Non-point Source Pollution across Headwater Catchments to Large River Networks

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

Deadline for manuscript submissions: closed (31 March 2022) | Viewed by 10302

Special Issue Editors

Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Science, Beijing, China
Interests: nutrients; carbon; nonpoint source pollution; river networks; watershed; modeling; GHGs emissions; water quality; eutrophication; land–ocean interactions
Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Science, Beijing, China
Interests: land use change; climate change; nutrients; precipitation; runoff and sediment; carbon

Special Issue Information

Dear Colleagues,

Surface water pollution of nutrients and eutrophication are one of prominent environmental issues in China and around the world. Non-point source is a fundamental source of pollution, and quantitative research on non-point source pollution is of significance in the effective management of water quality. Various factors, including nutrient budgets, land use and climate change, cropping system changes, mining, and fertilizer manufactures have been recognized to play important roles in nonpoint source pollution. However, technically quantifying nonpoint pollutants entering receiving waters (including streams, rivers, lakes, reservoirs, estuaries, etc) from terrestrial ecosystems is particularly difficult because of the heterogeneous characteristics of watersheds across different scales, from headwater catchments to large river networks. This Special Issue aims to study nonpoint source pollution of watersheds across various scales—from headwater catchments to large river networks, and from mountainous areas to coastal watersheds with stressing in situ observations and modeling.

Prof. Dr. Weijin Yan
Dr. Fang Wang
Guest Editors

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Keywords

  • nutrients
  • carbon
  • streams and rivers
  • river networks
  • GHGs emissions
  • modeling
  • land use and cropping system changes

Published Papers (4 papers)

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Research

22 pages, 2478 KiB  
Article
Seasonal Dynamics of Algal Net Primary Production in Response to Phosphorus Input in a Mesotrophic Subtropical Plateau Lake, Southwestern China
by Yue Wu, Jinpeng Zhang, Zeying Hou, Zebin Tian, Zhaosheng Chu and Shengrui Wang
Water 2022, 14(5), 835; https://doi.org/10.3390/w14050835 - 07 Mar 2022
Cited by 5 | Viewed by 2707
Abstract
A comprehensive 3-dimensional hydrodynamic and eutrophication model, the environmental fluid dynamics code model (EFDC) with three functional phytoplankton groups, was applied to simulate the algal dynamics in a mesotrophic P-limited subtropical plateau lake, Lake Erhai, Southwestern China. Field investigations revealed the seasonal patterns [...] Read more.
A comprehensive 3-dimensional hydrodynamic and eutrophication model, the environmental fluid dynamics code model (EFDC) with three functional phytoplankton groups, was applied to simulate the algal dynamics in a mesotrophic P-limited subtropical plateau lake, Lake Erhai, Southwestern China. Field investigations revealed the seasonal patterns in external total phosphorus (TP) input and TP concentration, as well as the composition of the phytoplankton community. The model was calibrated to reproduce qualitative features and the succession of phytoplankton communities, and the net primary production was calculated. The modeled daily net primary production (NPP) ranged between −16.89 and 15.12 mg C/m2/d and exhibited significant seasonal variation. The competition for phosphorus and temperature was identified as the primary governing factor of NPP by analyzing the parameter sensitivity and limitation factors of the lake. The simulation of four nutrient loading reduction scenarios suggested high phytoplankton biomass and NPP sensitivity to the external TP reduction. A significant positive correlation was found among NPP, total phytoplankton biomass and TP concentration. Overall, this work offers an alternative approach to estimating lake NPP, which has the potential to improve sustainable lake management. Full article
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22 pages, 3272 KiB  
Article
Differential Response of Nutrients to Seasonal Hydrological Changes and a Rain Event in a Subtropical Watershed, Southeast China
by Xiaolan Guo, Xiuli Yan, Hongyan Bao, Junwen Wu and Shuhji Kao
Water 2022, 14(5), 834; https://doi.org/10.3390/w14050834 - 07 Mar 2022
Cited by 1 | Viewed by 2339
Abstract
A large amount of terrestrial nutrients are discharged into the ocean through rivers. However, the impact of seasonal hydrological variations on riverine nutrient concentrations and fluxes remains unclear, especially in the medium-sized subtropical rivers that are highly influenced by human activities. In this [...] Read more.
A large amount of terrestrial nutrients are discharged into the ocean through rivers. However, the impact of seasonal hydrological variations on riverine nutrient concentrations and fluxes remains unclear, especially in the medium-sized subtropical rivers that are highly influenced by human activities. In this study, we investigated the monthly changes in nutrient concentrations (soluble reactive phosphorus, SRP; dissolved silicate, DSi; and dissolved inorganic nitrogen, DIN) in the North Stream (NS) and West Stream (WS) of the Jiulong River (JLR). The results show that the concentrations of SRP and DSi in the NS and the WS displayed a similar seasonal variability, which was different from the pattern of DIN. Hydrological conditions, chemical fertilizer loss and biogeochemical processes are responsible for the seasonal changes in the nutrients in the two streams, especially during extreme rain events. Nutrient concentrations in the NS exhibited a clockwise trajectory along with river discharge during rain events, while a reverse pattern in the WS was observed since it experienced a moderately long rain event. Different rainfall features between the two main tributaries resulted in the majority of nutrients being exported at the start of the rain event in the NS and the end of rain event in the WS. Indeed, the annual high flow (Q/Qm > 3) accounts for ~17.3% of the annual nutrient flux in the JLR even though this period spans only ~4.0% of a year, which suggests the importance of rain events on nutrient export in these subtropical rivers. Although the annual fluxes of DIN and SRP in the JLR were smaller than many rivers worldwide, higher areal yields of DIN and SRP were observed, indicating that the JLR is highly influenced by human activities. Our study systematically evaluated the response of nutrient concentrations to hydrological changes in two tributaries of the JLR, which is useful in better understanding the nutrient dynamics in medium-sized subtropical rivers. Full article
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15 pages, 2261 KiB  
Article
Simplified Modelling of Coupled Surface-Groundwater Transport Using a Subcatchment Mass Balance Approach
by Alexander Hewgill Elliott, Channa Rajanayaka and Jing Yang
Water 2022, 14(3), 350; https://doi.org/10.3390/w14030350 - 25 Jan 2022
Cited by 1 | Viewed by 2294
Abstract
Catchment models based on steady-state mass balances enable rapid assessment of contaminant fluxes and concentrations in rivers. However, such models often focus on surface drainage, without taking groundwater into account. This paper presents a novel steady-state mass-balance catchment model that includes groundwater. The [...] Read more.
Catchment models based on steady-state mass balances enable rapid assessment of contaminant fluxes and concentrations in rivers. However, such models often focus on surface drainage, without taking groundwater into account. This paper presents a novel steady-state mass-balance catchment model that includes groundwater. The model incorporates a conceptual reservoir under each surface subcatchment, with lateral subsurface exchanges between adjacent reservoirs and vertical exchanges between the reservoirs and the surface drainage network. This leads to an easily solved coupled algebraic system of equations. The approach is demonstrated for nitrogen in a meso-scale catchment in New Zealand. Exchange coefficients were extracted from a full groundwater model, while recharge sources were obtained from separate hydrological and leaching models. Other parameters such as decay coefficients were determined through calibration. Although the exchange coefficients are generated from a detailed groundwater model, alternatives such as simple groundwater models or phreatic contours could be used instead. The effective decay parameters were different from what was expected, which is partly due to the model structure (for example, the assumption of complete mixing in each reservoir), but may also be due to input uncertainty. The applications demonstrated the successful deployment of a novel, simple, fast-running and flexible coupled surface-groundwater model. Full article
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17 pages, 4317 KiB  
Article
Nitrogen and Phosphorus Diffusion Fluxes: Insight from High-Resolution Technology and Hydrodynamic Modeling
by Qingqing Sun, Fujun Yue, Jingan Chen, Jingfu Wang, Yulin Li, Xiaozheng Li, Mohd Aadil Bhat, Jing Liu and Siliang Li
Water 2021, 13(22), 3232; https://doi.org/10.3390/w13223232 - 15 Nov 2021
Cited by 1 | Viewed by 2437
Abstract
Nitrogen and phosphorus are key elements in controlling eutrophication in the aquatic system. Water and sediment samples were collected from Hongfeng Lake, a seasonally stratified reservoir in southwest China, in winter and summer. Diffusion fluxes of NH4+, NO3 [...] Read more.
Nitrogen and phosphorus are key elements in controlling eutrophication in the aquatic system. Water and sediment samples were collected from Hongfeng Lake, a seasonally stratified reservoir in southwest China, in winter and summer. Diffusion fluxes of NH4+, NO3, and labile P in summer using diffusive gradients in thin films technology were 3.4, −37.2, and 0.9 mg m−2 day−1, respectively, based on Fick’s first law. The diffusion flux of labile P was 2.05 mg m−2 day−1 in winter. The contributions fraction of the labile P diffusion flux from sediment to the overlying water were higher in winter than those in summer, because of the relatively lower external input, concentrations and higher diffusion fluxes in winter. After the external input decreased, all of the three diffusion fluxes were lower than the previous record. To understand the influence effect of hydrodynamics, environmental fluid dynamics code modeling was used to simulate the flow and temperature field in winter and summer. Modeling results showed that velocity in summer was higher than that in winter due to concentrated rainfall within the catchment. Moreover, the velocity and temperature in the euphotic zone were higher than that of the hypolimnion in summer. Less variation of velocity and temperature in vertical profile in winter than that in summer was observed, which may be attributable to the high specific heat capacity and the low heat conductivity of water. There was no significant correlation among velocity, hydrochemistry, nitrogen, and phosphorus concentrations. Hydrodynamics, solar radiation, and water depth affect the position of the thermocline, which was consequently to water temperature, hydrochemistry, dissolved nitrogen, and phosphorus concentration. Correlation analysis suggested that the higher bottom velocity and total bed shear may accelerate labile P, NH4+, and NO3 diffusion fluxes. These results provide evidence and suggestions for preventing and controlling reservoir eutrophication and water safety management. Full article
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