Abstract：
Re-wetting of agricultural areas reclaimed by draining peatlands reportedly entails risks of nutrient loads downstream because of leaching of dissolved nutrients from pools in the soil. On floodplain fens, nutrient retention and runoff function have been recognized as dependent upon the hydrological environments of re-wetted agricultural peatland (RAP). Although many studies have been conducted for artificially re-wetted agricultural peatlands (artificial RAPs), knowledge on naturally re-wetted agricultural peatlands (natural RAPs) has been lacking. This study assessed the natural re-wetting of agricultural areas in floodplain fens in terms of risks of nutrient loading in the basin of Kushiro Mire, northern Japan. Flooding of the adjacent river caused by heavy rainfall remarkably increased the water flow, and the inflow and outflow fluxes of nitrogen (N) and phosphorus (P) of a test plot in the natural RAP. Flood waters supplied mainly inorganic nutrients to the test plot, including NO3-N and PO4-P. Larger amounts of dissolved organic N and P, NH4-N, and PO4-P that had accumulated in surface water and surface groundwater in the plot flowed out. Consequently, the test plot represented net runoff of 3 and 0.4 mg m-2 day-1 as total N and total P, respectively, for the average of the whole observation period. The test plot was a source of N loading downstream, which was contrary to results obtained for artificial RAPs in many studies. However, the test plot showed a smaller amount of net phosphorus runoff. Our findings suggest that water level fluctuation and river flood water inflow affect the nutrient retention and runoff functions of RAPs. Repeated inundated and dried conditions, with no continuous inflow of river water, explain the nutrient runoff in the test plot.
摘要：
据报道，由于泥炭地排水而开垦的农业区的再润湿会带来下游养分负荷的风险，因为溶解的养分从土壤池中浸出。在洪泛区的芬斯，养分保留和径流功能已被认为取决于重新湿润的农业泥炭地（RAP）的水文环境。尽管已经对人工再湿润的农业泥炭地（人工RAP）进行了许多研究，关于自然再湿润的农业泥炭地(自然RAP)的知识一直缺乏。这项研究根据KushiroMire流域养分负荷的风险评估了洪泛区农业区的自然再湿润，日本北部强降雨导致邻近河流的洪水显着增加了水流量，以及天然RAP中测试地块的氮（N）和磷（P）的流入和流出通量。洪水主要向测试区提供无机养分，包括NO3-N和PO4-P大量溶解的有机N和P，NH4-N,和积累在该地块地表水和地表水中的PO4-P流出。因此,测试地块代表3和0.4mgm-2day-1的净径流作为总N和总P，分别,整个观察期的平均值。测试图是下游N负载的来源，这与许多研究中人工RAP的结果相反。然而,测试地块显示净磷径流较少。我们的发现表明，水位波动和河水流入会影响RAP的养分保留和径流功能。反复淹没和干燥的条件，没有连续的河水流入，解释测试地块中的养分径流。
