Bacterial chitin hydrolysis in two lakes with contrasting trophic statuses

Chitin, which is a biopolymer of the amino sugar glucosamine (GlcN), is highly abundant in aquatic ecosystems, and its degradation is assigned a key role in the recycling of carbon and nitrogen. In order to study the significance of chitin decomposition in two temperate freshwater lakes with contrasting trophic and redox conditions, we measured the turnover rate of the chitin analog methylumbelliferyl-N,N'-diacetylchitobioside (MUF-DC) and the presence of chitinase (chiA) genes in zooplankton, water, and sediment samples. In contrast to the eutrophic and partially anoxic lake, chiA gene fragments were detectable throughout the oligotrophic water column and chiA copy numbers per ml of water were up to 15 times higher than in the eutrophic waters. For both lakes, the highest chiA abundance was found in the euphotic zone--the main habitat of zooplankton, but also the site of production of easily degradable algal chitin. The bulk of chitinase activity was measured in zooplankton samples and the sediments, where recalcitrant chitin is deposited. Both, chiA abundance and chitinase activity correlated well with organic carbon, nitrogen, and concentrations of particulate GlcN. Our findings show that chitin, although its overall contribution to the total organic carbon is small (~0.01 to 0.1%), constitutes an important microbial growth substrate in these temperate freshwater lakes, particularly where other easily degradable carbon sources are scarce.     

Nutrient balances and phytoplankton dynamics in two agriculturally loaded shallow lakes

The impact of agriculture was estimated on two shallow, eutrophic lakes, Lake Kotojärvi and Lake Villikkalanjärvi in southern Finland. The main emphasis was on phosphorus and nitrogen budgets and on the phytoplankton dynamics. Special attention was paid to internal P loading and blue-green algal blooms. The mean Tot-P load from agricultural land was 1.2 kg ha^-1 a^-1 in both basins and Tot-N loads were 19 kg ha^-1 a^-1 in L. Villikkalanjärvi and 12 kg ha^-1 a^-1 in L. Kotojärvi. The Tot-P input to L. Kotojärvi was on an average 0.62 g m^-2 a^-1 (per lake surface area), and the Tot-N input 9.1 g m^-2 a^-1. The corresponding inputs to L. Villikkalanjärvi were 3.1 and 57 g m^-2 a^-1, respectively. The annual variation followed the runoff volumes. About half of the Tot-P and one third of the Tot-N load was retained in L. Kotojärvi. In L. Villikkalanjärvi the retention was only 24% for Tot-P and 19% for Tot-N. The difference was very probably due to a longer theoretical retention time in L. Kotojärvi. In L. Villikkalanjärvi the mean concentration of Tot-P was 120 µg 1^-1 and that of Tot-N 1700 µg 1^-1 and the corresponding figures in L. Kotojärvi 67 and 990 µg 1^-1, respectively. The mean chlorophyll a concentration was, however, higher in L. Kotojärvi (26 µg 1^-1) than in L. Villikkalanjärvi (20 µg 1^-1). This was probably due to an internal P load in L. Kotojärvi: in 1988 the internal load of dissolved P was estimated to be as much as twofold the external load. In L. Villikkalanjärvi the internal dissolved P load was only up to 50% of the external input. In L. Kotojärvi the high internal P load coupled with a low DIN:DIP ratio resulted in a strong blue-green algal bloom in the summer of 1988. In L. Villikkalanjärvi blue-green algae were observed only in small amounts. Even in August 1990, when the DIN:DIP ratio was low enough to favor the occurrence of blue-green algae, they contributed only up to 10–15% of the total phytoplankton biomass.     

Bottom dynamics in lakes

A proper understanding of the bottom dynamic conditions (erosion, transportation, accumulation) in lakes is essential in most sedimentological contexts. Fine cohesive materials generally dominate the open water areas, whereas coarser deposits (sand, gravel) dominate shallow regions where erosion and transportation of fine materials prevail. At present, there is no physical model available which describes the linkage between the energy content of the water-mass and the capacity for sediment entrainment in open water areas. Water-mass energy depends on, e.g. wind direction, duration, velocity, fetch, and the presence of a thermocline. Entrainment depends on, e.g. density, compaction, water and organic content of the sediments and the number and type of bottom fauna. Four different methods are used to determine bottom dynamics, two aresite typical and two arelake typical.Site andlake typical methods each include one method based on collected field data and one based on theoretical data. One method, the cone apparatus, is presented for the first time. It consists of two cones, one of which has a narrow angle and the other a wide angle, which are zero adjusted at the sediment surface before being released to penetrate the sediments. The differential cone penetration, refered to as the penetration ratio, is used to indicate the degree of surficial sediment compaction. This simple, inexpensive instrument provides quantitative data on physical sediment characteristics which may be related to bottom dynamic conditions.     

Contrasting microcystin production and cyanobacterial population dynamics in two Planktothrix-dominated freshwater lakes

Microcystin concentrations in two Dutch lakes with an important Planktothrix component were related to the dynamics of cyanobacterial genotypes and biovolumes. Genotype composition was analysed by using denaturing gradient gel electrophoresis (DGGE) profiling of the intergenic transcribed spacer region of the rrn operon (rRNA-ITS), and biovolumes were measured by using microscopy. In Lake Tjeukemeer, microcystins were present throughout summer (maximum concentration 30 microg l(-1)) while cyanobacterial diversity was low and very constant. The dominant phototroph was Planktothrix agardhii. In contrast, Lake Klinckenberg showed a high microcystin peak (up to 140 microg l(-1)) of short duration. In this lake, cyanobacterial diversity was higher and very dynamic with apparent genotype successions. Several genotypes derived from DGGE field profiles matched with genotypes from cultures isolated from field samples. The microcystin peak measured in Lake Klinckenberg could be confidently linked to a bloom of Planktothrix rubescens, as microscopic and genotypic analysis showed identity of bloom samples and a toxin-producing P. rubescens culture. Toxin-producing genotypes were detected in the microbial community before they reached densities at which they were detected by using microscopy. Cyanobacterial biovolumes provided additional insights in bloom dynamics. In both lakes, the microcystin content per cell was highest at the onset of the blooms. Our results suggest that while genotypic characterization of a lake can be valuable for detection of toxic organisms, for some lakes a monitoring of algal biomass has sufficient predictive value for an assessment of toxin production.     

Long- and short-term dynamics of submerged macrophytes in two shallow eutrophk lakes

1. Periods with clear water and abundant submerged vegetation have alternated with periods of turbid water and sparse vegetation during recent decades in Lake Tåkern and Lake Krankesjön, two shallow, calcium-rich, moderately eutrophic lakes in southern Sweden, Between 1983 and 1991, submerged vegetation (predominant species: Chara tomentosa, Nitellopsis obtusa, Myriophyllum spicatum) covered about 50% of the open lake area in Lake Tåkern. In Lake Krankesjön, submerged vegetation was sparse during 1983–84, but increased continuously in the following years and covered about 50% of the open lake area by 1990 and 1991. Potamogeton pectinatus was the first species to expand in Lake Krankesjön, but was later replaced by C. tomentosa. 2. During 1983–84, turbidity was high in Lake Krankesjön, which indicated that submerged macrophytes were light-limited. During 1986–91, there was a negative correlation between the areal coverage of charophytes and angiosperms, indicating that competition for space had become an important limiting factor. The same negative correlation was found in Lake Tåkern for 1983–91. 3. Charophytes had much higher biomass per unit area than angiosperms in both lakes and reduced water movement considerably. This was probably one reason for the increase of water transparency in Lake Krankesjön during the spatial expansion of these plants. Charophytes also stored large amounts of phosphorus and nitrogen, Charophytes are probably superior competitors for both space and nutrients and thus have competitive advantage over angiosperms in this lake type. 4. In Lake Krankesjön, both P. pectinatus and C. tomentosa were negatively affected by high water level during the growing period. Total disappearance of submerged vegetation occurred in both lakes after catastrophic events (dry-out during summer or mechanical damage by ice) caused by extremely low water level. Changes in water level are thus one of the most important reasons for among-year fluctuations in areal coverage of submerged macrophytes in these lakes.     

Contrasting bacterioplankton community composition and seasonal dynamics in two neighbouring hypertrophic freshwater lakes

We characterized the bacterioplankton community and its seasonal dynamics in two neighbouring hypertrophic lakes by denaturing gradient gel electrophoresis (DGGE) analysis of short (193 bp) 16S ribosomal DNA polymerase chain reaction (PCR) products obtained with primers specific for the domain Bacteria. Lake Blankaart is turbid and has a high phytoplankton biomass and episodic cyanobacterial blooms, whereas biomanipulated Lake Visvijver is characterized by clearwater conditions and the establishment of a dense charophyte vegetation. Both lakes were dominated by bacterial groups commonly found in freshwater habitats (e.g. ACK4 cluster of Actinomycetes; ACK stands for clones isolated from the Adirondack mountain lakes) . Yet, cluster analysis and principal components analysis (PCA) revealed that taxon composition of the bacterioplankton community of the two lakes differs substantially and consistently throughout the season. During the study year (1998), the bacterioplankton community of both lakes showed a distinct seasonal pattern. Lake Blankaart showed a clear differentiation between winter, spring, summer and autumn. In Lake Visvijver, summer samples differed greatly from spring, autumn and winter samples. We hypothesize that the contrasting bacterioplankton in the two neighbouring shallow lakes is determined largely by the presence or absence of macrophytes.     

Photosynthesis,mixotrophy and microbial plankton dynamics in two high Arctic lakes during summer

Photosynthesis and microbial plankton dynamics of two lakes in the Kongsfjorden catchment of Spitzbergen (Svalbard Archipelago, 78°N) were investigated during the summer of 2000. One of the lakes (Tvillingvatnet) served as the water supply for the village of Ny Ålesund. The other was a deeper, larger unnamed lake in the Ossian Sarsfjella reserve—named Lake OS in this study. Both lakes can be classified as oligotrophic on the basis of chlorophyll a and inorganic nutrient concentrations. Chlorophyll a concentrations ranged between 0.33 and 1.65 µg l ^-1 in Tvillingvatnet and 0.2 and 0.3 µg l ^-1 in Lake OS. The phytoplankton was dominated by chrysophytes and cryptophytes, with the diatom Rhizosolenia and a number of dinoflagellate species. Rates of photosynthesis were typically low, between 24.5 µg and 1.0 mg l ^-1 day ^-1 in Tvillingvatnet (photosynthetic efficiency 0.004–0.26), and between 3.1 and 29.5 µg l ^-1 day ^–1 in Lake OS (photosynthetic efficiency 0.0019–0.0085). Among the phytoflagellates (PNAN) there were a number of mixotrophs which reached their peaks of abundance before other PNAN. Mixotrophy appeared to provide a competitive advantage. Grazing rates for the mixotroph Dinobryon ranged between 0.063 and 1.12 pg C cell ^-1 day ^-1 in Lake OS and between 0.22 and 1.11 pg cell ^-1 day ^-1 in Tvillingvatnet, with rates increasing between July and August. However, Dinobryon removed less than 1% of bacterial biomass day ^-1, while the heterotrophic nanoflagellates (HNAN) removed up to 28% of bacterial biomass day ^-1. Bacterial concentrations were low, with a maximum of 28.8×10 ⁸ l ^-1 in Tvillingvatnet and 23.6×10 ⁸ l ^-1 in Lake OS. Ciliated protozoan and rotifer diversity in the plankton was low.     

Temperature, growth and dietary effects on fish mercury dynamics in two Ontario lakes

A bioenergetics-based model was used to investigate the effects of temperature, growth and dietary exposure on methylmercury dynamics in walleye (Stizostedion vitreum) and yellow perch (Perca flavescens) from two lakes sampled in northwestern Ontario. Orange Lake was smaller, warmer, had slower fish growth and higher mercury concentrations in yearling yellow perch and walleye (three fold difference in 40 cm walleye) than Trout Lake. The model was applied to test the hypothesis that higher water temperatures in Orange Lake increased metabolic needs, food consumption and mercury uptake in fish. The effects of different growths rates in the lakes were also considered. Temperature/metabolic effects and growth effects on internal methylmercury dynamics in walleye and perch were predicted to occur but be of secondary importance. Different dietary exposure to methylmercury was likely the dominant source of variation in fish mercury concentrations between the two lakes.     

安徽沿江两个浅水型湖泊越冬水鸟的季节动态(英文)

安徽沿江浅水型通江湖泊湿地是东亚-澳大利亚迁徙水鸟的重要越冬地和停歇地。近年来,高强度的渔业养殖使湿地严重退化,对越冬水鸟构成威胁。为了解湿地变化对越冬迁徙水鸟的影响,2007年11-2008年4月和2008年11月-2009年4月,对安徽菜子湖和升金湖11个样带内越冬水鸟的种类、数量及空间分布进行了调查,并分析了湖泊渔业模式对水鸟分布的影响。两个湖泊共统计到越冬水鸟7目12科43种。其中,菜子湖群38种,密度为8.2ind./hm2;升金湖42种,密度为3.5ind./hm2,优势种为鸿雁(Anser cygnoides)、豆雁(Anser fabalis)、小天鹅(Cygnus columbianus)和黑腹滨鹬(Calidris alpina)。越冬水鸟种类和数量在12月底-次年1月上旬达到最大值,但不同类型越冬群最大数量出现的具体时期有所不同。根据水鸟组成的聚类分析,可将水鸟栖息地分为三组。水鸟的分布与渔业模式有关,在自然捕捞区,鹤类、雁鸭类和鸻鹬类密度较大,在围网养殖区密度较小,而鹭类的密度在各湖区变化都较小。本研究结果提示,发展可持续渔业对于长江中下游浅水湖泊湿地越冬水鸟资源的保护具有重要意义。     

Phytoplankton and its dynamics in two tropical lakes: a tropical and temperate zone comparison

Temporal patterns of phytoplankton biomass and community structure are described for two Kenyan lakes and subsequently compared with patterns reported in other tropical and temperate lakes. Lake Naivasha had a lower and more seasonally variable (10×) biomass, with a seasonal shift between diatoms and blue-greens, while the L. Oloidien biomass was less variable (3.7×) and dominated by blue-greens. Biomass and chlorophyll a were strongly correlated and in turn were coupled to the level of total phosphorus. A total of 143 and 94 taxa were described for L. Naivasha and L. Oloidien, respectively.The comparative analysis showed: a) a paucity of exclusively tropical species; b) that more than 30 percent of the species in two highly saline Kenyan lakes were also present in the two freshwater lakes; c) no evidence for a postulated decline of phytoplankton species abundance with latitude from the temperate zone to the tropics; d) that the low fraction of chrysophyte biomass in tropical lakes is a function of trophy rather than of latitude; e) that the fraction of chlorophyte biomass in tropical lakes is generally higher than in temperate lakes; f) that the proportion of nannoplankton in the two Kenyan freshwater lakes is not different from that in temperate lakes of the same trophy; g) that seasonal or annual biomass oscillations in the tropics are not systematically lower than in the temperate zone; h) evidence for large inter-year difference in the max.:min. biomass ratio in the only tropical lake (L. Naivasha) for which such data are available; i) that an average biomass ratio appears predictable for tropical lakes from the proportion of the sediment surface in contact with epilimnetic water. Overall, no evidence was found that the freshwater tropical phytoplankton composition or dynamics differ in any fundamental fashion from that observed in the temperate lakes during the summer.Contribution number 147 of the Limnology Research Centre, McGill University.     

Continuous and discrete extreme climatic events affecting the dynamics of a high-arctic reindeer population

Climate at northern latitudes are currently changing both with regard to the mean and the temporal variability at any given site, increasing the frequency of extreme events such as cold and warm spells. Here we use a conceptually new modelling approach with two different dynamic terms of the climatic effects on a Svalbard reindeer population (the Brøggerhalvøya population) which underwent an extreme icing event (“locked pastures”) with 80% reduction in population size during one winter (1993/94). One term captures the continuous and linear effect depending upon the Arctic Oscillation and another the discrete (rare) “event” process. The introduction of an “event” parameter describing the discrete extreme winter resulted in a more parsimonious model. Such an approach may be useful in strongly age-structured ungulate populations, with young and very old individuals being particularly prone to mortality factors during adverse conditions (resulting in a population structure that differs before and after extreme climatic events). A simulation study demonstrates that our approach is able to properly detect the ecological effects of such extreme climate events.     

The North Atlantic Oscillation and plankton dynamics in two European lakes –- two variations on a general theme

Long‐term data on water temperature, phytoplankton biovolume, Bosmina and Daphnia abundance and the timing of the clear‐water phase were compared and analysed with respect to the influence of the North Atlantic Oscillation (NAO) in two strongly contrasting lakes in central Europe. In small, shallow, hypertrophic Müggelsee, spring water temperatures and Daphnia abundance both increased more rapidly than in large, deep, meso/oligotrophic Lake Constance. Because of this, the clear‐water phase commenced approximately three weeks earlier in Müggelsee than in Lake Constance. In Müggelsee, the phytoplankton biovolume during late winter/early spring was related to the NAO index. In Lake Constance, where phytoplankton growth was inhibited by intense downward mixing during all years studied, this was not the case. However, in both lakes, interannual variability in water temperature, in Daphnia spring population dynamics and in the timing of the clear‐water phase, were all related to the interannual variability of the NAO index. The Daphnia spring population dynamics and the timing of the clear‐water phase appear to be synchronized by the NAO despite large differences between the lakes in morphometry, trophic status and flushing and mixis regimes, and despite the great distance between the lakes (～700 km). This suggests that a great variety of lakes in central Europe may possibly have exhibited similar interannual variability during the last 20 years.     

Bacterial and algal symbiont dynamics in early recruits exposed to two adult coral species

Coral Reefs - Corals live in a symbiotic relationship with various microorganisms including bacteria, some of which are essential for host health and survival. Bacterial assemblages are typically...     

The Arctic Oscillation predicts effects of climate change in two trophic levels in a high-arctic ecosystem

During recent decades there has been a change in the circulation of atmospheric pressure throughout the Northern Hemisphere. These variations are expressed in the recently described Arctic Oscillation (AO), which has shown an upward trend (associated with winter warming in the eastern Arctic) during the last three decades. We analysed a 12‐year time series on growth of Cassiope tetragona (Lapland Cassiope) and a 21‐year time series on abundance of a Svalbard reindeer population. High values of the AO index were associated with reduced plant growth and reindeer population growth rate. The North Atlantic Oscillation index was not able to explain a significant proportion of the variance in either plant growth or reindeer population fluctuations. Thus, the AO index may be a better predictor for ecosystem effects of climate change in certain high‐arctic areas compared to the NAO index.     

Storm impacts on phytoplankton community dynamics in lakes

In many regions across the globe, extreme weather events such as storms have increased in frequency, intensity, and duration due to climate change. Ecological theory predicts that such extreme events should have large impacts on ecosystem structure and function. High winds and precipitation associated with storms can affect lakes via short‐term runoff events from watersheds and physical mixing of the water column. In addition, lakes connected to rivers and streams will also experience flushing due to high flow rates. Although we have a well‐developed understanding of how wind and precipitation events can alter lake physical processes and some aspects of biogeochemical cycling, our mechanistic understanding of the emergent responses of phytoplankton communities is poor. Here we provide a comprehensive synthesis that identifies how storms interact with lake and watershed attributes and their antecedent conditions to generate changes in lake physical and chemical environments. Such changes can restructure phytoplankton communities and their dynamics, as well as result in altered ecological function (e.g., carbon, nutrient and energy cycling) in the short‐ and long‐term. We summarize the current understanding of storm‐induced phytoplankton dynamics, identify knowledge gaps with a systematic review of the literature, and suggest future research directions across a gradient of lake types and environmental conditions.     

Bacterial community dynamics in two full‐scale wastewater treatment systems with functional stability

Aims: To characterize the bacterial community dynamics over 1 year in two full‐scale wastewater treatment systems operated under constant conditions and exhibiting stable performance. Methods and Results: Functional stability was defined and quantified by the effluent concentration of biological oxygen demand, total nitrogen and ammonia. Community dynamics were investigated using specific PCR followed by terminal restriction fragment length polymorphism (T‐RFLP) of the 16S rRNA gene. The T‐RFLP results indicated that during the period of functional stability, the bacterial community structures in two full‐scale wastewater treatment systems were not stable, and the average change rates every 15 days of the two systems were 22·6 ± 6·9 and 21·6 ± 7·3%, respectively. The corresponding species with dominant T‐RFs were determined by clonal sequencing and T‐RFLP. Based on Pareto–Lorenz distribution curves, it was observed that only a small number of micro‐organisms were numerically dominant in the two systems. Conclusions: The results of this study showed that, throughout the period of the study, the bacterial community structure changed significantly in two full‐scale wastewater treatment systems despite the stable function. Significance and Impact of the Study: The findings enrich the theory involving the relation between bacterial community dynamics and functional stability in full‐scale wastewater treatment plants.     

Bacterial activities in shallow lakes – a comparison between extremely acidic and alkaline eutrophic hard water lakes

Hydrobiologia - Bacterial abundance and activity were investigated by DAPI-staining and 3H-thymidine incorporation method in samples from a very shallow, hypertrophic hard water lake and from...     

Seasonal phosphorus dynamics in the surficial sediment of two shallow temperate lakes: a solid-phase and pore-water study

This study examined phosphorus (P) dynamics by surveying the solid-phase and pore-water of the surficial sediment in a mesotrophic and eutrophic shallow lake in Maine, USA. Both lakes were dimictic, developed hypolimnetic anoxia, and released sedimentary P. We examined the controls on sedimentary P release by considering two possible mechanisms; mineralization and release of sedimentary organic P, and dissolution of Fe hydroxide following the onset of anoxia. The temporal investigation of solid-phase included sequential chemical extraction and ³¹P NMR analysis, and the pore-water included use of equilibrium samplers. In both lakes, the relative contribution of organic P to total sedimentary P release was minor compared to Fe hydroxide-associated P. The eutrophic lake, however, had more evidence of microbial uptake of sedimentary P and a higher degree of rapid P transformation in the water column. Sediment polyphosphates were dynamic and possibly contributed to hypolimnetic P accumulation. The pore-water Fe and P profiles exhibited similar temporal patterns as the solid-phase results. Together, they showed an upward migration of the redoxcline in the sediment, from winter to summer, resulting in the accumulation of Fe-bound P at the sediment?Cwater interface in the winter followed by its release into the summer.