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The floodplain of Kopački Rit is one of the largest preserved and internationally significant natural floodplains in the middle Danube basin. Due to the preserved natural flood dynamics, the floodplain is characterized by great heterogeneity of habitats, which provides favorable conditions for the survival of many plant and animal species. Microphytes (cyanobacteria and algae) are not only primary producers and the basis of aquatic food chains but are also particularly important for monitoring ecological changes in floodplain microbiotopes. Microphyte communities, both phytoplankton and periphyton, have been studied continuously for several decades (since the 1970s). The results obtained indicate a high biological diversity – to date, more than 600 taxa of microphytes have been recorded. Flooding dynamics and intensity were identified as the most important factors for the development of microphyte communities. Occasional occurrence of pronounced cyanobacterial blooms with massive development of invasive taxa contributes to natural eutrophication of floodplains. Recent research has focused on the development of a national system for assessing the ecological status of inland waters based on the results of monitoring phytoplankton and phytobenthos in different types of freshwater biotopes along the floodplain. In addition, initial steps have been taken to apply DNA metabarcoding of microphytes in the environment as an additional method to morphology-based approaches. The results of the microphyte research are permanently used to define water protection measures in the Kopački Rit floodplain.

Digestat je nusprodukt anaerobne fermentacije koji nastaje tijekom proizvodnje bioplina, bogat je organskim i anorganskim tvarima (dušikom, fosforom, kalijem i drugim mikronutrijentima). Cilj ovog istraživanja je analizirati utjecaj različitih koncentracija digestata na razvoj prirodnih populacija mikroalga i cijanobakterija za proizvodnju biomase. Eksperiment je proveden s koncentracijama od 31, 06 i 53, 60 mg/l digestata u razdoblju od 49 dana pri temperaturi od 24, 00 °C, pH od 7, 89 i s konstantnom aeracijom. Na kraju eksperimenta došlo je do značajnog smanjenja koncentracija ukupnog dušika (TN) i ukupnog fosfora (TP) u obje eksperimentalne skupine (17, 01 i 15, 00 mg/l). Dominantne mikroalgalne zajednice bile su zelene klorokokalne alge vrste Chlorella, koje su se eksponencijalno razvijale u obje eksperimentalne skupine, a njihova dinamika ovisila je o koncentraciji digestata. U skupini s nižom koncentracijom digestata dnevni prinos biomase iznosio je 1, 84 mg/l, s prosječnom produktivnosti od 123, 86 mg/l, dok je u skupini s višom koncentracijom digestata dnevni prinos iznosio 4, 14 mg/l s prosječnom produktivnosti od 263, 01 mg/l. Dobiveni rezultati ovog istraživanja pokazali su da je digestat pogodan kao nutrijent u proizvodnji algalne biomase koja se može koristiti u proizvodnji bioplina na malim farmama. To može značajno pridonijeti ekonomskoj isplativosti i ekološkom gospodarenju.

Extreme hydrological events have become more frequent and intensive in the Danube River Basin. The highest ever recorded discharge of the Danube at the entrance to Croatia (river 1424.85 km) was in June of 2013. The aim of this study was to evaluate changes in the ecological status of the Danube according to the phytoplankton functional approach and applying the phytoplankton assemblage index (Q-index). The lowest phytoplankton abundance and biomass were found during extremely high water discharge. A total of 119 phytoplankton species sorted into 20 FGs were found. Codon TB, represented by benthic diatom species, was the most successful during the whole investigated period and dominant in the conditions of extreme floods. The highest value of the Q-index (4.49) was established in the condition of extreme floods, indicating the excellent ecological state. The worst ecological state was in April, in the conditions of high nitrogen concentrations in riverine water and the low value of the Q index (2.48) indicating poor ecological status. Our results have shown that the assemblage index is a reliable instrument to assess the ecological status of large lowland rivers influenced by extreme hydrological events.

Kromatografija je skup separacijskih tehnika koje služi za odjeljivanje, identifikaciju i kvantitativno određivanje sastojaka smjese. Kao najupotrebljivanija tehnika ističe se tekućinska kromatografija visoke djelotvornosti (HPLC). Vitamin C pripada skupini vitamina topljivih u vodi. Vrlo je jak antioksidans, blagotvorno djeluje na zdravlje čovjeka i jedan je od najistraživanijih vitamina. Najbolji izvori vitamina C su voće i povrće. Ovaj rad opisuje rezultate istraživanja udjela vitamina C u komercijalnim sokovima od rajčice, cikle, mrkve i kiselog kupusa određenog HPLC metodom. Udio vitamina C u sokovima od rajčice kretao se u rasponu od ispod limita kvantifikacije (< LOQ) do 8,67 mg/100 mL, u sokovima od cikle od < LOQ do 23,26 mg/100 mL, u sokovima od mrkve od < LOQ do 36,19 mg/100 mL te u sokovima od kiselog kupusa u rasponu od 13,39 mg/100 mL do 16,54 mg/100 mL. Chromatography is a set of techniques used for separation, identification and quantitative determination of the mixture components. The most used one is high performance liquid chromatography (HPLC). Vitamin C belongs to a group of water-soluble vitamins. It is a very strong antioxidant with a beneficial effect to human health. It is also one of the most explored vitamins. The most important sources of vitamin C are fruits and vegetables. This paper describes the results of the study on vitamin C content in commercial tomato, beetroot, carrot and sour cabbage juices determined by HPLC method. Vitamin C content in tomato juices was found to range from below the quantification limit (< LOQ) to 8.67 mg/100 mL, in beetroot juices from < LOQ to 23.26 mg/100 mL, in carrot juices from < LOQ to 36.19 mg/100 mL and in sour cabbage juices from 13.39 mg/100 mL to 16.54 mg/100 mL.

Fruits, vegetables and products are the most important source of vitamin C in human diet. Due to the low energy value and presence of many essential food constituents, the consumption of vegetable juices, as well as pallet of products at the market is increasing. Vitamin C encompasses the group of compounds that possess biological activity equivalent to the L-ascorbic acid, and is one of the most important antioxidant in human body. Furthermore, L-ascorbic acid is often added to food products as antioxidant food additive. Vitamin C content was determined in commercial tomato, carrot, beetroot and sour cabbage juices by high performance liquid-chromatography (HPLC) with photo-diode array detector (PDA). Determined values ranged from below limit of quantification up to 36.19 mg/100 mL with lowest values in tomato juice and the highest in carrot juice. Although these values seems to be low, the consumption of only one serving of juice per day (250 mL/day) could substantially contribute to estimated average requirements while some of them contribute to daily requirements completely.

Klimatske promjene koje se očekuju prema scenarijima ( IPCC, 2007), a kojima se predviđa smanjenje količine oborina i globalno zatopljenje koje mora utjecati i na povećanje temperature vode mogu imati dalekosežne posljedice na hidrološki ciklus i slatkovodne ekosustave umjerenog klimatskog pojasa. U tom kontekstu, ekosustavi kao što je Kopački rit postaju vrlo osjetljivi na klimatske promjene. Kopački rit se puni vodom iz Dunava koja se sustavom kanala i jezera širi cjelokupnim prostorom dok su količine vode koje dolaze sa zaobalne strane puno manje . Stoga se sve promjene koje se zbog klimatskih i/ili antropogenih utjecaja događaju na Dunavu i njegovom slivu reflektiraju i na Kopačaki rit – trendovi sniženja minimalnih i srednjih vodostaja, uzlazni trendovi maksimalnih vodostaja, morfološke promjene korita, učestala pojava suša i poplava i sl. Hidrološka I ekološka povezanost Dunava i Kopačkog rita vrlo je izrazita – pojavnost proljetnih i ljetnih velikih voda Dunava ima izuzetan utjecaj na cjelokupni ekosustav i svaka hidrološka promjena utječe na dinamiku ekoloških procesa. Posljednjih 20-ak godina pojavile su se ekstremne i poplave ( 2006, 2013, 2014.) i suše (2000, 2003.), najveće otkako postoje hidrološka opažanja na ovom području što je svakao ostavilo posljedice na floru i faunu Kopačkog rita. Promjene ekološkog stanja poplavnog područja najbolje pokazuje promjena količine fitoplanktona. Promjene stanja od stanja s malom količinom fitoplanktona ( “clear state”) do stanja sa velikom količinom fitoplanktona („turbid state“) ovisne su o dinamici intenzitetu plavljenja. U radu će se dati analize hidroloških i ekoloških pokazatelja stanja Kopačkog rita s naglaskom na navedene procese- intenzitet i dinamiku plavljenja i njihov utjecaj na biološke pokazatelje stanja Kopačkog rita.

This report provides a summary of the current knowledge about the invasive microalgal species in the Kopački Rit floodplain, one of the largest preserved river-floodplain systems in the Middle Danube (Croatia). Benefiting from their small size microalgae have a potential to spread very quickly between the main river bed and various floodplain biotopes, such as permanent and temporary shallow lakes, wetlands and channels. During the almost half century of algal research, several alien or potentially invasive species were observed. Among toxic cyanobacterial species, Raphidiopsis mediterranea blooming was registered only in the past. Nowadays (from 2003 onward) ubiquitous cyanobacteria of tropical origin Cylindrospermopsis raciborskii periodically formed massive blooms in the floodplain biotopes during the long isolation period from the income of floodwater in summer. Other potentially invasive cyanobacteria (Cuspidothrix issatschenkoi and Dolichospermum compactum in phytoplankton, Gloeotrichia echinulata in periphyton) and chlorophytes (Monactinus simplex and Staurastrum planctonicum in phytoplankton, Hydrodictyon reticulatum in periphyton) occur sporadically in the floodplain biotopes. Alien diatoms are found to be prominent in the river phytoplankton. Regular blooms of Skeletonema potamos and abundant populations of Actinocyclus normanii during the conditions of high water temperatures and low water levels in summer-autumn periods represent nowadays the characteristic feature of the Danube phytoplankton. Due to ongoing spread and severe bloom formation, diatom Didymosphenia geminata can be potentially invasive, but until now it was found in low abundance in phytoplankton and phytobenthos of the main river bed. It seems that introduction and spreading of these invasive algal species can be linked to the Southern Invasive Corridor going from the Black Sea along the Danube Canal–Main–Rhine. Further international and multidisciplinary investigations focused on the alien and invasive species in the Danube River Basin are needed to ensure a long-term conservation of this unique floodplain and the preservation of its biodiversity.

Dry grasslands of the alliance Festucion valesiacae with rich and unique steppe flora are very rare in Croatia since the majority of these grasslands have been greatly modified and converted to productive agricultural land. This study was carried out at the grassland area situated at the local cemetery in Bilje (45˚36'N ; 18˚45'E), Baranja region. The area has a moderately warm, rainy climate without extremely dry months during the year. The air temperature fluctuates from -1.4 °C in winter to 40 °C in summer. The annual precipitation range is between 600 and 700 mm. Geomorphologically, the study area mostly belongs to the lowland area built of Quaternary sediments formed during the Holocene and Pleistocene. Investigated dry grassland in Bilje covers approximately 0.63 ha. In order to preserve this very rare grassland type in Croatia, the area is protected as Natura 2000 site (code HR200078) and it is proclaimed as monument of nature. The floristic survey was performed from the beginning of April to the end of November 2015. In total, 157 plant taxa classified into 47 families were found. Families Poaceae (21), Fabaceae (14), Asteraceae (10), Caryophyllaceae (10), Cichoriaceae (8), Lamiaceae (8) and Rosaceae (8), contained the greatest number of taxa. Life form analyses showed that hemicryptophytes were dominant (56.05% of total number of plant taxa) followed by therophytes (22.29%), geophytes (14.65%), chamaephytes (3.18%), and phanerophytes (3.82%). According to phytogeographical analysis, Eurasian (45 taxa), Pontic-Central-Asian (36 taxa), Central European (33 taxa) and Cosmopolite (26 taxa) geoelements predominated. Among the identified taxa, three of them are critically endangered, four are nearly threatened, one is vulnerable and four are classified as invasive species. Mowing and controlling of spreading of invasive and woody plant species should be important steps toward long-term persistence of this diverse grassland flora.

Cvjetanje cijanobakterija je u današnje vrijeme prepoznato kao karakteristika slatkovodnih eutrofnih ekoloških sustava širom svijeta. U dinamičnim sustavima rijeka-poplavno područje, dinamika i intenzitet plavljenja može se okarakterizirati kao kontrolni čimbenik cvjetanja cijanobakterija jer su one posebno osjetljive na stres uzrokovan plavljenjem. U poplavnom području Kopačkog rita, jednom od najvećih prirodnih poplavnih područja u srednjem dijelu Dunava, tijekom osam godina (2003-2010) provedena su istraživanja fitoplanktona s posebnim naglaskom na razvoj cijanobakterija. Ukupno je utvrđeno 19 vrsta, od kojih 10 vrsta izazivaju cvjetanja. Najzastupljenije su bile nitaste vrste cijanobakterija iz funkcionalnih skupina H1 (Dolichospermum solitarium, D. sigmoideum, Anabaena planctonica i Aphanizaomenon flosaquae), S1 (Limnothrix redekei, Planktothrix agardhii, Pseudanabaena limnetica i Planktolyngbya limnetica) i SN (Cylindrospermopsis raciborskii). Najrazvijenije su bile vrste P. agardhii (166, 8 mg/L u rujnu 2008. godine) i L. redekei (73, 6 mg/L u rujnu 2004. godine) te invazivna vrsta europskih voda C. raciborskii (91, 4 mg/L u kolovozu 2003. godine). Redundancijska analiza pokazuje da su temperatura vode, koncentracija hranjivih tvari i vodostaj Dunava bili glavni čimbenici koji su pogodovali razvoju vrste C. raciborskii. Velika prozirnost vode i visoka koncentracija nitrata i nitrita pridonijeli su razvoju vrste L. redekeii te drugim vrstama roda Limnothrix (tankim nitastim vrstama reda Oscillatoriales), dok su niske koncentracije dušika pogodovale razvoju vrsta iz rodova Dolichospermum, Anabaena i Aphanizomenon. Dobiveni rezultati ukazuju da su intenzitet i učestalost poplava, zajedno s promjenama jezerskih varijabli, imali značajan učinak na pojavu cvjetanje cijanobakterija.

The present study aimed at assessing the floristic diversity of a semi-natural habitat mosaic consisting of different vegetation types such as grasslands, scrubland and forest fringes hosting a diverse assemblage of protected orchid species. The area under investigation covers approximately 0.8 ha and is situated above the village Stara Kapela (45°14'11"N, 17°41'16"E), with an altitude range of 100 to 225 m.a.s.l.. It is located at the southern slopes of Požeška Gora hill (616 m.a.s.l.) in the south-eastern part of the Slavonian mountain range (Eastern Croatia). The former large areas of characteristic oak forests were cut down almost to the ridge of Požeška Gora due to the spreading of villages and other anthropogenic habitats which prevail in the area of Stara Kapela, such as pastures, meadows, agricultural fields, hedges, orchards and vineyards. The weekly-based floristic surveys were undertaken from May through October 2015. The studied area was dominated by taxa characteristic of continental dry calcareous grassland communities (Festuco- Brometea) influenced by the surrounding vegetation of sub-continental thermoxerophilous forests of Quercus petraea and Quercus cerris. Among the total of 186 plant taxa recorded, the most diverse families were Fabaceae (17 taxa), Lamiaceae (15 taxa), Asteraceae (14 taxa) and Rosaceae (11 taxa). The family Orchidaceae was surprisingly diverse with 11 taxa sorted to 6 genera: Anacamptis, Cephalanthera, Epipactis, Gymnadenia, Ophrys and Orchis. All these orchids are strictly protected by the Croatian Nature Protection Act, two are additionally listed as nearly threatened, five as vulnerable and one as data deficient species. Habitats with similar features in Croatia and Europe, especially those that host a rich suite of orchid species, have been included in the NATURA 2000 Ecological Network as “important orchid sites” on semi-natural dry grasslands and scrubland facies on calcareous substrates (habitat code: 6210). Furthermore, the remnants of thermophilic forests in Croatia are excluded from regular harvesting being very important from the point of biodiversity. This site is not assigned to any nature conservation category so further investigation into the diversity and distribution of orchids, as well as many other important plant taxa growing on this relatively small area is needed to provide a basis for the assessment of priorities for conservation of this floristically very important habitat.

The cyanobacterium Cylindrospermopsis raciborskii (Woloszynska) Seenaya et Subba Raju is a toxic, invasive, originally tropical to subtropical species, which has spread in many freshwater ecosystems of temperate regions. The aim of this study was to determine the vertical distribution and morphological changes of C. raciborskii in summer of 2011 in Lake Sakadaš (Kopački rit Nature Park). Samples were collected at the surface and at every meter depth to the lake bottom. At the beginning of the development (in August), the presence of only one morphological form (primary filament) of C. raciborskii was recorded (1.21 x 106 ind./L). In September, the massive development of this species was found (27.81 x 106 ind./L). Together with the primary filament, there were six other morphological forms of secondary filament. The morphological forms differentiated according to t he size (length and width) of filament as well as akinete size. Trichomes with one heterocyte were the most represented secondary filaments in the whole water column. Their presence was between 59.01% (in the bottom layer) to 84.85% (in the surface layer) of the total number of C. raciborskii individuals. Continuous monitoring of this invasive species will contribute to spread control and promote water protection measures and biodiversity of Kopački Rit floodplain, as well as other freshwater ecosystems of central and southern Europe.

Travnjačka površina na mjesnom groblju u Bilju (Baranja, sjeveroistočna Hrvatska) među malobrojnim je preostalim suhim stepolikim travnjacima sveze Festucion vallesiacae u Hrvatskoj. Biljska je stepa odlukom Skupštine Osječko-baranjske županije zaštićena u kategoriji Spomenik prirode od 2001. godine. Prema Uredbi o ekološkoj mreži, uvrštena je u Popis područja očuvanja značajnih za vrste i stanišne tipove s oznakom HR2000728 te predstavlja sastavni dio ekološke mreže Republike Hrvatske, odnosno Europske unije NATURA 2000. Flora stepolikog travnjaka istraživana je u proljeće 2015. Ukupno je utvrđeno 109 biljnih svojti iz 35 porodica među kojima su Poaceae (11, 0 %), Fabaceae (9, 2 %), Asteraceae (7, 3 %), Caryophyllaceae (7, 3 %), Lamiaceae (5, 5 %) i Rosaceae (5, 5 %) imale najveći udio broja svojti. Prema analizi životnih oblika utvrđen je najveći udjel hemikriptofita (59, 6 %) ; slijede terofiti (22, 0 %) i geofiti (13, 8 %), dok su prema horološkoj analizi najbrojnije biljke euroazijskog flornog elementa (32, 1 %) i široko rasprostranjene biljne svojte (24, 8 %). U Crvenu knjigu vaskularne flore Hrvatske uvršteno je 7 vrsta, od kojih su tri u kategoriji kritično ugrožene (CR), jedna je osjetljiva (VU), dok su tri gotovo ugrožene (NT). Veliki broj zabileženih vrsta te prisutnost rijetkih i ugroženih vrsta hrvatske flore na ovom površinom malom području od svega 0, 64 ha, ukazuju da je stepolika livada u Bilju jedinstveno stanište koje je važno očuvati.

This report aimed at presenting the almost half century long investigations on phytoplankton species richness and dynamics of the most important taxa in the floodplain Lake Sakadaš, a part of the Kopački Rit Nature Park. According to the revised and updated data on taxonomic composition, a complete list of phytoplankton taxa in the lake summarized a total of 685 taxa belonging to 233 genera, among which, chlorophytes and diatoms were the most diversified groups. The appearance of the most abundant taxa shows certain regularity, indicating the seasonal periodicity of phytoplankton communities. Chlorophytes occur during all seasons, with higher abundance in late spring and summer communities. Beside regular seasonal development in colder water periods, overdomination of diatoms is connected with strong mixing events during the floodings. Cyanobacterial blooms, formed by different filamentous species regularly appear in summer, depending on the timing and magnitude of flooding. Anthropogenically derived pollution in the past, eutrophication as well as the extreme hydrological events which became more frequent in this part of the Danube Basin showed significant influence on lake phytoplankton community structure. Long-term studies have also resulted in several findings of alien and potentially invasive phytoplankton species, whose occurrence and spreading is continuously monitored. Investigating the diversity and ecological dynamics of phytoplankton in a long time period is very important as it provides a framework for the evaluation and monitoring of ecological status of riverine floodplains according to requirements of the European Water Framework Directive and is crucial in designing measures for floodplain conservation.

The cyanobacterium Cylindrospermopsis raciborskii (Woloszynska) Seenaya et Subba Raju is an invasive toxic, originally tropical to subtropical species, which is nowadays widely distributed in freshwaters of temperate regions. The occurrence of C. raciborskii blooming was detected occasionally in the Kopački Rit floodplain. The aim of this study was to determine the influence of environmental factors on the growth and development of C. raciborskii, with special emphasis on the development of different morphological forms and their vertical distribution in the water column. The research was conducted during the summer period of 2003, 2007, 2008 and 2011 in Lake Sakadaš (Kopački Rit Nature Park). The abundance of C. raciborskii filaments was always higher in the upper layers as compared to the deeper layers of the water column. At the beginning of the development, the presence of only one morphological form (primary filament) of C. raciborskii was recorded. At the later stage, besides primary filaments, six morphological forms of secondary filaments were found. The morphological forms differentiated according to filament length and width as well as akinete size. According to the redundancy analysis, high water temperature and high concentration of nutrients were the most important environmental factors that influenced the development and vertical distribution of C. raciborskii. Continuous monitoring of Kopački Rit waters is essential to track the spreading of this species in the Danube region.

Current efforts to yield an appropriate method that would simplify the use of phytoplankton in the ecological evaluation of freshwaters resulted in different approaches based on clustering phytoplankton organisms. In this study, we applied the morphology-based functional group (MBFG) concept to determine the spatial changes of phytoplankton in the natural riverine floodplain of the alluvial reaches of the Danube River along the horizontal gradient from the river towards the floodplain habitats. The obtained results showed that the magnitude of environmental changes depended on alternations in hydrological variables (hydropattern, water level) that influenced changes in the physical and chemical conditions. High intensity flood pulses caused environmental homogenizations and nitrate enrichment of the floodplain habitats. Phytoplankton dynamics were strongly associated with the environmental changes and using the MBFG approach two basic hydrological conditions were identified: inundation phase dominated by diatoms (GVI) and isolation phase dominated by filamentous cyanobacteria (GIII). Total diatom biomass decreased along the floodplain gradient with a diminishing of physical constraints and site- specific variables became more important in favouring diatom assemblages. The different response of cyanobacterial species to mixing regime was of particular significance for species successions during bloom period. Altogether, classifying very diverse diatoms (centrics and pennates, planktonic and benthic) and cyanobacterial taxa into single groups represents a weakness of the MBFG approach, which might make impossible to reflect all the ecological differences governed by environmental constraints along river-floodplain gradients.

The traditional taxonomic approach is today being supplemented by ecological classifications of phytoplankton following the concepts of functional groups (FG), morpho-functional groups (MFG), and morphology-based functional groups (MBFG). In this study, we compared the potential of all three concepts in the evaluations of phytoplankton changes in the Danube River (rkm 1 388). Redundancy analysis revealed that a higher percentage of variance is explained by using ecological classifications than by using the taxonomic approach. Diatoms were the most abundant representatives. Applying the MBFG classification, whereas all diatoms were sorted into a single group (G6), only the changes of total diatom abundance can be followed. According to the FG classification, diatoms were distributed into seven groups, among which the dominant codons were C, D, and TB, while the MFG classification separated diatoms into five groups. Different temperature requirements and sensitivity to flushing were found to be the key driving factors for the successions of dominant species within small centrics, sorted into only one group. The need for phytoplankton species integration according to their capability to cope with the specific river environments still persists and further investigations, focused on the changes of phytoplankton along the Danube River, would aid the improvement of the phytoplankton classification schemes.

Istraživanje razvoja fitoplanktonskih zajednica u rijeci Bosut provedeno je u razdoblju od veljače do srpnja 2013. godine na dvama lokalitetima koji su smješteni prije i poslije grada Vinkovaca. Praćeni su utjecaji promjena fizikalno-kemijskih čimbenika na kvantitativni sastav fitoplanktona. Visoke koncentracije nitrata i ukupnog dušika u vodi bile su u vrijeme nižih vodostaja dok je povišenjem vodostaja došlo do velikoga porasta koncentracija ortofosfata i ukupnoga fosfora. U strukturi fitoplanktonskih zajednica najbrojnije su bile zelene alge (funkcionalnih skupina J, X1 i X2) i dijatomeje reda Centrales i Pennales (funkcionalnih skupina D, P i TB), dok su cijanobakterije bile povremeno dobro zastupljene. Takav sastav fitoplanktonskih zajednica karakterističan je za sporotekuće dionice nizinskih rijeka. Međutim, pojava masovnog razvoja miksotrofne vrste Ochromonas sp. u svibnju i lipnju, posljedica je izuzetno velikoga opterećenja vode suspendiranim tvarima što ukazuje na zagađenje vodotoka. Na temelju svih dobivenih rezultata procijenjeno je „umjereno“ ekološko stanje rijeke Bosuta. Kontinuirani monitoring bioloških pokazatelja ekološkog stanja preduvjet je za definiranje mjera zaštite i revitalizacije rijeke Bosuta.

Obraštajne zajednice imaju važnu ulogu u vodenim ekosustavima jer pridonose većoj primarnoj produkciji, kruženju hranjivih tvari, fiksaciji ugljika te su dobri pokazatelji ekološkog stanja voda. Poplavno područje Kopačkog rita je izrazito pogodno za razvoj obraštajnih zajednica zbog dostupnosti različitih prirodnih podloga (plutajuća i submerzna vegetacija, srušena stabla, otpale grane) i visokih koncentracija hranjivih tvari. Promjene kvalitativnog i kvantitativnog sastava biljnih i životinjskih zajednica u obraštaju te utjecaj fizikalno-kemijskih čimbenika na razvoj obraštaja istražuju se na prirodnim i umjetnim podlogama na području Kopačkog rita već duži niz godina. Dobiveni rezultati ukazuju na veliku bioraznolikost obraštajnih zajednica. Rast obraštaja započinje akumuliranjem otopljene organske tvari te naseljavanjem bakterija i alga, a dalje se obraštaj razvija naseljavanjem i razmnožavanjem različitih vrsta. Sastav alga u obraštaju mijenja se ovisno o sezonskim uvjetima. Tijekom proljeća i zime u obraštaju dominiraju dijatomeje, a u ljeto i jesen su uz dijatomeje vrlo dobro razvijene cijanobakterije i zelene alge. Najprije se naseljavaju alge koje čvrsto priliježu uz podlogu, a potom se razvijaju alge koje se za podlogu prihvaćaju kraćim ili dužim stapkama te nitaste alge. Tako se stvara trodimenzionalna struktura obraštaja u kojoj zaklon i hranu pronalaze različiti heterotrofni organizmi (npr. Porifera, Nematoda, Oligochaeta, Cladocera, Dreissena polymorpha, ličinke Chironomidae, Bryozoa), dok cjelokupna obraštajna zajednica predstavlja važan izvor hrane za brojne vrste riba. Povećanje obraštajnih zajednica dovodi do nedostatka prostora na podlogama i velike kompeticije za hranom i svjetlosti, uslijed čega se biomasa obraštaja smanjuje. Različiti fizički, kemijski i biološki čimbenici kao što su intenzivna ispaša, zasjenjenje i mehanička oštećenja mogu negativno utjecati na razvoj obraštaja. U uvjetima disturbancije biodiverzitet zajednica se smanjuje, ali s prestankom negativnog djelovanja, obraštajne zajednice se vrlo brzo obnavljaju. Autotrofna komponenta obraštajnih zajednica, u odnosu na fitoplankton, sporije odgovara na promjene uvjetovane plavljenjem i zbog toga je obraštaj izuzetno važan za trofičku stabilnost voda poplavnog područja. Nužno je nastaviti sustavna istraživanja obraštaja u svrhu praćenja promjena ekološkog stanja voda na području Kopačkog rita.

Floodplains are extremely dynamic environments in which the flood pulse is the most important environmental parameter, causing rapid change in phytoplankton composition. The aim of study was to investigate the effectiveness of different ecological classifications versus taxonomic approach in description of phytoplankton changes in a river-floodplain system. The study was conducted at Kopački Rit Nature Park (Croatia), one of the largest conserved floodplain areas of the Danube River. During eight years of investigation (2003 to 2010), extreme hydrological events significantly influenced the environmental variables of the floodplain as well as phytoplankton abundance and successional pattern. A high number of phytoplankton species (271 taxa) was found and assigned to 23 functional, 26 morpho-functional and 7 morphology-based functional groups. Redundancy analysis revealed that using ecological classifications yields a higher percentage of variance explained (axes 1 and 2 from 78.5% to 91.3%) than that by the taxonomic approach (69.4% of the variance). Furthermore, the redundancy analysis showed a clear distinction between river and lake samples. The intensity and duration of flooding was the primary cause for the separation of samples during the years. Results indicate that ecological classifications constitute a comprehensive approach to assess the flood-induced changes of phytoplankton assemblages, although the lack of sensitivity for different functional properties of dominant small centric diatoms in the river phytoplankton seems to present certain disadvantages. Altogether, it seems that there is need for certain minor integrations and arrangements of species in current ecological classifications. Flexibility in species grouping according to the specific characteristics of each individual freshwater system, along with the simultaneous application of a taxonomic approach, would aid the development of morpho-functional schemes.

The changes in composition and abundance of phytoplankton and periphytic algae during the successions of dry and flood phases were investigated in a eutrophic, Danubian floodplain lake during the summer-autumn period. The in-lake conditions (high nutrient concentration, high water temperature) during the dry phase in summer, stimulated an increase of phytoplankton abundance and supported cyanobacterial bloom development. An extremely high flood pulse altered the physical and chemical environment of the lake. Consequently, phytoplankton abundance was low with dominance of species characteristic for a mixed environment. Contrary to phytoplankton, abundance of periphytic algae reached the peak value in the conditions of flooding with the predominance of diatoms with low to medium resistance to physical disturbance. Periphytic algal abundance was reduced during the dry phase in the conditions of high grazing pressure. The rapid increase in abundance of prostrate diatoms indicated the periphyton recovery. Altogether, flooding dynamic appeared as the most influential cause of dominance and abundance changes of phytoplankton. In the same time, periphytic algae were found to benefit from the environmental changes caused by flooding. Further investigations are necessary to elucidate a variety of factors important in controlling periphytic algal development in complex and dynamic ecosystems like temperate floodplains.

River-floodplain systems are characterized by a high level of habitat heterogeneity where the hydrological connection with the river has been recognized as the most important environmental parameter. The aim of the present research is to analyze phytoplankton spatial distribution in the different types of aquatic habitats (eupotamal, parapotamal and paleopotamal) in Kopački Rit Nature Park in relation to the hydrological connection with the river (Danube). The study included five floodplain habitats with their different location in the lateral direction: Danube - Channel Hulovo - Lake Kopačko - Channel Čonakut - Lake Sakadaš. Phytoplankton biomass was calculated from the number and volume of phytoplankton individuals and expressed as mg/L fresh mass. During the hydrological connectivity diatoms comprised the largest contribution to the total phytoplankton biomass in all studied sites. According to the redundancy analysis, the development of diatoms is associated with higher water depth, transparency and concentration of nutrients. Relative biomass of diatoms decreased with the distance of the floodplain sites from the river. The highest contribution of diatoms to the total biomass was found in the Danube (up to 96.6%) and Channel Hulovo (up to 82.9%), while in the other sites (Lake Kopačko, Channel Čonakut and Lake Sakadaš) their contribution was up to 51.8%. Besides different diatom species, other groups such as cryptophytes and colonial phytomonads which were well represented during the flood period appeared to indicate altered conditions in the floodplain driven by flooding. During the isolation period, different species of Cyanobacteria were dominant followed by chlorococcal green algae. In that time, high values of total phytoplankton biomass in the floodplain sites were found (up to 185.5 mg/L), with high contribution of Cyanobacterial species (up to 92.9%). In the Danube, diatoms remained dominant species exhibiting a different pattern of species succession. According to the redundancy analysis, the development of phytoplankton during the hydrological isolation was associated with a higher water temperature, lower water depth and transparency. Altogether, the location of the floodplain sites in relation to the river and hydrological connectivity between the river and its floodplain significantly influenced the phytoplankton community structure and the overall ecological condition of floodplain microlocalities.

Kopački Rit Nature Park is one of the largest preserved natural floodplains of the Middle Danube stretch. This internationally important wetland provides a diversity of water and wet biotopes continuously changing depending on the inflow of river water. The first complete checklist of its phytoplankton flora listing 303 species, 45 varieties and 14 forms was compiled by Dragica Gucunski (1973) whose results encouraged future research on the Kopački Rit phytoplankton and gave large contribution to the development of algology in Croatia. The investigations of phytoplankton community structure and ecology have been conducted continuously for several decades in order to define the ecological state and changes in this complex river-floodplain system. So far, more than 600 phytoplankton taxa have been listed. In general, the seasonal phytoplankton succession pattern is characterised by diatoms in early spring, late autumn and winter, Chrysophyceae later in the spring and autumn, “clear-water phase” and dominance of Cryptophyceae in May, as well as the development of chlorococcal green algae and Cyanobacteria in summer. It is interesting to note the appearance of a “red tide” caused by massive development of Peridinium species in the autumn of 1999. Invasive species Cylindrospermopsis raciborskii (Wol.) Subba Raju, a tropical element in temperate waters, was detected in the summer of 2003. Since then, massive blooms have occurred periodically. Changes in phytoplankton communities depend mostly on flooding dynamics and recent investigations showed dual impact of flooding on phytoplankton development. The stimulative effect in spring is seen through nutrient enrichment, while later in the summer flooding acts as a disturbance causing water column mixing, nutrient dilution and washout effect. Current research is focused on phytoplankton classifications based on species morphological and functional traits using different classification systems. Results show that the flood phase in the river-floodplain system is characterised by diatoms and chlorococcal green algae from different functional and morpho-functional groups characteristic for turbid and well-mixed waters, while large amount of nutrients and hydrological stability enabled the domination of Cyanobacteria. Extreme hydrological events such as long-term dry periods or extreme floods which are more frequent in this part of the Danube, result in the changes of phytoplankton abundance and community structure from “turbid state” to a “clear state” showing the possible consequences of global climatic changes.

Temporal variations in periphytic algal communities were studied in Lake Sakadaš, a part of a Danubian floodplain known as Kopački Rit Nature Park. An in situ investigation was performed using artificial substrata (glass slides) exposed in the lake in two study series, spring and summer, and incubated until the winter 2010. Due to the extremely high and long-lasting spring-summer flooding, the physical and chemical environment significantly varied, and metaphyton and macrophytes were spread along the lake. Based on the non-metric multidimensional scaling, three phases were identified in the periphytic algal development. The initial accrual phase, in both spring and summer series, was characterized by the continuous increase in periphyton biomass (dry weight, organic weight, and ash-weigh), chlorophyll concentrations, and algal abundance. Diatom successions from low-profile species (Stephanodiscus) to the stalk-forming species (Gomphonema, Encyonema) with a tendency towards vertical overgrowth characterized periphyton communities in spring. Rapid development of filamentous green algae (Oedogonium sp.) characterized periphyton accrual in summer. Huge stands of metaphyton and macrophytes acted as a disturbance to periphytic algal accrual. Shading and mechanical injuries together with high grazing pressure led to a periphyton loss phases. Resetting of the algal community to an earlier stage of development, with diatoms firmly attached to the substrata (e.g. Epithemia, Cocconeis) shows periphyton response to disturbance. The cessation of hydrological perturbations created an opportunity for periphyton development and the rapid accrual of algal communities occurred in autumn. In conclusion, the complexity of environmental changes caused by extreme flooding can significantly influence development of periphytic algal communities in a temperate floodplain. Further investigations are necessary to elucidate very complex interactions between periphyton and other aquatic biocenoses in river-floodplain systems.

Dreissena polymorpha (Pallas, 1771) (Bivalvia), školjkaš Ponto-kaspijske regije, još od 19. st. uspješno se širi vodama Europe, pa tako i Hrvatske. Vrsta je vrlo uspješna u širenju areala i razvijanju stabilnih zajednica, posebno na različitim tipovima čvrstih podloga. Jedan od ciljeva naših dugogodišnjih istraživanja flore i faune voda Parka prirode Kopački rit, bio je utvrđivanje prisutnosti i praćenje stanja invazivnih vrsta. D. polymorpha je pronađena u sedimentu te u obraštaju na makrofitama i srušenim stablima. Iako u bentosu i fitofilnim zajednicama nije činila veći udio u pronađenoj fauni, utvrđena je u velikom broju na umjetnim podlogama (stakalca) uronjenim u vodu s ciljem praćenja dinamike naseljavanja i razvoja obraštaja. Ovaj školjkaš je uspješan kompetitor, hrani se procjeđivanjem, i ima velik utjecaj na alge i cijanobakterije u stupcu vode, kao i na autotrofnu komponentu obraštaja. S obzirom na važnost obraštajnih zajednica kao izvora kisika, hrane te skloništa vodenim beskralježnjacima, ključno je proučiti međusobne odnose pojedinih komponenti obraštaja. Istraživanjima u 2008. godini, utvrđen je utjecaj prekomjerno razvijene zajednice Dreissene na razvoj stabilne zajednice i prirodnu sukcesiju autotrofne komponente obraštaja te razvoj vrsta otpornih na disturbancije. Temperatura vode, dostupnost hrane te hidrološke promjene prepoznati su kao značajni čimbenici za razvoj zajednice ovog školjkaša. Praćenje prisutnosti i brojnosti populacija školjkaša D. polymorpha kao potencijalne invazivne vrste na ovim prostorima, važno je radi sprječavanja njenog mogućeg prekomjernog razvoja koji bi mogao imati negativan utjecaj na očuvanje ravnoteže i biološke raznolikosti ritskog ekosustava.

The colonization of periphytic algae was studied in a shallow floodplain lake situated in the area of the Kopački Rit Nature Park (Croatia), one of the largest conserved floodplains of the Danube River. An in situ experiment was done in the summer (July-August) of 2010 using artificial substrata (glass slides vertically oriented and placed 20 cm below the water surface), in order to examine the short-time changes in algal community composition during the early phase of periphyton formation. The experiment was started at the end of the flood pulse which began in June. A long-lasting high flood pulse began at the end of July and lasted till the end of the experiment. PCA analysis showed significant changes of the physical and chemical water parameters as a consequence of the inflow of Danube floodwater. The BIOENV sub module showed a maximum correlation between environmental factors and algal species abundance data of 0.592, with water depth (6.51 - 8.66 m), nitrite (0.004 - 0.02 mgl-1), total nitrogen (0.67 - 5.81 mg l-1) and Danube water level (2.12 - 5.26 m) being the factors that mostly influenced algal species composition and abundance at all samplings. The periphyton formation was initiated on the first day of deployment due to the rapid formation of bacterial biofilm. Altogether, 214 algal taxa were identified during the investigated period. The number of algal taxa continuously increased from 38 taxa on the first day of colonization to 134 taxa on day 27. A stable algal community was achieved on day 18, as shown by the MacArthur-Wilson equilibrium model. According to the cluster and NMDS analysis based on qualitative composition and abundance of periphytic algal assemblages, the following sequences of periphyton colonization can be defined: the initial colonization (days 1-3), the intermediate phase (days 6-15) and the late phase (days 18-42). Initial colonization was characterized by species in polysaccharide matrix, Aphanocapsa delicatissima W. West et G. S. West and Asterococus superubs (Cienk.) Scherff. being attached directly to the substrata. The small stalk- forming, Characiopsis acuta (A.Br.) Borzi and a large filamentous green alga Cladophora glomerata (L.) Kütz., C-selected species, were significant during the intermediate phase in the conditions of stable, nutrient rich habitat. Oedogonium sp., an upright filamentous green taxa with heterotrichous holdfast cells, offered an additional substratum for small Characium as well as for Gomphonema species during the late phase of periphyton colonization in the conditions of flooding. In such an unstable habitat, the dominant diatom species was G. parvulum (Kütz.) Kütz., known as R-selected species with a high resistance to removal. In spite of the fact that the cohesive filaments of Oedogonium sp. can protect the periphyton communities from the total removal during the flooding, the significant decrease of algal abundance and total periphyton biomass was established on day 36. Intensive development of metaphyton and macrophyte vegetation in the conditions of long-lasting flood caused mechanical injuries of periphyton. Subsequently, in periphyton which had lost a considerable amount of its biomass, the dominant diatom species was Achnanthidium minutissimum (Kütz.) Czar, an early colonist of denuded habitats, indicating on recolonization process. According to all given results it is evident that the flooding caused environmental disturbance which can significantly influence the periphyton colonization.

Riverine wetlands are key territories for the conservation of biodiversity on a river basin scale. The analysis of available data can offer valuable information underlining the importance of recent investigations for the researches in the field of wetlands biodiversity. Data collected for five vertebrate groups (fish, amphibians, reptiles, birds and mammals) in eight chosen riverine wetlands distributed in five countries of the Upper, Middle and Lower Danube were submitted to comparative analyses. The main components and cluster analyses of the data calculated for basic environmental parameters and the species composition of fish, reptile and birds fauna, presents visible differences between functioning floodplain wetlands well connected with the river and those with lacking connection to the river. The calculated mean values of similarity between the wetlands present for some vertebrate groups - with exception of fish and reptiles - significant differences. From all the environmental factors considered the connectivity with the main river is the key factor, correlated statistically significant with the variability of species number of two vertebrate groups, fish and reptiles (Pisces, Reptilia).

Colonization processes of periphytic algae in the endangered and very complex river-floodplain systems of large European rivers have not yet been fully investigated. During the period April -August 2008, colonization of algae on glass slides (vertically oriented and placed 25 cm below the water surface) was investigated in Lake Sakadaš, a permanent water body within the Kopački Rit Nature Park, one of the biggest preserved Danubian floodplains. During the investigated period, different hydrological conditions altered the values of physical and chemical parameters of lake water: depth (6, 50 - 8, 30 m), transparency (0, 72 - 3, 20 m), total nitrogen (0, 10 - 3, 70 mg/L) and total phosphorus (0, 04 - 0, 33 mg/L). Total periphyton biomass (dry weight, organic weight) continuously increased during the investigated period, particularly from July when the invasive species Dreissena polymorpha (Pallas, 1771) comprised the largest portion of total periphyton biomass. Based on autotrophic index, periphyton communities were characterized as autotrophic at the beginning of the colonization, while heterotrophic communities prevailed from July till the end of the experiment. A total of 199 algal taxa were detected in periphytic communities, varied from 55 taxa during the first week to 94 taxa in the thirteenth week of colonization. The Simpson's diversity index values show that the beginning of colonization was characterized by higher diversity due to the colonization of new species, while from the seventh week, gradual domination of several algal species within the periphytic community has been detected. Cyanobacteria comprised the 90% of the total abundance during the first week with well developed species belonging to the genera Phormidium, Aphanocapsa and Gloeocapsa. From the second week till the end of the investigated period various diatom species prevailed. Firstly, the periphyton was dominated by the species of higher biovolume (genera Fragilaria, Melosira, Gomphonema) while in the later phase the species of smaller biovolume (genera Achnanthes, Cymbella, Amphora, Navicula) dominated. Algal abundance reached maximum value(614 x 103individuals/cm2) during the sixth week of exposition. Stabilization of the periphytic community in the seventh week of colonization, indicate the possible influence of the flood dynamics on the colonization processes.

Kopački Rit is one of the largest preserved natural wetlands in Europe. Scientific investigations of this ecologically particularly valuable ecosystem began already at the end of the 19th century and have been especially intensive in the last decades. Hundreds of scientific articles published up to the present time exhibit only a part of the biological diversity – more than 1000 plant and around 2000 animal species. Among them there are hundreds of rare and endangered species on national and global level. Contemporary research deals with the influence of floods on the species and the ecosystem as a whole with a particular emphasis on the impacts of antropogenic pressure and climatic changes. In order to preserve floodplain ecosystem in natural conditions sustainable management must be defined on the scientific basis.

Biodiversity, management and protection of wetlands (more than 30 wetlands sites) along the River Danube from the Upper Section (Austria) till the Danube Delta (Romania) were analyzed in the frame of the international project BIOWETMAN. The results of the comparative study of phytoplankton showed that phytoplankton biodiversity and seasonal successions varied significantly due to the wetland type. Under highly changeable and unstable conditions in the temporary wetlands (e.g. Murtvo Blato, Pischene, Dyulova bara) which are heavily overgrown with aquatic and swamp vegetation, low phytoplankton biodiversity and biomass were established. Phytoplankton seasonal sequences in the side-arms (e.g. Regelsbrunn) are basically similar to those found in most large rivers with temperate hydrological regimes: year-round predominance of diatoms, blooming in spring and autumn, and a mixed population of Chlorophyceae and diatoms during summer. Phytoplankton development in floodplain lakes (e.g. Sakadaš, Srebarna, Gorgostel, Erenciuc and Rosu) depends on the influence of riverine water. Bacillariophyceae dominance occurs during the open hydrological connection with the main river channel, while a long-lasting Cyanoprokaryota bloom characterize summer and early autumn conditions of the hydrological isolation from the river. Results obtained by comparative research of the Danubian wetlands clearly show that phytoplankton dynamics in all investigated types of wetlands are hydrology-driven.

Researches of algae in freshwater ecosystems of Croatia have been conducted since the beginning of 20th century. However, only within the last decade they have been systematic ecological and biocenological researches. Based on the results of the research, qualitative compositions of phytoplankton, periphyton and phytobentos communities as well as their succession in many freshwater ecosystems in Croatia have been determined. Great abundance of species is characteristic of natural ecosystems whilst artificial lakes and reservoirs are quantitatively poorer. The role of algae in transformation of energy during the primary production process has been determined as well – it is greatest in summer and lower in parts of ecosystem burdened by large quantities of organic sediment. Primary production of plankton in fish pond ecosystems has been stimulates by addition of nutrients, and continuous research of feeding relations in phytoplankton-zooplankton-fish chain has been made. Accelerated eutrophication has been noted as a consequence of anthropogenic influences in natural ecosystems (NP Plitvice Lakes and Special Zoological Reserve Kopački rit). Qualitative and quantitative compositions of algae, especially indicators of certain degrees of saprobity, have regularly been monitored through saprobiological analyses. A lower degree of saprobity has been determined for most water resources of Croatia, while eutrophic lakes, fish ponds and rivers at points of direct pollution influence have higher degree of saprobity. Significant role of algae in the process of travertine growth has been proven as well. Mucopolysaccharide excretions of periphyton bind calcite crystals and initialize the process of travertine growth. The results of previous research point out the primary role of algae in energetic and ecological stability of freshwater ecosystems in Croatia. Thus, further comprehensive, continuous and methodologically synchronous investigations are required in order to continuously protect Croatian freshwater ecosystems.

Floodplains are characterized by high biodiversity which is threatened mostly due to the increasing anthropogenic impacts (e.g. eutrophication, global warming). One of the threats is the appearance of invasive species which have a considerable influence on the autochthonous flora and fauna. In the last few years, appearance of four invasive species in Kopački Rit was reported. Potentially toxic tropical cyanobacterium Cylindrospermopsis raciborskii (Woloszynska) Seenayya et Subba Raju has been reported in Lake Sakadaš. It formed blooms during the summer months and reached its highest biomass in 2003 (91.41 mg/l). Invasive diatom Didymosphenia geminata (Lyngb.) M. Schmidt was detected in the phytoplankton of the Danube River (1388 r. km) during the extreme floods in 2006. Although formerly described as oligotrophic species preferring alpine freshwater habitats, it seems to be spreading, throughout European mesotrophic and euthrophic rivers. The other two invaders are Limnomysis benedeni (Czerniavsky, 1882) (Crustacea), recorded in 2004 within phytophylous communities in Lake Sakadaš, and Dreissena polymorpha (Pallas, 1771) (Bivalvia), found in phytophylous communities, sediment and covering natural and artificial substrates in the floodplain waters. D. polymorpha develops in large numbers and is a successful filter-feeding competitor. Spreading of invasive species in the area of Kopački Rit could have a negative impact on the preservation of its biodiversity.

In spite of the whole knowledge about cyanobacterial blooming in freshwater ecosystems, there are lots of unresolved questions concerning its appearance, especially in complex, dynamic ecosystems as Kopački Rit, one of the largest riverine wetlands in Europe. The main objective of the present study was to analyze the influence of flooding dynamics of the River Danube in the period from 2003 till 2007 on the development of Cyanobacteria in the fringing floodplain lake (Lake Sakadaš). During the investigated period, a total of 16 Cyanobacteria species were determined, among which 9 taxa achieved a biomass higher than 5% of total phytoplankton biomass. Cyanobacterial bloom was recorded in 2003, 2004 and 2007, only in the conditions of hydrological isolation of the lake from the income of riverine water. Different filamentous species from functional groups H1, S1 i SN were replaced during the Cyanobacteria bloom. Their contributions in total phytoplankton biomass reached up to more than 80% during the summer period. The highest biomass of Cyanobacteria species (245 mg/L) was recorded in August in extremely dry year 2003. In the conditions of extreme flooding (late spring and summer of 2005 and 2006), cyanobacterial blooming was absent and very low phytoplankton biomass was established (mean value less than 12 mg/L). All given results indicate that flooding could be qualified as a disturbance factor for the development of Cyanobacteria bloom in the investigated floodplain lake.

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Vertical distribution of species composition and abundance of phytoplankton in a shallow floodplain lake, Lake Sakadaš, (Nature Park Kopački Rit, Croatia) and in the Danube River (at 1388 r. km) were studied during the period March - November 2006, with emphasis on the diatom flora. Integrated phytoplankton samples were collected from the whole water column in the lake and in the Danube. In order to find out the vertical distribution, phytoplankton samples were collected every meter of the depth from the surface till the bottom of the lake. Quantitative analysis of phytoplankton was done according to the Utermöhl method. Data were analyzed using multidimensional statistic methods. Extremely high flooding during the whole spring and major floods in August characterized the hydrological conditions. Water depth of Lake Sakadaš varied between 4 – 8.25 m depending on the inflow of Danube water. The obtained results indicated that floodwater had altered the physical and chemical environment of the lake. The correlation of measured physico-chemical parameters between the Danube and the lake was high (r = 0.96, p < 0.01). The low mean phytoplankton abundances established in Lake Sakadaš (6.28x106 ind. l-1) as well as in the Danube (5.81x106 ind. l-1) with diatoms and chlorophytes numerically dominant, correspond with the extremely high flooding of the lake and high water discharge of the Danube. The total diatom biodiversity was higher in the Danube (99 species) than in Lake Sakadaš (83 species). Principal Component Analysis (PCA) showed that seven diatom species (Cyclotella radiosa, Epithemia turgida, Navicula menisculus, Nitzschia acicularis, N. heufleriana, N. vermicularis, N. sygmoidea) represent 35.29% of the variance described with PC1 axis which explained over 85% of the total variance in the species data. It is interesting to note that the invasive species Didymosphenia geminata was found in the River Danube almost in all samples. The highest abundance of diatoms was established in March and in November, both in the lake and in the Danube. According to Fuzzy Cluster Analysis (FCA), a similar distribution of phytoplankton in the water layers was established only in March, when diatoms represented from 74.54 – 92.31% of the total abundance. In all other months, vertical distributions of phytoplankton varied substantially with depth, and data series were optimally divided in 19 classes with fuzzy coefficient 0.21. The rank-abundance curve is best fitted by log-normal function (AIC=15577523 ; BIC=1557729) which indicates that influence of abiotic factors on phytoplankton abundance was equable during the investigation period.

The floodplains of the European rivers have almost all been altered by man and, as a result, natural floodplains are among the most threatened ecosystems in Europe. A notable exception to this is the area of Kopački Rit Nature Park which remained largely undisturbed. Kopački Rit, a Ramsar site (No.: 3HR002), is a fluvial floodplain along the Danube River (1410 - 1383 r. km), located in Northeast Croatia. It is one of the largest riverine wetlands in Europe, covering more then 23 km2. The environment of the area of overlap between land and water offers conditions for existence of a great diversity in numbers and kinds of species. A great diversity of plant (phytoplankton, vascular plants) and animal organisms (invertebrates, fishes, amphibians, reptiles, birds and mammals) is a proof of the ecological importance of Kopački Rit (more than 2000 species registrated till now). Many of those species are endangered in Europe and worldwide. There was a total lack of protection and management in the period 1991-1997 when the area of Kopački Rit was a war zone. Within GEF (Global Environmental Facility) Grant for Kopački Rit Wetlands Management Project investments in the nature protection were done to repair damaged infrastructure and to ensure sustainable management and provide long-term environmental protection of the area. The measures for protection of significant biodiversity of Nature Park Kopački Rit were analyzed, as key aspects of management and sustainable use of this highly threatened regional and global ecosystem.

Desetogodišnja (studeni 1997. – studeni 2007. godine) sustavna hidrobiološka istraživanja poplavnog područja Parka prirode Kopački rit obuhvatila su analize fizikalno-kemijskih svojstava vode te akvatičnih i bentoskih biocenoza vodenih mikrolokaliteta duž horizontalnog gradijenta poplavnog područja i Dunava. Analizama biocenoza utvrđen je sastav i dinamika bakterioplanktona, fitoplanktona, zooplanktona te faune beskralježnjaka sedimenta u uvjetima limnofaze (razdoblje izoliranosti poplavnog područja od matične rijeke) i potamofaze (razdoblje hidrološke povezanosti vodenih mikrolokaliteta s matičnom rijekom). Poseban osvrt bio je na utvrđivanju hranidbene kategorije faune oblića u sedimentu i makrofitskim zajednicama. Aktualnim istraživanjima analize su proširene na utvrđivanje sastava i dinamike naseljavanja obraštajnih zajednica (bakterijske, algalne i faunističke komponente) na umjetne podloge. Također se istražuju i veličinske kategorije makrofaune i meiofaune beskralježnjaka u sedimentu, te prisustvo invazivnih Ponto-kaspijskih vrsta. Rezultati provedenih istraživanja, objavljeni u brojnim znanstvenim i stručnim radovima te predstavljeni na mnogim međunarodnim konferencijama, temelj su za definiranje zaštite i upravljanja vodama Kopačkog rita u svrhu očuvanja tog izuzetno vrijednog ekološkog sustava.