Project Funding: 2011 - 2014

NRA: 2009 NASA: Interdisciplinary Research in Earth Science   

Funded by NASA

Abstract:
Although coastal wetlands and estuaries are known to play an important role in carbon sequestration and mobilization, it is unclear whether the coastal ocean is a net source or sink for carbon. Nor is it clear how coastal sources or sinks will be influenced by changes in climate. These fundamental gaps in our knowledge may be due to: a) the lack of parallel, coherent time series of carbon pools and fluxes, for land and coastal ocean, with which to close carbon budgets or b) error budgets for land and ocean carbon pools and fluxes (including land-to-sea export) that lack the statistical power to definitively test scientific hypotheses. To address these issues, we propose a coordinated land, river and  coastal ocean project in two large contiguous watersheds in NE North America, the Gulf of Maine (GoM) and Gulf of St. Lawrence (GoSL). The fundamental goal is to understand the nature of the land-to-sea carbon export term, relative to pools and fluxes in terrestrial and ocean biomes. The combined watershed area of the GoM and GoSL is 1.2 million km2. Rivers feeding these gulfs annually discharge ~17,000 m3 s-1, some 33% more than the annual discharge of the Mississippi River (12,750 m3 s-1) and they contribute 8-9% of all river discharge from N. America. Dissolved organic carbon (DOC) strongly dominates the carbon export of these systems. Despite the fact that the Gulf of Maine watershed is 1/6 the size of the GoSL, DOC exports to the GoM are ~50% of those entering the GoSL (due to greater runoff per unit area and higher DOC concentrations). The project team provides the required expertise for such a combined modeling, remote sensing, and field study, with strong international collaboration. We will address key questions associated with the export and fate of organic matter within these watersheds. The study will focus on terrestrial, river and marine components and the respective time scales that organic carbon is fixed, mobilized and exported. Biogeochemical and hydrologic modeling will focus on the carbon sources and fluxes. Satellite remote sensing provides the only synoptic means to address these questions over such a broad area. Established algorithms from the MODIS Land and Ocean program, as well as Shuttle Radar Topography Mission results, will be used to construct carbon time series. Highly- targeted field campaigns within watersheds and coastal waters--including the ongoing NASA Gulf of Maine North Atlantic Time Series (GNATS), now in its 12th year-- will provide the means to validate the satellite products, provide critical information on the quality and quantity of DOC, establish its overall importance relative to marine DOC and highlight the impact of climate change on the land and sea carbon cycles. The results of this work will represent a holistic analysis of carbon flow, through the watersheds, rivers and coastal waters; it will focus on the DOC mobilization/export from terrestrial photosynthesis to rivers and, ultimately, marine systems, integrating the combined effects of hydrological and climatic variability, microbial processes, soil effects, acid deposition, impoundments, burned areas, erosion etc. This project is most related to NASA sub- element 2.2 of the ROSES 2009 IDS announcement (effects of changing climate, local weather, and land use on watersheds and their connected coastal environments). It also has direct connections to the other sub-elements: 2.1) impact of extreme disturbances such as flooding (which is intensifying) 2.3) effects of changing seasonality of ice and snow melt on DOC mobility (snowmelt is occurring earlier) 2.4) role of coastal erosion increasingly associated with sea level rise in both watersheds and 2.5) water and energy cycle impacts of biomass burning (due to large fires common to the northern part of the study area).

Publications:

Balch, W., Huntington, T., Aiken, G., Drapeau, D., Bowler, B., Lubelczyk, L., Butler, K. 2016. Toward a quantitative and empirical dissolved organic carbon budget for the Gulf of Maine, a semienclosed shelf sea. Global Biogeochemical Cycles. 30(2), 268-292. DOI: 10.1002/2015GB005332

More details may be found in the following project profile(s):

• NASA Ocean Biology & Biogeochemistry (OBB) Project Profile