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The relationships between the hydrochemical and structural characteristics of the macrozoobenthos community, including biotic indices is analyzed in the rivers of the Neman basin in the spring and summer periods. The list of hydrochemical characteristics included pH, dissolved oxygen concentration, the concentration of ions of ammonium and nitrate nitrogen, dissolved phosphorus, and heavy metals. A close correlation was found to exist between the structural characteristics of zoobenthos and water hydrochemical composition; it can be clearly seen in the summer period. The maximal values of the correlation coefficients were obtained for the relationship between the shares of EPT and oligosaprobic species in the total number of macrozoobenthos. The correlation between the number of macrozoobenthos species and the hydrochemical characteristics was found to be unreliable. The importance of the multimetric approach, taking into account both the hydrobiological and hydrochemical characteristics was emphasized. [ABSTRACT FROM AUTHOR]

Plant nitrogen source in the soil is challenging to track. Compiling the most comprehensive global δ15N dataset, a new study shows the plant use of various available soil nitrogen forms (ammonium, nitrate, and organic nitrogen) is strongly controlled by temperature. [ABSTRACT FROM AUTHOR]

The extensive agricultural feedlot operations in the Neuse River Watershed (NRW) in North Carolina result in high nutrient loading, particularly of ammonium (NH4+). In September 2018, Hurricane Florence devastated large portions of the NRW, creating a unique opportunity to study the impact of such hydrological events on the biogeochemistry of riverine and riparian sediments. The high NH4+ concentrations, naturally acidic conditions, and elevated levels of ferric iron [Fe(III)] in Neuse River sediments and soils provide an ideal environment for Acidimicrobium sp. A6 (referred to hereon as A6), a bacterium capable of conducting the Feammox process in which NH4+ is oxidized while iron is reduced. A6 was observed in all sediment samples obtained from the Neuse River, and it is therefore predicted that this process may be an important mechanism for NH4+ removal in this river system. Incubations of NRW samples indicate that the NH4+ oxidation potential via the Feammox process in the NRW is comparable with aerobic NH4+ oxidation by heterotrophic microorganisms. Given the high demand for Fe(III) by the Feammox process, it has been unclear how such a process may occur in sedimentary environments where ferric iron [Fe(III)] might be depleted. The results presented here show that a major hydrologic storm event can result in an increase in Fe(III) and in an increase in the abundance of Fe-reducing bacteria, including Acidimicrobium sp. A6. These findings indicate that major hydrologic storm events may, via the delivery of Fe(III), be capable of enhancing Feammox activity in riverine sediments that favor the Feammox process. [ABSTRACT FROM AUTHOR]

Treatment and recycling of high concentrations of ammonia nitrogen (NH4+–N) and tatal phosphorus (TP) is a major challenge in today's wastewater industry, while microalgae not only captures CO2, but also provide a safe and cost-effective alternative to wastewater treatment according to its growth characteristics. However, we found that excessive NH4+–N is harmful to microalgae. Significantly higher accumulation rate of the biomass and chlorophyll, as well as removal rate of ammonia nitrogen and phosphorus were observed in an acclimated strain of Chlorella vulgaris (HPN-3#) compared to those of the original strain (CK). The results of photosynthetic performance indicated that although photosystem of both strains were inhibited by the stress of high concentration of NH4+–N. The photosynthetic efficiency of HPN-3# was also higher than that of CK. The results of chlorophyll fluorescence transients and parameters suggested that HPN-3# showed better performance of energy flux regulation and electron transportation that mitigates NH4+–N inhibition, whereas the mixotrophic cultivation strategy using additional carbon source also reduced the stress and helped to maintain the accumulation of microalgae. In addition, acidified environment has a negative effect on the luxury uptake of P, and subsequently reduced its removal efficiency. [ABSTRACT FROM AUTHOR]

The single PN-A (partial nitrification-anammox) reactor offers a cost-effective solution for nitrogen removal. However, optimal control of the PN-A reactor is challenging due to the interactive mechanisms among the oxygen supply, bulk liquid DO (dissolved oxygen) concentration, and the balance of various functional bacterial species. In this study, a mathematical model was used to derive the optimal control variable for the maximum nitrogen removal, and an experimental PN-A reactor was operated to verify the model simulation results. The model simulation results indicate that the oxygen supply to the ammonium load ratio is the key factor to control the single-stage PN-A reactor for optimal TN removal. For optimal TN removal, the oxygen supply to the ammonium load ratio should be 1.9 mg O2/mg N. The DO concentration is not the key control parameter to get the maximum TN removal as the optimal TN removal could be achieved under a wide range of DO concentration. The model simulation results were verified in the experimental PN-A reactor under oxygen transfer rate ( K L a ) at 52 day−1, HRT at 24 h, and ammonium load ratio of 0.55 kg N/(m3∙day). [ABSTRACT FROM AUTHOR]

This study examined the capacity of the giant kelp, Macrocystis pyrifera, to exhibit surge uptake as a mechanism to enhance nitrogen assimilation during seasons when nitrate is depleted. Surge uptake of nitrate, ammonium, and urea was assessed in the spring and summer with whole-blade incubation experiments using 15 N tracers. The incubation experiments showed evidence of surge uptake lasting up to 5 min for ammonium and 1 min for nitrate during the summer only. Giant kelp showed little capacity for surge uptake of urea regardless of season. The ecological importance of the patterns of surge uptake observed for ammonium and nitrate, however, is questionable, given the small scale and ephemeral nature of ammonium pulses most likely experienced by giant kelp, and the longer duration pulses of nitrate associated with internal waves and upwelling. Rather it seems more likely that uptake of ammonium and urea at ambient concentrations, combined with normal uptake of nitrate during longer duration pulses of high concentrations, sustains giant kelp growth during seasons when ambient concentrations of nitrate are low. [ABSTRACT FROM AUTHOR]

Downy mildew (Peronospora belbahrii) is a severe disease in sweet basil. The aim of the present research was to study the effect of total nitrogen (N) concentration and NH4+ partial concentration in sweet basil fertigation on sweet basil downy mildew (SBDM). The study was conducted under controlled conditions, semi-commercial conditions, and commercial-like (field) conditions. Increasing the total N concentration in the irrigation water from 1.1 to 10.7 mM resulted in a gradual increase in N concentration in the shoots, and SBDM severity in potted sweet basil plants. Similarly, under commercial-like greenhouse conditions, higher N in the irrigation water resulted in higher SBDM severity. A high rate of 30–40% of the total N of NH4+ in the irrigation water, was associated with lower SBDM severity. Mineral concentration in the shoots of sweet basil was measured in all greenhouse plots. Shoot concentrations of N, P, K, and Ca were positively correlated with SBDM severity, while shoot concentrations of Mg and Cl negatively correlated with disease severity. In conclusion, N fertigation affected SBDM severity. We suggest that the effect of N fertigation on disease may be due to the change in N concentration in the tissue, or the change in other nutritional element (s). [ABSTRACT FROM AUTHOR]

Historically, anthropogenic fixed nitrogen has been purposely increased to benefit food production and global development. One consequence of this increase has been to raise concentrations of nitrogen in aquatic ecosystems. To evaluate whether nitrogen pollution promotes changes in the estimates of niche space of fish communities, we examined 16 sites along a Brazilian river basin highly impacted by anthropogenic activities, especially discharge of domestic and industrial sewage from a region with more than 5 million inhabitants. We analysed the carbon (δ13C) and nitrogen (δ15N) isotope ratios of fish species and both autochthonous (periphyton) and allochthonous (course and fine particulate organic matter) basal food resources. To estimate the magnitude of nitrogen pollution, we measured the nitrate and ammonium concentrations at each site. Sampling was conducted in the dry and wet seasons to evaluate the influence of seasonality. Nitrogen pollution generally increased estimates of niche space, and seasonality influenced only the niche estimates of fish communities from polluted sites. In addition, isotopic analyses of nitrogen polluted sites yielded unrealistic estimates of trophic positioning (detritivores at the top of the food web). We conclude that changes in niche space estimates reflect both alterations in baseline isotopic values and differential trophic behaviour among fishes. Our study suggests that under conditions of high pollution, other factors appear to influence isotopic estimates of niche, such as isotopically distinct sources that have not been sampled, and/or differences in δ15N turnover rates between fish tissue and basal resources, creating isotopic baselines that are challenging to interpret. [ABSTRACT FROM AUTHOR]