Aquatic Systems Biology Unit, Department of Life Science Systems, Technical University of Munich, Muehlenweg 22, D-85354, Freising, Germany.
Aquatic Systems Biology Unit, Department of Life Science Systems, Technical University of Munich, Muehlenweg 22, D-85354, Freising, Germany.
Environ Pollut. 2021 Apr 1;274:116520. doi: 10.1016/j.envpol.2021.116520. Epub 2021 Jan 22.
Extensive fish production in earthen ponds is a common aquaculture practice, which requires draining of the ponds for fish harvesting. Despite their value for biodiversity and water retention, the impact of fish ponds on the receiving streams as regards fine sediment and nutrient pollution remains controversial. This holds particularly true for streams with endangered freshwater pearl mussels, requiring a highly permeable streambed with low fine sediment content for successful juvenile development. This study quantified the amount of fine sediment, suspended solids and nutrients delivered to pearl mussel streams in relation to the pond characteristics, distance to the receiving stream and applications of measures to prevent the input of fines. Comparing fine sediment deposition above and downstream of the pond inlets after 21 pond drainage operations, as well as continuous measurements of the turbidity for 12 operations revealed varying effects of pond fishing on the receiving streams. Average fine sediment deposition was increased by nearly six-fold compared to upstream and maximum turbidity values for single drainage operations exceeded 460 NTU. Draining between 1% and 92% of the water volume of individual ponds resulted in additional loading of 0.07-4.6 t suspended particles. Physical mitigation structures that prevent mobilized material from reaching the receiving stream significantly reduced the fine sediment input and deposition rates. Harvesting methods that do not require complete drainage of the pond reduced the turbidity by ten-fold. Without mitigation measures, the impact of pond drainage operations on the fine sediment deposition was comparable to high discharge events. No significant increase in nutrient concentration was observed during most drainage operations. These results reveal remarkable effects of pond drainage on the aquatic environment, as well as the possibility to minimize such impacts by switching to harvest methods that do not require complete pond drainage and installation of sedimentation structures.
大规模的池塘鱼类养殖是一种常见的水产养殖方式，这种方式需要将池塘的水排干以捕捞鱼类。尽管池塘对于生物多样性和水的保持具有重要价值，但它们对接收溪流中的细沉积物和营养物污染的影响仍然存在争议。对于那些有濒危淡水珍珠贻贝的溪流来说，情况尤其如此，这些溪流需要高度渗透的河床，且细沉积物含量低，以确保幼贻贝的成功发育。本研究量化了与池塘特征、与接收溪流的距离以及为防止细颗粒输入而采取的措施有关的细沉积物、悬浮物和养分输送到珍珠贻贝溪流的数量。比较了 21 次池塘排水作业后池塘入口处上下游的细沉积物沉积量，以及 12 次作业的连续浊度测量结果，发现池塘捕鱼对接收溪流的影响各不相同。与上游相比，平均细沉积物沉积增加了近六倍，单次排水作业的最大浊度值超过了 460 NTU。单个池塘排水 1%至 92%的水量会导致 0.07-4.6 吨悬浮物的额外负荷。防止移动物质到达接收溪流的物理缓解结构显著减少了细沉积物的输入和沉积速率。不需要完全排空池塘的捕捞方法将浊度降低了十倍。如果没有缓解措施，池塘排水作业对细沉积物沉积的影响与高流量事件相当。在大多数排水作业中，没有观察到养分浓度的显著增加。这些结果揭示了池塘排水对水生环境的显著影响，以及通过切换到不需要完全排空池塘和安装沉降结构的捕捞方法来最小化这种影响的可能性。
