Tatjana Simčič

Differences in tolerance to anthropogenic stress between invasive and native bivalves.

Tolerance towards environmental stress has been frequently considered as one of the key determinants of invasion success. However, empirical evidence supporting the assumption that invasive species can better endure unfavorable conditions compared with native species is limited and has yielded opposing results. In this study, we examined the tolerance to different stress conditions (thermal stress and trace metal zinc pollution stress) in two phylogenetically related and functionally similar freshwater bivalve species, the native Anodonta anatina and the invasive Sinanodonta woodiana. We assessed potential differences in response to stress conditions using several cellular response assays: efficiency of the multixenobiotic resistance mechanism, respiration estimate (INT reduction capacity), and enzymatic biomarkers. Our results demonstrated that the invasive species overall coped much better with unfavorable conditions. The higher tolerance of S. woodiana was evident from (i) significantly decreased Rhodamine B accumulation indicating more efficient multixenobiotic resistance mechanism; (ii) significantly higher INT reduction capacity and (iii) less pronounced alterations in the activity of stress-related enzymes (glutathione-S-transferase, catalase) and of a neurotoxicity biomarker (cholinesterase) in the majority of treatment conditions in both stress trials. Higher tolerance to thermal extremes may provide physiological benefit for further invasion success of S. woodiana in European freshwaters, especially in the context of climate change.

The role of river flow dynamics and food availability in structuring hyporheic microcrustacean assemblages: a reach scale study

The influence of river flow dynamics on the functioning and structure of microcrustacean assemblages (Copepoda, Cladocera, Ostracoda) in the shallow (SHz) and deep (DHz) hyporheic zone were studied in a Sava River (Slovenia) gravel bar over a 3 year period. Temperature, conductivity, dissolved oxygen concentrations, po- tential food resources (nitrates, dissolved organic carbon - DOC, particulate organic matter - POM, and electron transport system activity of biofilm - ETSA) were measured in the deep hyporheic zone (DHz, 210 - 240 cm, n = 39) on six sampling occasions (2007- 2010) and in the shallow hyporheic zone (SHz, 30 - 200 cm, n = 10) during the first two sampling dates. Microcrustaceans were collected using the Bou-Rouch pumping method. The physical and chemical properties of the deep hyporheic water, such as conductivity, pH, SO4 and POM varied significantly over time and distance from the river. Less variability was observed in ETSA. Altogether 28 microcrustacean species were recorded within the two distinct habitat types (SHz and DHz). In the latter, mainly stygobiotic species oc- curred, with Acanthocyclops venustus (Norman and T. Scott, 1906) being the most frequent and abundant. During periods of low flow, patchiness of physical and chemical properties and microcrustacean assemblages increased in comparison to periods of moderate or high flow. Similarly, the patchiness was high after severe flooding with extensive sediment movements and increased clogging of interstitial spaces by fine sediments. Fine sediments and nitrates had the strongest influence on assemblage composition. The study demonstrated a strong connection between river flow dynamics, hyporheic processes and distribution of microcrustaceans, spatially and temporally .

Aquatic Macroinvertebrates of the Sava River

The objective of this chapter is to present the data on aquatic macroinvertebrate communities along the Sava River, based on investigation performed during 2011 and 2012 at 12 sampling sites within the sector between Vrhovo (Slovenia) and Belgrade (confluence to the Danube). During our study 227 macroinvertebrate taxa were recorded in the Sava River. Having in mind that upper stretch of the Sava River was not covered by this work (alpine and subalpine stretch), as well as based on the review of previous works on the macroinvertebrate fauna of the Sava River, more than 300 species will be confirmed for the Sava River. The data on the distribution of aquatic macroinvertebrates revealed five different stretches—alpine, subalpine, Upper Sava plain, Middle Sava and Lower Sava. Physical habitat degradation, pollution and pressure caused by biological invasions were found to be the main factors of endangerment of aquatic macroinvertebrate fauna diversity. There is an obvious need for further investigation of the Sava River in order to complete the data on aquatic macroinvertebrates and to provide the basis for accurate assessment of environmental status of the river.

Spatiotemporal heterogeneity of actual and potential respiration in two contrasting floodplains

Floodplains are vital components of river ecosystems and play an important role in carbon cycling and storage at catchment and global scales. For efficient river management and conservation, it is critical to understand the functional role of spatiotemporally complex and dynamic habitat mosaics of river floodplains. Unfortunately, the fundamental understanding of mineralization and carbon flux patterns across complex floodplains is still fragmentary. In this study, respiratory potential (i.e., electron transport system activity – ETSA) was quantified seasonally across different aquatic and terrestrial habitats (wetted channels, gravel bars, islands, riparian forests and grasslands) of two Alpine floodplains differing in climate, altitude, discharge, flow alteration intensity and land use (Soca – natural flow regime, 12% grassland area; Urbach – mean annual discharge reduction by 30% due to water abstraction, 69% grassland area). In situ respiration (R) was measured and ETSA/R ratios calculated to examine differences in exploitation intensity of the overall respiratory capacity among floodplain habitats and seasons. ETSA and R provided potential and actual estimates, respectively, of organic matter mineralization in the different floodplain habitats. Hierarchical linear regression across habitat types showed organic matter, grain sizes 8 mm were also highly important for the Soca floodplain. The combination of ETSA and R measurements conducted in contrasting floodplains increased our understanding of the relationships between floodplain habitat heterogeneity, organic matter mineralization and human impacts; i.e., structural-functional linkages in floodplains. These data are integral towards predicting changes in floodplain function in response to environmental alterations from increasing human pressures and environmental change.