Nitrate sources and processes in the surface water of a tropical reservoir by stable isotopes and mixing model

AbstractNitrate (NO3−) pollution is a serious global problem, and the quantitative analysis of its sources contributions is essential for devising effective water-related environmental-protection policies. The Shengjin Lake basin, located in the middle to lower reaches of the Yangtze River in China was selected as the research area in our study. We first grouped 29 surface water samples and 33 groundwater samples using cluster analysis, and then analyzed potential nitrate sources for each dataset of δ15N–NO3− and δ18O–NO3− isotope values by applying a Bayesian isotope-mixing model. Our results show that the nitrogen pollution in the surface-ground water in the study area seriously exceeded to class V of the Environmental Quality Standard of Surface Water of China. The NO3− in surface water from the mid-upper reaches of the drainage basin mainly originates from soil nitrogen (SN) and chemical fertilizer (CF), with contribution rates of 48% and 32%, respectively, and the NO3− in downstream areas mainly originates from CF and manure and sewage (MS), with contribution rates of 48% and 33%, respectively. For the groundwater samples, NO3− mainly originates from MS, CF, and SN in the mid-upper reaches of the drainage basin and the northside of Dadukou near the Yangtze River, with contribution rates of 34%, 31%, and 29%, respectively, whereas NO3− in the lower reaches and the middle part of Dadukou mainly originates from MS, with a contribution rate of 83%. The nitrogen conversion of surface water in lakes and in the mid-upper reaches is mainly affected by water mixing, while the groundwater and surface water in the lower plains are mainly affected by denitrification. The method proposed in this study can expand the ideas for tracking nitrate pollution in areas with complex terrain, and the relevant conclusions can provide a theoretical basis for surface and groundwater pollution control in the hilly basin of Yangtze River.

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Combining dual isotopes and a Bayesian isotope mixing model to quantify the nitrate sources of precipitation in Ningbo, East China

The Science of The Total Environment ◽

10.1016/j.scitotenv.2021.146297 ◽

2021 ◽

Vol 778 ◽

pp. 146297

Author(s):

Yasheng Shi ◽

Cai Li ◽

Zanfang Jin ◽

Yongqi Zhang ◽

Jiazheng Xiao ◽

...

Keyword(s):

Mixing Model ◽

East China ◽

Nitrate Sources ◽

Bayesian Isotope Mixing Model

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Stable isotopes of oxygen and hydrogen in the Truckee River-Pyramid Lake surface-water system. 3. Source of water vapor overlying Pyramid Lake

Limnology and Oceanography ◽

10.4319/lo.1994.39.8.1945 ◽

1994 ◽

Vol 39 (8) ◽

pp. 1945-1958 ◽

Cited By ~ 27

Author(s):

L. V. Benson ◽

J. W. C. White

Keyword(s):

Stable Isotopes ◽

Water Vapor ◽

Surface Water ◽

Water System ◽

Lake Surface ◽

Truckee River ◽

Pyramid Lake

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Transformations and nitrate sources in an agricultural watershed(Quanshui River, China): An investigation using hydrogeochemistry, isotopes, and a Bayesian model

10.5194/egusphere-egu21-3618 ◽

2021 ◽

Author(s):

Mingda Cao

Keyword(s):

Surface Water ◽

Bayesian Model ◽

Field Investigation ◽

Climatic Conditions ◽

Agricultural Watershed ◽

Agricultural Activities ◽

Transformation Mechanism ◽

Chemical Fertilizers ◽

Nitrate Sources ◽

The Difference

The spatiotemporal changes of nitrate in agricultural watersheds are of global concern. Although numerous studies have explained the source and transformation mechanism of nitrate in groundwater and surface water, the transformation mechanism in groundwater remains poorly understood because of different hydrogeological and climatic conditions. Based on a field investigation and sampling, this study revealed the sources and transformation mechanism of nitrogen in surface water and groundwater in a karst agricultural watershed by comprehensively using water chemistry data, isotope components, and a Bayesian model (simmr). The results indicated that:1)Local agricultural activities have controlled the changes of &#948;15N-NO3-, &#948;18O-NO3- and &#948;15N-NH4+ in groundwater. The difference is that the concentration of NO3- is significantly affected by rainfall. However, the contribution of rainfall to groundwater NO3- is relatively small (<9%), indicating that there is a dual influence mechanism of leaching in the watershed that controls the concentration of groundwater NO3-, while agricultural activities control its isotope changes;2)The study observed that after fertilization, due to the influence of ammonia volatilization and nitrification, &#948;15N-NO3-, &#948;18O-NO3- in groundwater showed a simultaneous decrease, while &#948;15N-NH4+ showed an increasing trend, which may be due to the result of incomplete nitration of NH4+ in the vadose zone;3)According to the calculation results of the simmr model, in the two main fertilization periods in October 2018 and April 2019, the contribution of chemical fertilizers to groundwater NO3-reached the peak value(65% and 69%), which is in line with the seasonal variations of &#948;15N-NO3-, &#948;18O-NO3-and &#948;15N-NH4+;4)The surface water in the watershed is mainly supplied by groundwater, and the contribution of chemical fertilizers to surface water NO3- is generally higher than that of groundwater. This may be caused by the drainage of rice fields containing chemical fertilizers into the river.

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