaerobic ammonium oxidation in estuarine sediments in China

“…It was estimated that nearly 20% of the total nitrogen loss, mostly in the form of nitrate, was transported into estuarine and coastal ecosystems in the past three decades through riverine discharge and atmospheric deposition (Cui et al 2013), resulting in water pollution (e.g., coastal eutrophication, hypoxia, harmful algae blooms) (Deegan et al 2012). Thus, estuaries are thought to be a potential sink of nitrogen, especially nitrate, which is the substrate for many nitrogen cycling processes (e.g., denitrification and anammox).…”

Marine Phytophthora species can hamper conservation and restoration of vegetated coastal ecosystems

“…flood protection, carbon and nutrient storage, biodiversity enhancement) [25][26][27][28]. In addition, these vegetated coastal ecosystems are globally disappearing [29,30], and costly restoration efforts, with various success rates, are being undertaken to halt and revert these losses. Given the vital functions of marine plants, their worldwide declines, and the restoration efforts being undertaken to reverse these losses, it is important to identify agents of infection that may contribute to declines or may prevent successful restoration.…”