Abstract  The Clean Water Action Plan of 1998 provides a blueprint for federal agencies to work with states, tribes, and other stakeholders to protect and restore the Nation's water resources. The plan includes an initiative that addresses the nutrient-enrichment problem of lakes and streams across the United States. The U.S. Environmental Protection Agency (USEPA) is working to set nutrient criteria by nationwide nutrient ecoregions that are an aggregation of the Omernik level III ecoregions. Because low levels of nutrients are necessary for healthy streams and elevated concentrations can cause algal blooms that deplete available oxygen and kill off aquatic organisms, criteria levels are to be set, in part, using the relation between chlorophyll a and concentrations of total nitrogen and total phosphorus. Data from Pennsylvania and West Virginia, collected between 1990 and 1998, were analyzed for relations between chlorophyll a, nutrients, and other explanatory variables. Both phytoplankton and periphyton chlorophyll a concentrations from lakes and streams were analyzed separately within each of the USEPA nutrient ecoregions located within the boundaries of the two states. These four nutrient ecoregions are VII (Mostly Glaciated Dairy), VIII (Nutrient Poor, Largely Glaciated Upper Midwest and Northeast), IX (Southeastern Temperate Forested Plains and Hills), and XI (Central and Eastern Forested Uplands). Phytoplankton chlorophyll a concentrations in lakes were related to total nitrogen, total phosphorus, Secchi depth, concentration of dissolved oxygen, pH, water temperature, and specific conductivity. In nutrient ecoregion VII, nutrients were not significant predictors of chlorophyll a concentrations. Total nitrogen, Secchi depth, and pH were significantly related to phytoplankton chlorophyll a concentrations in nutrient ecoregion IX. Lake periphyton chlorophyll a concentrations from nutrient ecoregion XI were related to total phosphorus rather than total nitrogen, Secchi depth, and pH. In all cases, Secchi depth was inversely related to the chlorophyll a concentrations in a lake. Nutrient ecoregion VIII had too few samples for any type of analysis. Streams within the different nutrient ecoregions had many variables that were significantly related to periphyton chlorophyll a concentrations. These variables consisted of total nitrogen, total phosphorus, drainage area, percent forest cover, several macroinvertebrate indices, pH, basin slope, total residue, total suspended solids, and water temperature. Nutrients were not significantly related to periphyton chlorophyll a in streams within nutrient ecoregions VII or IX but were in nutrient ecoregion XI. Drainage area, percent forest cover, and several invertebrate indices were significant variables in nutrient ecoregion VII. Percent forest cover and several invertebrate indices had a negative relation with chlorophyll a concentrations in these streams. Percent forest cover and basin slope had a negative effect on periphyton in nutrient ecoregion IX streams. Light availability was more critical to periphyton growth in streams than nutrients. Ecoregion XI had enough samples to do seasonal analyses. Summer-season periphyton chlorophyll a concentrations in nutrient ecoregion XI streams were positively related to total phosphorus and drainage area but negatively related to percent forest cover. Summer-season phytoplankton in streams was related to different variables within the same nutrient ecoregion. Both total nitrogen and total phosphorus were positively related with chlorophyll a concentrations as well as basin slope, total residue, and total suspended solids but negatively related to pH. The winter stream phytoplankton chlorophyll a concentrations were related to water temperature only.

Abstract  We used complementary information collected using different conceptual approaches to develop recommendations for a stream nutrient criterion based on responses of algal assemblages to anthropogenic P enrichment. Benthic algal attributes, water chemistry, physical habitat, and human activities in watersheds were measured in streams of the Mid-Atlantic Highlands region as part of the Environmental Monitoring and Assessment Program of the US Environmental Protection Agency. Diatom species composition differed greatly between low- and high-pH reference streams; therefore, analyses for criterion development were limited to a subset of 149 well-buffered streams to control for natural variability among streams caused by pH. Regression models showed that TP concentrations were ?10 ?g/L in streams with low levels of human activities in watersheds and that TP increased with % agriculture and urban land uses in watersheds. The 75th percentile at reference sites was 12 ?g TP/L. Chlorophyll a and ash-free dry mass increased and acid and alkaline phosphatase activities decreased with increasing TP concentration. The number of diatom taxa, evenness, proportion of expected native taxa, and number of high-P taxa increased with TP concentration in streams. In contrast, the number of low-P native taxa and % low-P individuals decreased with increasing TP. Lowess regression and regression tree analysis indicated nonlinear relationships for many diversity indices and attributes of taxonomic composition with respect to TP. Thresholds in these responses occurred between 10 and 20 ?g/L and helped justify recommending a P criterion between 10 and 12 ?g TP/L to protect high-quality biological conditions in streams of the Mid-Atlantic Highlands. We used complementary information collected using different conceptual approaches to develop recommendations for a stream nutrient criterion based on responses of algal assemblages to anthropogenic P enrichment. Benthic algal attributes, water chemistry, physical habitat, and human activities in watersheds were measured in streams of the Mid-Atlantic Highlands region as part of the Environmental Monitoring and Assessment Program of the US Environmental Protection Agency. Diatom species composition differed greatly between low- and high-pH reference streams; therefore, analyses for criterion development were limited to a subset of 149 well-buffered streams to control for natural variability among streams caused by pH. Regression models showed that TP concentrations were ?10 ?g/L in streams with low levels of human activities in watersheds and that TP increased with % agriculture and urban land uses in watersheds. The 75th percentile at reference sites was 12 ?g TP/L. Chlorophyll a and ash-free dry mass increased and acid and alkaline phosphatase activities decreased with increasing TP concentration. The number of diatom taxa, evenness, proportion of expected native taxa, and number of high-P taxa increased with TP concentration in streams. In contrast, the number of low-P native taxa and % low-P individuals decreased with increasing TP. Lowess regression and regression tree analysis indicated nonlinear relationships for many diversity indices and attributes of taxonomic composition with respect to TP. Thresholds in these responses occurred between 10 and 20 ?g/L and helped justify recommending a P criterion between 10 and 12 ?g TP/L to protect high-quality biological conditions in streams of the Mid-Atlantic Highlands.

Abstract  1. Macroinvertebrates are frequently classified in terms of their tolerance to human disturbance and pollution. These tolerance values have been used effectively to assess the biological. condition of running waters.

2. Generalised additive models were used to associate the presence and absence of different macroinvertebrate genera with different environmental gradients. The model results were then used. to classify each genera as sensitive, intermediately tolerant or tolerant to different stressor gradients as quantified by total phosphorus concentration, sulphate ion concentration, qualitative habitat score and stream pH. The analytical approach provided a means of estimating stressor-specific tolerance classifications while controlling for covarying, natural environmental gradients.

3. Computed tolerance classification generally conformed with expectations and provided some capacity for distinguishing between different stressors in test data.

Abstract  Periphyton assemblage data collected from 233 stream site-visits (49 in 1993, 56 in 1994 and 128 in 1995) throughout the Mid-Appalachian region were used to develop a periphyton index of biotic integrity (PIBI) based on 1) algal genera richness; 2) the relative abundances of diatoms, Cyanobacteria, dominant diatom genus, acidophilic diatoms, eutraphentic diatoms, and motile diatoms: 3) chlorophyll and biomass lash-free dry mass) standing crops; and 1) alkaline phosphatase activity. Thirty-seven diatom genera and 38 non-diatom genera were collected. The relative richness and relative abundance (RA) of these genera were used to calculate the RA metrics of the PIBI. PIBI scores ranged from 48.0 to 85.1 among the 233 site-visits with an overall regional mean (+/-1 SE) of 66.1 +/- 0.5. The 10 metrics and the PIBI were correlated with 27 chemical, 12 physical habitat, and 3 landscape variables. Overalls PIBI was inversely correlated with stream depth, stream water color, and Fe. Component metrics were significantly correlated with several chemical (Al, acid neutralizing capacity, Cl, Fe,Mn, N, Na, P, pH, Si, SO4 total suspended solids), physical habitat (channel embeddedness, riparian disturbances, stream depth stream width, substrate composition), and landscape (% of the watershed in forest, agriculture and urban land uses) variables. Canonical correlation analysis revealed significant correlations between the 10 PIBI metrics and 4 significant environmental gradients related to general human disturbances (stream acidity, stream substrate composition, and stream and riparian habitat). Analysis of variance revealed significant differences in PIBI scores for lowland vs highland streams, and among stream orders. Annual differences were explained by differences in the proportions of sampling sites in lowland streams in each year. The univariate distribution of PIBI scores was used to set threshold PIBI values for the assessment of ecological condition in Mid-Appalachian streams.

Abstract  1. Algal-community metrics were calculated for periphyton samples collected from 976 streams and rivers by the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Programme during 1993-2001 to evaluate national and regional relations with water chemistry and to compare whether algal-metric values differ significantly among undeveloped and developed land-use classifications.

2. Algal metrics with significant positive correlations with nutrient concentrations included indicators of trophic condition, organic enrichment, salinity, motility and taxa richness. The relative abundance of nitrogen-fixing algae was negatively correlated with nitrogen concentrations, and the abundance of diatom species associated with high dissolved oxygen concentrations was negatively correlated with both nitrogen and phosphorus concentrations. Median algal-metric values and nutrient concentrations were significantly lower at undeveloped sites than those draining agricultural or urban catchments.

3. Total algal biovolume did not differ significantly among major river catchments or land-use classifications, and was only weakly correlated with nitrate (positive) and suspended-sediment (negative) concentrations. Estimates of periphyton chlorophyll a indicated an oligotrophic-mesotrophic boundary of about 21 mg m(-2) and a mesotrophic-eutrophic boundary of about 55 mg m(-2) based on upper and lower quartiles of the biovolume data distribution.

4. Although algal species tolerance to nutrient and organic enrichment is well documented, additional taxonomic and autecological research on sensitive, endemic algal species would further enhance water-quality assessments.

Abstract  We attempted to identify spatial patterns and determinants for benthic algal assemblages in Mid-Atlantic streams, Periphyton, water chemistry, stream physical habitat, riparian conditions, and land cover/use in watersheds were characterized at 89 randomly selected stream sites in the Mid-Atlantic region. Cluster analysis (TWINSPAN) partitioned all sites into six groups on the basis of diatom species composition, Stepwise discriminant function analysis indicated that these diatom groups can be best separated by watershed land cover/use (percentage forest cover), water temperature, and riparian conditions (riparian agricultural activities). However, the diatom-based stream classification did not correspond to Omernik's ecoregional classification, Algal biomass measured as chi a can be related to nutrients in habitats where other factors do not constrain accumulation. A regression tree model indicated that chi a concentrations in the Mid-Atlantic streams can be best predicted by conductivity, stream slope, total phosphorus, total nitrogen, and riparian canopy coverage. Our data suggest that broad spatial patterns of benthic diatom assemblages can be predicted both by coarse-scale factors, such as land cover/use in watersheds, and by site-specific factors, such as riparian conditions, However, algal biomass measured as chi a was less predictable using a simple regression approach, The regression tree model was effective for showing that ecological determinants of chi a were hierarchical in the Mid-Atlantic streams.