Quantifying the Response of Nitrogen Speciation to Hydrology in the Chesapeake Bay Watershed Using a Multilevel Modeling Approach

Excessive nitrogen (N) inputs to coastal waters can lead to severe eutrophication and different chemical forms of N exhibit varying levels of effectiveness in fueling primary production. Efforts to mitigate N fluxes from coastal watersheds are often guided by models that predict changes in N loads a...

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Bibliographic Details
Published in:Journal of the American Water Resources Association 2022-12, Vol.58 (6), p.792-804
Main Authors: Bertani, Isabella, Bhatt, Gopal, Shenk, Gary W., Linker, Lewis C.
Format: Article
Language:English
Subjects:
Annual variations
Anthropogenic factors
anthropogenic nitrogen inputs
Chesapeake Bay
Climate
Coastal waters
Eutrophication
hierarchical model
Human influences
Hydrology
Land use
Land use management
Loads (forces)
Nitrogen
nitrogen loads
nitrogen speciation
Primary production
Rivers
Spatial variations
Speciation
Stream discharge
Stream flow
Temporal variations
Watersheds
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Summary:Excessive nitrogen (N) inputs to coastal waters can lead to severe eutrophication and different chemical forms of N exhibit varying levels of effectiveness in fueling primary production. Efforts to mitigate N fluxes from coastal watersheds are often guided by models that predict changes in N loads as a function of changes in land use, management practices, and climate. However, relatively little is known on the impacts of such changes on the relative fractions of different N forms. We leveraged a long‐term dataset of N loads from over 100 river stations to investigate how the NO3‐ fraction, that is, the ratio of NO3‐ to total N (NO3‐/TN), changes as a function of spatio‐temporal changes in TN loads in the Chesapeake Bay watershed. We built a hierarchical model that separates the response of NO3‐ to changes in TN load occurring at different scales: Across river stations, where differences in TN loads are largely driven by spatial differences in anthropogenic inputs, and within stations, where inter‐annual variability in hydrology is a key driver of changes in TN loads. Results suggest that while increases in TN loads resulting from changes in anthropogenic inputs lead to an increase in the NO3‐ fraction, a decrease in the NO3‐ fraction may occur when increases in TN loads are driven by increased streamflow. These results are especially relevant in watersheds that may experience changes in N loads due to both management decisions and climate‐driven changes in hydrology.
ISSN:1093-474X
1752-1688
DOI:10.1111/1752-1688.12951