DISSERTATION RESEARCH: Biological Uptake of Dissolved Organic Matter in Streams and Self-Priming Effect

河流和溪流连接陆地和海洋，不仅是生物体的主要运输渠道，也是植物、土壤、动物和人类产生的化学物质的主要运输渠道。内陆沃茨，包括溪流、河流、池塘、湖泊和水库，也是这些物质被消耗和转化的动态生态系统。水环境中的主要化合物是溶解在水中的有机分子，它们包括单个分子的复杂溶液，这些分子可以影响水的颜色，饮用水的质量，光的可用性，溶解氧水平和生态系统功能。 然而，对这些有机分子如何加工的理解仍然有限，对于大型系统，如主要河流或整个排水网络，尤其如此。这个问题是在这个研究生研究项目中解决的，因为学生试图发现在新英格兰的三个流中有多少有机分子被生物和非生物过程去除。本研究建立在现有的研究基础上，采用了一种新的现场方法，其特征在于以可扩展的方式去除溶解性有机物（DOM），并假设生物吸收溶解性有机物是总去除量中相对较小的组成部分。这一假设是假定的初步数据，从一种方法，其中氧减少由于异养占溶解有机物去除流中的一小部分。新的现场方法涉及脉冲注入过滤枫叶渗滤液到三个不同的流在康涅狄格州，马萨诸塞州，佛蒙特州的流不断监测与多探头探测器检测电导率，DOM浓度和氧气水平的变化，作为脉冲的有机物向下游传播。溶质运移数据和抓斗样品在实验过程中获得的，然后用于计算总DOM的去除，由于异养氧的吸收，和有机质质量变化由于异养。除了主要假设，初步数据还暗示了一种新的启动机制，其中流中有机物脉冲的流内利用通过解锁先前不可用的不稳定有机物而导致生物利用度提高。第二个假说，恰当地命名为“自我启动”，旨在验证这个新概念的存在和机制。

Rivers and streams connect the land and the sea, and serve as the main transport channels for not only living organisms but also for chemical substances derived from plants, soils, animals, and humans. Inland waters, which include streams, rivers, ponds, lakes, and reservoirs, are also dynamic ecosystems where these substances are consumed and transformed. Among the major compounds in aquatic environments are organic molecules dissolved in the water, and they include a complex solution of individual molecules that can affect water color, drinking water quality, light availability, dissolved oxygen levels, and ecosystem function. Nevertheless, the understanding of how these organic molecules are processed remains limited, and this is especially true for larger systems like major rivers or entire drainage networks. This issue is addressed in this graduate student research project as the student seeks to discover how much of the organic molecules are removed by biological and non-biological processes in three streams in New England. This study builds upon existing research, applies a novel field method that characterizes the removal of dissolved organic matter (DOM) in a scalable manner, and hypothesizes that biological uptake of dissolved organic matter is a relatively minor component of the total removal. This hypothesis is postulated upon the preliminary data from a method where oxygen reduction due to heterotrophy accounted for only small portion of dissolved organic matter removal in streams. The novel field method involves pulse injection of filtered maple leaf leachate into three different streams in Connecticut, Massachusetts, and Vermont where streams are constantly monitored with multi-probe sondes to detect changes in conductivity, DOM concentration, and oxygen level as the pulse of organic matter travels downstream. The solute transport data and grab samples acquired during the experiments are then used to calculate the total DOM removal, oxygen uptake due to heterotrophy, and organic matter quality change due to heterotrophy. In addition to the primary hypothesis, the preliminary data also hints at a novel priming mechanism where in-stream utilization of organic matter pulse in streams leads to boosted bioavailability by unlocking previous unavailable labile organic matter. The second hypothesis, aptly named "self-priming," aims to verify the presence and mechanism of this novel concept.