| In recent years,under the combined influences of human activities and natural factors,nutrient concentrations in the coastal waters of the world have increased year by year,resulting in various levels of eutrophication,which threatens the health of the coastal ecological environment.However,there are relatively few studies on nutrient content,distribution and composition in Laizhou Bay and Liaodong Bay of Bohai Sea,and the comparative study on the commonness and difference of two bays is also rare.In this study,we combined field investigations with laboratory analyses,and focused on examining nutrient content,distribution and composition in Laizhou Bay,and conducted data mining on the historical survey data of Liaodong Bay,in order to systematically evaluate the nutrient limitation and eutrophication status of two bays.By means of this comparative study,the differences and commonness of the effects of terrestrial nutrient pollution on two bay ecosystems were investigated and discussed.Hopefully,this study could provide data support and scientific basis for the study of coastal ecological environment and the global carbon cycle.In the early summer of 2016,preliminary results show that the distribution patterns of nitrate and nitrite in Laizhou Bay were similar,and their concentrations were high in the western area of bay and the coastal areas outside the Yellow River,Xiaoqing River,the southern Meihe tributaries and Yuhe River.However,ammonium concentration and distribution were significantly affected by phytoplankton assimilation and pollution from the Wanghe River basin.Zones with both low phosphate and silicate concentrations appeared in the lower reaches of the Yellow River estuary in the bay,which might be caused by algal blooms.The distribution of chlorophyll a(Chi a)in Laizhou Bay was obviously different between the east and the west:Chi a concentrations in the west were higher than 3 mg/m3,and the highest was up to 6.52 mg/m3.There might be algal blooms in the local high-Chl a region.In contrast,although there were individual high-Chl a patches in the east,the number was small,and the average concentration of chlorophyll a was much lower than that in the western high-Chl a area.The comparison between these two bays shows that the investigation area of Liaodong Bay was affected more obviously by land runoff,and its average chlorophyll a content was almost twice as much as that in the surface of Laizhou Bay,while the average chlorophyll a contents in the bottom of two bays were close.The concentrations of dissolved inorganic nitrogen(DIN)and silicate in Liaodong Bay were about 2-3 times and 2-5 times as much as those in Laizhou Bay,respectively,but its phosphate concentrations were lower than those in Laizhou Bay,which might be directly related to the difference of pollution emissions from their surrounding rivers.Phytoplankton growth in these two bays was not limited by nitrogen and silieon,and phytoplankton at most sites were not absolutely limited by phosphorus,but phytoplankton in both bays might be potentially limited by phosphorus with the algal blooms in the future.The results of eutrophication evaluation show that at least 1/4 of the study area in Laizhou Bay was at the status of eutrophication,and the eutrophication level in the southwest cormer of Laizhou Bay was the most serious.However,the eutrophication zone in Liaodong Bay accounts for about 1/3-1/2 of the study area,and the Liaohe River estuary was the most serious.Other estuaries in Liaodong Bay were more or less at eutrophication status as well.Statistical analyses show that phosphate,nitrate and chemical oxygen demand(COD)had significant effects on eutrophication in Laizhou Bay,while eutrophication in Liaodong Bay was affected by multiple factors,such as temperature,transparency and suspended particulate matter(SPM),silicate and biomass of phytoplankton. |
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