Effects of trophic status on microcystin production and the dominance of cyanobacteria in the phytoplankton assemblage of Mediterranean reservoirs

Abstract

The aim of our study was to evaluate the abundance of cyanobacteria and microcystins in four Sardinian reservoirs (Italy) characterised by different trophic status to define a reference picture for future changes. Increasing levels of eutrophication and the abundance of cyanobacteria are expected to occur due to climate change, especially in the southern Mediterranean. Consequently, an in-depth study of the occurrence of harmful cyanobacteria is important to develop appropriate management strategies for water resources at a local scale. Monthly samples were collected at one station in each reservoir over an 18-month period. The Analysis of similarity indicated that cyanobacterial abundance and species composition differed significantly among the reservoirs. The Redundancy analysis highlighted their relationship to trophic, hydrological and seasonal patterns. Spearman’s analysis indicated that there were significant correlations among the most important species (Planktothrix agardhii–rubescens group, Aphanizomenon flos-aquae and Dolichospermum planctonicum), nutrients and microcystins. We highlighted that the species composition during periods of maximum microcystin concentrations differed from those typically reported for other Mediterranean sites. We found new potential microcystin producers (Aphanizomenon klebahnii, Dolichospermum macrosporum and Dolichospermum viguieri), which emphasised the high diversity of cyanobacteria in the Mediterranean area and the need for detailed research at the local scale.

Beyond Eutrophication: Vancouver Lake, WA, USA as a Model System for Assessing Multiple, Interacting Biotic and Abiotic Drivers of Harmful Cyanobacterial Blooms

“…[55]. Such a relationship between environmental conditions and cyanobacterial bloom toxicity has also been reported in other lake and reservoir systems throughout the Mediterranean island of Sardinia [93], as well as in the US Pacific Northwest [94], with a strong relationship observed between high orthophosphorous levels and high internal microcystin concentrations [95].…”

Plankton dynamics across the freshwater, transitional and marine research sites of the LTER-Italy Network. Patterns, fluctuations, drivers

“…At the two Mediterranean artificial lake sites, Lake Sos Canales and lake Bidighinzu, multiple signals of changes are observed, which cause a strong interannual variability of basic limnological parameters and phytoplankton (Sechi and Lugliè 1996;Lugliè et al, 2001;Mariani et al, 2015aMariani et al, , 2015bFadda et al, 2016), rather than a directional trend. Local drivers, such as operational water management, modification of anthropogenic activities in the watershed, wastewater diversion, as well as global drivers, such as warming and modification of precipitation regime, are affecting phytoplankton in complex ways (Mariani et al, 2015a), resulting in a high year to year variability of chl, total cell density and biomass (Mariani et al, 2015a).…”

Effects of Water Level Increase on Phytoplankton Assemblages in a Drinking Water Reservoir

“…Due to complete drawdown, zooplankton with no predation pressure grazed down increased algal biomass, which prevented algal blooms during the initial refilling process. In four Sardinian reservoirs (Italy), increasing levels of eutrophication and the abundance of cyanobacteria occurred due to trophic, hydrological, and seasonal patterns, especially in the southern Mediterranean, and the most important species had significant correlations with nutrients and microcystins [31]. Lack of algal blooms in response to water level increase in the Danjiangkou Reservoir may be attributed to several factors.…”