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NUTRIENTS, CANOPY COVER, AND GRAZERS: THEIR EFFECTS ON SUMMER PERIPHYTON IN SMALL MIDWESTERN STREAMS
Citation:
Griffith, M. B., F B. Daniel, J M. Lazorchak, AND M E. Troyer. NUTRIENTS, CANOPY COVER, AND GRAZERS: THEIR EFFECTS ON SUMMER PERIPHYTON IN SMALL MIDWESTERN STREAMS. Presented at Ecological Society of America, Savannah, GA, August 3-8, 2003.
Impact/Purpose:
The objective of this task is to develop molecular indicators to evaluate the integrity and sustainability of aquatic fish, invertebrate, and plant communities (GPRA goal 4.5.2). Specifically, this subtask aims to evaluate methods for the measurement of:
fish and invertebrate community composition, especially for morphologically indistinct (cryptic) species
population genetic structure of aquatic indicator species and its relationship to landscape determinants of population structure (to aid in defining natural assessment units and to allow correlation of population substructure with regional stressor coverages)
genetic diversity within populations of aquatic indicator species, as an indicator of vulnerability to further exposure and as an indicator of cumulative exposure
patterns of temporal change in genetic diversity of aquatic indicator species, as a monitoring tool for establishing long-term population trends.
Description:
Numerous studies in artificial streams suggest the relationship between nurients and periphyton biomass (AFDM) and chlorophyll a in streams is affected by ambient light, which is influenced by canopy cover, and by grazer densities. To assess the relationships between nutrients and eutrophication-type effects in small streams, we created a model to describe spatial and among year variations in periphyton collected duirng the summer of three years from 35 2nd-3rd order tributaries (Strahler order from RF3 digital maps) of the Little Miami River, Ohio. These streams are characterized by high concentrations of dissolved P (tdP, 0.026-0.30 mg L-1) and nitrate-N (0.016-14 mg L-1), agricultural land cover (row crop and grassland: 50-95%) and variable riparian canopies (6.3-93%). The basin also includes two ecoregions that differ in their relationships between land cover and nutrient inputs to streams. Grazer densities during the three years of study have ranged from 0.44-900 individuals m-2. Regression analysis showed that periphyton AFDM was positively related to tdP and inversely related to canopy density (decreasing light). Periphyton chlorophyll a was positively related to grazer density and nitrate-N, but relationship with nirate-N differed between the ecoregions. Grazer density was positively correlated with nitrate-N (r - 0.35, p<0.001), suggesting that grazers suppress the effects of nutrients and reduce the increase in periphyton accumulation as nutrient concentrations increase.