Yellagonga Regional Park wetlands water quality monitoring 2017/18 report

Abstract

After a pilot study in 2010, which investigated the distribution of metals and nutrients within the Yellagonga Wetlands, a regular monitoring program was established. This monitoring program is also part of the Yellagonga Integrated Catchment Management plan. This monitoring program was extended to cover groundwater in 2013. Monitoring for both surface and groundwater is conducted and reported on annually. Monitoring programs have been refined over the years, with sites removed and added. A review of the monitoring data was undertaken in 2016. Ten groundwater bores were sampled in 2017/18 every two months and surface water quality was sampled at 11 sites monthly June to October, December and in April. A range of physico-chemical measurements, metals and nutrients are measured. Although in previous years, ground and surface waters have been reported separately, this year the reports for 2017/18 have been combined. The bores on the western side of the park show an increase in conductivity and related parameters in late summer, following evapo-concentration of solutes in the lakes. High concentrations of P and N were recorded in a number of the eastern bores (particularly Mid E Joondalup), suggesting groundwater is an important source of nutrients into the northern end of Lake Joondalup. All parameters recorded were compared to the ANZECC & ARMCANZ (2000) national water quality trigger values for the 95% protection of aquatic ecosystems. In 2017/2018 water quality was improved compared to previous years with only limited exceedances of guideline concentrations over slightly fewer elements (Al, As, and Zn). It appeared that groundwater was a major source of Al and Zn identified in the wetlands. Sulphate to chloride and sulphate to alkalinity ratios suggest that there are acid sulphate soils within the catchment, but that natural buffering within the system is preventing low pH and high metal concentrations. The presence of acidification is also evident in the eastern bores. There is clear evidence of an ongoing trend of lower pH across the entire system as recently reported in DOW monitoring. Key recommendations from the study are: a. to continue monitoring at the current frequency as this appears to be striking a balance between detail and cost. b. consideration of expanding or modifying the suite of metals/metalloids measured to better target potentially problematic elements. c. development of nutrient/water budgets for both Lakes Joondalup and Goollelal to better understand key sources of enrichment would assist with better targeting of management efforts to limit algal blooms. This is likely a focus of the Smart Cities project. d. acid sulphate soils remains an ongoing issue and further work to locate major sources would aid in their management. e. tracing the source of P in the drain between sites 4 and 6, as there are very high concentrations recorded on occasion. f. a new bore is proposed for the eastern side of Lake Goollelal to assist in identificationon nutrients entering the lak