J.T. Lehman.
We learned how to live in Pallanza.

1-4

E. Suárez-Morales, M. Silva-Briano and M. Elías-Gutiérrez.
Redescription and taxonomic validity of Leptodiaptomus cuauhtemoci (Osorio-Tafall, 1941) (Copepoda, Calanoida), with notes on its known distribution

5-14

M. Manca and P. Comoli.
Biomass estimates of freshwater zooplankton from length-carbon regression equations

15-18

O. Ravera.
The Lagoon of Venice : the result of both natural factors and human influence

19-30

A. Lami, A. Marchetto, R. Lo Bianco, P.G. Appleby and P. Guilizzoni.
The last ca 2000 years palaeolimnology of Lake Candia (N. Italy): inorganic geochemistry, fossil pigments and temperature time-series analyses

31-46

R. Mosello, A. Marchetto, M.C. Brizzio, M. Rogora and G.A. Tartari.
Results from the Italian participation in the International Co-operative Programme on  Assessment and Monitoring of Acidification of Rivers and Lakes (ICP Waters)

47-54

R. Baudo, P. Barbero, M. Beltrami and D. Rossi.
Chemical composition of the sediment from Lake 20 (Antarctica)

55-60

D. Tait and B. Thaler.
Atmospheric deposition and lake chemistry trends at a high mountain site in the eastern Alps

61-71

C. Callieri and J. Stockner.
Picocyanobacteria success in oligotrophic lakes: fact or fiction?

72-76

We learned how to live in Pallanza.
J.T. Lehman.

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Redescription and taxonomic validity of Leptodiaptomus cuauhtemoci (Osorio-Tafall, 1941) (Copepoda, Calanoida), with notes on its known distribution
E. Suárez-Morales, M. Silva-Briano and M. Elías-Gutiérrez.

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Within the American freshwater calanoid copepods, Leptodiaptomus includes species whose taxonomical status is still unclear. One of them is L. cuauhtemoci (Osorio-Tafall), for decades considered to be a synonym of L. siciloides (Lilljeborg); another species involved in this problem is L. assiniboiensis (Anderson & Fabris) described from Canada, which had been found to be closely related to L. cuauhtemoci. This species remained of uncertain taxonomy because the type material was lost decades ago. In order to disen­tangle this controversy, type specimens of L. assiniboiensis, topotypic specimens of L. cuauhtemoci from a National Park in central Mexico, and confirmed specimens of L. siciloides from different locations in Mexico and the United States were used to define the status of these species. Leptodiaptomus cuauhtemoci was fully redescribed using SEM. Based on the main characters used to diffe­rentiate species of Diaptomidae, L. assiniboiensis (= Diaptomus intermedius Anderson & Fabris) turned out to be conspecific and a junior synonym of L. cuauhtemoci, which then becomes the valid name. The latter species shows taxonomically relevant differences with respect to L. siciloides. In the females the main differences is that the lateral spiniform processes on the genital somite are broader-based in L. cuauhtemoci, the genital field is different in both species. In L. cuauhtemoci the fifth leg endopods bear two large, broad, subterminal setae of about the same size, differently built than in L. siciloides. The male L. cuauhtemoci is slenderer, with wings of pediger 5 clearly more developed than those of L. siciloides. The armature of the modified right antennules and the structure of the fifth leg differ in both species. A large coxal spine is present on the right fifth leg of L. siciloides, whereas it is absent in L. cuauhtemoci. These differences were considered to be enough evidence for recognizing L. cuauhtemoci as a separate, valid species. Topotypic specimens of L. cuauhtemoci are designated as neotypes.

Biomass estimates of freshwater zooplankton from length-carbon regression equations
M. Manca and P. Comoli.

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We present length/carbon regression equations of zooplankton species collected from Lake Maggiore (N. Italy) during 1992. The results are discussed in terms of the environmental factors, e.g. food availability, predation, controlling biomass production of parti­cle- feeders and predators in the pelagic system of lakes. The marked seasonality in the length-standardized carbon content of Daphnia, and its time-specific trend suggest that from spring onward food availability for Daphnia population may be regarded as a simple decay function. Seasonality does not affect the carbon content/unit length of  the two predator Cladocera Leptodora kindtii and Bythotrephes longimanus. Predation is probably the most important regulating factor for the seasonal dynamics of their carbon biomass. The existence of a constant factor to convert the diameter of Conochilus colonies into carbon seems reasonable for an or­ganism whose population comes on quickly and just as quickly disappears.

The Lagoon of Venice : the result of both natural factors and human influence
O. Ravera

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This paper aims to present a picture of the lagoon of Venice and analyze the combined effects of natural factors and human in­fluence on this fragile ecotone. The structure, functioning and evolution of the lagoon are illustrated. Under natural conditions, the solid load from the tributaries would transform the lagoon into dry land or, if the violence of the sea exceeded the solid load from the watershed, the lagoon would evolve into a marine bay. This natural succession has been hindered by the works undertaken by the Republic of Venice uninterruptedly through the centuries, because the lagoon environment was essential to the life and power of Venice. The effects of human activities from the beginning of the Venetian Republic to the present are described. In addition, the in­fluence of socio-economic development on the lagoon area and, particularly, the impact of intensive agriculture and industrialization are discussed. A possible effect of eutrophication was the dramatic proliferation of the opportunistic macroalga Ulva rigida, which for about a decade played an important role in the physical, chemical and biological characteristics of the lagoon. At present, the most crucial problems of Venice and its lagoon are: the lowering of the level of the city in relation to that of the sea, the continuous decline in the number of inhabitants, the increasing frequency of the “high water” phenomenon, air and water pollution, and the in­creased erosion and salinity of the lagoon. The recent measures taken and those still to be applied for conserving and recovering Venice and its lagoon and, particularly, the works for preventing the risk of high water are compared. There is an evident need for a new type of socio-economic development in symbiosis with the environment and tradition of Venice.

The last ca 2000 years palaeolimnology of Lake Candia (N. Italy): inorganic geochemistry, fossil pigments and temperature time-series analyses
A. Lami, A. Marchetto, R. Lo Bianco, P.G. Appleby and P. Guilizzoni.

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The palaeoenvironmental history of Lake Candia, a small, shallow, eutrophic lake in Northern Italy, is described for the last ca 2000 years. Sediment samples from a sediment core collected in autumn 1995 were analysed for a range of palaeolimnological indi­cators, which included the principal algal and sulphur photosynthetic bacterial pigments, as well as magnetic susceptibility, organic matter, carbonates, organic carbon, total nitrogen, total sulphur and various forms of phosphorus. An accurate sediment chronology was determined using ²¹⁰Pb, ¹³⁷Cs and ¹⁴C. The results show that throughout a first, long phase of the history of this period (from ca AD 100 to 1830; zone 1) the sediments have an organic carbon content of ca 10% d.w. and low concentrations of algal pigments, suggesting a moderately productive environment. Sedimentary carotenoids unique to anaerobic photosynthetic bacteria indicate a seasonally hypolimnetic anoxia during the whole ca 2000 year period. Clear effects of climate changes on lake productivity were in­ferred from the carotenoid, ß-carotene, okenone and organic carbon estimates. Values were higher in the warm periods before AD ca 660 and during the so-called Little Optimum of the Medieval Warm Epoch (AD ca 1100-1300), and lower during cold moist periods, such as the main phase of the Little Ice Age (AD ca 1550-1700). After AD ca 1830 (zone 2), anthropogenic impacts resulted in a sharp increase in lake trophic state, leading first to a decoupling of the trophic state from natural (climate) variability, and then to "cultural" eutrophication. The onset of this latter process in the Turin area has been set around 1830, when a sharp increase of sedimentary sulphur concentration took place.

Results from the Italian participation in the International Co-operative Programme on Assessment and Monitoring of Acidification of Rivers and Lakes (ICP Waters)
R. Mosello, A. Marchetto, M.C. Brizzio, M. Rogora and G.A. Tartari.

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This paper describes the research activity carried out by the Istituto Italiano di Idrobiologia of the CNR, on behalf of the Minis­tero dell'Ambiente, Servizio Inquinamento Atmosferico e Acustico, in the context of the Italian participation in the International Co-operative Programme on Assessment and Monitoring of Acidification of Rivers and Lakes (ICP Waters). Atmospheric deposition chemistry shows that nitrate increased and sulphate decreased in the 70's and 80's, while acidity started to decrease in the early 90's. The studied rivers and lakes show variations in sulphate and nitrate in agreement with those of atmospheric deposition. Alkalinity is mainly determined by watershed geo-lithology and is always present in the studied lakes and streams; the lowest values of 0-10 µeq l^-1 are measured in the high altitude Lake Paione Superiore, which however shows an increasing trend of alkalinity and pH.

Chemical composition of the sediment from Lake 20 (Antarctica)
R. Baudo, P. Barbero, M. Beltrami and D. Rossi.

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Lake 20 (19,000 m²) is located on the coast of the Ross Sea, in the North-Central part of Victoria Land, and its surface is ice-free between the end of December and early February. Within the framework of the Italian National Research Programme in Antarctica, a study was made of the chemical composition of sediments from the lake, with the intention of using this information to contribute to a better understanding of the processes involved in the long range transport of pollutants and their role in global changes. A sedi­ment core from Lake 20 (Antarctica), 18 cm long, was collected in 1994, sliced into 2 cm sections and analysed using X Ray fluore­scence spectrometry for 17 elements (Si, Al, Ca, K, Fe, Mg, Ti, S, P, Pb, Zn, Cu, Ni, Mn, Cr, Na, Cl), by CHN Elemental Analyser for C and N, by Flameless Atomic Absorption Spectrometry for As, and by Cold Vapour Atomic Absorption Spectrometry for Hg. The chemical composition of the sediments is consistent with the known geochemical characteristics of the drainage basin. While the chemical analyses reveal that sedimentation in Lake 20 has changed through time, the variations along the core are most probably related to the climatic evolution of the area, to the consequent changes in weathering processes, and possibly to an increase in the primary productivity of the lake, rather than to anthropogenic influences on the biogeochemical cycles of the elements.

Atmospheric deposition and lake chemistry trends at a high mountain site in the eastern Alps
D. Tait and B. Thaler.

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Records of atmospheric precipitation chemistry starting in 1983 and a series of limnological investigations at two high mountain reference lakes starting in 1988 enable us to describe the response of lake water chemistry to changes in precipitation chemistry and climate. The lakes are located at an altitude well above the timberline in a watershed composed of acidic rocks. Despite the observed reduction in the sulphur atmospheric deposition, the reference lakes showed no corresponding decline in sulphate concentrations, but a marked increase in the acid neutralising capacity was apparent. Changes of the seasonal distribution pattern of the precipita­tion amounts and a general increase of the air temperature have likely produced an increased weathering which increased the con­centration of many inlake solutes and drove the lakes toward more buffered conditions. This phenomenon superimposed to changes like other physical factors (radiation), nutritional conditions and biological factors (enhanced production, competition, predation) has produced in the last years greater modifications than merely those to be expected from the decreased acidic input.

Picocyanobacteria success in oligotrophic lakes: fact or fiction?
C. Callieri and J. Stockner.

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Two approaches may be utilized to explain the predominance of picocyanobacteria (Pcy) in oligotrophic lakes: the analysis of their interannual evolution in one single lake and their relative importance in different lakes along a trophic gradient. Here we di­scuss results from field data on picocyanobacteria over several seasons from a deep oligotrophic subalpine lake - Lago Maggiore, and variables influencing their abundance. Comparing data from lakes along a trophic gradient, no simple relationship emerges between lake’s trophic state and picocyanobacteria abundance and contribution to total phytoplanktonic biomass. That is, trophic state alone cannot explain the success/absence of picocyanobacteria that appear to be favored under P limitation, but seem more sensitive to grazing pressure and light. In some oligotrophic lakes, if light climate, grazing, and competition are favorable, picocya­nobacteria can grow rapidly, out-compete competitors and become very abundant, but there are a host of factors that can influence the outcome of this competition, and ultimately influence Pcy success in lakes of all trophic types.