Dissolved organic carbon (DOC) concentrations have increased over the past few decades in surface waters across Europe and North America. This has drawn a lot of attention, given the key role of DOC in the global carbon cycle and in surface water biogeochemistry and ecology. While many reports have focused on DOC response to environmental changes in headwater streams and lakes taken separately, there is a lack of studies that combines streams and lakes with varying catchment characteristics in a network-scale perspective. Here, long-term (1987–2018) trends were analyzed and environmental drivers of year-to-year variations in DOC concentrations were examined in headwater streams, lakes and lake outflows at the Turkey Lakes Watershed (TLW) in Ontario, Canada. Results indicated significant increasing of DOC trends in ten out of 12 headwater streams and in four out of 12 lakes and lake outflows over the study period. In addition, piecewise regression analysis detected breakpoints in the 2000 s for DOC time series data in some stations. Multivariate analysis showed that variations in hydro-climatic conditions and the chemistry of atmospheric precipitations explained 13 % to 99 % of year-to-year variations in DOC concentrations. Air temperature emerged as the most influential factor for lakes and lake outflows while precipitation chemistry was the main driver of inter-annual DOC variation in headwater streams. For the latter, the rate of DOC increase and the proportion of explained variance were mainly dependent on catchment characteristics, notably wetland cover which was related to mean catchment slope and total relief. In the context of global change, further research is needed to better understand how changes in climate and atmospheric deposition may be modulated by catchment attributes and ecosystem types for determining future DOC fate and behaviour in surface waters.

中文翻译：

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森林流域地表水溶解有机碳浓度的长期趋势和年际变化的驱动因素

过去几十年来，欧洲和北美地表水中的溶解有机碳 (DOC) 浓度有所增加。鉴于 DOC 在全球碳循环以及地表水生物地球化学和生态学中的关键作用，这引起了广泛关注。虽然许多报告分别关注DOC对源头溪流和湖泊环境变化的响应，但缺乏从网络规模的角度将具有不同流域特征的溪流和湖泊结合起来的研究。本文分析了加拿大安大略省土耳其湖流域 (TLW) 的长期（1987-2018）趋势，并检查了源头溪流、湖泊和湖泊流出物中 DOC 浓度逐年变化的环境驱动因素。结果表明，在研究期间，12 条源头溪流中的 10 条以及 12 条湖泊和湖泊流出道中的 4 条 DOC 趋势显着增加。此外，分段回归分析在一些站点的DOC时间序列数据中检测到2000秒内的断点。多变量分析表明，水文气候条件和大气降水化学成分的变化解释了 DOC 浓度逐年变化的 13% 至 99%。气温成为湖泊和湖泊流出的最影响因素，而降水化学是源头水流中 DOC 年际变化的主要驱动因素。对于后者，DOC 的增加率和解释方差的比例主要取决于流域特征，特别是与平均流域坡度和总地形有关的湿地覆盖。在全球变化的背景下，需要进一步研究，以更好地了解流域属性和生态系统类型如何调节气候和大气沉降的变化，以确定未来 DOC 在地表水中的命运和行为。