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Factors controlling water‐column respiration in rivers of the central and southwestern Amazon Basin
Author(s) -
Ellis Erin E.,
Richey Jeffrey E.,
Aufdenkampe Anthony K.,
Krusche Alex V.,
Quay Paul D.,
Salimon Cleber,
da Cunha Hilandia Brandão
Publication year - 2012
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.2012.57.2.0527
Subject(s) - respiration , autotroph , phytoplankton , water column , environmental chemistry , organic matter , photosynthesis , chemistry , environmental science , ecology , zoology , biology , botany , nutrient , genetics , bacteria
We examined the factors controlling the variability in water‐column respiration rates in Amazonian rivers. Our objectives were to determine the relationship between respiration rates and the in situ concentrations of the size classes of organic carbon (OC), and the biological source (C 3 and C 4 plants and phytoplankton) of organic matter (OM) supporting respiration. Respiration was measured along with OC size fractions and dissolved oxygen isotopes ( δ 18 O‐O 2 ) in rivers of the central and southwestern Amazon Basin. Rates ranged from 0.034 µmol O 2 L −1 h −1 to 1.78 µmol O 2 L −1 h −1 , and were four‐fold higher in rivers with evidence of photosynthetic production (demonstrated by δ 18 O‐O 2 < 24.2‰) as compared to rivers lacking such evidence ( δ 18 O‐O 2 > 24.2‰; 1.35 ± 0.22 vs. 0.30 ± 0.29 µmol L −1 h −1 ). Rates were likely elevated in the former rivers, which were all sampled during low water, due to the stimulation of heterotrophic respiration via the supply of a labile, algal‐derived substrate and/or the occurrence of autotrophic respiration. The organic composition of fine particulate OM (FPOM) of these rivers is consistent with a phytoplankton origin. Multiple linear regression analysis indicates that [FPOC], C : N FPOC ratios, and [O 2 ] account for a high amount of the variability in respiration rates ( r 2 = 0.80). Accordingly, FPOC derived from algal sources is associated with elevated respiration rates. The δ 13 C of respiration‐derived CO 2 indicates that the role of phytoplankton, C 3 plants, and C 4 grasses in supporting respiration is temporally and spatially variable. Future scaling work is needed to evaluate the significance of phytoplankton production to basin‐wide carbon cycling.