Dynamics of carbon, nitrogen and phosphorus wet deposition fluxes in the karst forest of Lijiang River basin, Southwest China.

Monitoring wet deposition fluxes of carbon, nitrogen, and phosphorus in the karst forest of Lijiang River basin is helpful for accurately assessing the impact of environmental changes on carbon, nitrogen, and phosphorus pools of forests, and providing scientific reference for the management of nutrient resources. We collected rainwater of karst forest in the downstream of Lijiang River basin in Guilin, Guangxi from March 2022 to February 2024. We measured concentrations of dissolved organic carbon (DOC), dissolved nitrogen (DN), dissolved organic nitrogen (DON), NH₄⁺-N, NO₃^--N, and dissolved phosphorus (DP) in rainwater. Combining with the rainwater volume, we estimated wet deposition fluxes of carbon, nitrogen, and phosphorus and analyzed their seasonal patterns. The results showed that the total rainfall in 2022 (1860.0 mm) was higher than that in 2023 (1469.3 mm). The ave-rage concentration of rainwater DOC was 3.03 and 5.76 mg·L^-1, DN was 2.34 and 3.52 mg·L^-1, DP was 0.05 and 0.07 mg·L^-1 in 2022 and 2023, respectively. There were great fluctuations in rainwater DN, NH₄⁺-N, NO₃^--N, and DP concentrations. The total carbon wet deposition flux was 43.0 and 41.3 kg·hm^-2, total nitrogen wet deposition was 33.89 and 39.98 kg·hm^-2, and total phosphorus wet deposition was 0.43 and 0.85 kg·hm^-2 in 2022 and 2023, respectively. There was no significant difference in the total carbon or nitrogen wet deposition flux between the two years, while there was significant difference in the total phosphorus wet deposition flux. The wet deposition fluxes of carbon, nitrogen and phosphorus were greater in spring and summer than in autumn and winter. The carbon wet deposition flux was significantly positively correlated with the nitrogen wet deposition flux, while there was no significant correlation between carbon and phosphorus wet deposition fluxes or between nitrogen and phosphorus wet deposition fluxes. In conclusion, the wet deposition fluxes of carbon and nitrogen in karst forest of Lijiang River basin are relatively high and stable, while the wet deposition flux of phosphorus is relatively low but fluctuates greatly. High amount of nitrogen deposition is conducive to the alteration of soil nitrogen deficiency in the karst forest of the Lijiang River basin, and the contribution of organic nitrogen to the nitrogen wet deposition should not be neglected.