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Identifying Drivers of Seasonality in Lena River Biogeochemistry and Dissolved Organic Matter Fluxes
Frontiers in Environmental Science ( IF 4.6 ) Pub Date : 2020-05-15 , DOI: 10.3389/fenvs.2020.00053
Bennet Juhls , Colin A. Stedmon , Anne Morgenstern , Hanno Meyer , Jens Hölemann , Birgit Heim , Vasily Povazhnyi , Pier P. Overduin

Warming air temperatures, shifting hydrological regimes and accelerating permafrost thaw in the catchments of the Arctic rivers is affecting their biogeochemistry. Arctic river monitoring is necessary to observe changes in the mobilization of dissolved organic matter (DOM) from permafrost. The Lena River is the second largest Arctic river and 71% of its catchment is continuous permafrost. Biogeochemical parameters, including temperature, electrical conductivity (EC), stable water isotopes, dissolved organic carbon (DOC) and absorption by colored dissolved organic matter (aCDOM) have been measured as part of a new high-frequency sampling program in the central Lena River Delta. The results show strong seasonal variations of all biogeochemical parameters that generally follow seasonal patterns of the hydrograph. Optical indices of DOM indicate a trend of decreasing aromaticity and molecular weight from spring to winter. High-frequency sampling improved our estimated annual fluvial flux of annual dissolved organic carbon flux (6.79 Tg C). EC and stable isotope data were used to distinguish three different source water types which explain most of the seasonal variation in the biogeochemistry of the Lena River. These water types match signatures of (1) melt water, (2) rain water, and (3) subsurface water. Melt water and rain water accounted for 84% of the discharge flux and 86% of the DOC flux. The optical properties of melt water DOM were characteristic of fresh organic matter. In contrast, the optical properties of DOM in subsurface water revealed lower aromaticity and lower molecular weights, which indicate a shift toward an older organic matter source mobilized from deeper soil horizons or permafrost deposits. The first year of this new sampling program sets a new baseline for flux calculations of dissolved matter and has enabled the identification and characterization of water types that drive the seasonality of the Lena River water properties.

中文翻译:

确定勒拿河生物地球化学和溶解有机物质通量的季节性驱动因素

气温升高、水文状况变化和北极河流集水区的永久冻土融化加速正在影响它们的生物地球化学。北极河流监测对于观察永久冻土中溶解有机物质 (DOM) 动员的变化是必要的。勒拿河是北极第二大河流,其流域的 71% 是连续多年冻土。生物地球化学参数,包括温度、电导率 (EC)、稳定水同位素、溶解有机碳 (DOC) 和有色溶解有机物质的吸收 (aCDOM) 已作为新的高频采样计划的一部分在勒拿河中部进行测量三角洲。结果显示所有生物地球化学参数的强烈季节性变化通常遵循水文过程线的季节性模式。DOM 的光学指数表明,从春季到冬季,芳香性和分子量呈下降趋势。高频采样提高了我们估计的年度溶解有机碳通量 (6.79 Tg C) 的年度河流通量。EC 和稳定同位素数据用于区分三种不同的源水类型,这解释了勒拿河生物地球化学的大部分季节性变化。这些水类型与 (1) 融水、(2) 雨水和 (3) 地下水的特征相匹配。融水和雨水分别占排放通量的84%和DOC通量的86%。融水DOM的光学性质是新鲜有机物的特征。相比之下,地下水中 DOM 的光学性质显示出较低的芳香性和较低的分子量,这表明从更深的土壤层或永久冻土沉积物中转移到较旧的有机物质来源。这个新采样计划的第一年为溶解物质的通量计算设定了新的基线,并能够识别和表征驱动勒拿河水特性季节性的水类型。
更新日期:2020-05-15
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