三峡水库蓄水后水温变化对四大家鱼自然繁殖的影响

Effect of Water Temperature Variation After Impoundment of the Three Gorges Reservoir on Natural Reproduction of the Four Major Chinese Carps

三峡水库蓄水后,坝下水温变化对四大家鱼关键生活史阶段造成一定影响。本文使用水温变化指标定量评价蓄水后水温的改变程度,分析水温改变对四大家鱼自然繁殖的影响。基于宜昌水文站1983—2013年长系列逐日水温资料,建立了25个具有生态意义的水温参数,利用变动范围法计算了三峡水库蓄水后25个水温参数变化度,对高度改变的水温参数采用线性回归方法评估其变化倾向,基于F检验法检验回归效果。分析四大家鱼自然繁殖时间与水温参数变化的关系,研究四大家鱼自然繁殖对水温过程变化的响应。结果表明:整体水温改变度达44.2%,高度改变的水温参数有7个,分别是1、4、10、11、12月平均水温、最低水温出现日期、水温达到18℃日期,水温改变度达87.9%、75.8%、74%、100%、100%、74%、89.9%,说明三峡水库蓄水后坝下水温发生显著变化;下泄水温在消落期4、5份偏低趋势明显,较蓄水前平均降低2.3、1.7℃,由于4、5月水温偏低导致水温达到18℃的日期发生显著变化,由蓄水前4月19日推迟至蓄水后5月4日,平均推迟15 d。四大家鱼自然繁殖时间与水温达到18℃的日期密切相关,下泄水温偏低造成其自然繁殖时间推迟,首次产卵推迟至5月中旬,整个繁殖季节由4—7月份压缩至5—6月份,研究成果为三峡水库开展生态调度提供科学支撑。

Water temperature（WT） variation at downstream of the dam after impoundment of the Three Gorges Reservoir （TGR） influ- enced the critical life cycle stages of the Four Major Chinese Carps to a certain extent. The degrees of WT variation in the Middle Yangtze River after impoundment of the TGP were quantitatively assessed, then effects of WT variation on the Four Major Chinese Carps were analyzed. 25 WT parameters with ecological interpretations by Indicators of WT Alteration method were generated based on daily data of the Yichang hydrologic station from 1983 to 2013. The variation degree of 25 parameters after impoundment of the TGR was calculated by the range of variability approach, the linear regression method by F-test was used to evaluate trend of WT parameters with high alteration. Then relationship between spawning time of the Four Major Chinese Carps to variation of WT parameters was analyzed, to study the response of four carps spawning to WT change. The results showed：the total alteration of WT had reached to 44.2% ,7 parameters representing high alteration in WT were found out, which were mean monthly WT respectively in January, April, October, November and December,arising date in the lowest WT,and arising date that WT arriving in 18 ℃ ,the corresponding WT alteration degree had reached to 87.9% ,75.8% ,74%, 100%, 100% ,74% ,89.9% ;these all gave explanations of obvious change in WT alteration downstream of the dam after impoundment of the TGR. Compared to the same period before impoundment of the TGR, the average released WT were 2.3℃ and 1.7℃ lower in April and May during drawdown period,thereby the significant change of arising date that WT arriving in 18 ℃ was occurred, from 19 June in pre-impoundment period to 4 May in post-impoundment period, averagely postponed by 15 days. The spawning season of the Four Major Chinese Carps was closely related to the arising date that WT arriving in 18℃. Due to the tower released WT by the TGR, the first spawning time of the Four Major Chinese Carps had postponed from April to mid-May, and the whole spawning season had been shortened. The results might provide scientific reference for the experimental ecological operation of the TGR on natural reproduction of the Four Major Chinese Carps.