Earl Davey

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.

APPLICATION OF COMPUTER-AIDED TOMOGRAPHY (CT) TO THE STUDY OF ESTUARINE BENTHIC COMMUNITIES

Sediment cores were imaged using a Computer-Aided Tomography (CT) scanner at Massachusetts General Hospital, Boston, Massachusetts, United States. Procedures were developed, using the attenuation of X-rays, to differentiate between sediment and the water contained in macrobenthic tubes and tunnels. The effects of sediment type on the ability to discriminate tubes as small as 1.5 mm were examined. Soft sediments with mean X-ray attenuations (SXA) from 450 to 576 CT numbers were successfully scanned in cores of 15.2 cm diameter by 30 cm depth. We demonstrated the accessibility and availability of CT technology to ecological studies by negotiating a reduced research rate (

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

200 per core) for sediment scanning at a nearby small hospital. Additionally, we were able to transfer these image data from the local hospital environment to a personal computer, by developing specialized computer software. These steps allowed greater opportunity for data exploration, manipulation, and statistical evaluation than would be available in a medical facility. CT analysis was applied to intact sediment cores from five stations along a 31-km pollution gradient in Narragansett Bay, Rhode Island, United States. The percentage of tube and tunnel area (PTTA) within the top 18 cm of sediment from each station was measured and ranged from 0.07% to 1.13%. PTTA increased along this gradient with distance from the pollution sources (r2 = 0.81, P < 0.01). The mean X-ray attenuation for sediment (excluding animals, their tubes and tunnels, and shells) was determined at each station. It also showed a highly significant relationship along this gradient (r2 = 0.98, P < 0.01) and ranged from 271 to 576 CT numbers. The measurement of PTTA may be an effective management tool to assess and monitor the effects of organic carbon loading on benthic communities in Narragansett Bay and similarly impacted estuaries.

Influence of Size on Fate and Ecological Effects of Kepone in Physical Models

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.

Environmental Assessment of a Phthalate Ester, Di(2-Ethylhexyl) Phthalate (DEHP), Derived from a Marine Microcosm

Three different sizes of marine microcosms were used to study the influence of two features of spatial scale on the chemical fate and ecological effects of the pesticide Kepone. Increasing the size of microcosms reduced the ratio of wall surface area to volume of contained sea water, but increased the number of benthic species due to increasing sample size. Other features of spatial scale, such as water turbulence, water turnover, etc., were held constant. Intact water-column and benthic communities from a north-temperate marine system were coupled together in 9.1-, 35.0-, and 140.O-L containers. Kepone at 20.4 nmol/L was added to these microcosm systems over a 30-d period. A 3 x 2 factorial design was used to discern the effects of size and Kepone. In the absence of Kepone the phytoplankton community exhibited excessive growth relative to the field system for all system sizes. Growth was directly related to the size of microcosms. In addition, the time required to achieve maximum algal biomass was also directly related to size. Release of a growth-stimulating compound(s) from fouling organisms settling on the microcosm walls and size-dependent increases in benthic species provided the best explanation for the observed phytoplankton dynamics. Addition of Kepone indirectly increased phytoplankton densities by reducing through toxic effects, the grazing pressure of zooplankton. Because this effect and mechanism was dependent upon the size of the system, the sensitivity of future perturbation studies may be enhanced by producing similar or related variations in system size. The concentration of Kepone in surficial sediments was also size dependent. Since the average concentrations of Kepone in all water columns were statistically equivalent, these findings were the result of sediment bioturbation coupled with preferential partitioning of Kepone from liquid to the solid, organic phase of sediments. Ecological risk assessments based upon data derived from these systems are therefore dependent upon size. Furthermore, the smaller the size, the greater the underestimate in sediment exposure and the ecological risks of Kepone.

Significance of the surface microlayer to the environmental fate of di (2-ethylhexyl) phthalate predicted from marine microcosms

This study tested the influence of system complexity on the environmental assessment of a chemical. Marine microcosms were perturbed with a phthalate ester, di(2-ethylhexyl) phthalate (DEHP). Concentrations of 1, 10, and 100 ..mu..g of DEHP per litre were added to the water-column subsystem of marine microcosms for 30 days during the summer (18/sup 0/C) and winter (1/sup 0/C) seasons. Significant portions of the DEHP losses from the water-column subsystem during the experiments were due to the complete breakdown of the parent compound to carbon dioxide (CO/sub 2/). In the benthic subsystem, DEHP concentrations in the sediment were increased by more than 50 and 250 times the concentration in the water column during the winter and summer seasons, respectively. Statistically significant (..cap alpha.. = 0.05) reductions in the fluxes of ammonia (NH/sub 3/) from the benthic subsystem were observed in microcosms receiving 100 ..mu..g of DEHP per litre during the summer. Concentrations of DEHP in selected bivalves ranged from 174 to 229 000 ..mu..g of DEHP per wet kilogram, depending upon the water column exposure concentrations and the season of the year.

Varying Inundation Regimes Differentially Affect Natural and Sand-Amended Marsh Sediments.

Abstract The quantitative significance of the surface microlayer (SML) to the environmental fate of the industrial plasticizer di(2-ethylhexyl)phthalate (DEHP), in marine coastal systems was established by the use of experimental microcosms. The effects of season, sea-state and associated solvents were investigated. The results demonstrated that the SML community rapidly degraded DEHP to such an extent that under certain treatment conditions biodegradation was the dominant removal process compared with physical transport. Biodegradation of DEHP by the SML biota was estimated to account for at least 30% of the total budget. Extrapolation of the laboratory results to the simulated field system (the West Passage of Narragansett Bay, RI), is discussed within the context of potential artifacts of the marine microcosms.

Discontinuities in soil strength contribute to destabilization of nutrient‐enriched creeks

Climate change is altering sea level rise rates and precipitation patterns worldwide. Coastal wetlands are vulnerable to these changes. System responses to stressors are important for resource managers and environmental stewards to understand in order to best manage them. Thin layer sand or sediment application to drowning and eroding marshes is one approach to build elevation and resilience. The above- and below-ground structure, soil carbon dioxide emissions, and pore water constituents in vegetated natural marsh sediments and sand-amended sediments were examined at varying inundation regimes between mean sea level and mean high water (0.82 m NAVD88 to 1.49 m NAVD88) in a field experiment at Laws Point, part of the Plum Island Sound Estuary (MA). Significantly lower salinities, pH, sulfides, phosphates, and ammonium were measured in the sand-amended sediments than in the natural sediments. In natural sediments there was a pattern of increasing salinity with increasing elevation while in the sand-amended sediments the trend was reversed, showing decreasing salinity with increasing elevation. Sulfide concentrations generally increased from low to high inundation with highest concentrations at the highest inundation (i.e., at the lowest elevations). High pore water phosphate concentrations were measured at low elevations in the natural sediments, but the sand-amended treatments had mostly low concentrations of phosphate and no consistent pattern with elevation. At the end of the experiment the lowest elevations generally had the highest measures of pore water ammonium. Soil carbon dioxide emissions were greatest in the sand-amended mesocosms and at higher elevations. Differences in coarse root and rhizome abundances and volumes among the sediment treatments were detected with CT imaging, but by 20 weeks the natural and sand-amended treatments showed similar total belowground biomass at the intermediate and high elevations. Although differences in pore water nutrient concentrations, pH, salinity, and belowground root and rhizome morphology were detected between the natural and sand-amended sediments, similar belowground productivity and total biomass were measured by the end of the growing season. Since the belowground productivity supports organic matter accumulation and peat buildup in marshes, our results suggest that thin layer sand or sediment application is a viable climate adaptation action to build elevation and coastal resiliency, especially in areas with low natural sediment supplies.

The relation between pore water chemistry and benthic fluxes of nutrients and manganese in Narragansett Bay, Rhode Island

In a whole-ecosystem, nutrient addition experiment in the Plum Island Sound Estuary (Massachusetts), we tested the effects of nitrogen enrichment on the carbon and nitrogen contents, respiration, and strength of marsh soils. We measured soil shear strength within and across vegetation zones. We found significantly higher soil percent organic matter, carbon, and nitrogen in the long-term enriched marshes and higher soil respiration rates with longer duration of enrichment. The soil strength was similar in magnitude across depths and vegetation zones in the reference creeks, but showed signs of significant nutrient-mediated alteration in enriched creeks where shear strength at rooting depths of the low marsh–high marsh interface zone was significantly lower than at the sub-rooting depths or in the creek bank vegetation zone. To more closely examine the soil strength of the rooting (10–30 cm) and sub-rooting (40–60 cm) depths in the interface and creek bank vegetation zones, we calculated a vertical shear strength differential between these depths. We found significantly lower differentials in shear strength (rooting depth < sub-rooting depths) in the enriched creeks and in the interface zones. The discontinuities in the vertical and horizontal shear strength across the enriched marshes may contribute to observed fracturing and slumping occurring in the marsh systems. Tide gauge data also showed a pattern of rapid sea level rise for the period of the study, and changes in plant distribution patterns were indicative of increased flooding. Longer exposure times to nutrient-enriched waters and increased hydraulic energy associated with sea level rise may exacerbate creek bank sloughing. Additional research is needed, however, to better understand the interactions of nutrient enrichment and sea level rise on soil shear strength and stability of tidal salt marshes.