Special Issue "Nitrogen Removal in Agricultural Watersheds: Through Agricultural Practices and Phytodepuration"

A special issue of Water (ISSN 2073-4441). This special issue belongs to the section "Water Quality and Ecosystems".

Deadline for manuscript submissions: 30 June 2020.

Special Issue Editors

Prof. Dr. Giuseppe Castaldelli
Website
Guest Editor
Department of Life Science and Biotechnology, University of Ferrara, Via L. Borsari, 46, 44121 Ferrara, Italy
Interests: nitrogen cycling; eutrophication; sustainable agriculture; phytodepuration; aquatic ecosystem restoration
Dr. Elisa Soana
Website
Guest Editor
Department of Life Science and Biotechnology, University of Ferrara, Via L. Borsari, 46, 44121 Ferrara, Italy
Interests: nitrogen cycling; benthic metabolism; rhizosphere; denitrification; watershed nutrient budgets; eutrophication

Special Issue Information

Dear Colleagues,

In the last decades several studies from different disciplines have proven that the loss of reactive nitrogen from diffuse sources is one of the most serious threats to superficial and groundwater quality in industrialized and emerging countries, with multiple detrimental impacts on both ecosystems and human health. Notwithstanding this, eutrophication and groundwater nitrate contamination remain an unsolved issue and directives and international agreements have mostly failed to achieve the proposed amelioration goals.

The high performance of modern agriculture has been boosted by enhancing the amount of nitrogen fertilizer and the efficiency of irrigation. The latter has been made possible through the hydraulic streamlining of more and more ecologically simplified canal networks. In most cases, this has corresponded to the quantitative removal of aquatic vegetation and thus the loss of related ecosystem services, such as nitrogen removal via denitrification. On this view, it is not too speculative to hypothesize cascading effects to transitional and coastal zones, often underestimated or not considered at all, due to the reduction of denitrification capacity at the catchment scale.

To promote effective nitrogen excess mitigation strategies, we have to reconsider both the pathways of nitrogen load generation in watersheds and the buffer mechanisms in hydraulic networks. There are open questions concerning the parameters regulating denitrification in soil–aquifer systems, relative measurement methods, and the parameters regulating N removal via denitrification through microorganism–plant interactions in aquatic environments (i.e. drainage networks, wetlands, lagoons).

The general aim of this Special Issue is thus to add experimental and synthesised knowledge on the regulation of buffering capacity against nitrogen loads, both in groundwater and superficial waters. This calls for thematic and multidisciplinary contributions from a wide range of disciplines (e.g. biogeochemistry, hydrogeology, agronomy, engineering, environmental sciences, economy, etc.) focused on the following topics: regulation and parametrization of depuration capacity in drainage networks and its integration with modern canal management; insights on nitrogen retention/removal mechanisms in soil–aquifer systems, in relation to the specificity of hydrological regimes and agricultural and irrigation practices; economic analysis of the above-cited phenomena, with reference to eutrophication effects in terminal water bodies.

Prof. Dr. Giuseppe Castaldelli
Dr. Elisa Soana
Guest Editors

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Keywords

  • Agricultural watersheds
  • Nitrate pollution
  • N retention
  • Drainage networks
  • Aquatic vegetation

Published Papers (7 papers)

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Research

Open AccessArticle
Effects of Changing Fertilization since the 1980s on Nitrogen Runoff and Leaching in Rice–Wheat Rotation Systems, Taihu Lake Basin
Water 2020, 12(3), 886; https://doi.org/10.3390/w12030886 - 21 Mar 2020
Abstract
The nitrogen (N) loss associated with intensive agricultural activities is a significant cause of eutrophication and algal blooms in freshwater ecosystems. Taihu Lake has experienced serious surface water quality deterioration and eutrophication problems since the 1980s. The objective of this study is to [...] Read more.
The nitrogen (N) loss associated with intensive agricultural activities is a significant cause of eutrophication and algal blooms in freshwater ecosystems. Taihu Lake has experienced serious surface water quality deterioration and eutrophication problems since the 1980s. The objective of this study is to examine the effect of fertilization changes since the 1980s on the N loss with runoff and leaching in the rice–wheat cropping rotation system. According to the results published in the literature since the 1980s, we set up four fertilization scenarios—N1980s: a fertilization rate of 350 kg N·ha−1·year−1 with 30% in manure fertilization to simulate fertilization in the 1980s; NA1990s: a fertilization rate of 500 kg N·ha−1·year−1 with 10% in manure fertilization to simulate fertilization in the early 1990s; NL1990s: fertilization rate of 600 kg N·ha−1·year−1 with 10% in manure fertilization to simulate fertilization in the late 1990s; and N2000s: fertilization rate of 550 kg N·ha−1·year−1 with all chemicals to simulate fertilization in the 2000s. Then, we calibrated and validated the DNDC (denitrification–decomposition) model through field experiments in two rice–wheat rotation seasons from November 2011 to October 2013 and simulated the N loss with runoff and leaching since the 1980s. The results show that N losses with leaching in the four periods (N 1980s, NA1990s, NL1990s, and N2000s) were 5.2 ± 2.1, 9.4 ± 3.2, 14.4 ± 4.6 and 13.5 ± 4.6 kg N·ha−1·year−1, respectively. N losses with surface runoff were 7.9 ± 3.9, 18.3 ± 7.2, 25.4 ± 10.2, and 26.5 ± 10.6 kg N·ha−1·year−1, respectively. The total N loss through runoff and leaching showed an increasing trend from 1980 to the late 1990s, when it reached its peak. The increase in N export to water due to fertilizer application occurs mainly during the rainy season from March to August, and especially from June to August, when rainfall events and intensive rice fertilization activities are frequent. After the 1990s, when the fertilizer rate was above 500 kg N·ha−1·year−1, the crop yields no longer increased significantly, which indicates that the optimized fertilization rate to balance crop yields and N loss to water is lower than 500 kg N·ha−1·year−1. The increase in fertilizer use has been unnecessary since the early 1990s, and at least about 30% of the N loss could have been prevented without reducing crop yields. Full article
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Open AccessArticle
Vegetated Ditch Habitats Provide Net Nitrogen Sink and Phosphorus Storage Capacity in Agricultural Drainage Networks Despite Senescent Plant Leaching
Water 2020, 12(3), 875; https://doi.org/10.3390/w12030875 - 20 Mar 2020
Abstract
The utility of vegetated ditch environments as nutrient sinks in agricultural watersheds is dependent in part on biogeochemical transformations that control plant uptake and release during decomposition. We investigated nitrogen (N) and phosphorus (P) uptake and release across four P enrichment treatments in [...] Read more.
The utility of vegetated ditch environments as nutrient sinks in agricultural watersheds is dependent in part on biogeochemical transformations that control plant uptake and release during decomposition. We investigated nitrogen (N) and phosphorus (P) uptake and release across four P enrichment treatments in ditch mesocosms planted with rice cutgrass (Leersia oryzoides) during the summer growing and winter decomposition seasons. Measured N retention and modeled denitrification rates did not vary, but P retention significantly increased with P enrichment. At the end of the growing season, root biomass stored significantly more N and P than aboveground stem and leaf biomass. Decomposition rates were low (<10% organic matter loss) and not affected by P enrichment. Nitrogen and P export during winter did not vary across the P enrichment gradient. Export accounted for <10% of observed summer N uptake (1363 mg m−2), with denitrification potentially accounting for at least 40% of retained N. In contrast, net P retention was dependent on enrichment; in unenriched mesocosms, P uptake and release were balanced (only 25% net retention), whereas net retention increased from 77% to 88% with increasing P enrichment. Our results indicate that vegetated ditch environments have significant potential to serve as denitrification sinks, while also storing excess P in agricultural watersheds. Full article
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Open AccessFeature PaperCommunication
Combining Tools from Edge-of-Field to In-Stream to Attenuate Reactive Nitrogen along Small Agricultural Waterways
Water 2020, 12(2), 383; https://doi.org/10.3390/w12020383 - 31 Jan 2020
Abstract
Reducing excessive reactive nitrogen (N) in agricultural waterways is a major challenge for freshwater managers and landowners. Effective solutions require the use of multiple and combined N attenuation tools, targeted along small ditches and streams. We present a visual framework to guide novel [...] Read more.
Reducing excessive reactive nitrogen (N) in agricultural waterways is a major challenge for freshwater managers and landowners. Effective solutions require the use of multiple and combined N attenuation tools, targeted along small ditches and streams. We present a visual framework to guide novel applications of ‘tool stacking’ that include edge-of-field and waterway-based options targeting N delivery pathways, timing, and impacts in the receiving environment (i.e., changes in concentration or load). Implementing tools at multiple locations and scales using a ‘toolbox’ approach will better leverage key hydrological and biogeochemical processes for N attenuation (e.g., water retention, infiltration and filtering, contact with organic soils and microbes, and denitrification), in addition to enhancing ecological benefits to waterways. Our framework applies primarily to temperate or warmer climates, since cold temperatures and freeze–thaw-related processes limit biologically mediated N attenuation in cold climates. Moreover, we encourage scientists and managers to codevelop N attenuation toolboxes with farmers, since implementation will require tailored fits to local hydrological, social, and productive landscapes. Generating further knowledge around N attenuation tool stacking in different climates and landscape contexts will advance management actions to attenuate agricultural catchment N. Understanding how different tools can be best combined to target key contaminant transport pathways and create activated zones of attenuation along and within small agricultural waterways will be essential. Full article
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Open AccessArticle
A Mass Balance of Nitrogen in a Large Lowland River (Elbe, Germany)
Water 2019, 11(11), 2383; https://doi.org/10.3390/w11112383 - 14 Nov 2019
Abstract
Nitrogen (N) delivered by rivers causes severe eutrophication in many coastal waters, and its turnover and retention are therefore of major interest. We set up a mass balance along a 582 km river section of a large, N-rich lowland river to quantify N [...] Read more.
Nitrogen (N) delivered by rivers causes severe eutrophication in many coastal waters, and its turnover and retention are therefore of major interest. We set up a mass balance along a 582 km river section of a large, N-rich lowland river to quantify N retention along this river segment and to identify the underlying processes. Our assessments are based on four Lagrangian sampling campaigns performed between 2011 and 2013. Water quality data served as a basis for calculations of N retention, while chlorophyll-a and zooplankton counts were used to quantify the respective primary and secondary transformations of dissolved inorganic N into biomass. The mass balance revealed an average N retention of 17 mg N m−2 h−1 for both nitrate N (NO3–N) and total N (TN). Stoichiometric estimates of the assimilative N uptake revealed that, although NO3–N retention was associated with high phytoplankton assimilation, only a maximum of 53% of NO3–N retention could be attributed to net algal assimilation. The high TN retention rates in turn were most probably caused by a combination of seston deposition and denitrification. The studied river segment acts as a TN sink by retaining almost 30% of the TN inputs, which shows that large rivers can contribute considerably to N retention during downstream transport. Full article
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Open AccessArticle
Is Flood Irrigation a Potential Driver of River-Groundwater Interactions and Diffuse Nitrate Pollution in Agricultural Watersheds?
Water 2019, 11(11), 2304; https://doi.org/10.3390/w11112304 - 03 Nov 2019
Abstract
In the Po plain, northern Italy, rivers within agricultural basins display steep summer increases in nitrate (NO3) concentrations. Flood irrigation in overfertilized, permeable soils may drive such diffuse pollution, facilitating interactions between NO3-rich groundwater and surface waters. [...] Read more.
In the Po plain, northern Italy, rivers within agricultural basins display steep summer increases in nitrate (NO3) concentrations. Flood irrigation in overfertilized, permeable soils may drive such diffuse pollution, facilitating interactions between NO3-rich groundwater and surface waters. We discuss multiple, indirect evidence of this mechanism in the Adda, Oglio, and Mincio rivers. These rivers drain agricultural soils with elevated nitrogen (N) surpluses, averaging 139, 193, and 136 kg ha−1 in the Adda, Oglio, and Mincio watersheds, respectively. The three rivers cross a transitional area between highly permeable and impermeable soils, where summer NO3 concentrations may increase by one order of magnitude over short distances (8–20 km). Upstream of this transitional area, a major fraction of the river flow is diverted for flood irrigation, a traditional and widespread irrigation technique for permeable soils. We speculate that diverted water solubilizes soil N excess, recharges the aquifer, and transfers soil N surplus into groundwater, resulting in NO3 pollution. Groundwater–river interactions were estimated experimentally, via water and NO3 budgets in 0.3 to 1 m3 s−1 km−1 and in 1500 to 5400 kg NO3–N day−1. The data suggest a pronounced east–west gradient of groundwater to river diffuse water inputs among the three adjacent basins, reflecting the soil permeability and the width of the river–groundwater interaction zone. Given the large stock of NO3 in groundwater, management interventions performed at the basin scale and aimed at decreasing N excess will not produce an immediate decrease in river NO3 pollution. Full article
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Open AccessArticle
Enhancement of Agricultural Policy/Environment eXtender (APEX) Model to Assess Effectiveness of WetlandWater Quality Functions
Water 2019, 11(3), 606; https://doi.org/10.3390/w11030606 - 23 Mar 2019
Cited by 2
Abstract
The Agricultural Policy/Environmental eXtender (APEX) model has been widely used to assess changes in agrochemical loadings in response to conservation and management led by US Department of Agriculture (USDA). However, the existing APEX model is limited in quantification of wetland water quality functions. [...] Read more.
The Agricultural Policy/Environmental eXtender (APEX) model has been widely used to assess changes in agrochemical loadings in response to conservation and management led by US Department of Agriculture (USDA). However, the existing APEX model is limited in quantification of wetland water quality functions. This study improved the current model capacity to represent wetland water quality functions by addition of a new biogeochemical module into the APEX model. The performance of an enhanced APEX model was tested against five observed outgoing water quality variables (e.g., sediment, organic N, NO3, NH4 and PO4) from a wetland within the Eastern Shore of Maryland. Generalized Likelihood Uncertainty Estimation (GLUE) was implemented to assess model uncertainty. The enhanced APEX model demonstrated that it could effectively represent N and P cycling within the study wetland. Although improvement of model performance was limited, the additions of wetland biogeochemical routines to the APEX model improved our understanding of inner mass exchanges within N and P cycling for the study wetland. Overall, the updated APEX model can provide policymakers and managers with improved means for assessment of benefits delivered by wetland conservation. Full article
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Open AccessArticle
Cover Crops and Landscape Position Effects on Nitrogen Dynamics in Plant-Soil-Water Pools
Water 2019, 11(3), 513; https://doi.org/10.3390/w11030513 - 12 Mar 2019
Cited by 3
Abstract
Nitrogen dynamics and water quality benefits deriving from the use of cover crops (CCs) are mostly incurred from plot-scale studies without incorporating large-scale variability that is induced by landscape positions. Our understanding of how topography affects the N response in CC systems is [...] Read more.
Nitrogen dynamics and water quality benefits deriving from the use of cover crops (CCs) are mostly incurred from plot-scale studies without incorporating large-scale variability that is induced by landscape positions. Our understanding of how topography affects the N response in CC systems is limited. The objectives of this study were to evaluate the effects of topography (shoulder, backslope, and footslope) and CCs (cereal rye, Secale cereale L. and hairy vetch, Vicia villosa L.) on nitrogen (N) uptake, soil inorganic N content (nitrate-N, NO3-N and total N, TN), and N leaching in watersheds that were planted with or without CCs. The crop rotation in CC watersheds was corn (Zea mays L.)-cereal rye-soybean (Glycine max L.)-hairy vetch whereas control watersheds had corn-no CC-soybean-no CC rotation. Data from the watersheds was collected for three cash crop seasons and three CC seasons from 2015 to 2018. Nitrogen uptake of hairy vetch in CC watersheds was 110.9, 85.02, and 44.89 kg ha−1 higher at the shoulder, backslope, and footslope positions, when compared to shoulder, backslope, and footslope positions of no CC watersheds. About 12 to 69% reduction in soil solution NO3-N and TN was observed with cereal rye CC when compared to no CCs watersheds. However, reductions in soil solution N concentrations were only seen at the footslope position where the hairy vetch reduced NO3-N and TN concentrations by 7.71 and 8.14 mg L−1 in CC watersheds compared to no CC watersheds. During the corn and soybean growing seasons, similar reductions in soil solution N concentration were only seen at the footslope position in the CC watersheds. The excessive N at footslope positions of CC watersheds may have been fixed in CC biomass, immobilized, or lost through denitrification stimulated by higher water availability at the footslope position. The results of this research can help farmers and stakeholders to make decisions that are site-specific and topographically driven for the management of CCs in row-cropped systems. Full article
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