No 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.

Chelodina longicollis is an opportunistic carnivore that obtains its food from a wide variety of sourcesplankton, nekton, benthic macro-organisms, carrion, and terrestrial organisms that fall upon the water. Although there are some quantitative differences between the littoral components of the diet and the composition of the littoral fauna, these can be attributed to differences in accessibility or 'noticeability' among prey species. There is no evidence to suggest that C , longicollis is selective in what it eats, within the confines of carnivory. Comparison of the diet of C . longicollis with those of other sympatric chelids reveals considerable overlap; the relevance of this to geographic variation in abundance of the species is discussed.

The benthic invertebrates of the banks and main channel at 10 sites along 100 km of the lower reach of the La Trobe River, which flows entirely through agricultural and industrial areas, were quantitatively sampled every two months between May 1979 and March 1981; 23 chemical variables were measured concurrently. In all, 337 taxa were collected. Normal and inverse classifications of the faunal data with two similarity indices (Czekanowski, Canberra Metric) indicated that the uppermost two sites (upstream of the industrial areas) with a rich fauna were clearly distinct from the more depauperate downstream sites; these latter sites could be divided into two groups (main channel samples) or four groups (bank samples). In both habitats, eight groups of common (>0.5% of total numbers) taxa were evident: in each habitat, there were one or two groups of resistant taxa abundant at all sites (mostly Chironomidae), one or two groups of opportunistic taxa common at disturbed sites only (Caenidae, Corbiculidae, Ecnomidae, Chironomidae), and two groups of sensitive taxa that were most abundant at the two uppermost sites (Leptophlebiidae, Baetidae, Ecnomidae, Elmidae, Helodidae, Chironomidae, Ceratopogonidae, Hydracanna). Oligochaeta were abundant at all sites and as a group were considered resistant. Multiple discriminant analysis of the previously established site groups with 17 of the chemical variables indicated that high values for conductivity distinguished the most downstream site groups, which had the poorest fauna; the effect of this factor on the fauna was apparently indirect. The analysis also indicated that a decrease in suspended solids at site groups on an impounded section and an increase in nutrients at a site immediately downstream of the input of treated sewage were associated with changes in the fauna. The release of heated water (<25�C) from a power station at one of the sites on the impounded section had little effect on the fauna.

The life histories of the following species were studied over 2 years at various sites throughout the catchment of the La Trobe River: Tasmanocoenis tonnoiri and Tasmanocoenis sp. (Ephemeroptera : Caenidae), Atalophlebioides sp. and two Atalonella spp. (Ephemeroptera : Leptophlebiidae), two Baetis spp. (Ephemeroptera : Baetidae), Leptoperla primitiva and L. neboissi (Plecoptera : Gripopterygidae), Cyphon sp. (Coleoptera : Helodidae), Ecnomus sp. (Trichoptera : Ecnomidae). The life cycles of these species varied from univoltine (four taxa) to bivoltine (Leptophlebiidae, Baetidae, Ecnomus sp.) or trivoltine (T. tonnoiri). Although the species displayed various degrees of synchrony of growth, distinct changes in the size distribution of the larvae or nymphs occurred with time and thus cohorts were evident.