Geology

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    Nutrient Retention in Restored Streams and Rivers: A Global Review and Synthesis
    (MDPI, 2016-03-25) Newcomer Johnson, Tamara A.; Kaushal, Sujay S.; Mayer, Paul M.; Smith, Rose M.; Sivirichi, Gwen M.
    Excess nitrogen (N) and phosphorus (P) from human activities have contributed to degradation of coastal waters globally. A growing body of work suggests that hydrologically restoring streams and rivers in agricultural and urban watersheds has potential to increase N and P retention, but rates and mechanisms have not yet been analyzed and compared across studies. We conducted a review of nutrient retention within hydrologically reconnected streams and rivers, including 79 studies. We developed a typology characterizing different forms of stream and river restoration, and we also analyzed nutrient retention across this typology. The studies we reviewed used a variety of methods to analyze nutrient cycling. We performed a further intensive meta-analysis on nutrient spiraling studies because this method was the most consistent and comparable between studies. A meta-analysis of 240 experimental additions of ammonium (NH4+), nitrate (NO3−), and soluble reactive phosphorus (SRP) was synthesized from 15 nutrient spiraling studies. Our results showed statistically significant relationships between nutrient uptake in restored streams and specific watershed attributes. Nitrate uptake metrics were significantly related to watershed surface area, impervious surface cover, and average reach width (p < 0.05). Ammonium uptake metrics were significantly related to discharge, velocity, and transient storage (p < 0.05). SRP uptake metrics were significantly related to watershed area, discharge, SRP concentrations, and chl a concentrations (p < 0.05). Given that most studies were conducted during baseflow, more research is necessary to characterize nutrient uptake during high flow. Furthermore, long-term studies are needed to understand changes in nutrient dynamics as projects evolve over time. Overall analysis suggests the size of the stream restoration (surface area), hydrologic connectivity, and hydrologic residence time are key drivers influencing nutrient retention at broader watershed scales and along the urban watershed continuum.
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    HYDROLOGICAL, BIOLOGICAL, AND GEOCHEMICAL RELATIONSHIPS AMONG CARBON, NITROGEN, AND BASE CATIONS IN RESTORED AND UNRESTORED URBAN STREAMS
    (2017) Doody, Thomas Rossiter; Kaushal, Sujay S; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Urban infrastructure changes hydrologic flowpaths of water into streams and alters ecosystem function. Geomorphic stream restoration is commonly implemented to stabilize channels, while ecosystem function, and nutrient retention are of secondary concern. This research investigated whether restoration alone significantly influences N uptake in streams and if significant hydrological, biological, and geochemical relationships exist between coupled biogeochemical cycles that should be considered when evaluating restorations. Carbon, nitrogen, base cations, and stream metabolism dynamics were investigated in six urban streams in Baltimore,MD. Nitrate tracer injections were used to quantify nitrogen uptake dynamics. Results did not show significant differences in nitrogen uptake based on restoration. Organic carbon, inorganic carbon, and nitrogen each have distinct but interrelated hydrological, biological, and geochemical relationships across all sites. These dynamic relationships may also significantly affect nitrogen uptake, but more spatiotemporal data are needed to quantify and understand variability among restored and unrestored sites.