In urban stream networks, the headwaters are comprised of engineered headwaters where particulate organic matter collects during and between storms. During storms, dissolved organic matter leached from these pools is transported to the stream as stormflow connects these ephemeral channels to the network. Throughout the urban network, microbial processing consumes, produces, and transforms DOM, changing its chemical composition and concentration. In this study, we characterized how microbial processing changes the composition and inferred lability of DOM from stormflow samples and leachates of potential DOM sources by pairing optical measurements of DOM composition with measurements of DOC concentration during incubation with a common bacterial community. We found that over 6 days (the approximate residence time of water stored in urban headwater infrastructure) microbial processing significantly altered DOM composition, increasing the chemodiversity of DOM in leachates but not stormflow samples. Particularly in leachates, this initial change in composition was accompanied by little change in DOC concentration. After 60 days of microbial processing, both samples of stormflow and leachates lost more than half their initial DOC concentration on average, and became more similar in composition with indices indicating humic, aromatic DOM generally considered to be recalcitrant. This work provides new evidence that leached organic matter undergoes transient increases in chemodiversity through bacterial action on the DOM pool before further processing leaves behind more homogenous and recalcitrant DOM.

中文翻译：

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城市水源溶解有机物的生物有效性及组成变化

在城市河流网络中，源头由工程源头组成，其中颗粒有机物在风暴期间和风暴之间收集。在风暴期间，当风暴流将这些短暂的通道连接到网络时，从这些池中浸出的溶解有机物被输送到溪流中。在整个城市网络中，微生物加工消耗、产生和转化 DOM，改变其化学成分和浓度。在这项研究中，我们通过将 DOM 组成的光学测量与常见细菌群落培养期间 DOC 浓度的测量相结合，描述了微生物加工如何改变来自风暴流样本和潜在 DOM 源渗滤液的 DOM 的组成和推断的不稳定性。我们发现超过 6 天（城市源头基础设施中储存的水的大致停留时间）微生物处理显着改变了 DOM 组成，增加了渗滤液中 DOM 的化学多样性，但不会增加暴雨流样品中的化学多样性。特别是在渗滤液中，这种组成的初始变化伴随着 DOC 浓度的微小变化。经过 60 天的微生物处理后，暴雨流和渗滤液的样本平均损失了一半以上的初始 DOC 浓度，并且在组成上变得更加相似，指数表明腐殖质、芳香族 DOM 通常被认为是顽固的。这项工作提供了新的证据，表明在进一步处理留下更均匀和顽固的 DOM 之前，浸出的有机物质通过对 DOM 池的细菌作用而经历了化学多样性的瞬时增加。