The Mono Basin Ecosystem Effects of Changing Lake Level (1987) / Chapter Skim
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6. Ecological Responses to Changes in Lake Level
6. Ecological Responses to Changes in Lake Level
Pages 179-212
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From page 179... ...
Figure 6.1 illustrates the appearance of the lake and shoreline at representative lake elevations of 6400, 6380 (current lake level) , 6360, and 6340 ft above sea level.
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From page 180... ...
180 EIeva1Ion Bonn e EIev~on ~0 ant Me ~~o B~ Ero~~ age IN FEW n Ale IN FEW 1 0~ Do_ FIGURE 6.1 Sbore~ne of Mono Lake at lake elevations of 6400 and 6380 f1 above sea level
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From page 181... ...
Shoreline of Mono Lake at lake elevations of 6360 and 6340 ft above sea level.
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From page 182... ...
Most importantly, the bird populations would be unable to rely on Mono Lake if the lake level decreased to the point where the concomitant increase in salinity eliminated their food source, the brine shrimp and brine fly. Changes in
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From page 183... ...
Using both historical measurements and calculated data from hydrological models, one can estimate the salinity of Mono Lake at specific lake levels, as described in chapter 2. Historical measurements of lake level and salinity are presented in Table 6.1.
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From page 184... ...
Salinity (g/1 total dissolved solids) 6417 6414 6410 6407 6403 6380 6378 6377 6376 6375 6373 6372 51.3 54.0 56.3 58.1 60.2 89.3 86.8 91.6 89.3 93.4 97.7 99.4 TABLE 6.2 Predicted Salinity Values for Lake Elevations Below the Present-day Level of Mono Lake (LADWP, 1986)
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From page 185... ...
Therefore, surface water salinities should be less than the models predict at lake levels below the level at which these minerals begin to precipitate. This occurs because minerals precipitate throughout the water column at low temperatures in the winter and then redissolve near the bottom at higher temperatures in the summer.
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From page 186... ...
However, it is possible that photoautotrophic and chemoautotrophic bacteria may grow in the chemocline and saline bottom waters and augment the lake's primary productivity, though probably not sufficiently to replace the loss in algal growth. With lower algal abundance the food available to the first generation of brine shrimp would be reduced, the fecundity of the females would decline, and the switch to cyst production from live bearing could occur earlier each year.
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From page 187... ...
A summary of the impacts on planktonic and benthic algae is provided in Table 6.3 and on brine fly and brine shrimp populations in Table 6.4. Biological responses to meromixis, which would become more likely if lake levels fell, might have synergistic effects with those related to salinity per se.
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From page 188... ...
A decrease in hatching of dormant brine shrimp embryos would be expected if the salinity increased to approximately 130 g/1. This effect is attributable to a reduction in the "free water" of hydration of the embryos.
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From page 189... ...
Although it has not been possible to quantitatively estimate the brine fly larval population at the current lake level, a reduction of 40 percent of the hard substrate area that would result if lake level fell to
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From page 190... ...
Aquatic Bird Populations The critical food resources for aquatic birds using Mono Lake are brine shrimp and brine flies. Eared grebes and California gulls feed primarily on brine shrimp, while rednecked phalaropes, and to a lesser extent Wilson's phalaropes, specialize on brine flies.
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From page 191... ...
To the extent that these islets are important nesting sites, their accelerated erosion could result in greater restriction of gull nesting habitat than is apparent from the overall figures of island area. It should be noted that, if the lake level fell to the level that would significantly decrease island area, most gulls would likely have already deserted Mono Lake because of lack of food.
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From page 192... ...
Migrant grebes leave Mono Lake earlier than they do at higher lake elevations. Wilson's phalaropes find it difficult to complete molt and premigrating fattening before departing; red-necked phalaropes' stopover shortened.
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From page 193... ...
. Shoreline Environment The shoreline around Mono Lake would be inundated or exposed if lake level were to rise above or fall below the current level.
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From page 194... ...
The areal extent of the seepage zones may increase if the lake elevation were to fall below approximately 6380 ft because of the decreasing slope of the exposed lake bed. Similarly, at Navy Beach, where spring waters appear to be a mixture of shallow groundwater and fault-controlled flows, spring locations would migrate if lake levels changed.
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From page 195... ...
. Most of the shoreline north of Simon's Spring to the lakeshore southeast of Bridgeport Creek is bordered by salt flats, which have become progressively wider as lake levels have lowered.
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From page 196... ...
This situation would occur at lake levels of 6415 ft at the County Park and Bridgeport Creek tufa groves and at approximately 6425 ft at the Old Marina. Tufa towers occur above 6430 ft at Simon's Spring and Warm Springs and would consequently not be affected by lake elevations considered in this report.
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From page 197... ...
Some currently submerged tufa formations would be exposed with declining lake levels. NOTE: Locations of tufa groves are shown in Figures 5.8 and 5.9.
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From page 198... ...
The potential availability of aerosols depends on future mitigation efforts, including the use of sand fences, stabilization by vegetation, and other innovative projects. Snowy Plover Nesting Sites As summarized in Table 6.10, the alkali flats along the eastern shore of the lake that provide the nesting for the snowy plover would be gradually inundated if lake levels rose.
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From page 199... ...
Nesting population decreased from current level in proportion to area of exposed playa. Nesting population of approximately 350 pair.
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From page 200... ...
Upland Environment If the lake level were to be maintained at any given level, specific amounts of water would have to flow into the lake each year. Based on the modeling results described in chapter 2, necessary inflows required to maintain given lake levels are reported as average flows at the diversion points (Table 6.12~.
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From page 201... ...
Steep shorelines near Lee Vining and Rush creek deltas and around islands will erode and may prevent vegetation establishment. Most exposed lake bed will remain barren, especially northeast, east, and south shores.
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From page 203... ...
This surface flow regime in Rush Creek has apparently been sufficient to stimulate reestablishment of woody riparian vegetation. Below the water diversion points, Rush and Lee Vining creeks cross alluvial deposits.
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From page 204... ...
In light of the uncertainties in the model predictions and the committeets conservative approach to predicting effects of changes in streamflow on the riparian strand, the committee concludes that flows necessary to maintain lake levels above 6360 ft. regardless of which model is used, should maintain riparian strands on Rush and Lee Vining creeks.
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From page 205... ...
If the fully reestablished riparian strand along Rush Creek were to consume 3500 acre-ft/yr of water, the lake levels that could be maintained by a given release would be reduced by about 2 ft. Establishment of a riparian strand along Lee Vining Creek would lead to yet further reduction in lake level.
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From page 206... ...
, and others would be adversely affected by lower lake levels. In using the conclusions of this report to determine how the ecosystem should be managed, decisions about the relative importance of different resources will have to be made.
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From page 207... ...
~ , , If lake level fell 10 ft from its current level, the amount of hard substrate available as littoral habitat for brine flies would be reduced by 40 percent. The nesting and migratory bird populations at Mono Lake are affected by changes in lake level through changes in food chain productivity and availability of nesting habitat.
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From page 208... ...
Increases in lake elevation would gradually inundate tufa groves to 6430 ft. Sand tufa gradually destroyed with increases in elevation from 6410 to 6430 ft.
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From page 209... ...
Exposed tufa may be susceptible to vandalism. Riparian vegetation Currently maintained flows of 19 cfs in Rush Creek and 10 cfs in Lee Vining (approximate average flow at diversion points to maintain lake elevation at 6360 ft or 6330 ft depending on the model used)
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From page 210... ...
streamflow have consequences for the riparian vegetation and habitat. The flows currently maintained in Rush and Lee Vining creeks, l9 and lO cfs, respectively, appear adequate to maintain a healthy riparian community.
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From page 211... ...
1985. A Water Balance Forecast Model for Mono Lake, California.
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