Nitrogen removal via denitrification in Weeks Bay, AL

End Date: 7/19/10


Understanding water quality management in the state of Alabama:  
The goal of the proposed research is to better understand how ecological and biogeochemical processes in Alabama coastal ecosystems may act to reduce N delivered from upstream systems. Here, we will develop technologies that will allow us to contrast these laboratory results with in situ estimates of denitrification. 

Excess nitrogen input is recognized as the primary factor responsible for eutrophication and examining denitrification, a natural process that can remove this “pollutant” and reduce its impact on our coastal waters, is beneficial to our State. Benefits from this research will include the development of laboratory and field tools and techniques for assessing the potential for N removal via denitrification in Alabama waterways. 

Building cross-state collaborative relationships to address regional water quality issues:
The University of Alabama at Tuscaloosa has a large and interactive group of freshwater ecologists, which is nicely complimented by equally strong coastal, estuarine and marine science programs at the Dauphin Island Sea Lab.  Building partnerships, that integrate these strengths, will be essential if Alabama scientists and managers are to successfully deal with water use and quality problems that operate at the scale of the Mobile River basin, and require expertise across a range of freshwater and marine disciplines to solve. 

The goal here is to use this proposal as a springboard for building long-term collaboration amongst researchers at UA and the Dauphin Island Sea Lab.  The data generated from this effort will help us to generate proposals with broader geographic coverage that will aid in identifying ‘hot spots’ within the Mobile River drainage systems – where N loss via denitrification is high, and where conservation efforts may be focused to optimize this ecosystem service. While the proposed research is aimed at understanding water quality issues within Weeks Bay, the long-term goal is to focus more broadly on an integrated hydrologic continuum within Mobile Bay watershed that includes terrestrial, freshwater and marine elements. 

Method development and results from this study will be used to guide this long-term research agenda, which will be oriented towards understanding how to best manage the exceptional aquatic resources that exist within the state of Alabama. 


N2 flux measurements are widely used to estimate denitrification rates. This method is considered superior to other methods used for estimating denitrification, as the direct end-product of denitrification (N2) is measured, coupled nitrification-denitrification is not inhibited, and N2 flux from both the sediments and the water-column may be estimated (Seitzinger 1993, Cornwell et al. 1999).  My laboratory is set up with state-of-the-art technology to measure rates of denitrification. A membrane inlet mass spectrometer (Pfeiffer Vacuum, $50K) has been purchased with Mortazavi’s start-up fund and is currently being used to measure N2 gas concentrations in environmental samples.

The acetylene block technique will be used to measure potential rates of denitrification.  Four times a year, at several stations in Weeks Bay (March, July, November and January), water samples will be collected and processed for nutrient concentrations, organic carbon quantity and organic carbon quality (bioavailability).  In addition, 20 grams of sediment will be collected from 5 locations at each site and mixed with 50 ml of ambient water in duplicate 200-ml serum bottles that will be stoppered and sealed with crimps. The headspace of each bottle will be flushed with nitrogen gas for 10 minutes to remove traces of oxygen and to simulate anoxic conditions, prior to the addition of 10 ml of acetylene.  Headspace samples will be collected hourly during a 4-hour period and stored in preevaculated gas-tight vials. N2O production will be quantified with a Shimadzu gas chromatograph equipped with an electron capture detector.


This proposal focuses on priorities of Health and Restoration of Coastal Habitats and Environmental Education, as outlined in the action plan for the Gulf of Mexico Sea Grants Programs. The anthropogenic impact on estuarine ecosystems has led to a decline in total acreage of habitat. Estuaries provide critical habitat for numerous species of commercially and recreationally important waterfowl, migratory birds, marine mammals, and sea turtles. Because of their sensitivity to anthropogenic forces the Estuary Restoration Act of 2000 has called for a national strategy with a goal of restoring 1-million acres of estuarine habitat by 2010. Understanding nutrient cycling and factors that control that are involved in Nitrogen removal in estuarine system is a critical step towards achieving this goal.  The data obtained if this proposal is funded will be made available to managers for practical considerations and public outreach efforts at Weeks Bay national estuarine research reserve site.