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Existing models often face limitations in the understanding and prediction of nitrate nitrogen (NO 3 − -N) concentrations in karst groundwater. In this study, to tackle this issue, a Gaussian function model was coupled with the Groundwater Modeling System (GMS) to simulate NO 3 − -N concentration changes in the southwest karst wetland of China. Additionally, fluorescence spectroscopy was employed to measure dissolved organic matter (DOM) components in the groundwater, providing insights into their variation and influence on NO 3 − -N dynamics. The results demonstrated that coupling the Gaussian curve fitting method with the GMS model accurately simulated NO 3 − -N concentration changes in the study area. The simulation revealed lower NO 3 − -N levels in the northern region, with higher concentrations in the central area, peaking at 20.73 mg/L at lower elevations. NO 3 − -N was primarily distributed in the southwestern region and upper Mudong Lake, exhibiting a diffusion trend from west to east. DOM analysis indicated significant autochthonous contributions, particularly microbial metabolic by-products. The total fluorescence intensity and DOM components increased downstream, with the lowest values at the source and the highest values at river confluences. The humification index (HIX) was correlated with NO 3 − -N concentrations, where lower NO 3 − -N levels corresponded to lower HIX values, and higher NO 3 − -N levels corresponded to higher HIX values. In conclusion, this study provides valuable insights into NO 3 − -N prediction in groundwater and the role of DOM, offering a reference for groundwater protection in the southwest China karst basin.

Plastic film (FM) and gravel mulching (GM) have been used extensively to increase dryland agricultural productivity. Understanding mulching effects on nitrogen (N) use efficiency (NUE) and soil nitrogen dynamics is important for optimizing N management strategies. A 3-year field experiment was performed on the Loess Plateau of China to investigate the GM and FM effects on plant N accumulation, N translocation, N harvest index (NHI), NUE and soil NO₃⁻-N dynamics in dryland maize fields. Compared with the control (CK, non-mulching), the mulching treatments markedly promoted plant N accumulation and especially maintained higher N uptake rates during the post-silking stage. At harvest, the total N accumulation was 12.8–41.2 and 33.2–55.8 % higher in the GM and FM treatments, respectively, than in the CK treatment. The NHIs of the mulching treatments were significantly higher by 9.6–32.4 % than the CK treatment, primarily due to greater N translocation and N accumulation post-silking. Overall, compared with the CK treatment, the GM and FM NUEs increased significantly by 17.1 and 28.3 % in 2010, 70.3 and 87.6 % in 2011, and 16.7 and 38.2 % in 2012, respectively. In the wet years of 2010 and 2011, the increased amount of soil NO₃⁻-N in the 100–200 cm layer after harvest was 27.1–57.1 and 47.9–85.7 % lower in the GM and FM treatments, respectively, than in the CK treatment, indicating a lower NO₃⁻-N leaching loss. These results suggest that mulching (especially FM) is an effective measure for increasing NUE and grain yield and decreasing N leaching loss in dry farmland.

Nitrogen pollution in wastewater causes environmental and health issues, prompting regulations on nitrogen discharge. While traditional biological treatment converts nitrogen to dinitrogen gas, it requires substantial resources. Alternatively, recuperating nitrogen for fertilizers could mitigate resource demands. This study optimized plant and system design for nitrogen recovery from aquaculture wastewater using aquaponics. Five plant species—money plant (Epipremnum aureum), crotons (Codiaeum varigatum), arrowhead (Syngonium podophyllum), purple head plant (Tradescantia pallida), and brinjal (Solanum melongena) were screened for their ability to efficiently remove nitrate from aquaculture effluent in aquaponic systems. Their biochemical oxygen demand (BOD) removal efficiencies were also studied. The money plant showed superior biochemical oxygen demand (BOD) removal efficiency at 71.07%, indicating its potential as a BOD sink due to enhanced microbial activity in roots. The results also showed significant differences among species for nitrate extraction, with the money plant exhibiting the highest average nitrate-nitrogen removal efficiency at 78.92 ± 0.834%, surpassing crotons (73.6 ± 2.09%), arrowhead plant (73.07 ± 0.83%), purple heart plant (74.48 ± 0.9%), and brinjal (71.56 ± 1.54%). Optimal operational conditions were also determined. The results demonstrate that the selected plant species effectively maintained suitable water quality parameters for aquaponics cultivation, highlighting their potentials in treating aquaculture effluent. The findings provide valuable insights into selecting plants and engineering parameters to enhance aquaponics efficiency for sustainable wastewater and nutrient reuse.

Soil nitrate–nitrogen (NO3−-N) is one of the primary factors used to control nitrogen topdressing application during the crop growth period. The ion-selective electrode (ISE) is a promising method for rapid lower-cost in-field detection. Due to the simplification of sample preparation, the accuracy and stability of ISE-based in-field detection is doubted. In this paper, a self-designed prototype system for on-site soil NO3−-N detection was developed. The procedure of spinning centrifugation was used to avoid interference from soil slurry suspension. A modified Nernstian prediction model was quantitatively characterized with outputs from both the ISE and the soil moisture sensor. The measurement accuracy of the sensor fusion model was comparable with the laboratory ISE detections with standard sample pretreatment. Compared with the standard spectrometric method, the average absolute error (AE) and root-mean-square error (RMSE) were found to be less than 4.7 and 6.1 mg/L, respectively. The on-site soil testing efficiency was 4–5 min/sample, which reduced the operation time by 60% compared with manual sample preparation. The on-site soil NO3−-N status was dynamically monitored for 42 consecutive days. The declining peak of NO3−-N was observed. In all, the designed ISE-based detection system demonstrated a promising capability for the dynamic on-site monitoring of soil macronutrients.

Groundwater nitrate-nitrogen contamination typically involves several natural and anthropogenic factors, including those related to hydrology, hydrogeology, topography, and land use (LU). DRASTIC-LU-based aquifer contamination vulnerability could be used to characterize the pollution potentials of groundwater nitrate-nitrogen and to determine groundwater protection zones. This study used regression kriging (RK) with environmental auxiliary information on DRASTIC-LU-based aquifer contamination vulnerability to investigate groundwater nitrate-nitrogen pollution in the Pingtung Plain of Taiwan. First, the relationship between groundwater nitrate-nitrogen pollution and assessments of aquifer contamination vulnerability was determined using stepwise multivariate linear regression (MLR). Subsequently, the residuals between the nitrate-nitrogen observations and MLR predictions were estimated by kriging techniques. Finally, the groundwater nitrate-nitrogen distributions were spatially analyzed using RK, ordinary kriging (OK), and MLR. The findings indicated that the land used for orchards and the medium- and coarse-sand fractions of vadose zones were associated with groundwater nitrate-nitrogen concentrations. The fertilizer used for orchards was identified as the primary source of groundwater nitrate-nitrogen pollution. The RK estimates could be used to analyze the characteristics of the pollution source for land used for orchards and exhibited high spatial variability and accuracy after residual correction. Moreover, RK had an excellent estimate ability for extreme data compared to MLR and OK. Correctly determining groundwater nitrate-nitrogen distributions using RK was useful for administering environmental resources and preventing public health hazards.

Monitoring of drinking water has shown an increase in nitrate-nitrogen (NO ₃ ⁻ -N) concentration in groundwater in some areas of the Heihe River Basin, Northwest China. A combination of careful irrigation and nitrogen (N) management is needed to improve N uptake efficiency and to minimize fertilizer N loss. A 2-year experiment investigated the effects of different irrigation and N application rates on soil NO ₃ ⁻ -N distribution and fertilizer N loss, wheat grain yield and N uptake on recently reclaimed sandy farmland. The experiment followed a completely randomized split-plot design, taking flood irrigation (0.6, 0.8 and 1.0 of the estimated evapotranspiration) as main plot treatment and N-supply as split-plot treatment (with five levels of 0, 79, 140, 221, 300 kg N ha⁻¹). Fertilizer N loss was calculated according to N balance equation. Our results showed that, under deficit irrigation conditions, N fertilizer application at a rate of 300 kg ha⁻¹ promoted NO ₃ ⁻ -N concentration in 0-200 cm depth soil profiles, and treatments with 221 kg N ha⁻¹ also increased soil NO ₃ ⁻ -N concentrations only in the surface layers. Fertilizer N rates of 70 and 140 kg ha⁻¹ did not increase NO ₃ ⁻ -N concentration in the 0-200 cm soil profile remaining after the spring wheat growing season. The amount of residual NO ₃ ⁻ -N in soil profiles decreased with the amount of irrigation. Compared with N₀, the increases of fertilizer N loss, in N₇₉, N₁₄₀, N₂₂₁ and N₃₀₀ respectively, were 59.9, 104.6, 143.5 and 210.6 kg ha⁻¹ over 2 years. Under these experimental conditions, a N rate of 221 kg ha⁻¹ obtained the highest values of grain yield (2775 kg ha⁻¹), above-ground dry matter (5310 kg ha⁻¹) and plant N uptake (103.8 kg ha⁻¹) over 2 years. The results clearly showed that the relative high grain yield and irrigation water productivity, and relative low N loss were achieved with application of 221 kg N ha⁻¹ and low irrigation, the recommendation should be for those farmers who use the upper range of the recommended 150-400 kg N ha⁻¹, that they can save about 45% of their N and 40% of their irrigation water application.

This study investigated the effects of nitrogen form on root activity and nitrogen uptake kinetics of Camellia oleifera Abel. seedlings, providing a scientific basis for improving nitrogen use efficiency and scientific fertilization in C. oleifera production. Taking one-year-old C. oleifera cultivar ‘Xianglin 27’ seedlings as subjects, 8 mmol·L−1 of nitrogen in varied forms (NO3−:NH4+ = 0:0, 10:0, 7:3, 5:5, 3:7, 0:10) was applied in this study as the treatment conditions to investigate the effects of different nitrogen forms on root activity and nitrogen uptake kinetics in C. oleifera seedlings. Comparing the performance of nutrient solutions with different NO3−:NH4+ ratios, the results showed that a mixed nitrogen source improved the root activity of C. oleifera seedlings based on total absorption area, active absorption area, active absorption area ratio, specific surface area, and active specific surface area. When NO3−:NH4+ = 5:5, the total absorption area and active absorption area of the seedling roots reached the maximum. The results of uptake kinetic parameters showed that Vmax NH4+ > Vmax NO3− and Km NO3− > Km NH4+, indicating that the uptake potential of ammonium–nitrogen by C. oleifera seedlings is greater than that of nitrate–nitrogen. The conclusion was that compared to either ammonium– or nitrate–nitrogen, the mixed nitrogen source was better for promoting the root activity of C. oleifera seedlings, and the best nitrate/ammonium ratio was 5:5.

Excessive fertilizer application, majorly nitrogen- and phosphorus-based fertilizers, in farmland has intensified environmental pollution of rivers, lakes, and other surface water bodies worldwide by agricultural non-point sources, especially the highly-mobile nitrogen. To solve nitrogen pollution in sugarcane areas, exploring the nitrogen output characteristics of agricultural watersheds in crop fields becomes necessary. Therefore, the objective of the study was to evaluate the characteristics of nitrogen output during typical rainfall events in different sugarcane growth stages in a southern tropical watershed in China. Dynamic monitoring of runoff and nitrogen concentration was carried out for four rainfall events and compared among four sugarcane growth stages (Establishment; Vegetative growth; Grand growth; Ripening) during the growing season of 2018 in the Nala watershed, Kelan Reservoir, Guangxi, China. The results showed that the total dissolved nitrogen flux of the 4 rainfall events ranged from 0.08 to 9.88 kg·hm−2 for the different growth stages. Nitrate nitrogen was the main component of the total flux, accounting between 75.7 and 92.1% of the total dissolved nitrogen while ammonium nitrogen accounted between 1.80 and 5.26% of the total flux for the 4 rainfall events. Total dissolved nitrogen and nitrate-nitrogen were significantly and negatively correlated with runoff (p < 0.05), while total dissolved nitrogen concentration did not correlate with runoff. The incipient scouring effect of total dissolved nitrogen and nitrate-nitrogen was not noticeable. The concentration of total dissolved nitrogen in the Nala watershed was inferior to class V water quality standard, indicating water eutrophication danger. The study showed that nitrogen nutrient inflow into the river was promoted by N-fertilization time and rainfall. Therefore, reasonably reducing N-fertilization dose and post-rain fertilization could effectively reduce nitrogen inflow into rivers and avoid the intensification of eutrophication in sugarcane areas. We recommend multiple years of studies to verify the possible impacts of differences in weather conditions.

The World Health Organization (WHO) and the U.S. Environmental Protection Agency (EPA) provide guidelines on the maximum levels of nitrate nitrogen (NO3-N) contained in drinking water since excess nitrate ingestion may harm human health. Thus, monitoring and controlling the NO3-N concentration is of paramount importance, especially in sources of drinking water such as the Nakdong River in South Korea. This study addresses NO3-N pollution in the Nakdong River in South Korea, where such pollution mostly comes from diffuse sources in the catchment due to the agricultural use of fertilizers. The objective of this study is to suggest guidelines for designing strategies to control NO3-N in this river using a process-based model developed with HEC-RAS. The model was built based on water quality parameters (water temperature, dissolved oxygen, ammonia nitrogen, etc.) related to NO3-N dynamics incorporating hydraulic and meteorological data. This model simulated NO3-N dynamics downstream under 55 scenarios while focusing on a section near locations of drinking water intakes. The scenarios were constructed based on variations in water quantity and quality upstream. The simulation results showed that the peak concentration of NO3-N downstream could be directly controlled by limiting the NO3-N concentration upstream. Additionally, control of the flow rate upstream could also lead to a reduction in the overall average concentration of NO3-N downstream, but this predominantly occurred when the NO3-N concentration was decreasing. In conclusion, the design and implementation of strategies for the control of NO3-N downstream should be carried out after performing a quantitative analysis of the impact of different control measures for different downstream conditions using a water quality model.

Impacts of land use changes and groundwater management actions on groundwater quality were evaluated at the island scale with spatiotemporal trends of NO 3 -N and Cl concentrations in groundwater of Jeju Island, Korea. The temporal trends from 1993 to 2012 in the concentrations of NO 3 -N and Cl from more than 3900 wells were estimated using the Mann–Kendall trend test and Sen’s slope analysis and compared with the land use change trend for the period 1995–2009. The results indicate that the upward trends in NO 3 -N were associated with the expansion of agricultural lands, whereas Cl trends were considered to be affected by other factors in addition to the land use changes. In the mid-mountainous region, the deterioration in the groundwater quality by the both NO 3 -N and Cl was expected due to the continuous expansion of agricultural lands. In the lowland area, the NO 3 -N and Cl components showed different trends depending on the regions. In the eastern area, increasing trends in NO 3 -N were observed due to the development of new agricultural areas, while the Cl concentration was observed to decrease as a result of the regulation on groundwater extraction to reduce seawater intrusion. Our study highlights that a comprehensive interpretation of trends in NO 3 -N and Cl and land use changes for long-term periods can provide useful insights to prepare for suitable groundwater management plans in the whole island perspective.