Gillian Stewart

Marine Biogeochemistry

Science Building - Room E-218
Phone: 718-997-3104


Research Interests

Dr. Stewart is a biogeochemist with interest in the interactions between organisms and elemental cycling, particularly in the ocean. Currently she uses natural radionuclides to investigate the trophic transfer and bioaccumulation of metals by plankton, as well as to trace organic carbon cycling in the surface ocean. Her work sheds light on the mechanisms of contaminant accumulation in ecosystems as well as the ocean’s potential to sequester atmospheric carbon dioxide, a greenhouse gas. Further, her research into the behavior of present-day radioactive tracers may provide insight into the use of naturally-occurring paleotracers in the ocean. Thus far, she has focused her research on the unique, short-lived, particle-reactive isotope polonium-210. At Queens College she plans to pursue regional environmental contaminant studies and continue her work on large-scale oceanographic questions.

Possible Future and Student Projects:

·         Metal accumulation and distribution in local coastal waterways
·         The influence of dust on carbon assimilation in plankton
·         Development of more specific environmental tracers for elemental cycling
·         The importance of food web structure in determining bioaccumulation
·         The effect of different particle types on radioisotope fractionation
·         Species-specific nutrient uptake and loss in the plankton

Teaching Philosophy
My teaching philosophy is very straight-forward: Tough but fair.
Courses Taught:
·         GEOL 08 Oceanography (Fall '07)
·         GEOL 25 Natural Resources and the Environment
·         ENSCI 111 Introduction to Environmental Science
·         GEOL 799.3 Special Topics: Environmental Biogeochemistry



#(co-PI) Tang, Y., Stewart, G., Lam, P. J., Rigaud, S., & Church, T. (2017). The influence of particle concentration and composition on the fractionation of 210 Po and 210 Pb along the North Atlantic GEOTRACES transect GA03. Deep Sea Research Part I: Oceanographic Research Papers.

Schallenberg, C., Ross, A. R., Davidson, A. B., Stewart, G. M., & Cullen, J. T. (2017). Temporal variability of dissolved iron species in the mesopelagic zone at Ocean Station PAPA. Journal of Marine Systems172, 128-136.

#(PI) Rice E.J. and G. Stewart (2016) Decadal changes in zooplankton abundance and phenology of Long Island Sound reflect interacting changes in temperature and community composition. Marine Environmental Research, 120, 154-165.

#(PI) Rice E.J., Dam H., Stewart G. (2015) Impact of climate change on estuarine zooplankton: Surface water warming in Long Island Sound is associated with changes in copepod size and community structure. In Estuaries and Coasts, 38(1), 13-23.


#(Co-PI) Mackinson, B. L., Moran, S. B., Lomas, M. W., Stewart, G. M., & Kelly, R. P. (2015). Estimates of micro-, nano-, and picoplankton contributions to particle export in the northeast Pacific. Biogeosciences, 12(11), 3429-3446.

(Co-PI) Rigaud S., Stewart G., Baskaran M.,  Marsan D., Church T. (2015)  210Po and 210Pb distribution along the North Atlantic GEOTRACES GA03 section. Deep-Sea Research II, 116, 60 -78.  

#(PI) Choi H.-Y., Lomas M., Moran S.B., Kelly R., Stewart G. (2014) Linking the distribution of 210Po and 210Pb with plankton community along Line P, Northeast Subarctic Pacific.  Journal of Environmental Radioactivity, 138, 390-401.

#(PI) Rice, E. J. and G. M. Stewart (2013) Analysis of interdecadal trends in chlorophyll and temperature in the Central Basin of Long Island Sound. Estuarine, Coastal and Shelf Science, 128, 64-75.

#(Co-PI) T. Church, Rigaud S., Baskaran M., Kumar A., Friedrich, J., Masque, P., Puigcorbe V., Kim, G., Radakovitch, O., Hong, G., Choi, H-Y., Stewart, G. (2012) Intercalibration studies of 210Po and 210Pb in dissolved and particulate seawater sample. Limnology and Oceanography Methods, 10, 776-789.

#(PI) Rice, E.J., Panzeca, C., Stewart, G.M. (2012) Temperature-induced microbubbles within natural marine samples may inflate small-particle counts in a Coulter Counter. Marine Ecology Progress Series, 450, 275-280.

#Seebaugh DR, Wallace WG, L’Amoreaux WJ, Stewart GM (2012)  Assimilation of elements and digestion in grass shrimp pre-exposed to dietary mercury.  Archives of Environmental Contamination and Toxicology, 63(2), 230-240.

#Seebaugh, D.R., W.G. Wallace, W.J. L’Amoreaux, G.M. Stewart (2011) Carbon Assimilation and Digestive Toxicity in Naıve Grass Shrimp (Palaemonetes pugio) Exposed to Dietary Cadmium. Bulletin of Environmental Contaminant Toxicology, 88, 449-455.

(PI) Stewart, G., Moran, S.B., Lomas M., and Kelly, R.P. (2010) Direct comparison of 210Po, 234Th and POC particle-size distributions and export fluxes at the Bermuda Atlantic Time-series Study (BATS) site. Journal of Environmental Radioactivity, 102 (5), 479-489 (invited).

(PI) Stewart, G., Moran, S.B., and Lomas, M. (2009) Seasonal POC fluxes at BATS estimated from 210Po deficits. Deep-Sea Research I, 57(1), 113-124.

#Verdeny, E., Masqué P., Garcia-Orellana, J., Hanfland, C., Cochran, J.K., Stewart, G. (2008)  POC export from ocean surface waters by means of 234Th/238U and 210Po/210Pb disequilibria: a comparison of two radiotracer pairs. Deep-Sea Research II, 56, 1502-1518.

#Engel, A., Abramson, L., Szlosek, J., Liu, Z., Stewart, G., Hirschberg, D., Lee, C. (2008) Investigating the effect of ballasting by CaCO3 in Emiliania huxleyi: II. Decomposition of particulate organic matter. Deep-Sea Research II, 56, 1408-1419. 

#Cochran, J.K., Miquel, J-C., Fowler, S., Gasser, B., Hirschberg, D., Szlosek, J., Rodriguez y Baena, A.M., Armstrong, R., Stewart, G., and Masqué, P. (2008) Time-series measurements of 234Th in water column and sediment trap samples from the Northwestern Mediterranean. Deep-Sea Research II, 56, 1487-1501. 

Stewart G.M., J.K. Cochran, J. Xue, C. Lee, S. Wakeham, R.A. Armstrong, P.Masque, and J.C. Miquel (2007) Exploring the connection between Po-210 and organic matter in the northwestern Mediterranean. Deep Sea Research I, 54, 415 – 427.

Stewart G.M, P. Masque, J.K. Cochran, J.C. Miquel, J. Szlosek, A.M. Rodriguez, S.W. Fowler, B. Gasser, and D.J. Hirschberg (2007) Comparing POC flux estimates from 210Po/210Pb water column profiles with estimates from sediment traps and 234Th/238U profiles, 0-200 m northwest Mediterranean. Deep Sea Research I, 54, 1459-1570. 

Buesseler K., Benitez-Nelson C., Moran S. B., Burd A., Charette M., Cochran J.K., Coppola L., Fisher N., Fowler S., Gardner W., Guo L., Gustafsson O., Lamborg C., Masque P., Miquel J-C., Passow U., Santschi P., Savoye N., Stewart G., Trull T., (2006) An assessment of particulate organic carbon to thorium-234 ratios in the ocean and their impact on the application of 234Th as a POC proxy. Marine Chemistry, 100, 213-233.

Stewart G.M., S.W. Fowler, J.L. Tessyie, O. Cotret, and N.S. Fisher (2005) Contrasting the transfer of polonium-210 and lead-210 across three trophic levels in the marine plankton. Marine Ecology Progress Series, 290, 27-33

Liu X.F., G.M. Stewart, J.K. Cochran, C. Lee, R.A. Armstrong, D. Hirschberg, J.C. Miquel, and B. Gasser (2005) Constraints on the differences between POC measured in samples from Niskin bottles and in-situ pumps. Deep Sea Research I, 52(7), 1324-1344.  

Stewart G.M. and N.S. Fisher (2003) Experimental studies on the accumulation of polonium-210 by marine phytoplankton. Limnology and Oceanography, 48(3), 1193-1201.  

Stewart G.M. and N.S. Fisher (2003) Bioaccumulation of polonium-210 in marine copepods. Limnology and Oceanography, 48(5), 2011-2019.  

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