Trophic status and phytoplankton in Lake Bidighinzu

From March 1988 to April 1989 a survey was carried out on the phytoplankton of Lake Bidighinzu, a hypertrophic reservoir in Northern Sardinia. The purpose of this work was to assess the general limnological conditions of the reservoir after a diversion of the urban and industrial wastes. The dynamics of chlorophyll a, and the structure and composition of the phytoplankton density and of its biomass in the study period were determined. Moreover the found trends for trasparency, temperature, conductivity, alkalinity, pH, dissolved oxygen, reactive and total phosphorus, nitrate, nitrite, ammonium nitrogen, and reactive silica are reported. The effect of water aeration on the dynamics of the other parameters is discussed

The Trophic status of Bidighinzu Reservoir (Sardinia) before and after the diversion of waste waters

The purpose of this paper was to assess the effect of the diversion of wastewater on the trophic status of Lake Bidighinzu, a hypertrophic man-made lake in Northern Sardinia, used as a drinking water reservoir. There have been problems with potabilization since the early years of the diversion operation, particularly in the summer-autumn period. Data available (August 1978, February 1979 and March 1985) before the reservoir (1987) were compared with those collected during a study carried out in the annual cycle immediately after (1988-1989) and after some years (1994 and 1996-1997). The study examined the dynamics of temperature, main nutrients (total phosphorus, nitrate and ammonia), chlorophyll-a and phytoplanktonic biomass. No particular variation in the water nutrient availability emerged from the comparison between these two situations - especially for total phosphorus, whose annual mean concentrations were similar in the two annual cycles (386 mg P m-3 in 1988-1989 and 305 mg P m-3 in 1996-1997). Chlorophyll- a and biomass were high during each period of study (annual mean values were 17 mg m-3 and 3.7 mg l-1 in 1988-1989 and 11 mg m-3 and 4.6 mg l-1 in 1996-1997). However, peaks were never higher than values recorded in August 1978 (112 mg m-3 and 133 mg l-1) due to an extraordinary bloom of Ceratium hirundinella (O.F. Müller). Species composition of phytoplankton was typical of highly trophic conditions and was frequently characterised by the presence of Cyanophyceae and Bacillariophyceae. Results demonstrated that, ten years after construction of the by-pass, the lake had shown no improvement in its trophic status. This might depend on many factors, among which the most likely might be the non-use or partial use of the diversion system, which allows the sewage to continue to flow into the lake and keep its trophic status almost unchanged

Santa Giusta Lagoon (Sardinia): phytoplankton and nutrients before and after waste water diversion

The purpose of this paper was to assess the effect of the diversion of waste water on the trophic status of the Stagno di Santa Giusta, a hypertrophic lagoon on the centre-western coast of Sardinia. The data available (1990, 1992-1994) before the diversion (1995) were compared with those collected from 1995 to 1999. The lagoon has an area of about 8 km2; its mean depth is about 1 m and is well mixed as regards circulation and stratification. This study examined temperature, salinity, pH, main nutrients (reactive and total phosphorus, nitrate and ammonium nitrogen, reactive silica), chlorophyll-a, phytoplanktonic density and phytobenthic biomass. A comparison of the condition of the water before and after the diversion showed that there was an insufficient reduction in nutrient concentrations. The mean concentrations of nitrate nitrogen and ammonium nitrogen fell from 33 and 87 mg N m-3, respectively, to 28 and 66 mg N m-3, respectively. There was a more marked reduction in phosphorus (from 107 mg P m-3 as reactive phosphorus and from 190 mg P m-3 as total phosphorus to 77 and 127 mg P m-3, respectively), and in reactive silica, from 3 to 1.7 mg l-1. Chlorophyll-a decreased from 11.3 to 10.2 mg m-3; the total density of phytoplankton dropped considerably, but this was due to a different species composition. Phytobenthic biomass showed no particular variations. There were no changes in trophic level, so that dystrophic crises still occurred after the diversion. The results showed that there were no substantial improvements in the trophic status of the lagoon during the years after the diversion, except for some months in 1995. A possible explanation may lie in the structure of the diversion system, which does not completely stop the inflow of sewage into the lagoon

Studi limnologici sul Lago Alto Flumendosa (Sardegna centrale): stato trofico e fitoplancton

Alto Flumendosa Reservoir (Central Sardinia), was investigated from February 1990 to February 1993, to study either long time period phytoplankton variations in a mesotrophic mediterranean reservoir and to value the influence of a cage rearing pisciculture on its trophic status. The annual mean values of clorophyll a varied from 2.3 mg m-3 in 1991 to 11.1 mg m-3 in 1990, annual mean values of biomass from 0.5 mg l-1 in 1993 to 3.9 mg l-1 in 1990 and annual mean values of cellular density from 6 x 106 cells l-1 in 1993 to 11.3 x 106 cells l-1 in 1990. Despite great variations in the species composition of phytoplankton in each year, a general scheme in the algal succession was found with Cryptophyceae in the colder months, Chlorophyceae in the spring months (sometimes in autumn), Cyanophyceae and Dinophyceae in summer, Bacillariophyceae in autumn, Chrysophyceae between winter and spring and Conjugatophyceae in summer or in winter. The trophic status on the basis of phytoplankton composition, clorophyll a, annual mean values of total phosphorus (from 19 mg P m-3 in 1993 to 25 mg P m-3 1990) was mesotrophic but in 1990 the eutrophic probability, on the basis of chlorophyll a, was higher. The cage rearing pisciculture was presumed to be responsible of the strong oxygen decreases in hypolimnetic water at the end of the stratification periods

Indice per la valutazione della qualità ecologica dei bacini artificiali mediterranei (MedPTI) a partire dalla composizione del fitoplancton: documento presentato al Ministero dell’Ambiente e della tutela del territorio e del mare

Secondo la Direttiva 2000/60/CE (WFD, Water Framework Directive), la valutazione della qualità ecologica dei corpi idrici deve essere ottenuta con l’uso di indici numerici costruiti a partire dai parametri biologici, confrontando il valore assunto nel sito in esame con quello di un sito di riferimento, attraverso il calcolo di un quoziente di qualità ecologica (Ecological quality ratio, EQR). L’indice qui proposto è stato sottoposto alla procedura di intercalibrazione, per ottenere i valori dell’indice corrispondenti alle condizioni di riferimento e ai limiti tra le classi di qualità e quindi il rispettivo EQR

Temporal distribution of phytoplankton species composition and main environmental variables in Santa Giusta Lagoon (central-western Sardinia) = Distribuzione temporale della composizione specifica del fitoplancton e dei principali parametri ambientali nello stagno di Santa Giusta (Sardegna centro-occidentale)

Water samples and environmental data were examined at four stations at biweekly or monthly intervals, depending on the period, from February 1990 to December 1999. Phytop/ankton composition was estimated in these samples. The abiotic parameters revealed a difference in environmental conditions between the outer area of the lagoon and those closer to the coast. Phytoplankton structure was quite consistent among different areas of the lagoon. Absolute abundance was very different among classes, with Chlorophyceae much more abundant than Bacillariophyceae. Haptophyceae and Chrysophyceae were the least represented classes. Density of classes reached peaks in different periods of the year, suggesting a recurrent pattern in taxa succession

A Numerical index for evaluating phytoplankton response to changes in nutrient levels in deep Mediterranean reservoirs

This paper proposes a new ecological index based on phytoplankton (MedPTI) as suggested by the European Directive 2000/60/CE, Water Framework Directive (WFD). The index is a useful tool to verify the impacts of eutrophication in Mediterranean reservoirs belonging to different categories of the WFD. Multiple data sets were employed to develop the MedPTI index. The calibration data set included data collected from 30 Sardinian reservoirs in 1994. A list of 44 selected taxa was obtained and used for index calculation. A second dataset including 48 averaged annual values from 10 reservoirs was used. Results showed good correlation between MedPTI and concentration of total phosphorus, which was the limiting nutrient in these reservoirs. The trophic classifications determined using the index agreed with the results from the OECD probabilistic model on the same series of data. Finally, the index was included in an international exercise to compare the definition of reference conditions and quality class boundaries against indices used in other Mediterranean countries

Variabilità spazio-temporale della struttura del fitoplancton nel Golfo dell'Asinara (Sardegna) = Spatial and temporal variability of phytoplankton structure in the Asinara Gulf (Sardinia)

The spatio-temporal variability of phytoplankton and some environmental parameters in the gulf of Asinara are examined (05/97-04/98). Along the whole coastal area, stations at 500 and 3000 mfrom coast across 6 transects are considered. Results point out some variations in phytoplankton composition and dynamics. Multidimensional Scaling ordinations and Bray-Curtis cluster analuses identified two major zones at 500 m from coast, one for the site of Lu Bagnu and one for the other five sites; at each stations, a great similarity was found in its respactive share. On the contrary, at 3000 m from coast, no cluster was identified

Water quality evaluation in Mediterranean Lagoons using the Multimetric Phytoplankton Index (MPI): study cases from Sardinia

1 - Water quality in four Sardinian lagoons (western Mediterranean Sea) was assessed using the Multimetric Phytoplankton Index (MPI), which is consistent with the EU Water Framework Directive. The index was developed using data on phytoplankton abundances, species structure and chlorophyll a concentrations in Venice Lagoon, Italy. 2 - The aim of this study was to test the MPI on a larger geographical scale and across a range of lagoon types. Therefore, it was applied to assess water quality in the Cabras, S’Ena Arrubia, Santa Giusta and Calich lagoons in Sardinia. These lagoons are all “choked”, but exhibit a range of sizes and morphometric features. They are directly affected by human activity within the lagoons themselves, such as fisheries, aquaculture and the construction of dams and canals, and are indirectly affected by anthropogenic activities in their catchments, including intensive agriculture, industrial activity and urban development. 3 - The data used in the present study were collected monthly over a period of 4 years (Calich, Santa Giusta and S’Ena Arrubia) to 7 years (Cabras). Samples were collected at three stations at each of the Cabras, Santa Giusta and Calich lagoons, and at two stations at the S’Ena Arrubia Lagoon, providing a total of 220 samples. 4 - The water quality in three of the four lagoons investigated (Cabras, S’Ena Arrubia and Calich) was classified as bad using the MPI. Among these three, water in Cabras Lagoon exhibited the worst condition. Water quality in Santa Giusta Lagoon was classified as poor using the MPI. 5 - Although we present preliminary results that require further verification, the index appears to be a useful tool for assessing the ecological status of typical Mediterranean lagoons

Chamaepinnularia thermophila (Bacillariophyceae) : synonymy with Navicula tongatensis Hustedt and update of its geographic distribution and ecology

Abstract Chamaepinnularia thermophila is a small and poorly known diatom species. After the first description from a hot spring in Guadalupe in 1952, its presence appeared to be limited to a few other springs of the French Antilles. The objective of this study is to report new information on aspects of taxonomy, distribution and ecology of this species. Accurate analysis under light and scanning electron microscope of the material collected on different substrates (cobbles, macrophytes and fine sediments) from a thermo-mineral spring of Sardinia (Italy) allowed us to document the first record of the species in the Mediterranean area. Furthermore, the comparison with Navicula tongatensis from Hustedt's original material, carried out because of their similarity, revealed identical morphological characteristics suggesting their consequent synonymy. Based on the information available in the literature and our data, C. thermophila is a rare species present mainly in tropical areas, in thermal springs with alkaline pH, medium to high conductivity and low to moderate nutrient content. The occurrence of the species at sites with very different environmental characteristics seems unusual, but it could indicate a broader ecological range. This study contributes to the standardization of the nomenclature used for this species so far and provides the first framework on its global geographic distribution and ecology