Abstract：
Catchment-scale understanding of water and contaminant fluxes through all pathways is essential to address land use and climate change impacts on freshwater. However, few options exist to obtain this understanding for the many catchments worldwide for which streamflow and low-frequency water chemistry, but little other data exists. We applied the Bayesian chemistry-assisted hydrograph separation and load partitioning model (BACH) to 47 catchments with widely differing characteristics. As BACH relies on concentration differences between pathways, chemodynamic behaviour of a water constituent indicates its likely suitability as tracer. Typical tracers (e.g. silica, chloride) were unavailable, but Electrical Conductivity and a few monitored nutrients proved chemodynamic in most catchments. Using one of two tracer combinations (Total Nitrogen + Electrical Conductivity, Total Nitrogen + Total Phosphorus) allowed in 85 % of the catchments to estimate streamflow contributions by near-surface (NS), shallow groundwater (SGW), and deep groundwater (DGW) pathways and pathway-specific tracer concentrations and yields with acceptable confidence. In 46 catchments, at least two pathways contributed ≥20 % of the streamflow, and all three ≥20 % in 12 catchments, cautioning against the notion of a single \'dominant\' pathway. In contrast to hydrometric hydrograph separation, BACH allows differentiation between \'young\' (NS + SGW) and \'old\' (DGW) water, which is crucial for the understanding of pollution in catchments with strong temporal gradients in land use intensity. Consistent with generally increasing land use intensity, and groundwater denitrification occurring in some catchments, Total Nitrogen (TN) concentrations were in most catchments higher in NS and SGW compared to DGW. In most catchments, the greatest fraction of the TN yield was conveyed by SGW (≈ 40-90 %). Exceptions were wet and hilly catchments under bush, where the NS transferred most of the very low yields, and three young volcanic catchments where the DGW transferred the majority of the yield due to particularly high DGW flow contributions.
摘要：
通过所有途径对水和污染物通量的流域规模了解对于解决土地利用和气候变化对淡水的影响至关重要。然而,对于世界各地的许多集水区，几乎没有选择可以获得这种理解，这些集水区的流量和低频水化学，但是几乎没有其他数据存在。我们将贝叶斯化学辅助水文分离和负荷分配模型（BACH）应用于47个特征差异很大的集水区。由于BACH依赖于途径之间的浓度差异，水成分的化学动力学行为表明其可能适合用作示踪剂。典型的示踪剂(如二氧化硅、氯化物)不可用，但是在大多数集水区，电导率和一些监测的营养素被证明是化学动力学的。使用两种示踪剂组合之一（总氮+电导率，总氮+总磷)允许在85%的集水区估算近地表(NS)的流量贡献,浅层地下水（SGW），和深层地下水（DGW）途径和途径特异性示踪剂浓度和产量具有可接受的置信度。在46个集水区，至少两条路径贡献了≥20%的流量，和所有三个≥20%的12个集水区，警惕单一“主导”途径的概念。与水文图分离相反，BACH允许区分\'年轻\'(NS+SGW)和\'老\'(DGW)水,这对于了解土地利用强度随时间梯度较大的流域污染至关重要。与土地利用强度普遍增加一致，和一些集水区发生的地下水反硝化，与DGW相比，NS和SGW的大多数流域的总氮（TN）浓度更高。在大多数集水区，TN产率的最大部分由SGW输送(≈40-90%)。例外是灌木丛下的潮湿和丘陵集水区，NS转移了大部分非常低的收益率，和三个年轻的火山集水区，由于DGW流量贡献特别高，DGW转移了大部分产量。
