Implementation of comparative detection approaches for the accurate assessment of sediment thickness and sediment volume in the Passaúna Reservoir.

Siltation has significant economic and social impacts as it directly reduces the useable amount of water in reservoirs. Giving a solution to the issue of sedimentation is a complicated task and maybe one of the most important engineering and environmental challenges of the 21st century. The deposited volume and the distribution pattern of the sediment are often unknown and not easy to assess. The sedimentation process is highly dynamic, initially due to the hydrological conditions of the incoming rivers, but also due to common internal phenomena like resuspension or density currents. Sediment remediation measures such as mechanical sediment removal or flushing are planned based on the sediment thickness distribution and the overall sediment volume/mass. Often, the sediment thickness is calculated through topographic differencing between the pre-impoundment reservoir lake bottom and the actual lake bottom. However, it is common that the previous depth distribution map is not available or in insufficient quality. In this regard, alternative measurement techniques have to be taken into consideration. In this study, we assessed the best possible approach depending on the characteristics of the sediment and of the reservoir. We combined three different acoustic systems (a multibeam, a sub-bottom profiler, and a single beam dual frequency system) with sediment coring and dynamic free fall penetrometer measurements for an improved assessment of sediment stock and sediment distribution in the Passaúna Reservoir. Our results showed that topographic differencing could not be applied, as the data for the pre-impoundment lake bottom was insufficiently accurate. The parametric sub-bottom profiler could detect the sediment thickness in high accuracy, but significant limitations were recorded in areas with high gas contents. The dual-frequency echosounder derived the sediment thickness with a normalized mean absolute error of 56% due to the high volumetric gas content in the sediment. The dynamic free-fall penetrometer showed satisfying results compared to the other systems. The normalized mean absolute error was 22%, and sediment thickness could be detected in areas with up to 1.8 m of sediment. Sediment coring is also a reliable technique for sediment thickness determination. However, the results showed that if only traditional coring devices are used (gravity corer), the limited penetration depth of the equipment combined with sampling disturbances often prevent a correct assessment of the sediment thickness. The overall results of this study can help for an improved decision-making regarding reservoir management. The accurate assessment of sediment volume and distribution can reduce costs for sediment removal and assist in having a precise overview of the reservoir lifetime.

Correction to: High-frequency measurements of gas ebullition in a Brazilian subtropical reservoir-identification of relevant triggers and seasonal patterns.

The original version of this article unfortunately did not contain all information in Figure 3.

High-frequency measurements of gas ebullition in a Brazilian subtropical reservoir-identification of relevant triggers and seasonal patterns.

Water bodies, either natural or constructed impoundments, are sources of methane to the atmosphere, in which ebullition is frequently mentioned to be the dominant pathway. Ebullition is a complex process that is spatially dependent on factors acting over large distances (atmospheric pressure changes, wind) and factors acting locally (sediment characteristics, gas production) and is temporally variable due to the parameters' oscillation with time. Its quantification through measurements is still limited, as is the identification of production processes and triggers for ebullition. This research focused on obtaining high temporal resolution measurements of gas ebullition from a water supply reservoir located in Brazil, to compare its temporal variability with changes in reservoir conditions, and obtain insights on its spatial patterns. Three automated bubble traps were deployed in the reservoir and measured gas flux from February 2017 to March 2018. The time series data showed a large temporal variability in ebullition. Less intense fluxes occurred with higher frequency, and short-duration events made a larger contribution to the total amount of gas emitted. A strong seasonal variation was observed, in which the mean flux recorded during periods when the reservoir was stratified was 2-16 fold the bubbling rates recorded during colder months and mixed water column. In addition, high flux events were correlated with decreasing atmospheric pressure and increased wind intensities. Lastly, we show that the mean gas emission flux tends to be underestimated during short sampling periods (probability > 41% for sampling periods shorter than 10 days).

Water quality dynamic during rainfall episodes: integrated approach to assess diffuse pollution using automatic sampling.

Diffuse pollution caused by rainfall events potentially affects water quality in rivers and, therefore, must be investigated in order to improve water quality planning and management recovery strategies. For these, a quali-quantitative approach was used to monitor the water quality parameters in a river located in a semi-urban watershed area based upon automatic sampling. Thirteen water quality parameters were measured during five rainfall events. Events ranged from 2.3 to 56.8 mm and water peak flows from 3.3 to 4.5 m3/s. The pollutographs measured showed a standard pattern for total suspended solids (TSS). However, for the other chemical parameters, as total phosphorous (TP) and dissolved organic carbon (DOC), the dilution effects were more evident. It was possible to observe the rainfall influence mainly for physical parameters indicating a mass transport pattern for diffuse pollutants, which increased, for example, the amount of TSS in the river. Furthermore, hydrological characteristics were relevant considering the pollutant behavior. Antecedent dry periods, ranging from 1.3 days to 21.4 days, and critical time, from 2.0 to 10.4 h, are determinants to evaluate non-traditional water quality impacts in the river. In general, each rainfall episode has its own characteristics, which produces distinct mass contribution and temporal behavior, being challenging in making generalization. Therefore, the results indicate that diffuse pollution has to be considered to establish future decision-making strategies to water resources management.

Exploring the temporal dynamics of methane ebullition in a subtropical freshwater reservoir.

The transport of methane from sediments to the atmosphere by rising gas bubbles (ebullition) can be the dominant, yet highly variable emission pathway from shallow aquatic ecosystems. Ebullition fluxes have been reported to vary in space and time, as methane production, accumulation, and bubble release from the sediment matrix is affected by several physical and bio-geochemical processes acting at different timescales. Time-series analysis and empirical models have been used for investigating the temporal dynamics of ebullition and its controls. In this study, we analyzed the factors governing the temporal dynamics of ebullition and evaluated the application of empirical models to reproduce these dynamics across different timescales and across different aquatic systems. The analysis is based on continuous high frequency measurements of ebullition fluxes and environmental variables in a mesotrophic subtropical and polymictic freshwater reservoir. The synchronization of ebullition events across different monitoring sites, and the extent to which ebullition was correlated to environmental variables varied throughout the three years of observations and were affected by thermal stratification in the reservoir. Empirical models developed for other aquatic systems could reproduce a limited fraction of the variability in observed ebullition fluxes (R2 < 0.3), however the predictions could be improved by considering additional environmental variables. The model performance depended on the timescale. For daily and weekly time intervals, a generalized additive model could reproduce 70 and 96% of ebullition variability but could not resolve hourly flux variations (R2 = 0.19). Lastly, we discuss the potential application of empirical models for filling gaps in ebullition measurements and for reproducing the main temporal dynamics of the fluxes. The results provide crucial information for emission estimates, and for the development and implementation of strategies targeting at a reduction of methane emissions from inland waters.

Determination of antibiotic resistance genes in a WWTP-impacted river in surface water, sediment, and biofilm: Influence of seasonality and water quality.

Many pathogenic bacteria are adapted to live in aquatic habitats, which makes rivers possible sources and spread pathways of antibiotic resistance, since they usually receive effluents from wastewater treatment plants (WWTP), possibly containing antibiotic residues and also antibiotic-resistant bacteria. This study investigates different monitoring strategies to identify the occurrence of antibiotic-resistant bacteria in rivers. We analyzed the presence of 13 antibiotic resistance genes (ARGs) and seven gene markers for facultative pathogenic bacteria (FPB) with qPCR in sampling sites upstream and downstream of a small WWTP in Southern Germany. Five sampling campaigns were conducted from February to June 2019. Surface water, sediment, and biofilm samples were analyzed. The biofilm was collected from an artificial sampler placed in the river. blaTEM, ermB, tetM, and sul1 genes were detected in all samples analyzed. The results showed there was a previous background in the river, but the WWTP and the water quality of the river influenced the concentration and occurrence of ARGs and FPB. Genes representing resistance against strong or last-resort antibiotics, such as mecA, blaCMY-2, blaKPC-3, and mcr-1, and multidrug resistance were also detected, mainly in samples collected downstream of the WWTP. Downstream of the WWTP, the occurrence of ARG and FPB correlated with ammoniacal nitrogen, while upstream of the WWTP correlated with turbidity, suspended solids, and seasonal factors such as UVA radiation and the presence of macrophytes. Biofilm samples presented higher abundances of ARGs and FPB. The biofilm sampler was efficient and allowed to collect biofilms from specific periods, which helped to identify seasonal patterns.

Emerging contaminants and antibiotic resistance in the different environmental matrices of Latin America.

This review aims to gather and summarize information about the occurrence of emerging contaminants and antibiotic resistance genes in environmental matrices in Latin America. We aim to contribute to future research by compiling a list of priority pollutants adjusted to the needs and characteristics of Latin America, according to the data presented in this study. In order to perform a comprehensive research and secure a representative and unbiased amount of quality data concerning emerging contaminants in Latin America, the research was performed within the Scopus® database in a time frame from 2000 to July 2019. The countries with higher numbers of published articles were Brazil and México, while most studies were performed in the surroundings of Mexico City and in Southern and Southeastern Brazil. The main investigated environmental matrices were drinking water and surface water. The presence of antibiotic resistance was frequently reported, mainly in Brazil. Monitoring efforts should be performed in other countries in Latin America, as well as in other regions of Brazil and México. The suggested priority list for monitoring of emerging contaminants in Latin America covers: di(2-ethylhexyl) phthalate (DEHP), bisphenol-A (BP-A), 4-nonylphenol (4-NP), triclosan (TCS), estrone (E1), estradiol (E2), ethinylestradiol (EE2), tetracycline (TC), amoxicillin (AMOX), norfloxacin (NOR), ampicillin (AMP) and imipenem (IMP). We hope this list serves as a basis for the orientation of the future research and monitoring projects to better understand the distribution and concentration of the listed emerging substances.

Redistribution of methane emission hot spots under drawdown conditions.

In the context of reservoirs, sediment trapping, and aquatic greenhouse gas (GHG) production, knowledge about the distribution of hot and low spots is essential for improved measurement strategies. It is also a key to a precise assessment of the GHG emissions of each reservoir. Large numbers of reservoirs are used mainly for hydroelectric power generation and, hence, affected by strong changes in water level. Drawdown events may lead to significant changes in spatial sediment and organic carbon distribution and, consequently, strongly alter the GHG emission patterns of the water body. We combined hydroacoustic sediment classification, sediment magnitude detection, and ebullition flux assessment with in-situ pore water investigations and sediment coring to detect ebullition distribution patterns after strong reservoir drawdown. The research was conducted in the Capivari Reservoir in the southeast of Brazil, which was affected by up to 15 m of drawdown within the last 10 years. Results show severe changes in sediment accumulation and composition. The focusing of sediment divides the reservoir in extreme hot and low spots. Methane pore water concentrations are highly correlated with acoustic backscatter values (r2 = 0.97) as well as with the organic carbon content (r2 = 0.55) and allow for a precise detection of the newly created emission patterns. Highly productive sediment could be acoustically distinguished from non-productive areas. Only 23.6% of the reservoir surface produced 64% of the detected bubbles. An organic carbon content in the sediment of 2.4% was found to be a prerequisite for the formation of GHG emission hot spots. These findings may help to complement the still insufficient knowledge of methane ebullition fluxes from reservoirs with changing water levels.

A method for the assessment of long-term changes in carbon stock by construction of a hydropower reservoir.

Sustainability of hydropower reservoirs has been questioned since the detection of their greenhouse gas (GHG) emissions which are mainly composed of carbon dioxide and methane. A method to assess the impact on the carbon cycle caused by the transition from a natural river system into a reservoir is presented and discussed. The method evaluates the long term changes in carbon stock instead of the current approach of monitoring and integrating continuous short term fluxes. A case study was conducted in a subtropical reservoir in Brazil, showing that the carbon content within the reservoir exceeds that of the previous landuse. The average carbon sequestration over 43 years since damming was 895 mg C m[Formula: see text] and found to be mainly due to storage of carbon in sediments. These results demonstrate that reservoirs have two opposite effects on the balance of GHGs. By storing organic C in sediments, reservoirs are an important carbon sink. On the other hand, reservoirs increase the flux of methane into the atmosphere. If the sediments of reservoirs could be used for long term C storage, reservoirs might have a positive effect on the balance of GHGs.