Open Waters Of Lake Research Articles

Dynamic changes in the abundance and chemical speciation of dissolved and particulate phosphorus across the river-lake interface in southwest Lake Michigan

Phosphorus (P) concentrations and primary production in the Great Lakes have declined since the 1980s, but changes in biogeochemical cycling pathways of different P species remain poorly understood. Water samples were collected for the measurements of different P species to examine the dynamics of P in the water column across the river-lake interface from the Milwaukee River to open Lake Michigan. Dissolved inorganic P (DIP) concentrations were as high as 3049 nM in river waters, but decreased dramatically to as low as 11 ± 7 nM in open lake waters. Total dissolved P was mostly measured in the form of DIP in river waters (73% ± 18%), whereas dissolved organic P (DOP) became the predominant species (85% ± 18%) in lake waters. Colloidal P (>1 kDa) comprised 58% ± 16% of the bulk DOP in river waters, but decreased to 23% ± 5% in ologotrophic lake waters, showing again contrasting biogeochemical regimes between river and lake waters. Biological processes and coagulation/sedimentation were largely responsible for the removal of river-derived P species and active transformation between inorganic and organic P occurred in both dissolved and particulate phases across the river-lake interface. Increased water column P inventory over the winter of 2013–2014 likely resulted from an accumulative effect of both atmospheric and riverine inputs in the upper water column, and benthic nepheloid layer processes coupled with quagga mussels excretion for the lower water column, respectively. High partition coefficient values (logKd of 4.33–7.01) and a “particle concentration effect” on the partitioning of P between dissolved and particulate phases attested the particle-reactive nature of P in lake waters.

Ecology and Fish Biodiversity of Man-Made Lakes of Southern Benin (West Africa): Implications for Species Conservation and Fisheries Management

Man-made lakes are alternative and potential habitats for biodiversity conservation, fisheries and extensive aquaculture. We investigated the ecology and the fish community structure of two (2) sand-dragged man-made lakes, Lake Ahozon and Lake Bewacodji of Southern Benin, with implications for species conservation, fisheries management and aquaculture valorization. From August 2014 to July 2015, habitats conditions were evaluated and fishes were sampled monthly with seine, cast net, experimental gill net and hooks in the open water and aquatic vegetation habitats of both lakes. Overall, the water quality of Lake Ahozon was globally favorable for the growth and the survival of the fish resources whereas Lake Bewacodji exhibited a poor water quality indicated mainly by an acid pH (mean: 6.32 ± 0.58) and low dissolved oxygen concentrations (mean: 3.52 ± 1.25 mg/l) caused by dense floating plants, Nymphea sp mainly and huge daily dumping of domestic wastes. The study revealed low species richness, d = 5.89 and d = 3.87, and low species diversity, H’ = 0.76 and H’ = 0.48 for Lakes Ahozon and Bewacodji, respectively, with Lake Ahozon more diverse than Lake Bewacodji. The fish community of Lake Ahozon comprised six (6) species, 3 cichlids Sarotherodon galilaeus, Oreochromis niloticus and Tilapia guineensis, the silver catfish, Chrysichthys nigrodigitatus (Claroteidae), the African bonytongue, Heterotis niloticus (Osteoglossidae), and the African catfish, Clarias gariepinus (Clariidae). Numerically, S. galilaeus dominated Lake Ahozon and made 85.21% of the sample. In Lake Bewacodji, the fish composition comprised four (4) species, Sarotherodon galilaeus multifasciatus, the dominant species making numerically 91.58% of the total sample, T. guineensis, C. gariepinus and C. nigrodigitatus. With regard to trophic structure, the fish assemblages of both lakes were numerically dominated by planktinovores/ detritivores, mainly S. galilaeus, O. niloticus, T. guineensis and C. nigrodigitatus making together 99.46% of Lake Ahozon fish community, and S. galilaeus multifasciatus, T. guineensis and C. nigrodigitatus accounting together for about 98.59% of Lake Bewacodji. In Lake Ahozon, standard length (SL) frequencies histograms showed an unimodal size distribution for H. niloticus, the nile tilapia O. niloticus and C. gariepinus whereas the two cichlids, S. galilaeus and T. guineensis exhibited a bimodal size distribution. In Lake Bewacodji, S. galilaeus multifasciatus, C. nigrodigitatus and C. gariepinus exhibited an unimodal size distribution. A sustainable exploitation of both man-made lakes requires the implementation of an integrated management scheme which should include habitat restoration and protection plan, fisheries/aquacultural valorization, ecological sound agriculture/ecotourism and environmental monitoring.

Holocene climate variability and anthropogenic impacts from Lago Paixban, a perennial wetland in Peten, Guatemala

Analyses of an ~6m sediment core from Lago Paixban in Peten, Guatemala, document the complex evolution of a perennial wetland over the last 10,300years. The basal sediment is comprised of alluvial/colluvial fill deposited in the early Holocene. The absence of pollen and gastropods in the basal sediments suggests intermittently dry conditions until ~9000cal yr.BP (henceforth BP) when the basin began to hold water perennially. Lowland tropical forest taxa dominated the local vegetation at this time. A distinct band of carbonate dating to ~8200BP suggests regionally dry conditions, possibly associated with the 8.2ka event. Wetter conditions during the Holocene Thermal Maximum are indicated by evidence of a raised water level and an open water lake. The timing of this interval coincides with strengthening of the Central American Monsoon. An abrupt change at 5500BP involved the development of a sawgrass marsh and onset of peat deposition. The lowest recorded water levels date to 5500–4500BP. Pollen, isotope, geochemical, and sedimentological data indicate that the coring site was near the edge of the marsh during this period. A rise in the water table after 4500BP persisted until around 3500BP. Clay marl deposition from 3500 to 210BP corresponds to the period of Maya settlement. An increase in δ13C, the presence of Zea pollen, and a reduction in the percentage of forest taxa pollen indicate agricultural activity at this time. In contrast to several nearby paleoenvironmental studies, proxy evidence from Lago Paixban indicates human presence through the Classic/Postclassic period transition (~1000BP) and persisting until the arrival of Europeans. Cessation of human activity around 210BP resulted in local afforestation and the re-establishment of the current sawgrass marsh at Lago Paixban.

The effects of forest fuel connectivity on spatiotemporal dynamics of Holocene fire regimes in the central boreal forest of North America

Understanding fire regime dynamics is central to predicting forest structure and the compositional dynamics of boreal forests. Spatial and temporal variations in fire frequency in central Canadian boreal forests over the last 10 000 years were examined to evaluate the influence of bottom-up controls on the regional fire regime. We analysed macroscopic charcoal larger than 160mm from sediment cores from six lakes to reconstruct fire history and performed GIS analysis of regional landscape features to investigate how fire frequency has changed temporally and how non-climatic factors may have affected long-term fire frequency. Our generalized linear mixed model revealed that temporal changes in fire return intervals (FRIs) were highly dependent on landscape connectivity as inferred through the abundance of natural firebreaks in the form of open water lakes and wetlands. FRIs did not change significantly among highly connected landscapes throughout the Holocene; in contrast, FRIs were significantly longer among poorly connected landscapes in the early Holocene (10-5 cal ka BP), suggesting that the abundant regional firebreaks limited fire spread. All sites had similar FRIs in the late Holocene. The diminishing influence of firebreaks suggests that the regional climate during the late Holocene has overshadowed the influences of the bottom-up controls on fire activities. Copyright © 2015 John Wiley & Sons, Ltd.

Age and growth of round goby Neogobius melanostomus associated with depth and habitat in the western basin of Lake Erie.

Round goby Neogobius melanostomus were examined from the Bass Islands area in the western basin of Lake Erie, U.S.A., to determine age and growth correlations. A total of 188 specimens were collected and examined during summer 2011 with 90 aged using scale analysis. Fish were grouped by sex, depth of habitat and habitat type (anthropogenically modified shallows, natural shallows and open lake deep water). Fish ranged from 17 to 117 mm total length (LT ) and 0+ to 3+ years. Males dominated the population (1·94:1) and backcalculated age showed that both sexes grew exponentially, with male growth rate increasing faster than female. Males were significantly larger than females in LT and mass (both P < 0·001). The relative mass index (Wr ) was low for the sampled population (mean ± s.d. = 32·00 ± 26·87 g), implying that the health of the Bass Island area population is very poor when compared with the species throughout its range. This could be due to a lack of food resources related to population size or that the fish is not optimally utilizing the available food resources. In contradiction to these findings, regression slope coefficient (b), calculated using Fulton's condition factor (K) (mean ± s.d. =1·50 ± 0·20), was very low for each habitat, implying a healthy population throughout. This seemingly opposite effect may be due to more individuals per unit area in shallow waters, which would cause increased competition for resources. Poor condition may indicate that the Lake Erie population has reached saturation or may reflect indirect fitness costs associated with increasing anoxic or hypoxic hypolimnion conditions.

Investigating the genetic variation and structure of a native unionid mussel in the Laurentian Great Lakes following an invasion of dreissenid mussels

Despite massive population declines in the open waters of Lake St. Clair due to invasive dreissenid mussels, the St. Clair River Delta has persisted as a refuge habitat for native unionid mussels. This study was conducted to determine how Dreissena-induced population declines might have impacted the genetic population structure of native unionid species. Nine variable microsatellite markers were used to assess the genetic population structure of the Fatmucket mussel (Lampsilis siliquoidea) across 18 sites (n = 341 individuals) within the delta and four of its tributaries. Results indicate that Fatmuckets within the various bays of the St. Clair Delta and tributaries show limited genetic differentiation by geographic distance but still represent a single population with evidence of recent gene flow, little differentiation among sampling sites, relatively high allelic richness at all sites, and little evidence supporting a recent genetic bottleneck. The Fatmucket is the most common species found in the delta and poor genetic health and connectivity of this species might have indicated a dire situation for less common and imperiled species found in the same habitats. Because this did not appear to be the case, little can be assumed about other mussel species.

Developing an understanding of dissolved organic matter dynamics in the giant Lake Baikal by ultrahigh resolution mass spectrometry

To elucidate the molecular characteristics of dissolved organic matter (DOM) in Lake Baikal, 3D excitation-emission matrix spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were employed. From the linear relationship between the humic-like peak intensities (excitation/emission = 305 nm/430 nm) and dissolved organic carbon (DOC) concentrations in the water samples extending from the Selenga River mouth to offshore (central lake in the south basin), allochthonous DOM appeared to be a main contributor to the DOC concentrations. However, DOM with fewer fluorophores dominated in the South Basin of the lake at stable DOC concentrations of ca. 0.84 mg C l−1. Meanwhile, FT-ICR MS analysis and subsequent principal component analysis across the transect revealed a transition of compounds with high H-deficiency (aromatic) to compounds with low H-deficiency (aliphatic) that dominate pelagic open-lake water. We believe that this molecular change is induced by photo-degradation, which mainly alters aromatic compounds.

The Randeck Maar: Palaeoenvironment and habitat differentiation of a Miocene lacustrine system

The Randeck Maar in S. Germany is a well-known fossil lagerstätte with exceptionally preserved fossils, particularly insects and plants, which thrived in and around the maar lake during the Mid-Miocene Climatic Optimum (late Early/early Middle Miocene, mammal zone MN5). We provide the first critical and detailed overview of the fauna and flora with lists of 363 previously published, partially revised, and newly identified taxa. Plant remains are the most diverse group (168 taxa), followed by insects (79). The flora points towards subhumid sclerophyllous forests and mixed mesophytic forests, the former being an indication for the occurrence of seasonal drought. Three main sections can be differentiated for the habitats of the Randeck Maar lake system: (1) Deep- and open-water lake habitats with local and short-termed mass occurrences of insect larvae, amphibians, and/or gastropods, while fish is particularly scarce. The interpretation of the water chemistry is problematic because contradictive palaeoenvironmental indicators for both brackish and freshwater conditions exist. (2) Shallow parts of the lake comprise a narrow reed-belt with insects and gastropods living on the exposed plant stems as well as turtles. (3) Crater slopes and surrounding plateaus were mainly covered by subhumid sclerophyllous to mixed mesophytic forests depending on sun exposition and soil conditions. Horses and other forest-dwellers preferably lived in forested habitats while proboscideans and rhinoceratids occupied more open habitats. Our study also brings up contradictive results that cannot be untangled with the current state of knowledge and thus directions for future studies are discussed.

Great Lakes rivermouth ecosystems: Scientific synthesis and management implications

At the interface of the Great Lakes and their tributary rivers lies the rivermouths, a class of aquatic ecosystem where lake and lotic processes mix and distinct features emerge. Many rivermouths are the focal point of both human interaction with the Great Lakes and human impacts to the lakes; many cities, ports, and beaches are located in rivermouth ecosystems, and these human pressures often degrade key ecological functions that rivermouths provide. Despite their ecological uniqueness and apparent economic importance, there has been relatively little research on these ecosystems as a class relative to studies on upstream rivers or the open-lake waters. Here we present a synthesis of current knowledge about ecosystem structure and function in Great Lakes rivermouths based on studies in both Laurentian rivermouths, coastal wetlands, and marine estuarine systems. A conceptual model is presented that establishes a common semantic framework for discussing the characteristic spatial features of rivermouths. This model then is used to conceptually link ecosystem structure and function to ecological services provided by rivermouths. This synthesis helps identify the critical gaps in understanding rivermouth ecology. Specifically, additional information is needed on how rivermouths collectively influence the Great Lakes ecosystem, how human alterations influence rivermouth functions, and how ecosystem services provided by rivermouths can be managed to benefit the surrounding socioeconomic networks.

The backscattering coefficient and its components in the Great Lakes: A review and synthesis

Backscattering of light by particulates, as quantified by the particulate backscattering coefficient, bbp (m–1), is important in regulating the optical signal available for remote sensing. A synthesis of the available information on bbp for the Laurentian Great Lakes is presented to support mechanistic approaches for remote sensing. This includes (1) direct measurements of bbp, (2) characterization of the backscattering attributes of minerogenic particles, (3) partitioning of bbp into contributing minerogenic (bb,m) and organic (bb,o) components, and (4) development of appropriate cross-sections (mass-specific coefficients) for retrieval of concentrations of backscattering constituents by remote sensing. Levels of bbp were particularly high in the western basin of Lake Erie and Green Bay, Lake Michigan, intermediate levels prevailed in parts of Lake Ontario during a whiting event, and values were substantially lower in the open waters of the upper Great Lakes. Minerogenic backscattering (bb,m) is an important component of bbp throughout the system. Clay mineral particles dominate this component, except during whiting events when calcite is dominant. Mie-theory calculations supported estimates of bb,m, and together with particle morphological considerations, guided the development of the optical cross-section for minerogenic particles. The collected data and associated analyses are appropriate to support initiatives to develop and preliminarily test mechanistic remote sensing approaches for the Great Lakes.

Spatial and Temporal Distribution of Singlet Oxygen in Lake Superior

A multiyear field study was undertaken on Lake Superior to investigate singlet oxygen ((1)O(2)) photoproduction. Specifically, trends within the lake were examined, along with an assessment of whether correlations existed between chromophoric dissolved organic matter (CDOM) characteristics and (1)O(2) production rates and quantum yields. Quantum yield values were determined and used to estimate noontime surface (1)O(2) steady-state concentrations ([(1)O(2)](ss)). Samples were subdivided into three categories based on their absorbance properties (a300): riverine, river-impacted, or open lake sites. Using calculated surface [(1)O(2)](ss), photochemical half-lives under continuous summer sunlight were calculated for cimetidine, a pharmaceutical whose reaction with (1)O(2) has been established, to be on the order of hours, days, and a week for the riverine, river-impacted, and open lake waters, respectively. Of the CDOM properties investigated, it was found that dissolved organic carbon (DOC) and a300 were the best parameters for predicting production rates of [(1)O(2)](ss). For example, given the correlations found, one could predict [(1)O(2)](ss) within a factor of 4 using a300 alone. Changes in the quantum efficiency of (1)O(2) production upon dilution of river water samples with lake water samples demonstrated that the CDOM found in the open lake is not simply diluted riverine organic matter. The open lake pool was characterized by low absorption coefficient, low fluorescence, and low DOC, but more highly efficient (1)O(2) production and predominates the Lake Superior system spatially. This study establishes that parameters that reflect the quantity of CDOM (e.g., a300 and DOC) correlate with (1)O(2) production rates, while parameters that characterize the absorbance spectrum (e.g., spectral slope coefficient and E2:E3) correlate with (1)O(2) production quantum yields.

A diatom record of recent environmental change in Lake Duluti, northern Tanzania

Lake Duluti is a small, topographically closed crater lake located on the flanks of Mt Meru, northern Tanzania. Analyses of diatoms in three short sediment cores and four modern samples from Lake Duluti were used to infer past environmental changes. 210Pb and 137Cs activity profiles combined with AMS 14C dates provide the chronological framework. Weak agreement between the 210Pb and 14C records, together with dating uncertainty, precludes construction of precise age models. The modern diatom flora, from plankton and three periphytic habitats, is dominated by Aulacoseira ambigua (Grunow) Simonsen, Gomphonema parvulum (Kutzing) Grunow and Nitzschia amphibia Grunow. All three cores display similar stratigraphic succession, but the relative ratio of habitats represented by the diatoms varies substantially between cores. Diatoms indicate that the oldest part of the record is characterized by relatively low lake level and swampy vegetation. In the late nineteenth or early twentieth century there was a rapid lake level rise and the swamp turned into an open-water lake. High lake levels have prevailed since that time.

Use of the flooded forest by fish assemblages in lakes of the National Park of Anavilhanas (Amazonas, Brazil)

We evaluated diversity and distribution of fish species in two habitats: flooded forest and open water of lakes of Rio Negro. Each of four lakes within the Anavilhanas Archipelago was sampled three times from 2009-2010. Species diversity generally was higher in flooded forests and at night, according to correspondence analysis. Predators were most active at night, but showed no preference between the flooded forest and open water habitats. Omnivores, filter feeders, and detritivores were most active during the day.

Rotifer communities in the Laurentian Great Lakes, 1983–2006 and factors affecting their composition

Rotifer communities were examined from the open waters of the Laurentian Great Lakes between 1983 and 2006 in the first inter-lake comparison involving all five lakes. Seventy rotifer taxa were found in summer samples, although most (> 80%) individuals were drawn from the following taxa: Conochilus unicornis, Polyarthra vulgaris, Keratella cochlearis, Kellicottia longispina, Keratella crassa, Synchaeta spp., Polyarthra major, Ploesoma truncatum, Keratella earlinae, and Keratella quadrata. Distributions of Filinia longiseta and several species of Brachionus and Trichocera were restricted to regions of higher trophy, notably the western basin of Lake Erie, but most taxa were widely distributed, differing in relative dominance rather than presence or absence. Rotifer community structure appeared to respond in tractable ways to differences in trophic state, with the four most common genera exhibited the following preferences, in order of decreasing trophy: Polyarthra, Keratella, Conochilus, and Kellicottia. Recent oligotrophication in Lake Huron was reflected in decreases in Keratella dominance and increased dominance of Conochilus, while in Lake Michigan oligotrophication was associated with decreases in Polyarthra and Keratella and increases in Conochilus, and Kellicottia. In Lake Ontario, the appearance of the exotic predatory Cercopagis pengoi was strongly associated with dramatic reductions in Polyarthra, while more gradual sequential increases in the dominance of Keratella, Conochilus and Kellicottia were probably the result of decreasing trophic state. Bythotrephes was identified in multivariate analyses as correlating strongly with rotifer composition, although only in Lake Michigan was a clear relationship between the predatory cladoceran and rotifer species shifts observed.

Biology of the Molluscivorous Fish Trematocranus placodon (Pisces: Cichlidae) from Lake Malaŵi

ABSTRACT Tramatocranus placodon is a facultative molluscivore endemic to the Lake Malaŵi catchment basin, Malaŵi, Africa. T. placodon feeds on both Bulinus nyassanus, which is a host of human urinary schistosomes, and Melanoides spp. in the open waters of Lake Malaŵi. We found that there was a dietary shift from insects and small snails to larger snails as the fish grew, and this correlated with the development of the lower pharyngeal bone, which is instrumental in crushing snails. There was also an increase of the proportion B. nyassanus in the diet just before the onset of spawning.

The application of geospatial analyses to support an integrated study into the ecological character and sustainable use of Lake Chilwa

Wetlands, which occupy a considerable proportion of Malawi, are an important resource for the rural-poor. In regions of low and erratic rainfall, they provide important opportunities for agriculture and fisheries and are often vital for food security. However, overutilization and some farming practices can result in environmental degradation and the loss of valuable ecosystem services. The Lake Chilwa wetland, a complex aquatic ecosystem comprising a shallow open water lake surrounded by marsh and floodplain grassland, is one of the most important wetlands in Malawi. Most of the 1 million people who live in the vicinity of the lake derive their livelihoods from the wetland. Increases in population in recent decades have increased the pressures on the wetland. In light of continued population growth, it is anticipated that some levels of resource use may be difficult to sustain in the long-term. Consequently, planning the use of wetland resources is a priority if the diverse benefits that local communities presently receive are to be sustained. Baseline wetland information is needed to determine appropriate sustainable management plans, as well as to identify limits to resilience. However, for many wetlands in southern and eastern Africa, these data are lacking, or not available to those who need them. This paper provides an overview of the distribution and characteristics of wetlands in Malawi. Using Lake Chilwa as an example, it illustrates how Earth Observation data, in combination with hydrometric and botanical data, can be used to provide information crucial for sustainable wetland management.

Lake nutrient variability inferred from elemental (C, N, S) and isotopic (δ 13C, δ 15N) analyses of aquatic plant macrofossils

This paper aims to highlight the potential of using elemental and stable isotope analyses of aquatic macrophytes in palaeolimnological studies. Potamogeton pectinatus material was collected from modern plants ( n = 68) and from late glacial and Holocene-aged sediments from Koucha Lake (northeastern Tibetan Plateau; 34.0°N; 97.2°E; 4540 m a.s.l.). It was analyzed for δ 13C Potamogeton (modern: −23 to 0‰, fossil: −19 to −4‰) and δ 15N Potamogeton (modern: −11.0 to +13.8‰, fossil: −9.5 to +6.7‰) in addition to elemental carbon and nitrogen (modern C/N Potamogeton : 7 to 29; fossil: 13 to 68) and sulfur (fossil: 188–899 μmol/g dry weight). Fossil data were interpreted in terms of palaeo-nutrient availability and palaeo-productivity based on the modern relationships between various proxies and certain environmental data. Productivity of Potamogeton pectinatus mats at Koucha Lake as indicated by palaeo-ɛ Potamogeton -TIC (i.e. the enrichment of δ 13C Potamogeton relative to the δ 13C TIC) was reduced during periods of high conductivity, especially between 10.3 and 7.4 cal kyr BP. Potamogeton pectinatus material from these periods was also characterized by high S Potamogeton indicating high sulfide concentrations and anoxic conditions within the sediments. However, C/N Potamogeton ratios and δ 15N Potamogeton from the lower core section were found to have been altered by decompositional processes. A pronounced shift in the aquatic productivity of Lake Koucha occurred at ∼7.4 cal kyr BP when the hydrological conditions shifted towards an open lake system and water depth increased. At this time a strong increase in productivity led to a strong decrease in the water HCO 3 – concentration as inferred from the application of a ɛ Potamogeton -TIC-lnHCO 3 − transfer function. A comparison of reconstructed productivity changes from Koucha Lake with further environmental proxies suggests that primary productivity changes are probably a function of internal lake dynamics and were only indirectly triggered by climate change.

Habitat associations of exploited fish species in the Lower Amazon river–floodplain system

Summary1. Modification of floodplain morphology and land use is widely recognized as a major threat to fish communities of river–floodplain systems. We assess habitat associations of major exploited fish species in the Lower Amazon, where modifications are more extensive than in the Central or Upper Amazon.2. Habitat was characterized in terms of physical environment, vegetation cover, distance from river and mean depth. Habitat associations of late juvenile and adult fish of the 14 major exploited species were established by comparing the distribution of the habitat sampled with the distribution of the habitat sampled weighed by a fish abundance index (catch per unit of effort).3. Eight species showed significant habitat associations, generally being most abundant in floodplain lakes. Five of these eight species were associated with open water. Of the three exceptions, two preferred flooded forest lakes and another macrophyte‐dominated channels. The majority of those species with significant associations also preferred waters shallower than 7.25 m and relatively distant from the river mainstream.4. While flooded forest is often assumed to be a key habitat for Amazon fish, only two of the main exploited species in the Lower Amazon had a significant association with this habitat. The majority of exploited species, including one that is associated with flooded forest in the central and upper Amazon, either showed no habitat associations or preferred open water lakes. The full range of pristine and modified floodplain habitats should be considered as important to fish conservation and fisheries productivity.

Morphology and ecology of a group of small, pelagic, tropical Tropocyclops (Crustacea, Copepoda, Cyclopoida), with the description of a new species from South China.

Tropocyclops bopingi n.sp. is a 0.4 mm cyclopoid found in Liuxi He Reservoir, Guangdong, South China. It is probably widespread in South China, and appears in the Fauna Sinica under the name T. parvus. True T. parvus is a Central American species that is here redescribed from its type locality, Lake Peten Itza in Guatemala. T. bopingi is related to T. tenellus from the limnetic zone of Lake Tanganyika and other lakes in Central Africa, and all of them live under climatic conditions that are transitory between subtropical and tropical. T. tenellus is even smaller and more buoyant than T. bopingi and, at least in Lake Tanganyika, it tends to occur closer to the water surface than other zooplankton during the daytime. It does not carry egg balls, but extrudes eggs one at a time. T. tenellus and T. bopingi appear morphologically closer to each other than to T. parvus, but all three are ecologically similar: extremely small, pelagic species that presumably feed on small particles in the water. I hypothesize that environmental conditions in subtropical-tropical transition zones combine with predation and competitive pressure to offer a selective advantage to such omnivorous species in the open water of large lakes or reservoirs.

Late Quaternary geohistory of Sárrét Basin, based on studies on core Sárrét-2, Hungary

The Sárrét marshland is situated along the northeastern foothills of the Bakony Mountains, along a NE-SW-trending neotectonic zone. Investigation of the marshland and the reconstruction of its evolution are especially interesting to compare to the present and the expected future stage of Lakes Balaton and Velence. Based on the sedimentological characteristics of the core sequence and the geochemical, physical, and mineralogical composition of the layers, three sedimentological cycles could be separated. The three cycles represent the most important evolutionary phases of lake formation: flourishing and progressive aging. First, a nutrient-poor, open-water lake existed, where clastic sediments (sand and silty clay) were deposited. During the second phase, phytoplankton-produced autogenic lime mud was deposited in the progressively more eutrophic water. Peat accumulation during the third stage indicates the marsh phase of the lake.The results suggest that the studied sequence developed from Late Glacial to Middle Holocene. According to radiocarbon dating the accumulation rate in Sárrét (Sümegi, this volume) corresponds to the sedimentation rates in the Tapolca Basin and Lake Balaton.