Monthly Water Balance of an Iconic Coastal Desert Wetland Under Reduced Flows and Increased Salinities; Implications for Management

The Cienega de Santa Clara is a brackish coastal wetland located in the Colorado River Delta Biosphere Reserve. It plays vital ecological roles that support endangered-migratory species and flora. Its main water supply comes from irrigation return flows from the United States with salinity levels (2–3 g L⁻¹) that promote the growth of Typha domingensis. This study conducted a water-mass balance during one year of reduced water volumes and high salinity levels caused by a trial run of the Yuma Desalting Plant. The analysis projected the effects that could be expected from the plant with permanent operation conditions. During the test run, inflows varied from 0.62 to 5 m³s⁻¹, supplying the wetland with 127.20 hm³ of water at 2–5 g L⁻¹. Forty-five percent of this volume exited as runoff, while 52 % exited by evapotranspiration. Water depth varied from 0.10–2.1 m at different time responses; also, during the summer water salinity levels increased above the tolerance limit for the vegetation, reducing its area by 20 %. Vegetation area returned when normal flows were resumed in the fall. The results indicate that permanent operation of the plant would reduce the vegetated area in the wetland due to reduced flows and increased salinities.