Water Journal : Water Journal April 2012
catchment management water APRIL 2012 119 system. However, phosphorus levels downstream of Penrith STP remain elevated compared to many other areas in the system. Nitrogen levels have also declined at many sites throughout the river system. Exceptions to this are Sharpes Weir (downstream of West Camden STP) and Wallacia Bridge, where nitrogen levels, particularly oxidised nitrogen, appear to be increasing. Despite decreasing trends at many sites, nitrogen levels often remain above ANZECC guideline levels throughout much of the river system. Dissolved oxygen and temperature levels have largely remained steady, although slight increases in temperature are suggested at sites upstream of Wallacia Bridge. Conductivity levels appear to be increasing at the majority of monitoring sites. Although the absolute magnitude of this increase is not large and conductivity levels are still well within ANZECC guidelines, the ANZECC guidelines for conductivity in lowland rivers are quite broad (125--2200 μS/cm). This is an area that requires further consideration of the causes underlying the increasing salinity and its potential consequences for the river system. Chlorophyll-a levels have mostly declined or remained stable at most sites. Cyanobacteria cell counts have largely remained stable, although slight increases are suggested at some sites. Most recent blooms downstream of the dams have been dominated by Aphanocapsa, and not Microcystis or Anabaena, although Anabaena was the dominant species in the January 2007 bloom at Maldon Weir. Upstream of the dams Water quality is variable across the catchment as a result of geology, land use and a variety of in-stream processes. The geomorphology of the catchments has been significantly modified in many areas (e.g. by dams, weirs, stream bank and gully erosion). Based on water quality percentiles, a number of areas in the catchment can be identified where water quality remains relatively poor when compared to ANZECC guidelines (see DECCW 2010 for more details). Increasing trends in total nitrogen were suggested at a number of sites in the Upper Coxs River and in the Woronora River at The Needles. Decreasing trends in total and dissolved phosphorus were suggested in the Nattai River and Wollondilly River at Murrays Flat. Increasing trends in chlorophyll-a were suggested in the Wollondilly River at Joorilands, Lake Cordeaux (Dam Wall), Lake Avon (Upper Avon Dam Chamber) and Wingecarribee Lake. Increasing trends in conductivity were suggested at a number of sites in the Upper Coxs River sub-catchment and in the Nattai River. A decreasing trend in conductivity was suggested for the Wollondilly River at Joorilands. Trends in other water quality indicators were variable among sites. Some of these putative trends at upstream sites need to be backed up by further statistical modelling (e.g. GLM and GAM), allowing for temporal variations in flow. The influence of STPs and urban centres on water quality in catchment streams upstream of the dam is particularly noticeable. The influence of other licensed discharges on water quality can also be important in some sub-catchments. This is particularly true for conductivity and metal levels downstream of power generation and mining discharges in the Upper Coxs River sub-catchment. High algal biomass (as reflected by chlorophyll-a levels) was identified at some river sites and in a number of the dams. Some of the dams and reservoirs in the Wingecarribee, Upper Coxs River and Upper Wollondilly River sub-catchments have both high nutrient levels and high algal biomass. Persistent algal blooms often occur in Wingecarribee Reservoir. Empirical cumulative distribution functions Analysis of the long-term flow records illustrated the effects of river regulation and major river management decisions overlaid on natural climatic cycles. In 2003, in response to the extended drought, the SCA commenced water transfers from the Shoalhaven to Fitzroy Falls Reservoir and Wingecarribee Reservoir, which were then released to the Nepean or Wingecarribee River (to flow by 'run of river' -- to Lake Nepean or Lake Burragorang respectively). In June 2005, due to continuing drought conditions, the environmental flows from Warragamba Dam were halved. The effects of the reduction in environmental Figure 2. Graphical summaries and quality control (Shewhart) chart for conductivity at Wisemans Ferry (N14), identifying outlying points (circled).
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