This project investigates the links between terrestrial and marine carbon cycling and fluvial transport of freshwater and dissolved organic carbon (DOC) to the near-coastal ocean. The project analyzes DOC export that integrates complex interacting processes in natural and human-impacted terrestrial and aquatic environments. Changes in DOC export may indicate changes in terrestrial ecosystem carbon cycling that are difficult to quantify directly but that may affect exchanges between the biosphere, geosphere, and atmosphere. Detecting changes in DOC export can provide insight into ongoing changes in terrestrial carbon cycling. In northern temperate forested ecosystems changes in carbon export may reflect a shift from carbon sink to carbon source or vice versa. Changes in freshwater and carbon export can influence aquatic and marine biogeochemical processes including eutrophication, hypoxia, carbon sequestration or release, ocean acidification, and ocean net primary productivity. This project examines the controls on the fluvial export of terrestrially-derived DOC including climatic variability and landscape variables.
Statement of Problem: This project is studying how ongoing and projected changes in climate are, or will likely, affect the export of freshwater and dissolved organic carbon (DOC) to the near-coastal ocean. This project is also examining the fate of DOC in rivers to address questions of whether DOC is transported conservatively or whether a substantial fraction of DOC is lost through biotic or abiotic processes during transport in rivers. Additionally, it is investigating whether concentration discharge (C-Q) relations for DOC may have changed over time that could indicate that the fundamental C-Q relation, that is generally assumed to be stationary, has changed.
Why this Research is Important: The evidence suggests that the global hydrologic cycle is intensifying (Huntington, 2006, 2010). The intensity of the water cycle increased over most of the conterminous United States between the periods 1945 to 1974 and 1985 to 2014 (Figure 1, Huntington and others, 2018). In the northeastern U.S. this hydrologic response to climate change includes an increase in precipitation and runoff and is projected to result in substantial changes in the seasonal delivery of water and organic carbon to the near-coastal ocean, and to an increase in summer drought severity. These hydrologic changes are altering the timing and magnitude of the delivery of DOC to the Gulf of Maine. Evidence suggests that increasing discharge is affecting nutrient inputs to the Gulf of Maine and that increasing export of DOC may be reducing light absorption by phytoplankton reducing primary productivity that could ultimately affect fisheries in the region. There are also concerns that increasing export of freshwater and DOC may be exacerbating ongoing ocean acidification and the harmful algal blooms (Figure 2).
If it is shown that the concentration discharge relations for DOC has changed over time this would indicate fundamental changes in carbon cycle processes including rates of microbial decomposition of soil organic carbon (SOC), primary production, or the partitioning of SOC decomposition into DOC or CO2.
Figure 1:

Objective(s): The project objectives include investigation of the links between terrestrial and marine carbon cycling by studying the fluvial transport of freshwater and dissolved organic carbon. The primary goal is to improve our understanding of how changes in climate are affecting the export of freshwater and dissolved organic carbon to the near-coastal ocean.
Methods: The project uses non-parametric time-series analysis to investigate historical and future projected trends in precipitation, runoff, and evapotranspiration over large watershed at the regional and continental scale. Through a partnership with other USGS researchers (Greg McCabe, Dave Wolock, and Peter Weiskel) this project employs a water-balance model in conjunction with climate and soils data to investigate historical changes in water cycle intensity defined as precipitation plus actual evapotranspiration.
This project employs the LOADEST regression model to estimate riverine dissolved organic carbon (DOC) fluxes (loads) exported to the near coastal ocean. Regression modeling is also used to study the relative importance of climate and landscape variables in controlling the carbon yield from individual rivers. In partnership with research scientists at the University of Massachusetts, Boston this project is studying DOC export from the Penobscot River using the Regional Hydro-Ecologic Simulation System (RHESSys) model.
Figure 2:

Below are publications associated with this project in the USGS pubs warehouse:
Northern forest winters have lost cold, snowy conditions that are important for ecosystems and human communities
It’s about time: A synthesis of changing phenology in the Gulf of Maine ecosystem
A new indicator framework for quantifying the intensity of the terrestrialwater cycle
Evidence for major input of riverine organic matter into the ocean
Grand challenges in understanding the interplay of climate and land changes
Evidence for conservative transport of dissolved organic carbon in major river basins in the Gulf of Maine Watershed
Toward a quantitative and empirical dissolved organic carbon budget for the Gulf of Maine, a semienclosed shelf sea
Evapotranspiration trends over the eastern United States during the 20th century
Soil: Organic Matter and Available Water Capacity
Trends in precipitation, runoff, and evapotranspiration for rivers draining to the Gulf of Maine in the United States
Controls on dissolved organic carbon quantity and chemical character in temperate rivers of North America
State of the Earth’s cryosphere at the beginning of the 21st century : glaciers, global snow cover, floating ice, and permafrost and periglacial environments: Chapter A in Satellite image atlas of glaciers of the world
- Overview
This project investigates the links between terrestrial and marine carbon cycling and fluvial transport of freshwater and dissolved organic carbon (DOC) to the near-coastal ocean. The project analyzes DOC export that integrates complex interacting processes in natural and human-impacted terrestrial and aquatic environments. Changes in DOC export may indicate changes in terrestrial ecosystem carbon cycling that are difficult to quantify directly but that may affect exchanges between the biosphere, geosphere, and atmosphere. Detecting changes in DOC export can provide insight into ongoing changes in terrestrial carbon cycling. In northern temperate forested ecosystems changes in carbon export may reflect a shift from carbon sink to carbon source or vice versa. Changes in freshwater and carbon export can influence aquatic and marine biogeochemical processes including eutrophication, hypoxia, carbon sequestration or release, ocean acidification, and ocean net primary productivity. This project examines the controls on the fluvial export of terrestrially-derived DOC including climatic variability and landscape variables.
Statement of Problem: This project is studying how ongoing and projected changes in climate are, or will likely, affect the export of freshwater and dissolved organic carbon (DOC) to the near-coastal ocean. This project is also examining the fate of DOC in rivers to address questions of whether DOC is transported conservatively or whether a substantial fraction of DOC is lost through biotic or abiotic processes during transport in rivers. Additionally, it is investigating whether concentration discharge (C-Q) relations for DOC may have changed over time that could indicate that the fundamental C-Q relation, that is generally assumed to be stationary, has changed.
Why this Research is Important: The evidence suggests that the global hydrologic cycle is intensifying (Huntington, 2006, 2010). The intensity of the water cycle increased over most of the conterminous United States between the periods 1945 to 1974 and 1985 to 2014 (Figure 1, Huntington and others, 2018). In the northeastern U.S. this hydrologic response to climate change includes an increase in precipitation and runoff and is projected to result in substantial changes in the seasonal delivery of water and organic carbon to the near-coastal ocean, and to an increase in summer drought severity. These hydrologic changes are altering the timing and magnitude of the delivery of DOC to the Gulf of Maine. Evidence suggests that increasing discharge is affecting nutrient inputs to the Gulf of Maine and that increasing export of DOC may be reducing light absorption by phytoplankton reducing primary productivity that could ultimately affect fisheries in the region. There are also concerns that increasing export of freshwater and DOC may be exacerbating ongoing ocean acidification and the harmful algal blooms (Figure 2).
If it is shown that the concentration discharge relations for DOC has changed over time this would indicate fundamental changes in carbon cycle processes including rates of microbial decomposition of soil organic carbon (SOC), primary production, or the partitioning of SOC decomposition into DOC or CO2.
Figure 1:
Sources/Usage: Public Domain. Visit Media to see details.Map showing the difference in annual average water cycle intensity between the averages of 1985 to 2014 minus 1945 to 1974. (Huntington, T. G., Weiskel, P. K., Wolock, D. M., and McCabe, G. J. 2018. A new indicator framework for quantifying changes in intensity of the water cycle. Journal of Hydrology, v. 559, p. 361-372.) Objective(s): The project objectives include investigation of the links between terrestrial and marine carbon cycling by studying the fluvial transport of freshwater and dissolved organic carbon. The primary goal is to improve our understanding of how changes in climate are affecting the export of freshwater and dissolved organic carbon to the near-coastal ocean.
Methods: The project uses non-parametric time-series analysis to investigate historical and future projected trends in precipitation, runoff, and evapotranspiration over large watershed at the regional and continental scale. Through a partnership with other USGS researchers (Greg McCabe, Dave Wolock, and Peter Weiskel) this project employs a water-balance model in conjunction with climate and soils data to investigate historical changes in water cycle intensity defined as precipitation plus actual evapotranspiration.
This project employs the LOADEST regression model to estimate riverine dissolved organic carbon (DOC) fluxes (loads) exported to the near coastal ocean. Regression modeling is also used to study the relative importance of climate and landscape variables in controlling the carbon yield from individual rivers. In partnership with research scientists at the University of Massachusetts, Boston this project is studying DOC export from the Penobscot River using the Regional Hydro-Ecologic Simulation System (RHESSys) model.
Figure 2:
Sources/Usage: Some content may have restrictions. Visit Media to see details.Data from the Visible Infrared Imaging Radiometer Suite (VIIRS) sensor on the Suomi NPP satellite was used to create this enhanced color composite image of the Gulf of Maine and the northwestern Atlantic Ocean on May 14, 2015. Light green colors indicate areas where water conditions and nutrients near the surface (including dissolved organic carbon) create phytoplankton blooms. (credit: Norman Kuring, NASA Ocean Color Group)Huntington et al. (2016) reported increasing export of dissolved organic carbon (DOC) to the Gulf of Maine in the latter half of the 20th and early 21st centuries and discussed projections for increasing DOC export in the 21st century based on climate projections. Huntington et al. (2016) suggested that increasing DOC export to the near coastal ocean may influence marine biogeochemistry including the development of nuisance and harmful algal blooms and carbon sequestration. In the near‐coastal ocean, colored dissolved organic matter (CDOM), which is a component of terrestrially derived DOC, can lower the accuracy of satellite‐derived chlorophyll concentrations. CDOM strongly absorbs in the blue wavelengths, thus lowering the water‐leaving radiance in those wavelengths that the satellite sensor's chlorophyll algorithm mistakenly interprets as chlorophyll absorption. Terrestrially derived DOC exported to the marine environment could also decrease phytoplankton productivity through increases in light attenuation (Balch et al. 2012, Balch et al. 2016).Cited ReferencesBalch, W. M., Drapeau, D. T., Bowler, B. C., and Huntington, T. G., (2012) Step-changes in the physical, chemical and biological characteristics of the Gulf of Maine, as documented by the Gulf of Maine North Atlantic Time Series (GNATS); Marine Ecological Progress Series, v. 450, p. 11-35. Balch, W. M., Huntington, T. G., Aiken, G R. Drapeau, D, Bowler, B., Lubelczyk, L. and Butler, Kenna, (2016) Toward a quantitative and empirical dissolved organic carbon budget for the Gulf of Maine, a semi-enclosed shelf sea; Global Biogeochemical Cycles, v. 30 p. 268-292.Huntington, T. G., W. M. Balch, G. R. Aiken, J. Sheffield, L. Luo, C. S. Roesler, and P. Camill, (2016) Climate change and dissolved organic carbon export to the Gulf of Maine; Journal of Geophysical Research; Biogeosciences, v. 121, p. 2700-2716. - Publications
Below are publications associated with this project in the USGS pubs warehouse:
Filter Total Items: 19Northern forest winters have lost cold, snowy conditions that are important for ecosystems and human communities
Winter is an understudied but key period for the socio-ecological systems of northeastern North American forests. A growing awareness of the importance of the winter season to forest ecosystems and surrounding communities has inspired several decades of research, both across the northern forest and at other mid- and high-latitude ecosystems around the globe. Despite these efforts, we lack a syntheIt’s about time: A synthesis of changing phenology in the Gulf of Maine ecosystem
The timing of recurring biological and seasonal environmental events is changing on a global scale relative to temperature and other climate drivers. This study considers the Gulf of Maine ecosystem, a region of high social and ecological importance in the Northwest Atlantic Ocean and synthesizes current knowledge of 1) key seasonal processes, patterns, and events; 2) direct evidence for shifts inA new indicator framework for quantifying the intensity of the terrestrialwater cycle
A quantitative framework for characterizing the intensity of the water cycle over land is presented, and illustrated using a spatially distributed water-balance model of the conterminous United States (CONUS). We approach water cycle intensity (WCI) from a landscape perspective; WCI is defined as the sum of precipitation (P) and actual evapotranspiration (AET) over a spatially explicit landscape uEvidence for major input of riverine organic matter into the ocean
The changes in the structure of XAD-8 isolated dissolved organic matter (DOM) samples along a river (Penobscot River) to estuary (Penobscot Bay) to ocean (across the Gulf of Maine) transect and from the Pacific Ocean were investigated using selective and two dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy coupled with elemental and carbon isotope analysis. The results provide importGrand challenges in understanding the interplay of climate and land changes
Half of Earth’s land surface has been altered by human activities, creating various consequences on the climate and weather systems at local to global scales, which in turn affect a myriad of land surface processes and the adaptation behaviors. This study reviews the status and major knowledge gaps in the interactions of land and atmospheric changes and present 11 grand challenge areas for the sciEvidence for conservative transport of dissolved organic carbon in major river basins in the Gulf of Maine Watershed
Transport and fate of dissolved organic carbon (DOC) in rivers are important aspects of the carbon cycle and the critical linkage between terrestrial, aquatic, and marine systems. Recent studies have quantified fluvial export to the marine environment in many systems, but in-stream losses of DOC are poorly constrained. This study compares DOC yields (kg C/ha) between the area-weighted averages ofToward a quantitative and empirical dissolved organic carbon budget for the Gulf of Maine, a semienclosed shelf sea
A time series of organic carbon export from Gulf of Maine (GoM) watersheds was compared to a time series of biological, chemical, bio-optical, and hydrographic properties, measured across the GoM between Yarmouth, NS, Canada, and Portland, ME, U.S. Optical proxies were used to quantify the dissolved organic carbon (DOC) and particulate organic carbon in the GoM. The Load Estimator regression modelEvapotranspiration trends over the eastern United States during the 20th century
Most models evaluated by the Intergovernmental Panel for Climate change estimate projected increases in temperature and precipitation with rising atmospheric CO2 levels. Researchers have suggested that increases in CO2 and associated increases in temperature and precipitation may stimulate vegetation growth and increase evapotranspiration (ET), which acts as a cooling mechanism, and on a global scSoil: Organic Matter and Available Water Capacity
No abstract available.Trends in precipitation, runoff, and evapotranspiration for rivers draining to the Gulf of Maine in the United States
Climate warming is projected to result in increases in total annual precipitation in northeastern North America. The response of runoff to increases in precipitation is likely to be more complex because increasing evapotranspiration (ET) could counteract increasing precipitation. This study was conducted to examine these competing trends in the historical record for 22 rivers having >70 yr of runoControls on dissolved organic carbon quantity and chemical character in temperate rivers of North America
Understanding the processes controlling the transfer and chemical composition of dissolved organic carbon (DOC) in freshwater systems is crucial to understanding the carbon cycle and the effects of DOC on water quality. Previous studies have identified watershed-scale controls on bulk DOC flux and concentration among small basins but fewer studies have explored controls among large basins or simulState of the Earth’s cryosphere at the beginning of the 21st century : glaciers, global snow cover, floating ice, and permafrost and periglacial environments: Chapter A in Satellite image atlas of glaciers of the world
This chapter is the tenth in a series of 11 book-length chapters, collectively referred to as “this volume,” in the series U.S. Geological Survey Professional Paper 1386, Satellite Image Atlas of Glaciers of the World. In the other 10 chapters, each of which concerns a specific glacierized region of Earth, the authors used remotely sensed images, primarily from the Landsat 1, 2, and 3 series of sp