Geology

Permanent URI for this communityhttp://hdl.handle.net/1903/2243

Browse

Subject: search.filters.subject.denitrification

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    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.
  • Thumbnail Image
    Item
    Geomorphic, hydraulic, and biogeochemical controls on nitrate retention in tidal freshwater marshes
    (2012) Seldomridge, Emily; Prestegaard, Karen; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Tidal freshwater wetlands are ideal sites for nitrate retention because of their position within the landscape (near the head of tide); they receive water, discharge, nutrients (N and P), and sediment loads directly from contributing watersheds. Nitrate retention (the difference between nitrate inputs and outputs in an ecosystem), however, is difficult to predict due to the complex interactions between flow processes and the multiple retention processes. The goal of the study was to evaluate both external and internal controls on nitrate retention, and to determine whether scaling procedures could be identified to estimate nitrate retention for an entire ecosystem. The external controls included temperature, dissolved oxygen concentrations, and incoming nitrate concentrations. Internal controls are the interactions among geomorphic, hydrologic, and biological systems within individual marshes that influence nitrate retention. This study was conducted in the upper Patuxent River Estuary where the ecosystem is composed of hundreds of individual marshes that are connected to the estuary through tidal inlets; marsh inlet geomorphology governs water and nitrate fluxes into the marshes. This study therefore took a mass balance approach to determine geomorphic, hydrologic, and biological influences on nitrate retention. Nitrate retention was measured over a 4-year period in three tidal freshwater wetlands, selected to represent a range of marsh sizes. An examination of the mass balance data suggest that nitrate retention is an outcome of complex interactions among inlet geomorphic characteristics, hydrologic flux, and biogeochemical processes. In cases where nitrate concentrations and temperatures are greater than critical (limiting) values, an emergent behavior in which nitrate retention is a simple function of water volume is observed. The wetland ecosystem is composed of numerous, small wetlands that process a small percentage of total nitrate; approximately 50% of retention is processed by the large marshes that comprise only 4% of the total population, but over 80% of the marsh area; therefore, any processes that affect tidal water volumes in large marshes is likely to affect net nitrate retention. The growth of vegetation in these large channels reduced ecosystem nitrate retention.