摘要
水温对沉水植被的生长和分布具有重要作用,水-沉积物界面热通量对浅水湖泊水温变化的影响值得关注.东太湖是我国东部典型的草型浅水湖区,采用自2013年11月至2015年10月对东太湖湖心进行的不同深度水体及沉积物温度高频观测数据,结合东太湖表层沉积物的热力学性质计算了水-沉积物界面热通量,分析了东太湖水温和水-沉积物界面热通量的变化特征并探讨了其影响因素.结果表明:东太湖各深度水体日升温过程随水深增加后延,升温过程夏季延长,冬季缩短;表层水温日变幅最大,底层水温日变幅次之,沉积物温度日变幅最小,各深度温度日变幅夏季最小、冬季最大;春季和夏季升温过程中各深度日均温变化沿水深存在约1天的延迟,秋季和冬季无此现象; 2015年与2014年东太湖温度变化趋势相同,同比月均温差与气温差呈线性相关.沉积物8:00-19:00向水体放热增加或从水体吸热减少,19:00至次日8:00放热减少或吸热增加; 3-9月从水体吸热,为热汇,10月至次年2月向水体放热,为热源,沉积物全年为湖泊热源;逐日水-沉积物界面热通量每月6至15日存在相对年变幅较小幅度的正弦式波动.水温和水-沉积物界面热通量的变化主要受太阳辐射和气温的影响,二者对气象参数的响应具有迟滞现象;水-沉积物界面热通量与水温呈负相关,其变化相对水温迟滞,水-沉积物界面热交换的主要作用为缓冲湖泊水体的热量变化;夏季,沉水植物能降低湖泊各层水温和垂向水温差.
Water temperature is critical for growth and distribution of submerged macrophyte and heat flux at water-sediment interface(WSI) is essential for water temperature changes. East Lake Taihu is a typical shallowmacrophyte-dominated lake in eastern China. Temperatures of water and sediment at different depths were monitored with high frequency from November 2013 to October2015 in the middle of East Lake Taihu. Heat flux at WSI was calculated with inferred thermodynamic parameters. Changing patterns of water temperature and heat flux at WSI were revealed and their influencing factors were discussed. Results showed that the temperature rising processes were delayed with the increase of water depth. Water temperature rising process was prolonged in summer and shortened in winter. Temperature ranges in averaged 24 hours: surface water temperature> bottom water temperature> temperature at WSI> sediment temperature. Temperature ranges in averaged 24 hours were smallest in summer and largest in winter. There was a 1-days' hysteresis of temperature changes along the water depth when the temperature rose in spring and summer,while not in autumn and winter. Annual trends of temperatures in 2015 was same with 2014,and differences of year-on-year monthly averaged temperatures were significantly correlated with differences of air temperatures. Heat absorption of sediment from water increased or its heat emission to water decreased from 8: 00 to 19: 00,while 19: 00 to 8: 00 next day in verse. From March to September,heat transferred from water to sediment,while from sediment to water from October to February next year. Sediment was heatsource of East Lake Taihu in a whole year. Heat flux at WSI also had smaller 6-15 days' periodic fluctuations. Although changes of water temperature and heat flux at WSI were mainly affected by solar radiation and air temperature,they had delayed response towards meteorological parameters. Heat flux at WSI was negatively correlated with water temperature,and its change lagged behind water temperature change. The main function of heat flux at WSI was to buffer heat changes of lake. Submerged plants can relief surface water temperatures of lake as well as the vertical temperature gradients in summer.
引文
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