Abstract Eutrophication is the prime water quality issue in inland waters. Eutrophication and its key symptom, harmful cyanobacterial blooms, is expected to further increase in the future, which highlights the importance of managing the issue. The reduction of external nutrient load is crucial but might not bring fast relief to eutrophic waters due to ongoing diffuse pollution and legacy nutrients in the sediment. In this context, in-lake measures are needed to speed-up recovery. In this review, we discuss different in-lake measures based on coagulation and precipitation of cyanobacteria and/or phosphate for different lake categories (e.g., shallow or deep, mainly external or internal nutrient load, occurrence of perennial or summer blooms). In deep lakes with an external nutrient load higher than the internal load, a “Floc and Sink” method could be used in which a coagulant (e.g. aluminium salts, Al-salts; chitosan) combined with a ballast (e.g. soil, clay) removes a cyanobacterial bloom out of the water column. In case the deep lake suffers from high internal load, a phosphate (P)-fixative (e.g. lanthanum modified bentonite or Al-salts) can be used to “Lock” the legacy P, possibly combined with a coagulant – a “Floc and Lock” technique. The latter approach will target both the particulate P in a bloom and the internal P load. A shallow lake that suffers from summer blooms and in which the internal load is higher than the external load, a “Lock” strategy of winter application of a P-fixative is proposed to prevent bloom development. In shallow lakes with perennial blooms, an agent to damage the cells (such as H2O2) is required together with a coagulant and a ballast to avoid recolonization of the water column due to resuspension – a “Kill, Floc and Sink/Lock” method. The selection of the most promising in-lake measures and materials should be based on a proper system diagnosis and tests prior to a full-scale intervention. These methods can be effective, but evidently reduction of external nutrient loads, both from point- and non-pointed sources, is an absolute necessity to restore aquatic ecosystems in a holistic sense.

中文翻译：

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蓝藻水华的凝结和沉淀

摘要 富营养化是内陆水域的首要水质问题。富营养化及其主要症状，有害蓝藻大量繁殖，预计未来将进一步增加，这凸显了管理该问题的重要性。减少外部养分负荷至关重要，但由于持续的扩散污染和沉积物中遗留的养分，可能无法快速缓解富营养化水域。在这种情况下，需要采取湖内措施来加速恢复。在这篇综述中，我们讨论了基于不同湖泊类别（例如，浅或深，主要是外部或内部养分负荷，常年或夏季水华发生）的蓝藻和/或磷酸盐的凝结和沉淀的不同湖内措施。在外部营养负荷高于内部负荷的深湖中，可以使用“絮凝沉淀”方法，其中混凝剂（例如铝盐、铝盐；壳聚糖）与压载物（例如土壤、粘土）结合从水柱中去除蓝藻水华。如果深湖受到高内部负载的影响，磷酸盐 (P) 固定剂（例如镧改性膨润土或铝盐）可用于“锁定”遗留 P，可能与凝结剂结合使用 - 一种“絮凝剂和锁定剂” ”的技术。后一种方法将针对浮华中的颗粒 P 和内部 P 负载。一个受夏季水华影响且内部负载高于外部负载的浅湖，提出了冬季应用 P 固定剂的“锁定”策略以防止水华发展。在常年开花的浅湖中，需要一种破坏细胞的药剂（如 H2O2）以及凝结剂和压载物，以避免由于再悬浮而导致水柱重新定植——一种“杀死、絮凝和下沉/锁定”方法。最有希望的湖内措施和材料的选择应基于在全面干预之前进行适当的系统诊断和测试。这些方法可能是有效的，但显然减少来自点源和非点源的外部营养负荷是从整体意义上恢复水生生态系统的绝对必要条件。