The Murray River in Australia is recognised as an agriculturally important river, and land use activities within its catchments have been implicated in the decline of its aquatic ecosystems. Sediments can act as a sink for pollutants and impact upon aquatic communities. Land use activities within the Murray-Darling Basin may be polluting aquatic sediments and may be, in part, responsible for the observed aquatic ecosystem declines. However, it is not known if sediment pollution in the Murray River is impacting its aquatic ecosystems, nor is it known where sediment pollution is a problem or which pollutants are of concern.

Sediment from fourteen sites along the Murray River and three tributaries, the Mitta Mitta, Murrumbidgee and Darling rivers, were used in a field-based microcosm experiment to assess the effects of sediment quality on macroinvertebrate communities. The microcosm experiment was dominated by the dipteran family Chironomidae. Several species from this family were useful as bioindicators of sediment quality.

This study showed that sediment pollution in the Murray Darling systems were affecting macroinvertebrate communities. Although a nutrient enrichment effect was evident at some sites, several sites within or downstream of irrigation areas had several species absent, low numbers of other species and a high incidence of larval mouthpart deformities.

This indicated a toxic effect from another stressor. Heavy metal and total petroleum hydrocarbon concentrations were below levels expected to affect aquatic macroinvertebrates. Possibly pesticides were affecting the macroinvertebrates although the pesticide results were inconclusive. We conclude that sediment contamination is a source of ecological stress in the Murray River and may be contributing to aquatic ecosystem degradation.