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

Lo Stato trofico dello stagno di Casaraccio (Sardegna settentrionale)

Monthly change of chemical and biological features in coastal brackish pond of Casaraccio have been investigated. Peak concentrations of total phosphorus (15 mg P m-3), nitrate nitrogen (50 mg N m-3) and ammonia nitrogen (130 mg N m-3) are low. Peak values of chlorophyll a (4 mg m-3) and average biomass macrophytes of the pond (120 g m-2) are also low, in spite of the fact that the crop of benthic macrophytes are very high (400 g m-2) in some parts of the pond. The resuls of this research represent a starting point for the evaluation of future possible changes which may derive by the implementation of new industrial aquaculture development

Lo Stato trofico di alcuni stagni salmastri costieri della Sardegna

Twelve coastal brackish ponds of Sardinia were examined three-four times during a year in relation to their trophic level. Seven parameters were measured including phosphorus, nitrogen, algal pigments and biomass of macrophytes. Considerable amount of algal nutrients, chlorophyll a and macrophytes, biomass were present in many ponds. Five ponds are proposed as hypereutrophic, four as eutrophic and three as oligotrophic

Le Problematiche legate al fitoplancton nelle acque lacustri destinate ad uso potabile

The problem of the algal interference with water treatment processes is discussed. The levels of removal of algae in some treatment plants of Sardinia (Italy) are presented. Il presente studio indaga il problema dell'interferenza algale nei processi di trattamento delle acque. Si presentano inoltre i livelli di rimozione delle alghe in alcuni impianti di trattamento in Sardegna (Italia)

Lo Stato trofico dello stagno di Pilo (Sardegna settentrionale)

Seasonal changes of nutrient concentrations and other chemical and biological parameters in Pilo's brackish pond were investigated to asses its trophic level. The pond shows eutrophic conditions. In the whole pond the mean biomass value of submersed macrophytes is high (500 g m-2). There is a large range of seasonal variations of total alcalinity concentrations (1,2-5 meq l-l), oxygen saturation (65-120%) and pH values (8-10). Nevertheless the mean concentrations of nitrate nitrogen (30 mg m-3), ammonia nitrogen (50 mg m-3), total phosphorus (17 mg m-3) and chlorophyll a (5 mg m-3) are low, as well as the phytoplankton biomass, (0,5 cm3 m-3)

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

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

Investigating on the occurrence of <i>Paracentrotus lividus</i> in rocky and <i>Posidonia oceanica</i> habitat

The sea urchin Paracentrotus lividus (Lamarck) is the most common grazer in the Mediterranean infralittoral that at high densities overgrazes complex algal assemblages turning them into barren areas. This study has the aim to investigate whether abundance and population structure of P. lividus is consistent between rocky boulders and Posidonia oceanica habitat. At this aim, we have sampled P. lividus at six sites in the Gulf of Alghero (North West Sardinia), 3 fished (sea urchin are harvested) and 3 controls (no harvest is allowed) and at each site the two habitats, 6-10 m deep, were considered. For each combination site x habitat 10 replicates were taken. Density of P. lividus was assessed using quadrats of 1 x 1 m. The size of 20 individual (test diameter without spines) per site was measured by means of a calliper (1#1 0.1mm). Sea urchins, finally were grouped into size classes to examine frequency distributions. Sampling was performed at the end of a harvesting period (April-May 2006). Analyses of data have highlighted a significant variability for both response variables among sites while in Posidonia oceanica habitat a lower density and a higher size were found rather than in rocky habitat. Further data collected at three types of Posidonia oceanica (patches close to rocky habitat, far from rocky habitat and patches bordered by sediment) suggest that the abundance of adults in the seagrass is probably sustained by immigration from the rocky habitat

Fitoplancton, nutrienti algali e stato trofico del lago Bunnari (Sardegna settentrionale)

Seasonal changes of nutrient concentrations, density and composition of phytoplankton and chlorophyll a contents in Bunnari lake were investigated to assess limnological conditions and trophyc status. Only 19 phytoplanktonic species are identified and only 2 species, during the seasonal succession, show high density and biomass; however seasonal succession is altered by a Cupper treatment with purpose of algal control. The 100% dominance of some species allow a good evaluation of chlorophyll aphytoplankton volume ratios. Since many of species found in the lake are typical of productive environments and the values of phytoplankton density and biomass, chlorophyll a and nutrient concentrations are very high, it has been argued a high eutrophic level of the lake

Il Problema dell'eutrofizzazione dei laghi: la situazione trofica degli invasi della Sardegna

The general problem of lake eutrophication is presented. The trophic situation of Sardinia man made lakes is also shown. Among 25 of 38 reservoirs located in Sardinia 4 are oligotrophic, 4 mesotrophic and 17 eutrophic. It is pointed out the need of monitoring the trophic status of all reservoirs and the need of eutrophication control because of drinking utilization of lake waters