胶州湾夏秋季大气湿沉降中的营养盐及其入海的生态效应

为揭示大气湿沉降对胶州湾营养盐的输送通量及其生态效应,分别于2015年6—8月(夏季)、9—11月(秋季)采集胶州湾降水样品,测定了降水中不同形态N、P、Si的浓度。结果表明,降水中不同形态营养盐的浓度变化较大,且均与降水量呈负相关关系,其中NH4-N和NO3-N的浓度较高,溶解有机氮(DON)占溶解态总氮(DTN)含量的25.9%,而NO_2-N,PO_4-P和SiO_3-Si的浓度均很低。溶解无机氮(DIN)、DON、PO_4-P以及SiO_3-Si的湿沉降通量分别为141.7、61.87、0.35 mmol m~(-2)a~(-1)和0.12 mmol m~(-2)a~(-1)。受降水量和营养物质来源制约,各项营养盐湿沉降通量时间变化显著。农业活动导致的无机氮排放构成了胶州湾湿沉降DIN的主要来源。大气湿沉降DIN、DON、PO_4-P和SiO_3-Si分别占胶州湾总输入负荷的9.04%、10.24%、0.57%和0.17%,湿沉降输入的PO_4-P在夏、秋季分别可以支持0.575 mgC m~2d~(-1)和1.42 mg C m~2d~(-1)的新生产力;雨水中DIN/P比值高达1 617,突发性强降雨带来的营养盐输入会加剧表层水体的P限制和Si限制,对胶州湾浮游植物群落结构和粒级结构产生重要影响。大气湿沉降是胶州湾生源要素生物地球化学过程的重要一环,对营养物质收支的贡献及可能引发的生态效应不容忽视。

Nutrients in atmospheric wet deposition and their ecological effects on Jiaozhou Bay in summer and autumn 2015

Recently, owing to anthropogenic activities such as fossil fuel combustion and agricultural fertilization, the amounts of nutrients and other pollutants entering the marine environment via atmospheric wet deposition have been increasing. Large amounts of nutrients input resulting from short-term heavy rainfall may result in the temporary eutrophication of surface waters, and could even lead to red tides. Therefore, research has presently been focused on atmospheric wet deposition. Jiaozhou Bay, North China, is a typical semi-closed bay negatively affected by natural changes and anthropogenic activities. With the rapid development of the economy, society, and the population growth of Qingdao City, anthropogenic activities have resulted in ecological environmental deterioration, such as frequent occurrence of smog and sandstorms. This has resulted in a considerable increase in the transfer rate of terrigenous pollutants into the sea via atmospheric wet deposition. Thus, research on the nutrients of atmospheric wet deposition in Jiaozhou Bay has received considerable attention from governments, society, and scientists. To evaluate the nutrients influxes by atmospheric wet deposition and their ecological effects on Jiaozhou Bay, 33 wet deposition samples were collected in Jiaozhou Bay from June to November 2015. The concentrations of nutrients (NH₄-N, NO₃-N, NO₂-N, PO₄-P, and SiO₃-Si), dissolved total nitrogen (DTN), and dissolved organic nitrogen (DON) were determined using a continuous flow analyzer. Results showed significant differences among the monthly average concentrations for nutrients, and negative relationships between several nutrients and the amount of precipitation. The concentrations of NH₄-N and NO₃-N in the rainwater were high, whereas the concentrations of NO₂-N, PO₄-P and SiO₃-Si were low. Dissolved inorganic nitrogen (DIN) was the dominant species, accounting for 74.1% of DTN with DON accounting for 25.9% of DTN. The wet deposition fluxes of DIN, DON, PO₄-P and SiO₃-Si were estimated as 141.7 mmol m^-2 a^-1, 61.87 mmol m^-2 a^-1, 0.35 mmol m^-2 a^-1, and 0.12 mmol m^-2 a^-1, respectively. Temporal variations of the wet deposition fluxes of nutrients were evident, since they were affected by the amount of precipitation and the origin of nutrients. Significantly positive correlations were observed among different nitrogen forms (except for DON), suggesting that they had the same origin. The emission of inorganic nitrogen from agricultural activities was the main source of the DIN wet deposition in Jiaozhou Bay. The fluxes of DIN, DON, PO₄-P and SiO₃-Si by atmospheric wet deposition accounted for 9.04%, 10.24%, 0.57%, and 0.17% of the total external influxes of Jiaozhou Bay, respectively. The total influxes of PO₄-P via atmospheric wet deposition in summer and autumn could support new productivities of 0.575 mg C m^-2 d^-1 and 1.42 mg C m^-2 d^-1, respectively. The average molar ratio of DIN/P in the rainwater was 1,617, which was well above that in the seawater of Jiaozhou Bay, indicating that large amounts of nutrients inputs from sudden heavy rainfall could aggravate the P and Si limitation and further affect the nutrient structures of surface waters, as well as phytoplankton community structures and size-fractioned structures in Jiaozhou Bay. As one of the essential branches of the biogeochemical cycle of biogenic elements, the contribution of atmospheric wet deposition to the nutrient budgets and possible potential ecological effects on Jiaozhou Bay ecosystem cannot be neglected