Human activities coupled with climate change impacts are becoming the main factors in decreasing inland surface water quantity and quality, leading to the disturbance of the aquatic ecological balance. Under such conditions, the introduction and proliferation of aquatic invasive alien species are more likely to occur. Hence, frequent surface water quality monitoring is required for aquatic ecosystem sustainability. The main objectives of the present study are to analyze the seasonal variation in the invasive plant species water hyacinth (Pontederia crassipes) and biogeochemical water quality parameters, i.e., chlorophyll-a (Chl-a) and total suspended matter (TSM), and to examine their relationship in Lake Tana (Ethiopia) during a one-year study period (2020). Sentinel-2A/B satellite images are used to monitor water hyacinth expansion and Chl-a and TSM concentrations in the water. The Case 2 Regional Coast Colour processor (C2RCC) is used for atmospheric and sunglint correction over inland waters, while the Sen2Cor atmospheric processor is used to calculate the normalized difference vegetation index (NDVI) for water hyacinth mapping. The water hyacinth cover and biomass are determined by NDVI values ranging from 0.60 to 0.95. A peak in cover and biomass is observed in October 2020, just a month after the peak of Chl-a (25.2 mg m⁻³) and TSM (62.5 g m⁻³) concentrations observed in September 2020 (end of the main rainy season). The influx of sediment and nutrient load from the upper catchment area during the rainy season could be most likely responsible for both Chl-a and TSM increased concentrations. This, in turn, created a fertile situation for water hyacinth proliferation in Lake Tana. Overall, the freely available Sentinel-2 satellite imagery and appropriate atmospheric correction processors are an emerging potent tool for inland water monitoring and management in large-scale regions under a global change scenario.

Diel primary production patterns of intertidal microphytobenthos (MPB) have been attributed to short-term physiological changes in the photosynthetic apparatus or to diel changes in the photoautotrophic biomass in the sediment photic layer due to vertical migration. Diel changes in primary production and vertical migration are entrained by external factors like photoperiod and tides. However, the role of photoperiod and tides has not been experimentally separated to date. Here, we performed laboratory experiments with sediment cores kept in immersion, in the absence of tides, with photoperiod or under continuous light. Measurements of net production, made with O₂ microsensors, and of spectral reflectance at the sediment surface showed that, in intertidal sediments, the photoperiod signal was the major driver of the diel patterns of net primary production and sediment oxygen availability through the vertical migration of the MPB photoautotrophic biomass. Vertical migration was controlled by an endogenous circadian rhythm entrained by photoperiod in the absence of tides. The pattern progressively disappeared after 3 days in continuous light but was immediately reset by photoperiod. Even though a potential contribution of a subjective in situ tidal signal cannot be completely discarded, Fourier and cross spectral analysis of temporal patterns indicated that the photosynthetic circadian rhythm was mainly characterized by light/dark migratory cycles.

The changes in the annual biomass distribution of microphytobenthos (MPB) have been addressed by different studies, although this information is scarce in southern European coastal systems when compared to Northern European estuaries. Moreover, there is little information regarding annual changes in the primary production of MPB related with those in the annual biomass. For this reason, we followed the net production in light, dark respiration rates (determined by oxygen microelectrodes) and MPB abundance (estimated by sediment chlorophyll a) along an intertidal gradient of the inner Cadiz Bay during an annual cycle. Sediment cores were collected seasonally along two transects (5 sampling stations per transect) with contrasting sediment granulometry: muddy (Puerto Real, PR) and muddy-sandy (San Fernando, SF). Our results show that MPB biomass and net production increased seawards reaching maxima in winter. The seasonal maximum of daily solar irradiance and high temperature reached in summer in southern Spain likely inhibits MPB production. Spatial patterns of MPB biomass and net production depend on season and environmental heterogeneity. Environmental variables, analyzed by principal component analyses, were used to explain the variability of MPB metabolism by multiple regression. The principal component axes explained up to 60 % of the microphytobenthic net production and 41 % of the respiration rates in the PR transect while they only explained about 25 % of the same rates in SF. The variability in the environmental variables contributing to the observed patterns implies that no single set of variables can be used to predict net production patterns in the entire system. The different patterns of net production observed between transects highlight the importance of considering the spatial heterogeneity of our system to estimate the contribution of MPB to the inner Cadiz Bay productivity. This production is of major importance since our data showed that microphytobenthic production can contribute up to 49 % of the total benthic production of intertidal sediments of the inner Cadiz Bay.

Intertidal mudflats are among the most productive coastal ecosystems, largely because of the activity of the photosynthetic microbial community on the sediment surface, known as microphytobenthos (MPB). While the dynamics of MPB have been extensively studied in temperate estuaries, there is limited research in tropical estuaries. To address this knowledge gap, we investigated the spatio-temporal dynamics of MPB in the Nicoya Gulf (Costa Rica), one of the world's most productive tropical estuaries, using Sentinel-2 images at 10 m spatial resolution from 2018 to 2022. We used Normalized Difference Vegetation Index (NDVI) values ranging from 0 to 0.4 to monitor MPB cover and growth rates (μNDVI, days^-1). Analysis of data using Generalized Additive Models (GAM) showed that up to 62 % of the temporal variability in average MPB NDVI, peaking in late wet and early dry seasons (November-December), can be explained by years and months. The high temperatures and irradiance during the dry season (December to April) in the Nicoya estuary may inhibit MPB growth, contrasting with patterns observed in temperate estuaries. We observed higher MPB NDVI in the upper intertidal zone (mean sea level > 0.5 m) as usually occurs in temperate estuaries. This research highlights the importance of high-resolution satellite imagery for long-term monitoring of MPB dynamics in tropical tidal flats, offering a valuable tool for estimating ecosystem services provided by intertidal MPB, such as primary production, climate regulation, and nutrient cycling on a global scale.