Friday, January 24, 2020
The Effects of Mono Lakes Hydrology on its Ecosystem :: Environment Biology Essays
The Effects of Mono Lake's Hydrology on its Ecosystem Situated at the foothills of the Eastern Sierra Nevada, Mono Lake has an unusual and unique hydrology that is highly influential in shaping the water chemistry (specifically the water's salinity and alkalinity) and biological life that survives there. Mono Lake is a hypersaline, highly alkaline, hydrographically closed basin in which the only natural means of water export is through evaporation. The basin itself was carved out by faulting of tectonic plates that occurred atleast 500,000 years ago. Mono Basin contains up to 7,000 ft. of glacial, fluvial, lacustrine and volcanic deposits in a large structural depression formed in part by down-dropping along the Sierra Nevada fault (Pakiser 1976). In addition to the water evaporated, the Los Angeles Department of Water and Power (DWP) began diverting Mono Lake's water and approximately 58% of its natural inflow (annually) to supply 13% of the city of Los Angeles's water supply in 1940 (Stine 1991). Because lake volume fluctuates in response to varying inflow and evaporation, the late-water concentration and composition can experience substantial change through time (Rogers 1992). A high concentration of soluble compounds and salts formed inherently as evaporation occurred, and minerals and compounds were left behind. Runoff, erosional sediments and precipitation (rain and snowfall are limited in the Eastern side due to the rainshadow effect) from the Sierra Nevada accumulate in the Mono Basin. Also ephemeral perennial streams from the Sierra Nevada flow into the Mono Basin. Because of this, a great deal of the groundwater and the groundwater hydrological system is dominated by stream losses from the mountains. Fault lines can also be highly influential to the production of groundwater. According to USGS's Ronald Oremland, The lake is usually monomictic, and undergoes one complete winter mixing event induced by the sinking of cold surface waters. However, inputs of large amounts of freshwater into the lake in the early 1980s and again in the late 1990s resulted in episodes of meromixis (Oremland 2000). Jellison predicts that the meromixis phase that is currently occurring will last several decades. Meromixis generally produces buildup of ammonia, sulfide and methane. In many cases diversions of freshwater inputs for irrigation or other human uses have resulted in diminished size and increased salinity (Jellison 1992). Diverting Mono Lake's streams has not only stirred political and environmental controversy over rights but has also led to the waters of Mono Lake being halved in lake volume, reduced by 45 ft.