Paper No. 9
Presentation Time: 11:00 AM
USING LEGACY SEDIMENT DEPOSITS TO "QUANTIFY" URBAN NUTRIENT AND TRACE METAL CONTRIBUTIONS TO STREAMS WITHIN A DOMINANTLY AGRICULTURAL LAND-USE REGION, CUMBERLAND COUNTY, PENNSYLVANIA
Legacy sediments are the result of sequestration of sediment runoff behind thousands of mill dams built on many streams in the eastern US from the late 17th to the early 19th centuries. Previous studies of legacy sediment chemostratigraphy and land-use relationships (Niemitz and others, 2013) have shown little temporal change in major, trace and nutrient element chemostratigraphy in forested regions of Cumberland County, PA. In agricultural land-use regions, the increase in nutrient and trace metal elements over pre-legacy sediment concentrations is 4 to 6 times greater than the forested land-use deposits suggesting sources from fertilizer and other soil amendments, and atmospheric deposition of Pb from gasoline. Here we examine the anthropogenic contributions for the third land-use component, urban inputs. Two known legacy sediment sites on the Letort Spring Run were chosen to determine the input of nutrient and trace metal elements from the rural town of Carlisle, PA. Neither site has an intact dam. The upper site (Letort Park) is upstream of one storm drain for Carlisle and thus represents only inputs from agricultural land-use. The lower site (Jacob's Rest) is downstream from the town and should represent agricultural land-use sediments once impounded at Letort Park plus all runoff from urban land-use. The absolute difference is inferred to be the chemical trends of urban land-use inputs over time. Preliminary results at the two sites compared to composite background soil chemistry show no difference in P/Al ratios with absolute concentrations higher than background by a factor of two. Zn/Al, Cu/Al, and Pb/Al ratios are all slightly enriched at Letort Park consistent with agricultural land-use but highly enriched (3-15 times) over background at Jacob’s Rest suggesting significant inputs of metals possibly in the forms of street debris, industrial fallout, leaded gasoline residue and leaded paint from older houses.