Background

Barrier lakes, formed by river interception, are particularly influenced by the upstream river. As such, spring freshet flooding and summer rainfall flooding due to wet precipitation (e.g. snow and rainfall) may sharply increase the concentrations of nitrogen, phosphorous, and carbon compounds in barrier lakes. Too much nutrients will lead to lake eutrophication. In this study, we used Lake Jingpo, the world’s second largest alpine barrier lake, to examine the impact of spring freshet flooding and summer rainfall flooding on its water quality by building a hydrodynamic water quality model with MIKE 21.

Results

The MIKE 21 HD hydrodynamic model and MIKE 21 AD convection and diffusion module were calibrated using meteorological data, hydrological data, and water quality data collected in 2018. All errors were in the acceptable range. According to model simulation results, the flow velocity in Lake Jingpo is generally weak (mostly lower than 0.015 m/s), but it increases to 0.045 m/s and above during spring freshet flooding (April–May) and summer rainfall flooding (August–September), which is much higher than in other months. The flow volume of its largest inflowing river reaches 4.81 × 10⁸ m³, 29.77 × 10⁸ m³, and 58.4 × 10⁸ m³ during spring freshet flooding, summer rainfall flooding, and 30-year frequency rainfall flooding period, respectively. The longest diffusion distances from the lake mouth to the downstream way are 16.3 km, 33.1 km, and 43.6 km during the spring freshet flooding, summer rainfall flooding, and 30-year frequency rainfall flooding period, respectively. A larger amount of precipitation leads to longer diffusion distances and increased concentrations of total nitrogen (TN), total phosphorous (TP), chemical oxygen demand (COD_Mn), and ammonia–nitrogen (NH₄-N) in the lake.

Conclusions

The sudden increase in water volume during spring flooding and summer rainfall flooding led to the rapid spread of nutrients and pollutants carried by the water into the barrier lake, resulting in a deterioration of lake water quality. In addition to pollution source control measures, ecological restoration, and the construction of a buffer system in the catchment are very important measures to effectively improve the buffer capacity of barrier lakes in light of spring freshet flooding and summer rainfall flooding.

中文翻译：

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春季大洪水和夏季降雨洪水对高山屏障湖水质的影响

背景

由截流形成的屏障湖泊尤其受上游河流的影响。因此，春季降雨和夏季降雨（由于降雨（例如降雪和降雨）引起的洪水）可能会急剧增加隔离湖中氮，磷和碳化合物的浓度。营养物质过多会导致湖泊富营养化。在这项研究中，我们使用世界第二大高山屏障湖景颇湖，通过使用MIKE 21建立水动力水质模型，研究了春季小洪水和夏季降雨洪水对其水质的影响。

结果

使用2018年收集的气象数据，水文数据和水质数据对MIKE 21 HD水动力模型和MIKE 21 AD对流和扩散模块进行了校准。所有误差均在可接受的范围内。根据模型模拟结果，景颇湖的流速通常较弱（大多低于0.015 m / s），但在春季小洪水（4-5月）和夏季降雨洪水（8月）时，流速增加至0.045 m / s及以上。 – 9月），比其他月份要高得多。其最大流入河流的流动体积达到4.81×10 ⁸ 米³，29.77×10 ⁸ 米³，和58.4×10 ⁸ 米³在春季大洪水，夏季降雨和30年频率降雨期间。在春季新生洪水，夏季降雨洪水和30年频率降雨洪水期间，从湖口到下游路径的最长扩散距离分别为16.3 km，33.1 km和43.6 km。较大的降水量导致更长的扩散距离，并增加了湖中总氮（TN），总磷（TP），化学需氧量（COD _Mn）和氨氮（NH ₄ -N）的浓度。

结论

春季洪水和夏季降雨洪水期间水量的突然增加导致水携带的营养物质和污染物迅速扩散到屏障湖中，导致湖泊水质恶化。除了污染源控制措施，生态恢复和集水区缓冲系统的建设都是非常重要的措施，可以有效地提高春季雨水洪水和夏季降雨洪水对堰塞湖的缓冲能力。