1 resultado para Inorganic

em Digital Commons at Florida International University


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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 âˆ14C) analyses and excitation emission matrix fluorescence with parallel factor analysis (EEMâPARAFAC). 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 = âˆ22.2 ± 3 â°; âˆ14C = 69 ± 14 â°), DIC in urbanized streams was influenced more by sedimentary carbonate weathering (δ13C = âˆ12.4 ± 1 â°; âˆ14C = âˆ270 ± 37 â°) and one of pasture streams showed a greater influence from young soil carbonates (δ13C = âˆ5.7 ± 2.5 â°; âˆ14C = 69 â°). 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 (âˆ14C = âˆ248 to âˆ202 â°, equivalent14C ages of 1,811â2,284 years BP) and POM (âˆ14C = âˆ90 to âˆ88 â°, 14C ages of 669â887 years BP) were observed exclusively in urbanized streams, presumably a result of autotrophic fixation of aged DIC (âˆ297 to âˆ244 â°, 14C age = 2,251â2,833 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.