Stressors

Keep up-to-date about Lake Mead NRA by following us via our social media sites:

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.

Contaminants

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.

Invasive Species

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).

Quagga Mussels

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.

 
Quagga mussel monitoring in Lake Mead.
Quagga mussel monitoring in Lake Mead.

PHOTO BY NPS SUBMERGED RESOURCES CENTER

 

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.

  • Giant Reed (Arundo donax)
  • Hydrilla (Hydrilla verticillata)
  • Eurasian Water Millfoil and Parrotfeather (Myriophyllum sp.)
  • Alligator Weed (Alternanthera philoxeroides)
  • Curly Leaf Pondweed (Potamogeton crispus)
  • Giant Salvinia (Salvinia molesta)

Climate Change

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.

References


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:


  • A healthy sport fishery
  • Healthy populations of native fish
  • Healthy populations of aquatic dependent wildlife
  • Healthy shoreline dependent native vegetation
  • A high quality setting for water-based recreation
  • Regional and community needs met for municipal and industrial uses, including domestic water supply and Colorado River System return flow credits

Management questions best answered by monitoring:

  • What are the status and trends of contaminants in the water column [e.g., disinfection byproduct precursors, VOCs, radionuclides, priority pollutants (EPA and State), and pathogens]? more

  • What contaminants are present in native and non-native fish tissues and to what extent is fish health impaired? Which contaminants, if any, pose a risk to the public (i.e., human health)? more
    See also Category 2. Fish and Aquatic Biota.

  • How effective are the new Las Vegas Wash wetlands in keeping contaminants out of Las Vegas Bay? more
    See also Category 4. Sediment.
  • What is the status and trend of re-suspension and transport of contaminants and nutrients from sediments? more
    See also Category 4. Sediment.

  • What are the status and trends of contaminants in sediments? more
    See also Category 4. Sediment.

  • What is the effect of dredging or other maintenance activities on contaminant release from sediment? more
    See also Category 4. Sediment.

  • What contaminants are present in aquatic dependant bird tissues, such as eggs? more
    See also Category 5. Birds.

  • What amount and type of contaminants are in aquatic dependant bird food sources? more
    See also Category 5. Birds.

  • What are the trends in aquatic invasive species (e.g., quagga mussel, Asiatic clam, New Zealand mudsnail) abundance and distribution? more

  • What are the trends in invasive species of aquatic plant (e.g., giant reed, hydrilla, Eurasian water milfoil, and giant salvinia) abundance and distribution? more

  • What are the impacts of invasive species on nutrients? more
    See also Category 2. Fish and Aquatic Biota.

  • What is the difference between historic lake levels and predicted lake levels due to climate change? more
  • What is the relationship of flows to lake levels? How does climate change relate to water availability? more

  • Are lake surface water temperatures changing as a result of climate change? more

  • What impacts are brought about by changes to waste water delivery systems to Boulder Basin? more

Management questions best answered by research:

  • What are the mass transport and internal cycling budgets for contaminants? more
    See also Category 1. Water Quality and Limnology.

  • To what extent are endocrine disruptors or hormonally active agents (contaminants) interfering with fish health and reproduction? more
    See also Category 2. Fish and Aquatic Biota.

  • How do sediments serve as nutrient and contaminant traps or sinks and how do they affect productivity more
    (see also Category 4. Sediment)? more

  • How do sediments and contaminants interact with the food web? more
    See also Category 4. Sediment.

  • What is the relationship between sediment accumulation and contaminant accumulation? What is the fate and transport of contaminants? Is there a subsurface barrier? more
    See also Category 4.
    Sediment.

  • What are the best management practices and treatment methods to deal with invasive species to sustain the biodiversity and function of the Lake Mead/Lake Mohave ecosystems? more

  • What is the life history of a selected invasive species under the environmental conditions of Lakes Mead and Mohave? more

  • What are impacts/potential impacts of aquatic invasive species on water quality related to drinking water and recreation? more

  • What are the impacts/potential impacts of invasive species on the Lake Mead and Mohave ecosystems, especially to fish and other aquatic living resources? more

  • What are impacts/potential impacts of climate change on water quality related to drinking water and recreation? more

  • What are the impacts/potential impacts of climate change on the Lake Mead and Lake Mohave ecosystems, especially to fish, other aquatic living resources, and birds? more

  • How are the inputs of metals changed over time and place by climate change? more
    See also Category 4. Sediment.

  • What food-web dynamics are in place in Lakes Mead and Mohave? How are these dynamics being altered by drought, contaminants, invasive species, climate change, and other emerging threats? more

  • - and - Are upper trophic levels being adequately maintained to support robust wildlife populations? more
    See also Category 2. Fish and Aquatic Biota and Category 5. Birds.

  • Can stressors impact water quality, water security, and water delivery systems in such a way that response actions are required that affect ecosystem components? more
 

Last updated: February 28, 2015

Contact the Park

Mailing Address:

601 Nevada Way
Boulder City, NV 89005

Phone:

(702) 293-8990

Contact Us