Vital Signs: Water

Surface Water Chemistry

Under the Clean Water Act, each state is required to conduct water quality surveys to determine the overall health of the waters of the state, including whether or not designated uses are being met. When impaired water bodies are identified, they are included in lists for ranking of priority sites and Total Maximum Daily Load (TMDL) development in order to limit discharges of specific pollutants to that water body. LAME is the only network park that contains waters designated as impaired. The Las Vegas Wash carries approximately 160 million gallons of treated sewage effluent and contaminated groundwater into Lake Mead each day. Effluent may also contain high levels of ammonia, nitrates, nitrites, and other nutrients. The addition of nutrients alters the productivity of aquatic plants and is a primary contributor to lake eutrophication. Significant levels of contaminants accumulated in organisms can lead to stress, illness, neurologic disorders, and/or death of aquatic biota.

Monitoring Questions:

1. How is water quality in selected water bodies changing over time?
2. What are the trends in input of nutrients, pollutants, sediments, etc. into lakes, streams, springs, and caves?
3. Is level of compliance with national drinking water standards changing over time?

Surface Water Dynamics

Water is the lifeblood of the desert. Infrequent precipitation and long periods of drought are defining characteristics of the Mojave and Sonoran Deserts, and water availability is the primary factor limiting plant productivity. Surface waters are fed by groundwater and surface run-off. Change in groundwater flow systems, climate change, and climate variability may have significant impacts on the availability of surface water. Pressures on groundwater resources in California and Nevada are expected to increase into the future, posing significant future threats to surface water availability in network parks. Hydrologic changes are of concern in relation to stream/spring high and low flows, impacts to special status species, impacts to recreational users, and impacts to drinking water resources for Las Vegas and surrounding areas.

Monitoring Questions:

1. How is water volume/lake level changing over time?
2. How is stream discharge and/or the timing of stream discharge changing over time?
3. How do aquatic and riparian communities respond to changes in surface water conditions (quality and quantity) over time?

Groundwater Dynamics and Chemistry

Increasing groundwater withdrawal is considered a significant ecosystem stressor within the MOJN. An understanding of water table levels, ground water flow paths, and the connection between groundwater and surface water resources is required for predicting the effects of natural and human-induced hydrological changes and the fate of contaminants. Precipitation events slowly recharge desert basin aquifers, and this recharge feeds scattered springs and wetland habitats. The chemical constituents of groundwater relate to groundwater source, age, and movement. Groundwater chemistry can provide information on changes in groundwater flow paths because the chemical signature of groundwater changes as it flows through different types of rock.

Monitoring Questions:

1. How is groundwater withdrawal in and around network parks changing over time?
2. What are the trends in groundwater quality across network parks and regionally?
3. How do biotic communities respond to changes in groundwater conditions over time?