Begum Most Shirina, Kadjeski Meredith, Fasching Christina, Xenopoulos Marguerite A
Department of Biology, Trent University, Peterborough, ON Canada.
Environmental and Life Sciences Graduate Program, Trent University, Peterborough, ON Canada.
Biogeochemistry. 2025;168(5):73. doi: 10.1007/s10533-025-01270-3. Epub 2025 Sep 12.
Export of dissolved organic carbon (DOC) from freshwater systems has been the focus of many studies owing to its pivotal role in regulating global carbon fluxes and ecosystem function. Both the flux and composition of dissolved organic matter (DOM) are critical for understanding its ecological impact, as similar compositions can have vastly different consequences depending on the magnitude of input and hydrological context. However, very little data exists on the composition of DOM export fluxes to downstream ecosystems. Here we investigate the interaction of water temperature and discharge on DOC and DOM composition export fluxes in two streams draining contrasting watersheds (agriculture versus forested) in southern Ontario, Canada across seasons. Using Generalized Additive Models, we observed that both stream discharge and water temperature significantly affected DOM composition, and the proportion of terrestrial humic-like DOM exhibited strong positive relationship with discharge. Although DOC loads were comparable between the two streams, the export loads and fluxes of DOM composition (in terms of fluorescent loads and fluxes) differed significantly. These patterns of DOM composition fluxes in both streams remained consistent across seasons, suggesting that watershed characteristics and nutrient availability primarily govern DOM dynamics and export, while seasonal drivers such as discharge and temperature further modulate these patterns. Export loads and fluxes of DOM components were higher in spring and winter months compared to summer and autumn in both streams, while fluxes also increased at medium (Q10-Q90) and high flow (> Q10) at a variable extent in the contrasting streams. Temperature and discharge regulated export of DOM can be further affected with changing climate and increasing frequency of extreme events and alter the processing and delivery of DOM to downstream ecosystems.
The online version contains supplementary material available at 10.1007/s10533-025-01270-3.
由于溶解有机碳（DOC）在调节全球碳通量和生态系统功能方面的关键作用，淡水系统中溶解有机碳的输出一直是许多研究的重点。溶解有机物（DOM）的通量和组成对于理解其生态影响都至关重要，因为相似的组成根据输入量和水文背景的不同可能会产生截然不同的后果。然而，关于向下游生态系统输出的DOM通量组成的数据却非常少。在这里，我们研究了加拿大安大略省南部两个排水流域（农业流域与森林流域）不同季节中水温与流量对DOC和DOM组成输出通量的相互作用。使用广义相加模型，我们观察到溪流流量和水温都显著影响DOM组成，且陆地类腐殖质DOM的比例与流量呈强正相关。尽管两条溪流中的DOC负荷相当，但DOM组成的输出负荷和通量（以荧光负荷和通量计）却有显著差异。两条溪流中DOM组成通量的这些模式在不同季节都保持一致，这表明流域特征和养分可用性主要控制着DOM的动态和输出，而诸如流量和温度等季节性驱动因素则进一步调节这些模式。与夏季和秋季相比，两条溪流中DOM组分的输出负荷和通量在春季和冬季月份更高，同时在不同的溪流中，通量在中等流量（Q10 - Q90）和高流量（>Q10）时也在不同程度上增加。温度和流量对DOM输出的调节可能会随着气候变化以及极端事件频率的增加而受到进一步影响，并改变DOM向下游生态系统的处理和输送。
在线版本包含可在10.1007/s10533 - 025 - 01270 - 3获取的补充材料。
