Instituto de Ciencias Marinas de Andalucía (CSIC), Avda. República Saharaui 2, 11519 Puerto Real, Cádiz, Spain.
Sci Total Environ. 2012 Dec 1;440:261-71. doi: 10.1016/j.scitotenv.2012.06.061. Epub 2012 Jul 15.
The aim of this 12-year study was to assess the nekton (fish, decapod crustaceans) response to freshwater inputs (rainfall, dam discharges) in a temperate estuary with regulated riverine inflow. Although interannual variability in river discharges to the Guadalquivir estuary has been extremely high since the construction of a dam in 1930, a significant decreasing trend in the dam's discharges has been observed in the last 80 years. During this study, an alternation of wet, standard and dry years occurred in the estuarine area but no significant long-term trend was observed. River discharge, in turn, showed a considerable interannual variability and a significantly decreasing long-term trend. Freshwater inputs had an immediate effect on estuarine salinity and turbidity, and consequently on prey availability (mysids). Although 124 nektonic species were collected, only 47 of them (adding up to 99.7% of total abundance) were regularly present in the estuary: 32 marine migrants, 13 estuarine species and 2 diadromous species. Well-defined temporal changes in species composition and abundance yielded clear seasonal patterns in the estuarine nektonic community. Considerable intermonth and interannual changes were occasionally observed relating to freshwater inputs, mainly in winter/autumn of wet years. Thus, within each two-month period, some significant interannual differences in the nektonic community were also observed, with marine migrants tending to be more abundant in dry years. However, changes in the studied nektonic community did not show long-term trends. In conclusion, natural and human-controlled freshwater inputs currently play a significant role in determining the physicochemical conditions and the biota of the Guadalquivir estuary. However, although freshwater input seemed to transitorily affect the estuarine nekton, either directly (flushing out) or indirectly (through changes in salinity, turbidity and prey availability), a quick reestablishment of the estuarine nekton (strong resilience) was observed following freshwater inputs together with the recovery of environmental conditions within the estuary.
本研究旨在评估淡水输入（降雨、大坝泄洪）对一个有调控河流入流的温带河口内洄游鱼类（鱼类、十足目甲壳动物）的影响。自 1930 年大坝建成以来，瓜达尔基维尔河河口的年际径流量变化极大，但在过去 80 年中，大坝的径流量呈显著下降趋势。在本研究期间，河口地区出现了湿润、标准和干燥年份的交替，但未观察到长期的显著趋势。河流径流量也表现出相当大的年际变化和显著的长期下降趋势。淡水输入对河口盐度和浊度有直接影响，从而影响了猎物的可获得性（糠虾）。尽管采集了 124 种洄游鱼类，但只有 47 种（占总丰度的 99.7%）经常出现在河口：32 种海洋洄游鱼类、13 种河口种和 2 种溯河洄游种。物种组成和丰度的明显季节性变化导致了河口洄游鱼类群落的明显季节性模式。偶尔会观察到与淡水输入有关的相当大的月际和年际变化，主要发生在湿润年份的冬/秋季。因此，在每个两个月的周期内，也观察到了一些与洄游鱼类群落有关的显著年际差异，在干旱年份，海洋洄游鱼类的丰度较高。然而，研究中的洄游鱼类群落没有显示出长期的趋势。总之，自然和人为控制的淡水输入目前在决定瓜达尔基维尔河河口的理化条件和生物群方面发挥着重要作用。然而，尽管淡水输入似乎会暂时影响河口洄游鱼类，无论是直接（冲洗）还是间接（通过盐度、浊度和猎物可获得性的变化），在淡水输入后，河口洄游鱼类会迅速恢复，河口环境条件也会恢复。
