MASAS—A user-friendly simulation tool for modeling the fate of anthropogenic substances in lakes

Underestimation of Anthropogenic Bromoform Released into the Environment?

Bromoform (CHBr₃) belongs to very-short-lived substances (VSLSs), which are important precursors of reactive bromine species (BrOx) contributing to tropospheric and stratospheric chemistry. To date, most models calculating bromine product emissions to the atmosphere only consider the natural production of CHBr₃ from marine organisms such as macroalgae and phytoplankton. However, CHBr₃ has many other anthropogenic sources (coastal industrial sites, desalination and wastewater plants, ballast waters, and seawater toilets) that may drastically increase the amounts emitted in the atmosphere. Here, we report the levels of CHBr₃ released in water and air (according to real-time and offline measurements by proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) and gas chromatography with electron capture detection (GC-ECD)) in a highly industrialized area where 3 million cubic meters of chlorinated seawater is released each day, which were measured during six field campaigns (at sea and on land) distributed over 3 years. The highest levels found during this survey (which were correlated to the physical-chemical characteristics of the water, meteorological and hydrological conditions, salinity, and temperature gradients along the water column) reached 34.6 μg L^-1 in water (100-10 000 times higher than reported natural levels) and 3.9 ppbv in the air (100 times higher than the maximum reported value to date). These findings suggest the need to undertake sampling and analysis campaigns as close as possible to chlorinated discharges, as anthropogenic CHBr₃ sources from industrial discharges may be a missing factor in global flux estimates or organic bromine to the atmosphere.

An integrated mechanistic modeling of a facultative pond: Parameter estimation and uncertainty analysis

Imitating natural lakes, pond treatment systems inherit a high complexity with interconnected web of biochemical reactions and complex hydraulic processes. As such, its simulation requires a large and integrated model, which has been a challenge for pond engineers. In this study, we develop an all-encompassing model to gain a quantitative and comprehensive understanding of the hydraulic, physicochemical and microbiological conversion processes in the most common pond, a facultative pond. Moreover, to deal with an evitable issue of large mechanistic models as overparameterization leading to poor identifiability, a systematic parameter estimation was implemented. The application of sensitivity analysis reveals the most influential parameters on pond performance. Particularly, physical parameters, such as vertical eddy diffusivity, water temperature, and maximum growth rate of heterotrophs induce the most changes of organic matters while microbial assimilation and ammonia volatilization appear to be main processes for nutrient removal. In contrast, the efficiency of phosphate precipitation and nutrient biological removal via polyphosphate accumulating organisms and denitrifying bacteria is limited. Identifiability problems are addressed mainly by the characterization of light dependence of algal growth, interaction between water temperature and its coefficient, and the growth of autotrophic bacteria while based on the determinant measures, the most important parameter subsets affecting model outputs are related to physical processes and algal activity. After the establishment of the influential and identifiable parameter subset, an automatic calibration with the data collected from Ucubamba pond system (Ecuador) demonstrates the effect of high-altitude climatic conditions on pond behaviors. An aerobic prevailing condition is observed as a result of high light intensity causing accelerated algal activities, hence, leading to the limitation of hydrolysis, anaerobic processes, and the growth of anoxic heterotrophs for denitrification. Furthermore, the output of uncertainty analysis indicates that a large avoidable uncertainty as a result of vast complexity of the applied model can be reduced greatly via a systematic approach for parameter estimation.

Multi-level approach for the integrated assessment of polar organic micropollutants in an international lake catchment: the example of Lake Constance

Polar organic micropollutants (MPs) can have ecotoxicological effects on aquatic ecosystems and their occurrence in drinking water is a threat to public health. An extensive exposure assessment of MPs in large river and lake catchments is a necessary but challenging proposition for researchers and regulators. To get a complete picture of MP exposure in a large catchment, we employed a novel integrated strategy including MP measurement in the international catchment of Lake Constance and mass-flux modeling. A comprehensive screening of 252 MPs in the lake water by high-resolution mass spectrometry was used to identify the most commonly present MPs for the study site. It was found that the wastewater borne MPs diclofenac, carbamazepine, sulfamethoxazole, acesulfame, sucralose, benzotriazole, and methylbenzotriazole accounted for the most frequent and prominent findings. The concentration pattern of these compounds in the catchment was calculated based on regionalized inputs from wastewater treatment plants (WWTPs) and substance specific elimination rates. In 52, 8, and 3 of the 112 investigated river locations the concentration exceeded the predicted no-effect levels for diclofenac, sulfamethoxazole and carbamazepine, respectively. By coupling the catchment and lake model the effect of future trends in usage as well as possible mitigation options were evaluated for the tributaries and the lake. The upgrade of the major WWTPs in the catchment with a postozonation step would lead to a load reduction between 32% and 52% for all substances except for sucralose (10%).

Factors responsible for rapid dissipation of acidic herbicides in the coastal lagoons of the Camargue (Rhône River Delta, France)

This study was aimed at investigating which processes cause acidic herbicides (e.g., bentazone, MCPA and dichlorprop) to rapidly disappear in the lagoons of the Rhône delta, which are peculiar brackish and shallow aquatic environments. The use of the model MASAS (Modeling of Anthropogenic Substances in Aquatic Systems) revealed that sorption, sedimentation, volatilization, flushing and abiotic hydrolysis had a minor role in the attenuation of the investigated herbicides. Laboratory scale biodegradation and photodegradation studies were conducted to better assess the significance of these two processes in the natural attenuation of herbicides in brackish (lagoons) waters with respect to fresh waters (canals draining paddy fields). Herbicide biodegradation rates were significantly lower in lagoon water than in canal water. Consequently, photodegradation was the main dissipation route of all investigated herbicides. The contribution of indirect photolysis was relevant for MCPA and dichlorprop while direct photolysis dominated for bentazone removal. There is a need to further investigate the identity of phototransformation products of herbicides in lagoons.