Using models to predict, understand and communicate changing water quality: some examples using dissolved organic carbon in freshwaters

Models can be used to predict what may happen, to understand causal relationships and to communicate uncertainties and possible future courses of action. As part of my research, I develop and use conceptual water quality models – software containing mathematical representations of the processes believed to control water chemistry - to predict when good or poor water quality will be seen in lakes and rivers; to understand why water quality may be changing and to communicate both the possible effects of a changing climate on future water quality and the gaps in our present-day knowledge.

Dissolved organic carbon (DOC) plays an important role in the water quality of lakes, streams and rivers. It is produced through the decomposition of plant material in soils and surface waters. High concentrations of DOC give many northern waters their characteristic "tea-stained" colour. Changing DOC concentrations have the potential to affect a number of societally important environmental issues including surface water acidity, eutrophication, contaminant transport and toxicity, and drinking water supply.

Increasing surface water DOC concentrations pose a threat to drinking water supply and are changing ecosystem function in many parts of the northern hemisphere. The reasons for this increase are complex, but are believed to be related primarily to declines in atmospheric acid deposition and the effects of a changing climate on temperature and river flows.

Conceptual models which incorporate the effects of changing climate, flow regimes, acid deposition and rates of plant material breakdown on surface water DOC concentrations are needed to predict current and future water quality. Such models also give us the ability to better understand the factors causing present day environmental conditions. This understanding is vital if we are to have confidence in our predictions as to what may happen in the future, and what mitigation options may be appropriate.

I will present examples of the work I am doing at well-studied sites in Sweden and elsewhere. The examples presented will show how the use of conceptual water quality models can lead to new insights and understanding about the relative importance of different controls on DOC in lakes and rivers, how this understanding can help to predict the possible effects of a changing climate on surface water DOC, and how these predictions can be used to communicate and manage an uncertain future.

/Martyn Futter