Waterfowl Habitat at Mono Lake
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Types and Functions:
There are several types of waterfowl habitat at Mono Lake. Each has a substantial and persistent influx of fresh water, and conditions that allow persistent hypopycnal stratification.1 Hypopycnal stratification is a phenomenon consisting of a fresh water layer floating on top of saline lakewater, a historically rich habitat for ducks. Scott Stine, an authoritative Mono Lake researcher, states, "Ducks inhabiting the hypopycnal skims on Mono Lake were essentially in a freshwater environment, with saltwater food resources available immediately below, or immediately beyond, the skim."2
Mono Lake itself provides an important source of food for ducks, and they historically spent the bulk of their time there. Northern shovelers forage primarily on brine shrimp, while other common ducks such as mallards, green-winged teal, American widgeon, and gadwalls consume mostly alkali flies.3
Lagoons, especially those near a source of fresh water, are valuable habitat for waterfowl. They form where brackish water is held behind shoreline berms of sediment,4 and often provide shelter from rough lake waters on windy days.
Spring fed open fresh water marshes are also important waterfowl habitat. It is the open water areas, however, not the marshes themselves, that seem to provide valuable duck habitat.5 Open fresh water provides areas for bathing and drinking, while marsh vegetation does provide some food and cover.
Deltas of creeks, after the lake itself, are the most important waterfowl habitat, because they often combine the above mentioned habitats with lots of fresh water. Since ducks rely on fresh water and don't tolerate salt well,6 the largest concentrations of waterfowl were historically at creek deltas.7 Hypopycnal stratification, which provides by far the most valuable duck habitat at Mono Lake,8 typically reaches its greatest extent at the mouths of creeks.
Historic Conditions--Habitat Extent:
Before diversions of water into the Los Angeles Aqueduct began in 1941, Mono Lake fluctuated around an elevation of 6,417 feet above sea level. The salinity of the lake at this elevation was 53 grams per liter,9 about one-and-a-half times that of the ocean.10 The lake also contained almost twice the volume of water as it does now,11 and its surface area was about one-third larger.12
The productivity of brine shrimp was higher and more habitat was available for them, while the productivity of alkali flies was also higher, probably due to lower salinity.13 These higher populations of brine shrimp and alkali flies resulted in more food being available for waterfowl, especially ducks.
There were 260 acres of brackish lagoon, with most of the acreage east of Sulphur Springs in the Dune Lagoons. When Mono Lake was at an elevation of 6,412 feet, a 23 acre lagoon would form at the DeChambeau embayment. There might have been a 1-mile-long lagoon at Simons Spring, and 38 acres of natural lagoon wetland occurred at the Rush Creek delta. Paoha Island supported 5 acres of lagoons in several small craters and cinder cones and behind a large slump on the south shore.14
Marsh vegetation is hard to separate from other wetland vegetation on early aerial photos, therefore exact acreages of marshes are not available. There were, however, 356 acres of marsh, wet meadow, alkali meadow, and wetland scrub habitat.15 Warm Springs and Simons Spring were the largest pre-diversion lake-fringing wetlands. Wilson Creek and Lee Vining Creek deltas and Lee Vining Tufa contained 60 acres of vegetated wetlands. There were 201 acres of vegetated wetlands at Horse Creek Embayment, County Marina, and County Park, most of these sustained by upslope pasture irrigation. On Paoha Island, Hot Spring Cove supported a minor meadow-marsh wetland.16 These marshes were of secondary importance to the preferred hypopycnal environment of certain areas on Mono Lake.
Larger freshwater inflows from creeks and springs into deltas, marshes, lagoons, and nearshore areas provided much needed fresh water for waterfowl. Periodic burning of marshes kept open water habitat available and vegetation vigorous.17
Historic Conditions--Waterfowl Abundance:
It is estimated that prior to 1940, at least 1 million ducks regularly stopped at Mono Lake during peak migration.18 Large concentrations of ducks arrived in early September and remained until alkali fly populations declined in late fall.19
Katherine Clover, a resident along Rush Creek before 1940, stated that "the sky would go black with huge flocks of ducks. There were so many! They fed in the lake near the mouth of Rush Creek and would rinse off their feathers in the fresh creek water."20
Ducks were abundant enough in fall to appear as a dark, moving, 10-foot-wide ring around the lakeshore, stretching from the mouth of Lee Vining Creek to beyond the mouth of Rush Creek. There were so many ducks along the shore that when they moved out all together the shore itself looked like it was moving out. Flocks of ducks looked like large sandbars when viewed from a boat.
Northern pintails, mallards, green-winged teals, and American widgeons were numerous through the 1940s. On windy days lagoons along the northern shoreline near Sulphur Springs attracted flocks of migratory waterfowl seeking protected resting areas away from the high waves of the lake. Ducks often concentrated at creek deltas. Large numbers also gathered in the Rush Creek bottomland marshes and ponds where watercress and other aquatic plants were plentiful.21
Mono Lake was a major stopover point for ducks migrating through the Great Basin, but geese and swans were far less abundant than ducks, since they are mostly herbivores, and would not be attracted by the abundant invertebrate prey in Mono Lake. Goose hunting, however, was relatively productive in the Rush Creek bottomlands during the early 1900s. Up to a few thousand geese visited the Mono Basin in Fall, including white-fronted geese and snow geese, and usually 200-300 Canada geese overwintered here.22 Also overwintering often were 200-300 tundra swans.23
Los Angeles Aqueduct Diversion Impacts:
Soon after diversions began in 1941, waterfowl habitat remained much the same as before.24 In the mid-1940s, 50 acres of artificial ponds were constructed for a duck club near the mouth of Rush Creek, but these only contained water intermittently after 1947.
A systematic survey on November 1, 1948, estimated that there still were about 1 million waterfowl visiting the Mono Basin. They were distributed around the lake as follows: 45% in the Rush Creek delta area, 15% in the Simons Spring area, 15% in the DeChambeau Ranch area, 10% in the Lee Vining Creek delta area, 5% in the Warm Spring area, 5% in the Monte Vista Springs area (County Park, Mill Creek, and Wilson Creek deltas), and 5% in the Tufa Rock area (South Tufa - Navy Beach). The most abundant species was northern shoveler.25
Despite reductions in freshwater flows and the loss of the Rush Creek ponds, there were large concentrations of ducks throughout the 1950s. The largest flocks were at lagoons on the north and east shorelines, DeChambeau Lagoon, marshlands at the Rush Creek delta, Warm Springs, and Simons Spring.26
In 1957, when Mono Lake dropped below the 6,405 foot elevation, the large lagoons on the northeast shore disappeared. In the early 1960s, when the lake dropped below the 6,400 foot elevation, open water areas at creek deltas were lost due to incision, and the DeChambeau Lagoon was stranded on the dry lakebed. Rush Creek incised its delta in 1967, causing a loss of the ponds and marshlands there.27
In 1964, the salinity of Mono Lake reached 70 grams-per-liter, almost one-and-a-half times the pre-diversion level.28 This would seem to be a significant increase to ducks, which do not tolerate salt well. In the early 1960s, the waterfowl populations were estimated to be half of their former numbers. Ruddy ducks, however, may have become more common during the 1960s, and were observed to be scattered across the lake, not concentrating at fresh water.29
Throughout the 1970s and 1980s, populations of migratory ducks declined across North America, and at Mono Lake only a few thousand were present at one time.30 Waterfowl populations in Californias Central Valley declined 40-60% since the mid-1960s, however populations at Mono Lake declined 97%. This indicates a local loss of habitat having a much greater impact than regional influences.31 The number of geese and swans has declined as well, but not to the same extent as the ducks.32
Present Conditions--Waterfowl Abundance:
Currently, it is estimated that only 11,000-15,000 migratory ducks visit Mono Lake in the fall, or about 1% of the pre-diversion numbers. This includes 5000 ruddy ducks, 400 cinnamon teals, 2000-5000 green-winged teals, 500-1000 mallards, 500 northern pintails, 250-750 American widgeons, 100-400 gadwalls, and possibly as many as 150-300 assorted individuals of other species.33
Present Conditions--Habitat Extent:
Mono Lake is now substantially smaller in volume and surface area, and as a result the level of salinity is 90 grams-per-liter, almost double the prediversion level.34 This has reduced the productivity of alkali flies and brine shrimp, the main source of food for ducks stopping here.35
There has been a nearly complete loss of lagoon acreage,36 which was historically an important waterfowl habitat. The former dune lagoons are now barren and salt-encrusted, however groundwater flows still reach the former DeChambeau Lagoon, which supports some annual forb and dry meadow vegetation.37
There has been an 8-fold increase in the area of marsh, wet meadow, alkali meadow, and wetland scrub over pre-diversion conditions.38 Although greater in quantity, the quality has suffered, and in many cases these wetlands contain sparse vegetation with very little wildlife diversity.39 Fire has been suppressed, and without periodic burning marshes contain less open water and less-vigorous vegetation. As a consequence, they now hold little value for waterfowl.
The creek deltas which once attracted tremendous numbers of waterfowl now are degraded due to incision of the streams into the former lakebed and the resultant loss of open water marsh and lagoon habitat. Freshwater inflows have resumed from the diverted streams, however, and this is improving some of the lost habitat by re-creating hypopycnal stratification in delta areas.
As the lake rises to 6,392 feet above sea level, there is the opportunity to restore some of the lost habitat which once supported one-million waterfowl, or 100 times the current number.40 The salinity of the lake at the 6,392 elevation will drop from the current 90 grams-per-liter41 to 72 grams-per-liter,42 which should increase the productivity of the brine shrimp and alkali flies by 30%. This significant increase will make more food available for ducks, and the lower salinity will allow them to more easily tolerate the lake water. At that higher elevation, 16 acres of ponds will form at the Rush Creek delta and on Paoha Island.43
In addition to raising the lake surface to the 6,392 foot elevation, which is the most important factor in restoring waterfowl habitat,44 several other waterfowl habitat restoration measures have been identified.
Rewatering Mill Creek is the next highest priority, because its delta suffers from lack of fresh water due to hydropower and irrigation diversions upstream. Fresh water in Mill Creeks Delta will cause hypopycnal rias, elongate embayments attributable to the flooding of a stream canyon by a rising lake or ocean,45 to occur in two trenches in the delta, which will provide extremely valuable habitat for waterfowl.
In addition, according to Stine,"...the lake surface is relatively sheltered from winds, and thus infrequently experiences high waves that would dissipate a hypopycnal lens. Hypopycnal conditions are further favored by the clockwise-spinning backset eddy that characterizes this corner of the lake. This eddy keeps the freshwater lens within the embayment, rather than allowing it to readily diffuse into the less protected areas of the lake."46
Another restoration priority is to rewater important distributary channels in the Rush Creek bottomlands,47 a historically valuable habitat for waterfowl. This, along with a hypopycnal ria forming at the mouth of Rush Creek, should create a productive complex of waterfowl habitat in this area.
Developing and implementing the DeChambeau Ponds/County Ponds Complex is another means of increasing the waterfowl habitat available in the Mono Basin.48 For this project to succeed, however, a feasible, reliable, and ecologically sound source of fresh water needs to be found.
Another waterfowl habitat restoration measure, developing and implementing a prescribed burn program,49 would also maintain and increase the value of existing marsh habitat.
The tremendous waterfowl habitat which existed before 1941 will never be fully restored, unless Mono Lakes surface rises above 6405 feet above sea level. Above this lake level, many features around the lakeshore would potentially attract large numbers of waterfowl once again.
But at 6392 and with certain restoration measures, some of the loss can be mitigated. In the words of Elden Vestal, District Fisheries Biologist for the California Department of Fish and Game in the Mono Basin from 1938 to 1950, "There can be no 'quick fixes' here. Only a great 'tincture of Time' and the best favors of Nature with the natural vicissitudes of climate and, especially, water can heal the Mono Lake environmental complex in the calculated (if not fervent) hopes of many that it will gradually return to a suitable state acceptable to waterfowl."50
(1)p. 9, Stine, Scott, Historical
and Future Waterfowl Habitat at Mono Lake, CA, 1995
Copyright © 1999-2019, Mono Lake Committee.
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