Abstract  Freshwater mussels are among the most rapidly declining components of global biodiversity, but causes of local species disappearances are frequently unknown. We estimated decade-scale local extinction by resampling 118 stream reaches representing the best mussel habitat across a region that was once rich in species and is now mostly converted from prairies and riparian woodlands to intensive agriculture (Iowa, USA). Average species richness was reduced from >5 to <2 species, maximum richness was reduced from 22 to 15 species, and all mussel species were extirpated from 47% of the reaches since 1984 to 1985. More than half of the sites lost >75% of their species. Although 5 of the species were found at 20% to 140% more sites in 1998 than 1984 to 1985, 29 species (83%) decreased an average of 80% in geographic coverage, whereas 8 species were completely lost from these stream sites. Correlation analyses with reach and watershed characteristics determined using GIS and local sampling methods linked the greatest declines to rarity of streamside woodlands, high siltation, and most intensive agricultural land uses, i.e., where conditions had changed most from the historical land cover. The surveys indicated a very large extinction debt has been created by large-scale habitat modification over the last century and ongoing agricultural land uses. Freshwater mussels are among the most rapidly declining components of global biodiversity, but causes of local species disappearances are frequently unknown. We estimated decade-scale local extinction by resampling 118 stream reaches representing the best mussel habitat across a region that was once rich in species and is now mostly converted from prairies and riparian woodlands to intensive agriculture (Iowa, USA). Average species richness was reduced from >5 to <2 species, maximum richness was reduced from 22 to 15 species, and all mussel species were extirpated from 47% of the reaches since 1984 to 1985. More than half of the sites lost >75% of their species. Although 5 of the species were found at 20% to 140% more sites in 1998 than 1984 to 1985, 29 species (83%) decreased an average of 80% in geographic coverage, whereas 8 species were completely lost from these stream sites. Correlation analyses with reach and watershed characteristics determined using GIS and local sampling methods linked the greatest declines to rarity of streamside woodlands, high siltation, and most intensive agricultural land uses, i.e., where conditions had changed most from the historical land cover. The surveys indicated a very large extinction debt has been created by large-scale habitat modification over the last century and ongoing agricultural land uses.

Abstract  Water resource managers face increasing challenges in identifying what physical and chemical stressors are responsible for the alteration of biological conditions in streams. The objective of this study was to assess the comparative influence of multiple stressors on benthic diatoms at 98 sites that spanned a range of stressors in an agriculturally dominated region in the upper Midwest, USA. The primary stressors of interest included: nutrients, herbicides and fungicides, sediment, and streamflow; although the influence of physical habitat was incorporated in the assessment. Boosted Regression Tree was used to examine both the sensitivity of various diatom metrics and the relative importance of the primary stressors. Percent Sensitive Taxa, percent Highly Motile Taxa, and percent High Phosphorus Taxa had the strongest response to stressors. Habitat and total phosphorous were the most common discriminators of diatom metrics, with herbicides as secondary factors. A Classification and Regression Tree (CART) model was used to examine conditional relations among stressors and indicated that fine-grain streams had a lower percentage of Sensitive Taxa than coarse-grain streams, with Sensitive Taxa decreasing further with increased water temperature (>30 °C) and triazine concentrations (>1500 ng/L). In contrast, streams dominated by coarse-grain substrate contained a higher percentage of Sensitive Taxa, with relative abundance increasing with lower water temperatures (<29 °C) and shallower water depth (<0.3 m). Quantile regression indicated that maximum water temperature appears to be a major limiting factor in Midwest streams; whereas both total phosphorus and percent fines showed a slight subsidy-stress response. While using benthic algae for assessing stream quality can be challenging, field-based studies can elucidate stressor effects and interactions when the response variables are appropriate, sufficient stressor resolution is achieved, and the number and type of sites represent a gradient of stressor conditions and at least a quasi-factorial design. © 2017

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  The March 2013 Iowa Nutrient Reduction Strategy emphasizes implementation of technology-based nutrient controls and practices in the near-term, while retaining as a long-term goal the development of appropriate nutrient criteria. In 2010 the Iowa Department of Natural Resources (IDNR), with the assistance of a technical advisory committee, initiated a new project to build a technical foundation for stream nutrient criteria. This report presents results from an analysis of Iowa-specific nutrient data and a review of scientific literature and other relevant technical information. As an outgrowth of this work, nutrient enrichment criteria recommendations have been prepared for B(WW-1) and B(WW-2) wadeable, warmwater streams and B(CW1) coldwater (trout) streams. Current data are not adequate to formulate criteria recommendations for B(CW2) coldwater spring runs, B(WW-2) and B(WW-3) marginally perennial, headwater creeks of watershed area less than ten square miles, and large wadeable/nonwadeable rivers of watershed area greater than 700 square miles. IDNR continues to gather and analyze nutrient and biological-response monitoring data needed to develop nutrient criteria recommendations for all stream classifications. Going forward, a strong commitment to nutrient-related monitoring, data analysis, and reporting will be necessary to support development and implementation of nutrient criteria and the objectives of the state nutrient reduction strategy.