J. Kevin Summers

A benthic index of environmental condition of Gulf of Mexico estuaries

An index was developed for estuarine macrobenthos in the Gulf of Mexico that discriminated between areas with degraded environmental conditions and areas with undegraded or reference conditions. Test sites were identified as degraded or reference based on criteria for dissolved oxygen levels, sediment toxicity tests, and sediment contamination. Discriminant analysis was used to identify a suite of measures of benthic community composition and diversity that would most successfully distinguish degraded from undegraded sites. The resultant benthic index was composed of a linear combination of three factors: the Shannon-Wiener diversity index, the proportion of total benthic abundance as tubificid oligochaetes, and the proportion of total benthic abundance as bivalve molluscs. This index was used to evaluate the spatial patterns of degraded benthic resources in the Gulf of Mexico.

Normalization of metal concentrations in estuarine sediments from the Gulf of Mexico

Metal concentrations were examined in sediments from 497 sites within the estuaries of the Gulf of Mexico by the United States Environmental Protection Agencys Environmental Monitoring and Assessment Program (EMAP). Data were normalized for extant concentrations of aluminum to isolate natural factors from anthropogenic ones. The normalization was based on the hypothesis that metal concentrations vary consistently with the concentration of aluminum, unless metals are of anthropogenic origin. Strong linear correlations (>75% variation explained) were observed between Al and Cr, Cu, Pb, Ni, and Zn. Moderate correlations (50–75% variation explained) were observed between Al and As or Ag. Weak but significant correlations (30–40% variation explained) were observed between Al and Hg or Cd. Based on these results, the spatial extent of contamination was examined. About 39% of sites with contamination by at least one metal occurred near population centers, industrial discharge sites, or military bases. The remainder of the observed contamination represented a dispersed pattern, including the lower Mississippi River (7%) and numerous agricultural watersheds (54%), suggesting that the contamination might be from nonpoint sources.

MACROBENTHIC RESPONSES TO NATURAL AND CONTAMINANT‐RELATED GRADIENTS IN NORTHERN GULF OF MEXICO ESTUARIES

Effects of pollution on biotic integrity are difficult to identify when correlations occur between environmental gradients and contaminant effects, as they do in estuaries. In this broad-scale study, we used canonical correspondence analysis (CCA) to distinguish influences of natural and contaminant-related gradients on macrobenthic community structure among 319 sites from estuaries throughout the northern Gulf of Mexico. Natural gradients in salinity, depth, and sediment composition obscured the detection of macrobenthic responses to sediment contamination. After adjusting for natural environmental variability, however, partial CCA revealed important macrobenthic variation in relation to sediment contamination. A rotated principal component analysis (PCA) distinguished five composite environmental factors, each largely reflecting contaminant or natural variation. Two complex gradients in sediment contamination identified by the PCA diverged in partial CCA space and correlated with different macrobenthic indicator taxa. Contaminant gradients represented variation in two different classes of sediment contaminants: trace metals and organic chemicals. Dispersion patterns of CCA site coordinates enabled cross validation of implied contamination-related variation in community function and the utility of several interpretive or management metrics. Trophic diversity decreased with sediment contamination, linking shifts in macrobenthic community function and community structure along contaminant gradients. The CCA model complemented an earlier benthic index developed from these data to examine biotic integrity, but the benthic index could not discern macrobenthic responses to the different contaminant gradients. Neither was the benthic index useful for showing transitions in macrobenthic community structure commensurate with different levels of contamination. Ampelisca amphipod sediment bioassays were inadequate for identifying contaminant effects on biotic integrity, whereas Mysidopsis mysid sediment bioassays conservatively reflected sediment contamination and associated macrobenthic indicators.

Utility of Splenic Macrophage Aggregates as an Indicator of Fish Exposure to Degraded Environments

Abstract The utility of splenic macrophage aggregates (MAs) as an indicator of fish exposure to degraded environments was evaluated in several species of estuarine fishes as part of the Environmental Protection Agencys Environmental Monitoring and Assessment Program–Estuaries (EMAP-E). Using image analysis, we measured the number and mean size of MAs per square millimeter on tissue sections of spleen from 983 fishes representing seven species from 266 stations scattered across coastal estuaries of the Gulf of Mexico. At 16 stations, at least one fish exhibited a high density of MAs (>40 MAs/mm2). Densities of MAs that exceeded 40/mm2 correlated with exposure to either hypoxic conditions or sediment contamination. Fishers exact test showed that the observed frequencies of joint occurrence between high numbers of MAs and both high sediment contaminants and low dissolved oxygen were significantly greater than the expected background frequencies. For all 16 sites where MAs were greater than 40/mm2, sediment...

Refinement, validation, and application of a benthic condition index for Northern Gulf of Mexico estuaries

By applying discriminant analysis to benthic macroinvertebrate data, we have developed an indicator of benthic condition for northern Gulf of Mexico estuaries. The data used were collected by the United states Environmental Protection Agency’s Environmental Monitoring and Assessment Program (EMAP) in the Louisianian Province from 1991 to 1994. This benthic index represents a linear combination of the following weighted parameters: the proportion of expected species diversity, the mean abundance of tubificid oligochaetes, the percent of total abundance represented by capitellid polychaetes, the percent of total abundance represented by bivalve mollusks, and the percent of total abundance represented by amphipods. We successfully validated and retrospectively applied the benthic index to all of the benthic data collected by EMAP in the Louisianian Province. This benthic index was also calculated for independent data collected from Pensacola Bay, Florida, in order to demonstrate its flexibility and applicability to different estuarine systems within the same biogeographic region. The benthic index is a useful and valid indicator of estuarine condition that is intended to provide environmental managers with a simple tool for assessing the health of benthic macroinvertebrate communities.

Using structural equation modeling to investigate relationships among ecological variables

Structural equation modeling is an advanced multivariate statistical process with which a researcher can construct theoretical concepts, test their measurement reliability, hypothesize and test a theory about their relationships, take into account measurement errors, and consider both direct and indirect effects of variables on one another. Latent variables are theoretical concepts that unite phenomena under a single term, e.g., ecosystem health, environmental condition, and pollution (Bollen, 1989). Latent variables are not measured directly but can be expressed in terms of one or more directly measurable variables called indicators. For some researchers, defining, constructing, and examining the validity of latent variables may be the end task of itself. For others, testing hypothesized relationships of latent variables may be of interest. We analyzed the correlation matrix of eleven environmental variables from the U.S. Environmental Protection Agencys (USEPA) Environmental Monitoring and Assessment Program for Estuaries (EMAP-E) using methods of structural equation modeling. We hypothesized and tested a conceptual model to characterize the interdependencies between four latent variables-sediment contamination, natural variability, biodiversity, and growth potential. In particular, we were interested in measuring the direct, indirect, and total effects of sediment contamination and natural variability on biodiversity and growth potential. The model fit the data well and accounted for 81% of the variability in biodiversity and 69% of the variability in growth potential. It revealed a positive total effect of natural variability on growth potential that otherwise would have been judged negative had we not considered indirect effects. That is, natural variability had a negative direct effect on growth potential of magnitude −0.3251 and a positive indirect effect mediated through biodiversity of magnitude 0.4509, yielding a net positive total effect of 0.1258. Natural variability had a positive direct effect on biodiversity of magnitude 0.5347 and a negative indirect effect mediated through growth potential of magnitude −0.1105 yielding a positive total effects of magnitude 0.4242. Sediment contamination had a negative direct effect on biodiversity of magnitude −0.1956 and a negative indirect effect on growth potential via biodiversity of magnitude −0.067. Biodiversity had a positive effect on growth potential of magnitude 0.8432, and growth potential had a positive effect on biodiversity of magnitude 0.3398. The correlation between biodiversity and growth potential was estimated at 0.7658 and that between sediment contamination and natural variability at −0.3769.

Accounting for Natural Resources and Environmental Sustainability: Linking Ecosystem Services to Human Well-Being

One of societys greatest challenges is to sustain natural resources while promoting economic growth and quality of life. In the face of this challenge, society must measure the effectiveness of programs established to safeguard the environment. The impetus for demonstrating positive results from government-sponsored research and regulation in the United States comes from Congress (General Accountability Office; GAO) and the Executive Branch (Office of Management and Budget; OMB). The message is: regulatory and research programs must demonstrate outcomes that justify their costs. Although the concept is simple, it is a complex problem to demonstrate that environmental research, policies, and regulations cause measurable changes in environmental quality. Even where changes in environmental quality can be tracked reliably, the connections between government actions and environmental outcomes seldom are direct or straightforward. In this article, we describe emerging efforts (with emphasis on the role of the U.S. Environmental Protection Agency; EPA) to frame and measure environmental outcomes in terms of ecosystem services and values-societally and ecologically meaningful metrics for gauging how well we manage environmental resources. As examples of accounting for outcomes and values, we present a novel, low-cost method for determining relative values of multiple ecosystem services, and describe emerging research on indicators of human well-being.

Incidence of Stress in Benthic Communities along the U.S. Atlantic and Gulf of Mexico Coasts within Different Ranges of Sediment Contamination from Chemical Mixtures

Synoptic data on concentrations of sediment-associated chemical contaminants and benthic macroinfaunal community structure were collected from 1,389 stations in estuaries along the U.S. Atlantic and Gulf of Mexico coasts as part of the nationwide Environmental Monitoring and Assessment Program (EMAP). These data were used to develop an empirical framework for evaluating risks of benthic community-level effects within different ranges of sediment contamination from mixtures of multiple chemicals present at varying concentrations. Sediment contamination was expressed as the mean ratio of individual chemical concentrations relative to corresponding sediment quality guidelines (SQGs), including Effects Range-Median (ERM) and Probable Effects Level (PEL) values. Benthic condition was assessed using diagnostic, multi-metric indices developed for each of three EMAP provinces (Virginian, Carolinian, and Louisianian). Cumulative percentages of stations with a degraded benthic community were plotted against ascending values of the mean ERM and PEL quotients. Based on the observed relationships, mean SQG quotients were divided into four ranges corresponding to either a low, moderate, high, or very high incidence of degraded benthic condition. Results showed that condition of the ambient benthic community provides a reliable and sensitive indicator for evaluating the biological significance of sediment-associated stressors. Mean SQG quotients marking the beginning of the contaminant range associated with the highest incidence of benthic impacts (73-100% of samples, depending on the province and type of SQG) were well below those linked to high risks of sediment toxicity as determined by short-term toxicity tests with single species. Measures of the ambient benthic community reflect the sensitivities of multiple species and life stages to persistent exposures under actual field conditions. Similar results were obtained with preliminary data from the west coast (Puget Sound).

Monitoring the ecological condition of estuaries in the United States

The purpose of the Environmental Monitoring and Assessment Program/ Estuaries component (EMAP‐E) is to determine the current status, extent, changes, and trends in ecological indicators of the condition of the nations estuarine resources on a regional and national basis. Monitoring activities in the Virginian (Mid‐Atlantic) and Louisianian (Gulf of Mexico) Provinces focus on measurements describing the benthic community, the fish community, water quality, levels of sediment and tissue contamination, sediment toxicity, wetlands extent/condition, and seagrasses extent/condition. Estuarine monitoring is based on an EMAP‐E probability‐based sampling design conducted over a 60‐day period during July‐September of each year. Monitoring activities in the Virginian Province began in 1990 and have continued annually while monitoring in the Louisianian Province was initiated in 1991. The results of 1990 monitoring in the Virginian Province show that 20% of the sediments of the Mid‐Atlantic region suffered from poor...

DISSOLVED OXYGEN CONDITIONS IN NORTHERN GULF OF MEXICO ESTUARIES

Because deficient dissolved oxygen (DO) levels may have severe detrimental effects on estuarine and marine life, DO has been widely used as an indicator of ecological conditions by environmental monitoring programs. The U.S. EPAs Environmental Monitoring and Assessment Program for Estuaries (EMAP-E) monitored DO conditions in the estuaries of the Gulf of Mexico from 1991 to 1994. DO was measured in two ways: 1) instantaneous profiles from the surface to the bottom were taken during the day, and 2) continuous measurements were taken near the bottom at 15 min intervals for at least 12 h. This information was summarized to assess the spatial distribution and severity of DO conditions in these estuaries. Depending on the criteria used to define hypoxia (DO concentrations usually <2 mg L-1 or <5 mg L-1) and the method by which DO is measured, we estimate that between 5.2 and 29.3% of the total estuarine area in the Louisianian Province was affected by low DO conditions.