The increase in dissolved organic carbon (DOC) concentrations in freshwater systems has received considerable attention due to its implications for drinking water treatment and numerous limnological processes. While past studies have documented the influence of recovery from acidification and climate change on long-term DOC trends, the emerging importance of these explanatory factors remains less understood. In addition, few studies have followed up on recent trends in sites that have undergone increases in DOC. Using a dataset from 1980 to 2020, we investigated interannual variations in DOC and dissolved organic nitrogen (DON) in 49 lakes across four eastern Canadian regions with a history of increases in DOC. We identified recent shifts in DOC patterns using LOESS smoothing and piecewise regression. We observed a stabilizing pattern or even a decrease (p < 0.001) in high acidification regions (Dorset and Nova Scotia), where increases in DOC were previously documented. At the low acid deposition region, IISD-Experimental Lakes Area, an increasing pattern in DOC stabilized in the early 2000s; however, DOC appears to be increasing again in recent years (p = 0.03). Our analysis identified precipitation and SO₄ deposition as the primary explanatory variables for DOC patterns (explaining 56–71% of variance). However, because acid deposition has declined substantially, climate and local watershed factors are becoming increasingly influential, leading to the emergence of new DOC patterns. Long-term changes in DOC and DON were not always synchronous, as these were often correlated with different factors (e.g., DON with ammonium deposition). This resulted in observable shifts in DOC:DON ratios, indicative of changes in dissolved organic matter (DOM) composition. We underscore the importance of ongoing monitoring in diverse regions because of the changing nature of environmental variables and new emerging trends.

中文翻译：

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湖泊褐变已经停止了吗？加拿大东部湖泊的稳定化、再褐变和其他与溶解有机物趋势相关的因素


淡水系统中溶解有机碳 （DOC） 浓度的增加因其对饮用水处理和众多湖沼学过程的影响而受到广泛关注。虽然过去的研究已经记录了从酸化和气候变化中恢复对 DOC 长期趋势的影响，但这些解释因素的新兴重要性仍然知之甚少。此外，很少有研究跟进 DOC 增加的地点的最新趋势。使用 1980 年至 2020 年的数据集，我们调查了加拿大东部四个地区 49 个湖泊中 DOC 和溶解有机氮 （DON） 的年际变化，这些湖泊有 DOC 增加的历史。我们使用 LOESS 平滑和分段回归确定了 DOC 模式的最新变化。我们在高酸化地区（多塞特郡和新斯科舍省）观察到稳定模式甚至下降 （p < 0.001），这些地区以前记录了 DOC 的增加。在低酸沉积区域 IISD-实验湖区，DOC 的增加模式在 2000 年代初期稳定下来;然而，近年来 DOC 似乎再次增加 （p = 0.03）。我们的分析确定降水和 SO₄ 沉积是 DOC 模式的主要解释变量（解释了 56-71% 的方差）。然而，由于酸沉积已大幅下降，气候和当地流域因素的影响力越来越大，导致新的 DOC 模式的出现。DOC 和 DON 的长期变化并不总是同步的，因为它们通常与不同的因素相关（例如，DON 与铵沉积）。这导致 DOC：DON 比值发生可观察的变化，表明溶解有机物 （DOM） 组成发生变化。 我们强调在不同地区进行持续监测的重要性，因为环境变量的性质不断变化和新出现的趋势。