Hydrochemistry and nutrient cycling in Yalgorup National Park, Western Australia

Lakes Clifton, Hayward, and Preston, Western Australia, are part of an east-west chain of 11 ground-water-fed lakes that make up the Clifton-Preston Lakeland system. Their hydrochemistries exhibit a large range in salinities (14–207 kg m −3 total dissolved solids (TDS)) both seasonally within each lake and among lakes. The chemistry of all the lake waters in the system is an NaClSO 4 brine, similar to seawater composition. However, all three lakes have less SO 4 Br, Sr, Mn, and probably Fe than seawater; the concentrations of Ca and HCO 3 vary seasonally. The variation of Ca and HCO 3 in all three lakes suggests that calcium carbonate is precipitated during the late summer and early autumn when evaporation is most intense. In the upper and lower water layers of Lake Hayward the concentrations of conservative ions such as Na, Cl, and K decrease in winter and increase in summer, indicating dilution by winter rain and concentration via evaporation in the summer. Concentrations of total Fe and Mn in the lower layer increase in winter, suggesting release from the sediments and/or decay of the benthic microbial mat on the lake floor. TIN (total inorganic nitrogen)/PO 4-P ratios and TN (total nitrogen)/PO 4-P ratios are high in all lakes, suggesting that P is the limiting nutrient in the system. Observed increases of the macroalgae Cladophora in Lake Clifton suggest that any potential increase in the PO 4 load to the lake will be taken up by the invigorated growth of these algae and may not be detected by measuring lake water PO 4 concentrations. The increased growth of Cladophora is detrimental to the health of the well-established microbialite community on the eastern shore of Lake Clifton.