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Regional Groundwater and Storms Are Hydrologic Controls on the Quality and Export of Dissolved Organic Matter in Two Tropical Rainforest Streams, Costa Rica
Author(s) -
Osburn Christopher L.,
OviedoVargas Diana,
Barnett Emily,
Dierick Diego,
Oberbauer Steven F.,
Genereux David P.
Publication year - 2018
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2017jg003960
Subject(s) - dissolved organic carbon , baseflow , streams , tributary , hydrology (agriculture) , groundwater , environmental science , environmental chemistry , chemistry , water quality , organic matter , total organic carbon , watershed , drainage basin , streamflow , ecology , geology , geography , computer network , cartography , geotechnical engineering , organic chemistry , machine learning , computer science , biology
A paired‐watershed approach was used to compare the quality and fluxes of dissolved organic matter (DOM) during stormflow and baseflow in two lowland tropical rainforest streams located in northeastern Costa Rica. The Arboleda stream received regional groundwater (RGW) flow, whereas the Taconazo stream did not. DOM quality was assessed with absorbance and fluorescence and stable carbon isotope (δ 13 C‐DOC) values. RGW DOM lacked detectable fluorescence and had specific ultraviolet absorption (SUVA 254 ) and absorbance slope ratio ( S R ) values consistent with low aromaticity and low molecular weight material, respectively. We attributed these properties to microbial degradation and sorption of humic DOM to mineral surfaces during transport through bedrock. SUVA 254 values were lower and S R values were higher in the Arboleda stream during baseflow compared to the Taconazo stream, presumably due to dilution by RGW. However, no significant difference in SUVA 254 or S R occurred between the streams during stormflow. SUVA 254 was negatively correlated to δ 13 C‐DOC ( r 2 = 0.61, P < 0.001), demonstrating a strong linkage between stream DOM characteristics and the relative amounts of RGW flow and local watershed runoff containing soil and throughfall C sources. Mean DOC export from the Taconazo stream during the study period was 2.62 ± 0.39 g C m −2 year −1 , consistent with other tropical streams, yet mean DOC export from the Arboleda stream was 13.79 ± 2.07 g C m −2 year −1 , one of the highest exports reported and demonstrating a substantial impact of old RGW from outside the watershed boundary can have on surface water carbon cycling.