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.