Identifying the spatial pattern and the drivers of the decline in the eastern English Channel chlorophyll-a surface concentration over the last two decades

• Published in: Marine pollution bulletin Vol. 199; p. 115870
• Main Authors: Huguet, Antoine, Barillé, Laurent, Soudant, Dominique, Petitgas, Pierre, Gohin, Francis, Lefebvre, Alain
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.02.2024; Elsevier
• Subjects: Chlorophyll - analysis; Chlorophyll A; Climate change; Dynamic linear model; Eastern English Channel; Environmental Monitoring - methods; Life Sciences; Phosphates; Rivers; Satellite; Sciences of the Universe; Seasons; Time series; Climate change; Dynamic linear model; Satellite; Chlorophyll-a; Eastern English Channel; Time series
• ISSN: 0025-326X; 1879-3363
• DOI: 10.1016/j.marpolbul.2023.115870

It has been established from previous studies that chlorophyll-a surface concentration has been declining in the eastern English Channel. This decline has been attributed to a decrease in nutrient concentrations in the rivers. However, the decrease in river discharge could also be a cause. In our study, rivers outflows and in-situ data have been compared to time series of satellite-derived chlorophyll-a concentrations. Dynamic Linear Model has been used to extract the dynamic and seasonally adjusted trends of several environmental variables. The results showed that, for the 1998–2019 period, chlorophyll-a levels stayed significantly lower than average and satellite images revealed a coast to offshore gradient. Chlorophyll-a concentration of coastal stations appeared to be related to the declining fluxes of phosphate while offshore stations were more related to nitrate-nitrite. Therefore, we can exclude that the climate variability, through river flows alone, has a dominant effect on the decline of chlorophyll-a concentration. •Chlorophyll declined during two decades in the Eastern English Channel.•Satellite images revealed coast to offshore chlorophyll decline gradient.•Changes in river flow were a minor driver of chlorophyll decline.•Phosphate was main explanatory variable for coastal stations chlorophyll decrease.•Nitrate-nitrite were related to offshore stations chlorophyll decrease.