Proposal to Determine Inter-Annual and Intra-Annual Population Dynamics of Soft Sediments Dwelling D. Bugensis in Boulder Basin, Las Vegas Bay and Overton Arm, Lake Mead

Affiliation(s)PIProject periodFunded by
DHS Acharya, Kumud 12/10/2010 - 01/30/2012 DOI - National Park Service

Project Description

Dreissenid mussel invasions have caused large-scale economic and ecological damage to water bodies in the eastern United States. Recently these invasions have threatened the function of impoundments, electricity generation, and water conveyance structures along the Colorado River Aqueduct. Lake Mead is the largest reservoir by water volume in the United States, and is the main source for drinking and irrigation water for the Las Vegas Valley and other lower Colorado River states (Arizona, California and Nevada) (LaBounty and Burns 2005). The reservoir is a popular site for recreational boaters and anglers because of its large size and a variety of sport fish including rainbow trout (Oncorhynchus mykiss), various catfish species, and striped bass (Morone saxitilis). In Lake Mead, the striped bass and presumably the smaller populations of the endangered Razorback sucker (Xyrauchen texanus) are driven primarily from benthic resources (Umek et al., unpublished; U.S. Fish and Wildlife Service 1998). Thus, alterations to the benthic ecology will likely impact fisheries in the lake. However, quantifying those impacts can only be tracked if we understand the quagga mussel (D. bugensis ) population structure, potential for reproduction, and benthic invertebrate shifts (community and abundance) post invasion, along with diet shifts to higher order consumers. The basins of Lake Mead offer a variety of ecosystems with different environmental parameters in which D. bugensis may persist and proliferate. Las Vegas Bay has higher average temperatures and is more eutrophic than deeper, cooler areas of the reservoir, such as Overton Arm and other areas of Boulder Basin (LaBounty and Burns 2005). Moreover, Las Vegas Bay is exposed to seep and tributary influenced inflow and diurnal wastewater discharge inflow fluctuations from Las Vegas Wash, which can have impacts on water quality delivery to the bay. For other basins (i.e. Boulder basin), variation in the Colorado River inflow contribute to stratification depth. When the lake is thermally stratified, the Colorado River inflow is introduced to the metalimnion, and when the lake is mixed, inflow enters the hypolimnion. Depending on this variable inflow, water temperature, oxygen and nutrient levels may vary. Production at different lake strata is currently more variable than prior to the development of impoundments upstream (Paulsen and Baker 1981). Thus, internal nutrient cycling and advection with connectivity to Las Vegas Bay can control productivity. Due to the nature of the canyons prior to filling and loading from the Colorado and other riverine inputs, Lake Mead also contains a combination of hard (pre-impoundment surfaces, rocks, dams, marinas, etc.) and soft substrates that are dominated by very-fine silt to clay sediment particles (Twichell et al. 2005), both of which contain established populations of adult D. bugensis. In an effort to understand the emerging issues our Science Team has been working with the Interagency Quagga Working Group, to address current and future mussel impacts to existing infrastructure and ecology of the lake. In the last 2 years we have quantified the benthic ecology of 3 basins to quantify the distributions of sediment dwelling benthic invertebrates including D. bugensis by depth and size class distribution within each basin along with their potential for reproduction at different depths. We also collected baseline food web structure from two of the basins prior to the widespread invasion to determine the reliance of fishes on benthic resources and specific taxa. At the same, we are also involved in studying ecological traits of D. bugensis through a series of laboratory experiments and analyses, providing information both for comparison with mussels in other locations, as well as for limnologic management decisions in Lake Mead.