Consequences of eutrophication in the management of water resources in Mediterranean reservoirs: A case study of Lake Cedrino (Sardinia, Italy)

Abstract One of the primary detrimental effects of eutrophication is the tendency of nuisance cyanobacterial species to increase in number and biomass in freshwater ecosystems. The aim of this study was to investigate possible management actions to control eutrophication and assure water use of a eutrophic deep Mediterranean climate reservoir, dominated by cyanobacteria. With this goal, we defined the trophic state of Lake Cedrino (Sardinia, Italy) and studied its phytoplankton, paying particular attention to cyanobacteria, and to seasonal variation of phytoplankton in relation to seasonal variation of environmental variables. The water samples were collected monthly from September 2010 to August 2011 at differing depths from the surface of the water to the bottom at a station located in the deeper portion of the reservoir. Physical, chemical, nutrient, qualitative and quantitative analyses of phytoplankton were performed, and the trophic state was evaluated based on the Trophic State Index and the OECD model. Abundance of nutrients and phytoplankton (cell density, biomass and chlorophyll a ) indicated a eutrophic condition of the reservoir. In summer, phytoplankton species composition was dominated by nuisance cyanobacteria, particularly Aphanizomenon flosaquae , thereby requiring management plans for harmful blooms. On the base of lake features, we propose management actions at different scales and levels to resolve eutrophication and to allow water use: from nutrient load reduction in the watershed (primarily from point-sources) to deep water aeration, to immediately face an attenuation of eutrophic effects. This study is the first explorative step in planning restoration of Lake Cedrino

Long-term ecological studies on phytoplankton in Mediterranean reservoirs: a case study from Sardinia (Italy)

Artificial lakes are strategic water resources in the Mediterranean region but are one of the most vulnerable areas to the impacts of climate change, particularly to the expected significant decrease in water resources; therefore, enhancing the ability of water management to improve water quality is crucial. This study contributes to the knowledge of the long-term ecological features of Mediterranean artificial lakes based on a case study of Bidighinzu Lake in Sardinia, Italy, a warm, monomitic and hypereutrophic reservoir mainly used for drinking water. Among the different restoration actions carried out in Bidighinzu Lake to improve water quality is the reduction of nutrient loads from the watershed. To study multiannual trends of the trophic state, a long-term series (1988–2012) of both environmental variables and phytoplankton was analysed. Mann-Kendall tests revealed increasing trends for total nitrogen to total phosphorus ratios (TN:TP; significant in spring, summer, and winter) and decreasing trends for ammonium (winter and autumn), TP (all seasons), orthophosphate (spring, summer, and winter), reactive silica (autumn), and pH (summer). Among phytoplankton, significant increasing trends were assessed in biomass of Bacillariophyceae, Chlorophyceae, Dinophyceae, and Chrysophyceae. Cyanobacteria did not show a clear trend, although at the order level, Chroococcales significantly increased in summer and decreased in winter. Despite these major tendencies, the lake did not show significant improvement in its eutrophic state, probably due to an inherent resistance and the insufficient and/or not well calibrated or applied recovery actions

Long-term ecological studies on phytoplankton in Mediterranean reservoirs: a case study from Sardinia (Italy)

Artificial lakes are strategic water resources in the Mediterranean region but are one of the most vulnerable areas to the impacts of climate change, particularly to the expected significant decrease in water resources; therefore, enhancing the ability of water management to improve water quality is crucial. This study contributes to the knowledge of the long-term ecological features of Mediterranean artificial lakes based on a case study of Bidighinzu Lake in Sardinia, Italy, a warm, monomitic and hypereutrophic reservoir mainly used for drinking water. Among the different restoration actions carried out in Bidighinzu Lake to improve water quality is the reduction of nutrient loads from the watershed. To study multiannual trends of the trophic state, a long-term series (1988–2012) of both environmental variables and phytoplankton was analysed. Mann-Kendall tests revealed increasing trends for total nitrogen to total phosphorus ratios (TN:TP; significant in spring, summer, and winter) and decreasing trends for ammonium (winter and autumn), TP (all seasons), orthophosphate (spring, summer, and winter), reactive silica (autumn), and pH (summer). Among phytoplankton, significant increasing trends were assessed in biomass of Bacillariophyceae, Chlorophyceae, Dinophyceae, and Chrysophyceae. Cyanobacteria did not show a clear trend, although at the order level, Chroococcales significantly increased in summer and decreased in winter. Despite these major tendencies, the lake did not show significant improvement in its eutrophic state, probably due to an inherent resistance and the insufficient and/or not well calibrated or applied recovery actions

Osservazioni limnologiche sul lago Simbirizzi (Sardegna meridionale) dal 1989 al 1993, con particolare riferimento alle dinamiche del fitoplancton

This paper reports the results of a limnological survey carried out from May 1989 to April 1993 on Lake Simbirizzi, a shallow man-made lake located in South Sardinia. The lake was filled in the 1986 and it is polimitic and hypertrofic. The aim of the study was to follow the dynamics of some parameters, in particulary those of phytoplankton, after the first years of the lake's life already studied by Mura et al. (1992). It is confirmed the high values of conductivity and, on the basis of the mean annual values of total phosphorus (between 67 mg P m-3 and 148), chlorophyll a (between 17 mg m-3 and 57 mg m-3), total density (between 26 cells 106 l-1 and 269 cells 106 l-1) and total biomass (between 4.5 mg l-1 and 19.4 mg l-1). the hypertrophic state. During the studied period 20 species among about a hundred were important for density and biomass. Cyanophyceae dominated the density whereas Bacillariophyceae, Dinophyceae and Conjugatophyceae were the most important groups, with Cyanophyceae, for the biomass

Benthic diatoms as indicators of biological quality and physical disturbance in Mediterranean watercourses: a case study of the Rio Mannu di Porto Torres basin, northwestern Sardinia, Italy

This study focused on expanding existing knowledge about benthic diatoms and their use as indicators of biological quality and physical disturbance in six Mediterranean watercourses within the Rio Mannu di Porto Torres basin in northwestern Sardinia, Italy. Benthic diatoms were collected from 11 stations during a 1-year cycle from summer 2010 to summer 2011. The Eutrophication/Pollution Index – Diatom-based (EPI-D) was used to evaluate biological quality, and the Navicula Nitzschia Surirella Index (NNS’) was used to estimate the degree of physical disturbance at each station. In addition, physico-chemical variables and Escherichia coli were measured and analyzed each month. In total, 193 diatom taxa were identified, of which 157 belonging to 57 genera were present in the counts and were used to calculate the diatom indices. Five taxa were recorded for the first time for Sardinian watercourses; of which, Amphora paraveneta Lange-Bertalot, Cavacini, Tagliaventi & Alfinito, Fallacia pygmaea ssp. subpygmaea Lange-Bertalot, Cavacini, Tagliaventi & Alfinito and Diploneis spec. (aff.?) modica Hustedt are biogeographically relevant, while Navicula kotschyi Grunow and Reimeria uniseriata Sala, Guerrero & Ferrario are of particular interest as exotic species with relatively restricted distribution. The EPI-D revealed mediocre and bad water quality for all the investigated stations, in agreement with the environmental variables and the heavy anthropogenic use of the study area. The EPI-D was effective at inferring the biological quality of the studied watercourses, although some of the species that were found (7% of the total) are not included in the method. We suggest including these species in the list to improve the performance of the index in Mediterranean rivers. A comparison between the results obtained by the EPI-D and seven other European diatom indices was made. Significant statistical correlations between the EPI-D and four of these indices were observed. The NNS’ was applied for the first time to Sardinian watercourses and it indicated a significant degree of physical disturbance at nearly all the stations, due to seasonal fluctuations in water flow, which are typical of the Mediterranean climate, combined with the effects of human activities

Diatoms and quality of watercourses in North-Central Sardinia

Eight watercourses in North-Central Sardinia were studied between 2008 and 2009 to ascertain their environmental quality and to gain insights into the requirements for their proper management. In addition to physicochemical and microbiological parameters, epilithic diatoms were analyzed at 15 stations. Data on the diatom community of each sample were used to calculate the diatom-based eutrophication/pollution index (EPI-D) and the biological diatom index (IBD). In the 21 collected samples, 153 taxa belonging to 36 genera were identified, but the diatom flora also included species that could not be determined with certainty. Most of the observed diatoms are considered cosmopolitan and were common to various sites, with Cocconeis placentula var. pseudolineata and Diadesmis confervacea among the most frequent and sometimes the most abundant taxa. Platessa hustedtii, which like Diadesmis confervacea is considered a tropical species, was recorded for the first time in Sardinia. While these species are not considered by the EPI-D proposed for use in Italian watercourses, their integration will improve the usefulness of this index in the assessment of islands of Mediterranean typology. The applicability of the EPI-D and IBD was confirmed with water quality at nearly all the considered stations ranging from mediocre to bad according to both indices. Moreover, these results were supported by physicochemical and microbiological variables and were consistent with the typology of the investigated environments

First detection of the bloom forming Unruhdinium penardii (Dinophyceae) in a Mediterranean reservoir: insights on its ecology, morphology and genetics

13 pages, 5 figures, 2 tables, supplementary material https://doi.org/10.4081/aiol.2020.9500The freshwater genus Unruhdinium includes dinoflagellates hosting a tertiary diatom endosymbiont. Some of the species belonging to this genus form high-biomass blooms. In this study, data on the ecology, morphology and molecular identity of Unruhdinium penardii were reported for the first time from a Mediterranean reservoir (Cedrino Lake, Sardinia, Italy). The ecology of the species and its bloom events were examined along a multiannual series of data (2010-2017). Cell morphology was investigated using field samples and six cultures established by cell isolation. A molecular identification of the six strains was performed. Wild and cultured cells shared the same morphology, showing a prominent apical pore complex and two/three more or less prominent hypothecal spines as distinctive characters in light microscopy. Molecularly, the six cultured strains corresponded to the same taxonomic entity with sequences only differing in a few polymorphic positions for the studied markers SSU rDNA, LSU rDNA, ITS and endosymbiont SSU rDNA. All markers showed 99.5%−100% similarity with the available U. penardii sequences. Seasonality of U. penardii revealed its preference for the colder semester (from December to June) with bloom events restricted to late winter/early spring months. Three blooms resulting in reddish water discolorations were observed along the study period (2011, 2012 and 2017). GLMs revealed a significant role of water depth, temperature, and reactive phosphorous in determining the highest cell densities (>5 x 104 cells L-1). The results obtained contribute to the increase of field ecology knowledge on this species, demonstrating it is well established in the Mediterranean area, and being able to produce recurrent high biomass blooms in the studied reservoiThe activities of Prof Antonella Lugliè and Dr. Mario Padedda were supported by the research fund of the University of Sassari (Fondo di Ateneo per la Ricerca 2019).With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)Peer reviewe

Multiannual phytoplankton trends in relation to environmental changes across aquatic domains: a case study from Sardinia (Mediterranean Sea)

We investigated multiannual trends in phytoplankton in relation to several environmental drivers. We analyzed ecological data collected during the past two decades from three aquatic sites: an artificial lake, a coastal lagoon, and a marine coastal area. Hydrographic, nutrient, and phytoplankton data were statistically analyzed to detect trends and interactions. In all ecosystems, the chlorophyll a concentration decreased with increasing abundance of small-sized phytoplankton. Phytoplankton dynamics were related to decreased nutrient concentrations in the lake, to dynamics of phosphorus and decreased salinity in the lagoon, and probably to combined top-down and bottom-up processes in the marine gulf

A Fast-response methodological approach to assessing and managing nutrient loads in eutrophic Mediterranean reservoirs

With many lakes and other inland water bodies worldwide being increasingly affected by eutrophication resulting from excess nutrient input, there is an urgent need for improved monitoring and prediction methods of nutrient load effects in such ecosystems. In this study, we adopted a catchment-based approach to identify and estimate the direct effect of external nutrient loads originating in the drainage basin on the trophic state of a Mediterranean reservoir. We also evaluated the trophic state variations related to the theoretical manipulation of nutrient inputs. The study was conducted on Lake Cedrino, a typical warm monomictic reservoir, between 2010 and 2011. We assessed the hypereutrophic condition of the reservoir by monthly samplings of the water column and compared these results with the amount of nutrient load originating from anthropic activities in the drainage basin [42.6 t P y−1 for total phosphorus (P) and 531 t N y−1 for total nitrogen (N)]. We verified how the predictive OECD management model could be confidently applied to predict the P concentration in the reservoir on the basis of estimated loads from the drainage basin (98.7 mg P m−3 assessed versus 101 mg P m−3 estimated, approximately 2.5% over). Different scenarios are presented showing how it is possible to reduce approximately 62% P and 43% N, altering the condition of the ecosystem to become more mesotrophic. We also propose some management strategies to improve water quality in this lake ecosystem