Photo of Charles Hopkinson
Professor
Campus: 
Athens
Office: 
289A Marine Sciences Bldg
Office Phone:  (706) 542-1855
Lab: 
106 Marine Sciences Bldg
Lab Phone: 
(706) 542-2915
Research Area: 

Education:

Ph.D., 1979, Marine Science, Louisiana State University

M.S., 1973, Marine Science, Louisiana State University

B.S., 1970, Biology, Ursinus College

 

Research Emphasis: 

Biogeochemistry and ecology of watersheds, wetlands, estuaries and continental shelves; ecosystem metabolism: stoichiometry and coupling of carbon, nitrogen, phosphorus and oxygen cycles; microbial ecology; land use change and land-water /  land-sea coupling; global ecology; systems ecology – modeling; ecology of coupled human and natural systems, integrated assessment.

Research Programs:

Estuarine Biogeochemistry I have been studying estuaries since graduate school and in collaboration with colleagues from around the world, but especially here at Georgia and in Louisiana and Massachusetts (MBL). Estuaries are the most productive natural ecosystems of the world because they receive nutrient and water subsidies from every land use upstream and because of tidal pumping. It’s their location relative to land inputs however that also makes them vulnerable to N-enrichment and eutrophication.

My interests focus primarily on C and N dynamics of estuaries and their metabolism. What are the fluxes of C, N and sediment between land, sea, atmosphere and estuaries? What is the capacity of coastal systems to transform and sequester organic C? How do variations in the inputs of organic matter and inorganic nutrients from watershed runoff affect estuarine food web structure, primary productivity and production of higher trophic levels? How do changes in land use, climate, sea level and other human activities alter the fluxes and retention of organic matter in estuaries? How will changes in coastal ecosystems affect the global carbon cycle?

I have been addressing these questions through estuarine research projects in Louisiana, Georgia, and Massachusetts.  My research in the Plum Island estuary has been examining how food web structure is influenced by the nature of watershed inputs, especially the interaction between organic matter and inorganic N.  I’m interested in understanding why different types of estuaries, e.g., stratified drowned river valley estuaries like Chesapeake Bay, tidal marsh dominated systems like Sapelo Island and Plum Island, or fjords like Oslo Bay, respond differently to organic and inorganic N and C inputs?  We have been using a combination of natural abundance and enrichment stable isotope studies, coupled with measures of system primary production and respiration to examine the relative importance of various organic matter sources (e.g., riverine, tidal wetland, phytoplankton) in supporting the production of higher trophic levels.

Recently my research interest has shifted to better understanding the effects of sea-level rise and climate change on the survival of tidal wetlands. Declining sediment inputs from land due to better land management practices and potentially increased rates of organic matter decomposition relative to primary production are likely to impact the ability of marshes to build elevation.  If marshes drown, blue carbon burial in tidal wetlands would decrease and greatly impact the rate at which CO2 is accumulating in the atmosphere.  We have initiated new studies to directly measure the net metabolic balance of coupled marsh / small tidal creek regions of estuaries to better quantify the C balance of these wetlands. Long-term observations of the atmospheric C balance along with horizontal fluxes of organic and inorganic C associated with marsh flooding will help us develop a mechanistic, predictive understanding of how C balance and flux varies in relation to variability in SL, temperature, rainfall and other driving factors.

In Plum Island Sound we have also been trying to determine if potential increases in estuarine eutrophication brought about by decreased in river discharge and increased N-runoff might be naturally controlled by shifts in the distribution of soft-shell clams (Mya arenaria). Clams in high density can filter large volumes of water and associated phytoplankton from the water column thereby preventing algal blooms. Our research suggests however, that clam distribution is primarily controlled by winter/spring snow melt and runoff, which is not likely to decrease substantially with climate and land use change. As long as the upper estuary is fresh water during spring runoff, clams will not move upstream to where we expect future algal blooms to occur.

Key Papers –

Hopkinson, C. S.  1988.  Patterns of organic carbon exchange between coastal ecosystems: The mass balance approach in salt marsh ecosystems, pp. 122-154.  In: B-O. Jansson (ed.), Coastal-Offshore Ecosystem Interactions.  Lecture Notes on Coastal and Estuarine Studies, Vol. 22.  Springer-Verlag.

Hopkinson, C. S.  1992. The effects of system coupling on patterns of wetland ecosystem development.  Estuaries 15(4):549-562.

Hopkinson, C. S. and J. Vallino.  1995. The nature of watershed perturbations and their influence on estuarine metabolism.  Estuaries 18:598-621.

Hopkinson, C. S., A. E. Giblin, J. Tucker and H. Garritt. 1999.  Benthic metabolism and nutrient cycling along an estuarine salinity gradient. Estuaries 22:825-843.

Howarth, R. W., D. Anderson, J. Cloern, C. Elfring, C. Hopkinson, B. Lapointe, T. Malone, N. Marcus, K. McGlathery, A. Sharpley and D. Walker.  2000.  Nutrient pollution of coastal rivers, bays and seas.  Issues in Ecology 7:1-15.

Raymond, P. and C. Hopkinson.  2003. Ecosystem modulation of dissolved carbon age in a temperate marsh-dominated estuary.  Ecosystems 6:694-705.

Driscoll, C., D. Whitall, J. Aber, E. Boyer, M. Castro, C. Cronan, C. Goodale, P. Groffman, C. Hopkinson, K. Lambert, G. Lawrence, and S. Ollinger. 2003. Nitrogen pollution in the northeastern United States: Sources, effects and management options.  BioScience 53:357-374.

Hopkinson, C. and E. Smith.  2004.  Estuarine respiration, pages 122-146. In- P. del Giorgio and P.J. leB. Williams.  Respiration of Aquatic Ecosystems of the World.  Academic Press, NY.  328 p.

Deegan, L.,  J. Bowen, D. Drake, J. Fleeger, C. Friedrichs, K. Galván, J. Hobbie, C. Hopkinson, D. Johnson, J. Johnson, L. LeMay, E. Miller, B. Peterson, C. Picard, S. Sheldon, M. Sutherland, J. Vallino, R. Warren. 2007. Susceptibility of salt marshes to nutrient enrichment and predator removal.  Ecol. Applications 17 (Supplement): S42-S63.

Battin, T. J., L. Kaplan, S. Findlay, C. Hopkinson, E. Marti, A. Packman, J. D. Newbold, F. Sabater. 2008. Biophysical controls on organic carbon fluxes in fluvial networks. Nature Geoscience DOI:10.1038/ngeo101.

Hopkinson, C. and A. Giblin. 2008. Salt marsh N Cycling. In- R. Capone, D. Bronk, M. Mulholland and E. Carpenter (eds), Nitrogen in the Marine Environment – 2nd Edition. Elsevier Publ. Pages 991-1036.

Hopkinson, C.S., A. E. Lugo, M. Alber, A. Covich and S. van Bloem. 2008. Understanding and forecasting the effects of sea level rise and intense windstorms on coastal and upland ecosystems: the need for a continental-scale network of observatories.  Frontiers in Ecology and Environment 6(5):255-263, doi:10.1890/070153.

Drake, D. C., B. Peterson, K. Galvan, L. Deegan, C. Hopkinson, J. Johnson, K. Koop-Jakobsen, L. Lemay and C. Picard. 2009. Salt marsh ecosystem biogeochemical responses to nutrient enrichment: a paired 15N tracer study. Ecology 90: 2535-2546.

Weston, N., A. Giblin, G. Banta, C. Hopkinson and J. Tucker.  2010.  The effects of varying salinity on ammonium exchange in estuarine sediments of the Parker River, Massachusetts.  Estuaries and Coasts 33:985-1003.

Millette, T. L., B. Argow, E. Marcano, C. Hayward, C. Hopkinson and V. Valentine. 2010. Salt marsh geomorphological analyses via integration of multispectral remote sensing with LIDAR and GIS.J. Coastal Research. 26:809-816.

Hopkinson, C. S., W-J. Cai and X. Hu. 2012. Carbon Sequestration in Wetland Dominated Coastal Systems - A Global Sink of Rapidly Diminishing Magnitude. Current Opinion On Environmental Sustainability 4:1-9. http://dx.doi.org/10.1016/j.cosust.2012.03.005

Morris, J.T., K. Sundberg and C. S. Hopkinson. 2013. Saltmarsh primary production and its responses to relative sea level and nutrients in estuaries at Plum Island, Massachusetts and North Inlet, South Carolina, USA. Oceanography 26(3):78-84.

Bauer, J., P. Raymond, W-J Cai, T. Bianchi, C. Hopkinson and P. Regnier. 2013.The changing C cycle of the coastal ocean. Nature 2013.

Wilson, C. A., Z. Hughes, D. FitzGerald, C. Hopkinson, V. Valentine and A. Kolker. 2014. Salt marsh pool and tidal creek morphodynamics: dynamic equilibrium of northern latitude saltmarshes? Geomorphology 213: 99-115. (http://).

Koo, K-A, E. Davenport, R. Walker, C. Hopkinson. In revision. Refining estimates of age and annual growth of Mya arenaria using oxygen stable isotopes: a tool for improved shellfish management. Fisheries Research

Watershed Biogeochemistry –What are the major drainage basin and fluvial processes regulating the distribution and flux of carbon, nitrogen, phosphorus and sediments in watersheds, their delivery to the coastal zone and the exchange of N and C with the atmosphere? What are the effects of human activities including population growth, land use change, water use, and climate change on the timing and magnitude of C, N, P and sediment delivery to the coastal zone?  What are the feedbacks between environmental condition and human activity? Can an ecosystem services approach be used to manage watersheds and coastal ecosystems?

I have been collaborating with scientists from the Marine Biological Laboratory Ecosystems Center, University of New Hampshire, Penn State, and Clark University in studies of the Ispwich and Parker River watersheds. The Ipswich and Parker River watersheds in northeastern Massachusetts are model systems to understand the impacts of suburbanization and climate change and variability. The watersheds are in the Boston Metropolitan region, which is an area with the 2nd highest rate of suburbanization in the country (next to Atlanta). Our studies have focused on the relation between hydrology, land use, floodplain connectivity and nitrogen dynamics. Water use is 2nd only to climate in controlling hydrology. Clean water and sewage exchange with adjacent communities, especially Boston, play a major role in overall N budgets, water export to the coastal zone, and the importance of riparian floodplains in helping to maintain good water quality. Dead zones (zones of slow water movement in stream beds and channel margins) in combination with wetland floodplains are hotspots of N retention that result in about 90% of watershed N inputs never reaching the coast. Suburban water use can result the river drying out in certain reaches and in a decoupling with riparian floodplains. As a result water bans are now widely used to limit water withdrawals. Results suggest that N retention efficiency will decrease with expanding population and continued suburbanization. We have been examining the potential impacts of reduced water export and increased N export on the estuarine ecosystem focusing primarily on the commercially important soft-shell clam, Mya arenaria.

Recently we have become interested in the importance of historic land use practices and the export of sediments to coastal wetlands. Hundreds of river road crossings, dams and beaver dams have greatly reduced sediment export relative to when the watershed had been cleared for agriculture in the 1800’s. Continued sediment storage may compromise the ability of coastal tidal wetlands to maintain elevation relative to sea-level rise.

Overall we find that water quality (in terms of N quantity and form) is high in the Ipswich and Parker Rivers. However, our models suggest that N export to the coastal zone will increase in the future in conjunction with continued urbanization. Maintaining integrity of headwater streams, riparian zones and river wetlands will be critical to controlling the increase in nutrient export (N and P, decrease in C) to the coastal zone. Dam removal may serve as a useful management option to make sediments available for tidal wetland survival.

Key Papers -

Williams, M., C. Hopkinson, E. Rastetter, J. Vallino and L. Claessens.  2005. Relationships of land use and stream solute concentrations in the Ipswich River Basin, northeastern Massachusetts.  Water, Air, and Soil Pollution 161:55-74.

Claessens, L., C. Hopkinson, E. Rastetter, and J. Vallino.  2006. Evaluating the effect of historical changes in land use and climate on the water budget of an urbanizing watershed. Water Resources Res. 42: WO3246, doi:10.1029/2005WR004131,2006.

Wollheim, W. M., C. Vörösmarty, B. Peterson, S. Seitzinger, and C. Hopkinson.  2006. Relationship between river size and nutrient removal. Geophysical Research Letters 33: LO6410, doi:1029/2006GL025845.4 p.

Battin, T. J., L. Kaplan, S. Findlay, C. Hopkinson, E. Marti, A. Packman, J. D. Newbold, F. Sabater. 2008. Biophysical controls on organic carbon fluxes in fluvial networks. Nature Geoscience DOI:10.1038/ngeo101.

Briggs, M. A., M. N. Gooseff, B. J. Peterson, K. Morkeski, W. M. Wollheim, and C. S. Hopkinson (2010), Surface and hyporheic transient storage dynamics throughout a coastal stream network, Water Resour. Res., 46, W06516, doi:10.1029/2009WR008222.

Stewart, R. J., W. M. Wollheim, M. Gooseff, M. A. Briggs, J. M. Jacobs, B. J. Peterson, and C. S. Hopkinson (2012), Separation of River Network Scale Nitrogen Removal Among Main Channel and Two Transient Storage Compartments, Water Resour. Res. 47

Wollheim, W.M., M. Green, B. Pellerin, N. Morse, and C. Hopkinson. 2013. Causes and consequences of ecosystem service regionalization in a coastal suburban watershed. Estuaries and Coasts. In press. DOI 10.1007/s12237-013-9646-8.

Wollheim, W. , T.K. Harms, B.J. Peterson, K. Morkeski, C. Hopkinson, R.J. Stewart, M. Gooseff, M. Briggs. Accepted with revisions. Nitrate uptake dynamics of surface transient storage in channels and fluvial wetlands. Biogeochemistry

Continental Shelves -  I have been collaborating with scientists from UMass-Dartmouth, NC State, Auburn, The Ecosystems Center (MBL), Ohio State, as well as U. Delaware in understanding the carbon cycle of the coastal ocean including continental shelves. The coastal carbon cycle connects and integrates the terrestrial and oceanic carbon budgets. Considering the substantial export of labile organic carbon from land via rivers, one would expect the coastal ocean to be heterotrophic and a net source of CO2 to the atmosphere. But rising atmospheric CO2 levels may have shifted the overall dynamics such that shelves are now a net sink. Indeed we estimate the coastal ocean as a whole to be a net sink at 0.45 Pg C yr-1. With atmospheric CO2 levels expected to rise substantially over the next few decades, continental shelves will take up even more CO2 from the atmosphere and export more DIC to the open ocean.

The importance of shelves in global carbon cycling is recognized, but the available evidence to date is equivocal as to why certain margins are sinks while others are sources of atmospheric CO2. Rather than attempt to evaluate multiple major margin systems, our approach has been to develop a predictive, mechanistic understanding of the C balance of margins from comprehensive, in-depth, whole-system investigations of a single temporally and spatially variable U.S. east coast continental shelf system, the South Atlantic Bight (SAB). The SAB is representative of a major class of continental shelf, i.e., western boundary current shelves, and therefore our findings should be easily translatable to similar shelves globally.

Our research seeks to answer hypotheses that i) the relative timescales of shelf water mixing, organic matter (OM) decomposition, autotrophic production, and air-sea CO2 exchange, along with seasonal temperature variation, are the primary factors controlling pCO2 variability and driving air-sea fluxes in ocean margins, and ii) differences in the stoichiometry, quantity and lability of allochthonous OM inputs relative to inorganic nutrient inputs determine the overall metabolic status (i.e., net CO2 production) of ocean margin systems.

We use geochemical mass balances to examine the role of net ecosystem production (NEP - biology), including analyses of DIC/pCO2, triple O2 isotope tracers, C:N:P stoichiometry of OM and nutrients, and Δ14C and δ13C of OM and DIC. We directly assess the relative importance of key physical (temperature, air-sea flux, mixing) and biological (NEP) processes on relevant temporal and spatial scales. We also use coupled hydrodynamic - biogeochemical models to "test" by simulation modeling our hypotheses about the factors controlling temporal and spatial variations in sea surface pCO2. Models help us extrapolate our results and understanding to other shelf systems.

Ocean margin C cycling is a high research priority of the U.S. North American Carbon Program (NACP) and the Ocean Carbon and Biogeochemistry Program (OCB). Our research addresses several of the key goals of these programs.

Key Papers –

Normann, B., U. Zweifel, C. Hopkinson and B. Fry.  1995.  Production and utilization of dissolved organic carbon during an experimental diatom bloom.  Limnology and Oceanography 40:898-907.

Chen, R., B. Fry, C. Hopkinson, D. Repeta and E. Peltzer.  1996. Dissolved organic carbon on Georges Bank.  Continental Shelf Research 16:409-420.

Fry, B., C. Hopkinson, A. Nolin, B. Norrman and U. Zweifel.  1996.  Long term decomposition of DOC from experimental diatom blooms.  Limnol. Oceanogr. 41:1344-1347.

Fry, B., E. Peltzer, C. Hopkinson, A. Nolin and L. Redmond.  1996.  Analysis of marine DOC using a reference dry combustion method.  Marine Chemistry 54:191-201.

Hopkinson, C. S., B. Fry, and A. Nolin.  1997.  Stoichiometry of dissolved organic matter dynamics on the continental shelf of the Northeastern U.S.A.  Continental Shelf Research 17:473-489.

Fry, B., C. Hopkinson, A. Nolin and S. Wainright. 1998. 13C/12C composition of marine dissolved organic carbon.  Chemical Geology 152:113-118.

Hopkinson, C. S., I. Buffam, J. Hobbie, J. Vallino, M. Perdue, B. Eversmeyer, F. Prahl, J. Covert, R. Hodson, M. Moran, E. Smith, J. Baross, B. Crump, S. Findlay, K. Foreman. 1998. Terrestrial inputs of organic matter to coastal ecosystems: An intercomparison of chemical characteristics and bioavailability. Biogeochemistry 43:211-234.

Tucker, J., N. Sheats, A. Giblin, C. Hopkinson, and J. Montoya.  1999. Using stable isotopes to trace sewage derived material through Boston Harbor and Massachusetts Bay.  Marine Environmental Research 48:353-375.

Fisher, T. R., D. Correll, R. Costanza, J. Hollibaugh, C. Hopkinson, R. Howarth, N. Rabalais, J. Richey, C. Vörösmarty and R. Wiegert.  2000.  Synthesizing drainage basin inputs to coastal systems, pages 81-106. In – J. Hobbie (ed.)., Estuarine Science, a synthetic approach to research and practice. Island Press, Washington, D.C. 539 p.

Hopkinson, C. S., A. E. Giblin, and J. Tucker.  2001. Benthic metabolism and nutrient regeneration on the continental shelf off eastern Massachusetts, USA.  Marine Ecology – Progress Series 224:1-19.

Hopkinson, C. S., J. Vallino and A. Nolin.  2002.  Decomposition of dissolved organic matter from the continental margin.  Deep-Sea Research II 49:4461-4478.

Hopkinson, C. S. and J. Vallino.  2005. Efficient export of carbon to the deep ocean through dissolved organic matter. Nature 433:142-145.

Bauer, J., P. Raymond, W-J Cai, T. Bianchi, C. Hopkinson and P. Regnier. 2013.The changing C cycle of the coastal ocean. Nature 2013.

Huang, W.-J., W.-J. Cai, Y. Yang, and C. Hopkinson. 2013. Impacts of a weather event on shelf circulation and CO2 and O2 dynamics on the Louisiana shelf during summer 2009. Biogeosciences Discuss. 10: 19867-19893.doi:10.5194/bgd-10-19867-2013.

Biogeochemistry of Sewage Treatment Alternatives - I recently began a study of alternative sewage treatment options for developed alpine environments – e.g., ski and golf course resorts. This research interest stems from the laboratory focus of the Ecosystems Center’s Semester in Environmental Science program, which I helped to organize and teach in from 1997 - 2008. The class took advantage of an ongoing “experiment” by the Town of Falmouth Massachusetts to dispose of 2nd treated sewage by spraying a pine-oak forest. The class investigated the effects of sewage on tree growth, N dynamics, and transport of dissolved nitrogen via groundwater to the nearby West Falmouth Harbor. There the class studied the effects of N-enrichment on estuarine biogeochemistry and food web ecology.

I have teamed up with the Moonlight Basin sewer and water department to assess the impact of 2ndary treated sewage on two alpine forests (about 8000’ elevation) near Big Sky, Mt. Approximately 40 m diameter plots of either young lodgepole pine or middle-aged Douglas Fir and Subalpine Fir are being spray irrigated during the snow-free summer months. I have been sampling streams along tributaries to the Gallatin and Madison Rivers to examine the effects of land use (golf course, housing, commercial, ski trails, forest) on stream nutrient quality. In 2014 control and spray-treated trees in both young and middle-aged stands were banded to assess growth rates. Streams draining the spray irrigated stand are also sampled to determine if and when nutrients carried by groundwater break through into streams. To date, on the basis of inorganic nutrient concentrations and benthic algal biomass, the drainage streams are as “clean” as any found in the region.  Ultimately, I plan to determine N budgets for sprayed and unsprayed regions to determine the fate of added N and to determine if this is a sustainable method for dealing with sewage.