Geoecological evolution of New Zealand's only inland salt lake

The Sutton Salt Lake is a rare occurrence of an inland evaporative saline lake on a small landmass with a temperate maritime climate. The lake lies on a bed of impermeable loess silt in a 2 ha depression between tor ridges of Otago Schist in inland east Otago. A rim of salt-tolerant plants (halophytes) occurs around parts of the lake margin. The vegetated lake margin has encroached laterally on to the lake bed by 5-30 m over the past 50 years. Salinity in the lake is dominated by Na and Cl (molar ratio similar to 1) that has been concentrated by annual cycles of evaporation and replenishment by rain with marine aerosols. Drying lake margin sediments lose NaCl via rain-driven recycling back into the lake, with the formation of a salt crust that contains Ca, Mg and Na carbonate minerals, gypsum, and remnant halite. The lake and lake sediment chemistry are affected by carbonate dissolution and deposition, and more than 10-fold Ca-Mg carbonate supersaturation in lake waters contributes to elevated water pH (8.9-9.3). Geoecological evolution of the lake margin involves the encroachment of exotic weeds behind active halophytic habitats as dilute surface water lowers salinity.