Patterns of diel variation in nitrate concentrations in the Potomac River
The Potomac River is a large source of N to Chesapeake Bay, where reducing nutrient loads is a focus of efforts to improve trophic status. Better understanding of NO3– loss, reflected in part by diel variation in NO3– concentrations, may refine model predictions of N loads to the Bay. We analyzed 2 y of high-frequency NO3– sensor data in the Potomac to quantify seasonal variation in the magnitude and timing of diel NO3– loss. Diel patterns were evident, especially during low flow, despite broad seasonal and flow-driven variation in NO3– concentrations. Diel variation was ~0.01 mg N/L in winter and 0.02 to 0.03 mg N/L in summer with intermediate values in spring and autumn, equivalent to <1% of the daily mean NO3– concentration in winter and ~2 to 4% in summer. Maximum diel NO3– values generally occurred in mid- to late morning, with more repeatable patterns in summer and wider variation in autumn and winter. Diel NO3– loss reduced loads by 0.7% in winter and 3% in summer. These losses were less than estimates of total in-stream NO3– load loss across the basin that averaged 33% of the annual groundwater contribution to the river. Water temperature and discharge had stronger relationships to the daily magnitude of diel NO3– variation than did photosynthetically active radiation. Estimated diel areal NO3– loss rates were generally >1000 mg N m–2 d–1, greater than most published values because measurements in this large river integrate over a greater depth/unit stream bottom area than do those from smaller rivers. These diel NO3– patterns are consistent with the influence of photoautotrophic uptake and related denitrification, but we cannot attribute these patterns to assimilation alone because the magnitude and timing of diel dynamics were affected to an unknown extent by processes, such as evapotranspiration, transient storage, and hydrodynamic dispersion. Improvements to diel loss estimates will require additional high-frequency measures, such as dissolved O2, dissolved organic N, and NH4+, and deployment of 2 measurement stations.
Citation Information
| Publication Year | 2016 |
|---|---|
| Title | Patterns of diel variation in nitrate concentrations in the Potomac River |
| DOI | 10.1086/688777 |
| Authors | Douglas A. Burns, Matthew P. Miller, Brian Pellerin, Paul D. Capel |
| Publication Type | Article |
| Publication Subtype | Journal Article |
| Series Title | Freshwater Science |
| Index ID | 70178393 |
| Record Source | USGS Publications Warehouse |
| USGS Organization | California Water Science Center; New York Water Science Center |
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Water Quality and Hydrologic Data (2011-13) for Freshwater Science Paper titled, "Patterns of Diel Variation in Nitrate Concentrations in the Potomac River"
Douglas A Burns
Coordinator, Delaware River Basin Next Generation Water Observing System (NGWOS)
Brian Pellerin
Program Manager, Next Generation Water Observing Systems (acting)
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Water Quality and Hydrologic Data (2011-13) for Freshwater Science Paper titled, "Patterns of Diel Variation in Nitrate Concentrations in the Potomac River"
This data set includes nitrate concentration, water temperature, and discharge collected every 15 minutes during Dec. 2011 - Nov. 2013 from the USGS gage at the Potomac River near Wash, DC, Little Falls Pump Sta (01646500). Additional data includes day length, and photosynthetically active radiation from USDA research station in Beltsville, MD. Several calculations derived from these data are incl - Connect
Douglas A Burns
Coordinator, Delaware River Basin Next Generation Water Observing System (NGWOS)EmailPhoneBrian Pellerin
Program Manager, Next Generation Water Observing Systems (acting)Program Manager, Water HazardsEmailPhone