Use of Community Data to Diagnose the Causes of Stream Impairment II
Presiding: M Paul, Howard University; J Gerritsen, Tetra Tech, Inc.
NB43B-01 INVITED 13:30h
Quantitative models and strength of evidence in causal inference
Human activities such as mining, logging, agriculture and residential development have caused biological degradation to streams of West Virginia. Total Maximum Daily Loads (TMDLs) are being developed for all biologically-impaired streams within the state, and require causes of impairment to be identified so that pollutants can be controlled. Using a statewide dataset, we examined macroinvertebrate community response to single and multiple stressors, and applied two quantitative modeling approaches for ranking stressors. A "dirty reference" approach examined community composition in clean and predefined stressed sites, and tolerance values of individual taxa were estimated with reciprocal averaging. We integrated the empirical models of biological impairment with onsite field observations of biota, habitat, water quality, watershed observations, within a strength of evidence approach to infer causes of impairment. Candidate causes were screened to eliminate those shown not to co-occur with effects. Remaining candidate causes were ranked according to considerations of evidence within each watershed, as well as from the statewide empirical models and from other published sources. Strongest inferences were obtained where the independent predictive model agreed with within-watershed observations of stressor measures. Final stressor determinations for each watershed will be used for the development and implementation of TMDLs.
NB43B-02 INVITED 13:45h
Mixture Toxicity and Habitat Alterations Attributed to Effects on Species Composition of Fish in Ohio Rivers
Biological assessments should both estimate the condition of a biological resource (magnitude of alteration) and provide managers with a diagnosis of the potential causes of any observed impairment. Although methods of quantifying condition are well developed, identifying and proportionately attributing causes of impairment remains problematic. To address this need, we developed a conceptual approach that 1) links fish, habitat, and chemistry data from hundreds of sites collected in Ohio streams, 2) assesses the biological condition at each site, 3) attributes impairment to multiple probable causes and 4) provides the results of the analyses in simple to interpret pie charts. Biological condition was assessed using a RIVPACS-like predictive model. Impaired biological condition was defined as the ratio of the number of observed native species to the probabilities of capture generated by the model. The potential toxic effects of exposure to mixtures of contaminants were estimated using Species Sensitivity Distributions and mixture toxicity principles. Generalized linear regression models described the relationship of species abundance as a function of habitat characteristics. Statistically linking the biological condition, mixture effects and species abundance provided the opportunity to evaluate the losses of species with environmental conditions.
NB43B-03 INVITED 14:00h
Integrating Descriptive and Experimental Approaches to Identify Stressor Effects on Stream Benthic Communities
Descriptive studies which compare composition of benthic macroinvertebrate communities upstream and downstream from contaminant discharges generally cannot be used to identify stressors or to demonstrate causal relationships between stressors and biological responses. In this study I describe results of stream microcosm and field experiments designed to support results of descriptive studies conducted in the metal-polluted Arkansas River, CO. Monitoring benthic communities before and after remediation of metal inputs provided correlative evidence that elevated heavy metal concentrations altered community composition and reduced abundance of metal-sensitive taxa. However, these field data were not especially useful for estimating safe concentrations of heavy metals that would be protective of benthic communities. Exposure pathways in the Arkansas River were quantified by measuring metal bioaccumulation in caddisflies (Trichoptera) collected upstream and downstream from metal inputs. Microcosm and field experiments were used to establish concentration-response relationships between heavy metals and several structural (abundance, richness) and functional (macroinvertebrate drift, community respiration) endpoints. Consistency of these responses was demonstrated by comparing results to a spatially extensive survey of metal-polluted streams in Colorado. This study demonstrates the power of integrating descriptive and experimental approaches for developing causal arguments and identifying stressors in ecological assessments.
NB43B-04 INVITED 14:15h
The use of Ordination of Invertebrate Communities to Diagnose Stress Response Type.
The variety of bioassessment methods converge in attempting to determine whether the invertebrate assemblage is disturbed. Detecting a site is disturbed is the first step for most environmental agencies. The next should be to establish the cause of the disturbance and what is required and feasible to restore the site. One assessment method uses the RCA to assess sites through HMDS ordination. This method examines reference and matched test sites in ordination space, the degree of departure from the "cloud" of reference sites quantifies the disturbance. However, this method provides additional information on both the nature of the stress and degree of restoration required to recover a site. Ordination uses all the information in the community and the change in the assemblage determines the position of the site in ordination space. Therefore, sites follow different trajectories in response to nutrient enrichment compared to broad spectrum toxicants. These changes are demonstrated in mesocosm communities showing dose response diagnostic trajectories. In addition using multiple regression community ordination axis scores can be related to stressor variables and provide quantitative information on the degree of amelioration required in a stress variable to bring sites into reference condition.
NB43B-05 INVITED 14:30h
Characterizing Common Diatom Species Distributions in the Mid-Atlantic Streams: A Statistical Modeling Approach
Autecological classifications of benthic diatoms in streams have been primarily qualitative. We used several statistical methods to characterize the relationships between some common benthic diatom species and associated environmental variables in the Mid-Atlantic streams. A total of 306 stream riffle sites were sampled for benthic algae, water quality, and physical habitat conditions as part of EPA's Environmental Monitoring and Assessment Program (EMAP). We selected 15 most abundant and widely occurred diatom species for our analyses. Generalized additive model, a semi-parametric method, showed that the species had significant linear or nonlinear relationships with environmental variables such as pH and total phosphorus. However, the percentages of individual species' variance explained by its corresponding environmental variables were in general low (<30%). Regression tree analysis, a binary recursive partitioning method, was used to capture possible interactive effects of these environmental variables on diatom species. The results may provide a quantitative base for improving current diatom autecological classifications.
NB43B-06 INVITED 14:45h
Ecological catchment management applied to the river Dinkel (The Netherlands)
As part of the European legislation the European Water Framework Directive (WFD) was published in 2002. A major point in this policy is ecological assessment, which results determine catchment management plans and future restoration measures. The assessment system uses reference condition as an endpoint of the evaluation scale. The objective of the WFD strives for Good Ecological Status; however,, a slight deviation from reference condition is accepted. We developed two approaches to select management measures. The Ecological Characterisation of Surface Waters in the Province of Overijssel (EKOO) software includes three steps: (1) assign a newly sampled site to a set of existing ecological water types (cenotypes), (2) choose an ecological management target (e.g. Good Ecological Status), (3) establish a set of restoration measures using a simple Decision Support System (DSS). Implementation of the measures will improve the respective water body. Additionally, the indicator approach compiles a list of target species to that indicate reference conditions. This approach is applied to the catchment of the river Dinkel. The DSS guides users through a list of questions concerning hydrology, nutrients/pollution, and morphology of the river. The link between the answers and the selected ecological target chosen are processed and results in a recommended measures for management or restoration plans.