ORCID

0000-0001-5320-7847 (Macías-Tapia), 0000-0001-8819-189X (Margaret R. Mulholland), 0000-0002-5721-3061 (Corday Selden), 0000-0001-7473-4873 (Clayton)

Document Type

Article

Publication Date

2025

DOI

10.1007/s12237-024-01473-1

Publication Title

Estuaries and Coasts

Volume

48

Issue

2

Pages

36 (1-13)

Abstract

In coastal urban areas, tidal flooding brings water carrying nutrients and particles back from land to estuarine and coastal waters. A statistical model to predict nutrient loads during tidal flooding events can help estimate nutrient loading from previous and future flooding events and adapt nutrient reduction strategies. We measured concentrations of dissolved inorganic nitrogen and phosphorus in floodwater at seven sentinel sites during 15 tidal flooding events from January 2019 to September 2020. The study area was the Lafayette River watershed in Norfolk, VA, USA, which is prone to tidal flooding and is predicted to experience more frequent and intense flooding in the future. We calculated the difference in dissolved inorganic nitrogen (ΔDIN) or phosphorus (ΔDIP) concentrations between floodwater and those measured in the estuary prior to tidal flooding for each sentinel site and flooding event. We calculated the correlations between ΔDIN and ΔDIP with corresponding data on precipitation, wind, flooding intensity, average estuarine nutrient concentrations, population density, income, land elevation, land use, and land coverage. Using the variables with the highest R2 values for the linear regression with either ΔDIN or ΔDIP, we built multi-variable random forest regression models. ΔDIN showed the strongest correlations with floodwater nutrient concentrations, water level, and water temperature. ΔDIP also had a strong correlation with floodwater nutrient concentrations and water temperature, but had also a strong correlation wind speed. Models indicated that inputs per flooding event ranged from − 5000 to 7500 kg N, for DIN, while those for DIP ranged from 2000 to 23,000 kg P, with net inputs of > 5000 kg N and > 100,000 kg P, respectively. Removing the dissolved nutrient concentration in floodwater variables from the models, we were able to calculate loads from events that occurred all the way back to 1946. Predicted DIN load per single flooding event ranged from ~ 0 to 1.5 × 105 kg N and showed a significant linear regression with time. Predicted DIP load estimates per single flooding event ranged from >  − 1.0 × 105 to < 1.5 × 105 kg P, with a significant positive trend over time. The positive trend in these load values over time shows that they have and will continue to be an increasing problem for the water quality of the local water systems. These results indicate that further action should be taken to control the input of dissolved nutrients during tidal flooding events in urban coastal areas.

Rights

© 2024 The Authors.

This article is licensed under a Creative Commons Attribution 4.0 International (CC BY 4.0) License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original authors and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

Original Publication Citation

Macías-Tapia, A., Mulholland, M. R., Selden, C. R., Clayton, S., Bernhardt, P. W., & Allen, T. R. (2025). Tidal flooding contributes to eutrophication: Constraining nonpoint source inputs to an urban estuary using a data-driven statistical model. Estuaries and Coasts, 48(2), 1-13, Article 36. https://doi.org/10.1007/s12237-024-01473-1

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