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Using Paired In Situ High Frequency Nitrate Measurements to Better Understand Controls on Nitrate Concentrations and Estimate Nitrification Rates in a Wastewater‐Impacted River
Author(s) -
Kraus T. E. C.,
O'Donnell K.,
Downing B. D.,
Burau J. R.,
Bergamaschi B. A.
Publication year - 2017
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1002/2017wr020670
Subject(s) - effluent , nitrate , nitrification , environmental science , wastewater , hydrology (agriculture) , ammonium , sewage treatment , tracer , sink (geography) , environmental engineering , nitrogen , ecology , chemistry , geography , geology , biology , physics , geotechnical engineering , cartography , organic chemistry , nuclear physics
We used paired continuous nitrate ( NO 3 – ) measurements along a tidally affected river receiving wastewater discharge rich in ammonium ( NH 4 + ) to quantify rates of change inNO 3 –concentration ( RΔ N O 3) and estimate nitrification rates.NO 3 –sensors were deployed 30 km apart in the Sacramento River, California (USA), with the upstream station located immediately above the regional wastewater treatment plant (WWTP). We used a travel time model to track water transit between the stations and estimatedRΔ N O 3every 15 min (October 2013 to September 2014). Changes inNO 3 –concentration were strongly related to water temperature. In the presence of wastewater,RΔ N O 3was generally positive, ranging from about 7 µ M d −1 in the summer to near zero in the winter. Numerous periods when the WWTP halted discharge allowed theRΔ N O 3to be estimated under no‐effluent conditions and revealed that in the absence of effluent, net gains inNO 3 –were substantially lower but still positive in the summer and negative (net sink) in the winter. Nitrification rates of effluent‐derived NH 4 ( R N i t r i f i c _ E ) were estimated from the difference betweenRΔ N O 3measured in the presence versus absence of effluent and ranged from 1.5 to 3.4 µ M d −1 , which is within literature values but tenfold greater than recently reported for this region.R N i t r i f i c _ Ewas generally lower in winter (∼2 µ M d −1 ) than summer (∼3 µ M d −1 ). This in situ, high frequency approach provides advantages over traditional discrete sampling, incubation, and tracer methods and allows measurements to be made over broad areas for extended periods of time. Incorporating this approach into environmental monitoring programs can facilitate our ability to protect and manage aquatic systems.