PARENT SESSION
7C Environmental Policy
9:00 AM to 7:00 PM, Monday, 07 May 2001

(M/FF247) In situ bioassays for assessing the ecological quality of fresh waters: detritus processing and detritivore feeding.

Hunt, Jenny¹, Maltby, Lorraine¹, Wood, Robert¹, Slijkerman, Diana², Jak, Robbert², ^{1 2}

ABSTRACT- The breakdown of detritus is an important process in stream and river ecosystems, both in terms of energy flow and nutrient cycling. Understanding how toxicants affect detritus processing and the flow of detrital energy to stream organisms (e.g. consumption by detritivores) is fundamental to the assessment of the ecological quality of flowing water ecosystems and hence to the implementation of the Water Framework Directive. Leaf litter is a major component of the detritus in streams and rivers and is consumed by a group of detritivores known as shredders. Here we describe the development of bioassays for quantifying leaf decomposition and shredder feeding in situ. Methods have been developed for amphipod, caddisfly and stonefly shredders. Leaf decomposition and amphipod feeding bioassays were tested in an outdoor mesocosm experiment using the fungicide carbendazim. Fourteen mesocosms (2.25 m diam) containing 90 cm depth of water overlying a 10 cm depth of sediment were allocated to one of four treatments (0.28, 2.16, 20.8, 226 g/L carbendazim). Leaf packs were deployed in the mesocosms for 28 d post treatment to measure the effects on leaf decomposition and the amphipod, Gammarus pulex, was deployed for 6 d post treatment to quantify effects on detritivore feeding. There was significant mortality of amphipods exposed to the highest test concentration (i.e. 266 g/L) and a significant inhibition of feeding at 20.8 g/L carbendazim. The effect of carbendazim on leaf decomposition was less marked.

Key words: bioassay, detritus processing, detritivore, carbendazim