Torulv Tjomsland

Quantitative microbial risk assessment combined with hydrodynamic modelling to estimate the public health risk associated with bathing after rainfall events

This study investigated the public health risk from exposure to infectious microorganisms at Sandvika recreational beaches, Norway and dose-response relationships by combining hydrodynamic modelling with Quantitative Microbial Risk Assessment (QMRA). Meteorological and hydrological data were collected to produce a calibrated hydrodynamic model using Escherichia coli as an indicator of faecal contamination. Based on average concentrations of reference pathogens (norovirus, Campylobacter, Salmonella, Giardia and Cryptosporidium) relative to E. coli in Norwegian sewage from previous studies, the hydrodynamic model was used for simulating the concentrations of pathogens at the local beaches during and after a heavy rainfall event, using three different decay rates. The simulated concentrations were used as input for QMRA and the public health risk was estimated as probability of infection from a single exposure of bathers during the three consecutive days after the rainfall event. The level of risk on the first day after the rainfall event was acceptable for the bacterial and parasitic reference pathogens, but high for the viral reference pathogen at all beaches, and severe at Kalvøya-small and Kalvøya-big beaches, supporting the advice of avoiding swimming in the day(s) after heavy rainfall. The study demonstrates the potential of combining discharge-based hydrodynamic modelling with QMRA in the context of bathing water as a tool to evaluate public health risk and support beach management decisions.

Increased spreading potential of the invasive Pacific oyster (Crassostrea gigas) at its northern distribution limit in Europe due to warmer climate

The Pacific oyster, Crassostrea gigas, is an invasive species with a large increase in prevalence globally, and with potential of spreading even more because of climate-change effects. We examined how future climate might affect its potential for spread at its northern distribution limit in a temperate ecoregion, by simulating spawning, larval dispersal, larvae settlement and adult survival, given different climate scenarios. The simulations were performed using a three-dimensional current model (GEMSS) and a specially designed oyster module, applied at the study site in the Oslofjord, Norway. The simulations showed that the expected climate in the middle and latter part of this century, with warmer summers and winters, very likely will lead to increased prevalence of the species within northern Europe. The warmer summers will more often provide favourable temperature conditions for oyster spawning and settlement, and warmer winters will more seldom cause high winter mortality. The simulations gave a realistic picture of the relative frequency and the main distribution pattern observed, given the current climate. The future climate-scenario simulations indicated influence of local differences in temperature on the dispersal pattern. The study indicated increased dispersal and successful establishment at the outer edge of the species present distribution in the future and, hence, an increased risk to native species and habitats in temperate regions.

Flow and pH Modelling to Study the Effects of Liming in Regulated, Acid Salmon Rivers

In the regulated river Ekso, Western Norway, liming of the headwater has been introduced as a mitigating action to improve the water quality for Atlantic salmon (Salmo salar L.). Supply of lime from a dosing plant situated 5 km above the salmon producing part of the river, aims to raise pH from 5,0 to 6,5 during the smolt period for Atlantic salmon, and to 6,2 for the rest of the year. Hydrological modelling based on the relationship between CaCO3 and pH is applied for the evaluation of the liming strategy, based on monitoring data from the spring 2000. The water quality demand was satisfied 80% of the time in the upper part of the salmon area, and 40% of the time in the lower part, influenced by power plant discharge. Flood forecasting and overdosing of lime ahead of floods will reduce the effects of acidified and unlimed tributaries. An additional lime doser is recommended to supply the power plant discharge.

Simulation of nutrient reduction scenarios with three different models. Does the selection of model affect the recommended set of measures

Abstract This article compares and discusses the results of applying three different models in order to quantify the phosphorus loads in Kapos catchment, Hungary. The models range from the very simple TEOTIL operating on statistical data and export coefficients, via the semi‐complex INCA‐P to the highly complex and process‐based SWAT. All models have been calibrated with use of basically the same input and calibration data. The models have, to the extent they are capable, been used further to simulate a set of theoretical pollution reduction scenarios. The calibration results showed that all the models are basically able to simulate historical loads of TotP on a catchment level, except maybe those years with particularly high or low loads (INCA‐P in 1999 and TEOTIL in 2002). The scenario analysis showed that the models are to a varying degree capable of simulating the simplified scenarios, where TEOTIL seems to a limited extent suitable for such analysis. This study demonstrated that the selection of model can influence the output of the scenario analysis significantly, and the selection of tool to be applied should therefore be made with great care. The most obvious example is the comparison of the simulation of the reduced runoff from area sources (scenario E) with the simulation of reduced discharges from point sources (scenario F). Based on the simulation results, TEOTIL considers reduction in nutrient runoff from areas to be the most efficient measures, while INCA‐P and SWAT results would suggest focusing on the reduction of point‐source discharges.

Application of a Mathematical Hydrodynamic model to lake Mjøsa

Abstract A three-dimensional model was used to compute current and temperature distribution in Lake Mjosa. The model was not calibrated for this specific lake. The values for the model parameters were obtained from the literature. The results show a good accordance with temperature observations in the field.