The impact of super-typhoon Mangkhut on sediment nutrient density and fluxes in a mangrove forest in Hong Kong

Xiaoguang Ouyang; Fen Guo; Shing Yip Lee

doi:10.1016/j.scitotenv.2020.142637

The impact of super-typhoon Mangkhut on sediment nutrient density and fluxes in a mangrove forest in Hong Kong

Sci Total Environ. 2021 Apr 20:766:142637. doi: 10.1016/j.scitotenv.2020.142637. Epub 2020 Oct 2.

Authors

Xiaoguang Ouyang¹, Fen Guo², Shing Yip Lee²

Affiliations

¹ Simon F.S. Li Marine Science Laboratory, School of Life Sciences, The Chinese University of Hong Kong, Shatin, Hong Kong Special Administrative Region, China. Electronic address: x.ouyang@cuhk.edu.hk.
² Simon F.S. Li Marine Science Laboratory, School of Life Sciences, The Chinese University of Hong Kong, Shatin, Hong Kong Special Administrative Region, China.

PMID: 33071132
DOI: 10.1016/j.scitotenv.2020.142637

Abstract

Cyclone disturbance results in mangrove foliage loss, tree mortality and other changes in ecosystem processes. However, the impact of cyclones on mangrove sediment nutrient density, sediment-air CO₂ and CH₄ fluxes and their isotopes remains largely unknown. Super-typhoon Mangkhut (maximum gust 256 km h^-1) hit Hong Kong in September 2018. We investigated the influence of the cyclone by comparing pre- and post-cyclone sediment carbon cycling processes as well as nitrogen density during an 8-month period in a mangrove forest at Ting Kok, Hong Kong. Time and/or nitrogen density are the dominant drivers of the variation of dark sediment-air CO₂ fluxes (R_d) and sediment nutrient density. Significant changes in R_d and their δ¹³CO₂ values, sediment organic carbon density (SOC) and nitrogen density (SON) occurred after the cyclone. R_d were highest one month after the cyclone (0.05 ± 0.01 mmol m^-2 min^-1) and lowest before the cyclone (8.32 ± 2.84 μmol m^-2 min^-1). δ¹³CO₂ of pre-cyclone R_d (-18.2 ± 1.7‰) was significantly higher than that of all post-cyclone fluxes (-22.9 ± 1.5‰ to -23.6 ± 1.8‰). Both SOC and SON were highest one month after the cyclone (23.05 ± 1.92 kg C m^-3, 2.42 ± 0.11 kg N m^-3, 20-40 cm). A significant positive relationship exists between R_d and SON. Sediment-air CH₄ fluxes did not show significant changes over time but along the sea-land gradient (0.28 ± 0.21 to 0.61 ± 0.22 μmol m^-2 min^-1). Cyclone disturbance results in the pulse input of litter, which may explain the significant increase in post-cyclone R_d and lower δ¹³CO₂ of R_d. With anticipated climate change-driven effects on cyclone occurrence and intensity, our data underscores the significance of incorporating the influence of cyclone disturbance in constraining the global nutrient budgets in mangroves.

Keywords: Carbon gas fluxes; Cyclones; Mangroves; Nutrient density; Sediments; Stable isotopes.