Stormwater and organic matter in the urban stream continuum

<p>Dissolved organic matter (DOM) is present in all natural waters and modulates</p><p>aquatic ecosystems by absorbing light and heat, and because it comprises a complex</p><p>mixture of organic molecules including amino acids, sugars, fulvic acids, and humic</p><p>material. DOM is derived from dissolution of organic matter and can be altered by</p><p>both biotic and abiotic processes that may its structure or mineralize it to CO₂.</p><p>Urbanization is a widespread agent of landscape change that can alter DOM</p><p>regimes by changing the amount and types of organic matter in the catchment and</p><p>by changing the way that water moves through the landscape (transporting DOM</p><p>from land to stream). This dissertation examines DOM in urban stream networks,</p><p>exploring its sources, bioavailability, and broad patterns throughout the continental</p><p>United States.</p><p>We determined the role of impervious infrastructure as a proximate source of</p><p>DOM to stormwater by a) constructing an annual carbon budget for the roof of a</p><p>house as a small catchment nested within the 60 h catchment of an urban headwater</p><p>stream and b) comparing the estimated fluxes of solutes and stormwater from imper</p><p>vious infrastructure in the catchment. We found that roofs convert nearly one-third</p><p>of the leaf litter carbon they receive into dissolved organic carbon (DOC), which</p><p>leaves through downspouts. On the event scale, we estimated fluxes of DOC and</p><p>total dissolved nitrogen from impervious surfaces that generally exceed the fluxes</p><p>that leave the catchment in stream stormflow.</p><p>When we compared the chemical composition of runoff from impervious surfaces</p><p>to stream stormflow, we found them to be distinct, despite the fact that the we</p><p>estimated a volume of runoff from impervious surfaces that generally matched the</p><p>volume of water flowing through the stream during storms. Our findings suggest</p><p>that a water source other than baseflow and impervious runoff contributes to stream</p><p>stormflow, and that a considerable proportion of impervious runoff is lost before it</p><p>reaches the catchment pour point.</p><p>An experimental incubation of potential DOM sources in the urban landscape and</p><p>DOM in stormwater showed that urban DOM is highly bioavailable. The composition</p><p>of DOM also became more homogeneous over the course of processing.</p><p>Finally, we examined continental-scale patterns and long-term trends in riverine</p><p>DOC. Unlike the widespread ’browning’ trends observed in far northern aquatic</p><p>systems, we did not find evidence for long-term increases in DOC throughout most</p><p>of the U.S. Instead, we both decreases and increases in long-term DOC concentrations</p><p>that differed among regions and generally seemed to be driven by changes in weltand</p><p>cover. We also found evidence for a marginal effect of impervious surfaces that</p><p>increases DOC concentrations at high canopy cover, consistent with our observations</p><p>that urban infrastructure can contribute considerable DOM loads in storm runoff.</p><p>Together, this research shows that urban stormwater infrastructure functions</p><p>as the ephemeral headwaters of the urban stream network. In catchments with</p><p>significant canopy cover, these ’engineered headwaters’ collect and transform organic</p><p>matter between storms and transport DOM during stormflow.</p>

Author dc:creator

• Fork, Megan L.

Advisor dc:contributor.advisor

• Heffernan, James B.

• Environmental science
• Ecology
• Limnology
• dissolved organic matter
• impervious surface
• stream ecology
• urban stream

Handle dc:identifier.uri

https://hdl.handle.net/10161/16399

OAI identifier oai:identifier

oai:dukespace.lib.duke.edu:10161/16399