Eutrophication

Increased loadings of nutrients to estuaries have altered ecosystem function by encouraging growth of phytoplankton and macroalgae while inducing large swings in dissolved oxygen and threatening the sustainability of seagrass meadows. We are measuring and modeling these processes to understand the future trajectory of estuarine ecosystems.

The past several decades have seen a massive increase in eutrophication of estuaries globally, leading to widespread hypoxia and anoxia, habitat degradation, alteration of food web structure, loss of biodiversity, and increased frequency, spatial extent, and duration of harmful algal blooms. A majority of estuaries in the USA are degraded as a result. Shallow seagrass dominated lagoons appear to be particularly sensitive. In many of these ecosystems, endemic species such as seagrass are lost as benthic algae and phytoplankton dominate under increased nutrient supply.

Our research of eutrophication began with developing methods to estimate nutrient loading from groundwater. Those methods integrated continuous monitoring as well as numerical modeling. Monitoring of nitrogen levels, salinity, chlorophyll, dissolved oxygen, and light attenuation have led to a better understanding of the mechanisms and timescales of eutrophication. We have now begun enhancing biogeochemical models to represent estuarine processes such as hypoxia, benthic fluxes, and seagrass kinetics. These models can then be used to simulate future scenarios of nutrient loading and sea-level rise, while also exploring biophysical feedbacks such as decreased sediment resuspension due to increased seagrass biomass.

Seagrass measurement

Measuring seagrass biomass in Chincoteague Bay, Maryland to constrain numerical models.

Publications:

Defne, Z., Ganju, N.K. and Aretxabaleta, A., 2016. Estimating time-dependent connectivity in marine systems. Geophysical Research Letters. (defne_et_at_connectivity.pdf)

Oestreich, W. K., Ganju, N. K., Pohlman, J. W., and Suttles, S. E., 2016. Colored dissolved organic matter in shallow estuaries: relationships between carbon sources and light attenuation, Biogeosciences, 13, 583-595, doi:10.5194/bg-13-583-2016. (oestreich_et_al_CDOM.pdf)

Ganju, N. K., Miselis, J. L., and Aretxabaleta, A. L., 2014, Physical and biogeochemical controls on light attenuation in a eutrophic, back-barrier estuary, Biogeosciences, 11, 7193-7205. (ganju_et_al_light.pdf)

del Barrio, P., Ganju, N. K., Aretxabaleta, A. L., Hayn, M., García, A., and Howarth, R. W., 2014, Modeling future scenarios of light attenuation and potential seagrass success in a eutrophic estuary, Estuarine, Coastal and Shelf Science, 149, 13-23. (delBarrio_et_al_seagrass.pdf)

Defne, Z., and Ganju, N. K., 2014, Quantifying the residence time and flushing characteristics of a shallow, back-barrier estuary: application of hydrodynamic and particle tracking models, Estuaries and Coasts, 38, 1719-1734. (defne_ganju_barnegat.pdf)

Ganju, N. K., Hayn, M., Chen, S. N., Howarth, R. W., Dickhudt, P. J., Aretxabaleta, A. L., and Marino, R., 2012, Tidal and groundwater fluxes to a shallow, microtidal estuary: constraining inputs through field observations and hydrodynamic modeling. Estuaries and Coasts, 35, 1285-1298. (ganju_et_al_fluxes.pdf)

Ganju, N.K., 2011, A novel approach for direct estimation of fresh groundwater discharge to an estuary, Geophysical Research Letters, 38, L11402, doi:10.1029/2011GL047718. (ganju_groundwater.pdf)

 

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