How to learn more about hydrological conditions and phytoplankton dynamics and diversity in the eastern English Channel and the Southern Bight of the North Sea: the Suivi Régional des Nutriments data set (1992–2021)
Authors: Lefebvre Alain , Devreker David 
Published: March 2023

Abstract. This article describes a 30-year data series produced by the SRN (“Suivi Régional des Nutriments” in French; Regional Nutrients Monitoring Programme) network managed by Ifremer. Since 1992, the
SRN network has been analysing phytoplankton species and measuring
physicochemical (temperature, salinity, oxygen, suspended matter, nutrients)
and biological (chlorophyll a, phytoplankton abundance) parameters at 10 different stations distributed along three different transects located in
the eastern English Channel and the Southern Bight of the North Sea. This geographic coverage allows for the study of three distinct ecosystems, i.e.
three transects (estuary, coastal region under freshwater influence, and
coastal region), as well as the investigation of coastal to offshore water
gradients. The SRN collects a maximum of 184 samples per year (3687 samples
spread over 10 stations during the studied period) and detects up to 291
taxa, including harmful algal bloom species (HABs), with a bi-weekly to
monthly sampling frequency (depending on the location and the season). The
objectives of this monitoring programme are to assess the influence of continental inputs on the marine environment and their implications for
possible eutrophication processes. It also aims to estimate the
effectiveness of development and management policies in the marine coastal
zone by providing information on trends and/or shifts in pressure, state, and impact variables. The regular acquisition of data allows the establishment
of long-term monitoring of the evolution of coastal water quality as well as
the observation of the consequences of large-scale alterations mainly driven
by climate change and modifications that are more related to local/regional
anthropogenic activities. This paper provides an overview of the main
characteristics of SRN data (descriptive statistics and data series main
patterns) as well as an analysis of temporal trends and shifts. We also
propose to the data user a specific numerical tool available as an R package
to optimize the data pre-processing and processing steps. Users will then
have easy access to statistics, trends, and anomalies as proposed in this
paper. The main results of several research projects based on SRN data and
dealing with hydrology, phytoplankton blooms, HABs, phenology, and niches are also highlighted, providing the readers with examples of what can be done
with such a data set. We hope that this synthesis will also save data users
time by allowing them to jump right into a deeper analysis based on previous
conclusions and perspectives or to investigate new scientific key challenges. These data should also be used at a wider geographical scale,
combined with other data sources, to define more global patterns of
environmental changes in a moving world subject to strong anthropogenic
pressures. Data can also be used by the remote sensing (ocean colour observation) and modelling communities to calibrate or validate products in
this complex and vital coastal region. The SRN data set is publicly available: https://doi.org/10.17882/50832 (SRN – Regional Observation and Monitoring program for Phytoplankton and Hydrology in the eastern English Channel, 2022).