Metal and semimetal loadings in sediments and water from mangrove ecosystems: A preliminary assessment of anthropogenic enrichment in São Tomé island (central Africa).

Mangroves act as buffer areas for marine systems, providing a barrier to contamination from continental sources by retaining metal pollutants. This study evaluates metal and semimetal contamination in the water column and sediments of four mangroves located on the volcanic island of São Tomé. Several metals had a widespread distribution, with occasional high concentrations, linked to potential sources of contamination. However, the two smaller mangroves, located in the northern part of the island, tended to have high metal concentrations. Arsenic and chromium concentrations were notably concerning, particularly if we consider this is an isolated and non-industrialized island. This work highlights the need for further assessments and a better understanding of processes and implications of metal contamination in mangroves. This assumes a particular relevance in areas that have specific geochemical compositions (i.e., volcanic origin) and in developing countries, where people often rely directly and heavily on resources obtained from these ecosystems.

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

Estuaries are highly productive ecosystems, which are strongly affected by several anthropogenic pressures. Phytoplankton is a key element for assessing the ecological quality status in these transitional waters. Moreover, understanding physico-chemical and biological drivers is crucial to disentangle their effect on the structure of phytoplankton community. The present work aims to study the effect of the main physico-chemical drivers on the phytoplankton community structure and dynamics in a temperate well-mixed estuary (Sado Estuary). Four sampling stations were analyzed monthly in three regions of the estuary, from 2018 to 2019. Surface water samples were collected to analyze the phytoplankton community and several concomitant physico-chemical parameters. Temperature, turbidity, salinity, and nutrients availability were the drivers that best explained the spatio-temporal patterns observed in the phytoplankton community. The upper estuary was characterized by higher phytoplankton cell abundances and biomass. Three phytoplankton groups stood out in the characterization of the estuarine assemblages: diatoms, cryptophytes, and dinoflagellates. Diatoms were the dominant group most of the year, being dominated by small cell species (single and chain-forming) upstream, and by larger chain-forming species downstream. Cryptophytes had a high contribution to the community in the inner regions of the estuary, while dinoflagellates contributed more for the community composition downstream, where high abundances of harmful algal species were sporadically found. Previous studies on the phytoplankton community dynamics in this estuary are limited to the 1990s. Thus, the present study provides insight into changes in the dominant phytoplankton groups of the Sado Estuary in the last 25 years, namely an increase in cryptophytes over diatoms in the inner estuarine regions, and an increase in dinoflagellates near the estuary mouth.

Use of multimetric indices to classify estuaries with different hydromorphological characteristics and different levels of human pressure.

The assessment of estuaries based on benthic communities is widely used to determine impacts caused by human pressure and is one of the required tools for the implementation of the European Water Framework Directive (WFD). Our study compared multimetric approaches (B-IBI and TICOR) to assess the benthic condition of three Portuguese estuaries (Mondego, Tejo, and Mira rivers) with different levels of natural and human induced stress. Benthic community condition was classified into quality status categories of the WFD and compared for consistency with a priori status categories based upon physical-chemical criteria. Both multimetric indices discriminated equally well between locations classified above or below the good status category but were unable to provide good separation between other quality classes (high/good, moderate, poor/bad). Metrics included in these indices are greatly affected by natural stress and we recommend the development of habitat-specific thresholds to increase the discriminatory ability of any benthic condition index.

Influence of seasonal variability in benthic invertebrate community structure on the use of biotic indices to assess the ecological status of a Portuguese estuary.

The present study focused on the use of benthic invertebrate communities to assess the ecological quality of a Portuguese estuary characterized by strong seasonal changes and with eutrophication problems. Seasonal benthic samples were collected during a flood year and the methodology proposed by the WFD Portuguese group was used to classify benthic assemblages into five different quality classes. Factor analysis was applied to classify stations based on their physical-chemical status. Different classifications were obtained with different indices and among seasons and there was low agreement between indices and index-season interactions. Diversity indices were better correlated to eutrophication related variables than AMBI and ABC method. Predictable responses of benthic indices to anthropogenic stress symptoms were stronger during the dry period.