MONITORING BIOGEOCHEMICAL CYCLES IN A LAKE IMPACTED BY INCREASING PHOSPHORUS AND HEAVY METALS

We examine nutrient and metal cycling in Green Valley Lake. Today, Green Valley Lake is a designated state fishing area, but prior to present land use, it was used as a water supply reservoir for the adjacent Green Valley Mine (operating from 1948 to 1963). Despite remediation attempts, the basin continues to be impacted by acid mine drainage (AMD) from the former coal mine. Remediation efforts have included techniques such as: levee and channel construction, adding carbonate rip-rap to the channels, and creating a low relief mound of mine waste covered by a thin lime layer, soil and a vegetative cap. Unfortunately, these efforts have not prevented AMD from entering West Little Sugar Creek, which borders the former mine to the west, and Green Valley Lake on the east. AMD continues to impact the lake and stream via groundwater and surface flow that enters the lake on the northwestern edge of the lake. Previous work with surface sediments in the lake show metal enrichment across the entire lake, and diatom analysis indicates increasing eutrophic conditions over time. This study began with a sequential phosphorus (P) extraction (SEDEX) of a sediment core (38cm) recovered in the spring 2014 on the southeastern side of the lake (39.510994°, -87.506388°) that is dominated by mineral P (46% of total) and oxide-associated P (42% of the total) at the base of the core (30-38 cm) and transitions to an average of 9% mineral P and 80% oxide-associated P at the top of the core (0-16 cm). Total P buried in the sediments is variable over short periods but relatively constant throughout the length of the core with an average concentration of 57 μmol∙g-1. Shifts in diatom species match the change in the sedimenatry distribution of the P species. Heavy metal data shows distinctly higher metal loads in the surface sediments compared to downcore. To build a more complete picture of lake biogeochemical and nutrient cycles, a second core (39cm) in the northwestern portion of the lake (39.513422°, -87.510018°) near the source of the acidic drainage into the lake system was recovered in spring 2015. The core was subdivided into 0.5 cm samples for detailed P geochemistry using (SEDEX) and metal analysis. Ongoing works aims to clarify the lake system response associated with acidic drainage by comparing the two core locations P, metal, and diatom assemblage trends.