Atmospheric dry deposition of nitrogen and phosphorus in Lake Qinghai, Tibet Plateau

Abstract

To investigate the fluxes and potential sources of the atmospheric dry deposition (ADD) of nitrogen (N) and phosphorous (P) in the Lake Qinghai area, atmospheric deposition dusts were collected monthly at the eastern coast of Lake Qinghai from October 2017 to September 2018. N and P species in the dusts were determined. Results indicated that the annual ADD flux (ADDF) of dusts was 215.64 g m−2 yr−1, 48% of which occurred in March and April. The annual ADDF of N was 7.98 kg ha−1 yr−1, 49% of which was water-soluble total nitrogen, including 23%, 16%, and 10% of water-soluble NH4+-N, NO3−-N, and organic N, respectively. The annual ADDF of the total P was 1.72 kg ha−1 yr−1, only 6% of which was water-soluble. The dusts as well as the N and P in the dusts primarily originated from western Inner Mongolia and northern Gansu, driven by the winter monsoon. However, relatively high concentrations of N and P in the dusts in summer might be related to the southeast Asian monsoon from southern Gansu and northern Sichuan. Overall, the ADDF of the total N was about half of the atmospheric wet deposition flux (AWDF) of N, while the ADDF of the total P was approximately equal to the AWDF of P. However, most of the P in the dusts was not water-soluble and thus not readily bioavailable. Therefore, N and P wet deposition provides most of the readily available nutrients to phytoplankton in Lake Qinghai.