Cross site synthesis of stream chemistry: long term trends and effects of disturbances
USFS and LTER researchers have studied stream hydrology and solute chemistry in disturbed and undisturbed watersheds at 11 Experimental Forests across the country for decades. These headwater streams provide high quality water as one of their important ecosystem services. Changes in land use land cover, as well as natural processes and disturbances, affect water quality in these streams.
Our objectives are to synthesize trends in water quality for reference basins and examine stream nutrient responses to disturbance regimes. We are also examining the long term data to inform EPA Nutrient Criteria across regions.
We are asking the following questions:
- Are there long-term trends in stream nitrogen concentrations at forested reference basins, given changes in discharge and atmospheric deposition over time?
- Is there more variation in trends among EFR sites than among basins within an EFR?
- How do the short and long-term responses of stream nutrients to forest harvest and disturbances vary across North America?
- Are responses to various types of disturbances similar?
- What biotic and abiotic factors explain the variation in responses (magnitude and timing) of stream solutes to forest disturbances?
These sites exist across gradients of precipitation, atmospheric nitrogen deposition, nutrient limitation, vegetation, and soil types. Preliminary results show that trends in reference basins vary with length of record used, and that adjacent basins within a site do not necessarily show similar responses. Comparison of responses to natural disturbances, such as hurricane, fire, insect outbreak, and forest management, indicate that following disturbance, all sites show increased stream nitrate concentrations. The magnitude and longevity of nutrient responses to disturbances varies within and among ecoregions. (See AGU 2008 Poster) Following forest harvest, concentrations of stream solutes have increased in some watersheds, but not others. Response times also vary; some sites respond immediately, while other responses are lagged. Changes in nutrient fluxes highlight the role of vegetation as a primary influence on nutrient cycling and the importance of watershed disturbances on instream biotic communities.
For more information or to contact us, visit: http://www.fsl.orst.edu/efr/