The effects of temperature on bacterial production in a dimictic eutrophic lake

Abstract The incorporation of [³H](methyl)thymidine into DNA by the planktonic heterotropic bacteria of Little Crooked Lake (Noble Country, IN) was determined at different incubation temperatures. The highest rates of thymidine incorporation generally occurred at temperatures exceeding the in situ temperature of the sample. The optimal temperature for thymidine incorporation ranged from 1.0–3.4 times the in situ temperature. As the summer of 1983 progressed, the optimal temperatures for thymidine incorporation by epilimnetic samples and the in situ temperatures converged. This trend was reversed as fall overturn was approached.     

On the dynamical response of Lake Chapala, Mexico to lake breeze forcing

Fluctuations in the atmospheric characteristics, as well as variations in the water level of Lake Chapala are discussed. Field measurements of the atmospheric characteristics and lake level during December 1996 through January 1997 are described; using spectrum analysis of synchronous time series. The findings suggest that the variability is due to the diurnal cycle of atmospheric elements. Lake breeze circulation plays an important role in the area of Lake Chapala; since it was registered in 83% of the data. Periodic fluctuations in atmospheric pressure and wind generate significant seiche amplitudes in the lake, with the periods of about 6 h. With the help of a simple model, the seiche parameters are estimated. The amplitude of one-nodal seiches on one of the edges of the lake; is on average equal to 18 mm. This wave should generate currents of approximately 0.012 m s^–1 at the lake`s centre in the area of the nodal line. The experimental results on the thermal regime and circulation of Lake Chapala are discusssed as well. Surface temperature variations were registered at the eastern part of the lake. In all cross-sections, typical spatial variations of 3 °C were registered, over a distance of 100–300 m. A bouy station registered movements of an internal thermal front in the body of the water. The leading edge of the front was accompanied by intense internal waves, in the form of internal KdeV solitones. The front near the buoy station was produced by the movement of a warm body of water travelling from the shallow eastern part of the lake and trigered by morning breeze.     

Mathematical models and computer programmes for the investigation of hydrophysical processes in Lake Shira

Physical processes determine to great extent the habitat of hydrobionts, as well as the transfer and sedimentation of substances, the intensity of pollution and rate of natural purification of water bodies. Mathematical models of different levels of complexity, developed to investigate hydrophysical processes in lakes, are discussed in this paper. The numerical algorithms and computer programmes described can be used to determine the influence of the morphometric characteristics and weather on the temperature regime of Lake Shira (Khakasia, Siberia) and the pattern of the wind currents. Examples of calculating the temperature regime in the context of a one- dimensional model and of calculating the parameters of wind currents in the water body of a simple geometrical form are given.The study suggests that the pattern of wind currents in Lake Shira is significantly affected by the density stratification, which depends not only on temperature but also on salinity. In order to construct a realistic pattern of currents a 3-D computer model of Lake Shira must be developed and used to estimate the validity of the two-dimensional and one-dimensional models. The present research can be further developed by extending the obtained algorithms to three-dimensional problems, taking into account the heat exchange, salinity and the geometry (bathymetric contours) of the water body. Calculations can be made for Lake Shira and the obtained data used in biophysical models.     

Field evaluation of a sound system to reduce estuarine fish intake rates at a power plant cooling water inlet

An acoustic deterrent system producing 20–600 Hz sound was used to repel estuarine fishes away from a power station cooling water inlet. During sound emission, total fish impingement decreased by 60%. The avoidance response varied among species from no effect to highly efficient deflection. Lampetra fluviatilis and Pleuronectiformes were less affected by the sound system while the deflection of clupeoid species was particularly effective. Average intake rates of Clupea harengus and Sprattus sprattus decreased by 94·7 and 87·9%, respectively. The results were explained as a function of species‐specific differences in hearing ability and swimming performance. In general, species without swimbladders showed no or a moderate response while intake rates of species with accessory structures increasing the hearing abilities, such as a swimbladder or a functional connection between the swimbladder and the inner ear, were significantly reduced during test periods.     

大型浅水湖泊鄱阳湖湿地微生物的研究现状

鄱阳湖是我国第一大淡水湖泊,同时也是一个典型的季节性通江浅水湖泊,独特的水文特征和多样的湿地景观类型形成了复杂多样的微生物群落。本文综述了鄱阳湖水文节律、营养盐及重金属含量对湖泊微生物群落组成的影响,以及水位高程和湿地围垦对鄱阳湖湿地土壤微生物分布特征的影响,同时还探讨了未来湖泊湿地微生物的研究方向和鄱阳湖所拥有的独特研究条件,以期为未来湖泊微生物研究提供重要参考。     

Geochemical processes of iron and manganese in a seasonally stratified lake affected by coal-mining drainage in China

Lake water, pore water, and sediments were sampled in a seasonally stratified lake affected by coal-mining drainage. Contrasting geochemical processes of iron and manganese in summer were investigated by studying the seasonal distributions of iron and manganese species in the water column, pore water, and sediments. The results show that iron buildup in the water during summer was mainly from the gradual dissolution of particulate matter due to the pH decrease, whereas manganese oxide reduction and manganese-bound carbonate dissolution near the sediment–water interface were mainly responsible for manganese accumulation in the stratified hypolimnion. The geochemical processes of iron and manganese in the sediments during early diagenesis were also discussed in terms of the possible influence on the overlying water. Received: November 29, 1999 / Accepted: June 30, 2000     

Migration and survival of Atlantic salmon Salmo salar smolts in a large natural lake

An investigation with acoustic telemetry of the passage of Salmo salar smolts through a large natural lake found heavy mortality occurred at the river‐to‐lake confluences (mean 31.2% km^?1), but was lower in the main body of the lake (mean 2.4% km^?1). Predation was a significant pressure on emigrating smolts as tagged pike Esox lucius aggregated at river‐to‐lake confluences during the peak of the smolt run. Tagged smolts mainly emmigrated into the lake in the late evening after dusk, possibly as a predator‐avoidance behaviour.     

Study of the sound produced byPimpla instigator [Hymenoptera,Ichneumonidae] during host selection

When females ofPimpla instigator inspect objects as possible oviposition sites, they use their antennae to make the objects resonate. The antennae are not used as drum sticks, but serve merely to transmit shock waves generated within the female's body. Transmission of the shock waves to the substrate is mediated through vesicles situated at the extreme tip of the distal segment of each antenna. The present results support the hypothesis that acoustical inspection of the environment is a part of the exploratory behaviour of this insect.      

Hydrologic and anthropogenic influences on aquatic macrophyte development in a large,shallow lake in China

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Factors controlling hypolimnetic ammonia accumulation in a lake

The factors controlling the degree of hypolimnetic ammonia accumulation in Lake Onogawa are discussed based on periodic observations since 1993. The standing stock of ammonia in the bottom 9 m of the water column was a good measurement for determining the extent of the hypolimnetic ammonia accumulation. It varied threefold from 144 mmol m⁻² in 1998 to 429 mmol m⁻² in 1996. The correlation between the annual maxima of the ammonia standing stocks and the annual maxima of the thickness of anoxic layers was significant at P = 0.01. This fact suggests that the degree of development of the anoxic layer is the primary factor controlling the extent of hypolimnetic ammonia accumulation. Sporadic local heavy rainfalls in 1998 perturbed the water column, and the formation of the anoxic layer was postponed more than one month, resulting in a lower level of hypolimnetic ammonia accumulation in 1998. A thick mineral deposit apparently formed during the local heavy rainfall and seemed to enclose the freshly deposited organic matter, which might be an effective source material of the hypolimnetic ammonia, and resulted in a low level of ammonia accumulation in 1999. By 2000, the lake seems to have recovered from the perturbation, suggesting that the major part of the hypolimnetic ammonia is derived from fresh organic matter deposited within a year. Received: March 11, 2001 / Accepted: August 26, 2001     

Major contribution of sulfide-derived sulfur to the benthic food web in a large freshwater lake

In freshwater systems, contributions of chemosynthetic products by sulfur-oxidizing bacteria in sediments as nutritional resources in benthic food webs remain unclear, even though chemosynthetic products might be an important nutritional resource for benthic food webs in deep-sea hydrothermal vents and shallow marine systems. To study geochemical aspects of this trophic pathway, we sampled sediment cores and benthic animals at two sites (90 and 50 m water depths) in the largest freshwater (mesotrophic) lake in Japan: Lake Biwa. Stable carbon, nitrogen, and sulfur isotopes of the sediments and animals were measured to elucidate the sulfur nutritional resources for the benthic food web precisely by calculating the contributions of the incorporation of sulfide-derived sulfur to the biomass and of the biogeochemical sulfur cycle supporting the sulfur nutritional resource. The recovered sediment cores showed increases in ³⁴S-depleted sulfide at 5 cm sediment depth and showed low sulfide concentration with high δ³⁴S in deeper layers, suggesting an association of microbial activities with sulfate reduction and sulfide oxidation in the sediments. The sulfur-oxidizing bacteria may contribute to benthic animal biomass. Calculations based on the biomass, sulfur content, and contribution to sulfide-derived sulfur of each animal comprising the benthic food web revealed that 58%–67% of the total biomass sulfur in the benthic food web of Lake Biwa is occupied by sulfide-derived sulfur. Such a large contribution implies that the chemosynthetic products of sulfur-oxidizing bacteria are important nutritional resources supporting benthic food webs in the lake ecosystems, at least in terms of sulfur. The results present a new trophic pathway for sulfur that has been overlooked in lake ecosystems with low-sulfate concentrations.     

Climatic effects on the phenology of lake processes

Populations living in seasonal environments are exposed to systematic changes in physical conditions that restrict the growth and reproduction of many species to only a short time window of the annual cycle. Several studies have shown that climate changes over the latter part of the 20th century affected the phenology and population dynamics of single species. However, the key limitation to forecasting the effects of changing climate on ecosystems lies in understanding how it will affect interactions among species. We investigated the effects of climatic and biotic drivers on physical and biological lake processes, using a historical dataset of 40 years from Lake Washington, USA, and dynamic time‐series models to explain changes in the phenological patterns among physical and biological components of pelagic ecosystems. Long‐term climate warming and variability because of large‐scale climatic patterns like Pacific decadal oscillation (PDO) and El Niño–southern oscillation (ENSO) extended the duration of the stratification period by 25 days over the last 40 years. This change was due mainly to earlier spring stratification (16 days) and less to later stratification termination in fall (9 days). The phytoplankton spring bloom advanced roughly in parallel to stratification onset and in 2002 it occurred about 19 days earlier than it did in 1962, indicating the tight connection of spring phytoplankton growth to turbulent conditions. In contrast, the timing of the clear‐water phase showed high variability and was mainly driven by biotic factors. Among the zooplankton species, the timing of spring peaks in the rotifer Keratella advanced strongly, whereas Leptodiaptomus and Daphnia showed slight or no changes. These changes have generated a growing time lag between the spring phytoplankton peak and zooplankton peak, which can be especially critical for the cladoceran Daphnia. Water temperature, PDO, and food availability affected the timing of the spring peak in zooplankton. Overall, the impact of PDO on the phenological processes were stronger compared with ENSO. Our results highlight that climate affects physical and biological processes differently, which can interrupt energy flow among trophic levels, making ecosystem responses to climate change difficult to forecast.     

The diatom flora of Lake Eyre South: a large episodically filled salt lake in South Australia

Thirty-three diatom taxa were collected from the large terminal salt lake, Lake Eyre South, located in south-central Australia. The diatom assemblage included taxa that were widely distributed in marine and saline athalassic habitats in both northern and southern hemispheres, with the diatom flora of Lake Eyre South most similar to that of southern Africa. This study represents the first report on the diatom flora of Lake Eyre South and supports the findings that episodically filled lakes do not appear to be good evolutionary loci.     

Transport and accumulation of bloom-forming cyanobacteria in a large, mid-latitude lake: the gyre-Microcystis hypothesis

 Toxic cyanobacterial blooms have occurred in the near-shore waters of the North Basin of Lake Biwa, Japan, since 1994, and have been attributed to deterioration of water quality in the enriched littoral zone of the lake. From 1997 onwards, the bloom-forming cyanobacteria have been observed with increasing frequency in the deep offshore waters of the North Basin. In the present study, we examined the mechanisms responsible for these bloom populations in the main body of the lake. Specifically, we addressed the hypothesis that buoyant, nutrient-replete colonies of cyanobacteria are generated inshore, are advected offshore by large-scale horizontal transport processes, and subsequently accumulate in the downwelling center of large surface gyres that characterize the overall circulation pattern in the epilimnion of the North Basin. Diel variations of Microcystis biomass at the center and the edge of the Lake Biwa gyre were monitored at 6-h intervals on August 23–24, 2000, and the horizontal distribution of buoyant Microcystis was determined on October 6. The hydrodynamic structure of the first gyre was determined over the preceding 2 days by an on-board Acoustic Doppler Current Profiler (ADCP). The gyre was characterized by a counterclockwise horizontal current that could potentially advect material large distances offshore, a downwelling current near the center of the gyre, and an upwelling current at the edge of the gyre, caused by the radial pressure gradients. The biomass of Microcystis near the water surface was greater at the center than at the edge of the gyre, and the biomass at 5 m depth at the edge of the gyre was greater than that at the water surface or at the thermocline near the edge of the gyre. The results are consistent with the gyre-Microcystis hypothesis, and show the potential for accumulation of large concentrations of cyanobacteria in deep offshore lake environments that are normally considered unsuitable for cyanobacterial blooms. Received: July 16, 2001 / Accepted: March 6, 2002     

Sequential rather than interactive effects of multiple stressors as drivers of phytoplankton community change in a large lake

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Invasive mussels modify the cycling,storage and distribution of nutrients and carbon in a large lake

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Carbon, nitrogen, and sulfur isotope changes and hydro-geological processes in a saline lake chain

The ionic concentrations,conductivity and pH of water in the Lake Chany complex in West Siberian Russia change from the mouth to the interior of the lake. This difference is indicative of marked evaporation of lake water from the closed water body system in the dry climate of Western Siberia. The carbon isotope composition of particulate organic matter (POM, composed mainly of phytoplankton) clearly changes, along with the pH of the water, reflecting the concentration of dissolved CO₂. Carbon and nitrogen isotope signatures of Chironomus plumosus larvae, a benthic invertebrate that may feed on bulk lake sediment, systematically increase, along with those of POM and sediment organic matter (SOM), through the lake chain. Both sulfate-sulfur and nitrogen isotope compositions of the POM and SOM increase with distance from the estuary into the Lake Chany complex. Heavier sulfur and nitrogen isotope recycling from the sediment, caused by microbial sulfate reduction and denitrification, respectively, may have led to the increased sulfate-sulfur and nitrogen isotope compositions of the POM and SOM.     

Estimation of the long-term nutrient budget and thresholds of regime shift for a large shallow lake in China

In this study, we apply an integrated empirical and mechanism approach to estimate a comprehensive long-term (1953–2012) total nitrogen (TN) and total phosphorus (TP) loading budget for the eutrophic Lake Chaohu in China. This budget is subsequently validated, firstly, by comparing with the available measured data in several years, and secondly, by model simulations for long-term nutrient dynamics using both Vollenweider (VW) model and dynamic nonlinear (DyN) model. Results show that the estimated nutrient budget is applicable for further evaluations. Surprisingly, nutrient loading from non-point sources (85% for TN and 77% for TP on average) is higher than expectation, suggesting the importance of nutrient flux from the soil in the basin. In addition, DyN model performs relatively better than VW model, which is attributed to both the additional sediment recycling process and the parameters adjusted by the Bayesian-based Markov Chain Monte Carlo (MCMC) method. DyN model further shows that the TP loading thresholds from the clear to turbid state (631.8 ± 290.16 t y⁻¹) and from the turbid to clear state (546.0 ± 319.80 t y⁻¹) are significantly different (p < 0.01). Nevertheless, the uncertainty ranges of the thresholds are largely overlapped, which is consistent with the results that the eutrophication of Lake Chaohu is more likely to be reversible (74.12%) than hysteretic (25.53%). The ecosystem of Lake Chaohu shifted from the clear to turbid state during late 1970s. For managers, approximately two-thirds of the current TP loading must be reduced for a shift back with substantial improvement in water quality. Because in practice the reduction of loading from a non-point source is very difficult and costly, additional methods beyond nutrient reduction, such as water level regulation, should be considered for the lake restoration.