|
Warra creek during a spate event; water coloured by humic acids from organic soils in the catchment. |
Image: Sven Meyer |
|
Warra creek during low summer flow; water coloured by algae associated with the relatively high nutrient status of the creek under these conditions. |
Image: Sven Meyer |
|
Project summary:
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.
This research was designed to investigate the source of naturally high concentrations of colour, turbidity and associated nutrients observed in the pristine forested catchment of Warra and Crystal Creeks. The results allow for comparison between the two creeks and 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 source 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, thirdly, to provide Forestry Tasmania with a range of guidelines to assess potential water degradation in the southern forest of Tasmania.
Results 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 Warra 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. There are implications from this study for the management of water quality by Forestry Tasmania.
Methodology: Water was collected and analysed at the two creeks for colour, turbidity and associated nutrients and for twenty physical and chemical parameters through three sampling procedures, designed to encompass the range of flow and water quality conditions experienced throughout a typical year. Fortnightly sampling was undertaken at the base of the catchments of Warra and Crystal Creeks where measurments of turbidity, conductivity, pH and temperature were undertaken. Temperature was recorded in the field, while conductivity, pH and turbidity were recorded the following day at Forestry Tasmania’s laboratory.
Two storm events at both Warra and Crystal Creek were sampled, one in autumn and the other winter. Water was collected over a 48-hour period and all samples were analysed for turbidity, conductivity and pH. From these samples, ten were selected for analysis of the full range of parameters. The samples were collected from just prior to the storm event, through to the peak of the flow height and up to 24 hours after the event.
A snapshot sampling regime was conducted at five locations up Warra Creek and at the base of Crystal Creek. Sampling occurred during summer, winter and spring baseflow levels and in a winter highflow level (storm), all parameters were analysed. The sampling locations were designed to collect water from above and below small tributaries leading into Warra Creek.A variety of parameters, used as both general and point source indicators were selected for analysis. These parameters were selected to identify inputs into the river systems and their potential sources. They do not necessarily indicate artificial pollution sources or logging impacts, but are aimed at collecting the majority of important constituents resulting from the atmosphere, vegetation and associated biological processes, geology and associated soils. Physical indicators
Temperature
Turbidity
Electrical conductivity
pH
Apparent colour
Total dissolved solids
Total suspended solids
Nutrients
Ammonium ion
Nitrate and nitrite
Nitrite
Total nitrogen
Ortho – phosphate
Total phosphorus
Major ions
Chloride
Sulphate
Total calcium
Total potassium
Total magnesium
Total sodium
Metals
Total copper
Total iron
Total manganese
Datasets: None available.
Publications: Meyer, S. (2002). Water quality in two small forested catchments in the Warra LTER site, Tasmania: source of colour and nutrient enrichment. Masters thesis, University of Tasmania, Hobart.
|
