We used data from 17 years of routine stream flow sampling to characterise hydrochemical dynamics in the Girnock Burn, an internationally important long-term catchment monitoring site. We combined hydrochemical time series analysis with hydrological modelling to understand short- and long-term dynamics in relation to dominant runoff processes. Isotopic tracer data employed within the model enabled flux tracking of water as it transited the catchment, facilitating water age estimates. The stream drains an upland 31 km catchment with complex topography and variable geology, which influences soil distributions; peaty soils dominate valley bottoms which receive drainage from more permeable podzolic soils on steeper slopes. Short-term hydrochemical dynamics largely reflect the relative dominance of hydrological sources: summer low flows are dominated by alkaline groundwater high in weathering products (Ca, Mg, SiO) whilst high flows generated by overland flow from peaty soils are more acidic, DOC enriched, and dominated by atmospheric solutes (Na, Cl, SO). Baseflows are dominated by older groundwater (>∼3years) in contrast to storm runoff dominated by younger (<∼0.5 years), near-surface, waters. Usual seasonal distributions of stream flows, with high flows in winter and summer low flows, result in strong seasonality in most solutes. However, coupled effects of hydroclimatic variability and catchment heterogeneity dictates marked scatter in flow-concentration relationships for most determinands. A long-term decreasing trend was evident for SOconcentrations, reflecting continuing effects of reductions in atmospheric deposition of pollutants from coal burning. Reductions in large storm event frequency post-2016 and protracted periods of low flows in the droughts of 2018 and 2022 have resulted in the catchment becoming dominated by low flows, derived from older groundwater with more alkaline chemistry for longer periods. Changing climatic conditions and stream flow responses seem likely to continue to cause changes in stream water quality and associated ecosystem services of the Girnock Burn and similar upland catchments.

中文翻译：

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水文气候非平稳性通过控制流域连通性和水龄来驱动河流水化学动力学

我们使用 17 年常规溪流采样数据来描述 Girnock Burn 的水化学动力学特征，Girnock Burn 是一个国际重要的长期流域监测站点。我们将水化学时间序列分析与水文建模相结合，以了解与主要径流过程相关的短期和长期动态。模型中使用的同位素示踪剂数据可以跟踪流经流域的水的通量，从而促进水龄估计。该溪流流经 31 公里长的高地流域，该流域地形复杂，地质条件多变，影响土壤分布；谷底以泥炭土为主，陡峭山坡上渗透性更强的灰化土为排水系统。短期水化学动态很大程度上反映了水文来源的相对主导地位：夏季低流量主要由富含风化产物（Ca、Mg、SiO）的碱性地下水主导，而来自泥炭土的地表水产生的高流量则酸性更强、DOC 丰富，以大气溶质（Na、Cl、SO）为主。基流主要由较老的地下水（>~3 年）主导，而暴雨径流主要由较年轻（<~0.5 年）的近地表水域主导。河流流量的通常季节性分布，冬季流量高，夏季流量低，导致大多数溶质具有很强的季节性。然而，水文气候变化和流域异质性的耦合效应决定了大多数测定对象的流量-浓度关系的显着分散。 SO 浓度的长期下降趋势很明显，反映出燃煤污染物大气沉降减少的持续影响。 2016 年后大型风暴事件频率的减少以及 2018 年和 2022 年干旱期间长期低流量的影响，导致流域以低流量为主，这些低流量源自长期碱性化学物质较多的老地下水。不断变化的气候条件和溪流响应似乎可能继续导致吉诺克伯恩和类似高地流域的溪流水质和相关生态系统服务发生变化。