Impacts of Hydrological and Biogeochemical Process Synchrony Transcend Scale

Abstract:

In portions of the circumpolar north, there are documented cases of increases in annual inorganic nitrogen loading. Confounding the explanation of this phenomenon is a lack of accompanying annual trends in streamflow, precipitation or atmospheric nitrogen deposition. Evidence from Canada’s subarctic suggests this dichotomy could be due to three key non-linearities in the predominant biogeochemical and hydrological processes. Because snowfall changes to rainfall near the zero degree air temperature isotherm, there has been an increase in late autumn rainfall across the region due to earlier passage of precipitation generating cold fronts. Runoff generation in cold regions is often a storage threshold-mediated process, and the enhanced rainfall results in more common exceedance of these thresholds and higher winter streamflow. Finally, net mineralization rates in regional lakes peak in winter following the onset of ice cover. Subtle increases in monthly rainfall at specific times of the year can permit hydro-chemical process synchrony within watersheds that enhances annual inorganic nitrogen loading, implying that the impacts of process synchrony transcend scale. The presence of shifts in nitrogen export suggests that sustained regular process synchrony can modify system states. Sound understanding of system processes and interactions across scales will be needed to properly predict impacts and make sound decisions when managing watersheds and competing resource demands.