Are nitrogen and carbon cycle processes impacted by common stream antibiotics? A comparative assessment of single vs. mixture exposures

A variety of antibiotics are ubiquitous in all freshwater ecosystems that receive wastewater. A wide variety of antibiotics have been developed to kill problematic bacteria and fungi through targeted application, and their use has contributed significantly to public health and livestock management. Unfortunately, a substantial fraction of the antibiotics applied to humans, pets and livestock end up in wastewater, and ultimately many of these chemicals enter freshwater ecosystems. The effect of adding chemicals that are intentionally designed to kill microbes, on freshwater microbial communities remains poorly understood. There are reasons to be concerned, as microbes play an essential role in nutrient uptake, carbon fixation and denitrification in freshwater ecosystems. Chemicals that reduce or alter freshwater microbial communities might reduce their capacity to degrade the excess nutrients and organic matter that characterize wastewater. We performed a laboratory experiment in which we exposed microbial community from unexposed stream sediments to three commonly detected antibiotics found in urban wastewater and urban streams (sulfamethoxazole, danofloxacin, and erythromycin). We assessed how the form and concentration of inorganic nitrogen, microbial carbon, and nitrogen cycling processes changed in response to environmentally relevant doses (10 μg/L) of each of these antibiotics individually and in combination. We expected to find that all antibiotics suppressed rates of microbial mineralization and nitrogen transformations and we anticipated that this suppression of microbial activity would be greatest in the combined treatment. Contrary to our expectations we measured few significant changes in microbially mediated functions in response to our experimental antibiotic dosing. We found no difference in functional gene abundance of key nitrogen cycling genes nosZ, mcrA, nirK, and amoA genes, and we measured no treatment effects on NO3- uptake or N2O, N2, CH4, CO2 production over the course of our seven-day experiment. In the mixture treatment, we measured significant increases in NH4+ concentrations over the first 24 hours of the experiment, which were indistinguishable from controls within six hours. Our results suggest remarkable community resistance to pressure antibiotic exposure poses on naïve stream sediments.

Geochemical Compositions and Detrital Minerals of Stream Sediments around the Zijinshan Copper-Gold Orefield and Their Implications

Regional geochemical anomalies in stream sediments often have close spatial relationships with metallogenic provinces or ore districts, but the relationships between them have not been examined in depth. In this study, stream sediments were collected around the Zijinshan Copper-Gold Orefield, Fujian Province, China. Element geochemistry, U–Pb geochronology and Hf isotope compositions of detrital zircons, and electron microprobe and LA-ICP-MS analyses of iron oxides were conducted. The aims of this study were to investigate the relationship between the provenance of the stream sediments and ore-bearing magmatic rocks in the Zijinshan Copper-Gold Orefield, and to explore the enrichment mechanism of the ore-forming elements in stream sediments. The results show that the ore-forming elements and their associated elements are most significantly enriched in stream sediments near the orefield. U–Pb ages and Hf isotopic compositions of detrital zircons in the sediments closest to the orefield carry information on the ore- bearing magmatic rocks in the orefield. However, as the stream sediments are relatively far from the orefield, the degree of enrichment of ore-forming elements and the detrital zircon U–Pb age signals of the ore-bearing magmatic rocks in the orefield rapidly weaken. This weakening of the geochemical signals may have been affected by many factors, such as lithological resistance to weathering, vegetation coverage, micro-topographic conditions, etc. In-situ elements analysis of iron oxides and elemental correlation analysis of stream sediments indicate iron oxides and clay minerals are the main carrier minerals for the migration of ore-forming elements.

Copper availability governs nitrous oxide accumulation in wetland soils and stream sediments

Denitrification is microbially-mediated through enzymes containing metal cofactors. Laboratory studies of pure cultures have highlighted that the availability of Cu, required for the multicopper enzyme nitrous oxide reductase, can limit N2O reduction. However, in natural aquatic systems, such as wetlands and hyporheic zones in stream beds, the role of Cu in controlling denitrification remains incompletely understood. In this study, we collected soils and sediments from three natural environments -- riparian wetlands, marsh wetlands, and a stream -- to investigate their nitrogen species transformation activity at background Cu levels and different supplemented Cu loadings. All of the systems displayed low solid-phase associated Cu (40 - 280 nmol g-1), which made them appropriate sites for evaluating the effect of limited Cu availability on denitrification. In laboratory incubation experiments, high concentrations of N2O accumulated in all microcosms lacking Cu amendment except for one stream sediment sample. With Cu added to provide dissolved concentrations at trace levels (10-300 nM), reduction of N2O to N2 in the wetland soils and stream sediments was enhanced. A kinetic model could account for the trends in nitrogen species by combining the reactions for microbial reduction of NO3- to NO2-/N2O/N2 and abiotic reduction of NO2- to N2. The model revealed that the rate of N2O to N2 conversion increased significantly in the presence of Cu. For riparian wetland soils and stream sediments, the kinetic model also suggested that overall denitrification is driven by abiotic reduction of NO2- in the presence of inorganic electron donors. This study demonstrated that natural aquatic systems containing Cu at concentrations less than or equal to crustal abundances may display incomplete reduction of N2O to N2 that would cause N2O accumulation and release to the atmosphere.

Sources of some heavy minerals and their association with gold-bearing stream sediments in the Gagare Drainage Basin, Wonaka Schist belt northwestern Nigeria

No Abstract.

ARCHAEOLOGICAL, SOIL AND MICROBIOLOGICAL STUDIES OF THE MOSKVA RIVER FLOODPLAIN DEPOSITS AT THE ZVENIGOROD BIOLOGICAL PLANT

В статье приводятся результаты применения методов почвенно-микробиологического исследования культурных слоев в пойменных отложениях Москвы-реки. Выявлена корреляция пиков численности сапротрофных и термофильных бактерий с горизонтами погребенных почв в толще аллювия, к которым приурочены археологические находки. Показано, что с помощью микробиологических анализов можно выявить следы хозяйственной активности, которая датируется ранним бронзовым веком. The paper describes results of soil and microbiological studies of the occupation layers in the Moskva River floodplain deposits. The study identified a correlation between peaks in the count of the saprotrophic and thermophilic bacteria with the horizons of buried soils in the stream sediments where archaeological finds were made. The paper shows that micro bioassays can help identify traces of economic activity dating to the early Bronze Age.

Evaluation of the Impacts of Abandoned Mining Areas: A Case Study with Benthic Macroinvertebrate Assemblages

Mining activities are among the most long-lasting anthropogenic pressures on streams and rivers. Therefore, detecting different benthic macroinvertebrate assemblages in the areas recovered from mining activities is essential to establish conservation and management plans for improving the freshwater biodiversity in streams located near mining areas. We compared the stability of benthic macroinvertebrate communities between streams affected by mining activities (Hwangjicheon: NHJ and Cheolamcheon: NCA) and the least disturbed stream (Songjeonricheon: NSJ) using network analysis, self-organizing map, and indicator species analysis. Species richness was lowest at sites where stream sediments were reddened or whitened due to mining impacts in NHJ and NCA. Among functional feeding groups, the ratio of scrapers was lower (i.e., NHJ) or not observed (i.e., NCA) in the affected sites by mining. The networks (species interactions) were less connected in NHJ and NCA than in NSJ, indicating that community stability decreased in the area affected by mining activity. We identified five groups based on the similarity of benthic macroinvertebrate communities according to the gradients of mining impacts using a self-organizing map. the samples from the reference stream (clusters 1 and 5), sites located near the mining water inflow area (cluster 4), sites where stream sediments acid-sulfated (cluster 2), and sites that had recovered from mining impacts (cluster 3). Among the 40 taxa selected as indicators defined from the five clusters in self-organizing map, only few (Physa acuta, Tipula KUa, and Nemoura KUb) indicator species were selected in each cluster representing the mining-impacted sites. Our results highlighted that the benthic macroinvertebrate community complexity was lower in streams affected by mining activity. Furthermore, the range of disturbed areas in the streams, where conservation and management plans should be prioritized, can be quantified by examining alterations in the benthic macroinvertebrate community.