Dr. John Lehrter

Dr. John Lehrter

Senior Marine Scientist I

Associate Professor, University of South Alabama

Bio

Dr. John Lehrter is an Associate Professor in the Department of Marine Sciences at the University of South Alabama and a Senior Marine Scientist at the Dauphin Island Sea Lab. Prior to joining the faculty at USA and DISL in August 2016, Dr. Lehrter was a Research Ecologist with the EPA Office of Research and Development. His research focuses on understanding the biogeochemical cycling of nutrients, organic matter, and oxygen in coastal systems and how these cycles are related to water quality issues such as eutrophication, hypoxia, coastal acidification, and water clarity.

The research is largely aimed at solving complex coastal resource management issues through applications of field and lab studies, satellite oceanography, and numerical ecosystem modeling.

Dr. Lehrter has served on local and national science committees and has won numerous awards for applying science to decision-making activities. He received his Ph.D. in Biology from the University of Alabama and post-doctoral training at the EPA Gulf Ecology Division.

Research Interest

My research focuses on eutrophication, hypoxia, and the biogeochemical cycling of carbon, oxygen, and nutrients in aquatic and marine ecosystems. Specifically, I aim to understand these processes in the context of anthropogenic changes occurring at local, regional, and global scales.

For a complete list publications, please visit Lehrter's Google Scholar site.

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. Therefore, the impacts to these systems are of great societal concern.  Work in our lab focuses 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.

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.

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.

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.

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.

Coastal Biogeochemistry and Modeling

To understand coastal ecosystems, it is necessary to quantify the budgets, i.e. the stocks and rates of change, of important elements such as carbon, oxygen, nitrogen, and phosphorus. Our observational studies seek to quantify and predict how these material budgets are impacted by anthropogenic stressors such as land-use change, increased nutrient loading, and climate change. Often, though, it is not possible to isolate how individual or cumulative stress 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 coastal systems. Our present work includes testing and inter-comparison of hypoxia models and development of new biogeochemical models to incorporate current scientific understanding of underlying processes such as controls on phytoplankton community dynamics and the fate of their produced organic matter in the water-column and benthos.

Selected publications:

Lehrter JC, Ko DS, Lowe L, Penta B. Predicted effects of climate change on northern Gulf of Mexico hypoxia. In: Justic D, Rose KA, Hetland RD, Fennel K (eds.). Modeling Coastal Hypoxia: Numerical simulations of Patterns, Controls, and Effect of Dissolved Oxygen Dynamics. Springer, New York (Accepted).

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.

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.

Lehrter JC, Cebrian J. 2010. Uncertainty propagation in an ecosystem nutrient budget. Ecological Applications 20:508-524.

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. 

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.

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.

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.

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.

Projects

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