A 3-D numerical model of the influence of meanders on groundwater discharge to a gaining stream in an unconfined sandy aquifer

Groundwater discharge to streams depends on stream morphology and groundwater flow direction, but are not always well understood. Here a 3-D groundwater flow model is employed to investigate the impact of meandering stream geometries on groundwater discharge to streams in an unconfined and homogenous sandy aquifer at the reach scale (10–200 m). The effect of meander geometry was examined by considering three scenarios with varying stream sinuosity. The interaction with regional groundwater flow was examined for each scenario by considering three groundwater flow directions. The sensitivity of stream morphology and flow direction to other parameters was quantified by varying the stream width, the meander amplitude, the magnitude of the hydraulic gradient, the hydraulic conductivity, and the aquifer thickness. Implications for a real stream were then investigated by simulating groundwater flow to a stream at a field site located in Grindsted, Denmark. The simulation of multiple scenarios was made possible by the employment of a computationally efficient coordinate transform numerical method. Comparison of the scenarios showed that the geometry of meanders greatly affect the spatial distribution of groundwater flow to streams. The shallow part of the aquifer discharges to the outward pointing meanders, while deeper groundwater flows beneath the stream and enters from the opposite side. The balance between these two types of flow depends on the aquifer thickness and meander geometry. Regional groundwater flow can combine with the effect of stream meanders and can either enhance or smooth the effect of a meander bend, depending on the regional flow direction. Results from the Grindsted site model showed that real meander geometries had similar effects to those observed for the simpler sinuous streams, and showed that despite large temporal variations in stream discharge, the spatial pattern of flow is almost constant in time for a gaining stream

Proficiency testing of national reference laboratories for fish diseases

Part of the functions and duties of the European Community Reference Laboratory for Fish Diseases (CRL) is to organise periodic comparative tests of diagnostic procedures at Community level as described in Council Directive 2006/88/EC (Anonymous, 2006), previously outlined in Council Directive 93/53/EEC (Anonymous, 1993). A qualitative and quantitative proficiency test was carried out annually since 1996. These tests were primarily designed to assess the ability of participating laboratories to identify the listed viruses: viral haemorrhagic septicaemia virus (VHSV) and infectious haematopoietic necrosis virus (IHNV) on list II in Council Directive 91/67/EEC, annex A (Anonymous, 1991). The tests have typically consisted of five coded ampoules of lyophilised supernatant from infected cell cultures. Participants were asked to identify and quantify the contents within a deadline of 8 weeks. The CRL collated the answers and processed them statistically and graphically to provide the individual laboratory with a unique picture of its performance in relation to the other participants. Each participant was assigned a code number to ensure discretion.\ud \ud Occasionally the test was designed with additional purposes; other common fish viruses were included for differential diagnosis, cell line susceptibility within and between laboratories were tested, and the ability of laboratories to detect double infections and differentiate between genotypes was also part of the test. This paper describes the different approaches in designing the test over a 10-year period and comments on the overall performance of participants during that period

Propagation and isolation of ranaviruses in cell culture

The optimal in vitro propagation procedure for a panel of ranavirus isolates and the best method for isolation of Epizootic haematopoietic necrosis virus (EHNV) from organ material in cell-culture were investigated. The panel of ranavirus isolates included: Frog virus 3 (FV3), Bohle iridovirus (BIV), Pike-perch iridovirus (PPIV), European catfish virus (ECV), European sheatfish virus (ESV), EHNV, Doctor fish virus (DFV), Guppy virus 6 (GF6), short-finned eel virus (SERV) and Rana esculenta virus Italy 282/102 (REV 282/102). Each isolate was titrated in five cell lines: bluegill fry (BF-2), epithelioma papulosum cyprini (EPC), chinook salmon embryo (CHSE-214) rainbow trout gonad (RTG-2) and fathead minnow (FHM), and incubated at 10, 15, 20, 24 and 28 °C for two weeks.\ud \ud BF-2, EPC and CHSE-214 cells performed well and titers obtained in the three cell lines were similar, whereas FHM and RTG-2 cells consistently produced lower titers than the other cell lines at all temperatures. The optimal temperature for propagating the isolates collectively to high titers in vivo was 24 °C.\ud \ud Additionally, three established methods for re-isolation of virus from EHNV-infected organ material were compared. Challenged fish were sampled twice weekly and 7 organs were processed separately according to the three methods. Samples incubated on BF-2 cells at 22 °C for 2 weeks + 1 week sub-cultivation (method 1) provided more positive results than the other 2 methods and when using the EPC cell line. Virus was most frequently isolated from the kidney, followed by brain, muscle, heart, liver, gills and lastly spleen