胶州湾水体和表层沉积物营养环境现状及影响因素

为了解胶州湾水体和表层沉积物营养环境状况及其主要影响因素，于2019年8月在胶州湾30个站位点采集了海水和表层沉积物样品，并于2021年5月在胶州湾沿岸采集了18个站位点的水样，对水体溶解无机态营养盐浓度和组成以及表层沉积物中总有机碳、总氮、总磷及生物硅含量和碳、氮稳定同位素（δ13C、δ15N）进行了分析。结果表明，胶州湾内水体和沿岸水体中溶解无机氮、溶解无机磷和溶解硅酸盐浓度空间分布相近，高值均位于湾东北部，主要受到河流输入和沿岸污水排放的影响，低值主要出现在湾中部和湾口处。结合近30年来的历史数据分析发现，胶州湾夏季营养盐浓度在1990?2008年期间呈持续上升的趋势，政府实施的污染物总量控制措施以及河流径流量下降使得2006年以来营养盐浓度呈现下降的趋势，该变化在空间上主要体现为大沽河氮、磷输入量的减少及其对应的湾西部营养盐高值的消失。胶州湾氮、磷营养盐输入的不平衡使得“磷限制”在2000年后逐渐加剧。胶州湾表层沉积物中总有机碳、总氮、总磷含量高值均集中于东北部和东部沿岸，结合生物硅和水体营养盐含量分析显示，这主要是河流与排污输入及其带来的高初级生产力造成的，沉积物生源要素与水体营养盐在空间分布上存在较好的耦合关系。沉积物粒度较粗对有机质保存的不利影响以及湾口较强的水动力作用共同导致了湾西部、中部以及湾口的生源要素含量较低。δ13C以及二端元混合模型显示，胶州湾表层沉积物有机质来源总体以海源为主，平均占比为64%，东部沿岸受陆源输入影响较明显。δ15N的空间分布显示，胶州湾表层沉积物中氮元素受到了海水养殖与污水排放的共同影响。水体和沉积物营养环境现状共同表明，对东北部河流和沿岸污水排放的控制是后期胶州湾污染治理的关键。

Nutritional environment and influencing factors of seawater and surface sediments in the Jiaozhou Bay

Seawater and surface sediment samples at 30 stations in the Jiaozhou Bay (JZB) and river water and coastal water samples at 18 stations along the JZB were collected in August 2019 and May 2021, respectively. Dissolved inorganic nutrient concentrations and structure in the water and the contents of total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), biogenic silica (BSi), and stable isotopes of carbon and nitrogen (δ13C, δ15N) in surface sediments were analyzed to clarify the present nutritional environment of seawater and surface sediment and its main influencing factors in the JZB. The results show that the spatial distribution of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and dissolved silicate (DSi) in seawater is consistent with that in the coastal water of JZB. The high values that occur northeast of the bay are mainly caused by river input and sewage discharge, and the low values mainly occur at the center and bay mouth. Combined with the analysis of historical data, we found that the nutrient concentrations of JZB in summer continued to rise from 1990 to 2008 and then declined since 2006 because of the declining nutrient loadings related to the implementation of total pollutant load control management and freshwater loadings from surrounding rivers. The decreased nutrient loadings were mainly found in rivers such as the Dagu River, causing the disappearance of high concentrations in the western region after 2010. The phosphorus limitation accelerated after 2000 as a result of the imbalanced input of nitrogen and phosphorus. The high values of TOC, TN, and TP in the surface sediments of JZB are concentrated along the northeast and east coasts, combined with BSi and water nutrient analysis, which is mainly caused by the river input and sewage discharge and the high primary productivity they bring. Sediment biogenic elements are well coupled with water column nutrients in spatial distribution. The adverse effect of coarse sediment grain size on the preservation of organic matter and the strong hydrodynamic effect of the bay mouth jointly lead to the low content of biogenic elements in the west, middle, and mouth of the bay. The δ13C and two-endmember mixing model show that the source of organic matter in the surface sediments of JZB is mainly marine-derived, accounting for an average of 64%. The eastern coast is obviously affected by terrestrial input. The spatial distribution of δ15N shows that the nitrogen in the surface sediment of JZB is jointly affected by mariculture and sewage discharge. The current situation of the water body and sediment nutrient environments shows that the control of sewage discharge from the northeast river and the coastal area is the key to the later pollution control of JZB.