Effects of Land Use on Sources and Ages of Inorganic and Organic Carbon in Temperate Headwater Streams

Authors

Yue Han Lu, Department of Geological Sciences, University of AlabamaFollow
James E. Bauer, Aquatic Biogeochemistry Laboratory, Department of Evolution, Ecology and Organismal Biology, Ohio State University
Elizabeth A. Canuel, Department of Physical Sciences, Virginia Institute of Marine Sciences
R. M. Chambers, Department of Biology, College of William and MaryFollow
Youhei Yamashita, Faculty of Environmental Earth Science, Hokkaido UniversityFollow
Rudolf Jaffe´, Southeast Environmental Research Center, Department of Chemistry and Biochemistry, Florida International University,Follow
Amy Barrett, Aquatic Biogeochemistry Laboratory, Department of Evolution, Ecology and Organismal Biology, Ohio State University

Abstract

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 (δ¹³C and ∆¹⁴C) 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, ¹⁴C-enriched organic matter (OM; δ¹³C = −22.2 ± 3 ‰; ∆¹⁴C = 69 ± 14 ‰), DIC in urbanized streams was influenced more by sedimentary carbonate weathering (δ¹³C = −12.4 ± 1 ‰; ∆¹⁴C = −270 ± 37 ‰) and one of pasture streams showed a greater influence from young soil carbonates (δ¹³C = −5.7 ± 2.5 ‰; ∆¹⁴C = 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 (∆¹⁴C = −248 to −202 ‰, equivalent¹⁴C ages of 1,811–2,284 years BP) and POM (∆¹⁴C = −90 to −88 ‰, ¹⁴C ages of 669–887 years BP) were observed exclusively in urbanized streams, presumably a result of autotrophic fixation of aged DIC (−297 to −244 ‰, ¹⁴C age = 2,251–2,833 years BP) from sedimentary shell dissolution and perhaps also watershed export of fossil fuel carbon. This study demonstrates that human land use may have significant impacts on the amounts, sources, ages and cycling of carbon in headwater streams and their associated watersheds.

Comments

The definitive publisher-authenticated version is available online at http://dx.doi.org/10.1007/s10533-014-9965-2

This material is based upon work supported by the National Science Foundation through the Florida Coastal Everglades Long-Term Ecological Research program under Cooperative Agreements #DBI-0620409 and #DEB-9910514. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Recommended Citation

Lu, Y., J.E. Bauer, E.A. Canuel, R.M. Chambers, Y. Yamashita, R. Jaffe. 2014. Effects of land use on sources and ages of inorganic and organic carbon in temperate headwater streams. Biogeochemistry DOI: 10.1007/s10533-014-9965-2