Effects of urbanization on streams of the Melbourne region, Victoria, Australia. I. Benthic macroinvertebrate communities

1. Macroinvertebrate community composition was assessed in small streams of the Melbourne region to test the effects of (a) urban density (catchment imperviousness 0–51%) and (b) stormwater drainage intensity (comparing the intensively drained metropolitan area with urban areas of the hinterland, which had open drains and some localized stormwater drainage).
2. Hinterland communities separated into two groups of sites correlating strongly with patterns of electrical conductivity (EC), basalt geology and annual rainfall. Community composition varied little in the high-EC, western group (imperviousness 0.2–1.2%), but in the eastern group it was strongly correlated with catchment imperviousness (0–12%), with lower taxon richness in more impervious catchments.
3. Metropolitan communities (imperviousness 1–51%) were all severely degraded, with high abundances of a few tolerant taxa. Community composition was poorly correlated with patterns of geology, rainfall or imperviousness. Differences between metropolitan and hinterland communities were well explained by patterns of biochemical oxygen demand and electrical conductivity, which were postulated to indicate the more efficient transport of pollutants to receiving streams by the metropolitan stormwater drainage system.
4. Degradation of macroinvertebrate community composition was well explained by urban density but intensive urban drainage increased degradation severely at even low urban densities. Quantification of relationships between imperviousness, drainage intensity and stream degradation can better inform the assessment, conservation and restoration of urban streams.     

Effects of urbanization on streams of the Melbourne region, Victoria, Australia. II. Benthic diatom communities

1. Epilithic and epiphytic diatom community composition were assessed in small streams of the Melbourne region to test the effects of (a) urban density (sub-catchment imperviousness 0–51%) and (b) stormwater drainage intensity (comparing the intensively drained metropolitan area with urban areas of the hinterland, which had open drains and some localized stormwater drainage).
2. Communities separated into three groups: eastern hinterland, western hinterland and a metropolitan group. Separation of eastern and western hinterland groups, and of eastern and western sites within the metropolitan group were best explained by patterns of electrical conductivity, basalt geology and annual rainfall. Separation of metropolitan and hinterland groups, and patterns within the hinterland groups were best explained by nutrient gradients (phosphorus, ammonia and total nitrogen).
3. Nutrient concentrations were not only apparently influenced by urban density but also by effluents from small sewage treatment plants and agricultural activities at a few sites.
4. Species richness did not vary consistently between the metropolitan and hinterland groups but within the western hinterland, sites with low nutrient concentrations tended to be more species-rich than mildly enriched sites.
5. Composition of both diatom and macroinvertebrate communities (assessed in a concurrent study) were sensitive indicators of urban-derived impacts. However, diatoms were better indicators of nutrient enrichment, while macroinvertebrates were better integrative indicators of catchment disturbance.