title: Tracing sources of organic matter in adjacent urban streams having different degrees of channel modification.
abstract: Urbanization and stream-channel modifications affect organic matter concentrations and quality in streams, by altering allochthonous organic matter input and in-stream transformation. This study uses multiple tracers (δ(13)C, δ(15)N, C/N ratio, and chlorophyll-a) to track sources of organic matter in two highly urbanized bayous in Houston (Texas, USA). Wastewater treatment plants (WWTPs) are located in headwaters of both bayous and contribute more than 75% to water flow. Low isotopic relatedness to natural end-members and enriched δ(15)N values suggest the influence of WWTPs on the composition of all organic matter fractions. The two bayous differ in degree of channel improvement resulting in different responses to hydrological conditions. During high flow conditions, the influence of terrestrial organic matter and sediment resuspension was much more pronounced in the Buffalo Bayou than in the concrete-lined White Oak Bayou. Particulate organic matter (POM) in White Oak Bayou had similar values of enriched δ(15)N in all subsegments, whereas in Buffalo Bayou, the degree of δ(15)N enrichment was less in the subsegments of the lower watershed. The difference in riparian zone contributions and interactions with sediments/soils was likely responsible for the compositional differences between the two bayous. Phytoplankton inputs were significantly higher in the bayous, especially in slow-flowing sections, relative to the reference sites, and elevated phytoplankton inputs accounted for the observed stable C isotope differences between FPOM and high molecular weight dissolved organic matter (HMW DOM). Relative to POM, HMW DOM in the bayous was similar to WWTP effluents and showed minor longitudinal variability in both streams suggesting that WWTPs contribute much of the DOM in the systems. Urbanization has a major influence on organic matter sources and quality in these urban water bodies and these changes seem further enhanced by stream channel modifications.
authors.affiliation: Department of Marine Sciences, Texas A&M University at Galveston, Galveston, TX 77553, USA. Electronic address: sduan@umd.edu.
authors.forename: Shuiwang
authors.initials: S
authors.lastname: Duan
authors.affiliation: Department of Marine Sciences, Texas A&M University at Galveston, Galveston, TX 77553, USA. Electronic address: amonr@tamug.edu.
authors.forename: Rainer M W
authors.initials: RMW
authors.lastname: Amon
authors.affiliation: Department of Marine Sciences, Texas A&M University at Galveston, Galveston, TX 77553, USA.
authors.forename: Robin L
authors.initials: RL
authors.lastname: Brinkmeyer
mesh_terms: D002247:Carbon Isotopes / Q000032:analysis; D002947:Cities; D004784:Environmental Monitoring; D009587:Nitrogen Isotopes / Q000032:analysis; D045483:Rivers / Q000737:chemistry*; D013781:Texas; D014507:Urbanization; D014865:Waste Disposal, Fluid; D062065:Wastewater / Q000737:chemistry* / Q000706:statistics & numerical data; D014872:Water Movements; D014873:Water Pollutants / Q000032:analysis*
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D062065:Wastewater; D014873:Water Pollutants
keywords: Channel modification; DOM; Organic matter; Stable isotopes; Urban streams; Wastewater