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Understanding the impacts of silvicultural activities on downstream sediment export and ecosystem function via experimental sediment additions
Proceedings of the 2022 Mississippi Water Resources Conference
Year: 2022 Authors: Kohler L.D., Speir S.L., Atkinson C.L.
Increased sediment export in streams has significant downstream impacts, decreasing water clarity, negatively impacting aquatic organisms, and increasing the export of sediment-bound nutrients. However, the construction of forest roads and other silvicultural activities are considered "non-point sources" of pollution under the Clean Water Act. This "silvicultural exemption" allows forestry companies to directly dispose of dredged material into streams without permits. Thus, it is critical to determine the impacts of dredged material on sediment dynamics in streams. Here, we quantified the impacts of sediment discharge on stream ecosystem function using a Before-After Control-Impact (BACI) design. We simulated a sediment discharge event in our impact stream reach, then measured stream turbidity, total suspended solids, and phosphorus concentrations in both the control and impact reaches; this was repeated twice to capture both low- and high-flow conditions. We also deployed dissolved oxygen sensors at the top and bottom of each reach to estimate stream metabolism. Preliminary results indicate that increased turbidity, associated with the disposal of dredged material, results in decreased light penetration in the water column and reduces in-stream primary productivity. Our study will shed light on the impacts of forestry-related sediment disposal on both in-stream function and sensitive downstream systems that can inform forestry best management practices and legislation.