Preprints
https://doi.org/10.5194/hess-2021-52
https://doi.org/10.5194/hess-2021-52

  09 Feb 2021

09 Feb 2021

Review status: this preprint is currently under review for the journal HESS.

Assessing inter-annual variability in nitrogen sourcing and retention through hybrid Bayesian watershed modeling

Jonathan W. Miller1, Kimia Karimi2, Arumugam Sankarasubramanian1, and Daniel R. Obenour1 Jonathan W. Miller et al.
  • 1Dept. of Civil, Construction and Environmental Engineering, North Carolina State University, Raleigh, NC, USA
  • 2Dept. of Geospatial Analytics, North Carolina State University, Raleigh, NC, USA

Abstract. Excessive nutrient loading is a major cause of water quality problems worldwide, including in North Carolina (NC), where reservoirs and coastal systems are often subject to excessive algae and hypoxia. Efficient nutrient management requires that loading sources are accurately quantified. However, loading rates from various urban and rural non-point sources remain highly uncertain especially with respect to climatological variation. Furthermore, statistical calibration of loading models does not always yield plausible results, given the noisiness and paucity of observational data common to many locations. To address these issues, we leverage data for two large NC Piedmont basins collected over three decades (1982–2017) using a mechanistically parsimonious watershed loading and transport model calibrated within a Bayesian hierarchical framework. We explore temporal drivers of loading by incorporating annual changes in precipitation, land use, livestock, and point sources within the model formulation. Also, different representations of urban development are compared based on how they constrain model uncertainties. Results show that urban lands built before 1980 are the largest source of nutrients, exporting over twice as much nitrogen per hectare than agricultural and post-1980 urban lands. In addition, pre-1980 urban lands are the most hydrologically constant source of nutrients, while agricultural lands show the most variation among high and low flow years. Finally, undeveloped lands export an order of magnitude (~ 7–13x) less nitrogen than built environments.

Jonathan W. Miller et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2021-52', Anonymous Referee #1, 06 Mar 2021
  • RC2: 'Comment on hess-2021-52', Anonymous Referee #2, 16 Mar 2021

Jonathan W. Miller et al.

Jonathan W. Miller et al.

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Short summary
Within a watershed, nutrient export can vary greatly over time and space. In this study, we develop a model to leverage over 30 years of streamflow, precipitation, and nutrient sampling data to characterize nitrogen export from various livestock and land use types across a range of precipitation conditions. Modeling results reveal that urban lands developed before 1980 have remarkably high levels of nitrogen export, while agricultural export is most responsive to precipitation.