Sources and export fluxes of inorganic and organic carbon and nutrient species from the seasonally ice-covered Yukon River
Sources and export fluxes of inorganic and organic carbon and nutrient species from the seasonally ice-covered Yukon River
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DOI：
10.1007/s10533-010-9545-z
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发表时间：
2012-02
期刊：
影响因子：
4
通讯作者：
Laodong Guo;Yihua Cai;C. Belzile;R. Macdonald
中科院分区：
文献类型：
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作者：
Laodong Guo;Yihua Cai;C. Belzile;R. Macdonald
气候和环境变化对北极河流流域产生了深远的影响，但生物地球化学反应仍然知之甚少。为了研究冰的形成对碳和营养物质组成和通量的时间变化的影响，从2004年7月到2005年9月，每月从育空河下游收集水和颗粒样品，测量有机和无机C、N和P的浓度，溶解硅酸盐（Si(OH)4），以及稳定同位素组成（δD和δ18O）。所有有机碳和营养物种类的浓度均在春季淡水期最高，冬季冰下最低，表明主要来源为流域融雪和土壤冲刷。而溶解无机碳（DIC）和Si(OH)4等无机物质的浓度在冬季最高，在春季最低，说明融雪过程中存在稀释作用，可能来源于地下水和矿物层的淋滤/风化作用。有机碳（如溶解有机碳（DOC））和无机碳（如DIC和Si(OH)4）与排放量的对比关系表明，水文控制了溶质浓度，但有机碳和无机碳以及营养物质的来源和运输机制不同。DOC浓度也表现出年际变化，2005年DOC（高流量）高于2004年DOC（低流量）。平均无机N/P摩尔比为110±124，冰下最高可达442，冰期最高可达38 ~ 70。冰下溶解有机质的C/N比值较高（45-62），而颗粒C/N比值在冬季（21-26）和春季（19）较低。冰与河水的C、N、P、Si、δD和δ18O的表观分异因子变化较大，DIC和Si(OH)4等无机组分的分异因子值较高（分别为45和9550），DOC的分异因子值较低（4.7）。河冰的形成可能导致无机溶质和有机溶质的分异，以及碳和养分种类的季节性通量的重新分配。2004-2005年育空河流域年输出通量分别为1.6 × 1012g-DOC、4.4 × 1012g-DIC和0.89 × 1012g-POC。无论采用何种通量估算方法，不进行春季淡水采样的通量估算结果对有机物种的估计相当低，但对无机物种的估计却明显过高。如果没有包括冰冻季节在内的时间序列采样，就会根据化学物质的不同，对碳和养分通量的估计会过高或过低。研究和采样年份之间碳输出通量的巨大差异表明，需要密集采样和长期观测来确定育空河对气候变化的响应。
Climate and environmental changes are having profound impacts on Arctic river basins, but the biogeochemical response remains poorly understood. To examine the effect of ice formation on temporal variations in composition and fluxes of carbon and nutrient species, monthly water and particulate samples collected from the lower Yukon River between July 2004 and September 2005 were measured for concentrations of organic and inorganic C, N, and P, dissolved silicate (Si(OH)4), and stable isotope composition (δD and δ18O). All organic carbon and nutrient species had the highest concentration during spring freshet and the lowest during the winter season under the ice, indicating dominant sources from snowmelt and flushing of soils in the drainage basin. In contrast, inorganic species such as dissolved inorganic carbon (DIC) and Si(OH)4had the highest concentrations in winter and the lowest during spring freshet, suggesting dilution during snowmelt and sources from groundwater and leaching/weathering of mineral layer. The contrasting relation with discharge between organic, such as dissolved organic carbon (DOC), and inorganic, such as DIC and Si(OH)4, indicates hydrological control of solute concentration but different sources and transport mechanisms for organic and inorganic carbon and nutrient species. Concentration of DOC also shows an inter-annual variability with higher DOC in 2005 (higher stream flow) than 2004 (lower stream flow). Average inorganic N/P molar ratio was 110 ± 124, with up to 442 under the ice and 38–70 during the ice-open season. While dissolved organic matter had a higher C/N ratio under the ice (45–62), the particulate C/N ratio was lower during winter (21–26) and spring freshet (19). Apparent fractionation factors of C, N, P, Si and δD and δ18O between ice and river water varied considerably, with high values for inorganic species such as DIC and Si(OH)4(45 and 9550, respectively) but lower values for DOC (4.7). River ice formation may result in fractionation of inorganic and organic solutes and the repartitioning of seasonal flux of carbon and nutrient species. Annual export flux from the Yukon River basin was 1.6 × 1012g-DOC, 4.4 × 1012g-DIC, and 0.89 × 1012g-POC during 2004–2005. Flux estimation without spring freshet sampling results in considerable underestimation for organic species but significant overestimation for inorganic species regardless of the flux estimation methods used. Without time-series sampling that includes frozen season, an over- or under-estimation in carbon and nutrient fluxes will occur depending on chemical species. Large differences in carbon export fluxes between studies and sampling years indicate that intensive sampling together with long-term observations are needed to determine the response of the Yukon River to a changing climate.