Impact of N-Saturated Upland Forests on Downstream N Pollution in the Tatara River Basin, Japan
Impact of N-Saturated Upland Forests on Downstream N Pollution in the Tatara River Basin, Japan
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DOI：
10.1007/s10021-011-9505-z
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发表时间：
2012-03-01
期刊：
影响因子：
3.7
通讯作者：
Kume, Atsushi
中科院分区：
文献类型：
--
作者：
Chiwa, Masaaki;Onikura, Norio;Kume, Atsushi
本研究评估了日本西部九州北部塔塔拉河流域饱和氮(N)的山地森林是否会降低下游水质。我们的假设是，在含氮饱和森林的流域中，大气氮沉降升高会降低下游水质，因为相当数量的大气氮沉降进入溪流而没有被保留。在一年多的时间里，在流域内不同土地用途类别的23个地点进行了天气性溪流采样。对近30年（1977-2007）的下游水质进行了长期时间分析，并与城市/农业活动、污水处理、大气氮沉降和森林条件等相关因素的长期趋势进行了比较。结果表明，大气中氮沉降到氮饱和森林中可能是一个足够大的非点源氮离开流域，影响下游水质。在过去30年中，城市/农业活动产生的污染物出口减少、大气氮沉降增加以及针叶人工林的成熟都突出了这一点。这些导致了下游水中总磷和有机氮浓度的降低，而下游硝酸盐（NO3-）浓度在过去30年中有所增加。随后下游氮磷比的增加表明磷的限制。减少氮饱和高原森林的NO3-出口被认为是改善区域下游NO3-污染的策略，但在减少大气N排放方面需要洲际尺度的行动。
This study evaluated whether nitrogen (N) saturated upland forests can degrade downstream water quality in the Tatara River Basin, northern Kyushu, western Japan. Our hypothesis is that elevated atmospheric N deposition degrades downstream water quality in a watershed containing N-saturated forests because a considerable amount of atmospherically deposited N passes into the streams without being retained. Synoptic stream water samplings were conducted at 23 sites across a wide range of land-use categories in the basin over 1 year. A long-term temporal analysis of downstream water quality over the last 30 years (1977-2007) was conducted and compared with long-term trends in related factors such as urban/agricultural activity, sewage wastewater treatment, atmospheric N deposition, and forest condition. The results showed that atmospherically deposited N to N-saturated forests can be a large enough non-point source of N leaving the watershed to impact downstream water quality. This was highlighted by the reduction in pollutant exports derived from urban/agricultural activities, an increase in atmospheric N deposition, and the maturation of coniferous plantation forests in the past 30 years. These have led to reductions in total phosphorus and organic nitrogen concentrations in downstream water, whereas downstream nitrate (NO3-) concentrations increased over the last 30 years. The consequent increase in the downstream N: P ratio indicated P limitation. Reducing the NO3- exports from N-saturated upland forests is suggested as a strategy to improve regional downstream NO3- pollution, but involves intercontinental-scale action in reducing atmospheric N emissions.