Water Chemistry

Major- and trace-element concentrations in water collected from the four sites are listed in table 3. The most dilute water was from the spring that discharges from glacial deposits near upper Lehman Creek campground; whereas, water from the permanent pool in Lehman Caves had the highest concentration of dissolved minerals.

Low-level nutrient concentrations are listed in table 4. Ammonia concentrations were below detection in all four samples and the maximum concentration of total nutrient nitrogen (ammonia, nitrate, nitrite, and organic nitrogen) was from the water sample collected from the permanent pool in Lehman Caves (0.94 mg/L as N). Dissolved phosphorus and orthophosphate were uniformly low and ranged from only 0.02 mg/L as P in water from the spring near upper Lehman Creek campground and Marmot Spring (sites 3 and 4, respectively) to about 0.05 mg/L as P in water collected from the permanent pool in Lehman Caves (site 2).

Specific conductance is a simple measurement typically used to ascertain the relative ionic concentration of water. However, because natural waters contain a variety of ionic and undissociated species of widely varying concentrations, the determination may not be related simply to individual or dissolved-solids concentrations (Hem, 1985, p. 67). With this precautionary note, the relation between specific conductance and dissolved solids among the four samples is exceptional (fig. 6). Specific conductance in water samples ranged from only 36 µS/cm at 25^°C from the spring near upper Lehman Creek campground (site 3) to 440 µS/cm at 25^°C from the permanent pool in Lehman Caves. Cave Springs has higher specific conductance and dissolved solids than that of the spring near upper Lehman Creek campground and Marmot Spring but less than that from the pool in Lehman Caves.

The low specific conductance and dissolved solids of the spring near upper Lehman Creek campground and water in Lehman Creek (30–40 µS/cm at 25^ºC as reported by Elliott and others, 2006, p. 32) is within the range of snowmelt in the Sierra Nevada (Feth and others, 1964). Although the specific conductance of snowmelt at Great Basin National Park was not measured, the low specific conductance and dissolved solids of the spring and Lehman Creek indicates rapid flow through the glacial deposits and little dissolution of Prospect Mountain Quartzite.

The reason for the good correlation between specific conductance and dissolved solids is that the dominant dissolved ions in all four samples are calcium, magnesium, and bicarbonate (fig. 7) and the concentrations of dissolved ionic species increases (1) with increased residence times (Marmot Spring) and (2) contact with the Pole Canyon Limestone (Lehman Caves). Although the water in the permanent pool in Lehman Caves has dissolved solids 16 times more than that from the spring near upper Lehman Creek campground, the overall proportions of the dissolved species are nearly the same. The only marked difference is that the ratio of magnesium to calcium is 0.45 at Lehman Caves, which is nearly twice the ratio of the spring near upper Lehman Creek campground. The increase in magnesium relative to calcium in the pool at Lehman Caves compared to the other samples is caused by the chemical precipitation of calcium carbonate that forms the many types of speleothems in the caves.

Water from Marmot Spring had proportionately more chloride and fluoride than either the spring near upper Lehman Creek campground or the pool in Lehman Caves, whereas Cave Springs had proportionately more calcium and bicarbonate and less magnesium and sulfate. An increase in calcium and bicarbonate at Cave Springs can be explained by dissolution of limestone without much magnesium. A decrease in sulfate is explained by the reduction of sulfate to hydrogen sulfide (dissolved oxygen is less than 1 mg/L). A faint but distinct hydrogen-sulfide smell was present during sampling. The chemical composition of Cave Springs in July 1987, 9 years prior to the reconstruction of the water supply at the springs, was nearly the same as Marmot Spring. The difference in chemistry before and after the reconstruction indicates that the reconstruction somehow altered the chemical composition of water discharging from Cave Springs.