Assessing nutrient loading and processing is crucial for water quality management in lakes and reservoirs. Quantifying and reducing external nutrient inputs in these systems remains a significant challenge. The difficulty arises from low monitoring frequencies of the highly dynamic external inputs and the limited availability of measures to reduce diffuse source loading. One option for the latter is the use of pre-dams, i.e. small impoundments at the inflow points into reservoirs, designed to retain nutrients by algal uptake and sedimentation. This study analyzes long-term (ranging from 8 to 22 years) nutrient and discharge time series for nine German pre-dams to assess their retention capacity. For that, we (i) quantified nutrient loading using four different mathematical methods, (ii) derived their retention efficiencies, and (iii) identified environmental factors determining the retention of nitrogen (N), phosphorus (P), and silica (Si). We show that retention of soluble reactive phosphorus (SRP) (43.6 %) and total phosphorus (TP) (39.9 %) is far higher than for nitrate (NO3) (15.3 %) and Si (15.9 %). The retention efficiency for SRP and TP was higher during the warm seasons because of higher algal nutrient uptake and thus higher nutrient sedimentation. Mixed effects models documented a significant positive effect of the pre-dams’ hydraulic residence time (HRT) on retention efficiency. Pre-dams provide substantial service in retaining nutrients and help to protect downstream waterbodies from nutrient inputs. They provide effective measures for trapping nutrients including those originating from non-point sources.

中文翻译：

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前坝作为水库守护者的效率如何？营养保留的长期研究


评估养分负荷和加工对于湖泊和水库的水质管理至关重要。量化和减少这些系统中的外部营养输入仍然是一项重大挑战。困难在于高动态外部输入的低监测频率和减少漫射源负载的措施有限。后者的一种选择是使用预坝，即在水库的流入点建造小型蓄水池，旨在通过藻类吸收和沉积来保留营养物质。本研究分析了 9 个德国前坝的长期（从 8 到 22 年不等）养分和排放时间序列，以评估它们的滞留能力。为此，我们 （i） 使用四种不同的数学方法量化了养分负荷，（ii） 得出了它们的保留效率，以及 （iii） 确定了决定氮 （N）、磷 （P） 和二氧化硅 （Si） 保留的环境因素。我们表明，可溶性活性磷 （SRP） （43.6%） 和总磷 （TP） （39.9%） 的保留率远高于硝酸盐 （NO3） （15.3%） 和硅 （15.9%）。在温暖的季节，SRP 和 TP 的保留效率更高，因为藻类养分吸收较高，因此养分沉降率较高。混合效应模型记录了前坝的水力停留时间 （HRT） 对保留效率的显着积极影响。预坝在保留养分方面提供了大量服务，并有助于保护下游水体免受养分输入的影响。它们为捕获营养物质提供了有效的措施，包括来自非点源的营养物质。