Effect of different seasonal conditions on the potential of wetland soils for groundwater denitrification

Abstract

Wetlands, as active riparian areas in denitrification processes, are largely dependent on the environment. The main objective of this paper is to evaluate changes in the denitrification potential of wetland soils at laboratory scale promoted by climatic and seasonal influences. Several batch denitrification tests were performed with fresh wetland soil (peat) from Brynemade (Denmark) under: three different temperatures (20, 10, and 5˚C), drought period, and freeze-thaw event. Results show that nitrate was eliminated in all the experiments in percentages over 90%. However, not all the nitrate removed was reduced to nitrogen gas via the denitrification process; dissimilatory nitrate reduction to ammonium (DNRA) was also present. In fact, the percentage of total nitrogen eliminated at the end of the tests was: 79.7% at 20˚C, 84.1% at 10˚C, 82.9% at 5˚C, 41.0% in the dried soil, and 57.0% in the frozen soil. Thus, it can be concluded that the drying and freezing of the soil favor the DNRA process. Furthermore, in these conditions, nitrite increased sharply and was also accumulated possibly, as a DNRA or denitrification intermediate. Nitrate removal was fitted to a zeroorder model, and an increase of the denitrification rates with the temperature was observed (3.8 mg NO À 3 L −1 d −1 at 20˚C, 3.0 mg NO À 3 L −1 d −1 at 10˚C, and 2.9 mg NO À 3 L −1 d −1 at 5˚C). These overall rates were modeled as a function of temperature by the Arrhenius equation and activation energy of 12.88 kJ mol −1 was determined. The fact that the activation energy is low in this work (unstirred batches) compared to previous publications (stirred batches) could be the result of a strong restriction on the nitrate mass transfer in the soil vs. reaction kinetics, which masks kinetic regulating factors of the denitrification rate. Thus, the variation of the denitrification rate with temperature is possibly the result of a combination of changes in mass transfer (diffusive transport) and kinetic constant variation, successfully modeled by the Arrhenius equation.

Cold spots and cold moments: The potential for sediment freezing to depress denitrification in wetland sediments

“…Gradients of soil moisture content both seasonally and spatially can have an important influence on FTC effects (Hung & Whalen, 2020), and the number of FTCs can yield important but variable effects (e.g., Liao et al., 2019; Lui et al., 2021; Sang et al., 2021). Ultimately, to better understand how FTCs affect N cycling in wetlands, work across a broader range of wetlands in human‐impacted and more pristine environments is required and across multiple processes and pools, for example, assessing effects on nitrification, NO 3 – assimilation via dissimilatory NO 3 – reduction to ammonia (Ribas et al., 2013), and pools of N and C. A key next step is to better understand the spatial extent of sediment freezing both within wetlands and at the scale of large landscapes under a range of winter conditions (Duguay & Lafleur, 2003). Ultimately, wetland size and depth could potentially be considered in design of temperate urban wetlands to influence the wetland area likely to be exposed to freeze–thaw conditions and the number, duration, and intensity of those FTCs.…”

Subsurface nitrate reduction under wetlands takes place in narrow superficial zones

“…[6,7] In addition, microorganisms are strongly influenced by environmental conditions: dissolved oxygen, mineralizable carbon, pH, nutrients (e.g. phosphorus) [8,9], water table elevation [10,11], temperature and other seasonal conditions, [12]. All these conditions are critical for the denitrification process.…”

In situ groundwater remediation treatments : natural denitrification study and nano zero valent iron production

“…Ribas, D., Calderer, M., Martí, V., & Rovira, M. (2015). Effect of different seasonal conditions on the potential of wetland soils for groundwater denitrification.…”