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.
