Stormflow Dynamics of Dissolved Organic Carbon and Total Dissolved Nitrogen in a Small Urban Watershed

Abstract

We examined patterns of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) loading to a small urban stream during baseflow and stormflow. We hypothesized that lower DOC and TDN contributions from impervious surfaces would dilute natural hydrologic flowpath (i.e., riparian) contributions during storm events in an urban watershed, resulting in lower concentrations of DOC and TDN during storms. We tested these hypotheses in a small urban watershed in Portland, Oregon, over a 3-month period during the spring of 2003. We compared baseflow and stormflow chemistry using Mann-Whitney tests (significant at p<0.05). We also applied a mass balance to the stream to compare the relative significance of impervious surface contributions versus riparian contributions of DOC and TDN. Results showed a significant increase in stream DOC concentrations during stormflows (median baseflow DOC = 2.00 mg l À1 vs. median stormflow DOC = 3.46 mg l À1 ). TDN streamwater concentrations, however, significantly decreased with stormflow (median baseflow TDN = 0.75 mg l À1 vs. median stormflow TDN = 0.56 mg l À1 ). During storms, remnant riparian areas contributed 70-74% of DOC export and 38-35% of TDN export to the stream. The observed pattern of increased DOC concentrations during stormflows in this urban watershed was similar to patterns found in previous studies of forested watersheds. Results for TDN indicated that there were relatively high baseflow nitrogen concentrations in the lower watershed that may have partially masked the remnant riparian signal during stormflows. Remnant riparian areas were a major source of DOC and TDN to the stream during storms. These results suggest the importance of preserving near-stream riparian areas in cities to maintain ambient carbon and nitrogen source contributions to urban streams.

Chemistry of growth medium and leachate from green roof systems in south-central Texas

“…Our DOC leachate was however almost four times higher than that reported from intensive vegetated roofs with more than 70 plant species planted in Aquasoil in Japan (Berndtsson et al 2009). Runoff carbon concentrations are also relatively high in urban streams (Hook and Yeakley 2005;Aitkenhead-Peterson et al 2009) with concentrations ranging from 20 to 54 mgL −1 in south-central Texas (Aitkenhead-Peterson et al 2009), concentrations which are similar to those observed in this study for the planted and unplanted modules. One consistent variable between DOC concentrations observed in surface water (e.g.…”

The influence of floodplain restoration on flow and sediment dynamics in an urban river

“…), water quality (Sonoda et al . ; Sonoda and Yeakley ; Pratt and Chang ; Chen and Chang ) and ecological problems (Hook and Yeakley ; Levell and Chang ) attributable to agricultural practices and urban development in the watershed.…”

An initial SPARROW model of land use and in-stream controls on total organic carbon in streams of the conterminous United States

“…Watershed studies highlight the importance of the coupled nature of the hydrological and biogeochemical processes, with examples from all major land-use types, including wetlands (Hinton and others, 1998), forests (McGlynn and McDonnell, 2003), agricultural settings (Dalzell and others, 2007;Morel and others, 2009), and urban lands (Hook and Yeakley, 2005). Applications at multiple spatial and temporal scales have shown that information on land use (as a proxy for carbon sources), climate (as related to runoff processes), temperature (affecting rates of biogeochemical processes), and watershed characteristics (mediating fate and transport) is important for understanding concentrations and loadings of organic matter in streams and rivers (Arvola, andothers, 2004, Mulholland, 2003;Sebestyen and others, 2009).…”