Abstract
Nitrate pollution remains an unsolved issue worldwide, causing serious effects on water quality and eutrophication of freshwater and brackish water environments. Its economic costs are still underestimated. To reduce nitrogen excess, constructed wetlands are usually recognized as a solution but, in recent years, interest has been raised in the role of ditches and canals in nitrogen removal. In this study, we investigated the environmental and economical sustainability of nitrogen removal capacity, using as a model study a lowland agricultural sub-basin of the Po River (Northern Italy), where the role of aquatic vegetation and related microbial processes on the mitigation of nitrate pollution has been extensively studied. Based on the Life Cycle Assessment (LCA) approach and costs and benefits analysis (CBA), the effectiveness of two different scenarios of vegetation management, which differ for the timing of mowing, have been compared concerning the nitrogen removal via denitrification and other terms of environmental sustainability. The results highlighted that postponing the mowing to the end of the vegetative season would contribute to buffering up to 90% of the nitrogen load conveyed by the canal network during the irrigation period and would reduce by an order of magnitude the costs of eutrophication potential.
Highlights
A vast body of literature exists on the positive role of aquatic vegetation and in particular of emergent macrophytes, such as common reed (Phragmites australis) and cattail (Typha latifolia), in contrasting eutrophication and nitrogen (N) pollution [1,2]
To deepen the analysis of the conservative management of aquatic vegetation, we have investigated its economical and environmental sustainability by the means of a costs and benefits analysis based on Life Cycle Assessment (LCA)
The mowing of aquatic vegetation in the canal network determines the loss of multiple interfaces in water and benthic compartments representing active denitrification hotspots responsible for the canal depuration capacity against NO3 − [3,8,11]
Summary
A vast body of literature exists on the positive role of aquatic vegetation and in particular of emergent macrophytes, such as common reed (Phragmites australis) and cattail (Typha latifolia), in contrasting eutrophication and nitrogen (N) pollution [1,2]. The most relevant mechanism involved in nitrate (NO3 − ) removal is denitrification, the reduction of NO3 − to nitrogen gas (N2 ), operated by bacteria under anaerobic conditions. It is considered as the most relevant biogeochemical process responsible globally for the permanent removal of anthropogenic reactive N along the terrestrial–freshwater–estuarine continuum [9,10]. Canal networks are ubiquitous elements of agricultural watersheds, the acquisition of experimental evidence about their high NO3 − mitigation potential, especially if vegetated, is so recent In the specific case of the macrophytes–bacteria consortium, denitrification was demonstrated to occur quantitatively within the biofilms, which cover the submerged stems and leaves of emergent macrophytes [11,12].
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