Sediment starvation destroys New York City marshes’ resistance to sea level rise

Abstract

New York City (NYC) is representative of many vulnerable coastal urban populations, infrastructures, and economies threatened by global sea level rise. The steady loss of marshes in NYC’s Jamaica Bay is typical of many urban estuaries worldwide. Essential to the restoration and preservation of these key wetlands is an understanding of their sedimentation. Here we present a reconstruction of the history of mineral and organic sediment fluxes in Jamaica Bay marshes over three centuries, using a combination of density measurements and a detailed accretion model. Accretion rate is calculated using historical land use and pollution markers, through a wide variety of sediment core analyses including geochemical, isotopic, and paleobotanical analyses. We find that, since 1800 CE, urban development dramatically reduced the input of marsh-stabilizing mineral sediment. However, as mineral flux decreased, organic matter flux increased. While this organic accumulation increase allowed vertical accumulation to outpace sea level, reduced mineral content causes structural weakness and edge failure. Marsh integrity now requires mineral sediment addition to both marshes and subsurface channels and borrow pits, a solution applicable to drowning estuaries worldwide. Integration of marsh mineral/organic accretion history with modeling provides parameters for marsh preservation at specific locales with sea level rise.

Climate and anthropogenic controls on blue carbon sequestration in Hudson River tidal marsh, Piermont, New York

“…To preserve marsh stability for a myriad of ecological and shoreline protection reasons, we advocate thin-layer mineral additions to replace the mineral supply that appears missing in both coastal (Peteet et al 2018) and riverine marshes. Enhanced removal of nitrogen from wastewater is extremely important because of the documented increased organic matter decomposition with higher nitrogen (Watson et al 2014, Bulseco et al 2019) and the evidence for decreased root and rhizome production in several salt marsh species (Deegan et al 2012, Wigand et al 2014).…”

“…A striking recent multidecadal analysis of aerial salt marsh extent in Rhode Island shows a loss of 17.3% in a mere 40 years (Watson et al 2017b). This loss of potential C sequestration is threatening because the upper meters of tidal marshes in urban regions such as Jamaica Bay, NYC also sequester abundant heavy metals (Peteet et al 2018). The importance of preserving the integrity of New York's marshes is critical for these reasons as well as for biodiversity, storm protection, water quality, and nursery habitat.…”

“…The importance of preserving the integrity of New York's marshes is critical for these reasons as well as for biodiversity, storm protection, water quality, and nursery habitat. Recent methodology that has proved to enhance our understanding of marsh preservation focuses on long-term sediment history reconstruction (Drexler et al 2009, Drexler et al 2011, Callaway et al 2012, Jones et al 2017, Peteet et al 2018, as declines in mineral contribution and nitrogen pollution have both been implicated in marsh instability.…”

Salt marshes for flood risk reduction: Quantifying long-term effectiveness and life-cycle costs

“…These marshes usually have a high organic content, and are sometimes affected by nutrients introduced via freshwater river diversions, which promotes poor rhizome and root growth (Kearney et al, 2011). Also sediment starvation can lead to increasing organic matter content, which results in structural weakness and edge failure (Peteet et al, 2018). Salt marshes rooted in mineral soils have much higher shear strengths, and are the most resilient wetlands to erosional storm impacts (Morton and Barras, 2011).…”

Carbon accumulation and vertical accretion in a restored versus historic salt marsh in southern Puget Sound, Washington, United States

“…If vegetation cannot immediately colonize restored lands due to prior land‐surface subsidence, the elevation of the marsh platform must ultimately be raised to provide the necessary conditions for plant growth. Vertical accretion (VA) is the natural process by which both inorganic sedimentation and organic accumulation raises and/or maintains the elevation of the marsh surface in the tidal frame, a process of great importance under continuous and accelerating sea‐level rise (Drexler ; Anisfeld ; Peteet et al ). If little vegetation is present, such accretion must occur chiefly from riverine and tidal allochthonous sources of inorganic and organic matter (Williams & Orr ; Neubauer ).…”