A. A. Orio

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.

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.

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.

Species composition, biomass, and net primary production in shallow coastal waters: The Venice lagoon

Abstract Three areas displaying the main characteristics of the central Venice lagoon were monitored in 1989–1991 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

Historical development of the Venice lagoon contamination as recorded in radiodated sediment cores

Abstract Three cores (length 60 cm, i.d. 10 cm) collected in the most contaminated area of the lagoon of Venice (Italy) were sectioned (14, 12 and 15 sections each respectively) and analysed. Concentrations of heavy metals (Hg, Pb, Cd, Co, Cu, Zn, Cr, Ni, Fe), organic carbon, total nitrogen and total phosphorus were determined. Eh and pH profiles are discussed. Background (pre-industrial) levels for metals were estimated from the deepest sections. The principal component analysis performed on the metal concentrations, normalized on the backgrounds, revealed that two components can account for 99% of the variability. The first clearly represents the mercury pollution, the second weights the contribution of zinc and, to a lesser degree, of other metals (Cd, Cu, Co, Pb) to a contamination mainly caused by discharges of industrial tailings. Radiodating of two cores permitted us to reconstruct the historical evolution of the sediment pollution as related to the development of specific activities in the industrial zone of Porto Marghera. Total phosphorus and organic carbon accumulation was significant in the upper 10–20 cm of the cores.

Time trend of PCB concentrations in surface sediments from a hypertrophic, macroalgae populated area of the lagoon of Venice

The 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 greater than 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.

The role of alkaline phosphatase in the sediments of Venice Lagoon on nutrient regeneration

Abstract Potential alkaline phosphatase activity and nutrient concentration have been determined in the seawater, interstitial water and sediments of the most polluted area in the Venice Lagoon, at 6 stations, during three cruises performed in the October/November 1982 period, when a minimum phytoplankton standing crop existed. The relationships between parameters were established by linear regression analysis. The results clearly indicate the important role of alkaline phosphatase (APA) in phosphorus regeneration. Indeed, APA appears to be a good indicator of the degree of nutrient regeneration occurring in surface sediments on a global basis. In the Venice Lagoon a significant nutrient release from the sediments to the overlying lagoon water takes place. This process appears to be at least as important as external contributions in both establishing and controlling the concentration of the nutrients in lagoon waters.

The relation of nutrient regeneration in the sediments of the northern adriatic to eutrophication, with special reference to the lagoon of Venice

Abstract An understanding of the dominant processes leading to eutrophication in the northern adriatic requires an integrated research program on the nutrient fluxes within the regional lagoons and between the lagoons and the adjacent sea. The first phase of the joint research was focused on nutrient exchange at the sediment-water interface and primary production dynamics in the Venice Lagoon, in which the habitat quality is seriously compromised. The first results obtained are briefly described and the future joint research plans presented.

Combined preparative and analytical use of normal-phase and reversed-phase high-performance liquid chromatography for the determination of aliphatic and polycyclic aromatic hydrocarbons in sediments of the Adriatic sea

Abstract High-performance liquid chromatography (HPLC) has been used for the preparative separation of environmentally relevant aliphatic and polycyclic aromatic hydrocarbons (PAHs), and for quantifying PAHs. Normal-phase HPLC was employed as a fractionation step, whereas the quantitative determination of the PAHs was accomplished by using reversed-phase HPLC. In both cases, GC and GC/MS were used as confirmatory techniques. The concentrations of twelve unsubstituted PAHs in sixteen surface and deeper sediments, taken from the northern and central Adriatic Sea, are reported, together with an evaluation of their dependence upon the percentages of fine material and total organic carbon.