The effect of agriculture on water environment in a subtropical island

本研究的目的是分析农业对缺水亚热带岛屿水环境的影响。大多数灌溉池塘被归类为富营养化状态，并观察到水华。结果表明，家畜径流是主要的营养来源。农田降雨径流对入水负荷的富营养化作用较小，主要是以道路径流为主，相应浓度较低。地下水中硝态氮浓度较高，推测硝态氮污染来源于化肥和有机肥。监测井中硝酸盐浓度的数值和趋势变化很大。这些结果表明，水平地下水流分布不均匀，各井集水自邻近地区。据估计，大约22%的人类活动产生的氮被淋溶到地下水中。

The purpose of this study was to analyze the effect of agriculture on water environment in a water-starved subtropical island. Most irrigation ponds were categorized as in eutrophic states and water blooms were observed. It is suggested that runoff from livestock is the main nutrient source. Rainfall runoff from farmland had few eutrophying effects on inflowing loads, because the runoff mainly consisted of roadway discharge and so relevant concentrations were low. Nitrate nitrogen concentrations of groundwater were high, assuming that the nitrate contamination originated from fertilizer and manure. The values and trends of nitrate concentrations at monitoring wells varied greatly. These results imply horizontal groundwater flow is not uniformly distributed and the each well gathers water from vicinal area. It was estimated that around 22% nitrogen output from human activity leached to the groundwater.