You are here:
Below the Disappearing Marshes of an Urban Estuary: Historic Nitrogen Trends and Soil Structure
Citation:
Wigand, C., C. Roman, E. Davey, M. Stolt, R. Johnson, Alana Hanson, E. Watson, S. Moran, D. Cahoon, J. Lynch, AND P. Rafferty. Below the Disappearing Marshes of an Urban Estuary: Historic Nitrogen Trends and Soil Structure. ECOLOGICAL APPLICATIONS. Ecological Society of America, Ithaca, NY, 24(4):633-649, (2014).
Impact/Purpose:
Sustainability of coastal wetlands is the focus of AED wetland research, and in the present study cultural eutrophication is examined as a possible contributer to the disappearance of coastal wetlands in the Jamaica Bay Estuary (JBE), NY. This report contributes to the products of Task SHC 3.3.1.11 (Wetlands and nitrogen in Narragansett Bay Watershed)and more specifically to the FY 14 SHC 3.3.1.11 product: Technical report on cultural eutrophication effects on belowground structure of northeast salt marshes. Jamaica Bay is an endpoint on a continuum of high to low impact and will be used as a New England reference high impact site. Little is known about the belowground structure (e.g., soil macro- and micro-morphology, roots, rhizome, peat, and soil shear strength) and processes (e.g., accretion, rate of elevation change, and soil respiration) associated with the JBE marshes. We used census data, radiometric dating, stable nitrogen isotopes, and soil surveys to examine the temporal relationships between the human population and the marsh soil characteristics, and computer-aided tomographic imaging, sediment elevation tables, plant surveys, gas analyzer, and geovane to examine for differences in soil structure and processes between disappearing marsh islands (Black Bank and Big Egg) and the stable, mainland JoCo marsh. The radiometric dating, stable nitrogen isotopes, and soil percent nitrogen results suggest a rapid increase in human wastewater nutrients beginning in the late 1840s, and a tapering off, approximately in the 1930s when wastewater treatment plants were first installed. We measured a significant inverse relationship between time and the soil dry bulk densities, supporting the idea that the JBE marsh soils became more organic-rich with increasing nitrogen loads over time. There was a significant positive relationship between the stable nitrogen isotopes and population over time, suggesting that anthropogenic eutrophication may be contributing to marsh loss. We measured significantly higher above/belowground ratios, lower abundance and mass of roots and rhizomes, lower soil organic matter, and higher soil respiration at Black Bank compared to JoCo. The rates of change of sediment elevation for JoCo (4.4 mm y-1) and Black Bank (4.8 mm y-1) approximated or were greater than the relative sea level rise estimated using tide gauge data from Sandy Hook, NJ (3.8 mm y-1). Even though there is a loss of soil organic matter at Black Bank, there is a volumetric expansion of the peat, explained by an increase in water associated with the peat. Although there is not an apparent elevation deficit at Black Bank, the marsh has lower soil shear strength. Changes in below-ground marsh structure and processes apparently leave the JBE marshes more susceptible to sea level rise, storms, and other erosional processes. With the additional stress of climate change (e.g., accelerated sea level rise; increases in the severity of storms and precipitation events), eutrophication effects in urbanized, northeastern USA could cascade into accelerated losses of marsh area as is now occurring in JBE.
Description:
Marshes in the urban Jamaica Bay Estuary, New York, USA are disappearing at an average rate of 13 ha/yr, and multiple stressors (e.g., wastewater inputs, dredging activities, groundwater removal, and global warming) may be contributing to marsh losses. Among these stressors, wastewater nutrients are suspected to be an important contributing cause of marsh deterioration. We used census data, radiometric dating, stable nitrogen isotopes, and soil surveys to examine the temporal relationships between human population growth and soil nitrogen; and we evaluated soil structure with computer-aided tomography, surface elevation and sediment accretion trends, carbon dioxide emissions, and soil shear strength to examine differences among disappearing (Black Bank and Big Egg) and stable marshes (JoCo). Radiometric dating and nitrogen isotope analyses suggested a rapid increase in human wastewater nutrients beginning in the late 1840s, and a tapering off beginning in the 1930s when wastewater treatment plants (WWTPs) were first installed. Current WWTPs nutrient loads to Jamaica Bay are approximately 13 995 kg N/d and 2767 kg P/d. At Black Bank, the biomass and abundance of roots and rhizomes and percentage of organic matter on soil were significantly lower, rhizomes larger in diameter, carbon dioxide emission rates and peat particle density significantly greater, and soil strength significantly lower compared to the stable JoCo Marsh, suggesting Black Bank has elevated decomposition rates, more decomposed peat, and highly waterlogged peat. Despite these differences, the rates of accretion and surface elevation change were similar for both marshes, and the rates of elevation change approximated the long term relative rate of sea level rise estimated from tide gauge data at nearby Sandy Hook, New Jersey. We hypothesize that Black Bank marsh kept pace with sea level rise by the accretion of material on the marsh surface, and the maintenance of soil volume through production of larger diameter rhizomes and swelling (dilation) of waterlogged peat. JoCo Marsh kept pace with sea-level rise through surface accretion and soil organic matter accumulation. Understanding the effects of multiple stressors, including nutrient enrichment, on soil structure, organic matter accumulation, and elevation change will better inform management decisions aimed at maintaining and restoring coastal marshes.
