Linking water, carbon, and nitrogen cycles in seasonally snow-covered catchments under changing land resource conditions

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Changes in snowpack accumulation, distribution, and melt in high-elevation catchments are likely to have important impacts on water, carbon, and nitrogen cycles, which are tightly coupled through exchanges of energy and biogeochemical compounds between atmospheric, terrestrial, and aquatic environments.  Our research helps to better understand how changes in climate will affect water availability, carbon and nitrogen cycles, and land resources in seasonally snow-covered catchments.  The geographic scope of this project is a suite of high-elevation, extensive and intensive basins in the western U.S.  This study includes three major components, including observation of drivers and responses, targeted field studies (experiments) to test hypotheses, and numerical modeling to predict future changes in water, carbon, and nitrogen cycling.

Statement of Problem:

Like the polar regions, high-elevation ecosystems are particularly sensitive to changes in climate.  Changes in snowpack accumulation, distribution, and melt in high-elevation catchments are likely to have important impacts on water, carbon (C), and nitrogen (N) cycles, which are tightly coupled through exchanges of energy and biogeochemical compounds between atmospheric, terrestrial, and aquatic environments.  Earlier snowmelt may lead to lower peak streamflow and a longer summer dry season with increased drought stress and fire risk, as well as changes in the magnitude and timing of carbon and nitrogen fluxes within and between terrestrial and aquatic environments.  Interactions between water, carbon, and nitrogen cycles are complex, but an improved understanding of their linkages is essential for predicting how ecosystems will respond to future changes in climate.

Traditionally, watershed scientists have measured fluxes of energy, water, and biogeochemical compounds within and between watershed compartments to track how these systems respond to stressors, such as climate variability or atmospheric pollution.  This approach has provided key insights into ecosystem functioning, but a more holistic approach using a combination of observations, experiments, and numerical modeling is required to predict how ecosystems may respond to stressors in the future.  It is also necessary to move beyond small research watersheds, and apply the techniques and insights developed there to other locations to determine how applicable they are at regional and national scale.

                                                                 

Why this Research is Important

This research uses an interdisciplinary and collaborative approach to address key goals of the USGS Climate and Land Use Change Science Strategy and USGS Science Plan by providing information on (1) hydrologic and biogeochemical responses to climate variability and trends, (2) rates, amounts, and forms of water, carbon, and nitrogen transferred among terrestrial and aquatic ecosystems and the atmosphere, and how they may change in the future, and (3)  hydrologic and biogeochemical processes that govern how water, carbon, and nitrogen cycles respond to climate change.  This study also supports the Department of the Interior by providing information that informs the national biological carbon assessment (LandCarbon), and that can help guide management of natural resources on National Park Service and other federal lands.

 

Objective(s)

The primary objective of this study is to better understand how changes in climate will affect water availability, carbon and nitrogen cycles, and land resources in seasonally snow-covered catchments in the future.  Key research questions include:

  • How will changes in snowpack accumulation, distribution, and melt affect the magnitude and timing of water, carbon, and nitrogen fluxes in high-elevation streams?
  • What are the key interactions between water, carbon, and nitrogen in seasonally snow-covered catchments? 
  • What are the fundamental processes driving these interactions, and how might their relative importance change in the future?
  • How will changes in water, carbon, and nitrogen cycles affect land resources, and vice versa?

 

Methods:

Measurements at the extensive sites consist of continuous streamflow and water temperature, and weekly to bi-monthly water chemistry collected in collaboration with the USGS stream water-quality reference network.  The intensive sites are in Rocky Mountain National Park (RMNP) and include the Loch Vale research watershed, where measurements include meteorological variables, atmospheric deposition, streamflow, stream chemistry, soil chemistry, soil moisture, and soil temperature.

Meteorological variables will be used to calculate snowpack energy balance and examine how snowmelt and streamflow respond to energy inputs.  Atmospheric deposition measurements will be used to quantify inputs of aeolian dust and nitrogen, which are driving variables in snowpack energy balance and nitrogen cycles, respectively.  Streamflow and aquatic carbon and nitrogen chemistry will be measured to document seasonal variations and interannual differences that may occur during low, medium, and high snow years.  Data from the intensive and extensive sites will be combined to examine how regional differences in landscape characteristics (e.g., topography, soils, geology, and vegetation) affect hydrochemical responses to climatic drivers.