The impact of nutrient enrichment on stream biology and quality in Ireland
Harrison, S. and Jansen, M.
University College Cork
Email: sharrison@ucc.ie
Nutrient enrichment is a current and growing threat to stream quality in Ireland,
particularly given the planned strategic increase in agricultural output. Despite this,
we still lack knowledge on the ecological consequences of nutrient enrichment in
streams. We quantified benthic algae and invertebrates from 32 streams from southern
Ireland across a gradient of nutrient enrichment. The responses of benthic algae to the
nutrient gradient were, surprisingly, unimodal. The low algal biomass at higher
nutrient concentrations in summer was correlated with a high abundance of benthic
invertebrate grazers, such as Baetis mayfly nymphs, suggesting effective top-down
control of the primary production in the more nutrient enriched streams. Biological
indicators (Q value, BMWP score and algal biomass) did not respond predictably to
the nutrient status of individual streams, however, indicating the need for a more
targeted approach to detect and monitor nutrient enrichment, as opposed to organic
pollution, of streams.