干湿交替期天鹅湖水质现状调查

Water Quality Status of the Swan Lake during Transition from Drying to Wetting

位于湖北省石首市境内的天鹅湖，由长江河道演变而成，其水域是江豚迁地保护场所，部分水域和边滩是糜鹿自然保护区；天鹅湖中央是拥有2000hm^2农田、6300农业人口的天鹅岛，天鹅湖水环境事关江豚和麋鹿生境保护以及天鹅岛农业用水安全。3、4月是由干到湿的过渡期，降水量适中，通过该时段水质调查可大体了解湖泊水环境现状。2014年和2015年调查结果表明：主要由于水体总氮或总磷含量高使湖泊水质总体上处于Ⅲ-Ⅳ类，局部（入湖口、出湖口）处于Ⅳ-Ⅴ类，综合多因素计算的湖泊营养状态处于中营养至轻度富营养化状态。为保护水环境，在湖泊流域农业生产中要大力推行节氮栽培技术，采取有效的控氮、控磷技术。

Swan lake is located in Shishou City of Hubei Province,which is formed due to Yangtze River course change,its water is a place for Yangtze finless porpoise protection,the partial water of the lake and its islet are national reserves for Milu,the center of the lake is Swan Island with farmland of 2000hm2 and rural population of 6300.Water environment of the lake is significant for the habitat protection of the finless porpoises and Milu as well as drinking water for human and animals.For one year,the period from March to April is a transition stage from drying to wetting,the precipitation is in the middle period,so that water environmental situation of the lake can be roughly understood by water quality survey which Is conducted in the period.Analysis of monitoring data collected from March to April in 2014 and 2015show that because of a great deal of nitrogen and phosphorus to be carried away by agricultural runoff,the water quality of the lake arrives to the grade of third to forth for whole water and of fourth to fifth for its partial water(at entrance and exit),based upon its integrated eutrophic index the lake is between the mesotropher and light eutropher in the period.For water environmental protection for Swan Lake,water environmental management should be strengthened in the whole watershed,meanwhile,the cultivation techniques of nitrogen fertilizer-saving should be vigorously implemented in agricultural practices,also some effective techniques should be adopted for controlling the dosage of nitrogen and phosphorus.