Variations in climatic and hydrological parameters in the Selenga River basin in the Russian Federation

The variations in average annual surface air temperature, precipitation, and runoff in the Selenga River basin (within Russia) are analyzed. It is demonstrated that the considerable increase in average annual temperature of surface air layers occurred in the 1980s-1990s. The decrease in peak water discharge in the rivers and the increase in the frequency of low-water periods were revealed in the forest-steppe and steppe zones of the Selenga River basin in 2001-2010. In the southwestern mountain regions (the Dzhida River basin) the river runoff increased during that period.     

Sediment pathways and transport rates through a tide-dominated entrance, Rangaunu Harbour, New Zealand

Bed load sediment traps were deployed at two sections across channels in Rangaunu Harbour entrance. Traps were inspected and emptied by divers at hourly intervals through both spring and neap tidal cycles for a total of 292 trap deployments. Current velocities were measured simultaneously with the trap inspections. Transport is concentrated in sandy megaripple fields on the channel banks and sub-tidal platforms flanking the channels. There, transport is almost continuous throughout the tidal cycle, increasing with flow velocity but lagging by approximately one hour. The channel floors are lined with shell-gravel lag across which bedload transport rates are low and discontinuous. Tidal asymmetry produces a net seaward transport through the channel troughs and a net landward transport across the channel banks and flanking sub-tidal platforms. Sediment leaving the harbour recirculates in anticlockwise gyres across the ebb-tide delta to re-enter the harbou and maintain the supply of sand to the megaripple field. Transport during spring tides is typically 25–30 times that during neaps. Predictions of transport rates, from a method developed by Black & Healy utilizing the Yalin bedload equation, produced transport rates similar to the traps over sand beds. Transport over shell lag surfaces appears independent of near-bed velocity and more dependent on the passage of ribbons of sand across the lag surface.     

Local hydraulic gradient estimator analysis of long-term monitoring networks

Three measurements of head at unique locations form a three-point estimator of the local magnitude and orientation of the hydraulic gradient. The relative head measurement error (RHME) is defined here as the measurement error normalized by the head drop across the three-point estimator. Monte Carlo simulation results show that estimators with base to height ratios between 0.5 and 5.0 and that are large enough to keep the RHME below 0.05 create the most accurate gradient estimates and provide criteria for identifying good estimators. These criteria are applied to an example ground water monitoring network design problem in the Culebra dolomite near the Waste Isolation Pilot Plant repository to both analyze temporal changes and modify and expand the current monitoring network. Limiting the three-point estimators to those that meet the shape and RHME criteria reduces the number of possible estimators by >50% and leads to approximately 1 order of magnitude decrease in the average estimated magnitude of the gradient relative to using all estimators. Application of these criteria also reduces the variability in estimated gradient magnitude and orientation between the two time periods of measurements. Redundant wells in the network are identified by removing each existing well in turn and determining which removals yield the smallest decrease in the number of acceptable estimators. Optimal new well locations are identified by mapping the increase in total number of acceptable estimators for a single new well placed in the study domain.     

Modeling rhamnolipids production by Pseudomonas aeruginosa from immiscible carbon source in a batch system

A mathematical model to predict the rhamnolipids production by Pseudomonas aeruginosa from oleic acid in a two phase liquid-liquid batch reaction system, was developed in this study. The model was based on two theoretical assumptions: 1) the convective oleic acid mass transfer is coupled to a bioreaction in the aqueous liquid bulk, and 2) the volume of the immiscible oleic acid drops and the saturation concentration at the interface are a function of rhamnolipids production. The model was able to accurately predict the experimental growth of the Pseudomonas aeruginosa strain, and the rhamnolipids production data with oleic acid as carbon source. This mathematical approach indicated a high correspondence between the saturation dimensionless profiles of oleic acid at the interface and the experimental profiles of surface tension difference. This modeling approach may constitute a useful tool in the design and scaling-up of bioreactors applied to the production of biosurfactants with immiscible carbon sources.     

Chemical composition of Russian Arctic precipitation in 2007-2015

The results of observations of the chemical composition of precipitation in the Russian Arctic in 2007-2015 are summarized including the data from NP-35 drifting ice station obtained in 2007-2008 in the framework of the joint program of Arctic and Antarctic Research Institute and Voeikov Main Geophysical Observatory. The qualitative and quantitative difference in the chemical composition of precipitation in the Atlantic, Siberian, and Pacific sectors of the Russian Arctic is revealed. It is found that the concentration of microelements (heavy metals) in precipitation at NP-35 ice station did not exceed 12% of total ions at the lowest mineralization. The comparative analysis is presented of the concentration of sulfate ions in precipitation in Norilsk and at NP-35 ice stations.     

Experimental evaluation of biases associated with sampling estuarine fishes with seines

Beach seines are widely used to estimate the density and species richness of fishes in estuaries. We evaluated the causes and extent of bias in estimates from seines using a series of field experiments in small estuaries in southern California, USA. Seining in spatially paired areas that were either enclosed by block nets or not, revealed that seines used without block nets und erestimated density by more than 4-fold and species richness by more than 2-fold relative to blocked areas. Seining in paired blocked areas with seines of two lengths revealed that net length affected estimates of density, but not species richness; a 7.6-m long seine produced 1.6-fold higher estimates of total density than did a 15.2-m long seine due to increased catches of demersal fishes, but not midwater species. Paired sampling in blocked areas also revealed that many fishes initially evaded capture by the seine. Estimates of density but not species richness were significantly higher in areas through which a seine was swept 5 times compared to once. This was due to higher catches of demersal fishes but not midwater fishes in areas seined 5 times. Repeated seining through blocked areas revealed that the vast majority (90% or more) of species and individuals of midwater fishes were captured within the first 5 sweeps, compared to only about 50% of the individuals of demersal species. A mark-recapture study in blocked areas revealed lower probabilities of capture for demersal species relative to midwater species.