Journal of Limnology

(formerly Memorie dell'Istituto Italiano di Idrobiologia)

vol. 60 (1), 2001

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J.L. NOTES

LAKE ORTA: A CASE STUDY (Part 1)

1
Life history traits in Darwinula stevensoni (Crustacea: Ostracoda) from Southern European populations under controlled conditions and their relationship with genetic features

Andrea GANDOLFI, Eletta B.A. TODESCHI, Valeria ROSSI and Paolo MENOZZI

We describe life history traits of the ostracod Darwinula stevensoni through laboratory experiments. This small (about 0.7 mm), ancient, obligate parthenogenetic species appeared to be particulary difficult to handle as its long life cycle (up to 3-4 years) has made lab experiments over several generations very difficult. D. stevensoni is an eurythermal and euryhaline species with low vari­ability in size and shape (both of the carapace and the soft parts). Its genetic variability has also been found to be very low. Survival, clutch size, deposition timing and hatching were evaluated in acclimated and non-acclimated females from seven populations: six from Northern Italy and one from Spain. The samples were collected from three different habitats: four lakes, two streams and one spring. A genetic survey using starch gel electrophoresis had previously revealed that only Glucose phosphate isomerase (Gpi) locus was polymorphic. A clone, homozygous at Gpi locus, is the most common in lacustrine and spring habitats in the whole bio­geographic range. Surprisingly, two heterozygous clones dominate in Northern Italian lotic environments. Enzymatic activity of het­erozygous and homozygous genotypes at Gpi locus was assayed in order to evaluate the relationship between Gpi activity and fit­ness. Survival and developmental time were not affected by acclimation, while reproductive potential decreased in acclimated fe­males. In females from running waters, reproduction started later and lasted for a shorter time, clutch size was smaller, and hatching percentage lower than females from lakes. These differences are not directly correlated with differences in enzymatic activities at Gpi locus. This does not rule out an overall genetic control of these characteristics since, in a parthenogenetic species, the whole ge­nome is transmitted without recombination. We stress the intriguing case of D. stevensoni in relation to the concept of the "general purpose genotype". 

2
On the taxonomical status of Arctodiaptomus dampfi Brehm (Crustacea: Copepoda: Diaptomidae) with comments on A. dorsalis (Marsh)

Eduardo SUÁREZ-MORALES and Manuel ELÍAS-GUTIÉRREZ

Arctodiaptomus dampfi Brehm is a diaptomid copepod described from Lake Petén, in Guatemala. Due to the fact that the type material is lost and no additional material was available, the taxonomical status of this species remained unclear for more than 65 years. Arctodiaptomus dampfi has been advanced as a synonym of A. dorsalis and some authors followed this position; instead, others recognized this species in regional checklists. We collected zooplankton samples at Lake Petén, A. dampfi type locality, and compared this material with confirmed museum specimens and material from Louisiana, the type locality of A. dorsalis. Our obser­vations with light microscopy and SEM allowed us to state that A. dampfi is in fact a synonym of A. dorsalis and should be excluded from regional lists. This was concluded after examination and comparison of the taxonomically relevant structures in both groups of specimens. Differences between both groups of specimens were slight. We found significative size differences between the Guatema­lan population and the other neotropical and nearctic ones, the former being the smallest sized populations known throughout the known distributional range of A. dorsalis.

3
Comparison between sedimentary and living diatoms in Lago Maggiore (N. Italy): implications of using transfer functions

Aldo MARCHETTO and Simona MUSAZZI

We compared the recent history of living planktonic diatom assemblages in Lago Maggiore with the remains found in the top­most section of 14 sediment cores taken from the lake. Sediment samples showed a marked domination of planktonic taxa, but a sig­nificant proportion of benthic taxa was found in cores collected close to river mouths. Between-core variability in diatom assemblage and in diatom-inferred total phosphorus concentration was also estimated. The implications of our results for calibration data sets relating environmental variables to diatom assemblages are also discussed.

4
Nitrogen budget of Lago Maggiore: the relative importance of atmospheric deposition and catchment sources

Rosario MOSELLO, Alberto BARBIERI, Maria Cristina BRIZZIO, Alcide CALDERONI, Aldo MARCHETTO, Stefania PASSERA, Michela ROGORA and Gabriele TARTARI

Hydrological and chemical data of 1996 and 1997 are used to evaluate the relative contributions of atmospheric deposition and urban/industrial wastewaters to the nitrogen budget of Lago Maggiore. The atmospheric load of nitrogen was about 80% of the total input to the lake, with negligible variations in dry (1997) and wet (1996) years. A comparison of the two study years with the yearly N budgets evaluated from 1978 to 1998, showed that the N load was higher with increasing amounts of precipitation/water inflow. Soils and vegetation act as N sinks; the % retention varies between 40-60% for the forested catchments with low population density in the central-northern part of the basin, to values close to zero or even negative in the south, indicating a net leaching from the soils. The Traaen & Stoddard (1995) approach revealed that all the catchments of the major inflowing rivers were oversaturated with nitrogen. The long-term trend of nitrogen concentrations in Lago Maggiore (1955-99) is analogous to the trend for atmospheric deposition (1975-99), which is related to emissions of nitrogen oxides and ammonia in the atmosphere. The relationships between the present N load and in-lake concentrations are discussed using a budget model, which is also used to infer the pristine load of N. The close relationships between N trends in lakes Maggiore, Como and Iseo, and the geographical and anthropogenic features com­mon to their catchments, suggest that the results obtained for Lago Maggiore can be extended to a wider area.

J.L. NOTES

5
Resurgence of human bothriocephalosis (Diphyllobothrium latum) in the subalpine lake region

Raffaele PEDUZZI and Renata BOUCHER-RODONI

Human bothriocephalosis is once again being found in various catchment basins in the subalpine region, including Lago Mag­giore and Lac Léman, which however are not isolated cases. Domestic animals are thought to be responsible for the survival of the parasite during the period when no human cases were reported. The new phenomenon of eating raw or poorly cooked fish is respon­sible for the resurgence of human bothriocephalosis, which affects various lake districts in Europe. This habit of eating raw fish might lead to the resurgence of a much more dangerous human parasitosis, transmitted in a similar way: infestation by Anisakis.

J.L. NOTES

6
Updating Anostraca (Crustacea, Branchiopoda) distribution in Italy

Graziella MURA

In this note recent records of some Anostraca species in Italy are presented. These data widen the known distribution in Italy of Branchipus schaefferi Fischer, 1834, Tanymastix stagnalis Linnaeus, 1758, Chirocephalus ruffoi Cottarelli & Mura, 1984 and Bran­chinella spinosa Milne-Edwards, 1840, and illustrate the problem of inadequate knowledge of our territory, at least as far as Anostraca (Branchiopoda) are concerned.

7
Lake Orta: a case study (Part 1)

Carla BONACINA and Renato BAUDO

Preface

The extraordinary case of industrial pollution in Lake Orta was followed and documented by the Istituto Italiano di Idrobiologia from its very origin in 1926. Many papers were published regarding the effects of the pollution on chemistry and biology of the lake but they were scattered in various scientific journals and in a long time period. Now the time has come to draw the conclusions of our long work and the long history of the lake.

We planned to publish a monographic volume, but technical reasons made it impossible to realise this project. The papers which could have formed the volume will be splitted into issues 60(1) and 60(2) of Journal of Limnology.

8
Lake Orta: the undermining of an ecosystem

Carla BONACINA

From 1927 to 1986 Lake Orta (North-western Italy) received loadings coming from a rayon factory, rich in copper and ammo­nium sulphate. Immediately after the onset of pollution, the food web was destroyed: first phytoplankton, then zooplankton, and fi­nally fish and ultraplankton disappeared from the lake. Twenty years later a rise in nitrate nitrogen and copper ions was recorded and in the early sixties ammonium nitrogen started to accumulate and pH to fall. In the meanwhile, a poorly structured biological community appeared, mainly composed of Cyclops abyssorum (copepod), Hexarthra fennica (rotifer) and Coccomyxa minor (green alga). Fish and benthonic animals were still absent. In 1986 the ammonium loading was substantially reduced (copper had been partially recovered since 1956), so that the in-lake ammonium concentration began to decrease. Some phyto- and zooplankton as well as benthic species were recorded in this period. Nevertheless, as pH was still very acid and alkaline reserve absent: a proposal to lime the lake was accepted and funded by regional authorities. Liming was performed in May 1989-June 1990 and resulted in a real improvement of the environment.

9
Temperature, heat content, mixing and stability in Lake Orta: a pluriannual investigation

Walter AMBROSETTI and Luigi BARBANTI

This paper describes the overall state of some physical phenomena occurring in Lake Orta, such as thermal stratification and de-stratification, accumulation and release of heat, vertical winter mixing, and stability of the water mass. The historical series of tem­perature distribution along the water column in the period 1984-1999, from which the holo-oligomictic character of Lake Orta emerges, is analysed. The monthly evaluation of the heat contents metre by metre from 0 to 143 m depth reveals how the complete winter mixing occurs only when the energy present within the whole column is less than 1,675 MJ m^-2; above this value the circula­tion is only partial, as in the other deep subalpine lakes. A water layer in the deep hypolimnion has been shown to contain a climatic memory, which has generally increased since 1981. Walker’s stability analysis has revealed that when at a depth below 90 metres there is a level where 0.07 J m^-2 are exceeded, total mixing cannot take place. In contrast, the Birgean work identifies, during the heating phase, the layers of the lake where energy is stored or lost.

10
Evolution of the water chemistry of Lake Orta after liming

Alcide CALDERONI and Gabriele A.TARTARI

Since 1963 Lake Orta has been an emblematic case of industrial pollution by heavy metals and acidifying compounds (ammo­nium sulphate), to the extent that up to 1989 it was the largest acidified deep lake in the world. The low pH values of between 3.9 and 4.4 helped to keep high the levels of toxic compounds in solution, such as copper, aluminium, zinc and nickel. The liming performed in 1989-1990 brought the pH back to neutral values, determining the precipitation of the metals and the recovery of normal chemical conditions. The main results of researches conducted continuously on the lake water chemistry from 1988 to March 2000 are as fol­lows. The whole water mass has been completely neutralised since the beginning of 1991; pH subsequently rose until in 1999-2000 it reached the values (6.7-6.9 units) of the years when the lake was in a natural condition. The alkaline reserve showed a continuous increase after the lake water was neutralised, until March 2000, when total alkalinity values levelled off at 0.19 meq l^-1. The increase in pH has allowed a full recovery of nitrification processes; in fact, during the liming period the concentration of ammonium was drastically reduced, by over 80%; ammonium has been practically absent since the end of 1992, and it may be affirmed that the pri­mary cause of the acidification of the lake has been completely removed. The nitrate content in the lake has almost halved compared with the mean concentrations measured before the liming; in March 2000 mean values of 2.0 mg N l^-1 were measured, and it is likely that these values will fall further in the next few years, to below 1.5 mg N l^-1. The concentrations of toxic metals have shown a pro­gressive reduction, to the extent that in 1999 the content of copper and aluminium was close to zero in the whole water mass. The situation of Lake Orta has therefore improved enormously, and is now very similar to the original condition of the lake before it was polluted. However, this situation cannot be regarded as definitive, as a stable balance between the input and output of some impor­tant chemical species, such as bicarbonate and nitrogen compounds has not yet been achieved. Moreover, recent investigations have revealed that insufficiently treated industrial and urban waste is once more being dumped in the lake. In this situation there can be no doubts as to the necessity for continuing research on Lake Orta, not only to document the evolution of the chemical and biological characteristics of the lake, but also to verify the effectiveness of the treatment measures adopted and to determine the need for ex­tending these measures to the whole watershed. In particular, the object of this research should be to quantify, control and reduce to an acceptable level the incoming loads of a) ammoniacal nitrogen, to eliminate the danger of the lake water becoming re-acidified; b) phosphorus, to prevent the onset of eutrophication processes; c) heavy metals, to minimise their toxic effects on the whole aquatic ecosystem.

11
Gases (CH₄, CO₂ and N₂) and pore water chemistry in the surface sediments of Lake Orta, Italy: acidification effects on C and N gas cycling

Donald D. ADAMS and Renato BAUDO

Lake Orta, a subalpine, warm monomictic lake in northwestern Italy was heavily polluted from rayon factory discharges of am­monium and copper since 1926. In the 1950s accumulations of contaminants resulted in whole lake pHs of 3.8-4.0 from ammonium oxidation. Partial remediation started in the 1950s, but by 1985-89 the water remained acidified at pHs of 4.0. Artificial liming (14,500 t) in 1989-90 resulted in improved water quality and substantial recovery of the biological community. Sediment gases, sam­pled in 1989 before liming, from the lake's four basins showed severe inhibition of methanogenesis (CH₄ = 0.0-0.15 mM) in the sur­face sediments (0.5-5 cm) of the southern basin, location of the plant effluent, as compared to the deep central and northern basins (0.9-1.4 mM). Four years after liming, cores collected in 1994 near the 1989 southern basin sites showed a slight change in surface sediment methane (0.07-0.82 mM), yet suggested continual sediment toxicity, at least to carbon cycling through methanogenesis. Calculations of diffuse flux of CH₄ at the sediment-water interface (SWI) in 1989 were 6.6-7.4 mM m^-2 day^-1 for the central and northern basins and 0.13 for the southern basin. CH₄ fluxes increased 16x to 2 mM m^-2 day^-1 in 1994 in the southern basin, possibly from remediation of near surface sediments. The impact of pollution on denitrification (formation of sediment N₂ gas) was not so ob­vious since two processes could counteract each other (high NO₃^- stimulating denitrification versus possible negative effects from acidity and metals). The calculated flux of N₂ from the southern basin sediments increased 5x four years after liming compared to the period of acidification, suggesting possible toxicity towards denitrifiers during the earlier period. Core overlying water (0.68 mM) exhibited N₂ concentrations close to saturation, while most surface sediments were twice as much (1.5 mM). Surface (0-6 cm) sedi­ment N₂ was similar at most sites, with the exception of 0.82 mM in the low porosity sediments of the Omegna basin at the lake’s outlet. The calculated diffuse flux of N₂ at the SWI averaged 4 mM m^-2 day^-1 for the entire lake and varied between 1.3 at Omegna to 7.3 at the Central basin. It is suspected that surface sediment N₂ production from denitrification and subsequent flux from sediments to overlying waters should resolve much of the deficit in the mass budget for water column nitrogen during the acidification period where only 35 percent of the ammonium oxidation could be accounted for as nitrate.

12
Trends of phytoplankton characteristics and their communities in pre- and post-liming time in Lake Orta (1984-1998)

Giuseppe MORABITO, Delio RUGGIU and Pierisa PANZANI

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 no­ticeable 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 reli­able hypotheses about the future evolution of the phytoplankton assemblage.

13
Zooplankton of Lake Orta after liming: an eleven years study

Carla BONACINA and Andrea PASTERIS

Lake Orta (N. Italy) was severely polluted from 1927 by an effluent from a rayon factory, which discharged great amounts of ammonium nitrogen and copper into the lake. In the mid nineteen fifties, some plating factories also started dumping chromium and aluminum. As a result of ammonium oxidation, the lake became very acid and the concentration of metals in the waters reached very high values. Phytoplankton, zooplankton and fish disappeared suddenly from the lake which was by 1930 classified as “sterile”. Later on, about the fifties, a small population of Cyclops abyssorum re-colonised the lake together with some rotifers, in particular Hexarthra fennica. In mid eighties following the introduction of anti-pollution legislation, ammonium loads were greatly reduced and Daphnia obtusa was recorded. The lake waters however were still very acid, prompting the proposal of the Istituto Italiano di Idro­biologia to lime the lake with calcium carbonate to neutralise the excess acidity and reconstruct the alkaline reserve. This was done successfully from May 1989 to June 1990. pH values began to rise and in the same time the metal concentrations decreased, so that at present the lake waters are almost “normal”. In the meantime, due to the increased pH values, D. obtusa was replaced by D. lon­gispina and, as toxic metal concentrations became lower, Megacyclops viridis, Bosmina longirostris, Diaphanosoma brachyurum, Keratella quadrata, Asplanchna priodonta. and other Brachionidae species appeared. Diaptomidae are still absent, except for some specimens of Arctodiaptomus wierzejskii.

14
First phase of macroinvertebrate repopulation of Lake Orta (Buccione Basin) after liming

Anna Maria NOCENTINI, Angela BOGGERO, Giovanna DE MARGARITIS and Marcella GIANATTI

The research described here was performed during 1993 and 1994 in the context of studies on the recovery of Lake Orta from acidification after the liming conducted from May 1989 to June 1990. The causes of the pollution were due to the oxidation of am­monium sulphate discharged from a factory producing rayon by a cupro-ammoniacal method and to the loads of heavy metals (Cu, Cr, Ni, Zn) derived from plating factories. One year after liming, an increase in pH and a marked decrease in metal concentrations were observed, and as a consequence some qualitative and quantitative changes were observed in 1992-93 in the planctonic commu­nities and in the littoral macrobenthic fauna. This paper presents qualitative and quantitative data on macrobenthos collected along a transect between the littoral and the maximal depth in the Buccione Basin, which was directly affected by the effluents of the rayon factory. The data revealed some quantitative repopulation of this community, especially along the littoral. Qualitatively, however, the macrobenthos was still quite poor, consisting essentially of Oligochaeta and Diptera Chironomidae. The former were rare and mainly represented by Naididae between 15 and 22 m, while the Tubificidae were well represented in the littoral and the profundal zones. As regards the Chironomidae, the genera Procladius and Chironomus gr. thummi extended as far as the maximum depth, while others, such as Ablabesmyia, Parakiefferiella bathophila and Dicrotendipes gr. nervosus were mostly distributed in the littoral layers. Among the other taxonomic groups only the Trichoptera and the Diptera Ceratopogonidae were quantitatively significant. However, many systematic entities typical of the less polluted Italian subalpine lakes are still absent. In fact, the colonisation of Lake Orta by macrobenthic organisms is still influenced by the increased concentrations of heavy metals in the sediment precipitated from the water column. The research included analysis of lake water and sediments chemistry to obtain information on the trophic level of the environment.

15
Breakdown rates and macroinvertebrate colonisation of alder (Alnus glutinosa) leaves in an acid lake (Lake Orta, N Italy), before, during and after a liming intervention

Gianpaolo SALMOIRAGHI, Bruna GUMIERO, Andrea PASTERIS, Susanna PRATO, Carla BONACINA and Giuliano BONOMI

To test the effectiveness of the liming intervention on Lake Orta, the speed of leaves decay and of colonisation processes by mac­robenthonic fauna were studied on alder leaves (Alnus glutinosa) placed on the bottom of the lake and recovered after appropriate time intervals. Experiments were performed at two sites (North and South) and two depths (-3 and –18 m), during three successive winters: 1988-1989 (pre-liming), 1989-1990 (liming), 1990-1991 (post-liming). Two main results emerged: 1) alder leaves, which are known to have a medium to high decaying speed in a number of aquatic environments, behave in Lake Orta as a low speed spe­cies. Decaying processes in the three years are significantly different only in station N3, where the mean breakdown rate in 1988-1989 is more than twice that measured in the two subsequent winters. 2) The species richness of colonising benthic fauna is low: the community is made up almost exclusively of Chironomidae, which form 70 to 100% of the whole population; among them, the genus Phenopsectra is always present, while Tanytarsus was collected only during the first year and in the less deep sampling sites. The mean population abundances were higher before liming.