Kopacki Rit Research Articles

Importance of floodplains for water beetle diversity: a crucial habitat for the endangered beetle Graphoderus bilineatus in Southeastern Europe

Natural floodplains are rapidly disappearing ecosystems worldwide, primarily due to changing hydrology. Continental Croatia harbours some of the largest remaining and best preserved natural riverine floodplains in Europe. To establish conservation priorities, we surveyed water beetle assemblages in three large floodplains situated in the Danube, Drava, and Sava basins (Ramsar sites Kopacki rit and Lonjsko polje, and Spacva riparian forest), with special focus on the red-listed beetle Graphoderus bilineatus. The main aim of our study was to investigate the key environmental factors driving variation of water beetle assemblage structure and occurrences of G. bilineatus. Environmental variables describing habitat types and various habitat characteristics were measured and/or estimated for each sampling site. A total of 4.339 water beetle specimens belonging to 98 species were recorded. G. bilineatus was recorded at two out of the three investigated floodplains at 14 out of 30 sampling sites. We found significant differences in water beetle assemblages among the three localities based on the total species dataset, accompanied by different environmental background and vegetation composition. The density of riparian vegetation, permanent water durability, shading, type of bank, and plant communities best explained the distribution of the water beetle species. Based on the regression model, human impact and shading have significant effects on the abundance of G. bilineatus. Sites with G. bilineatus presence have significantly higher species richness compared to the sites without the species. Co-existence analysis indicates various types of associations between G. bilineatus and other water beetle species.

Cycle reservoir with regular jumps for forecasting ozone concentrations: two real cases from the east of Croatia

Satisfying the national air quality standards represents a challenge nowadays for developing countries. Air pollution in industrial cities is one of the foremost problems that affect human health and might cause loss of human life. One of the main attributes that can cause a significant impact on people’s health is the ground-level ozone pollution. Ozone can raise the ratio of asthma attacks, permanent damage to lungs, and maybe death. Forecasting its concentration levels is essential for planning well-designed environment protection strategies. In this paper, a state-space reservoir model called cycle reservoir with jumps (CRJ) is used to predict the level of ozone concentrations in the east of Croatia utilizing some meteorological parameters including the temperature, relative humidity, wind speed, wind direction, and the pollutants PM10. CRJ is a particular type of recurrent neural networks with powerful performance when applied for complex temporal problems. Two cases from the east of Croatia are investigated in this work: the Kopacki Rit area and the Osijek city. The proposed CRJ model shows superiority of CRJ model in forecasting ozone concentrations compared to linear regression, multilayer perceptron (MLP) and radial basis function (RBF) network.

A comparison of methods for sampling aquatic insects (Heteroptera and Coleoptera) of different body sizes, in different habitats using different baits

Although various methods exist for sampling aquatic Heteroptera and Coleoptera in standing water, there are very few comparisons of their performance in different types of habitat. In this study, we evaluated and compared the efficiency and selectivity of three sampling methods: hand netting, bottle traps baited with canned tuna and bottle traps baited with canned cat food. The methods were compared over the period 2010-2012 in two different habitats (temporarily flooded areas and canals) in the Nature Park Kopacki rit, a floodplain on the banks of the River Danube. The results show that the effectiveness of the method differed in the two habitats. Overall, hand netting was the most successful method, mainly in canals. Tuna fish bait was more efficient than the commonly used cat food, especially for large and highly mobile species of Dytiscidae. These findings indicate that knowing the type of habitat and the habitat preferences of aquatic insects and their activity it is possible to predict which of these methods are the best for estimating species richness.

CROSS-CORRELATION MODELLING OF SURFACE WATER – GROUNDWATER INTERACTION USING THE EXCEL SPREADSHEET APPLICATION

Modelling responses of groundwater levels in aquifer systems, which occur as a reaction to changes in aquifer system boundary conditions such as river or stream stages, is commonly being studied using statistical methods, namely correlation, cross-correlation and regression methods. Although correlation and regression analysis tools are readily available in Microsoft Excel, a widely applied spreadsheet industry standard, the cross-correlation analysis tool is missing. As a part of research of groundwater pressure propagation into alluvial aquifer systems of the Sava and Drava/Danube River catchments following river stages rise, focused on estimating groundwater pressure travel times in aquifers, an Excel spreadsheet data analysis application for cross-correlation modelling has been designed and used in modelling surface water – groundwater interaction. Examples of fi eld data from the Zagreb aquifer system and the Kopacki rit Nature Park aquifer system are used to illustrate the usefulness of the cross-correlation application.

Tradicijski ribolov u Kopačkom ritu kao kulturno turistički potencijal i mjera zaštite okoliša

Kopacevo is a Croatian Danube Region wetland village where a unique type of fishery was developed. Due to the late 20th century ban on fishing and related traditional activities, today the last generation of fishermen, who have these skills, has all but disappeared. At the same time, this represents a threat to the ecosystem, because without maintenance the meanders are disappearing due to the plant deposits. Consequently, the Traditional Fishing Society seeks to protect the traditional skills as cultural property, tourism potential, and an environmental protection and monitoring measure. The aim of the research was to estimate the environmental, cultural, and economic sustainability of a possible revitalization of traditional fishing in Kopacki Rit.

Atmospheric VOCs measurement in Nature Reserve Kopački rit, Croatia

To determine the impact of volatile organic compounds (VOCs) on ozone formation, their identification as well as air concentration assessment is necessary. These were one of the first collections on adsorption tube samples of VOCs in air from the Nature Reserve Kopacki rit. The samples were analysed by gas chromatography coupled with flame ionisation detector (FID) and mass selective detector (MSD), and results for the hydrocarbons with two to six carbon atoms are reported. The results show that among the measured concentrations, ethane, propane and n-butane were the highest. Biogenic hydrocarbon isoprene, whose concentrations follow daily cycle of ozone formation during the summer, was also identified and quantified. We used the cluster analysis (CA) to indentify the possible common emission sources among the measured data. The measured data are discussed in relation to the EU guidelines (Directive 2008/112/EC; Directive 2004/42/EC).

Dynamics of the Kopački Rit (Croatia) wetland floodplain water regime

Kopacki Rit Nature Park is part of the Danube River natural floodplain and one of the last oases of wild life in the Danube River Basin. Due to its extraordinary value, it was inscribed on the list of Wetlands of International Importance in 1993. More than 2,000 species have been registered in this area, which consists of lakes, canals, grassland, marshland and forests. Even the number of investigations which have been performed on its biological and ecological features, hydrological and water resources characteristics, as a prerequisite for ecohydrological analyses, are still rather unknown in the scientific community. Mainly the Danube River and partly the River Drava cause flooding of Kopacki Rit and inundations enter the area from both the northern and southern parts. Results of hydrological and meteorological analysis show a decreasing trend of both mean and minimum, annual water levels in the Rivers Drava and Danube (respectively 1.8 and 1.38 cm/year). These reductions in water level can reduce the replenishment periods of Kopacki Rit Nature Park. In addition, a significant rise of mean annual air temperature and consequently water temperature (data 1988–2011) may be causing increasing evapotranspiration and loss of water within Kopacki Rit. But an encouraging counteracting finding is that, the results of frequency analysis show, even a discharge of 5-years’ return period on the River Danube inundates 70 % of the Danube floodplain and Kopacki Rit Nature Park.

A record of the North American paddlefish (Polyodon spathula Walbaum, 1872) in Croatia

On 22 May 2011, a recreational fisherman accidentally caught a paddlefish (Polyodon spathula, Walbaum, 1792). The fish was captured near the Kopacki rit Nature Park in the Croatian section of the Danube River at 1418 rkm. The paddlefish had an 80 cm TL, 71.5 cm FL, 69.5 cm SL, 24 cm snout length, and body weight of 1.435 kg. Neither recreation nor commercial fishermen caught another paddlefish during 2011 in the Croatian part of the Danube River.

Assessment of Variations of O3 Concentrations in Kopački Rit Nature Park, Eastern Croatia

Result of the first ozone monitoring in ambient air Nature Park of Kopacki Rit (Eastern Croatia) are reported for the growth season in 2008. The measured hourly concentrations of ozone in the air do not exceed the limit value of 110 mu g m(-3) statutory regulation by Croatian legalization for the protection of human health. There were only 13 days exceeding of the target value of 120 mu g m(-3) (8-h averages) as established in the European Union guidelines on ozone pollution in ambient air. In contrast to the measured AOT40 whose value does not exceed the critical level of 18 000 (mu g m(-3)).h for vegetation injury, an estimated AOT40 value was somewhat higher. The relationships between O-3 and meteorological variables were investigated by a principal component analysis (PCA). Fourier analysis methods applied to ozone concentrations data showed that the most important variations in the O-3 data are represented by usual daily cycles.

Cyanobacterial blooms in a temperate river-floodplain ecosystem: the importance of hydrological extremes

In the past decade, extreme hydrological events were expressed with extreme droughts and floods in temperate regions. The aim of this paper is to explain how such changes in hydrology can influence cyanobacterial populations in floodplain ecosystems. We therefore analyzed a 6-year (2003–2008) study of the phytoplankton in the Kopacki Rit floodplain, one of the largest natural floodplains in the middle section of the Danube River (Europe). During the studied period, the shallow floodplain lake shifted between a state of turbid water, characterized by high phytoplankton biomass and regular appearance of cyanobacteria blooms, to a state of clear water with very low phytoplankton biomass and absence of cyanobacteria, and back to the turbid state. Apparently, the major forces driving the cyclic shift were closely related to extremely high and long-lasting flood events. Significant increase in water level, low hydraulic residence time of water, decrease in transparency and low-light climate, together with mass developed aquatic macrophyte vegetation in the whole inundated floodplain were unfavorable conditions for growth and proliferation of cyanobacteria. With the establishment of the flood regime characterized by long-lasting periods without flooding, in-lake processes prevailed leading to cyanobacterial bloom. The most successful were filamentous non-N-fixing cyanobacteria tolerant to mixed and low-light conditions (Planktothrix and Limnothrix) and invasive species Cylindrospermopsis raciborskii. Their massive development led to the establishment of a phytoplankton steady state. All our results demonstrate that the altered intensity and frequency of flood events will have pronounced effects on the appearance of cyanobacterial blooms and generally on alternative stable states in the floodplain. Relating to this, management objectives should be focused on qualifications of changes in hydrology and projecting those effects for potential floodplain restoration.

Efficacy of mosquito attractants in various habitats of a floodplain

Efficacy of different mosquito attractants was invesigated at four sites in three plant communities (Galio-Salicetum albae, Populetum nigro-albae, Genisto elatae-Quercetum roboris) of flooded and forest habitats in Kopacki rit Nature Park, Croatia. The attractants were: dry ice, horse urine, horse urine + acetone, acetone, 1-octen-3-ol and ammonium hydroxide baited CDC traps. A total of 11,441 mosquito specimens of 12 species were collected. Aedes vexans (91.43%) was the most numerous species. A statistically significant difference between the efficacy of dry ice and the other attractants was shown, whereas there was no difference between the other attractants. A greater number of specimens and species number were noted in the flooded plant communities (Populetum nigro-albae). The response of Ae. vexans to dry ice was higher in flooded sites, and it was significantly lower in forest habitat (Genisto elatae-Quercetum roboris) according to fuzzy c-means cluster analysis. The same analysis shows a higher efficacy of other attractants (horse urine, horse urine + acetone, acetone, octenol and ammonium hydroxide) in forest habitat when compared to the flooded area habitats.

Interactions of weed-bed invertebrates and Ceratophyllum demersum stands in a floodplain lake

This investigation reports on weed-bed invertebrate abundance associated with the submersed macrophyte Ceratophyllum demersum L. in Lake Sakadas within Kopacki rit Nature Park (Croatia). Twenty five taxonomic groups, with the dominance of chironomids (79%), were recorded at three stations during the investigation from July 14 to September 8, 2004. Nematodes and large predatory larvae of Zygoptera with 6% were second in dominance, followed by oligochaetes with 5%. Weed-bed invertebrates on C. demersum were more abundant than on Myriophyllum spicatum L. due to different morphology of the host plants. Environmental parameters within C. demersum stands were found in the same range at all stations, but they changed during the season. They indicated eutrophy with the tendency to hypertrophy which is reflected by the composition of the weed-bed invertebrate community.

Genotoxicity monitoring of freshwater environments using caged carp (Cyprinus carpio)

The present study deals with genotoxicity assessment of freshwaters using caged carp (Cyprinus carpio). Carps were transplanted from a fish-farm to three differently polluted sites in eastern Croatia. Two polluted sites were situated in the river Drava, downstream from the cities of Belisće and Osijek, while the reference site was in the Nature Park Kopacki rit, a preserved wetland area with limited anthropogenic influence. Exposure lasted for 3 weeks and was repeated for 3 years (2002-2004). DNA damage was assessed in erythrocytes of the exposed animals by the Comet assay and micronucleus test (MNT). In order to evaluate possible differences in stress responses to polluted water in situ and in aquaria a laboratory exposure was performed with water from the studied location in the second year of the study. Carp from the sites with high anthropogenic influence (Belisće and Osijek) had higher average DNA damage as expressed in both the MNT and Comet assay. Of the two, the Comet assay appeared to be more sensitive following both caging and aquaria exposures. The results from this study suggest that 3 weeks caging exposure of C. carpio may be a useful strategy to monitor for genotoxic agents in freshwater ecosystems.

Epiphytic meiofauna in stands of different submerged macrophytes

Epiphytic meiofauna in association with pure stands of four macrophytes (Nymphoides peltata, Ceratophyllum demersum, Polygonum amphibium and Carex spp.) were studied in the slow-flowing Conakut Channel, within the Kopacki rit floodplain, Croatia, during two vegetation seasons (2001 and 2002). The meiofauna densities for different macrophyte types showed a significant variation between N. peltata and C. demersum stands with a total of 15 meiofauna taxa on the macrophytes. Insect larvae, mostly Chironomidae, and Oligochaeta juveniles were the most abundant taxa recorded during the entire investigated period in all stands of macrophytes, except in P. amphibium.

Response of Mosquitoes to different Synthetic and Natural olfactory Attractants (Diptera: Culicidae)

The study was conducted in the Kopacki rit Nature Park in Eastern Croatia with the aim of testing the efficacy of different natural and synthetic attractants for capturing mosquitoes. The following attractants were used as bait in CDC traps during mosquito sampling: carbon dioxide (dry ice), horse urine, acetone, 1-octen-3-ol, ammonium hydroxide, and the combination of horse urine + acetone. Out of the total of 3248 captured mosquitoes, 96.54% (3133) were trapped by using dry ice as attractant. Horse urine attracted the second largest number of mosquitoes (34), and the least number of mosquitoes (15) was attracted by 1-octen-3-ol. In addition to having attracted the largest number of mosquitoes, dry ice was the most effective in attracting the largest number of different mosquito species (11). Five species were attracted with horse urine + acetone and ammonium hydroxide, which has been used as a mosquito attractant for the first time. The Χ 2 test revealed statistical significance among attractants. Most captured mosquitoes (2404) were Ae vexans, followed by Cx modestus, An messeae with 655 and 133 mosquitoes, respectively. Not a single Culex mosquito was attracted to 1-octen-3-ol.

Changes in N and P limitation induced by water level fluctuations in Nature Park Kopački Rit (Croatia): nutrient enrichment bioassay

The importance of nutrients as limiting factors might vary in environments with different limnological characteristics. In this article we evaluate the effect of frequency and duration of flooding on nutrient limitation in a riparian floodplain. Variations in N and P limitations were studied in the period of low (2003) and high (2004) water level in two different floodplain habitat types in the Nature Park Kopacki Rit (Croatia), a floodplain area of the Danube River. In 2003 and 2004, the limnological characteristics of floodplain lake (Lake Sakadas) and the channel (Stara Drava) differed due to their hydrological regimes. Potential for nutrient limitation was determined by DIN:TP and TN:TP ratios, while the actual nutrient limitation was assessed by nutrient enrichment bioassay. A change from non-limited to N-limited conditions in the channel, and consistent actual N limitation in the lake was determined by the nutrient enrichment experiment. Of the two ratios, DIN:TP matched better with the bioassay data. Phosphorus limitation was only occasionally evident. Changes in trophic conditions from hypereutrophy to eutrophy (between low and high water levels) reflected the importance of the hydrologic regime as a factor which can modify the trophic state of Lake Sakadas. Compared with 2003, the increase of total nitrogen concentrations in 2004 calls attention to the importance of nitrogen inputs from the Danube to the system with excessive phosphorus concentrations.

SPATIOTEMPORAL MONITORING OF FLOODWATER MOSQUITO DISPERSAL IN OSIJEK, CROATIA

This paper demonstrates the possibility of using geostatistics to monitor the dispersal of mosquitoes for mosquito control programs at the municipal level. The case study objective was to quantify the dispersal of floodwater mosquitoes from the natural marshland Kopacki rit into the city of Osijek, Croatia, and to analyze the main factors controlling it. Fifty thousand adult Aedes vexans, Ochlerotatus sticticus, and Ochlerotatus caspius mosquitoes were marked with a powdered fluorescent pigment and released from the southern part of Kopacki rit on April 28, 2004. Forty CO2-baited Centers for Disease Control and Prevention traps were set in the area of the municipality of Osijek (171 km2) and were monitored for 10 days. A total of 582,471 mosquitoes were captured and examined in the laboratory. The mosquito counts from different sites were then interpolated using ordinary kriging and visualized dynamically to detect the dominant migrational directions. Mosquito dispersal and frequency were greatly influenced by wind speed (r = 0.82). The marked mosquitoes were found at 12 sites located from 1 km to 11.7 km away from the release point. The recapture rate was 0.044% (54% Oc. sticticus, 32% Ae. vexans, and 14% Oc. caspius). Based on the Lincoln index, the estimated total population size for floodwater mosquitoes in the study area ranged from 875 million to 2.0 billion mosquitoes. Limitations of the approach, recommendations for the improvement of the monitoring network, and spatial predictions are further discussed.

Alternation of Factors Affecting Bacterioplankton Abundance in the Danube River Floodplain (Kopački Rit, Croatia)

The purpose of this investigation was to determine the influence of different phases of the hydrological cycle on the abundance of colony-forming units (CFU) of bacteria in the Kopacki Rit floodplain and to assess temporal and spatial variations in the proportion of eutrophic and oligotrophic bacteria (r- and K-strategists) as a biological indicator of dissolved organic carbon (DOC) availability. Determination of bacterial abundance was performed with abiotic variables (water temperature, depth, Secchi disc transparency, dissolved oxygen, pH, electrical conductivity, ammonia, nitrates+nitrites, total nitrogen and total phosphorus) and one biotic (chl-a) variable, and dimensionality reduced with principal component analysis (PCA). The component scores were used as independent variables in a multiple regression and the relationship between scores (indirect variables) and bacterial abundance was examined. An elevated bacterial abundance was observed during the limnophase (floodplain isolated from the river) and potamophase (flood). During the limnophase also the highest chl-a concentrations were found and in Sakadas Lake during September 2003 significantly higher numbers of eutrophic than oligotrophic bacteria emerged (p = 0.026). During potamophase the opposite state was established. Elevated bacterial abundance occurred in parallel with minimal chl-a concentrations and during July 2004 in the Conakut Channel a significantly higher number of oligotrophic than eutrophic bacteria emerged (p < 0.001). Differentiation in the number of eutrophic and oligotrophic bacteria suggests the existence of a higher concentration of labile DOC during September 2003 than during July 2004. Multiple regression analysis explains 13.6% of the variation in abundance of eutrophic bacteria. The regression model for oligotrophic bacteria is not significant. The results suggest two different mechanisms control bacterioplankton numbers to some extent in the Kopacki Rit floodplain. In addition, two sources of DOC differentiating the quality of organic matter predominate under totally different hydrological regimes. Under these conditions, eutrophic bacteria may be partially bottom-up controlled, whereas it is not clear how the abundance of oligotrophs is controlled.

Diurnal Periodicity in the Biting Activity of Horsefly species in the Kopacki rit Nature Park, Croatia (Diptera: Tabanidae)

Adult females of Tabanidae species were collected during the summer of 2004 in the Tikves forest within the Kopacki rit Nature Park (E Croatia). Analysis of the biting activity was made on Tabanid collected by four linen canopy traps. The daily trapping period was between 07-19h by every two hours emptying the traps. Throughout 14 sampling days a total of 5.505 individuals was collected and classified to 20 species. The biting activity of horse flies was studied only for the five most abundant species: Atylotus loewianus (Villeneuve 1920), Tabanus bromius Linnaeus 1758, Tabanus maculicornis Zetterstedt 1842, Tabanus tergestinus Egger 1859 and Tabanus sudeticus Zeller 1842. The five most abundant species together represented 95.05% of the total catch. A single peak of the biting activity was established for all five of them: Atylotus loewianus, Tabanus bromius, Tabanus maculicornis and Tabanus sudeticus were most active during midday and early afternoon between 11-13h at air temperatures from 24-28C. In Tabanus tergestinus, the maximal activity occured earlier, from 9-11h, at air temperatures between 23-26C. Multiple regression analysis showed that the peak of the biting activity for the five most abundant Tabanidae species is significantly influenced by meteorological factors.

Algal responses to nutrient additions in water of Nature Park Kopacki Rit (Croatia) by Miniaturized Algal Growth Bioassay

The algal growth potential (AGP) in original water samples from Nature Park Kopacki Rit and the Danube, as well as the influence on the AGP due to adding nitrates (final concentration of 0,180; 0,360; 0,723 g 1 -1 ) and phosphates (final concentration of 0,028; 0,056; 0,169 g I -1 ) was investigated by miniaturized bioassay method. According to the classification for waters of Middle Europe, during March and April 2001 the waters of Kopacki Rit belonged to meso-mesoeutrophic waters, and in January 2001 to oligotrophic. During the period of investigation, the Danube River belonged to the meso-mesoeutrophic waters. On the basis of AGP results, toxic substances were equally present at all sites, except at Lake Sakadas. In all three concentrations the nitrates stimulated the growth of Chlorella kessleri. Samples from the Danube and Hulovo Channel from January 2001 were exceptions. In April 2001 phosphates inhibited the growth of alga Chlorella kessleri, mainly through samples from the bottom. During the whole investigated period, nitrates control the eutrophication in Kopacki Rit.