Download or read book The Impacts of Plant Nutrients and Riparian Shade on Primary Producers and Consumers in Lotic Systems written by Michael M. Sturt and published by . This book was released on 2010 with total page 249 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nutrient enrichment is common in Irish streams yet despite extensive reports of algal nutrient requirements, generally, this study found no differences in algal biomass across a wide nutrient gradient. In addition, increases in light levels resulted in no net change in algal biomass. Nevertheless, greater densities of grazing benthic macroinvertebrates (grazers), principally Baetis rhodani, were found in high nutrient, high light streams. The ability of grazers to effectively prevent the accrual of highly productive algae was demonstrated through a series of invertebrate grazer exclusion experiments. These experiments also revealed greater grazing pressures at more nutrient rich sites, presumably a function of greater productivity of the grazers{u2019} algal food source. Top-down grazer control of algae was also shown to be highly variable in time and space. Vigorous algal growth during periods of reduced grazing pressure resulted in rapid accrual of the nuisance filamentous alga Cladophora glomerata. Established filaments developed a degree of grazer resistance and there was evidence that these filaments benefitted from the presence of microphyte grazers, suggesting that grazing pressure can shift between a negative and a positive force depending on algal morphology. High-flow events overrode all other interactions and effectively reduced previously accrued algal biomass to levels near zero yet did not negatively effect grazers. Post-spate algal-invertebrate interactions were subsequently reverted to grazer top-down control. During a prolonged low-flow period, Cladophora in shaded habitats accrued to similar levels as in unshaded habitats. These results indicate that despite light-limited growth, algal biomass can attain similar levels over time in shaded habitats, the threshold of which is governed by flow conditions. This study has demonstrated the dominant roles that small bodied grazers and hydraulic disturbance play in regulating algal standing stock in streams in south-west Ireland. These aspects of stream ecosystem function deserve greater attention from a stream management perspective.