Shellfish aquaculture has a major socioeconomic impact on coastal areas, thus it is necessary to develop support tools for its management. In this sense, phytoplankton monitoring is crucial, as it is the main source of food for shellfish farming. The aim of this study was to assess the applicability of Sentinel 2 multispectral imagery (MSI) to monitor the phytoplankton biomass at Ebro Delta bays and to assess its potential as a tool for shellfish management. In situ chlorophyll-a data from Ebro Delta bays (NE Spain) were coupled with several band combination and band ratio spectral indices derived from Sentinel 2A levels 1C and 2A for time-series mapping. The best results (AIC = 72.17, APD < 10%, and MAE < 0.7 mg/m3) were obtained with a simple blue-to-green ratio applied over Rayleigh corrected images. Sentinel 2–derived maps provided coverage of the farm sites at both bays allowing relating the spatiotemporal distribution of phytoplankton with the environmental forcing under different states of the bays. The applied methodology will be further improved but the results show the potential of using Sentinel 2 MSI imagery as a tool for assessing phytoplankton spatiotemporal dynamics and to encourage better future practices in the management of the aquaculture in Ebro Delta bays.

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Sentinel-2 offers great potential for monitoring water quality in inland and coastal waters. However, atmospheric correction in these waters is challenging, and there is no standardized approach yet, but different methods coexist under constant development. The atmospheric correction Case 2 Regional Coast Colour (C2RCC) processor has been recently updated with the C2X-COMPLEX (C2XC). This study is one of the first attempts at exploring its performance, in comparison with C2RCC and C2X, in inland and coastal waters in the east of the Iberian Peninsula, in retrieving water surface reflectance and estimating chlorophyll-a ([Chl-a]), total suspended matter ([TSM]), and Secchi disk depth (ZSD). The relationship between in situ ZSD and Kd_z90max product (i.e., the depth of the water column from which 90% of the water-leaving irradiance is derived) of the C2RCC processors demonstrated the potential of this product for estimating water clarity (r > 0.75). However, [TSM] and [Chl-a] derived from the different processors with default calibration factors were not suitable within the targeted scenarios, requiring recalibration based on optical water types or a shift to dynamic algorithm blending approaches. This would benefit from switching between C2RCC and C2XC, which extends the potential for improving surface reflectance estimates to a wide range of scenarios and suggests a promising future for C2-Nets in operational monitoring of water quality.

Abstract:Beaches are natural environments of great interest for our society. They go through remarkable changes run by key factors that are interconnected according to the literature. A better understanding of these parameters, such as sediment texture and shoreline variability, would be of a great interest for coastal monitoring and planning.Shorelines of all Landsat 8 (OLI) images available over the course of one year have been obtained for determining the variability that has occurred in different Valencian beaches. Likewise, the relation between shoreline variability and sediment texture has been evaluated, showing that beaches with higher variability over the year have smaller sediment texture, which is also related with gentle slopes, and vice versa.The methodology allows obtaining the shoreline variability, a key parameter of beach morphodynamics, in a semiautomatic way. The variability allows developing a gross estimate of beach texture.Key words: Shoreline Detection, Coastline Variability, Beach Sediment, Sediment Texture, Landsat 8, Remote Sensing Resumen:Las playas son entornos naturales de enorme interés para nuestra sociedad. Estos espacios están sometidos a grandes cambios regidos por factores clave fuertemente interrelacionados según la literatura. Un mayor conocimiento de estos parámetros, como la textura del sedimento o la variabilidad de la línea de costa de las playas resultaría de gran interés para la monitorización y gestión de la costa.Se han obtenido las líneas de costa de todas las escenas Landsat 8 (OLI) disponibles a lo largo de un año para, a partir de ellas, determinar la variabilidad de diferentes playas valencianas. Asimismo, se ha evaluado la relación existente entre dicha variabilidad y la textura del sedimento de las playas, mostrando que las playas con mayores cambios en la línea de costa a lo largo del año son aquellas con un tamaño de grano menor, asociado a pendientes más suaves y viceversa.La metodología seguida incluye la obtención de forma semiautomática de la variabilidad de la línea de costa, un parámetro clave de la morfodinámica costera, y a partir de ella la estimación a grandes rasgos de la textura del sedimento de las playas.Palabras clave: Detección de la línea de costa, Variabilidad de la línea de costa, Sedimento de playa, Textura del sedimento, Landsat 8, Teledetección IntroducciónLas playas son espacios naturales que proporcionan protección frente al oleaje y temporales, representan un importante recurso socioeconómico (Prodger et al. 2016), y actúan como soporte físico para los organismos que allí habitan.Las actuaciones antrópicas en la zona costera generan cambios en el sistema, modifican la distribución y las características del sedimento y en consecuencia alteran la morfología de las playas. La textura del sedimento y la anchura de las playas son factores clave para permitir el mantenimiento de sus funciones. Por tanto, resulta de gran interés disponer de información actualizada de ambos elementos para conocer el estado de la playa y plantear una gestión a...