Associate Professor, University of South Alabama

Senior Marine Scientist, Dauphin Island Sea Lab

Ph.D. 2003, University of Alabama

 

Multiple Stressor Impacts to Coastal Ecosystems

Estuaries and coastal ecosystems located at the land-sea interface are among the most highly productive systems on Earth and due their proximity to land are also among the most susceptible to human activities. The impacts to these systems therefore are of great societal concern.  Work in our lab has focused on land-use change, nutrient pollution, eutrophication, and hypoxia as primary stressors.  We have hypothesized that these stressors along with a myriad of other stressors such as, ocean acidification, increasing sea surface temperatures, alterations in watershed hydrology, and harvesting of natural resources have combined to impact habitats and their supported flora and fauna.  Our research aims to disentangle and quantify how these stressors manifest both individually and cumulatively in coastal systems, and to predict how the systems may change following management or restoration activities.

Link to selected publications:

Le C, Lehrter JC, Schaeffer B, Hu C, MacIntyre H, Hagy JD, Beddick DL. 2015. Relation between inherent optical properties and land use and land cover across Gulf Coast estuaries. Limnology and Oceanography 60:920-933. 

http://onlinelibrary.wiley.com/doi/10.1002/lno.10065/full

Cai W-J,  Hu X, Huang W-J, Murrell MC, Lehrter JC, Lohrenz SE, Chou W-C, Zhai W, Hollibaugh JT, Wang Y, Zhao P, Guo X,  Gunderson K, Dai M, Gong G-C. 2011. Acidification of subsurface coastal waters enhanced by eutrophication. Nature Geoscience 4:766-770. 

http://www.nature.com/ngeo/journal/v4/n11/full/ngeo1297.html%3FWT.ec_id%3DNGEO-201111

Oliver LM, Lehrter JC, Fisher WS. 2011. Relating landscape development intensity to coral reef condition in the watersheds of St. Croix, US Virgin Islands. Marine Ecology Progress Series 427:293-302. 

http://www.int-res.com/abstracts/meps/v427/p293-302/

Lehrter JC. 2008. Regulation of eutrophication susceptibility in oligohaline regions of a northern Gulf of Mexico estuary, Mobile Bay, Alabama. Marine Pollution Bulletin 56:1446-1460. 

http://www.sciencedirect.com/science/article/pii/S0025326X08002579

 

Marine Biogeochemistry and Ecosystem Modeling

Our observational studies seek to quantify how marine biogeochemical cycles are affected by changes in biophysical forcing and in turn how the cycles affect lower trophic level metabolism. Often, though, it is not possible to isolate how individual or cumulative forcing affects an ecosystem through observation alone.  In such cases, we employ numerical ecosystem models to tease apart the complexity that cannot be observed directly. Ecosystem models are also useful for data synthesis and identification of knowledge gaps in our understanding of specific processes, which can lead to new hypotheses about how marine systems are organized and operate. We have developed and applied models ranging from coastal watershed hydrologic and nutrient exports models to coastal three-dimensional hydrodynamic and biogeochemical models to understand and predict how local and global anthropogenic perturbations impact marine systems.

Link to selected publications:

Devereux R, Lehrter JC, Beddick DL, Yates DF, Jarvis BM. 2015. Manganese, iron, and sulfur cycling in Louisiana continental shelf sediments. Continental Shelf Research 99:46-56.

http://www.sciencedirect.com/science/article/pii/S0278434315000618

 Lehrter JC, Ko DS, Murrell MC, Hagy JD, Schaeffer BA, Greene RM, Gould RW, and Penta B. 2013. Nutrient distributions, transport pathways, and fate on the inner margin of a river-dominated continental shelf. Journal of Geophysical Research: Oceans 118:1-17.

http://onlinelibrary.wiley.com/doi/10.1002/jgrc.20362/full

Lehrter JC, Beddick DL, Jr., Devereux R., Yates DF, Murrell MC. 2012. Sediment-water fluxes of dissolved inorganic carbon, O2, nutrients, and N2 from the hypoxic region of the Louisiana continental shelf. Biogeochemistry 109:233-252.

http://link.springer.com/article/10.1007/s10533-011-9623-x

 Fennel K, Laurent A, Hetland R, Justic D, Ko D, Lehrter JC, Murrell M, Wang L, Yu L, Zhang W. 2016. Effects of model physics on hypoxia simulations for the northern Gulf of Mexico: A model inter-comparison. Journal of Geophysical Research: Oceans DOI: 10.1002/2015JC011577.

http://onlinelibrary.wiley.com/doi/10.1002/2015JC011577/abstract

 

Ocean Color Remote Sensing
There has been a revolution over the past decade in the use of satellite ocean color data to better understand spatial and temporal dynamics of marine systems.  Current satellites provide global, spatially synoptic, coastal data on a daily frequency. Our work revolves around developing new algorithms to retrieve water quality data from satellites in optically complex coastal systems and in the application of these data to develop water quality time-series that can be analyzed to determine the main factors, human vs natural, that drive variability in water quality.

Link to selected publications:

Le C, Lehrter JC, Schaeffer BA, Hu C, Murrell MC, Hagy JD, Greene RM, Beck M. 2016. Bio-optical water quality dynamics observed from MERIS in Pensacola Bay, Florida. Estuarine, Coastal and Shelf Science, doi: 10.1016/j.ecss.2016.02.003.

http://www.sciencedirect.com/science/article/pii/S0272771416300464

Le C, Lehrter JC, Hu C, Obenour D. 2016. Satellite-based empirical models linking river plume dynamics with hypoxic area and volume. Geophysical Research Letters, doi: 10.1002/2015GL067521.

http://onlinelibrary.wiley.com/doi/10.1002/2015GL067521/abstract

Barnes BB, Hu C, Schaeffer BA, Lee Z, Palandro DA, Lehrter JC. 2013. MODIS-derived spatiotemporal water clarity patterns in optically shallow Florida Keys water: A new approach to remove bottom contamination. Remote Sensing of Environment 134:377-391.

http://www.sciencedirect.com/science/article/pii/S0034425713000953

Schaeffer BA, Hagy JD, Conmy RN, Lehrter JC, Stumpf R. 2012. An approach for developing nutrient-related numeric water quality criteria for coastal waters using SeaWiFS satellite remote sensing data. Environmental Science and Technology 46:916-922.

http://pubs.acs.org/doi/abs/10.1021/es2014105

Our lab offers research and training opportunities for graduate and undergraduate students and postdocs. 

PhD and MS graduate students are accepted through the Department of Marine Sciences at the University of South Alabama.  Admission is competitive and requires a minimum GPA of 3.0 and a GRE score of 300 or better for combined verbal and quantitative subtests.  If you meet these criteria, please send your GRE and GPA scores, a current CV, and a brief statement of research interests to jlehrter@disl.org. 

We accept undergraduate volunteers who are interested in pursuing science as a career.  We expect at least a semester-long commitment, during which time you will work on your own project with guidance and consultation from more senior lab members.  This means that during the semester we expect at least 12 hours per week and during summer at least 20 hours per week, preferably full time. Please contact John Lehrter to discuss interests and potential projects.