Impact of hydrology on aquatic communities of floodplain lakes along the Daugava River (Latvia)

During July 2004, various limnological characteristics of 24 floodplain lakes and reservoirs have been explored along the Middle Daugava for the first time in order to reveal possible impact of the long-term mean annual flooding frequency on their phytoplankton, zooplankton, macrozoobenthos and macrophyta communities. Obtained data series were analysed by Spearman’s rank correlation method, Principal Component Analysis (PCA) method and Renkonen’s similarity test. UPMGA method was used for single linkage clustering of the lakes based on the abundance of phyto- and zooplankton taxa. Low similarity between the obtained cluster trees and hydrological grouping was stated indicating minor impact of the flooding hydrology on summer plankton communities of these lakes. Significant correlation between the flooding frequency and several physicochemical and biological parameters was found. Six main factors, which explain observed variations, were extracted by PCA. Significant negative impact of hydrological connectivity on zooplankton species diversity as well as positive impact on Oligochaeta density was stated, whereas other biotic parameters were affected by local factors, such as lake morphology, internal loading of nutrients from sediments, throphic interactions as well as local source of dissolved organic matter.     

Length-weight relationship in adult huchen Hucho hucho (L., 1758) from Drina River, Serbia

Huchen Hucho hucho from the Drina River (Serbia) revealed recently the decrease in breakpoint values for both standard length (Sl) and weight (w) in relation to the values recorded in 1999 from 110 cm to 98.4 cm and from 16.5 kg to 10.5 kg, respectively. That might indicate to the change in certain population parameters that could have an influence to the growth in the adult period of life.     

Amur sleeper (Perccottus glenii Dubowski, 1877) spreading in the Danube River Basin

Whereas earlier Amur sleeper (Perccottus glenii) findings in the Danube River were only single specimens, data reported in this study represent the first record on establishment of a local population. An overview of the spread of the Amur sleeper in the Danube River basin is also presented.     

Rotifera of some lakes in the floodplain of the River Niger (Imo State,Nigeria)

The Rotifera of thirteen freshwater habitats in the upper floodplain of the River Niger were studied. Thirteen new species are described, viz. Lepadella berzinsi n. sp., L. discoidea n. sp., Squatinella lunata n. sp., Dipleuchlanis ornata n. sp., Euchlanis semicarinata n. sp., Itura deridderae n. sp., L. dumonti n. sp., L. nigeriensis n. sp., L. nwadiaroi n. sp., L. simonneae n. sp., L. stichoclysta n. sp., L. sylviae n. sp. and Trichocerca kostei n. sp., L. climacois Harring & Myers is reestablished as a valid species. The synonymy of Hemimonostyla Bartos and Monostyla Ehrenberg with Lecane Nitzsch is commented upon. The names Lecane myersi nom. nov. and L. robertsonae nom. nov. are proposed to replace L. ornata (Harring & Myers) non (Daday) and L. amazonica Koste & Robertson non (Murray) (new status), respectively. Lecane amazonica (Murray) and L. latissima Yamamoto replace L. murrayi Hauer non Korde and L. rotundata (Olofsson) non (Jakubski), respectively. The following new synonymies are proposed: Lepadella williamsi Koste & Shiel with L. vandenbrandei Gillard; Lecane longidactyla (Edmondson) comb. nov. (ex. Proales) with L. clara (Bryce); Lecane longidactyla Arora non (Edmondson) with L. curvicornis (Murray); L. truncata Yamamoto non (Leissling) nec (Turner) with L. brachydactyla (Stenroos); L. amazoniana Koste & Robertson with L. eutarsa Harring & Myers.     

Phytoplankton diversity (alpha,beta, and gamma) from the Araguaia River tropical floodplain lakes (central Brazil)

Alpha, beta and gamma are three components of species diversity. Knowing these attributes in floodplain lake phytoplankton communities is vital when selecting conservation areas. Species diversity is commonly used with other taxonomic groups, but rarely with phytoplankton. We compared the number of phytoplankton species (alpha diversity) from 21 Middle Araguaia River floodplain lakes in the 2000 and 2001 rainy and dry seasons. From these samples we estimated complete survey species richness (gamma diversity), quantified differences in species composition between lakes (beta diversity) and assessed the influence of abiotic variables on beta diversity. We recorded a total of 577 taxa. The Sjack1 estimator indicated that 62.31% of taxa were sampled in the 2000 rainy and 67.65% dry seasons, and 68.36% in the 2001 rainy and 73.5% dry seasons. In almost all seasons, alpha diversity negatively correlated with latitude. Beta diversity (β-1) was higher in high water periods, especially in 2000. This may have been caused by isolated heavy rainfall, which would have increased environmental heterogeneity and raised beta diversity. DCA showed differences in phytoplankton composition between rainy and dry seasons in 2000 and 2001, reflecting the influence of flood pulses on phytoplankton composition. The Mantel test indicated spatial distribution patterns where geographically more distant lakes had less-similar phytoplankton communities. Handling editor: J. Padisak     

Diet and growth of asp,Aspius aspius (Linnaeus, 1758), in the Danube River near the confluence with the Sava River (Serbia)

A sample of 198 asp (Aspius aspius) was collected over a 28.5 km long section of the Danube River, upstream and downstream from the mouth of the Sava River, in order to provide information on population structure, diet, growth, and condition of this species. Total body lengths of sampled fish were 90–405 mm, and body weights 5–567 g. The sample was predominantly sub‐adult fish aged 0+ to 4+ years. Sexually immature asp prevailed over the sexually mature asp. The sex ratio (1.4 : 1) was biased toward males. Male asps in the Danube become sexually mature only in their fifth year of life, and the females even later, as no sexually mature females were caught. The diet spectrum consists exclusively of fishes; of seven determined prey species, most important are bleak Alburnus alburnus, roach Rutilus rutilus, and goldfish Carassius auratus. Highest value of the seasonal vacuity index is in November (I_v = 94.1), and the smallest in July (I_v = 35.6). Trophic niche breadth is largest in May (H = 1.40), and smallest in November (H = 0.00). The largest average number of prey items is found in age class 4+ (2.33), the smallest in age class 0+ (1.00). Von Bertalanffy growth parameters are L_∞ = 526.46, K = 0.28, and t₀ = 0.22. The length–weight relationship is described as log W = ?5.16 + 3.03 log L. Fulton’s condition factor increases with fish length, from 0.70 to 0.83. Regarding seasonal fluctuations, this factor begins to increase in late spring, with the trend continuing until autumn, and then decreasing from autumn to spring.     

Possible Reason for the Expansion of Carassius auratus (Linnaeus, 1758) (Teleostei,Cyprinidae) in the Danube River Basin

The author found quite a close negative relationship between commercial catches of predatory fishes and of German carp (Carassius auratus) in the lower Danube. He supposes that the main reason for the population explosion and subsequent expansion of German carp in the Danube River basin seems to be a shift in the balance of the fish community due to a reduction in the density of predatory species.     

Ecological fish production in the inland delta of the Middle Danube, a floodplain river

Synopsis Ecological fish production in one parapotamal arm of the Middle Danube inland delta in Slovakia, based on 10 samplings during 5 consecutive years, ranged from 349 to 3272 (bar|x = 1066) kg ha^–1 in total production (P_T) and from 39 to 662 (bar|x = 204) kg ha^–1 in available production (P_A). Young-of-the-year fish made up an estimated 49–62% (bar|x = 54) of the P_T. According to the food production/food consumption budget calculated by three different methods, less than half of the P_T is of autochthonous origin, while most is from other sources. Floodplain fish production includes two components: fish originating within the floodplain and fish that are temporary immigrants. The latter component varies considerably in response to the hydrological regime. To assess the P_T in riverine ecosystems, different seasons and years are needed to give realistic values.This paper is dedicated to my friend and sometime co-worker, Eugene K. Balon, at the occasion of his 65th birthday and transition to University Professor Emeritus. He was one of the first ichthyologists to undertake quantitative studies in large rivers in the late 1950's, when most fish biologists thought that fishes inhabit only the sea, lakes, reservoirs and small streams.     

Morphometrics of two morphs of sterlet, Acipenser ruthenus L., in the middle course of the Danube River (Serbia)

Two morphs of the sterlet, Acipenser ruthenus, were clearly recorded in two samplings from the middle course of the Danube River in Serbia. The pooled samples comprised 47.9% pointed‐snout morphs and 52.1% blunt‐snout morphs. The most obvious differences were snout shape and length, mainly the differences in the snout area in front of the barbels. In addition to this snout difference, the two morphs also differed with regard to head lengths and the pre‐ocular, pre‐dorsal and post‐dorsal areas. The determination of morphs is not exclusively related to either location or body size as sources of this mode of variability, although it seems that it is easier to detect these in larger size sterlet.     

Environmental determinants of fish abundance in the littoral zone of gravel pit lakes

Hydrobiologia - The type and extent of habitats along the shoreline specify the distribution of fish in the littoral zone of lakes, but effects are likely species and size-specific and might be...     

Monogenean parasites of introduced pumpkinseed Lepomis gibbosus (Centrarchidae) in the Danube River Basin

The pumpkinseed, Lepomis gibbosus, a centrarchid fish native to eastern North America, was introduced into Europe at the end of the 19th century. Lepomis gibbosus now represents one of the most successful of introduced fish species, having spread widely throughout many European countries. In this study, we collected monogenean parasites of L. gibbosus from four sites in the Danube River Basin. We recorded four monogenean species: Gyrodactylus sp., probably acquired in the area of introduction, and Onchocleidus similis, O. dispar and Actinocleidus recurvatus, species introduced together with their host. Onchocleidus similis dominated the parasite community at all sampling sites. Actinocleidus recurvatus has only been reported from southern Europe to date and, therefore, this is the first report of A. recurvatus from Central Europe and the Danube River Basin. We observed high morphological variability in both anchor pairs of A. recurvatus. Only in O. similis was there a positive correlation observed between haptor metric traits and fish host length. Differences in metric traits between native and introduced O. similis populations may reflect a difference in fish host size, the introduced fish host achieving a smaller size than fish from native populations. A detailed analysis of microhabitat distribution indicated a preference for the second gill arch for both dominant species O. similis and A. recurvatus, with dissimilar site segregation.     

The significance of zooplankton grazing in a floodplain system of the River Danube

Floodplain systems along rivers are influenced by the hydrologicalregime of the river to an extent which depends on the degreeof connectivity. As a result, the age of water within the systemvaries widely. Zooplankton development is restricted to areasand periods of higher water age and thus the role of zooplanktonin planktonic carbon flow is strongly influenced by the hydrologicaldynamics. In 1997 and 1998 the plankton community was examinedin the floodplain system along the River Danube, at two sectionsdiffering in connectivity to the main river. Zooplankton grazingrates and consumption were calculated, using filtration ratesfrom the literature, based on qualitative and quantitative phyto-and zooplankton data. A succession in grazing dominance fromrotifers to cladocerans and copepods was found with increasingwater age. Maximal carbon flow and impact on algae by grazingrates of >100% (mean 40.5%) were observed at intermediateconnectivity, when zooplankton biomass peaked. Mean grazingimpact at high connectivity amounted to 2.5%, and at low connectivity8.8%, of the total phytoplankton biomass. The main grazers wereSynchaeta spp., Polyarthra spp., and the small cladoceran, Bosminalongirostris. Herbivory dominated carbon transfer in the planktonicfood webs during dynamic conditions. When conditions are stable,additional food pathways (bacterivory, predation) increase insignificance and result in an increased biotic control.     

The palaeolimnological potential of diatom assemblages in floodplain lakes of the Danube Delta, Romania: a pilot study

Within the framework of a palaeolimnological pilot study, the potential of sedimentary diatom assemblages for the reconstruction of the eutrophication history was studied in short sediment cores from five shallow lakes located in the Romanian Danube Delta. A total of 234 diatom taxa representing 57 genera could be identified but diatom assemblages are generally predominated by a few species only. Loss on ignition percentages, total diatom abundances and diatom downcore successions largely vary within the single sediment cores and between all five lakes. This suggests the presence of various lake environments within the Danube Delta, each characterized by lake-specific geomorphological, sedimentological, hydrological, and biological conditions. Highly variable depositional conditions are also confirmed by radiocesium measurements in two of the five cores suggesting distinct inter-lake differences in the sedimentation rate. Causes for the great intra-lake and inter-lake variability in diatom downcore successions are difficult to specify and may include changes in the physico-chemical conditions, aquatic vegetation cover, water depth, river influence, turbidity and inter-biotic interactions. However, based on this pilot study, it is likely that the spatial and temporal distribution of sedimentary diatom assemblages in Danube Delta lakes were not triggered by the trophic state. The delta lakes likely became meso- to eutrophic long before 1950, possibly during late-Holocene times.     

The typology of floodplain water bodies of the Middle Danube (Slovakia) on the basis of the superficial polychaete and oligochaete fauna

The oligochaete fauna of different side arms and other water bodies in the Slovak–Hungarian stretch of the River Danube below Bratislava (r.km 1840 – r.km 1807) was investigated. The structure of the oligochaete assemblages is correlated with the bottom substratum of the river. From data on the composition of the oligochaete fauna, the clustering and ordination analysis divided the inland delta water bodies into three groups supporting the river classification of Roux et al. (1982), i.e. eupotamon, parapotamon and plesiopotamon, but parapotamon and plesiopotamon divided furthermore into two subgroups, which better reflects hydrological conditions, type of substratum, depth of water bodies and presence of macrophytes. Oligochaete assemblages differ in individual type of group and subgroups, not only species composition, but mainly quantitative (average abundance). This revised version was published online in July 2006 with corrections to the Cover Date.     

Stream section types of the Danube River in Serbia according to the distribution of macroinvertebrates

The aim of this study was to use the data on the distribution of aquatic macroinvertebrates obtained from 14 sites within a 413 km long stretch of the Danube River in Serbia to show the relevance of the bordering zone between the Middle and Lower Danube. A total of 68 macroinvertebrate taxa were observed. Molluscs were the major component with regard to species richness and relative abundance. Lithoglyphus naticoides (C. Pfeiffer, 1828) was the most abundant species and Unio tumidus (Retzius, 1788) was the most frequent species. Product-moment correlation coefficients or Pearson r coefficient was used to analyse the relation between the sites based on macroinvertebrate distribution. The data obtained by product-moment correlation served as input for cluster analyses. According to a cluster analyses Danube River in Serbia could be separated in the free-flowing sector, the stretch with a backwater effect and the area of the Iron Gate.     

Mosquitoes (Diptera,Culicidae) of the Morava River floodplain,Slovakia

Research on the Morava River floodplain mosquito fauna was carried out from April to October in 2009 and 2010. Altogether, 5864 adults were collected and identified from 12 selected sites. The presence of 28 mosquito species belonging to 6 genera were confirmed in the study area. The floodplain of the Morava River is known for its frequent inundation every year. The floods are quite irregular and often followed by the mass production of mosquitoes. The most abundant species were Aedes vexans (41.4%), Ae. cinereus (7.5%), Ae. rossicus (16.7%), Ochlerotatus sticticus (20.5%), and Culex pipiens (3.1%). Ae. vexans and Oc. sticticus are typical outbreak species for the Morava River floodplain. The years 2009 and 2010 differed in the number of floods, which influenced the mosquito faunal composition and abundance during the year.     

Phytoplankton community of floodplain lakes of the Araguaia River, Brazil, in the rainy and dry seasons

This work analyses the attributes of the phytoplankton community(species richness, biovolume, diversity, equitability, abundance,dominance and size structure) associated with some physical,chemical and climatic variables of floodplain lakes of the AraguaiaRiver, central Brazil, in the rainy and dry seasons of 2000and 2001. The lakes in 2000 and 2001 presented different limnologicalcharacteristics between the periods of high and low water. Thephytoplankton comprised 292 taxa, mainly Chlorophyceae and nanoplankton.In the dry seasons of both years, the functional group Y (Cryptophyceae)was the most prominent association. In high-water periods, differentfunctional groups dominated the lakes. The canonical correspondenceanalysis (CCA) demonstrated a separation between the rainy anddry seasons of both years. The high and low water presenteddifferent dynamics in 2 years due to the influence of the floodpulse.     

The impact of regulation and salinisation on floodplain lakes: the lower River Murray,Australia

Floodplain lakes along the lower River Murray are subject to a wide range of human impacts including regulation, abstraction, elevated saline groundwater tables, increased nutrient and sediment fluxes and introduced biota. These perturbations are superimposed on those arising from high inter-annual rainfall variability, driven, at least in part, by variations in the southern oscillation. Sediment-based archives from two lakes within a complex of wetlands, situated near to the first site of irrigation development in the lower River Murray, reveal substantial changes over the last 800 years. While high levels of salinity are not foreign to the sites, the recent trend is towards sustained high salinity levels. As a result of European impact, freshwater diatom plankton now dominates Loch Luna, whilst Loveday Wetland is both more saline and nutrient rich than in the pre-European period. In Loveday Wetland, the post-1960 increase in Haslea spicula (Hickie) Lange-Bertalot, may be driven by increases in sulphur salt concentrations that are believed to be a cause of recent acidification episodes. A recent increase in more salt tolerant diatoms in Loch Luna suggests that this site, which has been largely buffered from substantial change, is becoming more vulnerable to perturbation. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.