Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences (SLU), Lennart Hjelms väg 9, SE, 750 07 Uppsala, Sweden.
Department of Forest Ecology and Management, Swedish University of Agricultural Sciences (SLU), Skogsmarksgränd, SE, 901 83 Umeå, Sweden.
Sci Total Environ. 2016 Aug 1;560-561:110-22. doi: 10.1016/j.scitotenv.2016.03.230. Epub 2016 Apr 17.
In boreal forest catchments, solute transfer to streams is controlled by hydrological and biogeochemical processes occurring in the riparian zone (RZ). However, RZs are spatially heterogeneous and information about solute chemistry is typically limited. This is problematic when making inferences about stream chemistry. Hypothetically, the strength of links between riparian and stream chemistry is time-scale dependent. Using a ten-year (2003-2012) dataset from a northern Swedish catchment, we evaluated the suitability of RZ data to infer stream dynamics at different time scales. We focus on the role of the RZ versus upslope soils in controlling sulfate (SO4(2)(-)) and dissolved organic carbon (DOC). A priori, declines in acid deposition and redox-mediated SO4(2)(-) pulses control sulfur (S) fluxes and pool dynamics, which in turn affect dissolved organic carbon (DOC). We found that the catchment is currently a net source of S, presumably due to release of the S pool accumulated during the acidification period. In both, RZ and stream, SO4(2-) concentrations are declining over time, whereas DOC is increasing. No temporal trends in SO4(2-) and DOC were observed in upslope mineral soils. SO4(2-) explained the variation of DOC in stream and RZ, but not in upslope mineral soil. Moreover, as SO4(2-) decreased with time, temporal variability of DOC increased. These observations indicate that: (1) SO4(2-) is still an important driver of DOC trends in boreal catchments and (2) RZ processes control stream SO4(2-) and subsequently DOC independently of upslope soils. These phenomena are likely occurring in many regions recovering from acidification. Because water flows through a heterogeneous mosaic of RZs before entering the stream, upscaling information from limited RZ data to the catchment level is problematic at short-time scales. However, for long-term trends and annual dynamics, the same data can provide reasonable representations of riparian processes and support meaningful inferences about stream chemistry.
在北方森林流域，溶质向溪流的转移受到河岸带（RZ）中水文和生物地球化学过程的控制。然而，RZ 具有空间异质性，溶质化学信息通常有限。这在对溪流化学进行推断时会造成问题。从理论上讲，河岸带和溪流化学之间的联系强度与时间尺度有关。利用瑞典北部一个流域的十年（2003-2012 年）数据集，我们评估了 RZ 数据在不同时间尺度上推断溪流动态的适宜性。我们重点关注 RZ 与上坡土壤在控制硫酸盐（SO4(2)(-))和溶解有机碳（DOC）方面的作用。我们假设，酸沉降的减少和氧化还原介导的 SO4(2)(-)脉冲控制硫（S）通量和库动态，进而影响溶解有机碳（DOC）。我们发现，该流域目前是 S 的净源，可能是由于酸化期间积累的 S 库的释放。在 RZ 和溪流中，SO4(2-)浓度随时间呈下降趋势，而 DOC 呈上升趋势。在上坡矿物土壤中未观察到 SO4(2-)和 DOC 的时间趋势。SO4(2-)解释了溪流和 RZ 中 DOC 的变化，但不能解释上坡矿物土壤中 DOC 的变化。此外，随着时间的推移，SO4(2-)的减少增加了 DOC 的时间变异性。这些观察结果表明：（1）SO4(2-)仍然是北方流域 DOC 趋势的重要驱动因素；（2）RZ 过程独立于上坡土壤控制着溪流 SO4(2-)和随后的 DOC。这些现象可能发生在许多正在从酸化中恢复的地区。由于水在进入溪流之前流经 RZ 的异质镶嵌体，因此将有限的 RZ 数据的信息扩展到流域水平在短时间尺度上是有问题的。然而，对于长期趋势和年度动态，相同的数据可以为河岸带过程提供合理的表示，并支持对溪流化学进行有意义的推断。
