Effects of land use on sources and ages of inorganic and organic carbon in temperate headwater streams

The amounts, sources and relative ages of inorganic and organic carbon pools were assessed in eight headwater streams draining watersheds dominated by either forest, pasture, cropland or urban development in the lower Chesapeake Bay region (Virginia, USA). Streams were sampled at baseflow conditions six different times over 1 year. The sources and ages of the carbon pools were characterized by isotopic (dC and DC) analyses and excitation emission matrix fluorescence with parallel factor analysis (EEM–PARAFAC). The findings from this study showed that human land use may alter aquatic carbon cycling in three primary ways. First, human land use affects the sources and ages of DIC by controlling different rates of weathering and erosion. Relative to dissolved inorganic carbon (DIC) in forested streams which originated primarily from respiration of young, C-enriched organic matter (OM; dC = -22.2 ± 3 %; DC = 69 ± 14 %), DIC in urbanized streams was influenced more by sedimentary carbonate weathering (dC = -12.4 ± 1 %; DC = -270 ± 37 %) and one of pasture streams showed a greater influence from young soil carbonates (dC = -5.7 ± 2.5 %; DC = 69 %). Second, human land use alters the proportions of terrestrial versus autochthonous/ microbial sources of stream water OM. Fluorescence properties of dissolved OM (DOM) and the C:N of particulate OM (POM) suggested that streams draining human-altered watersheds contained greater relative contributions of DOM and POM from autochthonous/ microbial sources than forested streams. Third, human land uses can mobilize geologically aged inorganic carbon and enable its participation in contemporary carbon cycling. Aged DOM (DC = -248 to -202 %, Electronic supplementary material The online version of this article (doi:10.1007/s10533-014-9965-2) contains supplementary material, which is available to authorized users. Responsible Editor: Dr. Melanie A. Vile. Y. H. Lu (&) Department of Geological Sciences, University of Alabama, 201 7th Ave, Tuscaloosa, AL 35485, USA e-mail: [email protected] J. E. Bauer A. Barrett Aquatic Biogeochemistry Laboratory, Department of Evolution, Ecology and Organismal Biology, Ohio State University, Columbus, OH 43212, USA E. A. Canuel Department of Physical Sciences, Virginia Institute of Marine Sciences, Gloucester Point, VA 23062, USA R. M. Chambers Department of Biology, College of William and Mary, Williamsburg, VA 23187, USA Y. Yamashita Faculty of Environmental Earth Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan R. Jaffé Southeast Environmental Research Center and Department of Chemistry & Biochemistry, Florida International University, Miami, FL 33199, USA