[Show abstract][Hide abstract] ABSTRACT: During the year 2002, the size variability of most of the species found in Lago Maggiore was analysed in detail, measuring
through image analysis the main morphological parameters (maximum linear dimension, surface, volume) of the algal cells. Many
individuals belonging to the same species were measured sampling by sampling, collecting about 28,000 data.
This data set allowed us to evaluate the morphological plasticity of many species across the seasonal succession: through
multivariate statistical analysis we compared the changes of cell volume, cell surface, maximum linear dimension and surface-to-volume
ratio to the fluctuations of the main physical and chemical parameters.
The responses we observed were variable, depending on the different taxonomic groups or species as well as on the morphometric
parameter considered. As a general pattern, a strong seasonality of the size changes was observed, mainly dependent on the
gradients of nutrients and temperature.
[Show abstract][Hide abstract] ABSTRACT: Two small high mountain lakes in the Alps were monitored in 1984-2003 to follow their response to changes in human impact, such as deposition of atmospheric pollutants, fish stocking and climate change. The results were compared to occasional samplings performed in the 1940s, and to the remains found in sediment cores. When monitoring started, the most acid-sensitive of them, Lake Paione Superiore, was acidified, with evident effects in its flora and fauna: benthic diatoms assemblage was shifted towards aci-dophilous species, and zooplankton lost the dominant species, Arctodiaptomus alpinus. Palaeolimnological studies outlined that lake acidification paralleled the increasing input of long-range transported industrial pollutants, traced by spherical carbonaceous parti-cles. On the contrary, the biota of Lake Paione Inferiore appeared to be mainly affected by fish stocking. In the last twenty years, de-crease in acid load from the atmosphere led to an improvement in lake water quality, with an increase in both pH and alkalinity. First signs of biological recovery were identified, such as change in diatom flora and appearance of sensitive species among benthic insects. However, climate change and episodic deposition of Saharan dust were important driving factors controlling lake water chemistry. Further monitoring to assess the effects of climate change and of the increasing load of nitrogen and other pollutants is recommended.
[Show abstract][Hide abstract] ABSTRACT: In 1996, we studied the phytoplankton seasonal succession in Lago Maggiore (N. Italy) through weekly sampling. Such a frequency enabled us to evaluate the changes of the phytoplankton assemblage in the light of the equilibrium and non-equilibrium theories. The distinct phases of changing of the species composition were identified separating the samples by means of cluster analysis and non-metric multidimensional scaling (NMDS). We recognised well distinct phytoplankton associations, whose seasonal succession followed a clear cyclic path throughout the year, with spring and summer phases respectively characterised by a rapid turn-over of the assemblages and by a relative stability. Moreover, we observed an increase of species number and Shannon-Wiener diversity during the spring, followed by a summer decline of the diversity in spite of an unchanged species number. Because of the dominance of the same few species for about two months during summer, coupled with small fluctuations of the total biomass, we could identify the summer assemblage as a steady state assemblage. The aim of the present contribution, although describing the whole seasonal succession, is to draw the attention towards the species composition at the steady state, taking into account the functional properties of the species involved. The possible role of the metalimnetic niche in selecting a particular summer assemblage in deep and large lakes will be discussed.
[Show abstract][Hide abstract] ABSTRACT: The main goal of the study presented here is to identify a repeatable pattern in the seasonal succession of phytoplankton assem-blages in Lago Maggiore. In order to fulfil this objective we analysed the phytoplaktonic succession during a five years period (1995-1999), through the calculation of the Bray-Curtis similarity index applied to biovolume data. A cluster analysis has been then applied to the distance matrix, allowing the identification of sample clusters possessing a similar species composition. The comparison, through the whole period considered, of the phytoplankton assemblages characterising each cluster allowed to recog-nise six seasonal periods (Winter, Early Spring, Late Spring, Early Summer, Late Summer, Autumn), each of them characterised by a peculiar and repeatable species assemblage. Among the most interesting findings we would mention the existence of a Late Spring/Early Summer association, dominated by Planktothrix rubescens and Fragilaria crotonensis, probably peculiar of the deep subalpine lakes, where these species can better take advantage of the physical and chemical environment of the metalimnetic niche. The identification of a pool of dominant and sub-dominant species common to other southern subalpine lakes and the existence of a similar time periodicity in the development and decline of most of them across this lake district seem to be promising in order to give our results a wider application.
[Show abstract][Hide abstract] ABSTRACT: This paper is an assessment of the changing properties of Lake Orta phytoplankton in the period 1984-1998, which includes the large-scale liming carried out in the lake in 1989 and 1990. The phytoplankton is analysed first in its general properties (abundance, biovolume, chlorophyll-a concentration, average cell size, diversity) by means of time courses of the mentioned variables based on monthly data through the entire period, and by correlations between the same variables. Moreover, through clustering techniques, the evolution of the species composition has been studied, showing the gradual decrease of chlorophytes after the liming and the no- ticeable increase of the diatom population, both as biovolume and diversity. Although the assemblage of the dominant species still mirrors the presence of some residual toxic compounds into the lake water, in the most recent period the evolution of the algal populations showed a clear trend towards a species assemblage more similar to those observed in the other deep italian subalpine lakes. After the improving of the chemical environment, the main abiotic factor that in the next years could play a major role in modifying the species assemblage is probably the phosphorus supply, whose in-lake concentration is low, despite the high annual load from the basin. A better understanding of the mechanisms underlying the phosphorus dynamics represent the basis to make reli- able hypotheses about the future evolution of the phytoplankton assemblage.
[Show abstract][Hide abstract] ABSTRACT: Diatom remains were analysed in two short sediment cores from a subalpine Italian lake (Lake Orta), known for its major industrial pollution dating from the late 1920s, which has only recently been stopped. Copper was recognised as the main toxic agent for diatoms during the first 30 years of pollution (peak value: 100 g l-1 in the late 1950s). A diatom community similar to other deep subalpine lakes existed in the past, and was disrupted by the pollution events. Acute and long-term effects of Cu contamination were tracked by changes in three distinct groups of species around the sharp boundary corresponding to the onset of the pollution. These groups were respectively composed of: (1) Species quickly extirpated by the discharge, mostly belonging to Fragilaria and Cyclotella and never reappearing; (2) Species apparently not affected, or not immediately affected, by the pollution, showing no definite trends with time. Synedra species, with various deformities, were conspicuous among these; (3) Species with accumulation rates increasing with time irrespective of pollution, mostly belonging to Achnanthes. Properties and tolerances of these groups (e.g. Synedra and Achnanthes) are discussed in detail.
Journal of Paleolimnology 11/1998; 20(4):333-345. · 2.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Lake Maggiore underwent a process of eutrophication in the course of the 1960s and 1970s which caused the lake status to change
from oligotrophy to meso-eutrophy, sewage phosphorus being the main responsible factor. Starting from the late 1970s the P
load has been gradually reduced, so that total phosphorus in-lake concentration is now below 10 µg l-1 at winter mixing, compared to a maximum value of 30 µg l-1 in 1978. Nearly two decades after the start of this reversal in trophic conditions, long-term analyses become fruitful, not
least because of a scarcity of published long-term data on lake re-oligotrophication, and consequently of agreed predictions
on specific points. This paper presents such an analysis, regarding some phytoplankton characteristics (numbers, biovolume,
cell size, chlorophyll a, species richness and composition) and their mutual relations in the time series 1981-1995, as well
as recent primary production compared with early observations. Notwithstanding phosphorus reduction, the phytoplankton remained
quite stable for many years. Only after 1987, when TP concentration fell to about 15 µg l-1 at mixing, definite changes in species diversity and composition appeared. At the same time, average cell size decreased
abruptly and persistently, together with chlorophyll and total biovolume while cell numbers were unchanged or rising. Annual
primary production was halved in comparison to a past reference period and the efficiency of the photosynthetic process was
[Show abstract][Hide abstract] ABSTRACT: We report here the results of four scientific expeditions in the Nepalese Himalayas, that were carried out in the period 1992-1997, in the framework of a Project on "The Long Dis- tance transport of micro-pollutants" (Ev-K2-CNR). Logistic and technical support was given by a laboratory located at 5050 m a.s.l. Phytoplankton, zooplankton and macrozoobenthos were collected from a total of 28 lakes, at altitudes between 4532 and 5580 m a.s.l. Very few phytoplankton species were found in high numbers. As expected, no phytoplankton communi- ties nor algal species characteristic of high altitude sites were found, being in general high mountain environments characterized by a rarefaction of the communities with respect to low altitude sites. We found low chlorophyll-a and biomass values, with a high contribution by small species. Data from the intensive sampling of Lake Piramide Inferiore in late summer 1993, suggest that net phytoplankton was at that time of the year already in a declining phase. An intense growth had probably occurred earlier in the season, possibly just after the ice- melting. We identified 9 species of Crustacea and 8 of Rotifera from the 26 lakes sampled for zooplankton. The most widely distributed was an endemic, well-known diaptomid of the pa- laeoarctic genus Arctodiaptomus (Arctodiaptomus jurisovitchi). Daphniidae were repre- sented by the dark-brown Daphnia tibetana and Simocephalus vetulus, and a pale Daphnia of the longispina group. A melanic Chydorus sphaericus was also widely distributed, with both parthenogenetic and ephippial females, as well as males. Rotifers were found in high numbers in lakes of the western side of the Region, with both genuine high mountain species, (Hexar- thra bulgarica var. nepalensis, Filinia maior), as well as the colonial Conochilus unicornis, never reported before. Anostraca, recovered from the littorals of two lakes, were identified as Branchinecta orientalis. We also counted the thecamoebian species occasionally found in some zooplankton samples. Three chironomid genera (Pseudodiamesa, Orthocladius and Mi- cropsectra) and oligochaetes dominated the communities of the nine examined lakes. We found two species of Diamesinae, already reported from the Region, and two larval forms of Micropsectra. All the genera of Orthocladiinae previously recorded in the Region, were pres- ent, namely, larvae and pupae of Cricotopus, as well as Acricotopus and Pseudosmittia. In most lakes Oligochaeta were represented by Lumbriculidae. Enchytraeidae and a Tubificid species, probably belonging to Rhyacodrilus cf. stephensoni, were also recovered from the littoral of some lakes.
[Show abstract][Hide abstract] ABSTRACT: Here we present the first edition of the "Khumbu Himal lake cadastre" build in the framework of the Ev-K2-CNR Strategic Project. The cadastre consists of 90 high altitude lakes, here we present the 69 lakes that was visited and sampled during scientific expedition between 1989 and 1997 in order to collect data on geology, chemistry and biology.