Water quality parameters and tipping points of dragonfly diversity and abundance in fishponds

Fishponds are often enriched with nutrients in order to increase phytoplankton and zooplankton populations to support fish production. This eutrophication often leads to a global decrease of biodiversity. This biodiversity shift may be identified by a tipping point, the value of an environmental parameter above which a significant change of species richness and abundance occurs. A total of 110 eutrophic to highly eutrophic fishponds were studied in two areas in France to investigate parameters governing dragonfly species richness and species abundance by determining tipping points. Parameters investigated were chlorophyll a (CHL), water transparency, total N (TN), total P (TP), aquatic plant richness and coverage, adult dragonfly richness and abundance, and fish harvest. A high species richness of dragonflies was found in fishponds, with a total of 34 species, including six species of conservation concern. Dragonfly richness and abundance was shown to be negatively influenced by higher degrees of eutrophication. A high diversity of dragonflies occurred in the fishponds with CHL concentrations below 127 µg/l, water transparency above 67 cm, TN concentrations below 2.30 mg/l, and a fish harvest smaller than 253 kg/ha. A minimum of 5% of aquatic plant cover and the presence of a minimum 9 aquatic plant species seem to promote the richness and abundance of dragonflies. According to tipping points, 19 dragonfly species could be determined as indicator species for water quality in fishponds.     

Physical and chemical features of a tropical hypertrophic reservoir permanently stratified

Physical and chemical parameters of Pao-Cachinche reservoir (Venezuela) were measured in four stations (S1-S4) during an eighteen months period from September 1997 to February 1999. The tributaries of this reservoir introduce high amounts of nutrients from domestic wastewaters and from poultry and pig farms located in the basin. Thermal stratification was well established throughout the study period. Mountainous topography protects the water surface from mechanical action of wind, preventing water mixing. Hypoxic/anoxic conditions prevailed from 6–7 m depth down to the bottom in the limnetic stations. A strong smell of H₂S was detected below the 10 m level. The low water transparency (max. 1.5 m) may be mainly attributed to a high biogenic turbidity. Water salinity was low, as the maximum conductivity measured (260 μS cm^?1) suggests. The water was alkaline in the upper layers during the day time (pH >8.0), due to the high phytoplanktonic productivity, whereas in deeper layers, where decomposition processes predominate, pH was acidic (close to 6.0). Orthophosphate concentrations were high, reaching maximal concentrations in the deeper part of the reservoir (greater than 800 μg l^?1). Total phosphorus exceeded 1000 μg l^?1 in the hypolimnion during the dry season. Ammonia was the dominant inorganic nitrogen species, and its values were greater than 4000 μg l^?1 in the hypolimnetic layer during the dry season. Nitrates and nitrites were present in relatively low concentrations, except for the Paito stream entrance, where nitrate concentrations remained above 260 μg l^?1. Pao–Cachinche reservoir can be considered hypertrophic, according to Salas & Martinó’s criteria for tropical warm lakes, and could be classified as meromictic and warm monomictic, according to Lewis tropical lake types.     

A comparison of zooplankton communities in saline lakewater with variable anion composition

Although salinity and aquatic biodiversity are inversely related in lake water, the relationship between types of salts and zooplankton communities is poorly understood. In this study, zooplankton species were related to environmental variables from 12 lakes: three saline lakes with water where the dominant anions were SO₄ and CO₃, four saline lakes with Cl-dominated water, and five dilute, subsaline (0.5–3 gl^?1 total dissolved solids) lakes of variable anion composition. Although this study comprised only 12 lakes, distinct differences in zooplankton communities were observed among the two groups of chemically defined saline lakes. Canonical correspondence analysis identified total alkalinity, sulphate, chloride, calcium, sodium, potassium, and total phosphorus as all contributing to the first two ordination axes (λ₁ = 0.97 and λ₂ = 0.62, P<0.05). The rotifer Brachionus plicatilis and the harpactacoid copepod Cletocamptus sp. prevailed lakes with Cl-dominated water. In contrast, the calanoid copepods Leptodiaptomus sicilis and Diaptomus nevadensis were dominant in the SO₄/CO₃-dominated lake water with elevated potassium (79–128 mg l^?1) and total phosphorus concentrations (1322-2915 μg l^?1). The contrasting zooplankton species distribution among these two saline lake types is likely explained by variable selective pressure on zooplankton and their predators from differing physiological tolerances to salt stress and specific ions. While inland saline lakes with Cl as the dominant anion are relatively rare in Canada and SO₄/CO₃ are the common features, our study provided an opportunity to compare zooplankton communities across the two groups of lakes.     

Benzo(a)pyrene Exposure Causes Genotoxic and Biochemical Changes in the Midge Larvae of <Emphasis Type="Italic">Chironomus sancticaroli</Emphasis> Strixino &amp; Strixino (Diptera: Chironomidae)

Benzo(a)pyrene (BaP) is a carcinogenic polycyclic aromatic hydrocarbon, also found in nature due to human activities. BaP adheres to sediments showing toxic effects on benthic organisms, including midge larvae of the family Chironomidae. We tested for toxic effects of benzo(a)pyrene on Chironomus sancticaroli Strixino & Strixino 1981 using biochemical and genotoxic biomarkers, to identify changes in metabolic and antioxidant pathways, besides neurotoxic and DNA damage. Enzyme activity was compared by exposing larvae to four nominal concentrations (0.47, 2.13, 3.41, and 4.73 μg l^?1) and DNA damage to two concentrations (0.47 and 4.73 μg l^?1), after exposure at 24, 48, 72, and 96 h. BaP caused neurotoxic effect, showing acetylcholinesterase alterations at different treatments. Changes in the biotransformation pathway were detected, with an increased activity of alpha and beta esterase in 48 h and reduction of glutathione-S-transferase activity in all periods at the highest concentrations. Damage to the antioxidant system was observed by the increase of the superoxide dismutase and reduction of the catalase, in 48 h. Genotoxicity was detected by an increased DNA damage at 48 and 72 h. The lowest concentration (0.47 μg l^?1), even presenting low mortality, also altered the biochemical parameters of the larvae. Thus, these results indicate that BaP causes metabolic, neurotoxic, and genotoxic effects on C. sancticaroli, even at low concentrations and short-term exposure. BaP can cause damage of immature invertebrates, and the ecological dynamics can be affected, since these organisms have trophic importance in the aquatic environment.     

Determining tipping points in aquatic ecosystems: The case of biodiversity and chlorophyll α relations in fish pond systems

The management of biodiversity in aquatic ecosystems requires knowing the state of water quality linked to regime shifts in various taxonomic groups. We examine this question by studying the fish ponds in the Dombes region, France. These waterbodies are characterized by a high diversity of species. High levels of nutrients due to certain fish farming practices may cause significant eutrophication leading to loss in biodiversity and a shift from high coverage of aquatic vegetation to phytoplankton dominance may also be observed. The aim of this study is to assess tipping points, thresholds for effect, along a gradient of chlorophyll α in different taxonomic groups: aquatic vascular plants, phytoplankton, dragonflies and aquatic macro-invertebrates. Tipping points are analyzed with three different statistical methods: a method which evaluates tipping points with a difference in the mean (TMEAN), a second method which evaluates tipping point by comparing the mean and linear regressions before and after the tipping point (FSTAT) and third a method which evaluates linear regressions with a pivotal tipping point (SEGMENTED). We also compare tipping points for the different taxonomic groups using five different diversity indices: Observed richness, Jackknife first order, Fisher's alpha, Simpson index and Evenness.Our results show that there is an important variation in tipping points following the three statistical methods, but the SEGMENTED is the best method for evaluating tipping points. We observe a high difference of tipping point values for the different taxonomic groups depending on the diversity indices used. Jackknife first order has a better performance to evaluate a eutrophic change according to the diversity than the other indices.In all taxonomic groups, aquatic vascular plants are the most impacted by the chlorophyll α and almost all their tipping points are observed around 60 μg/L chlorophyll α concentrations. No significant relationship is found between chlorophyll α and phytoplankton diversity, while the two other groups, dragonflies and macro-invertebrates, are both impacted by the chlorophyll α but their relevant tipping points are situated in higher values than aquatic vascular plants.     

A comparison of toxicant-induced succession for five antifouling compounds on marine periphyton in SWIFT microcosms

Five antifouling biocides, chlorothalonile, dichlofluanide, medetomidine, tolylfluanide, and zinc pyrithione, were evaluated regarding their effect on the composition of the periphyton community and the subsequent toxicant-induced succession (TIS). The periphyton communities were exposed in a semi-static setting for 96 h using a SWIFT microcosm. As a measure of community composition, pigment profiles from the exposed communities were used as effect indicators and compared with unexposed parts of the same community using the Bray–Curtis dissimilarity index. Chlorothalonile caused changes in the community starting at 85 μg l^?1 while dichlofluanide had no effect even at the highest concentrations used, 810 μg l^?1. The related substance tolylfluanide only affected the community composition at 2700 μg l^?1. Medetomidine had a different response curve with a small effect on the community composition at 0.8 μg l^?1 which then disappeared only to reappear at 240 μg l^?1. Zinc pyrithione had the largest effect on the periphyton community with changes starting at 10 μg l^?1 and no detectable pigments at 100 μg l^?1. The changes in the community composition for the five substances were also compared using multidimensional scaling. When all substances were analyzed and plotted together, chlorothalonile, dichlofluanide, medetomidine, and tolylfluanide showed surprisingly similar effects compared to zinc pyrithione that gave very different TIS. However, when only chlorothalonile, dichlofluanide, and tolylfluanide were plotted together, clear differences in TIS between the three toxicants were revealed. Dichlofluanide only induced small effects, while concentration-dependent TIS trajectories for chlorothalonile and tolylfluanide took off in opposite directions indicating very different responses of the periphyton communities. This study demonstrates that substances with a similar chemical structure and mechanisms of action can have different effects on the community composition. With the exception of zinc pyrithione, none of the recorded effect levels were at concentrations reported from marine environments so far.     

Estimation of reference conditions for phytoplankton in a naturally eutrophic shallow lake

Classification of waters using biological quality elements and determination of the degree of deviation from reference levels is a key issue in the Water Framework Directive of EU. Lakes in reference conditions with sufficient biological data are available for several boreal lake types with the exception of naturally eutrophic lakes. An empirical approach is one alternative for estimating the reference conditions of such lakes. We used the water transparency of the naturally eutrophic Lake Tuusulanjärvi recorded in August in the early 1910s to estimate reference values for phytoplankton biomass and chlorophyll a concentrations. Three phytoplankton samples during August 2000–2001 corresponded to the estimated reference values for total biomass (<5.6 mg l^?1) and chlorophyll a (<28 μg l^?1), as did the simultaneous Secchi depths. The phytoplankton assemblage in these samples with 24 eutrophy indicators (17% of the total taxa number) corresponded in general the species list from the early 1900s, which as such could be regarded as reference assemblage. Furthermore, in August 2000, 3 years after intensive fish removal a prominent decrease in cyanobacterial biomass and toxin concentration was observed. The costs of the measures and studies in Lake Tuusulanjärvi during 1989–2003 have been approximately 2.5 million euros.     

Re-flooding a Historically Drained Wetland Leads to Rapid Sediment Phosphorus Release

Wetland restoration provides many benefits, but re-flooding historically drained land can have unintended negative consequences, including phosphorus (P) release from sediments. To investigate the effects of re-flooding on P cycling, this study monitored a restoration in Michigan that back-flooded old drainage ditches and re-flooded former wetland soils. Immediately after re-flooding, previously exposed sediments released substantial amounts of P to the water column. Soluble reactive phosphorus (SRP) concentrations in re-flooded areas were as high as 750 μg P l^?1. At peak P concentrations, there were about 20 times more SRP and 14 times more total P in the surface water than in the much smaller flooded area that existed before re-flooding. Prolific growth of filamentous algae and duckweed was observed in subsequent summers. Sedimental analyses suggest that most of the P released originated from iron-bound fractions. The highest SRP concentrations occurred during the first year when surface water dissolved oxygen was low (<5.5 mg l^?1). Similarly low oxygen in the second year after flooding was not associated with such high P concentrations. After 1 year postflooding, SRP concentrations remained below 50 μg P l^?1 (but still high enough to produce eutrophic conditions) until the end of sampling about 15 months after re-flooding. When re-flooding historically drained soils, managers should consider the potential for sediment P release to jeopardize restoration goals and therefore should incorporate longer term monitoring of water quality into restoration plans. Knowledge of sediment P amounts and forms can indicate the potential for P release to overlying water.     

Lake Chapo: a baseline study of a deep, oligotrophic North Patagonian lake prior to its use for hydroelectricity generation: I. Physical and chemical properties

A baseline study on a temperate, oligotrophic North Patagonian lake (Lake Chapo, Southern Chile) was made prior to the installation of a hydroelectric power station. Throughout one year (September 1986–October 1987) the physical and chemical properties of the lake were investigated monthly from the surface to a depth of 40 m. Lake Chapo is a deep, transparent (Secchi depth: 17–25 m), glacial lake located at 41°?27.5′?S and 72°?30′?W. It has a maximum depth of 298 m, mean depth of 183 m, surface area of 45.3 km² and water volume of 8.296 km³. The theoretical residence time of the water was 5.5 years. The temperature regime is monomictic with the mixed temperature between 8.1–8.8?°C. Maximum temperature at the surface was 18.7?°C during thermal stratification in summer when the epilimnion had a thickness of about 20 m. The conductivity was low (20.3–23.8 μS cm^?1) as was the buffering capacity of a predominantly CO₂-carbonate system. The predominant cations were Ca⁺²¿ Na⁺¿Mg⁺²¿K⁺. The phosphorous and nitrogen contents were very low (soluble reactive ortophosphate: 0–1.5 μg P l^?1, total phosphorus: 0.3–4 μg P l^?1 and nitrate: 0–35 μg N l^?1), which is typical of North Patagonian lakes.     

Effect of photoperiod,light intensity and carbon sources on biomass and lipid productivities of Isochrysis galbana

Biomass and lipid productivities of Isochrysis galbana were optimized using nutrients of molasses (4, 8, 12 g l^?1), glucose (4, 8, 12 g l^?1), glycerol (4, 8, 12 g l^?1) and yeast extract (2 g l^?1). Combinations of carbon sources at different ratios were evaluated in which the alga was grown at three different light intensities (50, 100 and 150 μmol m^?2 s^?1) under the influence of three different photoperiod cycles (12/12, 18/6 and 24/0 h light/dark). A maximum cell density of 8.35 g l^?1 with 32 % (w/w) lipid was achieved for mixotrophic growth at 100 μmol m^?2 s^?1 and 18/6 h light/dark with molasses/glucose (20:80 w/w). Mixotrophic cultivation using molasses, glucose and glycerol was thus effective for the cultivation of I. galbana.     

Dust mediated transfer of phosphorus to alpine lake ecosystems of the Wind River Range,Wyoming, USA

Alpine lakes receive a large fraction of their nutrients from atmospheric sources and are consequently sensitive to variations in both the amount and chemistry of atmospheric deposition. In this study we explored the spatial changes in lake water chemistry and biology along a gradient of dust deposition in the Wind River Range, Wyoming. Regional differences were explored using the variation in bulk deposition, lake water, sediment, and bedrock geochemistry and catchment characteristics. Dust deposition rates in the Southwestern region averaged 3.34 g m^?2 year^?1, approximately three times higher than deposition rates in the Northwestern region (average 1.06 g m^?2 year^?1). Dust-P deposition rates ranged from 87 µg P m² day^?1 in the Northwestern region to 276 µg P m² day^?1 in the Southwestern region. Subalpine and alpine lakes in the Southwestern region had greater total phosphorus (TP) concentrations (5–13 µg L^?1) and greater sediment phosphorus (SP) concentrations (2–5 mg g^?1) than similar lakes elsewhere in the region (1–8 µg L^?1 TP, 0.5–2 mg g^?1 SP). Lake phosphorus concentrations were related to dissolved organic carbon (DOC) across vegetation gradients, but related to the percent of bare rock, catchment area to lake area, and catchment steepness across dust deposition gradients. Modern phytoplankton and zooplankton biomasses were two orders of magnitude greater in the Southwest than in the Northwest, and alpine lakes in the Southwest had a unique diatom species assemblage with relatively higher concentrations of Asterionella formosa, Pseudostaurosira pseudoconstruens, and Pseudostaurosira brevistriata. These results suggests that catchment controls on P export to lakes (i.e. DOC) are overridden in dominantly bare rock basins where poor soils cannot effectively retain dust deposited P.     

Nitrate availability and hydrophyte species richness in shallow lakes

1. Submerged plant richness is a key element in determining the ecological quality of freshwater systems; it has often been reduced or completely lost. 2. The submerged and floating‐leaved macrophyte communities of 60 shallow lakes in Poland and the U.K. have been surveyed and species richness related to environmental factors by general linearised models. 3. Nitrogen, and more specifically winter nitrate, concentrations were most important in explaining species richness with which they were inversely correlated. Phosphorus was subsidiary. Such an inverse relationship is consistent with findings in terrestrial communities. Polish lakes, with less intensively farmed catchments, had greater richness than the U.K. lakes. 4. The richest U.K. communities were associated with winter nitrate‐N concentrations of up to about 1–2 mg L^?1 and may correspond with ‘good’ ecological quality under the terms of the European Water Framework Directive. Current concentrations in European lowlands are often much higher.     

Controls of organic and inorganic carbon in randomly selected Boreal lakes in varied catchments

Organic and inorganic carbon concentrations in lakes and the links to catchment and water quality were studied in variable landscapes using the Finnish Lake Survey data base including 874 randomly selected lakes sampled during autumn overturn. The median total organic carbon (TOC) in these boreal lakes was 7.8 mg l^?1, the median total inorganic carbon (TIC) 1.6 mg l^?1 and the median partial pressure of CO₂ (pCO₂) 900 μatm. When the data was divided into subgroups according to land use in the catchment, the proportion of TIC of the total carbon (TC) in lakes was highest (31%) in agricultural areas and lowest (10%) in peatland areas. Elevated TIC concentrations were associated with agricultural land in the catchment, whereas elevated TOC concentrations were observed in lakes with high peatland proportion in the catchment. Two contrasting important sources of CO₂ in lakes were identified on the basis of statistical analysis of the data; weathering processes in the catchments and decomposition of organic matter. CO₂ was also strongly associated with total nutrients TN and TP, implying the importance of quality of organic matter and availability of nutrients for the decomposition processes.     

In vitro propagation of <Emphasis Type="Italic">Psoralea corylifolia</Emphasis> L. by somatic embryogenesis in cell suspension culture

An effective protocol was developed for in vitro propagation of Psoralea corylifolia via somatic embryogenesis in cell suspension culture. Embryogenic callus was obtained on Murashige and Skoog (MS) medium supplemented with 6 μM naphthaleneacetic acid (NAA) and 30 μM glutamine from transverse TCLs from 10-day-old hypocotyl explants with a 96.4% frequency. Embryogenic callus produced a higher number of somatic embryos (123.7 ± 1.24 per gram fresh weight callus) on MS medium containing 30 g l^?1 sucrose, 1 μM NAA, 4 μM benzyladenine (BA), 15 μM glutamine and 2 μM abscisic acid (ABA) after 4 weeks of culture. Somatic embryos successfully germinated (97.6%) on ½ MS medium containing 20 g l^?1 sucrose, 8 g l^?1 agar and supplemented with 2 μM BA, 1 μM ABA and 2 μM gibberellic acid (GA₃) within 2 weeks of culture. Somatic embryos developed into normal plants, which hardened with 100% efficiency in soil in a growth chamber. Plants were successfully transferred to greenhouse and subsequently established in the field. Plant survival percentage in the field differed with seasonal variations. Average psoralen content of 12.9 μg g^?1 DW was measured in different stages of somatic embryo development by high-performance liquid chromatography (HPLC). This protocol will be helpful for efficient propagation of elite clones on a mass scale, conservation efforts of this species and for secondary metabolites production studies.     

Determination of tipping points for aquatic plants and water quality parameters in fish pond systems: A multi-year approach

High levels of nutrients in fish ponds by fish farming may cause significant eutrophication leading to a loss in species richness and a decrease of cover of aquatic plants to phytoplankton dominance. This shift can be represented by a tipping point where a significant change in the state of the ecosystem is observed such as a change from high to low aquatic plants species richness and cover. A total of 100 fish ponds were studied during five years in the Dombes region, France, to determine tipping points in aquatic plant richness and cover using chlorophyll α (CHL), water transparency, Total N (TN) and Total P (TP) gradients with two statistical methods. The relationships between tipping points, nutrient loads and yearly variations in weather conditions were also evaluated. Looking at the five years data, tipping points were observed in aquatic plant richness at 6 and 60 μg/L for CHL, and at 3.90 mg/L for TN concentration; as well as at 70 cm for water transparency, but no tipping point was found with TP. For aquatic plant cover, tipping points were observed at 11 μg/L for CHL, 2.42 mg/L for TN, 0.05 mg/L for TP, and at 62 cm for water transparency. These tipping points showed a significant decrease of aquatic plant species richness and cover, linked to the nutrient concentrations which drive the competition between the primary producers phytoplankton and aquatic plants. However, tipping points could vary significantly between years. The inter-annual variability may be due to an early occurrence of phytoplankton blooms in some ponds in a year preventing the establishment of aquatic plants, and thus influencing the value of tipping points. Weather conditions influence the competition between primary producers by impacting chlorophyll α and nutrients concentrations. When weather conditions supported increased nutrient concentrations, the development of phytoplankton and aquatic plants was facilitated and tipping points in aquatic plant richness and cover occurred with relatively high values. Thus, a significant decrease of plant cover and richness occurred at higher level of nutrients compared to the other years. In these cases, aquatic plants dominated over phytoplankton for the spring period, and also often during summer. In conclusion, tipping points observed are mainly linked to the competition between aquatic plants and phytoplankton. In shallow and eutrophic systems like fish ponds where nutrients are not a limiting resource, weather conditions act temporarily during spring as the main regulator of this competition.     

<Emphasis Type="Italic">Elodea canadensis</Emphasis> (Michx.) in Polish lakes: a non-aggressive addition to native flora

Non-indigenous invasive aquatic plants affect macrophyte community composition, structure and abundance, and are recognised as one of the major causes of biodiversity loss in aquatic ecosystem. Their mass development poses serious ecological, sociological and economical threats in many countries. We investigated biological, physicochemical, hydromorphological and geographical data from 447 Polish lowland lakes to recognise the phenomenon of invasive macrophyte species and to identify environmental factors that determine their occurrence and abundance. We focused on Elodea canadensis (EC) as the most common and widespread alien hydrophyte in Poland. Phytocoenoses of EC were present in 40 % of analysed lakes. The area occupied by EC ranged from 2.3 to 5.5 % of the total vegetated area per year, on average, with a maximum of 37.8 %. A comparison between two sub-periods (2005–2009 and 2010–2013) revealed a lack of increase in EC mean abundance within the analysed period. Likewise, no evidence of EC effects on the native flora, its richness and diversity and no effects on the ecological status of the lakes were found. In the analysed period, EC did not demonstrate invasive character in Polish lakes. The habitat preference of EC was biased towards larger and deeper lakes located at higher altitudes, with longer water retention times, better water quality and better ecological status based on macrophytes compared with non-invaded lakes. We found altitude and water quality as the main determinants of EC occurrence within the sampled area. We suggest that both climate warming and accelerated eutrophication may contribute to reducing EC spread in Europe observed during recent decades.     

Reference conditions and WFD compliant class boundaries for phytoplankton biomass and chlorophyll-a in Alpine lakes

The intercalibration (IC) exercise is a key element in the implementation of the Water Framework Directive (WFD) in Europe. Its focus lies on the harmonization of national classification methods to guarantee a common understanding of ‘Good Ecological Status’ in surface waters. This article defines reference conditions and sets class boundaries for deep (mean depth >15 m, IC lake type L-AL3) and moderately deep (mean depth 3–15 m, IC lake type L-AL4) Alpine lakes >0.5 km². Data were collated from each of the five EU member states included in the Alpine Geographical Intercalibration Group (Alpine GIG: Austria, France, Germany, Italy and Slovenia). Hydro-morphological, chemical and biological data from 161 sites (sampling stations) in 144 Alpine lakes over a period of seven decades were collated in a database. Based on a set of reference criteria, 18 L-AL3 and 13 L-AL4 reference sites were selected. Reference conditions were defined using a combined approach, based on historical, paleolimnological and monitoring data in conjunction with trophic modelling and expert judgement. Reference values and class boundaries were set for annual mean total biomass (biovolume), and then derived for annual mean chlorophyll-a using a regression between the two parameters. In order to allow for geographical differences within the Alpine GIG and to facilitate the inclusion of the broadly defined common IC types and national lake types, ranges were defined for each reference value. Range of reference values are 0.2–0.3 mg l^?1 (L-AL3) and 0.5–0.7 mg l^?1 (L-AL4) for total biovolume and 1.5–1.9 μg l^?1 (L-AL3) and 2.7–3.3 μg l^?1 (L-AL4) for chlorophyll-a. Depending on lake type and variable, the ecological quality ratios (EQR) for setting the class boundaries lie between 0.60 and 0.75 for the high/good class boundary and between 0.25 and 0.41 for the good/moderate class boundary. The response of sensitive phytoplankton taxa along a nutrient gradient and the occurrence of ‘undesirable conditions and secondary effects’ as defined in the WFD was used to validate the class boundary values, which are thus considered to be compliant with the requirements of the WFD.     

Prokaryotic communities of the north-eastern Mongolian soda lakes

We have studied the activity and composition of several geochemically significant physiological groups of bacteria in more than twenty alkaline salt lakes of the north-east Mongolia steppe with water salinity from 3 to 390 g l^?1 and pH values ranging from 9.0 to 10.6. Active and diverse microbial communities have been found in most of the lakes. The methanotrophic bacteria were represented by the Type I members. Among the culturable forms of sulfur-oxidizing bacteria obligately chemolithoautotrophic and haloalkaliphilic representatives of the genera Thioalkalimicrobium and Thioalkalivibrio were detected in the sediments at high numbers (up to 10⁶ cells ml^?1). The largest population of anaerobic phototrophic bacteria was represented by purple sulfur bacteria of the Ectothiorhodospiraceae family. Salinity was the key factor in determining the activity and the composition of the microbial communities. The most diverse and active prokaryotic populations, including aerobic and anaerobic phototrophic, methanogenic, methanotrophic, sulfur-oxidizing, sulfate-reducing and nitrifying bacteria, were found in lakes with salinity less than 60 g l^?1. In hypersaline lakes with a salinity >100 g l^?1, the sulfur cycle remained active due to the activity of extremely halotolerant and alkaliphilic sulfur bacteria, while other important functional groups responsible for nitrification and methane oxidation processes were not detected. Overall, the prokaryotic communities of the Mongolian alkaline salt lakes represent an interesting new example of a diverse community of haloalkaliphilic bacteria well adopted to a broad salinity range.     

Winter bloom of picoeukaryotes in Hungarian shallow turbid soda pans and the role of light and temperature

The seasonal dynamics of picophytoplankton communities in shallow turbid alkaline pans in Hungary was studied between July 2006 and May 2007. Similarly to other aquatic environments in the temperate zone, dominance of picocyanobacteria was observed in summer and that of picoeukaryotes in winter. The mild winter in 2006–2007, with midday water temperatures of 5–10°C, resulted in large winter phytoplankton blooms (maximum chlorophyll a concentration 800 μg l^?1) in the shallow pans. The phytoplankton was composed of single-celled picoeukaryotes and had a maximum of 108 × 10⁶ cells ml^?1 in Büdös-szék pan, 50 × 10⁶ cells ml^?1 in Kelemen-szék pan in April 2007, and 47 × 10⁶ cells ml^?1 in Zab-szék pan in March 2007. In order to explain the winter dominance of picoeukaryotes, we isolated picoeukaryotic and picocyanobacterial strains and determined the temperature and light dependence of their photosynthesis. Under temperatures <15°C, the photosynthetic activity of the picoeukaryotic strain was higher and their light utilization was better than those of the picocyanobacterial strain. The results indicate that low temperature and light intensity in winter provide a competitive advantage to picoeukaryotes, while higher temperatures and light intensity are more favorable for picocyanobacteria.     

Contribution of transparent exopolymer particles to carbon sinking flux in an oligotrophic reservoir

Transparent exopolymer particles (TEP) compose an important pool of particulate organic matter (POM) in aquatic systems. However, no studies of TEP contribution to C export to sediment exist for freshwaters. We quantify the contribution of TEP to C sinking fluxes in an oligotrophic reservoir (Quéntar, Southern Spain) by monitoring TEP in the water column and TEP, particulate organic carbon (POC) and dry weight in sedimentation traps. TEP sinking fluxes ranged from 0.73 to 183.23 mg C m^?2 day^?1 and from 0.51 to 177.04 mg C m^?2 day^?1 at the surface and at the bottom layer, respectively. These values represent that, over an annual basis, 5.59 Ton TEP-C (over 61.32 Ton POC) are exported, on an average, from the water column to the sediment of Quentar reservoir. TEP concentrations (average = 48.0 μg XG eq l^?1) were lower than the scarce data reported for freshwaters. No significant relationships between TEP and Chl a concentrations or BA were observed. Average value for daily sedimentation flux (6.63 g Dry Weight m^?2 day^?1) in the study reservoir was higher than that documented for low productive natural aquatic ecosystems as a consequence of the high amount of allochthonous material input characterizing reservoirs. TEP contributed to C export to sediment with a value that range from 0.02 to 31%. Our results show that even in man-made systems, which are predominantly controlled by allochthonous inputs, TEP may be relevant for explaining POM settling fluxes.