Water quality in two small forested catchments in the Warra LTER site, Tasmania : source of colour and nutrient enrichment

Variations in water quality occur with changes in land use such as timber harvesting and land clearing for agriculture, and through natural environmental variations including vegetation, slope and geology. Water quality is regularly monitored by Forestry Tasmania to ensure streams and creeks maintain a healthy aquatic ecosystem. This research was conducted to investigate the source of natural elevated concentrations of colour, turbidity and associated nutrients observed in the pristine forested catchment of Warra Creek. A second catchment, Crystal Creek, was also studied and the comparison between the two creeks was used to help understand the natural variations. The primary objective of this study was to conduct a review of the naturally occurring environmental variables that affect water quality; and to evaluate the sources and ranges of concentrations of physical and chemical constituents expected in Tasmania waterways. A second objective was to investigate the reasons behind differences in water quality between the two pristine forested catchments; and to provide Forestry Tasmania with a range of guidelines to assess potential water degradation in the southern forest of Tasmania. Water was collected and analysed for twenty physical and chemical parameters through three sampling projects, designed to encompass the range of flow and water quality conditions experienced throughout a typical year. Samples were taken on fortnightly visits, through a snapshot sampling regime and during two storm events. Results from these three projects indicated that the source of colour and associated nutrient enrichment in Warra Creek can be attributed to the headwaters of this catchment. This area of the catchment contains organic rich soils on south facing slight slopes with large amounts of decomposing organic matter and prolonged water contact time with this organic matter. Increases in flow in both W arra and Crystal Creeks caused a significant flushing of accumulated organic material from these catchments, resulting in degraded water quality. A variety of environmental differences were discovered between the two catchments, which may explain the significant differences in water quality found, especially during periods of low flow. The implications from this study for the management of water quality by Forestry Tasmania are discussed.