Carbon isotope biogeochemistry of tropical small mountainous river, estuarine, and coastal systems of Puerto Rico

• Published in: Biogeochemistry Vol. 112; no. 1-3; pp. 589 - 612
• Main Authors: Moyer, Ryan P., Bauer, James E., Grottoli, Andréa G.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer 01-03-2013; Springer Netherlands; Springer Nature B.V
• Subjects: Agricultural watersheds; Animal and plant ecology; Animal, plant and microbial ecology; Biogeochemistry; Biogeosciences; Biological and medical sciences; Brackish; Carbon; Carbon isotopes; Catchments; Coastal waters; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Ecological function; Ecosystems; Environmental Chemistry; Estuaries; Exact sciences and technology; Food webs; Fundamental and applied biological sciences. Psychology; Headwaters; Irrigation canals; Isotope geochemistry; Isotope geochemistry. Geochronology; Land use; Life Sciences; Marine and continental quaternary; Mountains; Oceans; Organic foods; Organic matter; Particulate matter; Radiocarbon; River discharge; River flow; Rivers; Sedimentary soils; Surficial geology; Synecology; Terrestrial ecosystems; Watersheds; Puerto Rico; Antilles; Greater Antilles; West Indies; Caribbean region; ASW, Caribbean Sea, Greater Antilles, Puerto Rico; Dissolved organic carbon; Particulate organic carbon; Dissolved inorganic carbon; Carbon isotopes; Tropical small mountainous rivers; rivers; stable isotopes; canals; terrains; C-13/C-12; river discharge; sampling; concentration; transport; forests; drainage basins; irrigation; land use; modern; burial; organic materials; estuaries; export; dissolved organic carbon; organic carbon
• ISSN: 0168-2563; 1573-515X
• DOI: 10.1007/s10533-012-9751-y

Recent studies have shown that small mountainous rivers (SMRs) may act as sources of aged and/or refractory carbon (C) to the coastal ocean, which may increase organic C burial at sea and subsidize coastal food webs and heterotrophy. However, the characteristics and spatial and temporal variability of C and organic matter (OM) exported from tropical SMR systems remain poorly constrained. To address this, the abundance and isotopic character (δ¹³C and △¹⁴C) of the three major C pools were measured in two Puerto Rico SMRs with catchments dominated by different land uses (agricultural vs. non-agricultural recovering forest). The abundance and character of C pools in associated estuaries and adjacent coastal waters were also examined. Riverine dissolved and particulate organic C (DOC and POC, respectively) concentrations were highly variable with respect to land use and sampling month, while dissolved inorganic C (DIC) was significantly higher at all times in the agricultural catchment. In both systems, riverine DOC and POC ranged from modern to highly aged (2,340 years before present), while DIC was always modern. The agricultural river and irrigation canals contained very old DOC (1,184 and 2,340 years before present, respectively), which is consistent with findings in temperate SMRs and indicates that these tropical SMRs provide a source of aged DOC to the ocean. During months of high river discharge, OM in estuarine and coastal waters had C isotope signatures reflective of direct terrestrial input, indicating that relatively unaltered OM is transported to the coastal ocean at these times. This is also consistent with findings in temperate SMRs and indicates that C transported to the coastal ocean by SMRs may differ from that of larger rivers because it is exported from smaller catchments that have steeper terrains and fewer land-use types.