Concerns have been raised regarding the degradation of stream water quality due to the excessive influx of atmospheric deposition. This study aimed to reveal the long‐term variation in stream water chemistry in approximately 40 forested small watersheds in the northern Kanto region, based on 3 surveys conducted in 1991–1992, 2006–2007, and 2022. The factors influencing each dissolved element were investigated. Regarding long‐term variations in stream water chemistry, relatively stable concentrations of cations (Ca2+, Mg2+, K+, and Na+) and SiO2 were observed. However, the concentrations of anions (Cl−, , and ) decreased due to the improvement in the atmospheric environment and the diminishing effect of fertilization. Furthermore, the recent increase in stream water pH was attributed to an increase in bicarbonate (), compensating for the decrease in anion concentrations relative to cations. Geology was the most significant factor for inter‐watershed variations in cations and SiO2, and this influence remained relatively constant over 30 years. Forest practices, especially fertilization, had a significant effect on Cl− and , and contributed to higher concentrations in the fertilized watersheds than in the non‐fertilized watersheds over the 15 years following fertilization. Sulfate deposition was a significant influencing factor for , and the concentration fluctuated under long‐term variations in deposition over the past 30 years. Despite substantial acid deposition in the study area, the absence of stream water acidification could be attributed to the abundant cation supply from bedrock and volcanic ash, which underwent weathering processes.

中文翻译：

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关东地区北部小森林流域溪流水化学的长期变化

人们对由于大气沉降过多流入而导致溪流水质恶化表示担忧。本研究旨在基于 1991-1992 年、2006-2007 年和 2022 年进行的 3 次调查，揭示关东北部地区约 40 个森林覆盖的小流域溪流水化学的长期变化。影响每种溶解元素的因素是调查了。关于溪流水化学的长期变化，相对稳定的阳离子浓度（Ca2+, 镁2+, K+，和钠+）和二氧化硅2被观察到。然而，阴离子（Cl-由于大气环境的改善和施肥作用的减弱， 、 、 和 ) 减少。此外，最近溪流水 pH 值的增加归因于碳酸氢盐 () 的增加，补偿了阴离子相对于阳离子浓度的下降。地质是造成流域间阳离子和 SiO2 变化的最重要因素2，并且这种影响在 30 年来保持相对稳定。森林实践，特别是施肥，对氯有显着影响-和 ，并且在施肥后 15 年内，施肥流域中的浓度高于未施肥流域中的浓度。硫酸盐沉积是一个重要的影响因素，并且在过去30年沉积的长期变化下浓度发生波动。尽管研究区域存在大量酸沉积，但溪流水没有酸化可能归因于经历了风化过程的基岩和火山灰提供了丰富的阳离子。