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Understanding the different carbon sources sustaining nitrate reduction processes
Understanding the different carbon sources sustaining nitrate reduction processes
Introduction
Currently, nitrogen loads in natural waters remain high, particularly in inhabited and agricultural areas. This stoichiometric imbalance, especially concerning phosphorus, can have serious repercussions on ecosystems. Nitrate reduction is therefore a crucial step in the nitrogen cycle, essential for maintaining water quality and supporting biodiversity in aquatic and terrestrial ecosystems. Intertidal and submerged sediments play a significant role in mitigating elevated nitrogen levels in water by facilitating nitrate reduction through the metabolism of heterotrophic microbes. Among the microbial processes involved in this nitrate reduction, some rely on the use of organic carbon, providing the energy necessary for converting inorganic nitrogen, potentially leading to the complete removal of nitrate from the system. This includes denitrification, a key process in the breakdown of nitrogen compounds in aquatic and wetland environments.
However, carbon sources, primarily of plant origin, vary, and we do not fully understand the specific impact of organic carbon source quality these bacterial processes. Therefore, a part of my research has aimed to investigate how different sources of organic carbon impact these processes.
In the context previously outlined in the introduction, one of my research projects focused on the impact of microphytobenthos and their extracellular polymeric substances (EPS) as a source of organic carbon on nitrate reduction processes in intertidal sediments.
The findings revealed that microphytobenthos, particularly their secretion of labile extracellular polymeric substances, significantly increased nitrate reduction rates, confirming their role as a carbon substrate for nitrate reduction. Furthermore, the results suggest that these carbon sources promote complete denitrification, converting nitrogen to its gaseous form, which is ecologically desirable.
The results of this study were published in the journal 'Estuarine, Coastal and Shelf Science' in 2022. Access to the paper
Building on previous findings, we also investigated the influence of different wetland plant types on nitrate reduction processes in intertidal sediment.
Our study revealed that, unlike microphytobenthos which initially caused a significant increase in nitrate reduction rates but rapidly depleted due to its labile nature, organic carbon derived from wetland plants exhibited a delayed yet sustained enhancement in nitrate reduction rates. These results underscore the importance of both labile and recalcitrant carbon sources in sediments to effectively support the nitrogen biogeochemical cycle
The results were published in the journal 'Wetlands' in 2023. Access to the paper
Understanding the effect of wetlands water level management on nitrate reduction processes
Understanding the effect of wetlands water level management on nitrate reduction processes
Beyond the impact of organic carbon highlighted previously, other factors influence nitrate reduction in sediments. One such crucial aspect is the management of water levels in wetland areas, which can play a pivotal role in this ecological function. In this context, one of my research aims was to evaluate, in situ, how water level management impact the nitrate reduction capacity of wetland sediments.
Our findings reveal that permanent immersion of wetlands and water retention promote the supply of additional organic carbon sustaining nitrate reduction. However, with permanent immersion mainly occurring in winter, low temperatures limited bacterial activities. In contrast, in summer, despite favorable temperatures, intermittent immersion limited the supply of carbon necessary to support these processes. These results highlight the need for an integrated management approach to sustain ecological functions in managed wetlands.
Results were published in the journal 'Science of The Total Environment' in 2024. Access to the paper
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