Multi-isotope approach for the identification and characterisation of nitrate pollution sources in the Marano lagoon (Italy) and parts of its catchment area

Abstract Nitrate (NO 3 − ) pollution is of considerable concern because its threat to human health and ecosystems. Herein, we chose the Wen-Rui Tang River watershed, one of typical rural-urban watersheds in Southeast China, as a case study. According to the analyses based on hydro-chemical ions, land-use classification, dual nitrate isotopes ( δ 15 N-NO 3 − and δ 18 O-NO 3 − ), and a Markov Chain Monte Carlo mixing model, the knowledge of contributions of potential NO 3 − pollution sources was obtained. Results showed that the study river was highly polluted by nitrogen, especially the increased riverine NO 3 − . Variations in δ 15 N-NO 3 − and δ 18 O-NO 3 − revealed that microbial nitrification was the main transformation process of nitrogen in surface water of the watershed, while bacterial denitrification was unlikely to be an important process at the specific sampling period. The δ 15 N-NO 3 − vs. δ 18 O-NO 3 − diagram incorporating chloride content qualitatively identified the main contribution of riverine NO 3 − was from municipal sewage discharges. On the basis of land-use characteristics, we applied hierarchical cluster method for subgrouping 44 sampling sites into four classes, namely, classes I (ecological), II (industrial), III (agricultural), and IV (urban). The Markov Chain Monte Carlo mixing model was employed to calculate proportional contributions of NO 3 − sources and articulated predominantly municipal sewage (23.5 – 42.2%) sourced nitrate in all classes. In addition, river sediments (13.8 – 20.8%) and atmospheric deposition (12.7 – 19.6%) were identified as important pollution sources. This study demonstrated that the comprehensive isotope tracing approach can effectively quantify the nitrate pollution source contributions for surface waters across the rural-urban interface.

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Spring Waters as an Indicator for Non-Point-Source Nitrate Pollution of Rural Watercourses – Findings from Two Decades of Spring Monitoring in the Low Mountain Landscape of Saarland

10.21203/rs.3.rs-1133753/v1 ◽

2021 ◽

Author(s):

Gero Weber ◽

Jochen Kubiniok

Keyword(s):

Point Source ◽

Catchment Area ◽

Extreme Values ◽

Nitrate Pollution ◽

Point Sources ◽

Marine Ecology ◽

Nitrate Content ◽

Clear Correlation ◽

Limit Value ◽

Catchment Areas

Abstract Background:Interflow-dominated spring waters provide a comprehensive picture of emissions with nitrate and other pollutants caused by the type and intensity of land use in the topographic catchment area. One aim of this study was to develop a model for predicting the share of nitrate pollution from non-point sources based on the type of agricultural use in the catchment areas of small and medium-sized watercourses. Methods:Fifty-five springs in Saarland and the adjacent Rhineland-Palatinate were monitored for pollutants during three monitoring periods of at least twelve months duration between 2000 and 2019. The catchment areas are representative of the natural regions in the study area and are outside the influence of settlements and other developments. In addition to nitrate and other physicochemical parameters, 25 agriculturally impacted springs were screened for pesticides and their metabolites.Results:Since the first measurements were taken in 2000, the vast majority of agriculturally impacted springs have consistently exhibited high nitrate concentrations of between 20 and 40 mg/L NO3-. Springs not influenced by agriculture contain an average of 3.6 mg/L of nitrate. The extreme values observed in the early 2000s decreased to the limit value of 50 mg/L, but most of the springs with moderate levels exhibited an increase to approximately 30 mg/L. The number of pesticidal agents detected in the spring waters demonstrates a clear correlation with the intensity of agricultural usage and the nitrate content detected. A regression model derived from the highly significant correlation between nitrate content and the share of cropland in the catchment area can be used to quantify the share of nitrate pollution attributable to non-point-source inputs for larger catchments in the region under investigation.Conclusion:Nitrate discharged from farmland has not decreased since the EC WFD entered into force. At the extremely heavily polluted sites of the past, measures have been implemented in the meantime that have led to compliance with the limit value of the Nitrate Directive. As below this limit, nitrate levels are increasing significantly, we suggest to incorporate the marine ecology target as a binding mark for official water pollution control in the future.

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