Dissolved Inorganic Nitrogen Input via Net Nitrogen Mineralization under Antibiotics and Warming from the Water Level Fluctuation Zone of a Three Gorges Tributary

Junjie Lin,Chunmei Xiong,Chang Yan,Qingyu Nie,Yaling Du,Xiaoxia Yang,Dan Liu

doi:10.3390/w13182502

Abstract

The water level fluctuation (WLF) zone is one of the dominant sources of total dissolved inorganic nitrogen (TDN) export via net nitrogen (N) mineralization in the Three Gorges Reservoir (TGR). However, antibiotics pollution may impact the process of TND exports from WLF zone in the TGR, especially under drying-rewetting processes and climate warming, and thus increasing the risk of eutrophication in the tributaries of the TGR. The effects of the antibiotics Griseofulvin (GIN) and Fosfomycin (FIN) with 0, 0.2 and 0.4 g kg−1 net N mineralization rate (NMR) from WLF-zone soil in the Pengxi river, a typical tributary of the Yangtze River, under 25 and 35 °C were estimated in 30-day flooding and drying incubations. The results showed that GIN concentrations, temperatures and their interaction significantly affect net-nitrification rates (NNR) and NMR under drying and did not significantly affect NNR under flooding. FIN concentrations and temperatures solely influenced the NNR under flooding. The amounts of TDN exports via NMR without antibiotics from the WLF zone of Pengxi River are 6883.8 (flooding, 25 °C), 9987.3 (flooding, 35 °C), 9781.6 (drying, 25 °C), and 27,866.5 (drying, 35 °C) t year−1, which is 21.0, 29.8, 30.4 and 84.8 times of the permissible Class A discharge in China according to (GB18918-2002). Thus, the NMR of WLF zone should be controlled whether there is antibiotics pollution or not, especially during the dry period for alleviating water eutrophication. This study will be helpful for the assessment of nitrogen budgets in the WLF zone to eutrophication in the Three Gorges Reservoir.

Highlights

The water stored in the Three Gorges Reservoir (TGR) can reach 4 × 1010 m3/a, which is one of the world’s largest reservoirs with antiseasonal flow regulation [1]
The objectives of this study are to: (1) investigate the effect of the types and addition of antibiotics on the total dissolved inorganic nitrogen (TDN) inputs from the net N mineralization of the water level fluctuation (WLF)-zone soil under warming and drying/inundation condition; (2) estimate the contribution of TDN inputs induced by antibiotics via N mineralization processes of the WFL zone soil to water eutrophication in the TGR tributary
Our results showed that the amount of TDN exports originated from net N mineralization of WLF-zone soil without antibiotics was account for about 64.9%, 92.2%, 94.1% and 262.6% of that loads from the nonpoint source, respectively

Summary

Introduction

The water stored in the Three Gorges Reservoir (TGR) can reach 4 × 1010 m3/a, which is one of the world’s largest reservoirs with antiseasonal flow regulation [1]. The area of the water level fluctuation (WLF) zone is 348.9 km between 145 m above mean sea level (masl) and 175 masl in the TGR since 2003 [2]. Most of nutrients accumulated in the WLF zone during the dry period (summer season) may be released into the water under the anoxic condition during the submerging period from October to the March (winter season). The relatively slow flow velocity resulted in the weakened diffusion and exchange capacity in the tributaries of the TGR [3]. The decreased diffusion speed and self-purification capacity of various pollutants raise the risk of eutrophication in the TGR tributaries. The water bloom frequently occurred in the tributaries of the TGR [4,5]

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Conclusion