Integrating In Situ and Ocean Color Data to Evaluate Ecological Quality under the Water Framework Directive

Abstract

The Water Framework Directive (WFD) aims at evaluating the ecological status of European coastal water bodies (CWBs). This is a rather complex task and first requires the use of long-term databases to assess the effect of anthropogenic pressure on biological communities. An in situ dataset was assembled using concomitant biological, i.e., chlorophyll a (Chl a) and environmental data, covering the years from 1995 to 2014, to enable a comprehensive assessment of eutrophication in the Western Iberia Coast (WIC). Given the temporal gaps in the dataset, especially in terms of Chl a, satellite observations were used to complement it. Positive relationships between Chl a 90th percentile and nitrogen concentrations were obtained. The Land-Uses Simplified Index (LUSI), as a pressure indicator, showed no relationship with Chl a, except in Galicia, but it highlighted a higher continental pressure in the Portuguese CWBs in comparison with Galician waters. In general terms, the trophic index (TRIX) showed that none of the CWBs were in degraded conditions. Nevertheless, the relatively high TRIX and LUSI values obtained for the water body in front of Tagus estuary suggest that this area should be subject to continued monitoring. Results highlighted the usefulness of satellite data in water quality assessments and set the background levels for the implementation of operational monitoring based on satellite Chl a. In the future, low uncertainty and harmonized satellite products across countries should be provided. Moreover, the assessment of satellite-based eutrophication indicators should also include metrics on phytoplankton phenology and community structure.

Spatio-temporal dynamics of phytoplankton community in a well-mixed temperate estuary (Sado Estuary, Portugal)

“…However, higher Chl a concentration can occur at the Alcácer channel, as observed in a previous study (25 mg m −3 average in the 1990’s 22 ). Still, the present results agree with the current classification of Sado Estuary of High ecological condition based on the phytoplankton biomass indicator, as previously reported 9 , 10 This classification is based on the national methodology for the assessment of ecological quality, as described by Brito et al 9 , 10 .…”

“…In this study, the phytoplankton cell abundances were always below 500 × 10 3 cell L −1 , which is much lower than the maximum measured in 1992 for the same region, Alcácer channel (5300 × 10 3 cell L −1 ) 22 . The phytoplankton abundances obtained in this study were also much lower than the thresholds established within the framework of the WFD for the occurrence of a phytoplankton ‘bloom’ 9 , 10 . This result suggests that no significant phytoplankton blooms occurred in the Sado Estuary, during the studied period.…”

“…In this directive, several phytoplankton indicators are used to evaluate the ecological quality status (EQS) of both transitional and coastal waters, namely: i) phytoplankton biomass; ii) taxonomic composition and cell concentration; and iii) frequency and intensity of blooms 8 . However, in Portugal, only the method focused on phytoplankton biomass has been developed 9 , 10 , and according to this method the Sado Estuary is currently classified as High ecological condition.…”

Copernicus Ocean State Report, issue 6

“…Recently, several indicators to assess the eutrophic state of the mid-latitude lakes or ocean basins were developed using different percentile thresholds (75th, 90th, 95th) of the daily values distribution computed for the entire water bodies or locally in each point of the basin (e.g. Poikāne et al 2010;Desmit et al 2018;Greenwood et al 2019;Brito et al 2020;Pardo et al 2021). Here we use the 90th percentile as a measure of the richness in nutrients or fertilization of the euphotic layer in each point of the domain before the onset of stratified spring conditions, which lead to the phytoplankton blooms.…”

What if the upwelling weakens? Effects of rising temperature and nutrient depletion on coastal assemblages

“…These concentrations were little bit lower to those used by Franco et al (2018) in their experiments with L. ochroleuca but are in line with the natural concentration of nutrients in the area of study during summer with and without upwelling conditions ( J. Franco & F. Arenas per. comm., Brito et al 2020).…”