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Long-term Limnological and Aquatic Resource Monitoring for Lakes Mead and Mohave Category 3:
Significant alterations to the environment and community structure by abiotic and biotic stressors (i.e., contaminants, invasive species, and/or climate changes) could affect food webs and dynamics within Lakes Mead and Mohave and thereby cause profound ecosystem changes. Contaminants, invasive species, and climate change are discussed in further detail below.
Water quality in Lake Mead, particularly Las Vegas Bay, is affected by point and non-point sources emanating from Las Vegas Wash, an urban perennial stream that receives more than 175 million gallons per day of treated effluent from three wastewater treatment plants in Henderson, Las Vegas, and Clark County, Nevada. In addition, historic military and commercial industrial complexes located near the Wash have contributed known contaminants such as perchlorate, dichlorodiphenyltrichloroethane (DDT), and polychlorinated biphenyls (PCBs). Runoff and ground-water seepage from urban irrigation in Las Vegas also contribute organic contaminants (e.g., bacteria, oil, grease, pesticides, herbicides, nutrients from fertilizers) and metals to the Wash. Perchlorate has been detected in Lake Mead and downstream of the outlet from Hoover Dam in Lake Mohave in the area of Willow Beach. In addition, drought conditions in the region have lowered lake levels more than 100 ft, which may concentrate contaminants in some locations. Specific monitoring and research questions appear in other categories as appropriate, and are repeated within this section.
The spread of invasive species is recognized as one of the major factors contributing to ecosystem change and instability throughout the world. An invasive species is "a non-native species whose introduction does, or is likely to cause, economic or environmental harm or harm to human, animal, or plant health" (Executive Order 13112, 1999).
Adult quagga mussels (Dreissena bugensis) were detected in Lake Mead in January 2007; they subsequently spread throughout both Lakes Mead and Mohave. This invasive species has the potential to cause millions of dollars of damage by clogging engines and encrusting boats and facilities, disrupting the food chain, disrupting sport fishing, and littering beaches of Lakes Mead and Mohave. Following invasion, NPS developed a Lake Mead NRA Quagga Mussel Response Plan and an Interagency Management Action Plan (I-MAP) for Quagga Mussels with its partners. This document focuses monitoring of adults, juveniles, and veligers. Adults are monitored at 56 selected sampling stations locations that correspond to sub-surface rocky, sandy, and muddy areas. Veligers are monitored at 42 sampling sites. Monitoring intervals are described within the I-MAP.
Potential Noxious Aquatic Plant Invaders
The introduction of invasive plant species to United States water bodies has been escalating with widespread destructive consequences. Invasive plants are associated with significant habitat destruction, loss of animal communities, reduced fishing and water recreation opportunities, and large mitigation expenditures. Some potential aquatic plant invaders to Lakes Mead and Mohave include the following species listed below.
Colorado River water originates as spring thaws of snowpack in the Rocky Mountains; changes to snow processes in the Rockies will affect all reservoirs along the Colorado, including Lakes Mead and Mohave. Warmer temperatures may create significant water supply shortages in the Colorado River. "A warming climate is, in general, expected to increase water temperatures and modify regional patterns of precipitation, and these changes can have direct effects on water quality (Lettenmaier 2008)." Impacts to Lakes Mead and Mohave ecosystems would likely result from changes in water quantity within the Colorado River system, which would, in turn, correspond to higher probabilities of lowering lake levels, increases in surface water temperatures resulting in changes in plankton/biota and lake mixing, potential increases in urban runoff from increased probability of flash floods, and changes to shoreline vegetation and animal resources.
Lettenmaier, D., D. Major, L. Poff, and S. Running. 2008. Water Resources. In: The effects of climate change on agriculture, land resources, water resources, and biodiversity in the United States. A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. Washington, DC., USA.
Strategic fundamental objectives for this category:
Management questions best answered by monitoring:
Management questions best answered by research:
Last updated: February 28, 2015