Diet niche relationships among predator and prey fish species in their early life stages in Lake Võrtsjärv (Estonia)

In Lake Võrtsjärv pikeperch was observed not to shift to piscivory in their first autumn of life, although juvenile stages of a variety of fish species were abundant in the lake. It was hypothesized that the diets of predator and prey fish fry overlap and that coarse fish species are important food competitors for juvenile piscivores and thus, pikeperch and perch fry do not shift to piscivory during their first growing season. To discover the possible linkages in this pattern, in 2009 the feeding relationships of pikeperch, perch, ruffe and roach fry were analysed. The stomach content analyses showed that in the summer period, Mesocyclops leuckarti was the most frequent prey for perch and ruffe, pikeperch consumed Leptodora kindti in large quantities, and roach ate mostly plant material. Towards autumn, M. leuckarti was the most abundant prey for all percids. However, average stomach content weight and the number of prey items eaten by ruffe were considerably higher than for other fish fry. Since the feeding opportunities of fish fry are considered poor in the examined lake, the prey has the potential to restrict the recruitment to piscivory of their predators, as prey fish seem to have better abilities to persist in this ecosystem. Furthermore, supposed competition in the juvenile stage may result in a reduced top‐down effect on coarse fish.     

Functions of Calcium-bound Phosphorus in Relation to Characteristics of Phosphorus Releasing Bacteria in Sediment of a Chinese Shallow Lake (Lake Wabu)

Sediment phosphorus (P) release accelerates lake eutrophication, while retention capacity and release potential of different P fractions, calcium-bound P (CaCO₃～P) in particular, still remains unclear. Fractionation and sorption behaviors of phosphorus were studied in sediment of a Chinese shallow lake (Lake Wabu) and two inflowing rivers from December 2011 to December 2012. Abundance of P releasing bacteria was analyzed, and their main species were isolated using a culture-dependent method and identified by their 16S rDNA sequences. CaCO₃～P release abilities of these bacteria were also tested. In sediments of both the lake and rivers studied, the rank order of the different P extracts was CaCO₃～P > iron-bound P > acid-soluble organic P > hot NaOH-extractable organic P. At the same time, CaCO₃～P content and equilibrium P concentration (EPC₀) values in river sediments were significantly higher than those in the lake. Additionally, EPC₀ changes non-monotonically with increasing CaCO₃～P content, forming a V-shaped curve, with the lowest EPC₀ at an intermediate CaCO₃～P content (around 180 mg kg^?1). Below this threshold, CaCO₃～P was a component strengthening P retention; moreover, CaCO₃～P became an active species responsible for P release. Noticeably, between the two parts divided by this threshold, the differences in abundance of inorganic phosphorus solubilizing bacteria (IPB) and organic phosphorus mineralizing bacteria (OPB) were insignificant and the dominant IPB species clustered together. By contrast, OPB was distinguished from each other, whose dominant species isolated from the part with higher CaCO₃～P content, namely Novosphingobium sp., exhibited a stronger ability to solubilize CaCO₃～P. Shortly, with lower content, CaCO₃～P tends to stabilize P in sediment; while with higher content or under eutrophic condition, it shifted into P source, with some OPB species becoming the main factors to drive its release.     

Potential Mobility of Phosphorus in Different Types of Lake Sediment

The fractional composition and potential mobility of sediment phosphorus was investigated in a number of Swedish lakes with different characteristics. Differences between sediments regarding P release patterns in laboratory experiments with varying pH and redox conditions could largely be explained by differences in the fractional composition of the sedimentary P. Sediments from sewage-loaded lakes contained considerably more loosely adsorbed P than unpolluted lakes. P release was redox-sensitive and strongly favoured by high pH values in sediments with a high content of aluminium and iron-bound P. Other sediments released primarily organic and loosely adsorbed P, and in such cases less P was released and redox and pH conditions had less effect. Comparisons with P release rates determined by mass balance calculations were made.     

Seasonal Variation of Virioplankton in a Eutrophic Shallow Lake

Lake Donghu is a typical eutrophic freshwater lake in which high abundance of planktonic viruses was recently revealed. In this study, seasonal variation of planktonic viruses were observed at three different trophic sites, hypertrophic, eutrophic, and mesotrophic regions, and the correlation between their abundances and other aquatic environmental components, such as bacterioplankton, chlorophyll a, burst size, pH, dissolved oxygen, and temperature, was analyzed for the period of an year. Virioplankton abundance detected by transmission electron microscope (TEM) ranged from 5.48 × 10⁸ to 2.04 × 10⁹ ml⁻¹ in all the sites throughout the study, and the high abundances and seasonal variations of planktonic viruses were related to the trophic status at the sampled sites in Lake Donghu. Their annual mean abundances were, the highest at the hypertrophic site (1.23×10⁹ ml⁻¹), medium at the eutrophic site (1.19×10⁹ ml⁻¹), and the lowest at the mesotrophic site (1.02×10⁹ ml⁻¹). The VBR (virus-to-bacteria ratio) values were high, ranging from 49 to 56 on average at the three sampled sites. The data suggested that the high viral abundance and high VBR values might be associated with high density of phytoplankton including algae and cyanobacteria in this eutrophic shallow lake, and that planktonic viruses are important members of freshwater ecosystems.     

Isolation and Characterization of Organic Phosphorus-Mineralizing Bacteria in Sediment of a Chinese Large Shallow Eutrophic Lake (Lake Taihu)

The organic phosphorus mineralizing bacteria (OPB) play an important role in phosphorus cycling in lake sediment, to which less attention has been paid. Monthly sediment samples in 2009 ending in October, together with the samples from different seasons (May, July, October, and December) in 2008, were collected at 6 sites in a Chinese large shallow eutrophic lake (Lake Taihu). The sediment OPB numbers ranged from 2.2 × 10⁶ to 1.79 × 10⁸ cells g^?1 (dry weight) at different sampling sites and in different seasons, with the average being 3.88 × 10⁷ cells g^?1 (dry weight). Its number was highest at the most polluted site and peaked in spring and summer, which can be explained by the enrichment of organic matter in sediment. Furthermore, there existed a significant positive relationship between the OPB numbers and alkaline phosphatase activities in the sediment. The 6 OPB strains isolated from the sediment were distinct in terms of their colony morphology on the yolk agar, biochemical characteristics and phosphorus release abilities. According to the 16S rDNA sequences, these OPB belong to Bacillus cereus, Stenotrophomonas maltophilia, Stenotrophomonas sp., Bacillus cereus, Xanthomonas sp., Pseudomonas sp. They were distinguished from the OPB species recorded in a Chinese small shallow eutrophic lake whose sediment organic content was remarkably higher. Taken together, organic matter shaped the OPB community not only quantitatively but also qualitatively, which in concert facilitated the enzymatic hydrolysis of organic phosphorus in lake sediment.     

Distribution of Sediment Phosphorus Fractions in Hypertrophic Strongly Stratified Lake Verevi

Lake Verevi is a hypertrophic and strongly stratified (partly meromictic) small temperate lake. Vertical distribution of sediment phosphorus fractions as well as iron, manganese, organic matter and calcium carbonate of the deep bottom sediment was determined. The study focused on the ecologically important layer of the sediment [<20(45) cm]. In the uppermost layers of the sediment, NaOH-NRP (organic P) dominated while HCl-RP (apatite-P) became dominant in some deeper layers below 7 cm. Extremely high concentrations of labile phosphorus fraction (NH₄Cl-RP) indicated the low binding capacity of phosphorus by lake sediment. Due to sediment and hypolimnion anoxia, the internal load of phosphorus in this lake is most likely. Potentially mobile phosphorus fractions (NH₄Cl-RP, BD-RP, NaOH-NRP) formed 301 kg in upper 10 cm thick sediment layer of hypolimnetic bottom sediment (40% of lake bottom area).     

Phosphorfällung über Calciumcarbonat im eutrophen Wallersee (Salzburger Alpenvorland, Österreich). Coprecipitation of Phosphorus with Calcite in the Eutrophic Wallersee (Alpine Foreland of Salzburg,Austria)

By chemical analyses at the eutrophic Wallersee (Austria) a considerable precipitation of calcite during autumn overturn was found. It is a pure anorganic calcite precipitation, caused by the loss of free carbonic acid to the atmosphere during the mixing of epilimnic and hypolimnic water. An essential coprecipitation of phosphorus with the anorganic calcite precipitation could be shown by calcium and phosphorus balances and by SEM investigations. During the epilimnic biogenic calcite precipitation (in summer) phosphorus coprecipitation makes 0.19% of the calcium fallout. Phosphorus coprecipitation increases up to 0.42 % during the anorganic calcite precipitation when autumn overturn takes place. With respect to the total phosphorus sedimentation in the lake 25 % are coprecipitated with calcite.     

Sediment oxygen demand in man-made Lake Ton-Ton (Uruguay)

A study on sediment metabolism was carried out during 1986 in Lake Ton-Ton, Uruguay. Sediment oxygen demand (SOD) from chemical and biological origin was measured in undisturbed sediment cores taken from the deepest part of the lake. Mean SOD rate for the study period (51.56 mgO₂ m^–2 h^–1) corresponded well with the eutrophic state of the lake. During stratification, SOD from chemical origin accounted for 69–87% of total SOD, while SOD from biological origin was dominating for the rest of the year, except in July. Biological respiration was principally of microbial origin. Hypolimnetic temperature was the main factor controlling SOD rates (r = 0.771,p < 0.001). Nevertheless, freshly sedimented phytodetritus from anAnabaena bloom, together with a renewed input of oxygen to bottom water were responsible for the maximum SOD values, recorded at the beginning of a mixing period in April (72.51 mgO₂ m^–2 H^–1).     

Contribution to the Study on Bottom Sediment in Lake Balaton. I. Determination of Phosphorus Minerals in the Sediment

The aim of the investigation was to determine the phosphorus containing minerals present in Lake Balaton sediment. Chemical, electron microscope and X-ray diffraction analysis succeeded in identifying hydroxylapatite. No proof was found for the presence of other phosphorus minerals.     

Among-habitat and Temporal Variability of Selected Macroinvertebrate Based Metrics in a Mediterranean Shallow Lake (NW Spain)

According to the European Water Framework Directive, waterbodies have to be classified on the basis of their ecological status using biological quality elements, such as macroinvertebrates. This needs to take into consideration the influence of natural variation (both spatial and temporal) of reference biological communities as this may obscure the effects caused by anthropogenic disturbance. We studied the influence of among-habitat and temporal (seasonal and interannual) changes on the macroinvertebrate communities of an Iberian shallow lake and the variability of 21 measures potentially useful for bioindication purposes. Two series of data were examined: (a) macroinvertebrate samples taken on four occasions over an annual cycle were used to assess the effects of seasonality and among-habitat variability; (b) macroinvertebrate samples collected in three consecutive summers were used to assess interannual variability. Coefficients of variation, expressed as percentage, were used to quantify the effect of among-habitat and temporal variability on the selected metrics. According to our results, % Insecta, Shannon–Wiener diversity index and the qualitative taxonomic metrics (measures based on number of taxa) were robust in terms of temporal (seasonal and interannual) and among-habitat variability. Abundance ratio and some metrics based on functional feeding groups were highly variable. Therefore, qualitative taxonomic metrics may be promising tools in biomonitoring programs of Mediterranean shallow lakes due to their comparatively low variability.     

The relationship between Chironomus plumosus burrows and the spatial distribution of pore-water phosphate, iron and ammonium in lake sediments

1. To study the influence of chironomids on the distribution of pore‐water concentrations of phosphate, iron and ammonium, we conducted a laboratory experiment using mesocosms equipped with two‐dimensional pore‐water samplers, filled with lake sediment and populated with different densities of Chironomus plumosus. 2. Specially designed mesocosms were used in the study. A 6‐mm deep space between the front plate and the pore‐water sampler at the back plate was just thick enough to allow the chironomids to live undisturbed, yet thin enough to force all the burrows into a two‐dimensional plane. 3. The courses of the burrows were observed during the experiment as oxidised zones surrounding them, as well as being identified with an X‐ray image taken at the end of the experiment. 4. We investigated the relationship between C. plumosus burrows and spatial patterns of pore‐water composition. Concentrations of the three ions were significantly less around ventilated burrows (54% to 24%), as bioirrigation caused a convective exchange of pore‐water enriched with dissolved species compared with the overlying water, and also because oxygen imported into the sediment resulting in nitrification of ammonium, oxidation of iron(II) and a co‐precipitation of phosphate with Fe(III) oxyhydroxides. 5. In mesocosms with chironomids, new (redox) interfaces occurred with diffusive pore‐water gradients perpendicular to the course of burrows and the site of major phosphate, ammonium and iron(II) release shifted from the sediment surface to the burrow walls.     

Recruitment of Total Phytoplankton,Chlorophytes and Cyanobacteria from Lake Sediments Recorded by Photosynthetic Pigments in a Large,Shallow Lake (Lake Taihu,China)

Recruitment of total phytoplankton, chlorophytes and cyanobacteria from lake sediments to the water column was studied using photosynthetic pigments at one site (1.5 m) in Lake Taihu, a large shallow lake in China. Samples were taken weekly from the migration traps installed on the bottom from March to May 2004. Abundance of total phytoplankton, chlorophytes and cyanobacteria were represented by Chlorophyll (Chl) a, b, and phycocyanin (PC), respectively. Over the three months, total phytoplankton, chlorophytes, and cyanobacteria corresponding to 48.9%, 68.9% and 316.2% of their initial concentrations in surface sediments were recruited in Lake Taihu. However, compared with their increase in pelagic abundance over the same period, the recruitment accounted for a rather small inoculum. Accompanying the recruitment, total phytoplankton and chlorophytes declined and cyanobacteria increased in the upper 0–2 cm sediments; colonies of Microcystis aeruginosa in the water column enlarged from small size with several cells to large colonies with hundreds of cells. Thus, overwintering and subsequent growth renewal of pelagic phytoplankton merits further study and comparison with benthic survival and recruitment. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Deposition,resuspension, and decomposition of particulate organic matter in the sediments of Lake Itasca,Minnesota, USA

Sediment traps were used to investigate the settling, resuspension, and decomposition of particulate organic matter in Lake Itasca, MN (USA). Traps were deployed in the epilimnion and hypolimnion of the deepest basin during June, 1988, sampled twice during stratified conditions (August, September) and once after the lake had mixed (October). The downward flux of particulate material increased from summer to fall. The net sedimentation of organic matter ranged from 0.6 to 2.3 g m^–2 d^–1 at 4 m and increased to 2.1 to 3.2 g m^–2 d^–1 two meters above the bottom sediment indicating that resuspended sediment was at least 33% of the settling mass during all periods. The C:N ratios of captured particles (6.8–9.5) were between the ratios of plankton (5.8 to 6.8) and the sediments (9.9 to 10.2) but smaller than the ratios of terrestrial organic materials (13.5 to 222). The monosaccharide compositions of the entrapped particles were similar to plankton samples and different from the distinct composition of the sediments. Capture of rebound particles similar to the primary flux and not decomposition may have been responsible for this similarity. Total monosaccharide concentrations were lower in the sediments than in entrapped particles. Individual sugars exhibited different patterns of accumulation in the sediments. Glucose was lowest in sediments when the relative concentrations were compared to those in source materials and entrapped particles. In contrast, sediments had the highest rhamnose and fucose concentrations. Bacterial biomass could only account for small portions of these sugars in the sediment. The distinct monosaccharide composition of resuspended sediments was not strongly recorded in materials captured by the sediment traps even after the lake had mixed.     

Phytoplankton and Epipelon Responses to Clear and Turbid Phases in a Seepage Lake (Buenos Aires,Argentina)

Annual changes in the algal density and concentrations of chlorophyll a, total phosphorus, and organic matter were analyzed in water and sediments at four sites characterized by the presence or absence of submerged and emergent macrophytes, during turbid‐ and clear‐water conditions to determine the contribution of the algal components of the plankton and the epipelon and to identify the most typical species in each community. Three states were recognized: one turbid and two clear, with different submerged macrophyte cover. The peaks of phytoplankton and epipelon occurred in the turbid phase, whereas the highest proportion of true epipelic algae in sediments was reached in the second clear phase. The Oscillatoriaceae dominated during the turbid phase in the water and throughout the entire year within the sediments. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mass balance models of phosphorus in sediments and water

Models are presented in order of progressively more complex spatial resolution in which the effects on the sediment-water interactions are emphasized. For simple models, the diagnostic approach of calculating the net settling and return of total phosphorus is demonstrated with data from Lake Erie. For more complex models, the effects of interbasin transport and vertical mixing are shown to be important in determining the pathways of the sediment-released or sediment-bound phosphorus in the water column.