Journal of Limnology

vol. 63(1), 2004

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CONTENTS

1

Lake Bolsena (Central Italy): an updating study on its water chemistry

Rosario MOSELLO, Silvia ARISCI and Piero BRUNI

In spite of its importance as regards size (volume 9.2 10⁶ m³, max depth 151 m) and as a source of drinking water, Lake Bolsena has not been studied from a hydrochemical point of view since the second half of the 60s, when a group of researchers from the Isti­tuto Italiano di Idrobiologia co-ordinated a complete study of the limnology of the Latium lakes Bolsena, Albano, Vico, and Brac­ciano. In the following years analyses were performed sporadically; since the 90s, temperature and oxygen profiles and other studies were made by the Associazione Lago di Bolsena. Based on chemical profiles made in 2001-2003, this paper discusses the present chemical composition of Lake Bolsena waters, and compares them with those of other volcanic lakes in Latium (Bracciano, Albano, Nemi and Vico). The paper briefly considers the main factors influencing the water chemistry of Lake Bolsena, the variations ob­served from the analyses of the 60s, and the main sources of risk to water quality.

2

Spatial segregation of Darwinula stevensoni (Crustacea: Ostracoda) genotypes in lentic and lotic habitats of Northern Italy

Valeria ROSSI, Carlo BELLAVERE, Giorgio BENASSI, Andrea GANDOLFI, Eletta B.A. TODESCHI and Paolo MENOZZI

The clonal structure of apomictic populations of Darwinula stevensoni from Northern Italy lacustrine and riverine habitats has been analysed by allozyme electrophoresis. Thirty two sites were sampled and a total of 748 individuals were analysed. Only one polymorphic locus, Gpi, turned out to have enough variation to be informative. Two thirds of all individuals were homozygous for the most frequent allele but the frequency of this genotype was significantly lower in rivers (16%) than in lakes (92%). As a consequence homozygous clonal females are dominant in lacustrine habitats while heterozygous clonal females are dominant in riverine ones. Differences in genetic structure between habitats were observed even at distances of a few meters. Allele and genotype frequencies are significantly different between Lake Montorfano and its outflow (River Seveso) and between Mantova lakes and their two tribu­taries, the River Mincio and Corniano Channel. The former is also the outflow of Lake Garda. By laboratory experiments, we previ­ously reported difference between genotypes: homozygous females from Mantova lakes show significantly lower starvation tolerance than heterozygous females from River Mincio. We discuss the hypothesis that habitat segregation is related to this difference. River­ine females should be better adapted to low productivity ecosystems than lacustrine ones.

3

Geochemical response of a closed-lake basin to 20^th century recurring droughts/wet intervals in the subtropical Pampean Plains of South America

Eduardo L. PIOVANO, Favio E. LARIZZATTI, Deborah I.T. FÁVARO, Sonia M.B. OLIVEIRA, Sandra R. DAMATTO, Barbara P. MAZZILLI and Daniel ARIZTEGUI

Laguna Mar Chiquita is a highly variable closed saline lake located in the Pampean Plains of central Argentina. Presently is the largest saline lake in South America (~ 6,000 km²) and also one of the largest in the world. During the 20^th century the hydrological balance of the region was characterized by contrasting scenarios. Well-defined wet or dry climatic phases had ruled the lake level fluctuations and the rivers discharge, mainly controlling the geochemical composition of sediments. Sediments accumulated during positive hydrological balances (i.e., high lake level) are mainly composed of allogenic mineral due to higher riverine inputs into the lake. This fluvial-dominated lake phases are recorded as sediments enriched in Al₂O₃, SiO₂, K₂O, Fe₂O₃ and TiO₂ and in trace ele­ments such as Co, Cr, Cs, Rb, Sc, Hf, Ta, Th as well as rare earth elements (REE). Sediments accumulated during dry phases (i.e., low lake levels and high salinity) are evaporite mineral-rich with elevated concentrations of CaO, MnO, MgO, and P₂O₅. High con­tents of As and U are probably due to a co-precitation during high evaporative phases. The calibration of the sediment chemical composition of Laguna Mar Chiquita to well-defined water-level fluctuations of the 20^th century shows that elemental geochemistry can be a useful proxy to study former lake-water fluctuations. It may further provide a comparative model to evaluate past environ­mental conditions in other saline lacustrine basins.

4

Carbon assimilation and phytoplankton growth rates across the trophic spectrum: an application of the chlorophyll labelling technique

Giuseppe MORABITO, Waleed HAMZA and Delio RUGGIU

The chlorophyll labelling technique has been acknowledged to be a useful method for measuring phytoplankton growth rates while avoiding some of the problems involved in calculating growth rates derived from the ¹⁴C fixation rates. The results presented here are of experiments comparing phytoplankton growth rates during the summer season in three subalpine Italian lakes: Lago Maggiore, the second largest lake in Italy, and two smaller lakes, Lake Mergozzo and Lake Varese, both included in the Lago Maggiore drainage basin. The three lakes have different morphometric, physico-chemical and biological features. The first goal was to compare two different methods of estimating phytoplankton growth rates starting from ¹⁴C assimilation. The second goal of our experiments was to test the hypothesis that growth rates can be quite different across the trophic spectrum, due to the ecophysiologi­cal and morphological features of the phytoplankton assemblages. In particular, algal cell size should decrease from eutrophic to oligotrophic systems and growth rates should follow the opposite trend, as they are inversely scaled to the cell size. Two basic con­clusions can be drawn. The first is that, in spite of some drawbacks still affecting the use of the chlorophyll labelling technique, this appears to be one of the most promising methods for estimating the growth rates of phytoplankton in situ. The second conclusion is that this method, coupled with information on some algal morphological parameters, can provide useful indications about the func­tional properties of phytoplankton assemblages living in diverse lacustrine environments.

5

Population dynamics of the pioneer population of Daphnia parvula, Fordyce during the invasion of Lake Candia (Northern Italy)

Nicoletta RICCARDI, Gianluigi GIUSSANI, Fiorenza MARGARITORA and Bruno COUCHAUD

Since the 1970s Daphnia parvula, Fordyce, originally distributed in the New World, has been invading Europe. In Italy D. par­vula first appeared in the shallow, eutrophic Lake Candia (Piedmont, Northern Italy) during September 2002. Although several studies have documented D. parvula dispersal in European habitats, little is known about the life cycle and ecology of this invader in its new habitats. Invasion success depends on the ability of the invader population to perform well in the new ecosystem, which in turn results from the interaction between the characteristics of the invader and those of the invaded environment and its resident community. Early detection of D. parvula in the intensively studied Lake Candia offered an excellent opportunity to study the per­formance of the pioneer population and to document the early phases of invasion. Following the dynamics of the pioneer D. parvula population provided evidence of a high level of gamogenetic reproduction during most periods of population development. The pro­duction of males started at the onset of population growth prior to ephippia formation. The sex ratio ranged from 0.1 to 0.33 males per female with a maximum in October when males accounted for up to 24% of the total population density. The percentage of ephippia (free ephippia + ephippial females) out of the total population density ranged from 3 to 23%. The large pool of resting eggs produced by the pioneer population of D. parvula in Lake Candia might reflect a strategy for increasing the probability of sur­vival and establishment in the new environment.

7

Measured and modelled trends in European mountain lakes: results of fifteen years of cooperative studies

Aldo MARCHETTO and Michela ROGORA

Papers included in this Special Issue of the Journal of Limnology present results of long-term ecological research on mountain lakes throughout Europe. Most of these studies were performed over the last 15 years in the framework of some EU-funded projects, namely AL:PE 1 and 2, MOLAR and EMERGE. These projects together considered a high number of remote lakes in different areas or lake districts in Europe. Central to the projects was the idea that mountain lakes, while subject to the same chemical and biological processes controlling lowland lakes, are more sensitive to any input from their surroundings and can be used as early-warning indicators of atmospheric pollution and climate change. A first section of this special issue deal with the results of long-term monitoring programmes at selected key-sites. A second section focuse on site-specific and regional applications of an acidification model designed to reconstruct and predict long-term changes in the chemistry of mountain lakes.

8

A consideration of potential confounding factors limiting chemical and biological recovery at Lochnagar, a remote mountain loch in Scotland

Neil ROSE, Don MONTEITH, Helen KETTLE, Roy THOMPSON, Handong YANG and Derek MUIR

Lochnagar, a remote loch in the Grampian Mountains of Scotland is one of the most studied freshwater bodies in the UK. It represents a key site in a number of monitoring programmes and has become the UK’s 'flag-ship' mountain lake in various EU funded projects over the last 15 years. Palaeolimnological studies have revealed the extent and diverse provenance of atmospheri­cally deposited pollution at the site and show that the loch began to acidify in the mid-19th century. However, despite abatement strategies dramatically reducing the emission and deposition of non-marine sulphate and trace metals since the 1970s, the loch pH shows little sign of recovery and full basin fluxes of, for example, Pb and Hg show no decline or even a continued increase. It is sug­gested that the lack of recovery from acidification over the last 15 years of monitoring results from the balancing of the decline in sulphate by increased nitrate, and that this increase is related to winter duration and severity. The lack of response by the sediment record to declines in metal deposition is thought to be due to a continuing input of previously deposited metals from the catchment. Hypotheses for these enhanced catchment inputs involve responses to a changing climate. Site specific climate reconstructions and predictions for the 21st century suggest an accelerated increase in temperature rise and increased winter precipitation and stormi­ness. These predicted changes are likely to exacerbate the input of metals (and other stored pollutants) from the catchment but higher temperatures may also help to promote recovery from acidification.

9

The chemical and biological response of two remote mountain lakes in the Southern Central Alps (Italy) to twenty years of changing physical and chemical climate

Aldo MARCHETTO, Rosario MOSELLO, Michela ROGORA, Marina MANCA, Angela BOGGERO, Giuseppe MORABITO, Simona MUSAZZI, Gabriele A. TARTARI, Anna M. NOCENTINI, Alessandra PUGNETTI, Roberta BETTINETTI, Pierisa PANZANI, Michele ARMIRAGLIO, Pierluigi CAMMARANO and Andrea LAMI

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 aci­dophilous 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 parti­cles. On the contrary, the biota of Lake Paione Inferiore appeared to be mainly affected by fish stocking. In the last twenty years, de­crease 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.

10

Ecological relations and temporal changes in the pelagial of the high mountain lakes in the Rila Mountains (Bulgaria)

Roumen KALCHEV, Ivan BOTEV, Milena HRISTOZOVA, Wesselin NAIDENOW, Galerida RAIKOVA-PETROVA, Maya STOYNEVA, Dobrina TEMNISKOVA-TOPALOVA and Teodora TRICHKOVA

The high mountain lakes in the Rila Mountains (Bulgaria) were studied in the years 2000 and 2001 considering the following groups of variables: geography, geology, morphology, hydrology, water chemistry of the pelagial, biomass and size structure of bacterio- phyto- and zooplankton, and occurrence of three fish species. Multivariate analysis (RDA) revealed that the nutrient con­centrations in the lakes were significantly influenced by the soil percentage coverage of the catchment area. The explained variation in plankton components (bacterio-, phyto- and zooplankton) and plankton size structure was determined by biological as well as morphometrical and geographical variables. Changes in the Mg²⁺ and NO₃-N concentrations were traced over the period 1993-2001; the Ca²⁺ concentration, pH, nutrients, bacterio-, phyto- and zooplankton were monitored in the period 1995-2001. A nutrient decrease accompanied by an increase in size of zooplankton organisms in the period 1995-2001 led to a considerable increase of water transparency in the lakes.

11

Recovery of acidified mountain lakes in Norway as predicted by the MAGIC model

Richard F. WRIGHT and Bernard J. COSBY

As part of the EU project EMERGE the biogeochemical model MAGIC was used to reconstruct acidification history and predict future recovery for mountain lakes in two regions of Norway. Central Norway (19 lakes) receives low levels of acid deposition, most of the lakes have undergone only minor amounts of acidification, and all are predicted to recover in the future. Central Norway thus represents a reference area for more polluted regions in southern Norway and elsewhere in Europe. Southern Norway (23 lakes), on the other hand, receives higher levels of acid deposition, nearly all the studied lakes were acidified and had lost fish populations, and although some recovery has occurred during the period 1980-2000 and additional recovery is predicted for the next decades, the model simulations indicated that the majority of the lakes will not achieve water quality sufficient to support trout populations. Un­certainties in these predictions include possible future N saturation and the exacerbating effects of climate change. The mountain lakes of southern Norway are among the most sensitive in Europe. For southern Norway additional measures such as stricter con­trols of emissions of air pollutants will be required to obtain satisfactory water quality in the future.

12

Modelling hydrochemical and ecological trends in acid sensitive surface waters in the Scottish Highlands

Rachel C. HELLIWELL and Martin KERNAN

The dynamic model MAGIC is used to predict the future response of surface waters to reductions in S deposition as stipulated by the recently agreed emission protocol (the 1999 Gothenburg Protocol). MAGIC was calibrated to 30 sites in the Scottish mountains with the best available soil and deposition data derived from large scale spatial datasets, and surface water chemistry from a regional loch survey conducted in October 2000. A comparison of input parameters and model responses are made at Lochnagar, a site for which detailed, high resolution spatial/temporal data exist. The model is capable of reproducing observed trends in non-ma­rine SO₄^2-, however simulated NO₃^- from 1990 to 2000 is lower than the observed trends at Lochnagar due to possible hydrological controls and in-lake processes, rather than terrestrial processes. The Scottish Highlands are remote from emission sources and con­sequently peak deposition inputs of S in the 1980s are relatively low (33 kg S ha^-1 y^-1) compared to other regions in Europe. None­theless the amount of deposition appears sufficient to cause environmental damage in this acid sensitive region. During the 1980s, simulated Acid Neutralising Capacity (ANC) of 13% of the modelled lakes was <20 µeq l^-1, a chemical condition that potentially can cause damage to freshwater ecology. Regional and site simulations captured the recovery to 2000 in response to the existing emis­sion reductions. Predictions to 2016 indicates the potential for biological recovery and a return to 'good status' as required by the EU Water Framework Directive, although the hydrochemistry of some sites remain some way from simulated pre-acidification con­ditions.

13

Application of MAGIC to Lake Redó (Central Pyrenees): an assessment of the effects of possible climate driven changes in atmospheric precipitation, base cation deposition, and weathering rates on lake water chemistry

Lluís CAMARERO, Richard F. WRIGHT, Jordi CATALAN and Marc VENTURA

The process-oriented catchment-scale model MAGIC was used to simulate water chemistry at Lake Redó, a high mountain lake in the Central Pyrenees, Spain.  Data on lakewater and atmospheric deposition chemistry for the period 1984-1998 were used to calibrate the model, which was then used to reconstruct past and to provide forecasts for three hypothetical future scenarios of depo­sition. Forecast scenarios considered several combinations of changes in S and N deposition due to abatement strategies, and in base cation deposition due to climate-induced changes in air-mass trajectories from northern Africa. Scenario 1 assumed constant deposition of base cations at the present level plus the expected decrease in S and N deposition resulting from reduced emissions; scenario 2 (best case) assumed an increase in base cation deposition plus the same decrease in S and N deposition as in scenario 1; scenario 3 (worst case) assumed a decrease in base cation deposition plus no decrease in S and N deposition. The hindcast indicated that during the past 140-year period changes in lake water chemistry have been significant for a remote mountain catchment, al­though  no substantial acidification has occurred. In this regard Lake Redó can be described as a "non-sensitive lake" maintaining a reference condition. The forecasts indicated changes that do not affect this status, but the trends, even if slight, were different be­tween scenarios. A slight decline in the surface water ANC is predicted by Scenario 3. The N budget indicates an unusually low re­tention in the catchment, which may result in enhanced sensitivity to further increased N deposition. Some of the discrepancy be­tween modelled and measured Ca²⁺ in lake water during 1984-98 could be explained by changes in rainfall amounts and by in­creased weathering rates due to increases in air temperature.

14

Acidification and recovery at mountain lakes in Central Alps assessed by the MAGIC model

Michela ROGORA

The dynamic model MAGIC was calibrated and applied to 84 lakes in Central Alps to predict the response of water chemistry to different scenarios of atmospheric deposition of S and N compounds. Selected lakes were representative of a wide range of chemical characteristics and of sensitivity to acidification. The most sensitive lakes have already shown in the latest years signs of recovery in terms of pH and ANC. The model well captured the main trends in lake chemical data. According to the model forecast, recovery at sensitive lakes will continue in the next decades under the hypothesis of a further decrease of acidic input from the atmosphere. Re­sults clearly demonstrated the benefits of achieving the emission reductions in both S and N compounds agreed under the Gothen­burg Protocol. Nevertheless, besides the achieved reduction of SO₄^2- deposition from the peak levels of the 80s, also N deposition should be reduced in the near future to protect alpine lakes from further acidification. The condition of lake catchments with regard to N saturation will probably be the dominant factor driving recovery extent. Beside atmospheric deposition, other factors proved to be important in determining long-term changes in surface water chemistry. Climate warming in particular affects weathering proc­esses in lake catchments and dynamics of the N cycle. Including other factors specific to the alpine area, such as dust deposition and climate change, may improve the fit of experimental data by the model and the reliability of model forecast.

15

Response of alpine lakes and soils to changes in acid deposition: the MAGIC model applied to the Tatra Mountain region, Slovakia-Poland

Jiří KOPÁČEK, David HARDEKOPF, Vladimír MAJER, Petra PŠENÁKOVÁ, Evžen STUCHLÍK and Josef VESELÝ

A dynamic process-based model of surface water acidification, MAGIC, was applied to 31 representative alpine lakes in the Tatra Mountains (~50% of all alpine lakes >0.3 ha in the lake-district). The model was calibrated to observed lake chemistry for the period 1980-2002. Surface water and soil chemistry were reconstructed from 1860 to 2002, given estimates of historical acid depo­sition, and forecast to 2020 based on the reduction in sulphur and nitrogen emissions presupposed by the Gothenburg Protocol. In the 1860s, all lakes were buffered by the carbonate system and only ~6% of lakes had acid neutralising capacity (ANC) <20 µeq l^-1. Lake acidification progressed until 1980s, at which time 23% of lakes had a depleted carbonate buffering system and 33% of lakes had ANC <20 µeq l^-1. Reversal of water chemistry from acidification started in the late 1980s as a response to decreasing acid depo­sition. ANC has increased such that only ~16% of the lake population currently has ANC <20 µeq l^-1. The number of low ANC lakes is predicted to decrease to 10% by 2020, but the original carbonate buffering system of these lakes will not be re-established. The patterns in long-term changes of sulphate and chloride primarily reflected trends in atmospheric deposition and were similar for all lakes. Base cations (BC), ANC, nitrate, and pH, however, were significantly influenced by catchment characteristics. The water chemistry response to changes in strong acid anion (SAA) inputs varied among the lakes. The changes in SAA were compensated for (1) by parallel changes in BC concentrations (~75% of the SAA change) in non-sensitive lakes (high weathering rates and abundant soils with high base saturation), (2) by inverse changes in bicarbonate concentrations (>50% of the SAA change) in sensitive lakes with intermediate weathering rates and little soils (low BC exchangeable capacity and elevated terrestrial export of nitrate) and (3) by parallel changes in concentrations of protons and aluminium (each ~20% of the SAA change) in extremely sensitive lakes, with the lowest weathering rates and soil base saturation. The full implementation of the Gothenburg Protocol will not be sufficient to al­low recovery of the latter group of lakes, which will remain acidified after 2020.