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The interconnection between biotic and abiotic pathways involving the nitrogen and iron biogeochemical cycles has recently gained interest. While lacustrine ecosystems are considered prone to the biotic nitrate reduction (denitrification), their potential for promoting the abiotic nitrite reduction (chemodenitrification) remains unclear. In the present study, batch incubations were performed to assess the potential for chemodenitrification and denitrification in the saline inland lake Gallocanta. Sulfidic conditions are found in top sediments of the system while below (5-9 cm), it presents low organic carbon and high sulfate and ferrous iron availability. Anoxic incubations of sediment (5-9 cm) and water from the lake with nitrite revealed potential for chemodenitrification, especially when external ferrous iron was added. The obtained isotopic fractionation values for nitrite (ɛ 15 N NO2 ) were -6.8 and -12.3 ‰ and therefore, fell in the range of those previously reported for the nitrite reduction. The more pronounced ɛ 15 N NO2 (-12.3 ‰) measured in the experiment containing additional ferrous iron was attributed to a higher contribution of the chemodenitrification over biotic denitrification. Incubations containing nitrate also confirmed the potential for denitrification under autotrophic conditions (low organic carbon, high ferrous iron). Higher reaction rate constants were found in the experiment containing 100 μM compared to 400 μM nitrate. The obtained ɛ 15 N NO3 values (-8.5 and -15.1 ‰) during nitrate consumption fell in the range of those expected for the denitrification. A more pronounced ɛ 15 N NO3 (-15.1 ‰) was determined in the experiment presenting a lower reaction rate constant (400 μM nitrate). Therefore, in Gallocanta lake, nitrite generated during nitrate reduction can be further reduced by both the abiotic and biotic pathways. These findings establish the significance of chemodenitrification in lacustrine systems and support further exploration in aquatic environments with different levels of C, N, S, and Fe. This might be especially useful in predicting nitrous oxide emissions in natural ecosystems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The article presents the result of the study concerning the denitrification and its development in a hyporheic riparian zone controlled by river regulation in the Siene River in France. It mentions that the riparian zone between the chalky hillsides and the river shows an important depletion of nitrate during the summer and autumn period. This depletion is attributed to denitrification which goes with a consumption of dissolved organic carbon and a decrease of redox potential. Moreover, it keeps the wetness of the riparian zone constant which allows the isolation of high temperature in summer and autumn as an important factor for denitrification.

Abstract: There is concern that subsurface drainage, by destroying or by-passing active denitrification areas, may prevent nitrate retention processes and enhance nitrate contamination of surface water by agriculture. To address this question, we studied the flow and concentration signatures of drainage waters and their transformations in a series of 5 nested watersheds, from 1 to 100km2 area, in the Brie region near Paris (France). At all scales, nitrate concentrations are generally higher during the winter drainage season compared to the low flow periods (late spring to early fall). High nitrate concentrations characterizing drainage waters are visible at the 1st, 2nd and 3rd stream order but are “diluted” by surface runoff from forested zones and buffered by groundwater contributions. The analysis of nitrate chemographs and nitrate budgets established for the different nested watersheds show significant nitrogen retention. Isotopic measurements indicate that the nitrate pool is enriched in δ15N– as its concentration decreases. Direct estimation of benthic denitrification with benthic chambers allowed concluding that benthic denitrification is not the only retention mechanism and that “underground” denitrification, affecting nitrate on its way from the base of the root zone down to the limit of the river bed, may in fact dominate nitrogen retention processes even in this intensively drained watershed. [Copyright &y& Elsevier]

Indian estuaries are hypothesized to export a significant amount of nitrogen nutrients to the coastal waters due to the high use of fertilizers. To examine the possible sources of nitrogen nutrients and their modifications within the estuary, a study was conducted by collecting samples at monthly intervals for a period of a year. The river Godavari is the largest monsoonal estuary in India and is fed by monsoon rainfall. Hence the entire estuary is filled with fresh water from July to September (the wet period) whereas saline water is dominant during the dry period. An order of magnitude increase in nitrate concentrations was observed during the wet due to a peak in discharge compared to the dry period. The isotopic composition of nitrogen in nitrate (δ15N NO3) was lower during the wet than the dry period and displayed a significant linear relationship with Chlorophyll-a (Chl-a), particulate organic nitrogen (PON) and carbon (POC) indicating that biological process modified their composition. The lower δ15N NO3 and higher δ18O NO3 values were noticed during the wet than during the dry period. The δ15N NO3 versus δ18O NO3 plot suggests a possible source of nitrate through the nitrification of soil/sewage-borne nitrogen. The higher δ18O NO3 /δ15N NO3 ratios (>1) were observed during August and September than in other months indicating the occurrence of denitrification during the former months. In contrast, an insignificant change in δ15N NO3 and δ18O NO3 within the estuary suggested that denitrification occurred upstream and not within the estuarine zone. River discharge brought residual nitrate to the estuary leading to less input of nitrate to the coastal Bay of Bengal than hitherto hypothesized. [Display omitted] • δ15N NO3 and δ18O NO3 suggest the occurrence of denitrification during the wet period. • NO3 is contributed by river discharge and marine sources during wet and dry periods. • NO3 by sewage is high during and the least during the peak discharge period. • Contribution of fertilizer accounts for only 10–12% to the Godavari estuary. [ABSTRACT FROM AUTHOR]

The Orgeval watershed (104 km 2 ) is a long-term experimental observatory and research site, representative of rural areas with intensive cereal farming of the temperate world. Since the past few years, we have been carrying out several studies on nitrate source, transformation and transfer of both surface and groundwaters in relation with land use and agriculture practices in order to assess nitrate ( NO3-) leaching, contamination of aquifers, denitrification processes and associated nitrous oxide (N2O) emissions. A synthesis of these studies is presented to establish a quantitative diagnosis of nitrate contamination and N2O emissions at the watershed scale. Taking this watershed as a practical example, we compare curative management measures, such as pond introduction, and preventive measures, namely conversion to organic farming practices, using model simulations. It is concluded that only preventive measures are able to reduce the NO3- contamination level without further increasing N2O emissions, a result providing new insights for future management bringing together water-agro-ecosystems. [ABSTRACT FROM AUTHOR]