Assessing internal and external controls on lake water quality: limitations on organic carbon-driven alkalinity generation in acidic pit lakes

Organic carbon-driven alkalinity generation in acidic pit lakes may lead to amelioration of lake pH. However, characterization of a pit lake (pH 4–5) with respect to temporal and spatial variation in state variables in the water column and inflows indicated that while the lake was a net sink for organic carbon, this carbon was either not being converted to alkalinity on a significant scale, or there were additional sources of acidity, possibly in the form of iron-rich groundwater. Internal organic carbon generation is limited by the availability of phosphorus; this limitation, together with internal carbon sinks, may be enhanced by the acidic conditions in the lake. This study has highlighted that well-constrained external mass balances, as well as assessment of integrated effects of internal geochemical, physical, and biological processes, are critical for forward prediction of water quality in pit lakes.