Variations in Export of Nitrate and Other Solutes Across Lithologies and Land Uses in a Huc 10 Watershed Within the Susquehanna River Basin

Elaine Langone Center, Terrace Room

From catchment to watershed scale, the critical zone community is asking the question of what to measure—and where to measure it—to constrain models and make informed observations about critical zone processes. One of the primary goals of the Susquehanna Shale Hills Critical Zone Observatory (SSHCZO) is to scale-up hydrologic models from the catchment scale at Shale Hills (0.08 km2), Garner Run (1.21 km2), and Cole Farm (0.43 km2) catchments to the larger watershed scale of Shavers Creek watershed (~120 km2). The increase in drainage area of three orders of magnitude introduces a challenge of increased spatial heterogeneity in lithology, relief, and land use. Shavers Creek is an upland watershed within the Susquehanna River Basin (SRB) that drains a variety of lithologies and is overlain by both agricultural and forested land uses. To address the challenge of spatial heterogeneity in Shavers Creek, several synoptic sampling campaigns have been performed to develop datasets of solute fluxes at high spatial resolution in Shavers Creek. In addition, three monolithologic subcatchments have been monitored in regions of homogeneous land use. These data sets include hydrologic data collected from both forested (Shale Hills and Garner Run) and agricultural lands (Cole Farm). Using Cole Farm as a proxy for agricultural land use in Shavers Creek provides insight into groundwater quality in the agriculturally developed portion of the uplands of the SRB. Synoptic sampling data sets were collected during periods of both high and low hydrologic connectivity within the watershed. These data sets, combined with long term data from the SSHCZO subcatchments, show that the surface and ground water sources appear to have geochemical homogeneity during wet periods, but during dry periods, the various stream sites in Shavers Creek and its major tributaries become geochemically distinct, instead reflecting the solute signatures associated with local land uses and lithologies. This geochemical homogenization that occurs during wet periods is observed via principal component analysis which shows that stream water chemistry in Shavers Creek clusters together, close to the values associated with headwaters and precipitation.