Richard A. McKinney

Relationships of nitrogen loadings, residential development, and physical characteristics with plant structure in New England salt marshes

We examined the vascular plant species richness and the extent, density, and height ofSpartina species of ten Narragansett Bay, Rhode Island (United States) fringe salt marshes which had a wide range of residential land development and N-loadings associated with their watersheds. Significant inverse relationships of tallS. alterniflora with species richness and with the extent and density ofS. patens and shortS. alterniflora were observed. Extent and density ofS. patens and extent of shortS. alterniflora were positively and significantly related with plant species richness. Marsh elevation and area did not significantly correlate with plant structure. Flood tide height significantly and inversely correlated withS. patens, but did not significantly relate toS. alterniflora or plant species richness. Marsh width significantly and positively correlated with plant species richness andS. patens and inversely correlated with tallS. alterniflora. Significant inverse relationships were observed for N-load, % residential development, and slope withS. patens, shortS. alterniflora, and species richness, and significant positive relationships with tallS. alterniflora. The marsh slope and width were significantly correlated with N-load and residential development that made it difficult to determine to what extent anthropogenic stressors were contributing to the variation in the plant structure among the marshes. At five marhes with similar slopes, there were significant inverse relationships of N-load withS. patens (density and extent) and a positive relationship with tallS. alterniflora (extent). Although there were no significant relationships of slope with the plant metrics among the five sites, other physical factors, such as the flood tide height and marsh width, significantly correlated with the extent and density ofSpartina species. Significant relationships of N-load with plant structure (albeit confounded by the effect of the physical characteristics) support the hypothesis of competitive displacement of dominant marsh plants under elevated nitrogen. It is likely that the varying plant structure in New England marshes is a response to a combination of natural factors and multiple anthropogenic stressors (e.g., eutrophication and sea level rise).

Comparisons of patterns of polychlorinated biphenyl congeners in water, sediment, and indigenous organisms from New Bedford Harbor, Massachusetts

Polychlorinated biphenyl patterns were compared in samples of water, surface sediment, and the indigenous organisms ribbed mussels (Modiolus demissus), grass shrimp (Paleomonetes pugio), mummichogs (Fundulus heteroclitis), and eels (Anguila rostrata) collected from 1991 through 1993 at two stations in the highly contaminated New Bedford Harbor, Massachusetts. Principal component analysis of analytical data showed groups of points that corresponded to individual species, but little separation between stations for the same species was found. Linear correlations showed a high level of agreement between PCB patterns in samples of the exposure environment (water and sediments) and two species of organisms (ribbed mussels and mummichogs). However, due to two separate metabolic alterations of PCBs, the patterns in both shrimp and eels showed poor agreement with patterns in water and sediment. Selective enrichment factors (SEFs), the ratios of individual coplanar or mono-ortho substituted congeners to the total PCBs, were used to compare the relative abundance of congeners in samples. Due to metabolic differences, the SEFs were lower in eels and higher in shrimp than those found in Aroclor® standards.

RIBBED MUSSEL NITROGEN ISOTOPE SIGNATURES REFLECT NITROGEN SOURCES IN COASTAL SALT MARSHES

The stable nitrogen isotope ratio in tissue of the ribbed mussel (Geukensia demissa) was investigated as an indicator of the source of nitrogen inputs to coastal salt marshes. Initially, mussels were fed a diet of 15N-enriched algae in the laboratory to determine how the tissue nitrogen isotope ratio (δ15N) changed with time. Steady-state times were calculated and found to be size dependent, ranging from 206 to 397 d. This indicated that mussels are long-term integrators of δ15N from their diet and may reflect nitrogen inputs to a marsh. Next, indigenous mussels were collected from 10 marshes with similar hydrology and geomorphology in Narragansett Bay, Rhode Island, USA, and mussel δ15N values were evaluated as indicators of nitrogen source. Significant positive correlations were observed between δ15N in mussels and the fraction of residential development in the marsh watersheds. In contrast, mussel isotope ratios showed significant negative correlations with the fraction of combined agricultural and recreational land use. These correlations suggested that the mussel nitrogen isotope signature is influenced by nitrogen derived from human activities in the adjoining marsh watershed. A more detailed examination of these relationships indicated that land use practices in close proximity to marshes and estuarine characteristics may also influence the observed nitrogen isotope signature. A simple, empirical model based on the 10 watersheds was developed to predict mussel δ15N from land use characteristics. The predictive ability of the model was tested with data from 12 additional marshes having similar geomorphology as the original 10, but differing in hydrology and mode of nutrient input. The model showed that ribbed mussel nitrogen isotope signatures may provide information on the source of nitrogen to coastal areas. This could be of use in developing general policies or strategies for monitoring and assessing coastal eutrophication. In addition, the isotopic ratio of mussels is useful as a proxy for watershed land use practices when assessing ecological responses to nutrient enrichment in coastal marshes.

Extraction of organic contaminants from marine sediments and tissues using microwave energy

In this study, we compared microwave solvent extraction (MSE) to conventional methods for extracting organic contaminants from marine sediments and tissues with high and varying moisture content. The organic contaminants measured were polychlorinated biphenyl (PCB) congeners, chlorinated pesticides, and polycyclic aromatic hydrocarbons (PAHs). Initial experiments were conducted on dry standard reference materials (SRMs) and field collected marine sediments. Moisture content in samples greatly influenced the recovery of the analytes of interest. When wet sediments were included in a sample batch, low recoveries were often encountered in other samples in the batch, including the dry SRM. Experiments were conducted to test the effect of standardizing the moisture content in all samples in a batch prior to extraction. SRM1941a (marine sediment). SRM1974a (mussel tissue), as well as QA96SED6 (marine sediment), and QA96TIS7 (marine tissue), both from 1996 NIST Intercalibration Exercise were extracted using microwave and conventional methods. Moisture levels were adjusted in SRMs to match those of marine sediment and tissue samples before microwave extraction. The results demonstrated that it is crucial to standardize the moisture content in all samples, including dry reference material to ensure good recovery of organic contaminants. MSE yielded equivalent or superior recoveries compared to conventional methods for the majority of the compounds evaluated. The advantages of MSE over conventional methods are reduced solvent usage, higher sample throughput and the elimination of halogenated solvent usage.

Using mussel isotope ratios to assess anthropogenic nitrogen inputs to freshwater ecosystems

Stable nitrogen isotope ratios (δ15N) of freshwater mussels from a series of lakes and ponds wererelated to watershed land use characteristics to assess their utility in determining the source ofnitrogen inputs to inland water bodies. Nitrogen isotope ratiosmeasured in freshwater musselsfrom 19 lakes and ponds in Rhode Island, U.S.A., ranged from4.9–12.6‰ and were found tosignificantly correlate with the fraction of residential development in 100 and 200 m bufferzones around the ponds. Mussel δ15N values in 12 of the 19 ponds also showed significantcorrelation with average dissolved nitrate concentrations, which ranged from 23–327 μg L-1.These observations, in light of previous studies which link elevatedδ15N values of nitrogenderived from septic wastewater with those seen in biota, suggest that mussel isotope ratios mayreflect nitrogen source in freshwater ecosystems. We followed aniterative approach usingmultiple regression analysis to assess the relationship between musselδ15N and the land usecategories fraction residential development, fraction feedlotagriculture, fraction row-cropagriculture, and fraction natural vegetation in 100 and 200 m bufferzones and pond watersheds.From this we developed a simple regression model to predict musselδ15N from the fraction ofresidential development in the 200 m buffer zone around the pond.Subsequent testing with datafrom 16 additional sites in the same ecoregion led us to refine themodel by incorporating thefraction of natural vegetation. The overall average absolute differencebetween measured andpredicted δ15N values using the two-parameter model was 1.6‰. Potential sources of error inthe model include differences in the scale and categorization ofland-use data used to generate andtest the model, differences in physical characteristics, such asretention time and range ofresidential development, and exclusion of sources of enrichednitrogen such as runoff from feedlot operations or increased nitrogen loading from inefficient or failed septic systems.

Contaminant Levels in Harbor Seals from the Northeastern United States

The concentrations of polychlorinated biphenyls (PCBs), organochlorine pesticides, polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzofurans (PCDF), polychlorinated dibenzo-p-dioxins (PCDD), and mercury (Hg) were determined in blubber and liver tissues of harbor seals (Phoca vitulina) collected along the northeast coast of the U.S. Average PCB concentrations in seal blubber (sum of congeners) were 12.0 μg/g (wet weight) with a range of 7.30 to 24.3 μg/g in 1980 and 6.66 μg/g (wet weight) with a range of 2.61 to 11.3 μg/g in 1990–1992. Comparisons between blubber data from this study and previous work indicated that the concentration of PCBs along the northeast coast of the U.S. may have decreased over the past twenty years.The average p,p′-DDE concentrations in seal blubber were 10.9 μg/g (wet weight) in 1980 with a range of 6.95 to 21.9 μg/g and 4.12 μg/g (wet weight) with a range of 1.83 to 7.84 μg/g in 1990–1992. Only trace amounts of PCDFs and PCDDs were found in a few blubber samples; levels in most tissues were below detection (3–5 pg/g) (wet weight). Trace amounts (<30 ng/g) of phenanthracene, anthracene, and alkylated MW-178 compounds were found in some seal samples; all other PAH compounds were below the detection level (5–15 ng/g).Toxic equivalents (TEQ) of selected coplanar and mono-ortho PCB congeners and relative toxic equivalents (RTE) (pg total TEQ/μg total PCB) were calculated, using recently proposed dioxin toxic equivalent factors (Ahlborg et al. 1994). The TEQs ranged from 41 to 315, and the RTEs ranged from 2.25 to 16.3. The RTEs for seal blubber indicated that the present values were in the midrange of those reported in the literature. Toxic equivalents calculated on the basis of the concentrations of the coplanar PCBs, PCDDs, and PCDFs indicated that coplanar PCBs, rather than PCDDs and PCDFs, may pose a more important toxic threat to harbor seals.Mercury levels in liver tissue averaged 70.0 μg/g (wet weight) and 44.1 μg/g (wet weight) in the 1991 and 1980 samples, respectively, and are similar to those found in relatively polluted waters of the British Isles.

Outline of A New Approach to Evaluate Ecological Integrity of Salt Marshes

The integrity of coastal salt marshes can be determined from the extent to which they provide key ecosystem services: food and habitat for fish and wildlife, good water quality, erosion and flood control, and recreation and cultural use. An outline of a new approach for linking ecosystem services with metrics of structure and function to evaluate the ecological integrity of salt marshes is described. One main objective of the approach is to determine whether differences in structure and function can be detected among salt marshes with similar geomorphology and hydrology but different degrees of anthropogenic stress. The approach is currently being applied to salt marshes of Narragansett Bay, RI, USA. Stable nitrogen isotopic ratios of the marsh biota reflected the nitrogen sources from the adjacent watersheds and were significantly correlated with percent residential land use. Results show that plant zonation significantly ( r = –0.82; p < 0.05) relates with percent residential land use and is potentially a sensitive indicator of anthropogenic disturbance of New England salt marshes. We are currently examining species diversity, denitrification rates, and susceptibility to erosion among the sites for additional indicators of salt marsh condition. Our results to date suggest that this approach will provide the methods needed for managers to systematically monitor and evaluate the integrity of salt marshes.

Allometric length-weight relationships for benthic prey of aquatic wildlife in coastal marine habitats

We developed models to estimate the soft tissue content of benthic marine invertebrates that are prey for aquatic wildlife. Allometric regression models of tissue wet weight with shell length for 10 species of benthic invertebrates had r2 values ranging from 0.29 for hermit crabs Pagurus longicarpus to 0.98 for green crabs Carcinus maenas. As a class, bivalves had the highest r2 values (0.84) and crustaceans the lowest (0.48). Energy and nutrient content of soft tissue is also presented for the 10 benthic species. The energy content was lowest in crabs, and ranged within 2.20–4.71 kcal g-1 dry weight. Fat content was highly variable (range: 3.5–16.0%), and protein content ranged within 43.1–68.1% and was highest for shrimp Palaemonetes pugio. Comparison between classes of organisms of the amount of soft tissue per unit shell length showed that crustaceans yield five times more soft tissue per unit shell length than bivalves, and four times more than gastropods. The models we present use simple measures, such as the length of shell or wet weight of the entire animal, to quantitatively estimate the amount of available soft tissue in benthic prey that are usually consumed in total (with shell and soft tissue intact) but for which only the soft tissue is used for nutritional gain. This information can be combined with energy and nutrient content data to calculate energy or nutrient based carrying capacities that can help assess available resources for shorebirds, waterfowl and marine mammals.

Anthropogenic enhancement of Egypt's Mediterranean fishery

The highly productive coastal Mediterranean fishery off the Nile River delta collapsed after the completion of the Aswan High Dam in 1965. But the fishery has been recovering dramatically since the mid-1980s, coincident with large increases in fertilizer application and sewage discharge in Egypt. We use stable isotopes of nitrogen (δ15N) to demonstrate that 60%–100% of the current fishery production may be from primary production stimulated by nutrients from fertilizer and sewage runoff. Although the establishment of the dam put Egypt in an ideal position to observe the impact of rapid increases in nutrient loading on coastal productivity in an extremely oligotrophic sea, the Egyptian situation is not unique. Such anthropogenically enhanced fisheries also may occur along the northern rim of the Mediterranean and offshore of some rapidly developing tropical countries, where nutrient concentrations in the coastal waters were previously very low.

The chemistry and toxicity of sediment affected by oil from the North Cape spilled into Rhode Island Sound

Abstract On 19 January 1996, the barge North Cape spilled more than three million liters of No. 2 fuel oil into Rhode Island Sound near Matunuck, Rhode Island. The toxicity and chemistry of this oil in two subtidal sediments were followed for more than 9 months. Maximum concentrations of polycyclic aromatic hydrocarbons (PAHs) in the sediments reached 730 μg / g dry weight (DW). Water samples taken immediately after the spill were phototoxic to embryos of the bivalve Mulinia lateralis. Total PAHs and toxicity to the amphipod Ampelisca abdita were high immediately after the spill, decreasing to background values ( 10 μg / g DW and