- Author: Cameron Barrows
A "Natural History Note" From UC California Naturalist's new lead scientist, Dr. Cameron Barrows.
When scientists underestimate complexity, they fall prey to the perils of unintended consequences. Siddhartha Mukherjee
About five million years ago the uplifting Colorado Plateau changed regional drainage patterns and in doing so created the Colorado River. The Colorado River extends into western and southern Colorado where, depending on the year, the annual snowpack can yield very different flows down the river. Some years, by summer the river would run dry. Other years massive floods scoured through the Plateau's layers of sandstone (creating the Grand Canyon) and would sometimes shift the course of the river into the Salton Trough forming an immense lake (christened by geologists as “Lake Cahuilla”). Water flows toward the lowest point on a landscape, and at 277 ft (84.3 m) below sea level, the tough is one of the 10 lowest terrestrial elevations on earth. The lake's historical shoreline can be easily seen on the hillsides along the eastern edges of the Santa Rosa Mountains. Once the lake filled to an elevation equivalent to sea level, the river would return to its bed and empty into the ocean where it formed one of the largest estuaries and riparian forests in North America. After decades of summer heat the lake would incrementally evaporate and then finally disappear leaving a salt pan coating the lowest regions of the basin. Eventually the river would flood again, resurrecting Lake Cahuilla and repeating this cycle again and again…. a pattern of establishment, decline (drying), and then renewal (re-filling to its former self), again and again. An extensive sand dune system formed at the southeast edge of Lake Cahuilla, formed from sands carried by the flooding Colorado River, sand that eroded out of the sandstone that once filled the space that is now the Grand Canyon. When the basin was dry, northwest winds would blow those lake bottom sediments into sand dunes. We now call those dunes the Algodones, and where those dunes formed along the edges of the great estuary, they form what is the Gran Desierto in northwest Sonora, Mexico. Those sands, as well as other dune systems created by the flood cycles of the Colorado River, provided isolated dune fields where fringe-toed lizards thrived and eventually diverged into what today are six recognized species.
It would be hard to fully appreciate the biological richness created by Lake Cahuilla. The river would have delivered both water and fish to fill the lake. The fish then would form the base of a food web that would include millions of pelicans, cormorants, terns, grebes, and ducks, with storks, cranes, herons, rails, and egrets hunting along the shores. Some would have formed nesting colonies on the islands that would have been created by the lake. The filling of the lake would increase groundwater levels resulting in cottonwood, willow, desert fan palm, and mesquite forests becoming established along what are now ephemeral drainages. Those forests would have been populated by warblers, flycatchers, cuckoos and vireos. Some early visitors suggested jaguars may have hunted for deer and peccaries beneath the canopies of those forests. When the lake was dry, lush vegetation and aquatic species would then be concentrated at a few perennial springs and creeks. The millions of birds would have needed to shift elsewhere, to the Colorado River's estuary in the Gulf of California to the south and to lakes along the eastern base of the Sierra Nevada. Those isolated springs and creeks within the Salton Trough would sustain some species, albeit in low numbers, until the next filling of the lake. Sometimes that isolation, resulted in the evolution of new species. The Salton Sea Springsnail, Pyrgulopsis longinqua, is found only in the Salt Creek wetlands and nowhere else on earth.
The first humans to experience and document this ebb and flow and renewal of sand and water were the Cahuilla, as told through their oral traditions. For thousands of years, they enjoyed the cornucopia of resources when the lake was full, and their populations swelled. They caught fish and birds, enjoying the riches the lake provided, that were in contrast to the surrounding parched desert. When the lake was dry the Cahuilla moved into canyons where perennial water was still available and migrated seasonally up or down the mountain slopes to take advantage of agaves, pinyon seeds, acorns from oak trees, and junipers, along with deer and bighorn sheep. It was sometimes many decades and even centuries between floods sufficient in magnitude to jump the banks of the Colorado River, finding the low Salton Trough and filling the lake once again, so the Cahuilla needed versatility to survive. Prior to modern times, the last time Lake Cahuilla filled was in the 1400s, just before Christopher Columbus landed in the Caribbean Islands and set-in motion a migration from Europe to North America that would alter the lives of the first people of North America, and the natural diversity of this continent, forever.
In modern times the Colorado River may have flooded sufficiently to jump its banks for the final time in 1906. Engineers were creating a canal system to deliver water to meet the needs of a shift in land use to agricultural expansion in both Imperial and southeastern Riverside Counties when floodwaters broke through their canal and filled Lake Cahuilla once again. Multiple dams subsequently built on the Colorado river to siphon away water to quench the thirst southwestern cities will eternally regulate flows down the river, preventing any future flooding, preventing any future inputs of relatively fresh water to the Salton Trough. The building of dams on the Colorado River has forever changed the ebb and flow, flooding, drying and renewal cycle of what was once Lake Cahuilla, changing its character and changing its name to the Salton Sea. Entrepreneurs once thought that the Salton Sea would become a sportsman's mecca, providing fishing, boating, and waterskiing experiences like no other. There were a few decades where that dream seemed to be true. Then it wasn't.
Rather than drying up as it had so many times before, water running through the canals, through agricultural fields to hydrate crops and to dilute salts accumulating in the soils, drains into the Salton Sea and has, until recently, kept the lake from drying. That agricultural wastewater – “drool” – adds four million tons of salt into the Salton Sea annually. The Salton Sea currently has a salt concentration of 44 g/L, or about 25% saltier than the ocean. Some of that water once dedicated to solely to agriculture is now being sent to fill the faucets of a rapidly growing population in San Diego, so less drool for the Salton Sea, and it is now shrinking fast.
The flood and drying cycle that created the ephemeral Lake Cahuilla is what is called an ecosystem process – energy and resource inputs that create ecosystems that are the foundations for biodiversity. Alter an ecosystem process and there will be consequences to biodiversity. Fish can no longer live in the Salton Sea – it is too salty. The food web has been severed for fish-eating birds. There is little doubt that the Salton Sea will continue to shrink and continue to get saltier. There are of examples of what the Salton Sea's future could be. Those lakes that occurred along the eastern base of the Sierra Nevada have been similarly altered by water diversions to fuel Los Angeles' growth. One, Owens Lake, is now dry and toxic alkali dust blows off its dry bed. Another, Mono Lake, was headed in that same direction. A friend and mentor, David Gaines, spearheaded a battle to redirect a couple Sierra creeks back to their natural flow to stabilize Mono Lake. In a true David and Goliath fight, David won. Mono Lake has a salinity of 79.8 g/L, far saltier than the Salton Sea, but there is life there. There are of course no fish, but a food web does exist with algae, brine shrimp, and brine flies at its base. California gulls nest there and thrive, and eared grebes and Wilson's phalaropes use it as a critical refueling stop on their annual migrations, all gorging themselves on shrimp and flies. Back at the Salton Sea, the food web is already in transition from fish to invertebrates. No longer kept in check by hungry fish, the population of an insect called a water boatman (Corixa punctada) has exploded. The boatmen populations are so large that they are expanding beyond the confines of the Salton Sea, sometimes landing in backyard swimming pools throughout the Coachella Valley. Birds that are not fish-eating specialists can and do make a meal of the boatmen, and over time brine shrimp populations may become established when the waters become too saline for the boatmen. Nevertheless, pelicans, cormorants, terns, and other fish-eating specialists are among the first losers in this ecosystem transition.
Unlike before water diversions, there are no remaining lakes on the eastern side of the Sierra Nevada that can replace what was Lake Cahuilla, and due to the water diversions from the Colorado River that take nearly every drop before it reaches the Gulf of California, the estuary the estuary at the once great river's mouth no longer supports the biodiversity it once did. The Salton Sea was a last refugium, until it wasn't. Other losers are the people who live anywhere near the Salton Sea. As the Sea shrinks, exposing an ever-widening shoreline, winds blow alkali dust into communities of the folks, many of whom work the agricultural fields that put food on our tables. Respiratory diseases are already showing up. The cascade of impacts stemming from altering this ecosystem continues.
There are places that, at a much smaller scale, provide some resemblance of what Lake Cahuilla once was. One is the Dos Palmas Preserve, but that will be another story.
Go outside, tip your hat to a lizard (and a cactus), and be safe.