岩滩水库渔业生态环境变动研究

Changes in the Fishery Ecological Environment of Yantan Reservoir

分析岩滩水库渔业生态环境的变动,为库区渔业生产提供理论指导。使用岩滩水库1981-2014年间6个时间段共11个年度的监测数据,分析库区的水质、饵料生物、渔业生产的变化情况。从蓄水的1996年至2014年,总磷浓度由0.073 mg/L下降至0.02 mg/L,铁离子浓度由0.110 mg/L下降至0.053 mg/L,下降趋势明显;2008年监测结果显示,底层总磷浓度0.04～0.08 mg/L,是表层的4倍,全年垂直分层明显。蓄水后1996-2014年,浮游植物数量和生物量分别变化于101.3×104～263.6×104个/L和1.115～3.342 mg/L,浮游动物数量和生物量分别变化于332.5～1 045.5个/L和0.642～6.186 mg/L。1985-1986年调查共采集到鱼类4目17科71种,2003-2004年4目14科42种,2013-2014年4目14科55种。鲢、鳙年产量2003年以前近5 000 t,以后2 500 t左右。采用技术手段打破水体分层,使底层营养盐持续供给表层,满足生态养殖的饵料生物生长需要,是重振库区生态养殖的有效手段。

Yantan Reservoir,located in Yantan Town,Hechi City of Guangxi Province,is a large-scale hydro-project with electric power generation as the primary function,but also providing navigation,irrigation and aquaculture. The project began in 1985 and started producing electricity in 1992. Since the impoundment of Yantan Reservoir,enclosure culture and ecological net culture have developed quickly,on a large scale and with high stocking densities of silver carp and bighead carp. However,the growth rate of silver carp and bighead carp has declined sharply. In this study,changes in the fishery ecological environment in Yantan Reservoir were analyzed based on the monitoring data on water quality,food organisms and fishery production in the Yantan Reservoir from 1981 to2014,aiming to provide theoretical guidance for reservoir fishery production. Monitoring was carried out on six occasions,over 11 years,in the periods 1981- 1982,1985- 1986,1996- 1997,2003- 2004,2008 and 2013-2014. From the impoundment of Yantan Reservoir in 1996,until 2014,the concentrations of total phosphorus and iron declined dramatically,from 0. 073 mg / L to 0. 02 mg / L and from 0. 110 mg / L to 0. 053 mg / L,respectively.Total nitrogen has changed little,while ammonia and nitrite nitrogen,volatile phenols,cyanide,hexavalent chromium,arsenic,lead and copper have been consistently at low concentrations. Monitoring results from 2008 indicate that total phosphorus was distributed vertically through the year,with bottom total phosphorus concentrations ranging from 0. 04 to 0. 08 mg / L,four times that in surface waters. During the period 1996- 2014,the density and biomass ranges of phytoplankton were 101. 3- 263. 6 × 104 ind / L and 1. 115- 3. 342 mg / L,while the density and biomass ranges of zooplankton were 332. 5- 1 045. 5 ind / L and 0. 642- 6. 186 mg / L. Both communities sharply declined in 2008 and gradually increased,stabilizing since 2013. An outbreak of Limnoperna fortunei after 2006 resulted in a dramatic increase of benthic organism biomass. Fishery resources have decreased significantly during the monitoring period： a total of 71 fish species from 17 families and 4 orders were recorded in the period 1985- 1986,decreasing to 42 species from 14 families and 4 orders in the period 2003- 2004 and then 55 species from 14 families and 4 orders in the period 2013- 2014. The annual output of silver carp and bighead carp was nearly 5 000 t before 2003 and has been approximate to 2 500 t since 2003. Low iron concentrations,caused by stratification,may limit phytoplankton growth and consequently influence the growth of carp. On the other hand,filter-feeding and excretion by Limnoperna fortunei accelerated nutrient deposition to the sediment,especially phosphorus and iron,which also limits phytoplankton growth. The Limnoperna fortunei outbreak seems to have been controlled by the release of snail eating black carp,but fish continue to grow slowly. The use of technical means to mix stratified water may be an effective means to revitalize ecological farming in the reservoir by circulating nutrients from bottom to surface waters to meet the needs of the organisms being cultivated.