Impacts of dissolved organic nitrogen loading by submarine groundwater discharge in Little Lagoon, AL Jennifer Anders1,2, Behzad Mortazavi1,2, Justin Liefer1,2, William Burnett3, Hugh MacIntyre4 1Department of Biological Sciences, University of Alabama, Tuscaloosa, AL 35487, U.S.A. 2Dauphin Island Sea Lab, 102 B Bienville Blvd, Dauphin Island, AL 36528, U.S.A. 3Department of Earth, Ocean and Atmospheric Sciences, Florida State University, Tallahassee, FL 32306, U.S.A. 4Department of Oceanography, Dalhousie University, Halifax, NS, B3H 4J1, Canada
Little Lagoon, gulf Shores, AL • Exchanges with northern Gulf of Mexico • Freshwater inputs from submarine groundwater discharge (SGD) • Hot spot for toxic diatom blooms • Blooms are correlated with groundwater discharge • WHY?????
Why is Submarine Groundwater Discharge (SGD) Important? • Small freshwater input but still substantial nitrogen contribution • Transport of land-derived nutrients via SGD rival river runoff • Excess nutrients can affect phytoplankton community composition
Groundwater Monitoring in gulf shores, AL • Initial wells were set-up in 2010 • Biweekly sampling from 2010-2012 of groundwater environmental conditions and nutrients • Florida State University used tracers to as a proxy for groundwater discharge in Little Lagoon
Distribution of 222Rn concentrations (dpm L–1) throughout Little Lagoon on May 27, 2010 (Su et al. 2012) • Groundwater discharge correlates to diatom blooms • What is driving this???
What is Dissolved Organic Nitrogen (DON)? BLACK BOX!!! • Specific components of DON are largely unknown • Urea and amino acids (rapidly utilized) • DON frequently exceeds that of dissolved inorganic nitrogen in aquatic systems • Components of the DON have been shown to play a role in nitrogen nutrition to phytoplankton and bacteria
What is Dissolved Organic Nitrogen (DON)? • Specific components of DON are largely unknown • Urea and amino acids (rapidly utilized) • DON frequently exceeds that of dissolved inorganic nitrogen in aquatic systems • Components of the DON have been shown to play a role in nitrogen nutrition to phytoplankton and bacteria
Gulf of Mexico Ultimate Export Microbial/Phytoplankton DON utptake/remineralization Further Processing SW DON SGD Sediments GW DON Aquifer
Is groundwater derived DON biologically available? Is groundwater DON causing shift in the microbial community composition? Hypothesis: Certain micrbiota species from Little Lagoon dominate when inputs of groundwater DON are high Hypothesis: A fraction of the DON inputs from SGD is readily remineralized and/or directly assimilated by the microbial communities. • AND/OR........
Experimental Design Bioassay Experiments using LL site water: 2 Treatments: +Groundwater -Control (no addition)
At each time point….. • Samples are taken to measure nutrient uptake/production: • Dissolved Inorganic Nitrogen (ammonia, nitrate, and nitrite) • Total Dissolved Nitrogen • DON =TDN-DIN • Dissolved Organic Carbon • Oxygen consumption • Samples are collected to measure biomass and to look at community structure • HPLC (pigment analysis) • Chl-a • Flow Cytometry
3 Experiments in 2014: fEbRurary (Exp. 1), June (Exp. 2), and July (Exp. 3) • February (Exp. 1): • high salinity (~30 ppt) • low temperatures • low rain fall • June (Exp. 2): • low salinity (~5 ppt) • high temperatures • high rainfall • July (Exp. 3): • high salinity (~20 ppt) • High temperatures • high rainfall
Conclusions • Groundwater inputs of high DON concentrations to surface water from Little Lagoon can influence both phytoplankton groups and the bacterial community. As demonstrated by: • Increased chlorophyll concentrations • High rates of bacterial oxygen consumption • These results could indicate a response in microbiota groups that are able to utilize some portion of the groundwater DON under high input conditions • Environmental conditions such as SALINITY may play a role in DON bioavailability • DON production in the incubations could balance out DON consumption to result in not net change of DON concentrations
Thoughts for the Future • Characterize the DON • Fluorescent indicators • What is the quality of the DON and what are it’s sources? • How does the quality of the DON vary seasonally?
Acknowledgements • Little Lagoon Preservation Society • Alice Kleinhuizen • Eric Lachenmyer • Rebecca Bernard • Laura Linn • Dr. Alice Ortmann • Dr. Jeffrey Krause • Institution Support & Funding:
QUESTIONs???? Jennifer Anders contact information: firstname.lastname@example.org