枯水季和丰水季长江口海域生源硫的浓度变化特征及影响因素

摘要

为深入研究河口近岸海域DMS (二甲基硫)的生物地球化学过程,于2014年2月(枯水季)和7月(丰水季)对长江口及附近海域表层海水中DMS及其前体物质DMSP (二甲巯基丙酸内盐)的浓度分布及影响因素进行了研究,测定了DMSPd (溶解态DMSP)的降解速率和DMS的生物生产与微生物消费速率,并估算了DMS的海-气通量.结果表明:①枯水季和丰水季c(DMS)、c(DMSPd)、c(DMSPp) (DMSPp为颗粒态DMSP)的平均值±标准偏差分别为(0. 54±0. 28) (2. 04±1. 32) (6. 65±5. 07)和(3. 99±3. 70)(5. 57±4. 72)(14. 26±9. 17)nmol/L,长江口海域丰水季生源硫化物的浓度明显高于枯水季. ②枯水季和丰水季c(DMSPd)与ρ(Chla)均呈弱相关,说明浮游植物在控制长江口海域DMSP的生产分布中发挥重要作用. ③枯水季和丰水季c(DMS) /ρ(Chla)的平均值±标准偏差分别为(2. 62±3. 28)和(4. 60±7. 49)mmol/g,表明丰水季DMS的高产藻种(甲藻)在浮游植物生物量中所占比例高于枯水季. ④枯水季表层海水中DMSPd的降解速率和DMS的生物生产速率分别介于(2. 84～30. 53)和(0. 52～2. 19) nmol/(L·d)之间,平均值分别为14. 55和1. 30 nmol/(L·d),表明DMS并不是DMSPd的主要降解产物. ⑤枯水季和丰水季DMS的海-气通量平均值±标准偏差分别为(0. 36±0. 32)和(2. 17±2. 98)μmol/(m2·d),而且丰水季的硫排放量明显高于枯水季,这主要与夏季较高的c(DMS)有关.研究显示,长江口海域生源硫化物的浓度变化及分布特征呈明显的季节性差异,河口近岸海域是海洋有机硫排放的重要区域.%To further understand the biogeochemical process of dimethylsulfide (DMS) in the estuary and coastal areas,the spatial distributions of DMS,dimethylsulfoniopropionate (DMSP),the precursor of DMS,as well as their control factors were studied in the Changjiang River Estuary and its adjacent area in February (dry season) and July 2014 (wet season). Meanwhile,DMS biological production and microbial consumption rates,as well as dissolved DMSP (DMSPd) degradation rates,were determined and the sea-to-air flux of DMS was also estimated. The results showed that the average concentrations ± standard deviation of DMS,DMSPd,particulate DMSP (DMSPp) in the surface seawater were (0. 54± 0. 28) (2. 04± 1. 32) and (6. 65 ± 5. 07) nmol/L in the dry season and were (3. 99±3. 70) (5. 57±4. 72) and (14. 26±9. 17) nmol/L in the wet season,respectively. It suggested that the concentrations of biogenic sulfur compounds in the Changjiang River Estuary and its adjacent area in the wet season were significantly higher than those in the dry season. The concentrations of DMSPp in the dry and wet season were weakly correlated with the levels of Chla,indicating that phytoplankton might play an important role in controlling the production and distributions of DMSP in the survey area. The average values of c (DMS) /ρ (Chla) in the dry and wet season were (2. 62 ± 3. 28) and (4. 60 ± 7. 49) mmol/g,respectively,suggesting that the proportion of dinoflagellate in the total phytoplankton biomass in the wet season were apparently higher than that in the dry season. The rates of DMSPd degradation and DMS biological production in the surface seawater ranged from 2. 84 to 30. 53 and from 0. 52 to 2. 19 nmol/(L·d) in the dry season,respectively,with average values of 14. 55 and 1. 30 nmol/(L·d),manifesting that DMS was not the major degradation product of DMSPd. In addition,the sea-to-air fluxes of DMS were estimated to be (0. 36±0. 32) and (2. 17±2. 98) μmol/(m2·d) in the two seasons,and the sulfur emission during the wet season was higher than that in the dry season due to the higher c(DMS). In conclusion,the change of concentration and distribution characteristics of biogenic sulfur in the Changjiang River Estuary and its adjacent area exhibited obvious seasonal differences,it can be concluded that the estuarine sea areas are important sources for marine organic sulfur emission.