Can Forel–Ule Index Act as a Proxy of Water Quality in Temperate Waters? Application of Plume Mapping in Liverpool Bay, UK

Fronkova, Lenka, Greenwood, Naomi, Martinez, Roi, Graham, Jennifer A. ORCID: https://orcid.org/0000-0002-1950-5266, Harrod, Richard, Graves, Carolyn A., Devlin, Michelle J. ORCID: https://orcid.org/0000-0003-2194-2534 and Petus, Caroline (2022) Can Forel–Ule Index Act as a Proxy of Water Quality in Temperate Waters? Application of Plume Mapping in Liverpool Bay, UK. Remote Sensing, 14 (10). ISSN 2072-4292

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Abstract

The use of ocean colour classification algorithms, linked to water quality gradients, can be a useful tool for mapping river plumes in both tropical and temperate systems. This approach has been applied in operational water quality programs in the Great Barrier Reef to map river plumes and assess trends in marine water composition and ecosystem health during flood periods. In this study, we used the Forel–Ule colour classification algorithm for Sentinel-3 OLCI imagery in an automated process to map monthly, annual and long-term plume movement in the temperate coastal system of Liverpool Bay (UK). We compared monthly river plume extent to the river flow and in situ water quality data between 2017–2020. The results showed a strong positive correlation (Spearman’s rho = 0.68) between the river plume extent and the river flow and a strong link between the FUI defined waterbodies and nutrients, SPM, turbidity and salinity, hence the potential of the Forel– Ule index to act as a proxy for water quality in the temperate Liverpool Bay water. The paper discusses how the Forel–Ule index could be used in operational water quality programs to better understand river plumes and the land-based inputs to the coastal zones in UK waters, drawing parallels with methods that have been developed in the GBR and Citclops project. Overall, this paper provides the first insight into the systematic long-term river plume mapping in UK coastal waters using a fast, cost-effective, and reproducible workflow. The study created a novel water assessment typology based on the common physical, chemical and biological ocean colour properties captured in the Forel–Ule index, which could replace the more traditional eutrophication assessment regions centred around strict geographic and political boundaries. Additionally, the Forel–Ule assessment typology is particularly important since it identifies areas of the greatest impact from the land-based loads into the marine environment, and thus potential risks to vulnerable ecosystems.

Item Type: Article
Additional Information: Funding Information: Funding: This research was funded by Department for Environment, Food and Rural Affairs (DE-FRA), grant number GiA03, and Cefas through various projects (DP423 and DP434—internal Cefas projects, C8395—GIA OSPAR support, C8374—Ocean Country Partnership Programme). Publisher Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
Faculty \ School: Faculty of Science > School of Environmental Sciences
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Depositing User: LivePure Connector
Date Deposited: 14 Apr 2023 12:30
Last Modified: 14 Apr 2023 12:35
URI: https://ueaeprints.uea.ac.uk/id/eprint/91776
DOI: 10.3390/rs14102375

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