Below the disappearing marshes of an urban estuary: historic nitrogen trends and soil structure.

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.

Use of computed tomography imaging for quantifying coarse roots, rhizomes, peat, and particle densities in marsh soils.

Computed tomography (CT) imaging has been used to describe and quantify subtidal, benthic animals such as polychaetes, amphipods, and shrimp. Here, for the first time, CT imaging is used to quantify wet mass of coarse roots, rhizomes, and peat in cores collected from organic-rich (Jamaica Bay, New York) and mineral (North Inlet, South Carolina) Spartina alterniflora soils. Image analysis software was coupled with the CT images to measure abundance and diameter of the coarse roots and rhizomes in marsh soils. Previously, examination of marsh roots and rhizomes was limited to various hand-sieving methods that were often time-consuming, tedious, and error prone. CT imaging can discern the coarse roots, rhizomes, and peat based on their varying particle densities. Calibration rods composed of materials with standard densities (i.e., air, water, colloidal silica, and glass) were used to operationally define the specific x-ray attenuations of the coarse roots, rhizomes, and peat in the marsh cores. Significant regression relationships were found between the CT-determined wet mass of the coarse roots and rhizomes and the hand-sieved dry mass of the coarse roots and rhizomes in both the organic-rich and mineral marsh soils. There was also a significant relationship between the soil percentage organic matter and the CT-determined peat particle density among organic-rich and mineral soils. In only the mineral soils, there was a significant relationship between the soil percentage organic matter and the CT-determined peat wet mass. Using CT imaging, significant positive nitrogen fertilization effects on the wet masses of the coarse roots, rhizomes, and peat, and the abundance and diameter of rhizomes were measured in the mineral soils. In contrast, a deteriorating salt marsh island in Jamaica Bay had significantly less mass of coarse roots and rhizomes at depth (10-20 cm), and a significantly lower abundance of roots and rhizomes compared with a stable marsh. However, the diameters of the rhizomes in the deteriorating marsh were significantly greater than in the stable marsh. CT imaging is a rapid approach to quantify coarse roots, rhizomes, peat, and soil particle densities in coastal wetlands, but the method is unable at this time to quantify fine roots.

Using stable isotopes to monitor anthropogenic nitrogen inputs to estuaries.

Use of stable nitrogen isotope ratios is one method that has been proposed to indicate anthropogenic nutrient enrichment in estuarine systems. However, the role of stable isotopes as a tool in long-term ecosystem monitoring has not been fully developed. Resident producer and consumer species were collected from marshes dominated by Spartina alterniflora and subject to a range of anthropogenic impacts in Cape Cod, Massachusetts, and in Great South Bay and Jamaica Bay, New York. Tissue isotope ratios of Spartina alterniflora, Ulva lactuca, Fundulus heteroclitus, and Geukensia demissa were analyzed in order to determine which organisms are the most sensitive indicators of changes in anthropogenic nitrogen source and loading. Power analysis was used to determine the sample sizes necessary to detect change in nutrient source using the species sampled. Relationships between the delta15N values of the species sampled and watershed population density and residential development were evaluated. Population density was a better indicator of anthropogenic nitrogen impact than residential development, since most anthropogenic nitrogen in the study marshes was derived from wastewater. Consumer species demonstrated lower within-site variability than producer species and would therefore require smaller sample sizes to detect changes in nitrogen source and loading.

Monitoring nekton as a bioindicator in shallow estuarine habitats.

Long-term monitoring of estuarine nekton has many practical and ecological benefits but efforts are hampered by a lack of standardized sampling procedures. This study provides a rationale for monitoring nekton in shallow (< 1 m), temperate, estuarine habitats and addresses some important issues that arise when developing monitoring protocols. Sampling in seagrass and salt marsh habitats is emphasized due to the susceptibility of each habitat to anthropogenic stress and to the abundant and rich nekton assemblages that each habitat supports. Extensive sampling with quantitative enclosure traps that estimate nekton density is suggested. These gears have a high capture efficiency in most habitats and are small enough (e.g., 1 m2) to permit sampling in specific microhabitats. Other aspects of nekton monitoring are discussed, including spatial and temporal sampling considerations, station selection, sample size estimation, and data collection and analysis. Developing and initiating long-term nekton monitoring programs will help evaluate natural and human-induced changes in estuarine nekton over time and advance our understanding of the interactions between nekton and the dynamic estuarine environment.