洞庭湖DOM组成与有机碳收支对江湖水力连通的响应

Response of DOM composition and organic carbon balance to the hydraulic connectivity of the Lake Dongting watershed

洞庭湖是我国最大的通江湖泊之一,为探究洞庭湖溶解性有机物(DOM)组成、(DOC)收支与江湖水力连通间的内在关联,于2018年5月、7月、9月和11月在洞庭湖湘、资、沅、澧4支流和长江荆南松滋、虎渡、藕池3个入湖口以及洞庭湖出湖口城陵矶采集水样,并探究洞庭湖流域DOM的组成分异特征及其对江湖水力连通的响应.结果表明,入湖河流和城陵矶DOM吸收系数a254和陆源类腐殖酸组分C1在7月最高.DOC由入湖口(2.4±1.3mg)/L下降至出湖口(2.1±0.3)mg/L,而a254由入湖口(9.7±2.2)m^(-1)上升至出湖口(10.1±1.7)m^(-1).微生物培养前的DOC浓度为(2.4±1.0)mg/L,微生物降解后的DOC浓度为(2.1±0.9mg)/L,DOC的微生物活性,即BDOC最高值出现在澧水为50.3%.5月、7月、9月和11月入湖的DOC通量分别为(63.7±43.6)×10^(3)t,(60.1±7.3)×10^(3)t,(27.6±3.6)×10^(3)t,(31.9±13.9)×10^(3)t.洞庭湖因自身水力滞留时间短,导致DOM在湖内运移过程中较少被降解,全湖DOM来源组成受流域不同季节来水条件影响较大.

Dongting is one of the largest freshwater lakes in China and is connecting to the Yangtze River.In order to investigate the relationship between the composition of dissolved organic matter(DOM)and dissolved organic carbon(DOC)budget of Lake Dongting and the hydraulic connectivity between rivers and the lake,we collected water samples from the four inflowing tributaries Xiang,Zi,Yuan,and Li,and also the Yangtze River via the three inlets Songzi,Hudu,and Ouchi and only one outlet of Lake Dongting to Yangtze River at Chenglingji in May,July,September,and November 2018,and to investigate the compositional divergence characteristics of Dongting Lake basin DOM in response to river-lake hydraulic connectivity.The study shows that DOM absorption a254 and terrestrial humic-like C1of the input rivers and sole outlet was the highest in July when the inflow discharge to the lake was high.DOC decreased from(2.4±1.3)mg/L at the inlet to(2.1±0.3)mg/L at the outlet,while a254 increased from(9.7±2.2)m^(-1)at the inlet to(10.1±1.7)m^(-1)at the outlet.Dissolved organic carbon(DOC)concentration decreased from(2.4±1.0)mg/L prior to microbial incubation to(2.1±0.9)mg/Lpost microbial degradation,and the highest level of biodegradable DOC(BDOC)was found in the River Li(50.3%).The summed DOC fluxes into the lake in May,July,September,and November were(63.7±43.6)×10^(3)t,(60.1±7.3)×10^(3)t,(27.6±3.6)×10^(3)t,and(31.9±13.9)×10^(3)t,respectively.The results show that Dongting Lake is marginally degraded during the process of intra-lake transport due to the short water retention time of the lake itself,and the composition of DOM sources in the whole lake is greatly influenced by the inflowing discharge in different seasons.