桑沟湾表层水春夏两季二氧化碳分压变化和影响因素

Seasonal variations(spring and summer) of the surface seawater pCO_2 in Sanggou Bay and corresponding impact factors

为研究季节变化和养殖活动对桑沟湾表层海水二氧化碳分压(pCO_2)的影响,尤其是海带(Saccharina japonica)养殖活动对表层水pCO_2的影响,本研究分别在海带收获前(2015年5月)、后(2015年8月)采用走航式二氧化碳分压仪对中国北方典型的贝藻筏式养殖海域——桑沟湾养殖区表层水pCO_2及有关环境参数进行了大面调查,探讨了季节、养殖模式以及海带收获前、后表层水pCO_2的变化规律及影响因素。调查结果显示:(1)春夏两季桑沟湾湾内表层海水中pCO_2的平均值分别为(346.78±13.85)μatm(1 atm=101325 Pa,1 μatm=10^(-6) atm)和(351.50±8.00)μatm;湾外自然海域pCO_2值分别为(353.42±0.71)μatm和(358.05±2.01)μatm,均小于大气中pCO_2。(2)pCO_2的平面分布特性为:由湾底向湾外递减并在外海空白区升高,两个季节最低值都出现在海带养殖区,最高值都出现在贝类养殖区。(3)春季表层海水pCO_2与水温相关性不显著(P>0.05),而与叶绿素a(Chl a)、溶解氧(DO)显著相关(P<0.05),反映了生命活动对pCO_2影响较大;夏季,养殖海带已收获,表层海水pCO_2与水温、溶解无机碳(DIC)、Chl a、DO显著相关(P<0.05)。(4)桑沟湾养殖区以及外海自然海域表层水pCO_2都低于大气中pCO_2,表现为二氧化碳(CO2)的汇区。藻类养殖区表层水pCO_2远低于自然海域,表现为CO2的强汇区;贝类养殖区表层水pCO_2略高于自然海域,表现为CO2的弱汇区,贝藻混养区则介于二者之间。春季海带的光合作用是影响表层水pCO_2的主要因素之一,养殖活动对海区表层水pCO_2的影响使得桑沟湾pCO_2表现出不同于自然海域的特性。夏季养殖活动减少导致物理因素的影响开始显现。

This study aimed to assess the effect of aquaculture activity, especially the cultivation of large algae such as kelp, on the seasonal variation ofpCO2 in surface seawater. The pCO2 and related parameters of the sur- face water were measured by the OceanPackTM （SubCTech, Kiel, Germany） before and after kelp harvesting （May and August, 2015） in a typical polyculture area in Sanggou Bay, China. The variations of pCO2 and its corre- sponding impact factors are discussed for different seasons and culture modes, and before and after kelp harvesting The results showed that： （1） the mean values ofpCO2 in the surface seawater during the spring and summer sea- sons were （346.7±13.85） μatm（1 atm=101325 Pa） and （351.50±8.00） μatm in the inner bay, and those of the outer waters were （353.42±0.71） μatm and （358.05±2.01） μatm, respectively. All these values were lower than atmos- pheric pCO2. （2） The horizontal distribution ofpCO2 decreased from the coast of the bay to the outside waters and rose at the reference outer region. The lowest pCO2 values in both seasons appeared in the algal culture area and the highest values appeared in the shellfish culture area. （3） No significant correlation was found between pCO2 and water temperature in the spring; however, pCO： was significantly correlated with chlorophyll a and dissolved oxygen, indicating that organic activity had a great impact on pCO：. In summer, after kelp harvesting, pCO2 and water temperature, dissolved inorganic carbon, chlorophyll a, and dissolved oxygen were significantly correlated. （4） The pCO2 values of Sanggou Bay and the adjacent outer surface waters were lower than the atmospheric pCO2, showing that the bay acted as a sink for CO2. The algal culture area was a strong carbon sink zone, because its pCO2 value was much lower than that of the natural sea area. The shellfish culture area was a weak carbon sink zone, because its pCOz value was slightly higher than that of the natural sea area. The pCO2 values in the al- gae-shellfish polyculture area were intermediate between the two monoculture areas. The photosynthetic activity of kelp in spring was a major factor affecting the surface water pCO2. The aquaculture activity in Sanggou Bay resulted in altered pCO2 values compared with those of the natural sea area. The effects of physical factors on surface waterpCO2 became apparent in summer owing to a lack of aquaculture in that season.