Bruno Pavoni

Macroalgae, nutrient cycles, and pollutants in the lagoon of Venice

The 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 laggon 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 wasUlva rigida, and the levels of plant nutrients and pollutants were influenced by the seasonal cycles of the macroalgal community.

Relationships between macroalgal biomass and nutrient concentrations in a hypertrophic area of the Venice Lagoon

Abstract Macroalgae biomass and concentrations of nitrogen, phosphorus and chlorophyll a were determined weekly or biweekly in water and sediments, during the spring-summer of 1985 in a hypertrophic area of the lagoon of Venice. Remarkable biomass production (up to 286 g m −2 day −1 , wet weight), was interrupted during three periods of anoxia, when macroalgal decomposition (rate: up to 1000 g m −2 day −1 ) released extraordinary amounts of nutrients. Depending on the macroalgae distribution in the water column, the nutrients released in water varied from 3·3 to 19·1 μg-at litre −1 for total inorganic nitrogen and from 1·8 to 2·7 μg-at litre −1 for reactive phosphorus. Most nutrients, however, accumulated in the surficial sediment (up to 0·640 and to 3·06 mg g −1 for P and N respectively) redoubling the amounts already stored under aerobic conditions, Phytoplankton, systematically below 5 mg m −3 as Chl. a , sharply increased up to 100 mg m −3 only after the release of nutrients in water by anaerobic macroalgal decomposition. During the algal growth periods, the N:P atomic ratio in water decreased to 0·7, suggesting that nitrogen is a growth-limiting factor. This ratio for surficial sediment was between 6·6 and 13·1, similar to that of macroalgae (8·6–12·0).

Heavy metal contamination in the seaweeds of the Venice lagoon

The concentrations of heavy metals (Fe, Zn, Cu, Cd, Ni, Pb, Cr, As) were determined in seven seaweeds of environmental and commercial relevance (Ulva rigida C. Ag., Gracilaria gracilis (Stackhouse) Steentoft, L. Irvine and Farnham, Porphyra leucosticta Thuret, Grateloupia doryphora (Montagne) Howe., Undaria pinnatifida (Harv.) Suringar, Fucus virsoides J. Agardh, Cystoseira barbata (Good. et Wood.) Ag.) collected in four sampling sites in the lagoon of Venice, in spring and autumn 1999. Metals were extracted using hot concentrated acids in a Microwave Digestion Rotor and analysed by absorption spectrophotometry using a flame mode for Fe and Zn and a graphite furnace for Pb, Cr, Cd, Cu, Ni and As. High contamination levels, especially for Pb, were detected in Ulva and to a lesser extent in Gracilaria. Brown seaweeds, especially Cystoseira was highly contaminated by As. The least contaminated genera with all metals except As were Porphyra and Undaria. A concentration decrease for Zn and Cd was observed from the inner parts of the central lagoon, close to the industrial district, towards the lagoon openings to the sea.

Correlation between inorganic (heavy metals) and organic (PCBs and PAHs) micropollutant concentrations during sewage sludge composting processes

The nature and congener composition of PCBs and PAHs present in sewage sludge composting processes was investigated. These studies included analysis of the most significant process parameters (such as pH, temperature, weight percentage variation) and in addition heavy metals whose typical composting speciation and behaviour were also considered in order to better understand organic compound time profiles. The significant correlation found between Pb, Cd, Cu and PCBs and between PAHs and Hg implies that quite a strong adsorption of PCBs onto organic matter takes place and also provides evidence for the volatilisation of PAHs. Chemical characteristics of inorganic species and organic compounds are summarised to account for the observed correlation and time trend profiles. Moreover, single congener concentrations demonstrate that the number of Cl substituents for PCBs and condensed benzene rings for PAHs determine to what extent they can be broken down for biodegradation and removed through volatilisation respectively.

Persistent metabolites of alkylphenol polyethoxylates in the marine environment

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.

Annual variations of nutrients in the Lagoon of Venice

Abstract Nutrient concentrations (P, N compounds and C org ) 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.

Macroalgae and phytoplankton standing crops in the central Venice lagoon: Primary production and nutrient balance

Biomass measurements carried out in the central part of the Venice lagoon during the season of the highest macroalgal production, at the beginning of June 1987, showed that 85 km2, corresponding to 65% of the examined area, were covered by remarkable amounts of nitrophile macroalgae. Total macroalgal biomass was 546 900 tons, accounting for 17 679, 1911 and 170 tons of carbon, nitrogen and phosphorus, respectively. The annual net primary production, calculated from the maximum production/biomass (P/B) ratio determined in a hypertrophic area of the central lagoon, was estimated to be 866 160–1154 880 tons (wet wt). Therefore, in Spring-Summer, macroalgae recycled 78–104% and 38–51% of the total annual nitrogen and phosphorus which entered the central lagoon. Phytoplankton standing crop appeared negligible in most of the studied area. High chlorophyll-a concentrations were only measured near the Porto Marghera industrial zone where macroalgae were almost absent; in the area between the islands of S. Angelo and Gidecca, where the water depth was > 1 m; and in the area facing the island of Lido used by the Municipality of Venice as a test area for algal removal experiments. Based on both space and time measurements, nanoplankton accounted for about 80% of the total phytoplankton.

Macroalgae and phytoplankton competition in the central Venice lagoon

Abstract The presence‐absence of macroalgae and/or phytoplankton in some areas of the Venice lagoon and the factors controlling the prevailing of one over the other were tested by monitoring two critical sites over March‐December 1990. One, Sacca Sessola [B1], was the lagoon area more densely populated by macroalgae, vice versa the other, namely Fusina [D] displayed only phytoplankton blooms. For this purpose macroalgae and phytoplankton biomass variations were studied directly in field. In addition, macroalgal biomass growth was studied by resuspending pre‐determined biomass amounts into net cages placed at different depths. These semi‐natural methods were not able to reproduce the real algal growth, however allowed to identify the main causes of phytoplankton blooms and macroalgal absence at Fusina.

Heavy metal contamination in surface sediments from the Gulf of Venice, Italy

Abstract The authors studied surface sediments from 102 stations in four areas of the three port entrances to the Lagoon of Venice, examining the relationships between textural character, mineralogical composition, and Hg, Pb, Cd, Cu, Ni, Cr, Zn, Co and Fe content. Heavy metal distribution allowed boundaries to be fixed between polluted and nonpolluted zones. While the Cavallino area is not polluted, very high concentrations of Zn, Pb and Hg in the two central areas, facing the Lido and Malamocco port entrances, respectively, suggest that wastes mainly from industrial production of zinc are present. High concentrations of Cr in the southern part of the Chioggia area are probably due to tannery wastes reaching the sea from the Brenta river.

Sediment toxicity measured using Vibrio Fischeri as related to the concentrations of organic (PCBs, PAHs) and Inorganic (metals, sulphur) pollutants

Sediments of the inner canals of the city of Venice (Italy) contain heavy metals and organic contaminants. In order to assess the toxicity of these compounds the Microtox® test was applied to the whole sediment (solid-phase test) and to organic extracts containing separated classes of compounds (i. e. PCBs and PAHs). This study showed that results of solid-phase tests may be correctly interpreted only if supported by results obtained with tests on extracts, An efficient of sulfur and Fe was measured with solid-phase tests of sediments, while an EC50 value for PAHs was detected in tests with organic extracts. The sediment concentrations of heavy metals and PCBs resulted lower than the sensitivity limits of Microtox® test for these compounds.