This article is part of the Fall 2022 issue of the Earth Science Matters Newsletter.
Sleepers River Research Watershed and the Value of Long-term Datasets: Scientific insights and opportunities to support the next generation of scientists
Sleepers River Research Watershed was established in 1958 as an Agricultural Research Service watershed, to understand hydrology in the glaciated New England landscape. The template for the research at Sleepers River is the small watershed approach, where study in a small area simplifies hydrologic process understanding. This approach was pioneered at nearby, well-known, Hubbard Brook Experimental Forest in New Hampshire, where the watershed is the test subject used to explore underlying hydrologic processes.
The U.S. Geological Survey began operations at Sleepers River in 1991, continuing prior research on streamflow generation processes and snow hydrology, using new chemical and isotopic approaches (Shanley et al., 2002; 2015). We added to a rich legacy of hydrologic research with biogeochemical process research, aiming to understand how climatic warming and extreme events affected carbon and nutrient cycling. Further, we recently published chemical and physical data in two comprehensive data releases (Shanley et al., 2021; Matt et al., 2021), and described these and other data releases, such as the 60-year snow record and 35-year ground frost depth record, in a recent data note (Shanley et al., 2022).
The long-term datasets allow assessment of climatic influences on the ecosystem by comparing chemical response in wet and dry, or warm and cold years as proxies for future climate. These kinds of long-term records on snow and streamflow are valuable to assess the magnitude and direction of climatic change and its effects. For example, as a possible indicator of what's in store if future droughts intensify, only in the driest year of our 30-year record did groundwater levels get so low that deep subsoils were exposed to air, causing chemical oxidation that released a large pulse of sulfate to stream water for eight months.
Of note, as a way to enhance the USGS science at Sleepers River, we have also developed productive collaborations with other federal agencies and universities, which includes mentoring the next generation of scientists. Notable student-led research includes papers from the Ph.D. dissertations of Stephen Sebestyen (2009) on seasonal stream carbon and nitrate dynamics and how they are affected by climate change, and Kevin Ryan (2021) on the role of the forest canopy in aqueous carbon contributions to streamwater. Most recently, the new data releases inspired two student-led papers in Hydrological Processes (Porter et al., 2022) and Water Resources Research (Stewart et al., 2021) which capitalize on the long-term data to examine the role of the subsurface in shaping stream chemistry. Veronica Porter of Michigan Tech applied time series of groundwater and soil water chemistry to show that stream chemistry changes can be explained by the depth of water flow paths in the soil. Bryn Stewart of Penn State differentiated solutes with deep sources from those with shallow sources and linked solute dilution or increases during storms to their sources in the soil. Both authors took advantage of the uniquely high temporal and spatial resolution of these datasets to make their findings possible. Their papers were self-motivated but were iteratively shaped and directed through coordinated mentorship from their academic and USGS advisors.