Assessing effects of eutrophication in streams based on breakdown of eucalypt leaves

Abstract

Breakdown of eucalypt leaves and the associated communities of invertebrates and fungi were examined in two 2 nd order streams of northwestern Portugal impacted by eucalypt plantations, human settlements and agricultural activities. Breakdown rates of eucalypt leaves were at the upper limit found in streams of the Iberian Peninsula, probably due to high levels of nitrate and phosphate in the stream water. The highest breakdown rates were found in the Guisande River and were associated with high fungal diversity, biomass and sporulation. Also, higher richness in invertebrate taxa and percentage of detritivores occurred in the Guisande River than in the Este River. In the latter stream, fungal biomass and sporulation were depressed, probably because of sedimentation and low current velocity, which could have negatively affected decomposer activity on leaves. Our results suggest that breakdown rates of eucalypt leaves and the associated decomposer communities were sensitive to changes in water quality, supporting the contention that breakdown experiments using poor quality leaf species might be useful for assessing stream integrity.