Though high rates of nitrate (NO₃⁻) leaching from forests are undesirable, the factors significantly regulating stream NO₃⁻ concentration is not clarified yet. In Japan, not only near metropolitan areas but also the Japan Sea-side area with heavy snowfall is well known for receiving more than 10 kg-N ha⁻¹ year⁻¹ of nitrogen (N) deposition. However, NO₃⁻ concentration in stream water is relatively low in the Japan Sea-side area compared with its concentration in other areas. We examined important environmental factors regulating stream NO₃⁻ concentrations at baseflow condition in a large region of Japan, the Kinki region (KIN) including a part of Japan Sea-side (JSK) using Random Forest regression. The amounts of N deposition and precipitation were common regulating factors for stream NO₃⁻ concentration at baseflow condition. Random forest showed the significant correlation between the factors related to ecosystem N retention and stream NO₃⁻ concentration at baseflow condition, and it suggests that large N deposited during the growing season was incorporated into the ecosystem in the entire KIN. Heavy rain and snow flush N and wash out N accumulated in the surface soil, causing small N accumulation in forests. Also, large precipitation dilute NO₃⁻ concentration in baseflows. These things lowered stream NO₃⁻ concentration at baseflow condition. Especially in JSK, most of N deposed with the heavy snow flushed out during the snowmelt period. We provided the first statistical confirmation using Random Forest regression that N accumulation and cycling in forest ecosystems were related to NO₃⁻ leaching from forests into streams.

中文翻译：

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在包括气候梯度在内的大区域内，基本流量条件下调节河流硝酸盐浓度的环境因素

虽然硝酸盐的高速率（NO ₃ ^- ）从森林浸出是不希望的，所述因子显著调节流NO ₃ ^-浓度是尚未阐明。在日本，不仅大都市地区附近，而且降雪量大的日本海边地区也因接收到超过10 kg-N ha - ¹ 年^-1的氮（N）而闻名。然而，NO ₃ ^- ，其在其他领域的浓度相比浓度在流水是在日本海侧区域相对较低。我们研究了调节流NO _3的重要环境因素^-使用随机森林回归法，在日本大片地区（近畿地区（KIN），包括日本海边（JSK）的一部分）的基流条件下的浓度 N沉降和沉淀的量为用于流公共调节因子NO ₃ ^-浓度在基流条件。随机森林表明对生态系统氮沉积和流NO相关的因素之间的相关性显著₃ ^-在基流条件浓度，它表明，在生长季节沉积大的N被纳入在整个KIN的生态系统。大雨和大雪冲刷氮并冲走表层土壤中累积的氮，从而在森林中造成少量氮累积。此外，大降水稀NO ₃ ^-基流中的浓度。这些东西降低流NO ₃ ^-浓度在基流条件。特别是在JSK中，大部分融雪中N都被大雪冲走了。我们提供了使用随机森林回归，在森林生态系统氮素的积累和自行车均与NO第一统计确认₃ ^-从森林浸出到流。