By synthesizing 30 years of water flow and water quality research from one of the most well studied catchments at northern latitudes, Laudon and Sponseller take a step toward better understanding how stream chemistry is regulated across space and time.

In this work, which is based on the Krycklan Catchment Study (KCS) in northern Sweden, they show the benefit of closely coupling long-term monitoring and research programs for advancing our understanding of natural processes. Specifically, they use this approach to show how, when, and where different changes in water quality are most likely to occur within river networks. This work is urgently needed, as the pressures on water quality from ongoing changes in climate, deposition of air pollutants, and land-use transitions have never been greater.

Laudon and Sponseller demonstrate how different catchment features are responsible for regulating surface water quality at multiple scales, from processes controlled in headwaters, to the downstream mixing of water from different landscape sources, to what happens in large river systems. While this set of features is perhaps specific to the study region, similar multi-scale controls are likely to be widespread.

Resolving these scale-dependent processes is important for predicting, preventing, or mitigating environmental changes that may influence patterns of surface water chemistry within river systems. For example, this perspective is of obvious importance for preventing water quality perturbations caused by human interventions such as large scale forestry, point sources of air pollutants, and construction of new infrastructure.

Kindly contributed by Hjalmar Laudon and Ryan A. Sponseller.