| As an important part of water resource, lake has been one of the the most biologicallydiverse landscapes in nature and the most significant living environments for human being.Lake has enormous environmental function and benefit that can be used for regulating surfacerunoff, preventing floods in water conservancy, controlling soil erosion, supporting navigation,improving environment and so on. The management and protection of lake resource should bestrengthened to realize the coordination between lake resource utilization, social economydevelopment and environement protection. Sand Lake is located in Pingluo province ofShizuishan city, Ningxia Hui Autonomous Region. Because of the intense evaporation andrare preicpittion, a plentiful supply of water is needed to maintain the ecological balance ofSand Lake. Hence, the quanlity and quantity of supplemental water have been the most keyfactors which affect the aquatic environment of Sand Lake. In this paper, an early warningstudy has carried out to investgate the influence of supplemental water on the aquaticenvironment of Sand Lake. The primarily conclusions are as following:(1) Sand Lake is a semi-saltwater lake with high salinity and hardness. The chemicaltype is Cl·SO4-Na·Mg. Eight indices, namely pH, DO, CODMn, CODGe, BOD5, Hg, TP andTN, exceed Calss III of quality standards for surface water. Wherein, nitrogen and phosphorusare the main pollution factors.(2) Based on the study of eutriphication theory, six indices are selected to assesseutrophicate degree of Sand Lake by Hamming osculating method, which are chlα、TP、TN、SD、COD and BOD5. Water quality data are from five monitoring points of Sand Lake (mainchannel, aquaculture, bird island, boat pier and center of lake) during the period of March2010to August2012. The results show that water quality of Sand Lake reaches to eutrophyand it gets worse in recent years.(3) The water recharge of Sand Lake includes precipitation, groundwater recharge andartificial water replenshment, and the discharge contains evaporation and groundwaterdischarge. The artificial water replenishment and evaporation are the main recharge anddischaege approaches, respectively. Taking1300×104m3/a as the artificial waterreplenishment, during August2012and July2013, the total recharge capacity of salt is51.59×108g, the artificial water replenishment acconts for99.25%in the total amount, andthe total discharge capacity of salt is41.90×108g which is all from groundwater discharge.(4) In the lake stage early warning, the status alert level is blue, and the results of trending early warning are obtained with different artificial replenishment cases. When theartificial water replenishment is less than1380×104m3/a, the lake stage continuouslydecreases and the alert level of lake stage aggravates; when the artificial water replenishmentis greater than1380×104m3/a, the lake stage slowly increases and the alert level of lake stagealleviates. According to the relationship between Sand Lake and groundwarer, the artificialwater replenshment of1380×104m3/a is defined as the optimal water quantity for Sand Lake.Under this circumstance, the lake stage remains stable with realizing the highest utilization ofwater replenishment.(5) In the water quality early warning of sand lake, the status alert level of salinity isyellow. Trending early warning is based on the1380×104m3/a artificial replenishment water.When the artificial water replenishment is all from Yellow River, Sand Lake is in desalinationcondition after30years and the alert level is still yellow. The results show that the largepropotion of Yellow River quantity can decelerate water salinization. Groundwater should beproperly exploited to replenish the shortage of Yellow River, and the water of lotus pond isavoided becaused of poor quanlity. In order to keep lake stage and alleviates water salinity,the approach of discharging the quantity which is larger than1380×104m3can effectivelydecrease water salinity and its alert level of salinity. |
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