Nitrogen is the limiting nutrient in many estuaries and increasing the availability of this nutrient often leads to the eutrophication of these systems. Estuarine eutrophication is associated with higher rates of algal net primary production, seasonal hypoxia, decreased habitat, toxic algal blooms, fish kills, and changes to the plant and animal communities. In order to reduce nitrogen loading to coastal waters it is necessary to determine the relative significance of both point and non-point sources. Researchers have repeatedly found that non-point sources often contribute the majority of nitrogen to coastal watersheds. While the dominance of non-point sources is not true of all systems, deciphering their role in the total nitrogen export to any estuary is an important step towards effectively managing nitrogen loads. Large-scale empirical models have repeatedly shown that there is a significant reduction in N loads by a variety of in-stream processes. However, the role of individual processes, such as assimilation and denitrification, within riverine environments is still largely uncertain.
My research focuses on determining the processes and fluxes important to nitrogen export from temperate watersheds. In order to examine nitrogen fluxes and processes I am sampling at multiple watershed scales, ranging from ~5 km2 to ~1700 km2. Sampling occurs throughout the Connecticut River watershed, encompassing both spatial and seasonal variations in source contributions and biogeochemical processing. An integral component of this work is with the measurement of stable isotopes, including ?15N and ?18O of NO3- (the most mobile form of nitrogen) on a variety of spatiotemporal scales. Additional measurements on various nitrogen fractions (e.g. [NO3-], [NO2-], [TN]), carbon (e.g. ?13C of DIC, alkalinity), and other chemical constituents provide further information about nitrogen sources and watershed processes.
My research is funded by the U.S. Environmental Protection Agency's Science To Achieve Results (STAR) Fellowship Program, Yale School of Forestry & Environmental Studies, & The Sound Conservancy.
Barnes, R.T., P.A. Raymond, & K.L. Casciotti. 2008. Dual isotope analyses indicate efficient processing of atmospheric nitrate by forested watersheds in the northeastern U.S. Biogeochemistry, DOI: 10.1007/s10533-009-9227-2
Barnes, R.T. & P.A. Raymond. Land use controls on the delivery, processing, and removal of nitrogen from small watersheds: insights from the dual isotopic composition of stream nitrate. in review Ecological Applications
Barnes, R.T. & P.A. Raymond. The contribution of agricultural and urban activities to inorganic carbon fluxes within temperate watersheds. in prep.
Walters, A.W., R.T. Barnes, & D.M. Post. Anadromous alewife contribute marine-derived nutrients to coastal stream food webs. in review Freshwater Biology
Griffith, D.R., P.A. Raymond, & R.T. Barnes. Carbon isotope signature of wastewater treatment plant effluent. in prep
Anisfeld, S.C., R.T. Barnes, M.A. Altabet & T. Wu, 2007. Isotopic apportionment of atmospheric and sewage nitrogen sources in two Connecticut Rivers. Environmental Science & Technology, 41(18):6363-6369