Publications from CRCFE project E301

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 was strongly correlated to 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. 

Abstract

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 apparently influenced by urban density, but also by effluents from small sewage treatment plants and, at a few sites, agricultural activities. 
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.

Abstract

Rehabilitation of physical habitat in urban streams is unlikely to increase instream biological diversity if factors other than habitat simplification limit community development.  We used a study of regional variation in macroinvertebrate communities to develop a model predicting which degrading processes limit community composition in urban streams.  Organic pollution (as indicated by biochemical oxygen demand, BOD) and increased run-off (as indicated by proportion of catchment that is impervious)?both products of catchment-scale perturbations?were the best environmental variables to explain differences between communities in metropolitan sites and those in surrounding rural sites.  We hypothesized that catchment-scale processes limited community development in metropolitan sites.  This was supported by a second study that showed little change in community composition in metropolitan sites after the placement of artificial riffles, which were designed to increase habitat complexity.  We thus propose a decision-making framework for urban stream rehabilitation, wherein community structure of a physically degraded site is assessed.  If the community is similar to those of surrounding rural sites, site-specific physical habitat restoration is considered likely to be successful.  If the community is similar to those of metropolitan sites, rehabilitation measures to improve water quality or hydrology are recommended as first priority.  Levels of BOD and catchment impervious area are used to prioritize appropriate actions.

(Full text pdf 72K)

(output of CRC FE Mk I project E301: Biological Assessment and Management of Urban streams)

Abstract

Experimental placement of rocks, designed to restore pool-riffle differentiation, in five channelized urban streams resulted in little change to macroinvertebrate community composition.  We hypothesise that, in such urban sites, quality and hydrology of urban stormwater are primary determinants of community composition. Site-specific restoration will have little effect without concomitant improvement of water quality throughout the catchment. When compared to a regional dataset, communities of the experimental sites were similar to those of most other urban streams in Melbourne, Australia.  However, some urban sites supported communities less likely to be limited by urban run-off.  Such sites are proposed as better candidates for site-specific restoration.

(output of CRC FE Mk I project E301 - Biological Assessment and Management of Urban streams - and CRC FE Mk II project B705 - Experimental assessment of physical habitat restoration in urban streams: limitations to recruitment)

Abstract

The depauperate macroinvertebrate communities of two disturbed urban streams were used to demonstrate a technique for determining optimal subsample size for the multivariate representation of community structure. Although multivariate analyses have commonly been applied to subsampled data, the effect of subsampling on multivariate patterns has not previously been investigated in detail. The minimum requirement for applying the method is eight fully processed community samples distributed across two treatments, with n = 4 (being a representative subset of a larger study to which subsampling will be applied). The data from each sample are subsampled repeatedly with the aid of a simulation program. Variation in community structure between treatments is tested by analysis of similarity for the complete data and for multiple sets of subsampled data. The optimal subsampling strategy is defined as the minimum effort required to achieve a median R-statistic no less than the value derived for the complete data. Subsampling to a fixed proportion is a less efficient strategy than subsampling to a fixed number of individuals. For the urban stream communities, subsampling to 300 individuals was adequate for four out of six comparisons and was adequate for all comparisons when a minimum proportion of 10% was applied. Several non-abundant taxa were found to be important contributors to differences between treatments. Subsamples need to be large enough to adequately estimate the abundance of such taxa. Further investigation is required to assess the relationship between optimal subsample size for multivariate analysis and the shape of cumulative species-abundance curves.

(For more information and some related software, see the Virtual Marchant Subsampler page)

(output of CRC FE Mk I project E301 - Biological Assessment and Management of Urban streams)