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Water quality in native forests


Map of the Warra LTER site showing catchments for which the relationship between water quality and environmental and disturbance factors was investigated.  The three catchments coloured green have low water colour and low turbidity, the five catchments co

The quality of water in streams flowing through forested catchments is determined both by the natural attributes of catchments, and by their history of disturbance and management. Previously, research at the Warra Long-Term Ecological Research site had shown distinct differences in the turbidity of

different creeks, possibly related to the position of their catchments in the wider landscape. We are thus working to develop a better understanding of the im

pacts of environmental variables on water quality, and in particular on turbidity.

For each 1 hectare in each of 14 Warra catchments, information on disturbance factors (including roads, harvesting and fire history), geographic and environmental factors (such as soil type, geology, vegetation, slopes, altitude, forest age, and wetness index) and stream morphology was related to water quality measurements. Geographic and environmental factors had the greatest impact on water quality, accounting for the majority of variation between catchments. Road density was the most important of the disturbance factors in regard to determining water quality.

Small, narrow catchments with talus geology, a high proportion of wet eucalypt forests, and a high wetness index, had the poorest water quality. Large catchments with high stream densities were associated with better quality water. Younger forests with high road densities were also associated with poorer quality water. Overall, water quality variation at Warra is mainly due to natural features of the landscape. Understanding the contribution of natural factors is required before any impacts of disturbance on water quality can be distinguished.


Dr Sandra Roberts


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