In fresh waters, the origins of dissolved organic matter (DOM) have been found to exert a fundamental control on its reactivity, and ultimately, its ecosystem functional role. A detailed understanding of landscape scale factors that control the export of DOM to aquatic ecosystems is, therefore, pivotal if the effects of DOM flux to fresh waters are to be fully understood. In this study we present data from a national sampling campaign across the United Kingdom in which we explore the variability in DOM composition in three broad landscape types defined by similar precipitation, geology, land use and management, hydrology, and nutrient enrichment status. We characterised samples from fifty-one sites, grouping them into one of three major underlying classifications: circumneutral streams underlain by clay and mudstone (referred to as ‘clay’), alkaline streams underlain by Cretaceous Chalk or by Carboniferous or Jurassic Limestone (‘limestone’), and acidic streams in peatland catchments underlain by a range of low permeability lithologies (‘peat’). DOM composition was assessed through organic matter stoichiometry (organic carbon: organic nitrogen; organic carbon: organic phosphorus; C/N(P)_DOM) and metrics derived from ultra-violet (UV)/visible spectroscopic analysis of DOM such as specific UV absorption (a₂₅₄ nm; SUVA₂₅₄). We found similar SUVA₂₅₄, C/N_DOM and DOM/a₂₅₄ relationships within classifications, demonstrating that despite a large degree of heterogeneity within environments, catchments with shared environmental character and anthropogenic disturbance export DOM with a similar composition and character. Improving our understanding of DOM characterisation is important to help predict shifts in stream ecosystem function, and ecological responses to enrichment or mitigation efforts and how these may result in species composition shifts and biodiversity loss in freshwater ecosystems.

在淡水中，已发现溶解有机物 (DOM) 的来源对其反应性以及最终对其生态系统功能的作用具有根本性的控制作用。因此，如果要充分了解 DOM 通量对淡水的影响，详细了解控制 DOM 向水生生态系统输出的景观尺度因素至关重要。在这项研究中，我们提供了来自英国全国抽样活动的数据，我们在其中探索了由相似降水、地质、土地利用和管理、水文和养分富集状况定义的三种广泛景观类型中 DOM 组成的变异性。我们对来自 51 个地点的样本进行了表征，将它们分为三个主要的潜在分类之一：粘土和泥岩（称为“粘土”）下的环绕中性河流，白垩纪白垩或石炭纪或侏罗纪石灰岩（“石灰岩”）下覆的碱性溪流，以及一系列低渗透率岩性（“泥炭”）下方的泥炭地集水区中的酸性溪流。DOM 组成通过有机质化学计量（有机碳：有机氮；有机碳：有机磷；C/N(P)_DOM ) 和源自 DOM 的紫外 (UV)/可见光谱分析的指标，例如特定的紫外吸收 (a ₂₅₄ nm; SUVA ₂₅₄ )。我们发现了类似的 SUVA ₂₅₄、 C/N _DOM和 DOM/a ₂₅₄分类之间的关系，表明尽管环境内部存在很大程度的异质性，但具有共同环境特征和人为干扰的流域输出具有相似组成和特征的 DOM。提高我们对 DOM 表征的理解对于帮助预测河流生态系统功能的变化以及对富集或缓解努力的生态响应以及这些可能如何导致淡水生态系统中的物种组成变化和生物多样性丧失非常重要。