MERIS phytoplankton time series products from the SW Iberian Peninsula (Sagres) using seasonal-trend decomposition based on loess

The European Space Agency has acquired 10 years of data on the temporal and spatial distribution of phytoplankton biomass from the MEdium Resolution Imaging Spectrometer (MERIS) sensor for ocean color. The phytoplankton biomass was estimated with the MERIS product Algal Pigment Index 1 (API 1). Seasonal-Trend decomposition of time series based on Loess (STL) identified the temporal variability of the dynamical features in the MERIS products for water leaving reflectance ((w)()) and API 1. The advantages of STL is that it can identify seasonal components changing over time, it is responsive to nonlinear trends, and it is robust in the presence of outliers. One of the novelties in this study is the development and the implementation of an automatic procedure, stl.fit(), that searches the best data modeling by varying the values of the smoothing parameters, and by selecting the model with the lowest error measure. This procedure was applied to 10 years of monthly time series from Sagres in the Southwestern Iberian Peninsula at three Stations, 2, 10 and 18 km from the shore. Decomposing the MERIS products into seasonal, trend and irregular components with stl.fit(), the (w)() indicated dominance of the seasonal and irregular components while API 1 was mainly dominated by the seasonal component, with an increasing effect from inshore to offshore. A comparison of the seasonal components between the (w)() and the API 1 product, showed that the variations decrease along this time period due to the changes in phytoplankton functional types. Furthermore, inter-annual seasonal variation for API 1 showed the influence of upwelling events and in which month of the year these occur at each of the three Sagres stations. The stl.fit() is a good tool for any remote sensing study of time series, particularly those addressing inter-annual variations. This procedure will be made available in R software

Technical note: Algal Pigment Index 2 in the Atlantic off the southwest Iberian Peninsula: standard and regional algorithms

In this study, Algal Pigment Index 2 (API2) is investigated in Sagres, an area located in the Atlantic off the southwestern Iberian Peninsula. Standard results provided by the MEdium Resolution Image Spectrometer (MERIS) ocean colour sensor were compared with alternative data products, determined through a regional inversion scheme, using both MERIS and in situ remote sensing reflectances (R-rs) as input data. The reference quantity for performance assessment is in situ total chlorophyll a (TChl a) concentration estimated through a phytoplankton absorption coefficient (i.e. equivalent to API2). Additional comparison of data products has also been addressed for TChl a concentration determined by high-performance liquid chromatography. The MERIS matchup analysis revealed a systematic underestimation of TChl a, which was confirmed with an independent comparison of product map analysis. The study demonstrates the importance of regional algorithms for the study area that could complement upcoming standard results of the current Sentinel-3/OLCI space mission

Sources of anthropogenic nutrients and their implications on nutrient chemistry and ecological conditions of Ria Formosa lagoon, Portugal

Shallow coastal waters receive high anthropogenic nutrients (nitrogen-N and phosphorus-P) from land that can change their nutrient chemistry, algal composition, and food webs with serious effects on marine life, human health, and local livelihoods. Managing anthropogenic nutrient inputs is thus key to ensuring healthy and productive coastal ecosystems. This study conducted a bimonthly sampling for eight months between 2014 and 2015 to determine the influence of agriculture, sewage, and natural nutrient sources on nutrient chemistry, ecological status, and possible implications for aquaculture production in the western side of Ria Formosa lagoon. Ecological Quality Ratios (EQR) were calculated from nutrient ratios (N: P: Si) computed from nutrient concentrations with the Redfield ratio (N: P: Si =16:1:16) used as a reference for ecological status determination. A mean of 3.7, 1.0, and 4.6 mu mol/L; 6.7, 1.12, and 5.5 mu mol/L; and 4.6, 0.7, and 2.8 mu mol/L were recorded for dissolved inorganic nitrogen, phosphorus and silicates concentrations at sewage, agriculture, and natural sites respectively. The site mean EQR values ranged between 0.55 and 0.69. The overall ecological status of the west part of the lagoon was 'Moderate', with all the sites grouped under 'Good'/'Moderate' and 'Moderate'/'Poor' classes based on nutrient ratios. This study demonstrates that the western part of the lagoon's nutrient chemistry is highly influenced by the nutrient sources with agricultural run-off and sewage discharges associated with nitrates, and ammonia and phosphates respectively. The elevated ammonium and phosphates registered can transform the phytoplankton composition to non-diatomic species and affect the current ecological functions of the lagoon. We recommend further studies, including biological quality elements, to get more comprehensive results on the study area.(c) 2023 Elsevier B.V. All rights reserved.LA/P/0069/2020info:eu-repo/semantics/publishedVersio

Absorption coefficient of particulate matter on the south-west coast of Europe: a contribution to the validation of the MERIS-Medium Resolution Imaging Spectrometer sensor

Dissolved oxygen (DO) is one of the most important environmental variables of water quality, especially for marine life. Consequently, oxygen is one of the Chemical Quality Elements required for the implementation of European Union Water Framework Directive. This study uses the example of the Ria Formosa, a meso-tidal lagoon on the south coast of Portugal to demonstrate how monitoring of water quality for coastal waters must be well designed to identify symptoms of episodic hypoxia. New data from the western end of the Ria Formosa were compared to values in a database of historical data and in the published literature to identify long-term trends. The dissolved oxygen concentration values in the database and in the literature were generally higher than those found in this study, where episodic hypoxia was observed during the summer. Analysis of the database showed that the discrepancy was probably related with the time and the sites where the samples had been collected, rather than a long-term trend. The most problematic situations were within the inner lagoon near the city of Faro, where episodic hypoxia (<2 mg dm3 DO) occurred regularly in the early morning. These results emphasise the need for a balanced sampling strategy for oxygen monitoring which includes all periods of the day and night, as well as a representative range of sites throughout the lagoon. Such a strategy would provide adequate data to apply management measures to reduce the risk of more persistent hypoxia that would impact on the ecological, important natural resource. economic and leisure uses of this important natural resource

Water framework directive implementation: intercalibration exercise for biological quality elements: a case study for the south coast of Portugal

This work summarises the Intercalibration Exercise (IE) required for the Common Implementation Strategy of the Water Framework Directive (WFD; 2000/60/EC) that was carried out in Portugal, and applied to a coastal region. The WFD aims to achieve good ec ological status for all waters in the European Community by 2015. The Ecological Status of a water body is determined us ing a range of Hydromorphological and Physico-Chemical Quality Elements as well Biological Quality Elements (BQE ). In coastal waters, the Biological Elements include Phytoplankton, Other Aquatic Flora and Benthic Inverteb rate Fauna. Good cooperation with the other Member States allowed the IE to proceed without a complete da ta set, and Portugal was ab le to intercalibrate and harmonise methods within the North Ea st Atlantic Geographica l Intercalibration Group for most of the BQE. The appropriate metrics and corre sponding methods were agreed under the framework of the RECITAL (Reference Conditions and Intercalibra tion) project, funded by the Port uguese Water Institu te, INAG. Some preliminary sampling was undertaken, but not su fficient to establish the Reference Conditions. The study area was a coastal lagoon in the southern part of Portugal. The focus was on the Phytoplankton Quality Element, but other BQE were also taken into account. Two sampli ng stations in Ria Formosa coastal lagoon were considered in this exercise: Ramalhete a nd Ponte. The metrics adopted by the Intercalibration Exercise groups were applied enabli ng the classification for the two sta tions of Good/High Status for the majority of the BQE parameters

Validation of the MERIS- Medium Resolution Imaging Spectrometer satellite products in oceanic waters off Cape Sagres on the south-west coast of Portugal

Eight images were obtained under cloud free conditions between September 2008 and July 2009 at an oceanic site off Cape Sagres on the south-west coast of Portugal during a contract with the European Space Agency to evaluate the marine products of the MERIS (Medium Resolution Imaging Spectrometer) sensor. The results of the MERIS water-leaving reflectances (ρw) showed that there was reasonable agreement with the measured reflectances, but tended to be overestimated in the blue bands and underestimated in the rest of the spectrum. With respect to the water products, the MERIS suspended particulate matter was underestimated in relation to the in situ data, whilst the values for the MERIS chlorophyll (Algal I and Algal II) and yellow substances were overestimated.The error analysis for the in situ ρw has identified where the accuracy of the data could be improved to validate the retrieved MERIS ρw and the water products

Light absorption by particulate and dissolved organic matter in coastal and oceanic off the South west coast of Europe: a contribution to MERIS sensor validation

The two variable components of light absorption, which are important contributors to the correct adjustments of ocean colour algorithms, are considered and discussed in this study, conducted in the Southwest coast of Portugal; these are particulate absorption – separated into phytoplankton and non-algal particles absorption, and coloured dissolved organic matter absorption, expressed in terms of their coefficients – ap(), aph(), anap() and aCDOM(), respectively. This study is part of a global effort to collect data to validate marine products of MERIS, the ENVISAT ocean colour sensor, as contracted by European Space Agency (ESA). Particulate absorptions were determined with Transmittance-Reflectance approach, using NaClO bleaching to remove phytoplankton contribution to the total particulate matter absorption spectra; YSBPA absorption coefficient was assessed according to MERIS validation protocols. Phytoplankton absorption coefficients were transformed into specific coefficients – a*ph(), normalizing it with respect to chlorophyll a concentrations determined both by HPLC and spectrophotometric methods. Results show that the absorption of light by particulate matter is almost totally dependent on the phytoplankton, with no significant contribution from non-algal particles (mean contribution of 10% to total particulate absorption), both in coastal and oceanic waters, emphasising the dominance of case 1-type waters. Specific chlorophyll absorption coefficients show significant fluctuations between seasons and stations, ranging from 0.007 to 0.09 at 678 nm; however, a good correlation between ap(443) and ap at other MERIS equivalent wavelengths was found. Particulate matter has generally more weight than dissolved matter absorption in the total absorption budget. These results may contribute to improve and correct regional ocean colour algorithms