Abstract  Variation in watershed land use is known to influence the physical and chemical conditions in resident streams; however, few studies have evaluated variation in ecosystem structure and function, in a quantitative sense, whereby specific environmental break-points in land use could be defined. We conducted seasonal sampling (spring, summer, and fall of 2005-2006) in 43 third order streams that were representative of conditions throughout the mid-Atlantic region. Stream physical, biological, and chemical conditions were measured as represented by 19 environmental variables (physical-chemical), in addition to benthic chlorophyll concentrations and the relative abundance of diatom species collected from each stream. Watershed forest cover explained significant variation in stream benthic chlorophyll (stepwise linear regression, r(2) = 39.2 %) as selected from a set of relevant variables (total nitrogen, total phosphorus, % Forest cover, and stream temperature). Benthic chlorophyll (range 0.1 to 917 mg m(-2)) and nutrient tolerant diatom guilds were inversely correlated with forest cover, while nutrient sensitive diatom species had a positive correlation. Loess trend analysis coupled with regression tree analysis (RPART) identified abrupt changes in benthic chlorophyll and the relative abundance of diatom nutrient guilds at breakpoints of 60 % and 80 % forest cover. Despite the correlative nature of this study, the findings here suggest individual ecosystems may exhibit abrupt changes in ecosystem function following declines in forest cover, particularly at the breakpoints identified here.

Abstract  Many streams within the United States are impaired due to nutrient enrichment, particularly in agricultural settings. The present study examines the response of benthic algal communities in agricultural and minimally disturbed sites from across the western United States to a suite of environmental factors, including nutrients, collected at multiple scales. The first objective was to identify the relative importance of nutrients, habitat and watershed features, and macroinvertebrate trophic structure to explain algal metrics derived from deposition and erosion habitats. The second objective was to determine if thresholds in total nitrogen (TN) and total phosphorus (TP) related to algal metrics could be identified and how these thresholds varied across metrics and habitats. Nutrient concentrations within the agricultural areas were elevated and greater than published threshold values. All algal metrics examined responded to nutrients as hypothesized. Although nutrients typically were the most important variables in explaining the variation in each of the algal metrics, environmental factors operating at multiple scales also were important. Calculated thresholds for TN or TP based on the algal metrics generated from samples collected from erosion and deposition habitats were not significantly different. Little variability in threshold values for each metric for TN and TP was observed. The consistency of the threshold values measured across multiple metrics and habitats suggest that the thresholds identified in this study are ecologically relevant. Additional work to characterize the relationship between algal metrics, physical and chemical features, and nuisance algal growth would be of benefit to the development of nutrient thresholds and criteria.

Abstract  The species composition of benthic diatoms was related to environmental conditions in streams throughout the western US to develop diatom traits, indicators for assessment of biological condition and indicators for diagnosing stressors. We hypothesized that indicators based on species traits determined for subsets of streams with similar natural landscape features would be more precisely related to environmental conditions than would be indicators calculated based on species traits for all Streams in the data set. The ranges of many environmental conditions were wide among western streams, and these conditions covaried greatly along a major environmental gradient characterized by positive correlations among % watershed disturbed by agricultural and urban land uses (% WD), conductivity, total N, total P, and % fine sediments. Species traits were calculated for 242 diatom taxa. Weighted average (WA) methods were used to define species environmental optima, and regression approaches were used to determine whether species were sensitive or tolerant to environmental conditions indicated by % WD, total P, total N, a nutrient multivariate index, pH, conductivity, % fine sediments, % embeddedness, and a watershed disturbance multivariate index. Indicators based on WA optima and sensitive/tolerant traits were highly correlated with these environmental conditions. Natural and anthropogenic conditions varied greatly among classes of streams grouped by climate regions, but indicators developed for the entire western US were consistently more accurate than were regional indicators. Indicators for individual stressors, such as total P, conductivity, and % embeddedness, were highly correlated with values of respective stressors, but covariation among all indicators and stressors indicated that only 1 environmental gradient was reliably reflected by the indicators. Thus, robust indicators of the biological condition of diatom assemblages were developed for streams of the western US, but development of stressor-specific indicators will require application of additional analytical approaches.

Abstract  We assessed the importance of spatial scales (catchment, stream network, and sample reach) on the effects of agricultural land-use on lotic diatom assemblages along a land-use gradient in the agricultural Willamette Valley Ecoregion of Oregon. Periphyton, water chemistry, and physical habitat conditions were characterized for 25 wadeable streams during a dry season (July to September, 1997). Additional water chemistry samples were collected in the following wet season (February 1998) to assess seasonal effects of land-use on stream water chemistry. Percent agricultural land-use in the study catchments ranged from 10% to 89% with an average of 52%. Partial canonical correspondence analysis (CCA) with the first axis constrained by % agricultural land-use showed that % agricultural land-use at 3 spatial scales explained between 3.7%-6.3% of variability in the diatom species dataset. Monte Carlo Permutation tests indicated that the variance explained by % agricultural land-use was only significant at the spatial scale of the stream network with 10- and 30-m band width (p < 0.05, 999 permutations). In addition to the effects of % agricultural land-use, partial CCAs with a forward selection option showed that water chemistry (e.a., SiO2), reach-scale stream channel dimensions (e.g., width, depth, and slope), reach-scale in-stream habitats (substrates and filamentous algal cover in stream beds), and riparian vegetative buffer were all important with relation to diatom species assemblages. Percent of obligately nitrogen-heterotrophic taxa was the only diatom autecological metric that showed a significant but weak correlation with % agricultural land-use along the stream network (r = 0.50), but not at catchment or sample reach scale. Correlation between % agricultural land-use and water chemistry variables varied among the spatial scales and between seasons. Physical habitat variables (log(10) erodible substrate diameters and stream reach slope) were significantly correlated with % agricultural land-use along the stream network but not at catchment or sample reach scale. Our data suggest that spatial scales are important in assessing effects of land-use on stream conditions but the spatial scale effects may vary between seasons. Direct linkages between agricultural land-use and lotic diatom assemblages were weak during summer base-flow time regardless of the spatial scales. Summer sampling may underestimate the effects of catchment land-use on stream conditions in areas where seasonal patterns are so distinctive as in the Willamette Valley.

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  Anthropogenic nitrogen and phosphorus loading to streams has the potential to shift ecosystems from inorganic nutrient limitation toward increased carbon flux. We tested the hypothesis that relative patterns in the activities of carbon-, phosphorus- and nitrogen-acquiring extracellular enzymes associated with stream microbial communities could potentially indicate a transition from nutrient limitation to increased carbon flux. Biofilm extracellular enzyme activities (beta-glucosidase, beta-xylosidase, phosphatase, and leucine-aminopeptidase) were measured in 23 streams along an agricultural nutrient gradient in north central Pennsylvania. We also measured water column total nitrogen and total phosphorus along with biofilm chlorophyll a, ash free dry mass, and phosphorus concentrations. Although most absolute enzyme activities tended to be positively correlated with phosphorus concentrations, relative activities between carbon- and phosphorus-acquiring enzymes indicated a shift away from phosphorus limitation within a relatively narrow and low range of phosphorus concentrations. These results have potential implications for establishing nutrient guidelines for streams because they indicate that nutrients such as phosphorus might elicit a significant ecosystem-level response at relatively low concentrations of phosphorus before more apparent changes in community structure or biomass are observed.

Abstract  Nutrient enrichment, in particular by nitrogen and phosphorus, can result in the proliferation of algal biomass and may have implications for ecosystem health. The United States Environmental Protection Agency (EPA) has required the states to develop nutrient criteria for waterbodies within their jurisdictions. In response to the development of nutrient criteria guidance documents by EPA, based in part at least upon the assumptions of periphyton and water column chlorophyll a (chl a) relationships with total nitrogen (TN) and total phosphorus (TP), nutrient and chl a data collected as part of NCASI’s Long-Term Receiving Water Study (LTRWS) were examined to determine spatial and temporal variation in nutrient concentrations, periphyton chlorophyll a (chl a), and water column chl a, and nutrient-chl a relationships. Nutrient and chl a patterns were examined in the four LTRWS rivers (Codorus Creek, and the Leaf, McKenzie, and Willamette Rivers) with respect to spatial (site relative to mill location) and temporal (year and season) variation to determine the applicability and relevance of EPA’s guidelines to these systems. Measured TN and TP concentrations were not influenced by the mill discharges at any of the four study locations. Seasonal nutrient concentrations were generally greatest in Codorus Creek (TN=2.4 to 5.3 mg/L, TP=0.08 to 0.18 mg/L) with mean seasonal TN and TP concentrations in the other rivers ranging from 0.07 to 1.1 mg/L and 0.05 to 0.22 mg/L, respectively. Mean seasonal TN concentration in the LTRWS river tributary streams was greater than concentrations in the main channels of Codorus Creek and the Willamette River, but similar or lower to that seen in the Leaf and McKenzie Rivers.

Abstract  Increased nutrient concentrations in streams and rivers have altered biological Structure and function. Manipulative studies have provided insights into different mechanisms by which changes in nutrient concentrations influence aquatic biota. but these studies are limited in spatial scope and in their quantification of nutrient effects oil aggregate measures of the invertebrate assemblage. Observational data provide it complementary Source of information to manipulative studies, but these data must be analyzed Such that the potential effects Of Spurious correlations are minimized. Propensity scores, a technique developed to analyze human health observational data, are applied here to estimate the effects of increased nutrients oil the total taxon richness of stream invertebrates in a large observational data set collected from the western United States. The analysis indicates that increases in nutrient concentration are strongly associated with and Cause decreases in invertebrate richness ill large, but wadeable, open-canopied streams. These decreases in invertebrate richness were not mediated by periphyton biomass, a commonly proposed mechanism by which nutrients influence invertebrates. fit smaller, closed-canopied streams, increases in nutrients Were associated with small increases in total richness that were not statistically significant. Using propensity scores can greatly improve the accuracy of insights drawn from observational data by minimizing the potential that factors other than the factor of interest may Confound the results.

Abstract  The trends of biological and chemical data collected for 12 years (1969-80) from 46 sites in Chester County were evaluated by using the seasonal Kendall test. Calculated Brillouin 's diversity indices were plotted against time for each site. Seven sites had upward trends significant at the 99% confidence level, 9 sites had upward trends significant at the 95 to 98% confidence level, 11 sites had upward trends significant at the 90 to 94% confidence level. Of the remaining 19 sites, 17 had upward and 2 had downward trends, but these trends were not statistically significant. The seasonal Kendall test was used to test the chemical data for temporal trends at eight sites having stream discharge data. Significant trends were found at one or more sites for specific conductance, pH, total nitrate, total phosphorus, dissolved chloride, and dissolved sulfate. The chemical data for 11 sites, which were not flow adjusted were tested for trends by plotting against time and determining a correlation coefficient. Significant trends were found in nitrate and chloride. Selected chemical constituents were tested by regression analysis for correlation with diversity index. Only total dissolved solids correlated significantly with diversity index. Several suggestions are made to improve the monitoring program. (USGS)

Abstract  Biocriteria are becoming increasingly adopted into monitoring programs and formally adopted into water quality standards intended to protect waters from deterioration. Biological monitoring programs have typically focused on fish and macroinvertebrate communities, largely excluding benthic algae communities. However, many states are examining the use of algal communities, especially diatoms, as ecological indicators because of their clear response to physical and chemical environmental changes, brief life cycles and rapid rates of reproduction, and specific ecological requirements that correlate strongly with environmental conditions. Spatial and temporal patterns of diatom diversity (Diatom Species Richness, Shannon-Wiener Diversity Index, % Dominant Taxa) and ecological descriptive (%Achnanthes minutissima, Pollution Tolerance Index, % Sensitive Diatoms, % Motile Diatoms) measures were examined in the Long-Term Receiving Waters Study (LTRWS) rivers (Codorus Creek, Leaf River, McKenzie River, Willamette River) to determine the usefulness of this group in determining site differences. Additionally, the relationship between these metrics and the concentration of total nitrogen (TN) and total phosphorus (TP) was studied. The only clear spatial pattern in metric response occurred in diversity measures in Codorus Creek. However, this pattern was unrelated to the mill location with sites in the upper reach (both upstream and downstream of mill effluent) having greater species richness and diversity than sites in the lower reach of the study area. Metric patterns were more variable across sites and sampling periods in the other LTRWS rivers, but unrelated to mill location. The relationship between metric score and TN and TP concentrations was river-dependent. In Codorus Creek and the McKenzie and Willamette Rivers, metric-nutrient patterns collected from rock substrates were generally weak. Formost metric-nutrient relationships, nutrient concentration accounted for less than 5% of the variation in metric response, with ecological descriptive measures showing stronger nutrient relationships than diversity metrics. There was a relatively strong relationship between algal metrics and nutrient concentrations in the Leaf River, but relationships differed with natural (sand) or artificial (Hester-Dendy Plate (HD) Samplers) substrate. For both substrate types, there was a relationship between TN and TP and motile diatoms (negative) and sensitive diatoms (positive). Significant relationships between TN and TP and Shannon-Wiener Diversity Index (negative) and % Dominant Taxa (positive) were seen only with algal communities on HD samplers. For most Leaf River metrics, the amount of variation in measures explained by nutrient concentration was greater for TP (21 to 66%) than for TN (29 to 33%). The ratio of TN:TP accounted for a significant amount of variation in all HD sampler algal metrics except % Achnanthes minutissima. In contrast, only the percent abundance of sensitive diatoms was significantly related to TN:TP in sand communities. The ratio of TN to TP accounted for 26 to 61% of the variation in metric response for all metrics showing significant TN:TP relationships. Variation in metric response across sites was not related to a measured Stressor and Biocriteria are becoming increasingly adopted into monitoring programs and formally adopted into water quality standards intended to protect waters from deterioration. Biological monitoring programs have typically focused on fish and macroinvertebrate communities, largely excluding benthic algae communities. However, many states are examining the use of algal communities, especially diatoms, as ecological indicators because of their clear response to physical and chemical environmental changes, brief life cycles and rapid rates of reproduction, and specific ecological requirements that correlate strongly with environmental conditions. Spatial and temporal patterns of diatom diversity (Diatom Species Richness, Shannon-Wiener Diversity Index, % Dominant Taxa) and ecological descriptive (% Achnanthes minutissima, Pollution Tolerance Index, % Sensitive Diatoms, % Motile Diatoms) measures were examined in the Long-Term Receiving Waters Study (LTRWS) rivers (Codorus Creek, Leaf River, McKenzie River, Willamette River) to determine the usefulness of this group in determining site differences. Additionally, the relationship between these metrics and the concentration of total nitrogen (TN) and total phosphorus (TP) was studied. The only clear spatial pattern in metric response occurred in diversity measures in Codorus Creek. However, this pattern was unrelated to the mill location with sites in the upper reach (both upstream and downstream of mill effluent) having greater species richness and diversity than sites in the lower reach of the study area. Metric patterns were more variable across sites and sampling periods in the other LTRWS rivers, but unrelated to mill location. The relationship between metric score and TN and TP concentrations was river-dependent.

Abstract  Changes in macroinvertebrate communities exposed to pulp and paper mill effluent (PPME) have been seen in mesocosm and short-term field studies. However, long-term patterns of macroinvertebrates in PPME receiving streams have not been examined. We conducted a study of 4 PPME receiving streams (Codorus Creek, PA; the Leaf River, MS; and the McKenzie and Willamette rivers, OR) over 9 y to assess temporal patterns in macroinvertebrate community structure and metrics related to PPME discharge. Study streams represented different ecoregions, warm-/cold-water systems, gradients of PPME concentration (<1%-33%), and mill process types. Bray-Curtis similarity and nonmetric multidimensional scaling showed significant community differences across sites in Codorus Creek, but differences were related to stream temperature patterns and not PPME. In the other study streams, seasonal community differences across years were greater than differences across sites. General linear models were used to examine spatial and temporal variation in macroinvertebrate metric response (% dominant taxa, density, richness, Hilsenhoff Biotic Index [HBI], Simpson's Index, and ash-free dry mass). Mean HBI scores indicated that the macroinvertebrate community reflected fair to very good water quality conditions, with water quality typically classified as "good" at most sites. Significant site differences in macroinvertebrate metric response were uncommon in the Leaf, McKenzie, and Willamette rivers but were seen in all metrics in Codorus Creek, where metric response was spatially variable. In the McKenzie River, there was an increase in mean HBI scores at sites downstream of the mill relative to 1 of the 2 upstream sites. However, significant differences were seen only between 1 upstream and downstream site, and HBI scores at all downstream sites consistently reflected "good" water quality. Significant annual differences in metric response were typical in all rivers. Water quality (pH, conductivity, total nitrogen) and habitat (velocity, depth, substrate composition) variables explained community structure patterns in the Leaf and McKenzie rivers, but macroinvertebrate-environment relationships were weak in the other 2 streams. The results of this study indicate that macroinvertebrate community structure is temporally variable and reiterate the importance of long-term studies for accurate determination of the effects of point sources such as PPME on receiving systems.