Baseline water quality survey : Joshua Tree National Park

Larson, G; Stonum, S; Mcintire, C; Herrmann, R

Joshua Tree National Park (JOTR) is located in the Transverse Mountain Range of the California Desert. Water is one of the scarcest resources in JOTR. Annual precipitation ranges from 8.4 cm (2.4 in) in the south part of the Park to 18.0 cm (5.1 in) in Lost Horse Valley in the central portion of the park. The quantity of water at most surface water sources at JOTR is small. Many springs are ephemeral and some remain dry for years at a time. Little historic information exists about the basic water quality of the water resources of JOTR. The objectives of this baseline water quality survey include mapping of all water sources in the park, documentation of the basic water quality of selected water resources, documentation of possible changes in the depth to ground water at selected drilled wells at the Oasis of Mara, and establishment of a longterm water quality monitoring program. A total of 266 aquatic ecosystems were identified in the park. These included 46 drilled and 49 dug wells, 32 developed (disturbed) and 54 natural tanks, and 29 developed and 56 natural springs. The results of this study of 37 aquatic sites indicated that there was considerable diversity among six types of water resources at JOTR relative to water quality. In general, natural tanks had higher pH values and concentrations of dissolved oxygen and lower alkalinity than did the other habitat types. Reservoirs tended to have the highest water temperatures and some natural springs had the lowest temperatures. Water temperatures had a positive correlation with air temperature. Although small in sample size, a reservoir had the highest turbidity and concentrations of total Kjeldahl-N and total phosphorus relative to the values in four springs and one tank. Springs had much higher concentrations of sulfate-S than did water samples from the tank and reservoir. The depth to ground water appeared to be increasing at six drilled wells at the Oasis of Mara. Long-term water quality monitoring was recommended at selected sites throughout the park. This project should include basic water quality measurements and concentrations of nitrogen, phosphorus, and sulfate-S. For springs, it also was recommended that the wetted surface perimeter, distance of surface flow, and the amount of flow should be recorded. Temporal variation in the volumes of tanks also should be recorded. Park staff was encouraged to seek the advice and assistance of local, state, and federal agencies to interpret its water quality data and to assess the importance of the data to the management of the Mojave Desert.

Baseline water quality survey : Joshua Tree National Park

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