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Long‐term variations in the dissolved oxygen budget of an urbanized tidal river: The upper Delaware Estuary
Author(s) -
Tomaso Daniel J.,
Najjar Raymond G.
Publication year - 2015
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2014jg002758
Subject(s) - oxygen , biogeochemical cycle , environmental science , estuary , biochemical oxygen demand , sink (geography) , tidal river , respiration , nitrification , hydrology (agriculture) , chemical oxygen demand , primary production , wastewater , environmental chemistry , ecology , environmental engineering , nitrogen , ecosystem , chemistry , biology , geology , geography , cartography , botany , organic chemistry , geotechnical engineering
The dissolved oxygen budget in the upper Delaware Estuary between 1970 and 2014 was inferred from oxygen concentration measurements using a box model approach. The region was found to be a net biogeochemical sink of oxygen, with net oxygen consumption greater in the tidal fresh portion than in the oligohaline portion. Net oxygen consumption decreased from the 1970s to the 1990s by roughly a factor of 2 before increasing slightly in the 2000s. The dramatic decline in oxygen consumption was presumably due to improvements in wastewater treatment, though a comparison with biological oxygen demand measurements in wastewater was equivocal. Nonalgal oxygen consumption (i.e., oxygen consumption due to heterotrophic respiration and nitrification) was computed as the sum of the estimated net oxygen consumption and historical measurements of primary production. Nonalgal oxygen consumption was found to be highly seasonal and positively correlated with temperature, with Q 10 values ranging between 1.4 and 2.3. Annual nonalgal oxygen consumption was found to be several times annual primary production. Exchange with the atmosphere is the main process that balances the net oxygen consumption throughout the study region, with advection also an important process in the tidal fresh portion. Decadal scale variability in oxygen concentration, including the recent decline in the 2000s, appears to be mainly driven by biological, not physical, processes.