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Volume 2021 |Article ID 9957731 | https://doi.org/10.1155/2021/9957731

Yuxian Hu, Ke Zhang, Yuan Li, Yanan Sun, Hongyan Li, Gaiqiang Yang, "Human Activities Increase the Nitrogen in Surface Water on the Eastern Loess Plateau", Geofluids, vol. 2021, Article ID 9957731, 9 pages, 2021. https://doi.org/10.1155/2021/9957731

Human Activities Increase the Nitrogen in Surface Water on the Eastern Loess Plateau

Academic Editor: Yi Xue
Received25 Mar 2021
Revised30 Apr 2021
Accepted18 May 2021
Published01 Jun 2021

Abstract

Human activities have greatly accelerated the input of nitrogen into waters, resulting in water quality degradation. Facing the water crisis of nitrogen pollution, the state of surface water in arid areas needs close attention. Although numerous studies have indicated that waters’ nitrogen is often impacted by land use covers, the correlation between the two remains obscure. This paper explored the spatial relationship between anthropogenic activity and waters’ nitrogen on the eastern Loess Plateau, based on the Geographic Information System (GIS) spatial analysis using land use covers. There were 3 human land use types and 2 nitrogen indices used to assess the rivers’ state at the watershed scale. The results showed that rivers’ nitrogen was closely associated with human land use covers. Nitrogen pollution was most serious in urban areas. This study provided new evidence for the relationship between anthropogenic activities and river ecology. The findings may be helpful for policymakers to make strategic decisions of water resource management and land use planning in arid areas.

1. Introduction

Nitrogen (N) is one of the most important nutrients for ecosystem function and also a limiting factor for the productivity of many ecosystems in the world [1]. Nitrogen pollution can cause adverse ecological effects on the environment, including soil acidification, hypoxia, and subsequent fish death [2]. High concentration of nitrogen is the main factor leading to eutrophication of the water environment, resulting in the reduction of biodiversity and deterioration of water quality [3]. To make matters worse, some high levels of nitrogen forms in drinking water increase the risk of human disease [4]. How to make rational use of nitrogen and reduce the negative effects of nitrogen while meeting human needs has become a scientific challenge that human beings must solve in the 21st century [5].

About 99% of the global nitrogen is stable atmospheric nitrogen, which is not available to ecosystems unless it is converted into active nitrogen species, such as nitrate (NO3), nitrite (NO2), ammonia (NH3), and ammonium (NH4+), and organic nitrogen [6]. Through nitrogen fixation, plants make inorganic nitrogen exist in soil in the form of NO3, NO2, and ammonia nitrogen (NH3-N). Through rainfall erosion and surface runoff, inorganic nitrogen in soil migrates to water [7]. Biological nitrogen fixation can input 120 Tg N yr–1 nitrogen to the ecosystem [8]. Due to the nonuniformity of the spatial distribution of nitrogen flux, there are great differences in the nitrogen cycle in different regions of the world. Human beings enlarge the differences and make the process more complicated. Human activities have greatly accelerated the input of nitrogen into water, resulting in water quality degradation, including eutrophication, acidification, and nitrate pollution [915].

Anthropogenic nitrogen entering waters comes from industrial, municipal, residential, and agricultural sources [16]. Nitrogen deposition from fossil fuel combustion in the atmosphere is another important anthropogenic nitrogen source, which is discharged into surface water. Chemical inputs to water bodies are also classified by point sources (such as municipal wastewater treatment plants) and nonpoint sources (such as agricultural activities and atmospheric deposition). Annual nitrogen fixation from human sources has exceeded that from natural sources [17]. As time goes on, human activities increase the input of nitrogen into water. The nitrogen load of major rivers in the United States has increased [18]. It is expected that the nitrogen input into the water body will continue to increase all over the world. Kroeze and Seitzinger [19] predicted that by 2050, 90% of the dissolved inorganic nitrogen load in the world’s rivers will be anthropogenic.

The water quality of several major rivers in northern China, Huaihe River, Yellow River, Haihe River, Liaohe River, and Heilongjiang River, cannot meet the Class III standard of China’s surface water, plus China has large nitrogen fertilizer applications but lower nitrogen utilization efficiency, which greatly increases the nitrogen accumulation in waters [20]. Soil nitrogen may also increase because of the interference of human activities, such as the large amount of nitrogen fertilizer application in farmland and urban soil covered by impervious layers. Schlesinger [21] traced the final fate of 150 Tg nitrogen per year from human emissions. It was found that there was about 9 Tg N yr–1 nitrogen accumulating in the biosphere. Human activities have profoundly influenced the long-term dynamics of nitrogen concentrations in rivers, lakes, and aquifers worldwide. Under the disturbance of human activities, the reserves of terrestrial ecosystems may be increasing [22].

Land use/cover change (such as farmland expansion, afforestation, deforestation, urbanization, and industrialization) increases the vulnerability of the water ecosystem, which is an important way and response of human activities to the surface environment [23]. Nitrogen in industry, city, and people’s life mainly comes from sewage. Agricultural nitrogen fertilizers include fertilizers, nitrogen-fixing crops, human and animal excreta, and soil erosion caused by land use changes such as deforestation and grassland reclamation. Construction sites also contribute to nitrogen input into the water body [24]. Nitrogen concentration in surface water is strongly affected by land use in settlement areas, especially by agriculture [25]. Zhao and Huang [26] found that nitrate concentration decreased with the increase of woodland proportion. Changing a paddy field to dry land or construction land will increase water yield while changing a water area to a paddy field or dry land will reduce water yield. The transfer of land use to the surface with a high evaporation rate will reduce runoff [27]. Agricultural coverage explained the 69% variability of mean nitrate concentrations in the Mediterranean river basin during the 25 years (1981–2005) [28]. In fact, land use is always associated with fertilization (cropland) and soil erosion (conversion of natural vegetation to arable land), which increases the concentration of nitrogen in the rivers discharging disturbed catchments.

Land use change plays an extremely important role in the fields of ecological environment, climate change, and food production. It plays a very important role in maintaining biodiversity and water environment systems. Land use/cover has become the main cause of global change [29]. However, few studies focused on the spatial relationship between land use and waters’ nitrogen. In particular, the water ecosystem-based management in the arid areas lacked strong technical support. Here, we seek to develop a strategy to study the impact of human activities on surface water through a case study of a typical arid area in the Loess Plateau of northern China. Specifically, we analyzed the characteristics of different land use covers and waters’ nitrogen by adopting remote sensing and field investigation. Our results contribute to a better understanding of the ecological effects that anthropogenic activities have on different landscape configurations in the study area. This research will provide scientific guidance for water ecosystem management and regional sustainable development for maintaining ecological balance and regulating anthropogenic activities in arid areas.

2. Materials and Methods

2.1. Study Area

Loess covers about 10% of the earth’s land surface and lies in semiarid zones [30]. The Loess Plateau of China is located in the middle reach of the Yellow River in northwestern China [31]. The Loess Plateau (Figure 1(a)) is the most concentrated and largest loess area on the earth. The Loess Plateau is more than 1000 kilometers long from east to west and 750 kilometers wide, with a total area of . It is located on the second step of China, with an altitude of 800–3000 meters.

Lvliang City (Figure 1(b)) is located in the west of Loess Plateau and the west of Shanxi Province. It is located between a latitude of 36°43N and 38°43N and a longitude of 110°22E and 112°19E. The city basically belongs to the temperate continental monsoon climate zone, cold in winter and hot in summer, with four distinct seasons. The total area of the city is , and the average annual precipitation is only 472 mm. Lvliang has wide loess coverage, broken terrain, steep slope, less flat land, rare vegetation, and serious soil erosion.

2.2. Sampling Strategy
2.2.1. Sample Collection

The surface water samples were collected from 28 rivers in the Loess Plateau. The sampling time was from January to December 2019 (the dry and wet seasons), and the sampling frequency was tested once a month, which was from Yellow River and Fen River Basins. The details of the sampling sites are shown in Figure 1(b). The water samples were stored in 5.0 L polypropylene (PP) bottles, which were prewashed with the water samples 3 times before collection. All the samples were stored at 4°C for no more than 7 days before the analysis.

2.2.2. Sample Determination

We determined TN and NH3-N using the methods of potassium persulfate ultraviolet spectrophotometry and Nessler’s reagent colorimetry with reference to GB3838-2002. The standard of TN and NH3-N in this paper referred to the Class III standard value of surface water (1 mg L–1).

2.3. Data Statistics and Analyses

We conducted box plots to compare the spatiotemporal variations of nitrogen concentrations based on SigmaPlot 14.0 (Systat Inc., US). Data on human land use was collected from the Resource Environment Data Cloud Platform (http://www.resdc.cn/) and was accurate to 1 km. Considering the heterogeneous distribution of sampling scatters, inverse distance weighting (IDW) interpolation was used to evaluate the spatiotemporal distribution and density of nitrogen [32]. We predicted the spatial distributions of eutrophication and water quality state using Kriging interpolation based on ArcGIS 10.2 (ESRI Inc., US).

3. Results and Discussions

3.1. Spatial Variations of Nitrogen Concentrations

The spatial variations of nitrogen concentrations are shown in Table 1. The range of NH3-N is in 0.11–13.20 mg L–1 (mean ) and 0.10–34.10 mg L–1 (mean ) in Yellow River (YR) and Fen River (FR) Basins, respectively. The range of TN was in 2.09–22.30 mg L–1 (mean ) and 1.47–70.50 mg L–1 (mean ) in YR and FR, respectively. All the mean concentrations of NH3-N and TN (>1.0 mg L–1) exceeded the Class III standard of surface water (shorter form Class III). As shown in Figure 2, both NH3-N and TN in FR were higher than those in YR. The nitrogen in FR had more volatility than that in YR to the spatial distribution.


BasinNitrogen (mg/L)
NH3-NTN
MinimumMaximumMeanSDMinimumMaximumMeanSD

Yellow River0.1113.201.822.552.0922.3010.424.83
Fen River0.1034.104.285.911.4770.5017.4814.75

Lvliang is a hilly and ravine area with a shortage of water resources and inconvenient transportation and is relatively closed to external communication. The population is mostly concentrated in the small river basin near the two sides of Lvliang Mountain. Lots of studies have proved that agriculture (fertilizer), population, and industry increased nitrogen input in the river basin [33]. In the Yellow River Basin, most areas are rural land, and the industries in the basin are not well developed. Therefore, industrial wastewater does not have a major impact on nitrogen transportation. The nitrogen load is sufficiently impacted by fertilizer use and population growth. In addition, the wastewater and soil erosion in the Loess Plateau intensified the input and transportation of nutrients (phosphorus) [34]. The Lvliang area is the most serious area of soil erosion in the Yellow River Basin. Considering the western part of the FR basin is high and the eastern part is low, the pollutants in the west basin are easily spread in FR. Excess nitrogen is enriched in surface water, which can negatively affect water quality and cause eutrophication.

3.2. Temporal Variations of Nitrogen Concentrations

The Loess Plateau is a typical semiarid area with a wide range, which is short of water due to its low precipitation and high evaporation. The annual precipitation is 538.6 mm, and the annual evaporation is 1120 mm [35, 36]. The unreasonable and excessive development of water resources leads to the serious consequences of the reduction of groundwater storage. Some rivers even dried up in the dry season.

We calculated and compared the nitrogen concentrations in the wet/dry season and every month (Tables 2 and 3; Figures 3 and 4). The results showed that the NH3-N in the dry season (YR: 3.32, FR: 7.35 mg L–1) was higher than that in the wet season (July to September: YR: 1.21, FR: 2.19 mg L–1). The NH3-N in FR in dry and wet seasons had more volatility. The NH3-N was highest in YR (4.26 mg L–1) and FR (10.41 mg L–1) in January. Rainfall is the major source of surface water supply in FR and YR. Precipitation has a certain dilution effect on the NH3-N concentration in the rainy season. The dry season is the main period of farmers applying nitrogen and nitrogen-containing substances, and nutrients easily enter the surface water with rainfall and runoff [37]. These are the important reasons for the high nitrogen content in the dry season.


Nitrogen (mg/L)

BasinNH3-N (dry season)TN (dry season)
MinimumMaximumMeanSDMinimumMaximumMeanSD
 Yellow River0.1113.203.323.392.0922.2011.596.03
 Fen River0.1234.107.358.111.4763.1021.2518.20
BasinNH3-N (wet season)TN (wet season)
MinimumMaximumMeanSDMinimumMaximumMeanSD
 Yellow River0.225.711.211.742.7520.609.523.81
 Fen River0.109.092.192.731.997.0514.7113.50


Nitrogen (mg/L)Month

NH3-N123456789101112
 Yellow River4.263.662.641.752.111.501.580.530.540.720.922.05
 Fen River10.418.995.564.785.853.510.952.101.781.453.342.42
 Eastern Loess Plateau8.767.674.743.794.622.921.401.551.311.262.452.62
TN123456789101112
 Yellow River12.3012.549.0712.6810.6710.5610.667.359.729.8210.0910.01
 Fen River21.9623.6715.2320.5114.4014.9115.6213.5815.8516.6319.4418.07
 Eastern Loess Plateau20.0321.4913.8518.8914.0514.4214.7011.8414.3715.0416.7116.14

The above research results also showed TN (dry season: YR: 11.59, FR: 21.25 mg L–1; wet season: YR: 9.52, FR: 14.71 mg L–1). The TN was highest in YR (12.68 mg L–1) and in FR in February (23.67 mg L–1). TN is defined as the total amount of dissolved inorganic nitrogen and dissolved organic nitrogen in water. Figure 4 shows that the change of TN is mainly due to the change of NH3-N, which means NO3--N is basically unchanged. The NO3--N is the main existing form of dissolved inorganic nitrogen in the Fen River [35]. NO3--N is the final product of oxidative decomposition of nitrogenous organic compounds, which indicates that the FR is polluted not only by agricultural pollution but also by industrial pollution. In the dry season, TN is 23.67 mg L–1 which means that the river in the FR region is extremely polluted.

3.3. Relationship between Nitrogen and Human Land Use

We predicted the spatial distribution of nitrogen in YR and FR, based on GIS interpolation (Figure 5). The results showed that the concentrations of NH3-N were mostly <3.0 mg L–1 and 3.0–6.0 mg L–1 in YR and FR, respectively. The concentrations of TN were mostly 5.0–10.0 mg L–1 and 15.0–30.0 mg L–1 in YR and FR, respectively. The NH3-N (12.0–13.4 mg L–1) and TN (45.0–63.0 mg L–1) were highest in the east of the study area. It should be noted that the NH3-N and TN were much higher in FR than in YR. As shown in Table 4, the human land use in the Yellow River Basin (1.4%) was smaller than that in the Fen River Basin (8.12%). The land use types have an obvious impact on the nitrogen concentration distributions in FR. The sampling sites of the FR were mostly located near the Fen River Reservoir Two. There are some industrial facilities and human activities around this area. The sewage is discharged around the sampling sites. The results showed that high nitrogen contents should be related to anthropogenic sources, such as domestic sewage, animal manure and nitrogenous fertilizer, and industrial sewage. Xing and Liu [38] pointed that the TN in the Yellow River is mainly formed by soil organic nitrogen. Figure 5 shows that the highest TN region is at the southeast of Lvliang, the land use type of which is rural land. Another possible reason is that Lvliang’s Fen River comes from the Taiyuan Basin, so the Taiyuan Basin might also be a source of nitrogen pollution in FR. Human beings affect surface water quality by interfering with land use and cover types [39]. The dynamic characteristics of water quality, nutrient density, and landscape will be affected [40]. The loss of nitrogen and sulfur in the landscape has a great impact on the water quality of rivers, estuaries, and coastal waters.


BasinLand use type (%)
Human landUrban landRural landIndustrial land

Yellow River1.400.390.650.36
Fen River8.122.333.022.77

Lvliang is located in the central of Shanxi Province, which has high GDP, population density, and concentrated industry. The large numbers of artificial land use in this area might be the cause of nitrogen pollution. In order to reduce the risk of water quality degradation, policymakers should carry out management and care assessment mechanisms at the source of rivers and pollution in accordance with the principle of Beneficiary Pays Principle and User Pays Principle. They should focus on the proportion of complete interference land use types by increasing the area of green land and natural water.

4. Conclusions

A GIS spatial analysis based on land use covers was used to understand the correlation between anthropogenic activity and rivers’ nitrogen. The results showed that rivers’ nitrogen was closely associated with human land use covers. Nitrogen pollution was most serious in urban areas. The method used in this study was effective and feasible for assessing the rivers’ nitrogen under the background of different anthropogenic activities.

Our results suggest caution in developing cities and industries and stress the importance of sustainable intensification of land use. Overall, people have to a fair extent managed to protect water resource security and ecological sustainability. This research provided useful results concerning the relevant management decisions to reduce anthropogenic disturbance to the water resource management and land use planning in arid areas.

Data Availability

The data used to support the findings of this study are included within the article.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Authors’ Contributions

The contributions of the authors involved in this study are as follows: conceptualization: Yuxian Hu and Gaiqiang Yang; data curation: Yuxian Hu, Yanan Sun, and Hongyan Li; funding acquisition: Yuxian Hu, Gaiqiang Yang, and Hongyan Li; investigation: Yuxian Hu and Ke Zhang; supervision: Yuxian Hu and Ke Zhang; writing—original draft: Yuxian Hu; and writing—review and editing: Yuxian Hu and Yuan Li.

Acknowledgments

This work was partially supported by the Shanxi Natural Fund (No. 201901D111251), the Teaching reform and innovation project of colleges and universities of Shanxi (No. J2017081), the National Natural Science Foundation of China (No. 51709195), and the Shanxi Provincial Key Research and Development Project (International Cooperation) (No. 201803D421095).

References

  1. Q. Wang, D. Sun, W. Hao, Y. Li, X. Mei, and Y. Zhang, “Human activities and nitrogen in waters,” Acta Ecologica Sinica, vol. 32, no. 4, pp. 174–179, 2012. View at: Publisher Site | Google Scholar
  2. I. Paredes, F. Ramírez, M. Forero, and A. Green, “Stable isotopes in helophytes reflect anthropogenic nitrogen pollution in entry streams at the Doñana World Heritage Site,” Ecological Indicators, vol. 97, pp. 130–140, 2019. View at: Publisher Site | Google Scholar
  3. P. Shi, Y. Zhang, J. Song et al., “Response of nitrogen pollution in surface water to land use and social- economic factors in the Weihe River watershed, northwest China,” Sustainable Cities and Society, vol. 50, p. 101658, 2019. View at: Publisher Site | Google Scholar
  4. F. Sajedi Hosseini, A. Malekian, B. Choubin et al., “A novel machine learning-based approach for the risk assessment of nitrate groundwater contamination,” Science of the Total Environment, vol. 644, pp. 954–962, 2018. View at: Publisher Site | Google Scholar
  5. Y. Yu, Z. Jin, G. Chu, J. Zhang, and Y. Zhao, “Effects of valley reshaping and damming on surface and groundwater nitrate on the Chinese Loess Plateau,” Journal of Hydrology, vol. 584, p. 124702, 2020. View at: Publisher Site | Google Scholar
  6. F. Mackenzie, L. Ver, C. Sabine, M. Lane, and A. Lerman, “C N P S global biogeochemical cycles and modeling of global change,” in Interactions of C N P and S Biogeochemical Cycles and Global Change, vol. vol. 14 of NATO ASI series, pp. 1–61, Springer-Verlag, Berlin Heidelberg, 1993. View at: Publisher Site | Google Scholar
  7. S. G. Gardner, J. Levison, B. L. Parker, and R. C. Martin, “Groundwater nitrate in three distinct hydrogeologic and land-use settings in southwestern Ontario, Canada,” Hydrogeology Journal, vol. 28, no. 5, pp. 1891–1908, 2020. View at: Publisher Site | Google Scholar
  8. J. Galloway, E. Cowling, S. Seitzinger, and R. Socolow, “Reactive nitrogen: too much of a good thing?” Ambio, vol. 31, no. 2, p. 60, 2002. View at: Publisher Site | Google Scholar
  9. Q. Guan, L. Feng, X. Hou, G. Schurgers, and J. Tang, “Eutrophication changes in fifty large lakes on the Yangtze Plain of China derived from MERIS and OLCI observations,” Remote Sensing of Environment, vol. 246, article 111890, 2020. View at: Publisher Site | Google Scholar
  10. H. Kim, S. Yu, J. Oh et al., “Assessment of nitrogen application limits in agro-livestock farming areas using quantile regression between nitrogen loadings and groundwater nitrate levels,” Agriculture, Ecosystems & Environment, vol. 286, p. 106660, 2019. View at: Publisher Site | Google Scholar
  11. P. Murdoch and J. Stoddard, “The role of nitrate in the acidification of streams in the Catskill Mountains of New York,” Water Resources Research, vol. 28, no. 10, pp. 2707–2720, 1992. View at: Publisher Site | Google Scholar
  12. Y. Xue, J. Liu, F. Dang, X. Liang, S. Wang, and Z. Ma, “Influence of CH4 adsorption diffusion and CH4-water two-phase flow on sealing efficiency of caprock in underground energy storage,” Sustainable Energy Technologies and Assessments, vol. 42, p. 100874, 2020. View at: Publisher Site | Google Scholar
  13. Y. Xue, F. Gao, and X. Liu, “Effect of damage evolution of coal on permeability variation and analysis of gas outburst hazard with coal mining,” Natural Hazards, vol. 79, no. 2, pp. 999–1013, 2015. View at: Publisher Site | Google Scholar
  14. Y. Xue, P. G. Ranjith, F. Gao et al., “Mechanical behaviour and permeability evolution of gas-containing coal from unloading confining pressure tests,” Journal of Natural Gas Science and Engineering, vol. 40, pp. 336–346, 2017. View at: Publisher Site | Google Scholar
  15. Y. Xue, P. G. Ranjith, F. Dang et al., “Analysis of deformation, permeability and energy evolution characteristics of coal mass around borehole after excavation,” Natural Resources Research, vol. 29, no. 5, pp. 3159–3177, 2020. View at: Publisher Site | Google Scholar
  16. J. Allan and M. Castillo, Stream Ecology: Structure and Function of Running Waters, Springer, The Netherlands, second ed. edition, 2007. View at: Publisher Site
  17. F. Chapin, M. Power, and J. Cole, “Coupled biogeochemical cycles and earth stewardship,” Frontiers in Ecology & the Environment, vol. 9, no. 1, p. 3, 2011. View at: Publisher Site | Google Scholar
  18. D. Fowler, C. Steadman, D. Stevenson et al., “Effects of global change during the 21st century on the nitrogen cycle,” Atmosphere Chemistry Physics, vol. 15, no. 24, pp. 13849–13893, 2015. View at: Publisher Site | Google Scholar
  19. C. Kroeze and S. Seitzinger, “Nitrogen inputs to rivers, estuaries and continental shelves and related nitrous oxide emissions in 1990 and 2050: a global model,” Nutrient Cycling in Agroecosystems, vol. 52, no. 2/3, pp. 195–212, 1998. View at: Publisher Site | Google Scholar
  20. X. Chen, Z. Cui, M. Fan et al., “Producing more grain with lower environmental costs,” Nature, vol. 514, no. 7523, pp. 486–489, 2014. View at: Publisher Site | Google Scholar
  21. W. H. Schlesinger, “On the fate of anthropogenic nitrogen,” Proceedings of the National Academy of Sciences of the United States of America, vol. 106, no. 1, pp. 203–208, 2009. View at: Publisher Site | Google Scholar
  22. B. Gu, D. Liu, X. Wu, Y. Ge, Y. Min, and J. Chang, “Utilization of waste nitrogen for biofuel production in China,” Renewable & Sustainable Energy Reviews, vol. 15, no. 9, pp. 4910–4916, 2011. View at: Publisher Site | Google Scholar
  23. H. Tu and H. Chen, “From deforestation to afforestation: effect of slopeland use policies on land use/cover change in Taiwan,” Land Use Policy, vol. 99, article 105038, 2020. View at: Publisher Site | Google Scholar
  24. M. Martínková, C. Hesse, V. Krysanova, T. Vetter, and M. Hanel, “Potential impact of climate change on nitrate load from the Jizera catchment (Czech Republic),” Physics & Chemistry of the Earth Parts, vol. 36, no. 13, pp. 673–683, 2011. View at: Publisher Site | Google Scholar
  25. Y. Yan, L. Wang, J. Li et al., “Diatom response to climatic warming over the last 200 years: a record from Gonghai Lake, North China,” Palaeogeography Palaeoclimatology Palaeoecology, vol. 495, pp. 48–59, 2018, (in Chinese). View at: Publisher Site | Google Scholar
  26. X. Zhao and M. Huang, “Spatial distribution of nitrogen of topsoil in the Wangdonggou Watershed of the Loess Plateau,” Research of Soil and Water Conservation, vol. 26, pp. 62–67, 2019, (in Chinese). View at: Google Scholar
  27. Y. Zheng, C. Duarte, J. Chen, D. Li, Z. Lou, and J. Wu, “Remote sensing mapping of macroalgal farms by modifying thresholds in the classification tree,” Geocarto International, vol. 34, no. 10, pp. 1098–1108, 2019. View at: Publisher Site | Google Scholar
  28. L. Lassaletta, H. Garcia-Gomez, B. S. Gimeno, and J. Rovira, “Agriculture-induced increase in nitrate concentrations in stream waters of a large Mediterranean catchment over 25 years (1981-2005),” Science of the Total Environment, vol. 407, no. 23, pp. 6034–6043, 2009. View at: Publisher Site | Google Scholar
  29. F. Zhang, T. Tashpolat, H. Kung, and J. Ding, “The change of land use/cover and characteristics of landscape pattern in arid areas oasis: an application in Jinghe, Xinjiang,” Geo Spatial Information Science, vol. 13, no. 3, pp. 174–185, 2010. View at: Publisher Site | Google Scholar
  30. J. Zhou, S. Li, X. Liang et al., “First report on the sources, vertical distribution and human health risks of legacy and novel per- and polyfluoroalkyl substances in groundwater from the Loess Plateau, China,” Journal of Hazardous Materials, vol. 404, p. 124134, 2021. View at: Publisher Site | Google Scholar
  31. T. Huang, B. Ma, Z. Pang, Z. Li, Z. Li, and Y. Long, “How does precipitation recharge groundwater in loess aquifers? Evidence from multiple environmental tracers,” Journal of Hydrology, vol. 583, p. 124532, 2020. View at: Publisher Site | Google Scholar
  32. Y. Li, Y. Bi, W. Mi, S. Xie, and J. Li, “Land-use change caused by anthropogenic activities increase fluoride and arsenic pollution in groundwater and human health risk,” Journal of Hazardous Materials, vol. 406, article 124337, 2021. View at: Publisher Site | Google Scholar
  33. M. Gregory, M. David, and Z. Gertner, “Nitrate flux in the Mississippi River,” Nature, vol. 414, no. 6860, pp. 166-167, 2001. View at: Publisher Site | Google Scholar
  34. Y. Tao, M. Wei, E. Ongley, L. Zicheng, and C. Jingsheng, “Long-term variations and causal factors in nitrogen and phosphorus transport in the Yellow River, China,” Estuarine, Coastal and Shelf Science, vol. 86, no. 3, pp. 345–351, 2010. View at: Publisher Site | Google Scholar
  35. Z. Meng, Y. Yang, Z. Qin, and L. Huang, “Evaluating temporal and spatial variation in nitrogen sources along the lower reach of Fenhe River (Shanxi Province, China) using stable isotope and hydrochemical tracers,” Water, vol. 10, no. 2, p. 231, 2018. View at: Publisher Site | Google Scholar
  36. Y. Yang and B. Fu, “Soil water migration in the unsaturated zone of semiarid region in China from isotope evidence,” Hydrology and Earth System Sciences, vol. 21, pp. 1–24, 2017. View at: Publisher Site | Google Scholar
  37. W. Shao, J. Cai, J. Liu et al., “Impact of water scarcity on the Fenhe River Basin and mitigation strategies,” Water, vol. 9, no. 1, p. 30, 2017. View at: Publisher Site | Google Scholar
  38. M. Xing and W. Liu, “Using dual isotopes to identify sources and transformations of nitrogen in water catchments with different land uses, Loess Plateau of China,” Environmental Science & Pollution Research, vol. 23, no. 1, pp. 388–401, 2016. View at: Publisher Site | Google Scholar
  39. Y. Wang, “Urban land and sustainable resource use: unpacking the countervailing effects of urbanization on water use in China, 1990-2014,” Land Use Policy, vol. 90, p. 104307, 2020. View at: Publisher Site | Google Scholar
  40. P. Shi, Y. Zhang, Z. Li, P. Li, and G. Xu, “Influence of land use and land cover patterns on seasonal water quality at multi-spatial scales,” Catena, vol. 151, pp. 182–190, 2017. View at: Publisher Site | Google Scholar

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