The Impact of Microbial Communities on Water Quality in an Acid Mine Drainage Impacted Watershed
Abstract
Acid mine drainage (AMD) from the former Leona Heights Sulfur mine in Oakland, CA, contributes toxic levels of Cu, Cd, and Zn and elevated levels of Fe2+ and SO42- to downstream reaches of Lion Creek via Leona Creek. To investigate the extent of AMD and its relationship to microbial community structure, water samples were collected from three tributaries (two natural, and one with AMD) as well as the inlet and outlet of Lake Aliso (a reservoir downstream of the confluence of the three tributaries) beginning in July 2009. Lake Aliso was dammed in the late 1800s but since the early 1990s it has been full during the dry season and drained during the wet season, thus dramatically altering the geochemical conditions on a seasonal basis. Natural waters from Lion Creek and Horseshoe Creek tributaries dilute the water from Leona Creek, thus reducing concentrations of major ions and metals below toxic levels before water discharges into Lake Aliso. Precipitation events lead to episodes of increased mobilization of Cu and Cd in Leona Creek and produce toxic levels of these metals below the confluence with Lion Creek. Tributary mixing calculations suggest that even though Leona Creek contributes the smallest volume of water of the three tributaries, it is the main source of metals entering Lake Aliso. The input of the metal-rich AMD from Leona Creek changes the redox conditions of Lion Creek. In addition, Lake Aliso has a significant impact on water quality in the Lion Creek watershed. Observations of temperature, conductivity, pH, and dissolved oxygen in lake depth profiles indicate that Lake Aliso is stratified during the dry season when the lake is full. Based on concentration differences between the inlet and outlet of the lake, Na, Mg, SO42-, Ca, Mn, Zn, Cd, Cu and Ni are removed from the water while K, As, Pb and Fe are mobilized when Lake Aliso is full. Geochemical modeling using PhreeqcI suggests the deposition of minerals containing the metals that are being removed from the water. We hypothesize that microbes play a vital role in metal cycling in this watershed. Microbial community structure was analyzed in water samples by creating and sequencing a16S DNA clone library and using terminal restriction fragment length polymorphism (TRFLP). The sequencing and TRFLP results reveal that there are differences in microbial communities between sites. Sediment cores were also collected from Lake Aliso and used for microbial analysis to provide a longer history of metal cycling in the Lion Creek watershed. Understanding the impact of microbes on metals cycling in this watershed is significant as Lion Creek ultimately discharges into the San Francisco Bay. In addition, there are more than 200 reservoirs and 50 mine sites in the Bay Area; therefore, understanding the role of microbes in metals cycling in AMD will help with remediation efforts across the Bay Area.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.H43J1369M
- Keywords:
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- 0461 BIOGEOSCIENCES / Metals;
- 0471 BIOGEOSCIENCES / Oxidation/reduction reactions;
- 1065 GEOCHEMISTRY / Major and trace element geochemistry