Pacific climate modes and landform interact to control multi-decadal patterns of river nutrient concentration and transport in Washington state

Understanding the role of climate in driving river nitrogen (N) and phosphorus (P) dynamics is critical to evaluate long-term changes in aquatic ecosystem function from rivers to the coast. Climate variation, however, operates across multiple time scales, including seasonal, multi-annual, and decadal oscillations, which can obscure our understanding of long-term change. Further complicating these different modes of variability is the interaction between climate and heterogenous landscapes, which can generate varied ecosystem responses and make the sensitivity of individual rivers to climate difficult to predict. Here, we apply multivariate time series analyses to assess the role of climate in driving the long-term state (30+ years) of river inorganic N and P concentrations and yields across 15 rivers that drain the Puget Sound Basin, a spatially complex region located in western Washington State. Our findings reveal that multi-decadal changes in river N and P concentrations and yields are strongly influenced by shifts in North Pacific climate modes, particularly by the Pacific Decadal Oscillation (PDO). Moreover, we found that the response of N and P concentrations and yields to PDO shifts varied among rivers, and that a substantial proportion of this variation was explained by a simple topographic feature, mean watershed slope. These results demonstrate the strong influence of climate oscillations on long-term river nutrient patterns, while also highlighting the distinct role of watershed topography in modulating the sensitivity of river N and P dynamics to climatic change.

Primary Presenter: Elizabeth Elmstrom, University of Washington (elmstrom@uw.edu)

Authors:

Gordon Holtgrieve, University of Washington  (gholt@uw.edu)

Mark Scheuerell, University of Washington  (scheuerl@uw.edu)