Some Observations on Phytoplankton Community Structure, Dynamics and Their Relationship to Water Quality in Five Santiago Island Reservoirs, Cape Verde

Manuela Morais,Alexandra Marchã Penha,Maria Helena Novais,Leonel Landim,Luciana Gomes Barbosa,Sónia Silva Victória,Eduardo A Morales

doi:10.3390/w13202888

Abstract

Reservoirs provide valuable services to human beings, especially in arid, semi-arid, and Mediterranean regions affected by water scarcity. The present effort aims to study the environmental descriptors of variation and the main factors influencing phytoplankton composition, structure, and diversity in five reservoirs in Santiago Island, Cape Verde, a region affected by water availability. Five campaigns took place from 2016 to 2020 to sample phytoplankton and measure environmental variables according to standard analytical methodologies. Environmental results (17 water physicochemical variables, air temperature, and precipitation) revealed that reservoirs differ in the geological influence variables. The high levels of P and N in water seem to be related to Land Use/Land Cover and are responsible for water-quality degradation. Cyanobacteria dominated the phytoplankton community and posed high risk levels, especially considering that the identified taxa are potential producers of different toxins. Taxa responsible for this dominance were not the same in all reservoirs, emphasizing the dominant role of local habitat factors on community composition and diversity. Overall, the results reveal the importance of defining integrated management plans/strategies for the set of five studied reservoirs, since the processes influencing variation in the phytoplankton community are temporal-scale dependent, with similar biogeographic patterns.

Highlights

Dams have been used as important strategies to face water scarcity in regions where this resource needs to be stored for human development
The archipelago is formed by ten islands, nine of which are inhabited, and thirteen islets, which occupy a total area of 4033 km2 and an exclusive economic zone (EEZ) that extends over approximately 700,000 km2 (Figure 1)
The reservoirs were not different according to organic variables, which can be explained by the high concentrations of P and N recorded in the five reservoirs above the

Summary

Introduction

Dams have been used as important strategies to face water scarcity in regions where this resource needs to be stored for human development. In this situation, arid, semi-arid, and Mediterranean regions stand out since reservoirs have provided valuable services such as drinking water supplies, hydropower, and irrigation [1,2,3,4]. Phytoplankton plays an important role in maintaining the balance of reservoirs by consuming carbon dioxide and nutrients and releasing oxygen. The structure of this community is closely related to environmental factors, nutrients, water temperature, and light availability [5,6,7]. Monitoring and forecasting of the phytoplankton community are of great importance, especially when changes are driven by human activities, such as agriculture, livestock, wastewater, and urban runoff

Methods

Results

Discussion

Conclusion