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Eutrophication downstream from small reservoirs in mountain rivers of Central Spain

机译：西班牙中部山区河流小型水库下游的富营养化

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In this research we examined the hypothesis that upper reaches of rivers and streams can experience eutrophication as a consequence of deep releases from dams. Field studies were conducted in four mountain rivers (Tormes, Riaza, Eresma and Miraflores Rivers) of Central Spain. The watersheds of these rivers are underlain by siliceous rocks. A small deep-release storage reservoir is found in the upper reaches of each river. Two sampling sites, upstream and downstream from the reservoir, were established in stony riffles of each impounded river. Significant (P < 0.01) increases in conductivity and nutrient (NO_3-N, NH_4-N, PO_4-P) concentrations downstream from the reservoirs were measured. Significant (P < 0.01) increases in periphyton chlorophyll a and ash-free dry biomass were also quantified at downstream sites. Significant (P < 0.01) correlation coefficients indicated that phosphate would play a more important role as the limiting nutrient for periphyton. Relative abundances of macroinvertebrate scrapers and collector-gatherers increased downstream from the reservoirs. Furthermore, taxon dominance, total density and total biomass of macroinvertebrates tended to be higher at downstream sites than at upstream sites. In contrast, taxon diversity and relative abundance of macroinvertebrate shredders decreased downstream from the reservoirs. It is concluded that small deep-release storage reservoirs, located in upper reaches of siliceous rivers, can act as nutrient sources, causing eutrophication downstream. Nutrients would ultimately come from land/forest runoff. The fact that terrestrial vegetation was not completely removed before filling reservoirs could also contribute to the eutrophication process.
机译：在这项研究中，我们检验了以下假设：由于大坝的深度释放，河流和小溪的上游可能会发生富营养化。在西班牙中部的四个山区河流（托尔梅斯河，里亚扎河，埃雷斯马河和米拉弗洛雷斯河）进行了实地研究。这些河流的分水岭被硅质岩包裹着。在每条河的上游都发现了一个小的深层释放蓄水池。在每个蓄水河的石质浅滩上建立了两个采样点，分别位于水库的上游和下游。电导率显着增加（P <0.01），并测量了储层下游的营养物（NO_3-N，NH_4-N，PO_4-P）浓度。下游站点的周生植物叶绿素a显着增加（P <0.01），并且无灰的干生物量也得到了定量。显着的（P <0.01）相关系数表明，磷酸盐作为围生植物的限制养分将发挥更重要的作用。大型无脊椎动物刮板和采集器的相对丰度在水库下游增加。此外，大型无脊椎动物的分类单元优势，总密度和总生物量在下游地区往往高于上游地区。相反，水库下游的大型无脊椎动物切碎机的分类群多样性和相对丰度降低了。结论是，位于硅质河上游的小型深层释放水库可以作为营养源，引起下游的富营养化。营养最终将来自土地/森林径流。在填满水库之前未完全清除陆地植被这一事实也可能有助于富营养化过程。

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