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<br />000312 <br /> <br />separated from the northern Gulf of California by a low, natural land barrier, <br />which delineates the southwestern edge ofthe basin. In 1993, the Mexican <br />government declared the Upper Gulf of California and the Colorado River delta as <br />a Biosphere Reserve to protect threatened and endangered species. The Cienega <br />is included within the Reserve's core boundaries. <br /> <br />The Cienega is sustained by three water sources. The present day Cienega <br />began to form in 1977 following the discharge of water from the Main Outlet <br />Drain Extension (MODE). The annual MODE flow has ranged from 97,285 af- <br />145,928 af/yr of drainage from WMIDD with a mean flow from 1994-2003 of <br />approximately 109,100 af/yr at the border. The second source is the Riito Drain <br />which carries approximately 12,800 af/yr of agricultural drain water from the San <br />Luis irrigation district for disposal near the discharge point ofthe MODE canal. <br />The third source is the natural seepage via artesian springs, of groundwater onto <br />the mud flats. <br /> <br />The inflow water is not all consumed in the vegetation, but can be seen <br />exiting the southern end, where it dries on the mud flats or mixes with ocean <br />water that is occasionally driven into the southern end of the basin by wind and <br />high tides. <br /> <br />Salinity of the inflow averages about 3,000 ppm for the MODE and about <br />4,000 ppm for the Riito Drain. Salinity concentration increases as the water <br />disperses away from the MODE outfall. Water moves down the marsh in a plume <br />following the Cerr.o Prieto fault line, a natural channel in the Cienega. <br /> <br />The continued release of MODE water to the Cienega has resulted in the <br />expansion of the wetlands from several hundred acres in the 1970's to nearly <br />40,000 acres today, including a vegetated area of approximately 14,000 acres in <br />the Biosphere Reserve, and an open water area of approximately 25,000 acres. <br />The wetlands are a dynamic system, with the size and extent of the vegetated and <br />open water areas varying with seasonal changes in inflows and evaporation; <br />whether these areas will continue to grow under current inflow conditions is not <br />known. Most of the vegetated portion ofthe Cienega is dominated by cattail. In <br />the tidally influenced southwestern margin saltgrass is the dominant vegetation. <br /> <br />It appears that salinity in the lagoon likely limits the southern extent of <br />emergent vegetation; studies of the Cienega have suggested that salinity is the <br />major determinant of the size ofthe vegetated area as well as of the distribution of <br />individual species within the vegetated area. Aside from areas influenced by <br />natural artesian flows on the eastern boundary ofthe Cienega, salinity levels in <br />the Cienega gradually increase southward, and are generally at their lowest in the <br />northern portions of the lagoon nearest the inputs from the MODE and Riito <br />Drain (where levels are driven by the salinity of the water in the two canals), <br />increasing due to evaporation and evapotranspiration as the water flows <br />southward along the plume. Vegetation begins to fail as salinity reaches critical <br />levels; current science indicates the salinity tolerance of the cattails is reached in a <br />range between 7,000 and 10,000 ppm, which delineates the southern extent of the <br />vegetated area. <br /> <br />Recommendations of the YDP/Cienega Workgroup <br /> <br />5 <br />