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ANNUAL VARIATIONS OF NUTRIENTS IN THE LAGOON OF VENICE
No full textNutrient concentrations (P, N compounds and Corg) and chemical-physical parameters (T, DO%, pH, Eh) were monitored in water and sediment in the Lagoon of Venice for one year. Large variations appeared to depend mainly on macroalgal biomass fluctuations which occurred during spring-summer. Sediment was the main sink of nutrients from decomposing macroalgae. Sedimentary phosphorus, nitrogen and carbon increased 75, 160, and 70%, respectively. When macroalgae were negligible, in August-March, nutrients accumulated in sediment were released to the overlying water. Due to the occurrence of anaerobic conditions, the highest concentrations of phosphorus in water were observed in spring-summer. The release of sedimentary nitrogen was higher in September-March. Macroalgal assimilation varied the N:P atomic ratio in water from 50-78 in winter to 0.7-5 in spring-summer. In addition, the N:P ratio in sediment increased from values around 7 in winter to more than 13 between May and July, approaching the N:P values found in macroalgae (8.5-12). Therefore, in spring-summer, the availability of nitrogen in water appeared to be the limiting factor for the macroalgal growth.Nutrient concentrations (P, N compounds and Corg) and chemical-physical parameters (T, DO%, pH, Eh) were monitored in water and sediment in the Lagoon of Venice for one year. Large variations appeared to depend mainly on macroalgal biomass fluctuations which occurred during spring-summer. Sediment was the main sink of nutrients from decomposing macroalgae. Sedimentary phosphorus, nitrogen and carbon increased 75, 160, and 70%, respectively. When macroalgae were negligible, in August-March, nutrients accumulated in sediment were released to the overlying water. Due to the occurrence of anaerobic conditions, the highest concentrations of phosphorus in water were observed in spring-summer. The release of sedimentary nitrogen was higher in September-March. Macroalgal assimilation varied the N:P atomic ratio in water from 50-78 in winter to 0.7-5 in spring-summer. In addition, the N:P ratio in sediment increased from values around 7 in winter to more than 13 between May and July, approaching the N:P values found in macroalgae (8.5-12). Therefore, in spring-summer, the availability of nitrogen in water appeared to be the limiting factor for the macroalgal growth. © 1988
PERSISTENT METABOLITES OF ALKYLPHENOL POLYETHOXYLATES IN THE MARINE-ENVIRONMENT
No full textThe persistent metabolites of the nonionic surfactant nonylphenol polyethoxylates (NPnEO, n=1-18), namely nonylphenol (NP), nonylphenol monoethoxylate (NP1EO) and nonylphenol diethoxylate (NP2EO), were analysed in marine samples including sediment, artificially resuspended sediment and water. The UV-fluorescence high-performance liquid chromatography determination was carried out after Soxhlet extraction with hexane from the sedimentary matrices followed by clean-up on aminosilica minicolumns. Four sampling campaigns at five representative stations of the Venice lagoon were conducted to ascertain temporal and spatial variability of the examined chemicals. A portable resuspending device allowed us to analyse the first 0.01-0.15-mm sediment layer, where the sum of NP, NP1EO and NP2EO was in the range 0.15-13.7 μg g-1 (dry weight basis), at least five times higher than in the underlying 5 cm of sediment. Amounts of resuspended material, and concentrations of NP, NP1EO, NP2EO bound to it, showed a marked seasonal dependence: as much as twice the resuspended material, per unit of sediment surface, was measured in April and July, compared with that in February, but resuspended NP, NP1EO and NP2EO per unit of sediment surface were in February one order of magnitude higher. A major factor responsible for this trend was related to the proliferation of macroalgae which contained an average NP+NP1EO+NP2EO concentration of 0.25±0.15 μg g-1 (dry wt.). In water, NPEO oligomers with up to 13 ethoxy units were found at an overall concentration range of 0.6-4.5 μg l-1.The persistent metabolites of the nonionic surfactant nonylphenol polyethoxylates (NPnEO, n=1-18), namely nonylphenol (NP), nonylphenol monoethoxylate (NP1EO) and nonylphenol diethoxylate (NP2EO), were analysed in marine samples including sediment, artificially resuspended sediment and water. The UV-fluorescence high-performance liquid chromatography determination was carried out after Soxhlet extraction with hexane from the sedimentary matrices followed by clean-up on aminosilica minicolumns. Four sampling campaigns at five representative stations of the Venice lagoon were conducted to ascertain temporal and spatial variability of the examined chemicals. A portable resuspending device allowed us to analyse the first 0.01-0.15-mm sediment layer, where the sum of NP, NP1EO and NP2EO was in the range 0.15-13.7 μg g-1 (dry weight basis), at least five times higher than in the underlying 5 cm of sediment. Amounts of resuspended material, and concentrations of NP, NP1EO, NP2EO bound to it, showed a marked seasonal dependence: as much as twice the resuspended material, per unit of sediment surface, was measured in April and July, compared with that in February, but resuspended NP, NP1EO and NP2EO per unit of sediment surface were in February one order of magnitude higher. A major factor responsible for this trend was related to the proliferation of macroalgae which contained an average NP+NP1EO+NP2EO concentration of 0.25±0.15 μg g-1 (dry wt.). In water, NPEO oligomers with up to 13 ethoxy units were found at an overall concentration range of 0.6-4.5 μg l-1. © 1990
Species composition, biomass, and net primary production in shallow coastal waters: The Venice lagoon
No full textThree areas displaying the main characteristics of the central Venice lagoon were monitored in 1989-91 to study macroalgal production in relation to different biomass densities and species compositions. Two areas that were covered by dense (0-20 kg m-2, wet wt), monospecific, Ulva rigida populations (> 96%) showed a net biomass production of 7-16 kg m-2 year-1, wet wt, corresponding to 149-358 g C m-2 year-1, and daily biomass yields up to 1500 g m-2, wet wt. A third area, characterized by a biomass of 5 kg m-2, wet wt) and very high (up to 200%) when biomass was 96%) showed a net biomass production of 7-16 kg m-2 year-1, wet wt, corresponding to 149-358 g C m-2 year-1, and daily biomass yields up to 1500 g m-2, wet wt. A third area, characterized by a biomass of 5 kg m-2, wet wt) and very high (up to 200%) when biomass was < 100 g m-2, wet wt. The ratio of annual biomass production to highest measured biomass (ABP/HMB) was inversely related to the biomass density and ranged from 1·5 to 4·5. On the basis of these ratios and of the standing crops measured by 180 sampling sites in the late summer during the highest-algal-growth period, the annual net biomass production in the central Venice lagoon was estimated to be approximately 1 550 000 tons on a wet-weight basis. © 1993
Time trend of PCB concentrations in surface sediments from a hypertrophic, macroalgae populated area of the lagoon of Venice
No full textThe concentrations of polychlorinated biphenyls have been determined over a period of 1 year in surface sediments sampled monthly and semi-monthly in the lagoon of Venice. At the sampling station, due to the poor water circulation and an over-abundance of nutrients, macroalgae thrive in spring-summer and standing crops > 12 kg m-2 were determined. As a consequence of rapid algal decomposition, sediment PCB concentrations were observed to increase. In particular, on occasions when anoxia occurred at the end of July and all the biomass had decayed, PCB concentrations increased by more than one order of magnitude. In March, when macroalgae started to grow, concentrations were 13 ng g-1 (dry wt); in July-August they exceeded 100 ng g-1. The sediment PCB concentrations were restored to the previous values after algal biomass became negligible, in November. Concentrations of PCBs in young algae fronds were 27 ±12 ng g-1, and 121 ± 4 ng g-1. in older frondsThe concentrations of polychlorinated biphenyls have been determined over a period of 1 year in surface sediments sampled monthly and semi-monthly in the lagoon of Venice. At the sampling station, due to the poor water circulation and an over-abundance of nutrients, macroalgae thrive in spring-summer and standing crops > 12 kg m-2 were determined. As a consequence of rapid algal decomposition, sediment PCB concentrations were observed to increase. In particular, on occasions when anoxia occurred at the end of July and all the biomass had decayed, PCB concentrations increased by more than one order of magnitude. In March, when macroalgae started to grow, concentrations were 13 ng g-1 (dry wt); in July-August they exceeded 100 ng g-1. The sediment PCB concentrations were restored to the previous values after algal biomass became negligible, in November. Concentrations of PCBs in young algae fronds were 27 ±12 ng g-1, and 121 ± 4 ng g-1. in older fronds. © 1990
INFLUENCE OF WASTE-WATERS FROM THE CITY OF VENICE AND THE HINTERLAND ON THE EUTROPHICATION OF THE LAGOON
No full textFour seasonal samplings of lagoon waters were carried out during successive phases of high and low tide at stations located within Venice and its surroundings to monitor various physico-chemical parameters (pH, redox potential, temperature), salinity, nutrient concentrations (nitrogen, phosphorus, carbon compounds) and bacteria (total coliform bacteria). Salinity was used as a parameter for estimating the hydrographic distance from the Adriatic Sea, and for grouping stations into five homogeneous areas. A negative correlation was found between salinity and the concentrations of nutrients. Gradients of increasing concentrations of nutrients were observed at increasing hydrographic distance from the sea. The contributions to eutrophication of fresh waters entering the lagoon from the hinterland and of waste waters from the city have been estimated and found to be comparable. Some necessary interventions for the restoration of the lagoon are suggested. © 1990.Four seasonal samplings of lagoon waters were carried out during successive phases of high and low tide at stations located within Venice and its surroundings to monitor various physico-chemical parameters (pH, redox potential, temperature), salinity, nutrient concentrations (nitrogen, phosphorus, carbon compounds) and bacteria (total coliform bacteria). Salinity was used as a parameter for estimating the hydrographic distance from the Adriatic Sea, and for grouping stations into five homogeneous areas. A negative correlation was found between salinity and the concentrations of nutrients. Gradients of increasing concentrations of nutrients were observed at increasing hydrographic distance from the sea. The contributions to eutrophication of fresh waters entering the lagoon from the hinterland and of waste waters from the city have been estimated and found to be comparable. Some necessary interventions for the restoration of the lagoon are suggested. © 1990
Macroalgae, nutrient cycles and pollutants in the lagoon of Venice.
No full textThe Lagoon of Venice is a wide, shallow coastal basin that extends for about 50 km along the northwest coast of the Adriatic Sea. The lagoon has been substantially modified through the actions of man over the last century through the artificial control of the hydraulic dynamics of the lagoon including the construction of channels to facilitate navigation. The lagoon is subjected to considerable pollutant loading through the drainage of land under cultivation, municipal sewage, and industrial effluents. In this paper are reported the results of observations designed to document recent changes in macroalgal species composition, seasonal cycles of primary producers and nutrient levels, and the effects of the macroalgal community on concentrations of organic and inorganic pollutants. The dominant macroalgae in the lagoon was Ulva rigida, and the levels of plant nutrients and pollutants were influenced by the seasonal cycles of the macroalgal community
FLORA AND MACROALGAL BIOMASS PRODUCTION IN DIFFERENT NUTRIENT-ENRICHED AREAS OF THE VENICE LAGOON
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