Preprints
https://doi.org/10.5194/bg-2022-197
https://doi.org/10.5194/bg-2022-197
 
09 Nov 2022
09 Nov 2022
Status: this preprint is currently under review for the journal BG.

Long-term changes of nitrogen leaching and their contributions to lake eutrophication dynamics on the Yangtze Plain of China

Qi Guan1,2, Jing Tang3,4, Lian Feng1, Stefan Olin3, and Guy Schurgers2 Qi Guan et al.
  • 1School of Environmental Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, Guangdong, China
  • 2Department of Geosciences and Natural Resource Management, University of Copenhagen, Copenhagen, Denmark
  • 3Department of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden
  • 4Department of Biology, University of Copenhagen, Copenhagen, Denmark

Abstract. Over the past half century, drastically increased chemical fertilizer have entered agricultural ecosystems to promote the crop production on the Yangtze Plain, potentially enhancing agricultural nutrient sources for eutrophication in freshwater ecosystems. However, long-term trends of nitrogen dynamics in terrestrial ecosystems and their impacts on eutrophication changes in this region remain poorly studied. Using a process-based ecosystem model, we investigated the temporal and spatial patterns of nitrogen use efficiency (NUE) and nitrogen leaching on the Yangtze Plain from 1979 to 2018. The agricultural NUE for the Yangtze Plain significantly decreased from 50 % in 1979 to 25 % in 2018, with the largest decline of NUE in soybean, rice and rapeseed. Simultaneously, the leached nitrogen from cropland and natural land increased with annual rates of 4.5 kg N ha-1 yr-2 and 0.22 kg N ha-1 yr-2, respectively, leading to an overall increase of nitrogen inputs to the fifty large lakes. We further examined the correlations between terrestrial nutrient sources (i.e., the leached nitrogen, total phosphorus sources, and industrial wastewater discharge) and the satellite-observed probability of eutrophication occurrence (PEO) at an annual scale, and showed that PEO was positively correlated with the changes in terrestrial nutrient sources for most lakes. Agricultural nitrogen and phosphorus sources were found to explain the PEO trends in lakes in the western and central part of Yangtze Plain, and industrial wastewater discharge was associated with the PEO trends in eastern lakes. Our results revealed the importance of terrestrial nutrient sources for long-term changes in eutrophic status over the fifty lakes of the Yangtze Plain. This calls for sustainable nitrogen applications in agriculture systems to improve water quality of local lake ecosystems.

Qi Guan et al.

Status: open (until 05 Jan 2023)

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Short summary
Understanding terrestrial sources of nitrogen is vital to examine lake eutrophication changes. Combining process-based ecosystem modeling and satellite observations, we found that land-leached nitrogen in the Yangtze Plain significantly increased from 1979 to 2018 and terrestrial nutrient sources were positively correlated with eutrophication trends observed in most lakes, demonstrating the necessity of sustainable nitrogen management to control eutrophication.
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