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Contributions of carbon and nitrogen from the Andes Mountains to the Amazon River: Evidence from an elevational gradient of soils, plants, and river material
Author(s) -
Townsend-Small Amy,
McClain Michael E.,
Brandes Jay A.
Publication year - 2005
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2005.50.2.0672
Subject(s) - soil water , environmental chemistry , altitude (triangle) , organic matter , dissolved organic carbon , transect , particulates , δ13c , tributary , environmental science , isotope analysis , nitrogen , deposition (geology) , total organic carbon , isotopes of nitrogen , chemistry , hydrology (agriculture) , stable isotope ratio , geology , sediment , soil science , oceanography , geotechnical engineering , paleontology , geometry , mathematics , organic chemistry , physics , quantum mechanics , cartography , geography
We determined the carbon (C) and nitrogen (N) elemental and stable isotopic composition of riverine and terrestrial organic matter (OM), as well as the concentration of dissolved organic C (DOC), δ 15 NO 3 − and δ 18 O of river water along an altitudinal (4,043–720 m above sea level [masl]) transect in the Andes of Peru. Plant δ 13 C increased with increasing elevation, but unlike previous studies, foliar 13 C and %N were negatively correlated. Soil δ 13 C values did not exhibit similar trends and were enriched by 1–3‰ over plants. Isotopically, riverine fine particulate OM (FPOM, <60 µm) resembled soils, and coarse particulate OM (CPOM, >60 µm) resembled leaves. Both FPOM and CPOM exhibited OM levels beyond those attributable to sorption. Percentage OC and N of soils and FPOM were positively correlated with altitude and highlight a trend of sequential downstream dilution of OM with inorganic material. FPOM began to resemble plant OM isotopically at lower altitudes, perhaps due to increased plant and surface soil inputs to lower rivers. The compositional similarity of particulate organic matter to terrestrial plants and soils indicates that the dominant processes affecting riverine OM are occurring on the landscape, not within the river. Dissolved OC (<0.2 µm) concentration, δ 15 NO 3 − , and δ 18 O of H2O are variable in high‐altitude tributaries but approach constant values downstream. Elemental and isotopic analyses of riverine OM suggest compositional differences between size fractions, similar to the lower Amazon; however, unlike previous studies, we have found significant within‐stream changes with altitude in OM composition.