Effects of runoff from land clearing and urban development on the distribution and abundance of macroinvertebrates in pool areas of a river

Abstract

We examined the effects of runoff from urban land clearing and development on the macroinvertebrate pool fauna of the Murrumbidgee River, Australia, over 1 year. Tuggeranong Creek, which flows through the urban development, often recorded higher instantaneous (storm) discharges than did the Murrumbidgee River. Monitoring of suspended solids during one storm event revealed high concentrations of suspended solids (max. 560 mg L^-1) entering the Murrumbidgee River for an 8 h period. Such concentrations were not detected by regular two-monthly sampling, although concentrations were generally higher downstream of Tuggeranong Creek. Analysis of substratum particle size revealed a higher proportion of fine inorganic material (<250 pm) at stations downstream of Tuggeranong Creek, suggesting a settling of fine material discharged during storm events. Number of taxa and macroinvertebrate density were lower at downstream stations. We conclude that the deposition of fine inorganic sediment following storm events, and the resulting change in the composition of the substratum, was the major cause of low invertebrate numbers in pools downstream of the cleared catchment.