Metal Debris in Rivers: Links to Geomorphology and Macroinvertebrate Communities

Metal contamination of aquatic environments is a global occurrence and consequence of urbanisation. While the impacts of dissolved and fine particulates on rivers are well documented, there is little knowledge of the effects of coarse particulate metal debris in upland streams. This study investigates the distribution and ecological significance of particulate and large metal debris in Glenbrook Creek, NSW, Australia. It was hypothesised that metals would accumulate in discrete pockets relating to geomorphology, and that macroinvertebrate communities would respond to the accumulation and contamination.

Twenty-two locations were selected along mid and lower sections of Glenbrook Creek, and its tributaries. Riffle habitats in each location were categorised into Pre-riffle, riffle-Head, and Mid-riffle zones. Sediment samples were taken in each zone and analysed for metals using xray fluorescence spectrometry, and manual debris collection. Artificial substrates and decomposition assays were used to assess stream biota and function. 

Metal loads and macroinvertebrates differed between Creek sections but not between zones. Mean particulate metal concentrations were below the default sediment quality guideline values. Despite this, the SIGNAL scores below 5 in the presence of metal debris may indicate some negative effects. Findings are compared to studies conducted in the area. Potential future directions are discussed.