Dubravka Špoljarić

Changes of phytoplankton functional groups in a floodplain lake associated with hydrological perturbations

During the past decade, basic hydrological conditions of a floodplain lake in the middle Danube section have been altered with long-lasting extremely high flooding. The objective of the paper is to show the effectiveness of the functional approach to explain phytoplankton changes associated with hydrological events. Intensity and duration of flooding were qualified as the primary cause for the changes of functional groups. Flooding phase was characterised by diatoms (B, C, D, P, TB) tolerant to water column mixing. Due to the dilution and washout effect their biomass was low during the long-lasting flooding despite their input from the river. Co-occurrence of coccoid green algae (X1, J, F) was associated with turbid and mixed waters. High-nutrient concentrations and water column stability during the long-term dry conditions led to the dominance and high biomass of cyanobacteria. Low-nitrogen H1 group was particularly sensitive to stress caused by flooding, while filamentous N2-fixing (SN) and non N2-fixing species (S1) showed tolerance to short-term flooding. The development of euglenoids and dinoflagellates (W1, W2, LO) was also associated with dry conditions and seasonal changes in autumn. The functional classification allows representing of the hydrological phases which characterise the phytoplankton succession in highly disturbed river-floodplain systems.

Endogenous 4-hydroxy-2-nonenal in microalga Chlorella kessleri acts as a bioactive indicator of pollution with common herbicides and growth regulating factor of hormesis.

Oxidative stress, i.e. excessive production of reactive oxygen species (ROS), leads to lipid peroxidation and to formation of reactive aldehydes (e.g. 4-hydroxy-2-nonenal; HNE), which act as second messengers of free radicals. It was previously shown that herbicides can induce ROS production in algal cells. In the current paper, the unicellular green microalga Chlorella kessleri was used to study the effect of two herbicides (S-metolachlor and terbuthylazine) and hydrogen peroxide (H(2)O(2)) on oxidative stress induction, HNE formation, chlorophyll content and the cell growth. Production of HNE was detected in this study for the first time in the cells of unicellular green algae using the antibody specific for the HNE-histidine adducts revealing the HNE-histidine adducts even in untreated, control C. kessleri. Exposure of algal cells to herbicides and H(2)O(2) increased the ROS production, modifying production of HNE. Namely, 4h upon treatment the levels of HNE-histidine conjugates were below controls. However, their amount increased afterwards. The increase of HNE levels in algae was followed by their increased growth rate, as was previously described for human carcinoma cells. Hence, changes in the cellular HNE content upon herbicide treatment inducing lipid oxidative stress and alterations in cellular growth rate of C. kessleri resemble adaptation of malignant cells to the HNE treatment. Therefore, as an addition to the standard toxicity tests, the evaluation of HNE-protein adducts in C. kessleri might indicate environmental pollution with lipid peroxidation-inducing herbicides. Finally, C. kessleri might be a convenient experimental model to further study cellular hormetic adaptation to oxidative stress-derived aldehydes.

Assessment of flood-induced changes of phytoplankton along a river–floodplain system using the morpho-functional approach

In this research, we aimed to find out how the differences in hydrological connectivity between the main river channel and adjacent floodplain influence the changes in phytoplankton community structure along a river–floodplain system. The research was performed in the River Danube floodplain (Croatian river section) in the period 2008–2009 characterised by different flooding pattern on an annual time scale. By utilising the morpho-functional approach and multivariate analyses, the flood-derived structural changes of phytoplankton were analysed. The lake stability during the isolation phase triggered the specific pattern of morpho-functional groups (MFG) which were characterised by cyanobacterial species achieving very high biomass. Adversely, the high water turbulence in the lake during the frequent and extreme flooding led to evident similarity between lake and river assemblages. Besides different diatom species (groups of small and large centrics and pennates), which are the most abundant representatives in the river phytoplankton, many other groups such as cryptophytes and colonial phytomonads appeared to indicate altered conditions in the floodplain driven by flooding. Having different functional properties, small centric diatom taxa sorted to only one MFG cannot clearly reflect environmental changes that are shown by the species-level pattern. Disadvantages in using the MFG approach highlight that it is still necessary to combine it with taxonomical approach in monitoring of phytoplankton in the river–floodplain ecosystems.

Heavy Metal-Induced Oxidative Stress in Plants: Response of the Antioxidative System

Heavy metals (HMs) are among the most important environmental pollutants, particularly in areas with strong anthropogenic pressure. For plants, high levels of HMs are extremely toxic since they may act in several different modes: by the direct inhibition of plant growth and biosynthetic pathways or through the production of reactive oxygen species (ROS). Certain metals generate ROS due to their involvement in redox reactions like Fenton and/or Haber–Weiss reactions, while metals without redox capacity enhance ROS production by reducing the antioxidant glutathione pool, activating calcium-dependent systems and influencing iron-mediated processes. ROS production affects lipids, proteins, and DNA and consequently leads to cell death. In response, plants are equipped with complex enzymatic and nonenzymatic mechanisms involved in antioxidative defense to neutralize HM toxicity, and the main components of these mechanisms will be reviewed in this chapter.

The importance of microphytic composition on coarse woody debris for nematode colonization: a case study in a fluvial floodplain environment

Abstract Coarse woody debris (CWD) are an important structural feature of many aquatic ecosystems. This study focused on the relationships between nematode colonization and microphytic community structure on CWD. In situ investigations were performed using white willow branches introduced into the floodplain lake, a part of the large natural floodplain in the middle section of the Danube River (Europe) impacted by strong sandy and silt accumulations. Our results showed that CWD support rapid colonization and high species richness of microphytes, regardless of seasonality and flood-induced environmental changes. Successional stages during the accrual of microphytic communities were expressed. Nematode functional feeding group compositions closely followed microphytic composition. The epistrate feeder Chromadorina bioculata over-dominated in diatom-dominated communities with adnate/prostrate and stalk-forming species in spring and autumn. The complex structure of cyanobacterial mats associated with green algae and diatom assemblages in summer attracted suction feeders, represented by the Dorylaimidae family. The obtained results indicated that nematodes are involved in strong trophic coupling with a microbial habitat on CWD. The retention of CWD in aquatic environments or addition of CWD to systems with little or no wood may have important implications for the primary and secondary production in these ecosystems.