Water Scarcity and Not a Drop to Filter: The Effects of Water Temperature and Sediment on Unionid Freshwater Mussels
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Date
2021-11-19
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Abstract
The natural thermal and sediment regimes of freshwater systems are globally changing due to climate change, river regulation, and urban development resulting in water quality and quantity issues. Freshwater mussels are especially sensitive to increasing water temperatures and sedimentation due to their unique life history and physiology. Understanding temperature and sediment tolerances of mussels may prove critical in ensuring species persistence. However, knowledge on lethal temperatures of mussels is limited and a debate remains regarding the role sediment plays in mussel declines.
To determine the effects of elevated water temperature, I tested upper thermal tolerances of glochidia and juvenile Lampsilis bracteata (Texas Fatmucket), a species under review for protection under the U.S. Endangered Species Act, from the San Saba and Llano Rivers (central Texas). Upper thermal tolerances were evaluated from one population within each river. Mussels were acclimated to 27˚C and tested across a range of experimental temperatures (30 - 39˚C) in standard acute (24 h and 96 h) laboratory tests. The thermal thresholds for both life stages were related to in situ water temperature and discharge data using a uniform continuous above-threshold analysis. Analysis showed LT50 thresholds were not exceeded for L. bracteata within the San Saba, but LT05 thresholds were exceeded. Water temperature loggers were lost in the Llano River due to a large flood; however, samples reported by the Texas Commission on Environmental Quality show the LT05 and LT50 for both life stages were exceeded within the Llano River.
To determine the effects of sediment, I reviewed literature focused on potential impacts of suspended sediment and sedimentation on freshwater mussels. I focused my search on suspended sediment, expressed either as suspended sediment concentration (SSC) or total suspended solids (TSS), and sediment deposition and scour. I found increases in suspended solids could impact mussels by decreasing food availability, physically interfering with filter feeding and respiration, and impeding various aspects of the mussel–host relationship. I also found mussel–sediment thresholds, wherein certain concentrations of sediment caused significant declines in population performance. Findings from my study indicate increased sedimentation and water temperature negatively impact the population persistence of mussels.
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climate change, environmental flow, freshwater mussels, hydrology, thermal tolerance, Unionidae, sedimentation, population performance, North America, anthropogenic activities