Nataša Mori

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 .

Intensity of mineralization in the hyporheic zone of the prealpine river Baca (West Slovenia)

Respiratory electron transport system (ETS) activity and oxygen consumption in the interstitial water, and in the fine (i.e. silt) and coarse (sand) sediment fractions from the hyporheic zone of the prealpine river Bača (W Slovenia) have been measured in order to estimate the intensity of potential and actual carbon mineralization through microbial communities. Hyporheic samples from the river bed (RB) and gravel bars (GB) were compared. ETS activity and oxygen consumption of all fractions from the RB did not differ significantly from those from the GB. ETS activity and oxygen consumption of biofilm attached to 1 g of the silt were higher than of that attached to the same mass of the sand. A significant correlation between ETS activity and oxygen consumption indicated that the former should be a good indicator of intensity of bioactivity in hyporheic sediments. The ratio of ETS activity to oxygen consumption (ETS/R ratio) revealed that the oxygen consumption of microorganisms is responsible for approximately 60% of the metabolic potential in the hyporheic sediments. The contributions of different fractions of sediment to the total ETS activity differed between RB and GB. The contribution of microorganisms in the interstitial water and silt was higher in GB than in the RB, but the sand fraction contributed less to potential carbon loss in GB than in the RB. Average total respiratory carbon loss per volume through the hyporheic zone was higher in the RB than in GB. The main reasons suggested are the different intensity of exchange of surface water with the hyporheic zone, and the rate of consolidation of sediments, which is primarily a function of river hydrology and geomorphology.

Differences in aquatic microcrustacean assemblages between temporary and perennial springs of an alpine karstic aquifer

Microcrustacean (Copepoda, Ostracoda) assemblages were investigated at the interface of the vadose and phreatic zones in the alpine karstic aquifer from the Julian Alps in Slovenia (SE Europe). Two temporary and one perennial karstic outlets were sampled by filtering the water several times over 2 years. Concurrently, benthos from the mouth of a perennial spring and from an adjacent spring brook were collected. Altogether 24 microcrustacean species were recorded. The spatial and temporal variation in drift densities and species composition was high indicating complex groundwater hydrological pathways being dependent on precipitation regime. Non-metric Multidimensional Scaling (NMDS) clearly separated drift samples from temporary springs and other sample groups (drift in perennial spring, spring mouth and spring brook benthos). ANOSIM revealed statistically significant differences between all sample groups (Diacyclops zschokkei, Elaphoidella phreatica and Mixtacandona sp. B contributed over 50 % to the observed differences among sample groups. Three species (Nitocrella sp., Speocyclops infernus, Lessinocamptus pivai), known to be typical epikarst species, were collected only in the drift from one temporary spring (T2). Mao Tau species accumulation curves did not reach asymptote for the drift from temporary springs, but did for the drift from perennial spring, and for the spring mouth and the spring brook benthos. The results on drift composition indicated the variation in the origin of the water discharging at the interface of vadoze and phreatic zones depending greatly on water level conditions, while the drift densities were higher in the water presumably discharging from phreatic zone (perennial spring and temporary springs during low water levels). Julian Alps; alpine karst; groundwater; drift; Copepoda; Ostracoda

Groundwater Drift as a Tracer for Identifying Sources of Spring Discharge

Groundwater invertebrate drift, collected from the spring outlets at the interface of vadose and phreatic zones, has been examined for its potential for identifying sources of discharge from a karst aquifer. Concurrently, major ion geochemistry, dissolved inorganic carbon (δ13CDIC), particulate organic carbon (δ13CPOC), and naturally occurring stable isotopes of oxygen and tritium (δ18O, 3H) were investigated over a period of 1 year in two outlets, a temporary (TS) and a perennial (PS) spring. A few differences in major ion geochemistry and stable isotope composition were found between the two springs together with moderate seasonal variability. In contrast, invertebrate drift showed clear differences between TS and PS springs in density and composition. Canonical correspondence analysis showed the presence of two distinct groups of samples from TS and PS, with Ca2+ as the only significant explanatory variable for differences in drift composition. Finally, certain species from the drift were found to be useful tracers for distinguishing between the phreatic and the epikarst and vadose zones as the origin of spring water.

Invertebrate drift during in-stream gravel extraction in the River Bača, Slovenia

Spatial and temporal variation in invertebrate drift during in-stream gravel extraction in a gravel-bed river in south western Slovenia (SE Europe) was investigated. Drift samples were collected at three sites (an upstream control site and two downstream impacted sites) on the first and third days of gravel extraction. Drift measured during gravel extraction was compared to the hyporheic invertebrate community at the site of gravel extraction. Significant differences in drift were observed between the sites (ANOVA, n = 18, F = 23.29, p <0.001 for the number of individuals h -1 , and F = 13.15, p <0.001 for the number of taxa h -1 ). Two way analysis of ANOVA revealed the significance of site (p < 0.01) for number of individuals h -1 , and of site (p <0.001) and site * date interaction (p < 0.001) for taxa number h -1 . Insect larvae dominated drift at the control site, while crustaceans dominated the drift on the third day at both impacted sites. PCA of drift and hyporheic samples explained 37.8 % of the variance in data by the first two ordination axes. Drift composition was most similar to the shallow hyporheos on the third day of excavation. The study demonstrates that gravel extraction induces drifting of meiofauna which normally do not occur in the drift and that mass drift can occur up to 200 m from the site of excavation. Drift rates were much higher (approximately 30 fold) than the rates observed during increased discharge (from 2-5 fold).

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.