Imtiazy Md Noim, Paterson Andrew M, Higgins Scott N, Yao Huaxia, Houle Daniel, Hudson Jeff J
Department of Biology, University of Saskatchewan, Collaborative Science Research Building, 112 Science Place, Saskatoon, SK S7N5E2, Canada.
Inland Waters Unit, Ontario Ministry of the Environment, Conservation and Parks, 1026 Bellwood Acres Road, Dorset, ON P0A1E0, Canada.
Water Res. 2025 Feb 1;269:122814. doi: 10.1016/j.watres.2024.122814. Epub 2024 Nov 19.
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 SO 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.
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泊学过程的影响而受到了广泛关注。虽然过去的研究记录了从酸化和气候变化中恢复对DOC长期趋势的影响，但这些解释性因素的新重要性仍鲜为人知。此外，很少有研究跟进DOC增加的地点的近期趋势。利用1980年至2020年的数据集，我们调查了加拿大东部四个地区49个有DOC增加历史的湖泊中DOC和溶解有机氮（DON）的年际变化。我们使用局部加权回归（LOESS）平滑和分段回归来识别DOC模式的近期变化。我们在高酸化地区（多塞特和新斯科舍）观察到一种稳定模式甚至下降趋势（p<0.001），此前这些地区记录了DOC的增加。在低酸沉降地区，国际可持续发展研究所实验湖区，DOC的增加模式在21世纪初趋于稳定；然而，近年来DOC似乎又在增加（p = 0.03）。我们的分析确定降水和硫沉降是DOC模式的主要解释变量（解释了56 - 71%的方差）。然而，由于酸沉降已大幅下降，气候和当地流域因素的影响越来越大，导致出现了新的DOC模式。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与铵沉降）。这导致了DOC:DON比值的明显变化，表明溶解有机物（DOM）组成发生了变化。由于环境变量的性质不断变化和新出现的趋势，我们强调在不同地区进行持续监测的重要性。
