Intra- and inter-annual changes in chemistry of Australian glacial lakes

Abstract

The chemical characteristics of five seasonally ice-covered lakes in the Snowy Mountains were measured monthly from 2006 to 2009. Although N and P concentrations were significantly higher in rainfall than snowfall, concentrations peaked in lakes in winter rather than summer. This was linked to continuous winter nutrient flow into the lakes from melting snowpack and continued biogeochemical processes in unfrozen soil at a time when biological activity beneath the lake ice was depressed. In contrast to high altitude lakes elsewhere, there was no spring ionic pulse of nutrients. Lake pH fluctuated throughout the ice-free period between 6.9 and 6.5, falling to 6.1–6.0 beneath ice cover, before rising abruptly after ice break-up. Earlier ice break-up in recent years has resulted in an earlier increase in pH, and decrease in concentrations of NH3-N and NOx-N. In years with least snowfall and early ice break-up, winter peaks of NH3-N were lowest whereas both PO4-P and NOx-N showed winter peaks of various concentrations in medium years rather than extreme years. Rising winter and/or spring temperatures resulting in changes in precipitation from snow to rain could lead to increased nutrient deposition, with rain carrying an order of magnitude more nutrients than does snow.