Final Report: Ecoregion-specific Comparison of Stream Community Responses to Nutrient Gradients Using Both Survey and Experimental Approaches

EPA Grant Number: R824783
Title: Ecoregion-specific Comparison of Stream Community Responses to Nutrient Gradients Using Both Survey and Experimental Approaches
Investigators: Stevenson, R. Jan , Wiley, Michael J. , Holomuzki, Joe
Institution: University of Michigan , Transylvania University , University of Louisville
EPA Project Officer: Packard, Benjamin H
Project Period: October 1, 1995 through September 1, 1998
Project Amount: $390,000
RFA: Water and Watersheds (1995) Recipients Lists
Research Category: Water and Watersheds , Water

Objective:

Nutrient loading commonly causes an increase in primary productivity and replacement of oligotrophic algal-invertebrate communities with a new suite of organisms, which may result in very different stream structure and function. Quantitatively assessing the relationships between nutrient concentrations and algal-invertebrate communities in streams has been challenging because stream ecosystems are so physically variable and biologically dynamic. Our research was designed to develop a better predictive understanding of nutrient effects on stream communities in ecoregions with different hydrological stability.

The predictions of Oksanen-Fretwell and Arditi-Ginsberg models formed the theoretical foundation of our work, with the first predicting thresholds along a productivity gradient (i.e., sudden changes in ecological response and specific threshold levels of nutrient availability) and the second predicting ratio-dependent changes along a productivity gradient. Thresholds along nutrient (productivity) gradients could provide valuable goals for nutrient regulation in watersheds. Thus, the following objectives and approaches were established to test these models and to advance our understanding and assessment of nutrient effects on stream communities:

  1. To relate, quantitatively, variation in algal and invertebrate communities to different nutrient concentrations by sampling 130 streams in two hydrologically different ecoregions: Kentucky, which is largely unglaciated and has hydrologically variable streams and Michigan, which is glaciated and has more hydrologically stable streams;
  2. To assess, experimentally, the cause-effect relationships between changes in stream communities and nutrient concentrations in artificial, flow-through streams; and
  3. To develop algal and invertebrate indicators that characterize biotic integrity and infer specific nutrient conditions with results from our intensive surveys of Kentucky and Michigan streams, our experiments in experimental streams in Michigan and Kentucky, and from the EPA's EMAP-SW Streams Program.

Summary/Accomplishments (Outputs/Outcomes):

Benthic algal and invertebrate assemblages, water chemistry, and habitat conditions were monitored in 65 streams in Kentucky and 65 streams in Michigan for 8 weeks either during 1996 or 1997. Our results showed that diatoms reached peak algal biomasses in very low nutrient concentrations in Kentucky, but grazing invertebrates limit diatom accrual on rocks in Michigan regardless of nutrient concentration. So nutrient concentrations had relatively little effect on diatom biomass. In both Kentucky and Michigan, the filamentous green algae Cladophora grew in nutrient concentrations above a threshold concentration of 10-20 µg TP/L and was responsible for the positive relation between algal biomass and nutrient concentration in the two ecoregions.

Monitoring also showed that invertebrate abundances were much lower in Kentucky than in Michigan. Biomass of invertebrates increased with nutrient concentrations in Kentucky and Michigan, but the rate of increase was less in Kentucky. In other words, the efficiency of transfer of primary production to secondary production was much lower in Kentucky streams than in Michigan streams. Fish survey data from another project in Michigan were related to our data and showed that the positive effect of nutrients on productivity could be related to fish as well. Path analysis shows that the frequent floods and droughts of Kentucky constrain invertebrate response to stream productivity. Nuisance algal levels of Cladophora do not have negative effects on invertebrate biomass.

Species composition of diatom assemblages in surveyed streams of Kentucky changed rapidly around the 15 µg TP/L threshold that enabled growth of Cladophora. Taxonomic composition of invertebrate assemblages were much less sensitive to nutrient concentrations and only showed major loss of taxa in high nutrient conditions.

Experiments were designed to isolate cause-effect relationships in nutrient-algal-invertebrate interactions, to reduce complexity of ecological systems, and to increase the chances for observing threshold responses along productivity gradients. Growth rates of low-density, diatom-dominated periphyton were increased rapidly at increasing nutrient concentrations up to saturating concentrations of 16 µg PO4-P/L and about 75 µg dissolved inorganic N/L. Like growth rates, peak biomass of periphyton increased rapidly with increasing nutrients in low nutrient conditions, less than 16 µg PO4-P/L and about 75 µg dissolved inorganic N/L; however, peak biomass continued to increase with increasing nutrient concentrations in higher nutrient conditions even though the effects of nutrients were reduced. The lack of a clear nutrient saturation level for peak biomasses was probably due to high algal densities retarding transport of nutrients to cells in thicker periphyton mats.

Experiments showed that grazers in densities similar to those found in Michigan streams could limit diatom accrual. Herbivorous invertebrates in densities similar to those found in Michigan streams can be limited by algal availability, and increases in nutrient availability can have an indirect positive effect on invertebrate health (as indicated by increased growth rates and reduced migration rates). However, no major threshold effects were observed in algal biomass or invertebrate growth rates, even though complexity of habitats was reduced in these simple experimental ecosystems. Spatial variability in algal growth patterns and invertebrate feeding behaviors were major factors affecting the observation of resource thresholds.

Experiments also showed that overgrowths of streams by long filamentous green algae (Cladophora) can have a positive effect on some stream invertebrates, particularly hydropsychid caddisflies that build nests on the surface of the mass of Cladophora filaments. Several experiments showed that these invertebrates prefer rocks with Cladophora compared to bare rocks. We also found that stoneflies preyed more successfully upon hydropsychid caddisflies on bare rocks than on rocks covered with Cladophora.

Results of indicator development showed that diatom species composition and percent Cladophora cover of the stream bottom were good indicators of nutrient concentrations in streams; however, invertebrate metrics were much less sensitive. Indicators of nutrient enrichment of streams based on species composition of diatom assemblages and nutrient preferences of diatom species were more precise indicators of nutrient concentrations than one-time sampling of nutrients in streams. Algal indicators of nutrients were transferable among ecoregions.

In conclusion, nutrient effects on algae and invertebrates in streams are highly dependent upon hydrologic stability of streams. Experiments confirmed in-stream patterns and showed nutrients stimulate algal growth in streams, but reach saturating levels for diatom-dominated periphyton at low concentrations. Higher enrichment is necessary for significant accrual of Cladophora filaments compared to diatom-dominated periphyton. The positive effect of nutrients is observed in invertebrate and fish biomass, as well as algal biomass. Hydrologic variability (either from scouring floods or drought) may constrain invertebrate densities, which causes two main effects: diatoms can easily overgrow substrata when nutrients are abundant in hydrologically variable streams, and nutrients have a less positive effect on invertebrate biomass in surveyed streams of hydrologically variable than stable streams. Even though responses of algal and invertebrate biomass to nutrient concentrations were relatively linear, responses of individual species occurred at nutrient thresholds. Thus, keystone species (e.g., Cladophora) responses and shifts in species composition of diatom assemblages may provide valuable targets for nutrient criteria to protect the biotic integrity and ecosystem services of streams. These indicators should be relatively transferable among ecoregions. Changes in invertebrate species composition were relatively insensitive to nutrient concentrations.


Journal Articles on this Report : 9 Displayed | Download in RIS Format

Other project views: All 31 publications 12 publications in selected types All 9 journal articles
Type Citation Project Document Sources
Journal Article Biggs BJF, Stevenson JR, Lowe RL. A habitat matrix conceptual model for stream periphyton. Archiv fur Hydrobiologie 1998;143(1):21-56. R824783 (Final)
  • Abstract: University of Michigan-Abstract
    Exit
  • Journal Article Fairchild M, Holomuzki JR. Spatial variability and assemblage structure of stream hydropsychid caddisflies. Journal of the North American Benthological Society 2002;21(4):576-588. R824783 (Final)
  • Abstract: University of Michigan - Abstract
    Exit
  • Other: JSTOR-Abstract
    Exit
  • Journal Article Hill BH, Herlihy AT, Kaufmann PR, Stevenson RJ, McCormick FH. Use of periphyton assemblage data as an index of biotic integrity. Journal of the North American Benthological Society 2000;19(1):50-67. R824783 (Final)
  • Full-text: ResearchGate - Full Text PDF
    Exit
  • Abstract: Google Scholar-Abstract
    Exit
  • Journal Article Holomuzki JR, Pillsbury RW, Khandwala SB. Interplay between dispersal determinants of larval hydropsychid caddisflies. Canadian Journal of Fisheries and Aquatic Sciences 1999;56(11):2041-2050. R824783 (Final)
  • Abstract: CJFAS-Abstract
    Exit
  • Journal Article Pan Y, Stevenson RJ, Hill BH, Herlihy AT, Collins GB. Using diatoms as indicators of ecological conditions in lotic systems: a regional assessment. Journal of the North American Benthological Society 1996;15(4):481-495. R824783 (Final)
  • Abstract: University of Michigan-Abstract
    Exit
  • Other: JSTOR-Abstract
    Exit
  • Journal Article Pan Y, Stevenson RJ, Hill BH, Kaufmann PR, Herlihy AT. Spatial patterns and ecological determinants of benthic algal assemblages in Mid-Atlantic streams, USA. Journal of Phycology 1999;35(3):460-468. R824783 (Final)
  • Abstract: Wiley-Abstract
    Exit
  • Other: Research Gate-Abstract
    Exit
  • Journal Article Pan Y, Stevenson RJ, Hill BH, Herlihy AT. Ecoregions and benthic diatom assemblages in the Mid-Atlantic Highlands streams, USA. Journal of the North American Benthological Society 2000;19(3):518-540. R824783 (Final)
  • Full-text: Portland State University-Full Text PDF
    Exit
  • Abstract: Google Scholar-Abstract
    Exit
  • Other: JSTOR-Abstract
    Exit
  • Journal Article Stevenson RJ. Resource thresholds and stream ecosystem sustainability. Journal of the North American Benthological Society 1997;16(2):410-424. R824783 (Final)
  • Abstract: University of Michigan-Abstract
    Exit
  • Other: JSTOR-Abstract
    Exit
  • Journal Article Stevenson RJ. Diatom indicators of stream and wetland stressors in a risk management framework. Environmental Monitoring and Assessment 1998;51(1-2):107-118. R824783 (Final)
  • Abstract: Springer-Abstract
    Exit
  • Supplemental Keywords:

    nutrient criteria, risk assessment, biocriteria, dose-response, ecological effects, food webs, water, watersheds, biology, ecology, hydrology, surveys, experiments, nitrogen, phosphorus, central region, Great Lakes region, Michigan, Kentucky, Indiana, MI, KY, IN., RFA, Scientific Discipline, Geographic Area, Water, Ecosystem Protection/Environmental Exposure & Risk, Hydrology, Nutrients, Water & Watershed, exploratory research environmental biology, Ecosystem/Assessment/Indicators, Chemical Mixtures - Environmental Exposure & Risk, Ecosystem Protection, State, Ecological Effects - Environmental Exposure & Risk, Ecological Effects - Human Health, Ecology and Ecosystems, Social Science, Watersheds, Ecological Indicators, ecological effects, EMAP, environmental monitoring, fate and transport, nutrient supply, nutrient transport, surveys, aquatic ecosystem, basin hydrology, hydrological stability, ecological exposure, nutrient sensitive ecosystems, dose response, NAPL contaminants, stream ecosystems, nutrient gradiants, algal-invertebrate habitat, community response, nutrient gradients, biological integrity, ecosystem indicators, aquatic ecosystems, ecoregion, nutrient cycling, ecoregions, public policy, Kentucky (KY), Michigan (MI), stream ecosystem

    Progress and Final Reports:

    Original Abstract
  • 1996
  • 1997