Littoral Stations Research Articles

Structure and dynamics of plankton communities in the coastal zone of the Curonian Lagoon of the Baltic Sea in 2017–2021 in the period of Cyanobacterial bloom

The structure and dynamics of plankton communities in the coastal zone of the Curonian Lagoon of the Baltic Sea in January-December 2017–2021 was studied. It was found that at the coastal shallow littoral station surrounded by macrophytes the species diversity was higher, and the quantitative characteristics of phytoplankton and zooplankton were lower in all seasons and years of the study than at the deeper coastal station located behind the macrophyte belt. The exception was the period when, as a result of surge events, the phytoplankton biomass in the coastal littoral in October–November 2018 increased to 326–627 g/m3. Every year, “blooms” of water by Cyanobacteria with different intensity and duration were observed at the Lagoon. The abundant of cells of potentially toxic Сyanobacteria exceeded the World Health Organization standard, as a rule, in the summer months at a deep-water coastal station, especially in 2017–2018. This had a negative impact on the state of the entire ecosystem, primarily on zooplankton organisms, in which communities the proportion of dead individuals increased. Water during the period of Cyanobacterial “blooms” in summer and autumn 2017–2018 also had an acute toxic effect on planktonic test organisms.

Nonspecif ic response of Lake Baikal phytoplankton to anthropogenic impact.

In this study, we present the first results on oxidation stress in Lake Baikal phytoplankton and its adaptation to environmental changes under anthropogenic impact. As was shown, the changing of the dominant species of phytoplankton collected from the surface water layer (~0.3 m) took place from February to June 2021. Phytoplankton were collected at a nearshore station (a littoral station at a distance of ~0.01 km from the shoreline, depth to bottom is ~5 m) and an offshore station (a pelagic station at a distance of ~1 km from the shoreline, depth to bottom is ~543 m). In February, dinoflagellates were dominant (~40 %) as well as diatoms (≤33 %) and green algae (≤12 %). Their biomass was 100 mg·m–3. In March, chrysophytes were dominant (up to 50 %) as well as cryptophytes (≤43 %) and dinoflagellates (≤30 %). Their biomass was 160–270 mg·m–3. In April, biomass increased up to 700–3100 mg·m–3 with the dominance of large cell dinoflagellates (up to 99 %), chrysophytes (up to 50 %), and cryptophytes (up to 35 %). By the end of the first decade of May, the percentage of dinoflagellates decreased and that of cryptophytes increased. In the second decade of May, the percentage of diatoms increased up to ~26–38 % but phytoplankton biomass was minimal (13–30 mg·m–3). By June, the percentage of diatoms in the samples reached 44–75 % at 60–550 mg·m–3. The oxidation stress of phytoplankton as a nonspecific adaptive response to a prolonged, intensive, or recurrent effect of a stress factor was estimated from the content of thiobarbituric acid reactive substances (TBARS). The mean content of these substances (markers of the lipid peroxidation) was determined spectrophotometrically. The oxidation stress of phytoplankton was revealed only when diatom algae dominated. It can be explained by adaptation of algae of other classes to the stress factor. The content of the lipid peroxidation markers in the coastal phytoplankton collected close to the settlement of Listvyanka known as a large touristic center was estimated from 100 to 500 μg·g–1 of dry weight of sample. During the period of diatom blooming in 2016 and 2018, oxidation stress of phytoplankton collected near large settlements was found. In phytoplankton from deep-water pelagic stations most remote from settlements, stress was not revealed. Using the method of gas chromatography, we showed a lower (up to 15 %) content of polyunsaturated fatty acids in phytoplankton characterized by stress occurrence. This confirms cell membrane damages. In Lake Baikal surface water, we found a higher content of synthetic anionic surfactants (sodium alkylbenzene sulfonates), which are components of detergents and cause oxidation stress of hydrobionts (up to 30 ± 4 μg·L–1). The presence of these substances in a water ecosystem can result in exhausting of phytoplankton cell resources, homeostasis imbalance, stress, pathological changes, and rearrangements in phytoplankton assemblage

Fatty Acid Changes in Nearshore Phytoplankton under Anthropogenic Impact as a Biodiversity Risk Factor for the World’s Deepest Lake Baikal

In this study, we present results on fatty acid analysis of phytoplankton of Lake Baikal, the world’s deepest lake, which differs from other lakes by its oceanic features. Since we used a large-mesh net, the net sample phytoplankton were primarily represented by the large elongated diatom Synedra acus. subsp. radians (Kützing) Skabichevskij. The similar algae composition of net samples of spring season phytoplankton collected at different sites of the lake allows us to compare results of the fatty acid analysis of these samples. The phytoplankton diversity of the sedimentation samples was contrary represented by 32 algae species. There are clear changes in the fatty acid composition of net phytoplankton exposed to anthropogenic impacts of varying intensity. The content of polyunsaturated fatty acids in phytoplankton collected from central stations (pelagic stations at a distance of ~10–30 km from the shoreline) without anthropogenic impact was higher by up to 15% than phytoplankton collected from nearshore stations (littoral stations at a distance of ~0.01–0.05 km from the shoreline) and offshore stations (pelagic stations at a distance of ~3 km from the shoreline). The interlaboratory precision of fatty acid determination of phytoplankton is estimated as ≤10%. We found high content of the lipid peroxidation marker (80–340 μg g−1 of dry weight) in phytoplankton from nearshore and offshore stations with intensive anthropogenic impact. In phytoplankton from central stations, we did not find any lipid peroxidation. Determination of unsaturated fatty acids, coupled with analysis of fatty acid peroxidation products, can be used to evaluate the level of anthropogenic impact in terms of ecological health and biodiversity conservation.

Floating Littoral Zone (FLOLIZ): A solution to sustain macroinvertebrate communities in regulated lakes?

Artificial water-level fluctuations (WLF) seriously threaten the biodiversity and functioning of littoral zones in lake ecosystems. The use of artificial floating islands (AFI) to compensate for the deleterious effects of WLF on littoral habitats has been of increasing interest to environmental managers. Yet, the ecological efficiency of this solution is still very poorly documented. AFI are usually designed as simple vegetated floating mats. In this study, we designed an artificial Floating Littoral Zone (FLOLIZ), which mimics a natural littoral zone composed of a terrestrial section vegetated with helophytes and several underwater levels containing soil and hydrophytes. Next, we aimed to assess the effectiveness of FLOLIZ in supporting macroinvertebrate communities. Three FLOLIZs were installed in three bays of a French hydroelectric reservoir marked by high WLF. Taxonomic and functional metrics of macroinvertebrate communities in the three FLOLIZs were compared with control littoral stations over four seasons of one year. The cumulated abundance, taxonomic richness and diversity were significantly higher in the FLOLIZs than in the control littoral stations, particularly when water level rose abruptly (i.e., in spring) and during the post-drawdown season (i.e., in summer). Functional profiles of macroinvertebrate communities significantly differed between FLOLIZs and control littoral stations. More specifically, communities in littoral control stations were dominated by highly mobile and resistant taxa (e.g., Beetles, Bugs, Chironomids), while communities in the FLOLIZs were dominated by less mobile species with longer life cycles (e.g., Hydra sp., Oligochaeta). These findings show that FLOLIZs were more successfully colonized by original, diversified, and abundant macroinvertebrate communities with respect to littoral control stations. These preliminary results suggest that FLOLIZs could provide suitable, biogenic habitats for macroinvertebrates in reservoirs exhibiting high WLF. Longer term monitoring, including of other compartments than macroinvertebrates (e.g., fish), could provide additional evidence that FLOLIZs mitigate the deleterious effects of high WLF on aquatic biodiversity.

Zooplankton Diversity of a Sub-Tropical Small Urban Wetland of Meghalaya, Northeast India with Remarks on Spatial Variations

Limnological survey of a small urban wetland of Meghalaya state of northeast India (NEI), undertaken at the littoral and semi-limnetic stations, reveals one of the biodiverse zooplankton assemblages (148 species belonging to 72 genera and 30 families) known from any lentic environ of the Indian sub-region. The speciose nature, peak constellation/sample of 83 zooplankton species, and diverse Rotifera (90 species) are hypothesized to environmental heterogeneity of this urban wetland in contrast to the general pattern of reduced richness expected in highly modified urban aquatic environments. The soft and de-mineralized waters are characterized by low zooplankton abundance. This study records high species diversity and evenness, and low dominance attributed to low and equitable abundance depicts ‘generalist’ nature of all species. Rotifera > Cladocera and Chydoridae > Lecanidae > Lepadellidae > Daphniidae are important at both stations, and Testudinellidae, Trichocercidae, and Macrothricidae are notable at the littoral station. Individual abiotic factors exert limited and differential spatial influence on various taxa, while the CCA registers a high cumulative influence of 10 abiotic factors on the littoral (87.37%) and semi-limnetic (75.81%) zooplankton assemblages. The spatial variations of composition, richness, similarities, abundance, diversity indices, and of the influence of individual abiotic factors are hypothesized to habitat heterogeneity amongst the sampled stations.

Study of zooplankton community structure for aquaculture planning in Lony dam reservoir

Zooplanktons form an important intermediary step in the grazing food chain in aquatic ecosystem. The qualitative analysis of zooplankton has shown that the rotifers, protozoans, cladocerans and copepods were the major components of its total bulk in lony dam. The maximum magnitude of zooplanktons abundance was found in summer months and minimum was noted in early monsoon months. The study includes 28 species of zooplanktons which shows its moderate bio-diversity. The remarkable seasonal changes of total zooplanktons at present water body were registered. The littoral stations had high zoo planktonic density than limnetic sites. The quantitative variability of zooplankton has high-lighted their mesotrophic nature. The mean maximum and minimum values of zooplanktons were recorded.

Habitat use by early life stages of the re-established striped bass and conspecific fish species along the St. Lawrence estuary

The St. Lawrence estuary (SLE) supports important nursery habitats for many fish species, including the newly re-established population of striped bass (Morone saxatilis).The present study aims to describe pelagic (5 m isobaths) and littoral (<1.5 m-deep) nearshore habitats of the SLE and to document their use by fish larvae and age-0 juveniles, especially for striped bass. From June to September 2014, 162 pelagic and 188 littoral stations were characterized in terms of biophysical conditions (turbidity, salinity, temperature, dissolved oxygen and chlorophyll-a concentration), abundance of main preys and fish assemblages. Striped bass larvae identification was confirmed with genetic analyses. In the pelagic and littoral zones, four estuarine habitats were defined based on turbidity and salinity: an upstream freshwater section (UP), an oligohaline (O-ETM) and a mesohaline (M-ETM) estuarine turbidity maximum zone, and a downstream polyhaline section (DOWN). Our results emphasized the spatial partitioning of fish early life stages among contrasting habitats, potentially to minimize interspecific competition. In the SLE, striped bass is using the wide spectrum of habitats available. At the onset of striped bass development, the UP and the O-ETM were the main nursery habitats, which is consistent with the known location of spawning grounds. Results suggest that the O-ETM provided the most suitable conditions for the species with optimal physical properties and abundant food resources. Later in the season, the M-ETM provided a favourable trade-off habitat offering a less optimal physical environment although potential for new prey.

Factors influencing the heterogeneity of benthic diatom communities along the shoreline of natural alpine lakes

Littoral benthic diatom communities are pivotal indicators which react to coastline sources of pollution. Littoral communities, however, may be also strongly influenced by other environmental factors: we assumed that even in lakes without anthropogenic pressure, communities could be heterogeneous. To investigate the natural causes of community heterogeneity along shoreline, we sampled 58 pristine high-altitude lakes in the French Alps. Inside each lake, three different littoral stations were sampled. Water chemical composition was measured with major environmental settings. Lakes with homogeneous communities along their shoreline were dominated by pioneer species adapted to strong physical disturbances. The water renewal time in these lakes was short (a few days) and this conveyed strong turbulences. Lakes with heterogeneous communities along their shore had longer water renewal time and were dominated by high-profile diatoms that were able to compete for light and nutrients. The within-lake heterogeneity could be explained by the variability in coastline terrestrial habitats. This study illustrates how water turbulences can limit the expression of some ecological processes like interspecific competition and reduce heterogeneity when it is an overriding stressor. Finally, implications for lake managers are given in terms of monitoring efforts.

Ecological studies on macrobenthic invertebrates in four northern Khors of Lake Nasser (Egypt); Community Structure, Relative Abundance and Diversity.

The community structure, abundance and diversity of macrobenthic invertebrates were studied in relation to major physical and chemical characteristics of water and sediment during 2015 in the four northern khors of Lake Nasser (EL-Ramla, Kalabsha, Rahma and Wadi-Abyad). Twenty six macrobenthic invertebrates species belonging to Insecta (15 species), Annelida (5 species), Mollusca (5 species) and Decapoda (1 species) were recorded. The study indicated that the western khors sectors (El-Ramla and Kalabsha) or lying nearby the main stream were higher in species richness and abundance than that of the eastern khors (Rahma and Wadi-Abyad).This may be attributed to their sandy loamy bottom nature that provided with patches of aquatic plants. At the littoral stations, the magnitude of the standing crop of macrobenthic invertebrates showed the highest counts and biomass during winter with an average of 3016 orgs./m2, weighting 9.9 g. fresh wt./m2. In autumn, the standing crop was with an average of 2662 orgs./m2, weighting 19.5 g. fresh wt./m2, when the water temperature fluctuated between18.9 & 25.2°C. On the other hand, the macrobenthic invertebrates at the offshore stations remained low throughout most of the year due to the shortage of suitable substrate. Pearson correlation coefficient showed that the aquatic insects, annelids and molluscs were categorized in relation to water temperature, organic matter and dissolved oxygen, respectively.

Source and Biogeochemical Distribution of Organic Matter in Surface Sediment in the Deep Oligotrophic Lake Fuxian, China

The source, quantity and quality of sedimentary organic matter (SOM) were investigated in the surface sediments of Lake Fuxian, a deep oligotrophic lacustrine system in China. Granulometry, biochemical organic composition, bulk organic proxies and their stable isotopes were determined in the surface sediments (0–4 cm). The values of δ13C, δ15N and atomic ratio of total organic carbon to total nitrogen (TOC/TN) indicated that the sediments in the large partial lake were influenced by autochthonous organic matter. The concentrations of TOC, protein (PRT) and total hydrolysable amino acids may be mainly modulated by phytodetritus sinking from euphotic zones since they correlated significantly with chlorins. Otherwise, the lack of correlation between chlorins concentrations and carbohydrate (CHO) and lipid (LIP) indicated that the latter may have an additional terrestrial source. The highest sediment quantity was found in the deepest station NC owing to its fine sediment. Stations near northwestern shore accumulated more SOM than other littoral stations, which was in accordance with sewage discharge strength. Degradation quality indices, such as chlorin index, degradation index, PRT/CHO, and LIP/CHO, were in general agreement in showing the degraded status of SOM in Lake Fuxian. No clear spatial patterns were found in sediment degradation quality, which may be influenced by bottom oxygen concentration in the deep stations.

Spatial and temporal dynamics of virioplankton in a high mountain tropical reservoir, El Neusa (Cundinamarca, Colombia)

Temporal and spatial changes of virioplankton abundance (VLP), chlorophyll-a (Chl-a) concentration, and some environmental variables, were assessed from October 2004 to April 2005 at four sampling sites in a high-mountain reservoir in the Colombian Andes. VLP ranged from 2.4-10.5×10 7 and 3.6- 6.5×10 7 VLP mL −1 in the samples from the photic zone and hypolimnion, respectively. Surface VLP showed a progressive increase from November to April in the limnetic zone, and until February in the littoral stations. This trend coincided with the gradual increase of the water column stratification, as well as the augment of the reservoir hydraulic volume. Principal components analysis showed a grouping of environmental (dissolved oxygen, pH, water temperature) and biological variables (VLP, Chl-a, bacterioplankton abundance and biomass) within the first component (26.4% of explained variance), associated to an increase of photosynthetic activity, as a potential supplement of organic substrates to heterotrophic viral hosts. High values of virus-to-prokaryote ratio (VPR), and a negative relationship between VLP and average biomass per prokaryotic cell, indicate strong viral control which is probably more intense on active and larger cells. These results provide a framework for understand the virioplankton responses to regional hydrological conditions and hydraulic behavior of this reservoir. The spatiotemporal scale of this study does not allow to confirm that viral dynamics is significantly affected by human activities causing potential alterations on nutrient cycling.

Anomalous propagation conditions of electromagnetic wave observed over Bosten Lake, China in July and August, 2014

Atmospheric duct is a common phenomenon over large bodies of water, and it can significantly affect the performance of many radio systems. In this paper, a two-month (in July and August, 2014) sounding experiment in ducting conditions over Bosten Lake was carried out at a littoral station (41.89° N, 87.22° E) with high resolution GPS radiosondes, and atmospheric ducts were observed for the first time in this area. During the two months, surface and surface-based ducts occurred frequently over the Lake. Strong diurnal variations in ducting characteristics were noticed in clear days. Ducting occurrence was found at its lowest in the early morning and at its highest (nearly 100%) in the afternoon. Duct strength was found increasing from early morning to forenoon, and reaching its maximum in the afternoon. But contrarily, duct altitude experienced a decrease in a clear day. Then the meteorological reasons for the variations were discussed in detail, turbulent bursting was a possible reason for the duct formation in the early morning and the prevailing lake-breeze front was the main reason in the afternoon. The propagation of electromagnetic wave in a ducting environment was also investigated. A ray-tracing framework based on Runge–Kutta method was proposed to assess the performance of radio systems, and the precise critical angle and grazing angle derived from the ray-tracing equations were provided. Finally, numerical investigations on the radar performance in the observed ducting environments have been carried out with high accuracy, which demonstrated that atmospheric ducts had made great impacts on the performance of radio systems. The range/height errors for radar measurement induced by refraction have also been presented, too, which shows that the height errors were very large for trapped rays when the total range was long enough.

Phytoplankton in Coqueiro Lake (Pantanal de Poconé, Mato Grosso, Brazil)

Studies on floristic composition are key to understand qualiquantitative changes on phytoplankton assemblages over the year. Spatial-temporal variation in composition, richness, frequency of occurrence, and abundance (semi-quantitative) of the phytoplankton community was analyzed monthly (from April 2002 to May 2003), at 3 stations, in Coqueiro Lake (Pantanal, Mato Grosso, Brazil). We registered 256 taxa, mainly represented by Zygnematophyceae (36%), Chlorophyceae (21%), and Euglenophyceae (14%). The highest abundance occurred at the limnetic station (2), but Bacillariophyceae, Cyanophyceae, Chlorophyceae, and Zygnematophyceae prevailed at the 3 stations. The highest average richness was obtained at the littoral station (3), but this station showed a significantly lower abundance (p < 0.05) than the 2 limnetic stations. The system was characterized for higher contributions of Chlorophyceae in the falling water period, Bacillariophyceae in the low waters, Cyanophyceae in the rising waters and Zygnematophyceae in the high waters, and, on average, the highest richness and abundance were registered in the drought (Aulacoseira spp., Coelastrum spp., Anabaena spp., Aphanocapsa minutissima, Planktolyngbya spp. and Eutetramorus fottii). The attributes of phytoplankton community showed spatial and temporal variations, influenced by the presence of macrophytes, but defined, above all, by seasonal hydrologic changes, caused by the flooding pulse.

Distributions and biomass of benthic ciliates, foraminifera and amoeboid protists in marine, brackish, and freshwater sediments.

The quantitative importance of ciliates, foraminifers, and amoebae was investigated in marine, brackish, and freshwater sediments from 15 littoral stations. Total protozoan communities were usually dominated by ciliates in term of abundance, while amoebae often dominated in terms of biomass. Applying the biomass-metabolic rate equation, ciliates, amoebae, and foraminifera were estimated to contribute 66% of the total abundance and 33% of the biomass, but up to 55% of the combined metabolic rate to the micro- and meiobenthos in the 15 sediments. Statistical analyses using ciliate data demonstrated: (1) species composition and community structures represented significant differences between freshwater and marine/brackish sediments, and subsequently between temperate and arctic sampling sites; (2) the occurrence of dominant ciliates and their allocation to feeding types indicated that herbivory was the most common feeding strategy in these sediments; (3) multivariate analyses showed all of the tested environmental factors (temperature, salinity, silt/clay, carbon, nitrogen, and chlorophyll a) to be important to varying degrees, but especially the combination of salinity, temperature, and silt/clay. Multiple factor effects or comprehensive influences might be important in regulating the distribution of protozoa in sediments. The importance of protozoa in sediment systems and the potential ecological significance of cysts are discussed.

Spatial and seasonal distribution of macroinvertebrates in high altitude reservoir (Beyler Reservoir, Turkey)

A highland reservoir in the West Black Sea region of Turkey which belongs to the Mediterranean climatic zone was examined. Both littoral and profundal zones were sampled from October 2009 to September 2010, to determine taxonomic composition, biodiversity and abundance of benthic invertebrates as well as the seasonal variation of these measures. A total of 35 taxa were identified, of which 12 belong to Chironomidae and 10 to Oligochaeta groups. The highest diversity and abundance of benthic macroinvertebrates were found at the littoral stations. Macroinvertebrates showed significant positive correlations with water temperature and NO2 and NO3 concentrations, and negative correlation with dissolved oxygen.

Phosphorus Mobilization at the Sediment–Water Interface in Softwater Shield Lakes: the Role of Organic Carbon and Metal Oxyhydroxides

The adsorption of phosphorus on natural diagenetic iron (Feox) and manganese (Mnox) oxyhydroxides was studied in deep and littoral zone sediments of mesotrophic Lac Saint-Charles (46°56 N, 71°23 W), using a Teflon sheet technique for collecting diagenetically produced metal oxyhydroxides. Collected metal oxide amounts were greater at the deep-water station, relative to littoral zone stations reflecting sediment and local diagenetic differences. Two-layer surface complexation modeling on iron oxyhydroxide was consistent with the measured total P/Fe molar ratios except for the upper mixed Mn–Fe oxide layer from the littoral stations, where measured phosphorus exceeded the modeled phosphorus by more than fivefold. Soluble reactive phosphorus (SRP) exchange between oxyhydroxide samples and natural lake water in the laboratory revealed a labile phosphorus pool. Phosphorus determined on the Teflon sheets from the littoral zone stations appears to be related to a distinct non-humic organic carbon pool that readily exchanges SRP, while little exchange was observed from material collected from the deep-water station. We suggest that the enhanced SRP release from littoral zone sediments is due to an organic carbon and/or metal oxide-impoverished sediment matrix, limiting microbial oxide reduction and allowing phosphorus to be rapidly recycled at the sediment–water interface, instead of being slowly incorporated into humic material. The SRP fluxes revealed in our study, which originate from the solid phase at the sediment–water interface, would be difficult to resolve using interstitial pore-water samplers and might be a quantitatively important source of inorganic phosphorus in Shield lakes.

Chironomid mouthpart deformities as indicator of environmental quality: a case study in Lake Trasimeno (Italy)

The aim of the present study was to monitor mouthpart deformities of Chironomus plumosus (Insecta-Diptera) in Lake Trasimeno (2000-2010) in relation with sediment contamination by heavy metals, which is one of the main causes of deformity induction. In Lake Trasimeno, concentrations of heavy metals in the investigated littoral zone were low, in comparison with those of the central area. By contrast, the incidence of deformities was much higher in the littoral station (2006-2009) than in the central area. In the littoral zone, the deformities progressively decreased and by 2010 reached values similar to those observed in the central area (2000-2002, 2010). This decrease was mainly due to the reduction of severe deformities, thus indicating an environmental quality recovery of this littoral sector. Chemical analysis revealed that the higher incidence of deformities in the littoral zone was not caused by heavy metal contamination, unless they may have contributed to a joint action with other toxicants. The present study on Lake Trasimeno provided additional evidence that chironomid mouthpart deformities can be used in biomonitoring programs to evaluate sediment contamination by toxicants. Since mouthpart deformities may also be induced by compounds not included in routine chemical analyses, they may better reflect sediment quality than chemical analysis alone.

Assessment of methods for obtaining rainfall intensity-duration-frequency ratios for various geographical areas

Several procedures for obtaining rainfall intensity-duration-frequency (IDF) relationships for storm durations ranging from 10 min to 24 h and for several return periods were analyzed. The data recorded for the period 1966–1997 are from five different locations in southern Spain: one mountain, two inland, and two littoral stations. We analyzed the original equations of Wenzel, Bell, Chen and Témez, and other ones modified from the last two. The first step was to determine the parameters of each equation for each geographical location. Subsequently, the coefficient of variation (CV) and index of agreement (ia) of each equation were calculated in order to compare their estimations for rainfall durations of less than 2 h and less than 24 h. The results show that there is not one equation which is best suited for all the geographical areas or rainfall durations. The reference method, Wenzel apos;s equation, is the best for rainfall periods of less than 24 h, but only for the littoral and inland geographical areas. If Wenzel apos;s equation is not taken into account, the modified Témez equation proved to be the best at generating series for mountain areas and for the two rainfall periods studied. Therefore, in a regional study of rainfall durations of less than 24 h, where only 24 h data are available, and with littoral, inland and mountain areas, the modified Témez equation is strongly recommended.

Spatial and Temporal Dynamics of Anabaena flos-aquae Akinetes in Bottom Sediments of a Small Siberian Reservoir

Spatial distribution of akinetes of Anabaena flos-aquae (cyanobacteria) in littoral bottom sediments of a small Siberian reservoir was studied. Akinete abundance in bottom sediments is found to be related with type of sediments and presence of higher water plants. The highest abundance of akinetes was observed in silty sediments at stations located in higher plants bed (mainly emerged plants Typha latifolia L. and Phragmites australis (Cav.) Trin. ex Steud.). These results demonstrate that macrophyte beds could increase the size of the potential cyanobacterial inoculum by accumulation of akinetes in shallow bottom sediments and, as a result, favour cyanobacterial bloom development. In addition, seasonal dynamics of Anabaena flos-aquae, including vegetative cells and akinetes, in bottom sediments and water column in open water and littoral of the reservoir was studied. Dynamics of Anabaena abundance in the water column at the central station and littoral stations were very similar, but the number of cells in the littoral achieved higher year maximum than that at the central station. The highest seasonal peak of vegetative cells and akinetes in the water column was observed at the littoral station, located in emerged higher plants bed. However, at this part of the reservoir lowest intensity of akinete production was recorded. Deposition of akinetes to bottom sediments occurred both in open water and littoral. Nevertheless, seasonal dynamics of akinetes in bottom sediments differed between these sites. At the central station accumulation of akinetes in bottom sediments occurred throughout the summer, but in the littoral abundance of akinetes decreased just after their sedimentation. Hence, abundance of akinetes in the littoral sediments of the reservoir is markedly lower than that in the deeper central part.

Sedimentation Status of Lake Victoria: Loading from River Mouth and In-lake Sedimentation

Lake sediments consist of the input of suspended solids by river discharges, the autochthonous produced particulate matter in the water column and the settled material on the lake bottom. The loading, transport, formation and decay of the sediments entering the Lake Victoria from Tanzanian side was monitored for the period 2000 to 2005. The sedimentation study focused on; quantification of settling fluxes of particulate nutrients and organic carbon at the off-shore(Pelagic) and near-shore(Littoral) monitoring stations. Monitored data on sedimentation rate and settling velocities has been sampled and analysed in the period November 2000 to March 2005. The mean sedimentation rate at littoral stations for total particulate phosphorous (TPP) was about twice as compared to pelagic stations. The same situation was observed for total particulate carbon (TPC), however, total particulate silica did not show a clear pattern of variability between littoral and pelagic stations though there was a general tendency of decreasing towards the pelagic stations. Mean value for TPC /TPP sedimentation rate ratio was 117.61 for littoral and 90.74 for pelagic stations respectively compared to TBSi/TPP which was 3.15 for littoral and 2.10 for pelagic stations. The results show that sedimentation rates are highest at the littoral stations compared to pelagic stations. The differences in settling velocities indicate that the settling material consists dead and living material with a contribution of diatoms. The stoichiometriccomposition of the settling material indicates nitrogen limitation and a non-dominance of diatoms.