Catalan Institut e for Water Research, Carrer d'Emili Grahit, 101, 17003 Girona, Spain.
Faculty of Science and Technology, University of the Basque Country, P.O. Box 644, 48080 Bilbao, Spain.
Sci Total Environ. 2016 Jan 1;540:168-77. doi: 10.1016/j.scitotenv.2015.07.017. Epub 2015 Jul 30.
River regulation has fundamentally altered large sections of the world's river networks. The effects of dams on the structural properties of downstream reaches are well documented, but less is known about their effect on river ecosystem processes. We investigated the effect of dams on river nutrient cycling by comparing net uptake of total dissolved nitrogen (TDN), phosphorus (TDP) and organic carbon (DOC) in river reaches located upstream and downstream from three reservoir systems in the Ebro River basin (NE Iberian Peninsula). Increased hydromorphological stability, organic matter standing stocks and ecosystem metabolism below dams enhanced the whole-reach net uptake of TDN, but not that of TDP or DOC. Upstream from dams, river reaches tended to be at biogeochemical equilibrium (uptake≈release) for all nutrients, whereas river reaches below dams acted as net sinks of TDN. Overall, our results suggest that flow regulation by dams may cause relevant N cycling discontinuities in rivers. Higher net N uptake capacity below dams could lead to reduced N export to downstream ecosystems. Incorporating these discontinuities could significantly improve predictive models of N cycling and transport in complex river networks.
河流调节从根本上改变了世界上大部分的河流网络。水坝对下游河段结构特性的影响已有充分的记录，但对其对河流生态系统过程的影响知之甚少。我们通过比较三个水库系统上下游河段的总溶解氮（TDN）、磷（TDP）和有机碳（DOC）的净吸收，研究了水坝对河流养分循环的影响。在大坝以下，水力学形态稳定性的增加、有机物质储量和生态系统代谢增强了整个流域的 TDN 净吸收，但 TDP 或 DOC 的净吸收没有增加。在大坝的上游，所有营养物质的河流河段都倾向于达到生物地球化学平衡（吸收≈释放），而大坝以下的河流河段则是 TDN 的净汇。总的来说，我们的结果表明，水坝的水流调节可能会导致河流中氮循环的明显不连续性。大坝下游更高的净氮吸收能力可能导致向下游生态系统的氮输出减少。纳入这些不连续性可以显著提高复杂河流网络中氮循环和输运的预测模型。
