Climate-driven changes on phytoplankton–zooplankton coupling and nutrient availability in high mountain lakes of Southern Europe

1. The effect of climate variability on phytoplankton and zooplankton dynamics and nutrient availability was studied in two high mountain fishless lakes (La Caldera and Río Seco) of contrasting morphology, hydrology and dissolved inorganic nitrogen : soluble reactive phosphate (DIN : SRP) ratios during 1986 and after a 10‐year‐long drought in 1996 and 1997. 2. Thaw was delayed and water temperatures were lower in both lakes in 1996 than in 1986 and 1997. However, the lake‐specific DIN : SRP ratio was maintained in the 3 years studied, reflecting its local control. 3. On other hand, the presumptive limiting nutrient in each lake, P in La Caldera and N in Río Seco, showed higher concentrations in 1996 versus 1986 and 1997. Significant positive correlations between temperature and chlorophyll a were found in both lakes in 1996 but these relationships were negative or not significant in 1986 and 1997. Zooplankton biomass showed lower values in 1996 than in 1986 or 1997. 4. These findings can be explained by a decoupling of the phytoplankton–zooplankton interaction because of a constraint on zooplankton growth by low temperatures in the coldest year studied. This observation furnishes evidence that regional climatic control on the phytoplankton–zooplankton link can modulate the overall demand for nutrients.     

A hotspot for cold crenarchaeota in the neuston of high mountain lakes

We have surveyed the first 1 m of 10 oligotrophic high mountain lakes in the Central Pyrenees (Spain) for both abundance and predominant phylotypes richness of the archaeaplankton assemblage, using CARD-FISH and 16S rRNA gene sequencing respectively. Archaea inhabiting the air-water surface microlayer (neuston) ranged between 3% and 37% of total 4,6-diamidino-2-phenylindole (DAPI) counts and were mainly Crenarchaeota of a new freshwater cluster distantly related to the Marine Group 1.1a. Conversely, most of the Archaea from the underlying waters (the remaining first 1 m integrated) were mainly Euryarchaeota of three distantly related branches ranging between 0.4% and 27% of total DAPI counts. Therefore, a consistent qualitative and quantitative spatial segregation was observed for the two main archaeal phyla between neuston and underlying waters at a regional scale. We also observed a consistent pattern along the lakes surveyed between lake area, lake depth and water residence time, and the archaeal enrichment in the neuston: the larger the lake the higher the proportion of archaea in the neuston as compared with abundances from the underlying waters ( n  = 10 lakes; R ² > 0.80; P  < 0.001, in all three cases). This is the first report identifying a widespread non-thermophilic habitat where freshwater planktonic Crenarchaeota can be found naturally enriched. High mountain lakes offer great research opportunities to explore the ecology of one of the most enigmatic and far from being understood group of prokaryotes.     

Acidification and weathering processes in high mountain lakes in Southern Alps

About 200 lakes in Southern Alps (Italy and Switzerland) were studied in order to quantify their acidification. Although samplings were carried out in summer, long after the acid shock caused by snowmelt, some lakes were found to be acidic and 47% of them show alkalinity values of below 50 μeq 1^-1. Losses in alkalinity (acidification levels) were evaluated using a titration model with variable F-factor. Factor analysis shows that the main factors influencing water chemistry are related to rock weathering and nitrate uptake by vegetation. In watersheds containing carbonatic rocks the weathering of calcite is responsible for the most of the alkalinity production. We therefore focused on a set of 19 low-alkalinity lakes in the Maggia Valley lying in watersheds containing mainly acidic rocks. Results show that the weathering of silicate and calcite (present in small quantities, but highly soluble) and nitrate uptake account for most of the alkalinity production. Other watershed and in-lake processes may be important in some cases, but they never account for more than 27 % of the alkalinity production in these lakes.     

A survey on water chemistry and plankton in high mountain lakes in northern Swedish Lapland

A helicopter survey was carried out on 56 water bodies in the Abisko mountains, Swedish Lapland, in August 1981. Water chemistry was found to be highly correlated with bedrock quality in the drainage area of the lakes. Low pH values (down to 5.1) appeared in the neighbourhood of sulphuric iron-ores. Natrium and chloride concentrations showed large scale patterns which can be explained by orographic rainfall. Biologically, northern high mountain conditions are reflected in species composition rather than in biomass or possibly in diversity. Small chrysomonades and dinoflagellates, as well as Keratella hiemalis and Cyclops scutifer characterize the most ‘arctic’ waters. A comparison with data from earlier investigations did not confirm expected signs of acidification.     

Patterns in the composition of the rotifer communities from high mountain lakes and ponds in Sierra Nevada (Spain)

On the basis of periodic collections of rotifers from 29 lakes and ponds over 2500 m above sea level in the Sierra Nevada (Southern Spain), patterns of species richness, distribution and community composition were evaluated. Results allow us to distinguish communities which fall into two major lake types. One is defined by the presence of typically planktonic species as well as lower specific richness whereas the other includes communities of mainly benthic and periphytic species. Both lake types seem to be related to small differences in their physical and chemical characteristics. These relationships and the influence of littoral vegetation are discussed.Research supported by CAICYT Project n° 3069/83     

Osmoadaptation in representatives of haloalkaliphilic bacteria from soda lakes

The adaptation of microorganisms to life in brines allows two strategies: the accumulation of organic osmoregulators in the cell (as in many moderate halophiles, halomonads in particular) or the accumulation of inorganic ions at extremely high intracellular concentrations (as, for example, in haloanaerobes). To reveal the regularities of osmoregulation in haloalkaliphiles developing in soda lakes, Halomonas campisalis Z-7398-2 and Halomonas sp. AIR-2 were chosen as representatives of halomonads, and Natroniella acetigena, as a representative of haloanaerobes. It was established that, in alkaliphilic halomonads, the intracellular concentrations of inorganic ions are insufficient for counterbalancing the environmental osmotic pressure and balance is attained due to the accumulation of organic osmoregulators, such as ectoine and betaine. On the contrary, the alkaliphilic haloanaerobe N. acetigena employs K+, Na+, and Cl- ions for osmoregulation. High intracellular salt concentrations increasing with the content of Na+ in the medium were revealed in this organism. At a concentration of 1.91 M Na+ in the medium, N. acetigena accumulated 0.83 M K+, 0.91 M Na+, and 0.29 M Cl- in cells, and, with an increase in the Na+ content in the medium to 2.59 M, it accumulated 0.94 M K+, 1.98 M Na+, and 0.89 M Cl-, which counterbalanced the external osmotic pressure and provided for cell turgor. Thus, it was shown that alkaliphilic microorganisms use osmoregulation strategies similar to those of halophiles and these mechanisms are independent of the mechanism of pH homeostasis.     

High similarity between bacterioneuston and airborne bacterial community compositions in a high mountain lake area

The bacterioneuston (bacteria inhabiting the air–water interface) is poorly characterized and possibly forms a unique community in the aquatic environment. In high mountain lakes, the surface film is subjected to extreme conditions of life, suggesting the development of a specific and adapted bacterioneuston community. We have studied the surface film of a remote high mountain lake in the Pyrenees by cloning the PCR-amplified 16S rRNA gene and comparing with bacteria present in underlying waters (UW), and airborne bacteria from the dust deposited on the top of the snow pack. We did not detect unusual taxa in the neuston but rather very common and widespread bacterial groups. Betaproteobacteria and Actinobacteria accounted for >75% of the community composition. Other minor groups were Gammaproteobacteria (between 8% and 12%), Alphaproteobacteria (between 1% and 5%), and Firmicutes (1%). However, we observed segregated populations in neuston and UW for the different clades within each of the main phylogenetic groups. The soil bacterium Acinetobacter sp. was only detected in the snow–dust sample. Overall, higher similarities were found between bacterioneuston and airborne bacteria than between the former and bacterioplankton. The surface film in high mountain lakes appears as a direct interceptor of airborne bacteria useful for monitoring long-range bacterial dispersion.     

Taxonomic and ecological notes on Hexarthra bulgarica from high mountain lakes and ponds in the Sierra Nevada (Spain)

Hexarthra bulgarica was found in 16 of the 37 high mountain lakes (over 2500 m) studied in the Sierra Nevada (Southern Spain). These populations resemble closely the subspecies H. b. canadensis. Data on the morphology and ecology of the Sierra Nevada populations are given, and these are compared to published information on the three other subspecies of H. bulgarica.Research supported by CAICYT Project No. 3069/83.     

Two- and three-year life cycles in the planktonic copepod Cyclops scutifer in two high mountain lakes

The life cycles of Cyclops scutifer Sars (Copepoda, Crustacea) in two high mountain lakes in Norway, Gjende and Bessvatn in Jotunheimen, are presented. The population in Gjende has an exclusive 2-yr life cycle and that in Bessvatn a 3-yr cycle which is exceptionally long both among freshwater and marine zooplankton. Bessvatn is situated about 400 m higher than Gjende, and the heat preservation is lower with longer periods of ice cover and lower primary production explaining the difference in cycle length. The prolongation of the life cycle is due mainly to retardation of the developmental rate during the long periods of winter stagnation with water temperatures mostly below 2°C. The retardation is especially evident in the nauplii and in the copepodid instars III, IV, and V. Neither population diapauses. Reproduction takes place only in late summer and no adults survive the winter.     

An assessment of the meiobenthos from nine mountain lakes in Western Canada

The numbers and biomass of meiobenthic invertebrates of nine representative mountain lakes were assessed relative to the macrobenthic invertebrates retained on 0.425 mm mesh. The meiobenthos accounted for an average of % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaSGaaeaaca% aIXaaabaGaaG4maaaaaaa!3777!\[{\raise0.7ex\hbox{$1$} \!\mathord{\left/{\vphantom {1 3}}\right.\kern-\nulldelimiterspace}\!\lower0.7ex\hbox{$3$}}\]of the total biomass and 97% of total numbers retained on 0.045 mm mesh. In general surveys in these lakes, the use of 0.250 mm mesh instead of 0.425 mm mesh would be unlikely to improve estimates of total numbers and biomass enough to justify the additional effort needed. Accepting the meiobenthic turnover rate to be three to five times that of the macrobenthos, meiobenthic production is probably close to or much higher than the macrobenthic production in these lakes.     

Radiometric dating of sediment records from mountain lakes in the Tatra Mountains

Sediment cores from nine different lakes in the Tatra Mountains, collected as part of the EU funded AL:PE, MOLAR and EMERGE projects investigating natural environmental records stored in remote mountain lake sediment sequences, were dated radiometrically by ²¹⁰Pb and ¹³⁷Cs. At five sites, D?ugi Staw G?sienicowy and Zielony Staw G?sienicowy on the Polish side of the Tatra Mountains and Starolesnianske pleso, Ni?né Terianske pleso, and L’adové pleso on the Slovak side of the Tatra Mountains, the cores were sectioned at close intervals and analysed in detail to produce a high resolution chronology. For the remaining four sites, Zmarzly Staw G?sienicowy (Poland), and Vel’ké Hincovo pleso, Vy?né Temnosmre?inské pleso, Vy?né Wahlenbergovo pleso (Slovakia), it was sufficient to establish a low resolution sketch chronology and only a few samples were analysed from each core. At L’adové pleso, multiple cores were collected in order to establish spatial distribution of sediments over the bed of the lake. Cores from all sites had good records of the fallout radionuclides from which it was possible to construct reliable chronologies of the recent sediments.     

Macrophytes from some high Andean lakes of Ecuador and their low potential as bioindicators of eutrophication

The occurrence of macrophyte in three high Andean lakes of Ecuador, Lago San Pablo, Laguna La Mica and Lago Cuicocha was recorded in 5-9 transects per lake. The first two lakes are eutrophic, the third is an extremely oligotrophic caldera lake. The dominant species in eutrophic lakes are Ceratophyllum demersum, Myriophyllum quitense, Polamogeton illinoensis, P. striatus and Elodea matthewsii. In the oligotrophic lake P. pectinatus, P. illinoensis, and the Characeae Chara rusbyana, Ch. globularis and Nitella acuminata occur. The maximum depth of the macrophyte's presence can be used as an indicator of the trophic state, ranging from about 5 m in Mica to 35 m in Cuicocha. The bioindication value of the macrophyte species in these high Andean lakes is low, because few species occur and because some of them are not specific to environmental conditions.     

Biomass and production of Euchlanis dilatata in high mountain lakes and ponds of Sierra Nevada (Spain)

Biomass and production of the rotifer Euchlanis dilatata wereestimated during the ice-free period of 1 year in 14 high mountainlakes of the Sierra Nevada (Southern of Spain). Results showa high variability between lakes both in biomass and productionand, what is more noticeable, in the P/B ratios for the growingseason. The possible relation between these ratios and meantemperature, body weight and number of individuals in each lakewas tested and discussed.     

Water level fluctuations may decrease phosphate adsorption capacity of the sediment in oligotrophic high mountain lakes

The effect of sediment desiccation and re-wetting on phosphate adsorption and desorption properties was examined in two oligotrophic high mountain lakes (La Caldera and Río Seco, altitude ~3000 m) in the Sierra Nevada National Park, Spain. Decrease in phosphate sorption properties was observed in transects from the littoral zone to dry land (up to the high water mark) in both lakes concomitantly with loss of amorphous oxides of iron and aluminum as revealed by oxalate and dithionite extractions. X-ray diffraction did not indicate increased amounts of crystalline metal oxides, but there was a loss of fine particles (<20 μm) with distance from the shore, probably due to wind erosion. Likely this explains the loss of amorphous metal oxides as they are often enriched in the fine sediment fraction. Changes in P-speciation toward less available pools were also observed as a result of desiccation. When re-wetted under oxic conditions, the sediments, especially those closest to the shore, released phosphate to the overlying water. The loss of adsorption capacity for phosphate upon re-wetting was associated with loss of amorphous iron oxides, and the changes appear to be non-reversible. Thus, both desiccation and re-wetting will lead to a decrease in sediment phosphate sorption capacity and increased water level fluctuations, a possible scenario in climate change, can therefore increase P availability in the water column of these oligotrophic systems.     

Site-specific chlorophyll reference conditions for lakes in Northern and Western Europe

The Water Framework Directive (WFD) requires EU Member States to assess the “ecological status” of surface waters. As a component of ecological status, many European countries are developing a classification scheme for chlorophyll concentrations as a measure of phytoplankton biomass. The chlorophyll classification must be based on the degree of divergence of a water body from an appropriate baseline or ‘reference condition’. This article describes the development of a series of regression models for predicting reference chlorophyll concentrations on a site-specific basis. For model development, a large dataset of European lakes considered to be in reference condition, 466 lakes in total, was assembled. Data were included from 12 European countries, but lakes from Northern and Western Europe dominated and made up 92% of all reference lakes. Data have been collated on chlorophyll concentration, altitude, mean depth, alkalinity, humic type, surface area and geographical region. Regression models were developed for estimating site-specific reference chlorophyll concentrations from significant predictor ‘typology’ variables. Reference chlorophyll concentrations were found to vary along a number of environmental gradients. Concentrations increased with colour and alkalinity and decreased with lake depth and altitude. Forward selection was used to identify independent explanatory variables in regression models for predicting site-specific reference chlorophyll concentrations. Depth was selected as an explanatory variable in all models. Alkalinity was included in models for low colour and humic lakes and altitude was included in models for low colour and very humic lakes. Uncertainty in the models was quite high and arises from errors in the data used to develop the models (including natural temporal and spatial variability in data) and also from additional explanatory variables not considered in the models, particularly nutrient concentrations, retention time and grazing. Despite these uncertainties, site-specific reference conditions are still recommended in preference to type-specific reference conditions, as they use the individual characteristics of a site known to influence phytoplankton biomass, rather than adopt standards set to generally represent a large population of lakes of a particular type. For this reason, site-specific reference conditions should result in reduced error in ecological status classifications, particularly for lakes close to typology boundaries.     

Amphibiotic insects of mountain lakes and small watercourses in the Urals

A total of 127 species of stoneflies, dayflies, caddisflies, and chironomids were found in the lakes and small watercourses of the Northern and Pre-Polar Urals. The highest species diversity (78 species) and number were the characteristics of chironomids. Along with widely distributed species, Siberian and Arctic species were revealed in the fauna. The Arctic stonefly Capnia zaicevi Klap and 24 chironomid species were found for the first time on the territory of Komi Republic. Lists of registered insect species and data on their occurrence, abundance, and biomass are given.