Karst aquifers in subtropical regions are characterized by high variability of water availability and quality due to changes associated with rainy and dry seasons. An additional challenge for water management is the combination of surface-water and karst groundwater systems since high spatiotemporal dynamics cause high variability of water quality. In these cases, adapted protection strategies are required. In this study, a protection approach for the catchment of a river-water diversion point in a rural area in northern Vietnam is developed. The variability of water quality was evaluated by rainy and dry season synoptic surveys of suspended particles and microbial contamination at 49 sites and time series at three sets of paired sites under constant hydraulic conditions. The anthropogenic land-use activities in the catchment were mapped to identify potential contamination sources and to highlight the challenging combination of surface-water and karst groundwater management. The analyzed data indicate differences in water quality between the dry and rainy seasons and a higher influence on water quality from land use than from hydrologic conditions. Furthermore, the results suggest a high risk of contamination resulting from residential areas, agriculture, and livestock farming, and reveal the necessity of implementation of appropriate measures such as restricted farming and the hook-up of buildings to municipal sewage disposal. Finally, the data show that water quality can be improved by adjusting water withdrawals by the time of day. The applied methods can be transferred to other surface-water and karst groundwater systems in similar subtropical environments.

由于与雨季和旱季相关的变化，亚热带地区的喀斯特含水层的特点是水的可用性和水质变化很大。水资源管理的另一个挑战是地表水和岩溶地下水系统的结合，因为高时空动态会导致水质的高度可变性。在这些情况下，需要调整保护策略。在这项研究中，开发了一种保护越南北部农村地区河水分流点集水区的方法。在恒定水力条件下，通过雨季和旱季对 49 个地点的悬浮颗粒和微生物污染的天气调查以及三组配对地点的时间序列来评估水质的变化。绘制了集水区人为土地利用活动的地图，以确定潜在的污染源，并突出地表水和岩溶地下水管理的挑战性组合。分析的数据表明，旱季和雨季之间的水质存在差异，土地利用对水质的影响大于水文条件。此外，结果表明居住区、农业和畜牧业造成污染的风险很高，并揭示了实施适当措施的必要性，例如限制农业和将建筑物与城市污水处理相连接。最后，数据显示可以通过按一天中的时间调整取水量来改善水质。