Many boreal lakes are experiencing an increase in concentrations of terrestrially derived dissolved organic matter (DOM)—a process commonly labeled “browning.” Browning affects microbial and photochemical mineralization of DOM, and causes increased light attenuation and hence reduced photosynthesis. Consequently, browning regulates lake heterotrophy and net CO₂‐efflux to the atmosphere. Climate and environmental change makes ecological forecasting and global carbon cycle modeling increasingly important. A proper understanding of the magnitude and relative contribution from CO₂‐generating processes for lakes ranging in dissolve organic carbon (DOC) concentrations is therefore crucial for constraining models and forecasts. Here, we aim to study the relative contribution of photomineralization to total CO₂ production in 70 Scandinavian lakes along an ecosystem gradient of DOC concentration. We combined spectral data from the lakes with regression estimates between optical parameters and wavelength specific photochemical reactivity to estimate rates of photochemical DOC mineralization. Further, we estimated total in‐lake CO₂‐production and efflux from lake chemical and physical data. Photochemical mineralization corresponded on average to 9% ± 1% of the total CO₂‐evasion, with the highest contribution in clear lakes. The calculated relative contribution of photochemical mineralization to total in‐lake CO₂‐production was about 3% ± 0.2% in all lakes. Although lakes differed substantially in color, depth‐integrated photomineralization estimates were similar in all lakes, regardless of DOC concentrations. DOC concentrations were positively related to CO₂‐efflux and total in‐lake CO₂‐production but negatively related to primary production. We conclude that enhanced rates of photochemical mineralization will be a minor contributor to increased heterotrophy under increased browning.

中文翻译：

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光矿化对沿溶解有机物梯度的北方湖泊CO2排放的作用

许多北方湖泊的陆地溶解有机物（DOM）浓度都在增加，这一过程通常称为“褐变”。褐变影响DOM的微生物和光化学矿化，并导致增加的光衰减，从而降低光合作用。因此，褐变调节了湖泊的异养性和向大气中净CO _2的外流。气候和环境变化使生态预测和全球碳循环建模变得越来越重要。对CO ₂的大小和相对贡献的正确理解因此，湖泊中溶解有机碳（DOC）浓度范围的生成过程对于限制模型和预测至关重要。在这里，我们的目的是研究沿着DOC浓度的生态系统梯度，光矿化对70个斯堪的纳维亚湖泊中总CO ₂产生的相对贡献。我们将湖泊的光谱数据与光学参数和特定波长的光化学反应性之间的回归估计值结合起来，以估计光化学DOC矿化的速率。此外，我们根据湖泊化学和物理数据估算了湖内CO _2的总产生量和流出量。光化学矿化平均相当于总CO _2的9％±1％逃避，在清澈的湖泊中贡献最大。在所有湖泊中，计算出的光化学矿化对总湖中CO _2产生的相对贡献约为3％±0.2％。尽管湖泊的颜色差异很大，但不管DOC浓度如何，所有湖泊的深度综合光矿化估算值均相似。DOC浓度与CO ₂流出量和湖内CO ₂总产生量呈正相关，而与一次生产负相关。我们得出的结论是，光化学矿化速率的提高将在褐变增加的情况下对增加异养菌的贡献很小。