PARENT SESSION
Oral Session # 74: Riparian Ecology I: Nutrient Cycling; Decomposition.
Presiding: K Bushaw-Newton
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 205.
Nutrients, canopy cover, and grazers: Their effects on summer periphyton in small Midwestern streams.
Griffith, Michael*,1, Daniel, F.2, Lazorchak, James2, Troyer, Michael1, 1 USEPA, ORD, National Center for Environmental Assessment, Cincinnati, OH, USA2 USEPA, ORD, National Exposure Research Laboratory, Cincinnati, OH, USA
ABSTRACT- Numerous studies in artificial streams suggest the relationship between nutrients 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 during 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 nitrate-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.
Key words: nutrients, invertebrate grazers, stream periphyton, canopy cover