Assessment Of Pressure Impacts Of Human Activities On China’s Offshore Marine Ecosystems

Marine ecosystems have rich and powerful service functions that enormously contribute to human well-being,including food and fishery production,climate regulation,water quality improvement,waste disposal,biodiversity maintenance,and habitat provision for key species.However,with the rapid development of industrialization and urbanization,human activities such as large-scale reclamation,coastal vegetation felling,pollutant discharge,and overfishing have been increasingly intensified.In addition,with global warming,sea surface temperature rise,sea-level rise,ocean acidification,and frequent occurrence of extreme climate events,the global marine ecosystem is facing unprecedented pressure brought about by global climate change and regional human activities and is undergoing rapid and substantial changes.In this study,taking China’s offshore waters as the study area,the spatial distribution of 14 human activities from the three aspects of land-based pollution,marine activities,and climate change are considered,and the methods of dasymetric mapping technology,minimum cost path plume dispersion model,modified general soil loss equation,spatial analysis,spatial quantitative model of cumulative pressure effect and so on are applied in this study.Combined with the spatial distribution of 9 types of China’s offshore marine ecosystems(key species and habitats)and a matrix of ecosystem vulnerability weights,the cumulative pressure exposures of marine human activities and the cumulative pressure impacts of China’s offshore marine ecosystems are evaluated and analyzed in the three assessment window periods in 2006-2010,2011-2015 and 2016-2020.This study mainly answers the four practical questions:"The extent to which China’s offshore marine ecosystems are exposed to human activity stressors";"The historical evolution,modern state and future trend of pressure hot spots of marine ecosystems in China’s offshore waters";"The composition of human activity pressure factors and key pressure sources";and "What measures and programs should we choose or take to effectively weaken the driving factors and impacts of multiple marine pressure sources".The main conclusions of this study are as follows:(1)Analysis of temporal and spatial variations of marine human activity pressures in China’s offshore waters.In terms of land-based pollution,nutrient pollution,organic chemical pollution and phytoplankton biomass in China’s offshore waters show a downward trend.The high-value areas are mainly distributed in the Bohai Sea area,the northern Jiangsu sea area,the Changjiang Estuary,and the Pearl River Estuary.Sediment input,inorganic chemical pollution and direct human impact show an upward trend.The high-value areas are mainly distributed in the Bohai Sea,the Yangtze River Delta,and the Pearl River Delta.In terms of marine activities,areas with high shipping traffic density are mainly concentrated in the Liaodong Bay,Bohai Bay,Weihai,Yantai,Qingdao,Rizhao,Lianyungang,the coast from the Yangtze River estuary to the Beibu Bay,and the Taiwan Strait.The areas with greater stress caused by artisanal fishing are mainly located in China’s offshore waters.Among them,the pressure intensity and coverage of artisanal fishing are larger at the mouth of the Yangtze River,the coast of Zhejiang,and the Taiwan Strait.Commercial fishing activities have relatively great pressure on the whole exclusive economic zone.The areas with high-pressure of coastal ports are mainly distributed in the Bohai Bay,Yangtze River Delta,Fujian Delta,and Pearl River Delta.The areas where the coastal power plants put a lot of pressure on the offshore marine ecosystem are mainly concentrated in the coastal areas of Jiangsu,Hangzhou Bay,and the coastal waters around the Bohai Sea.In terms of climate change,from 1982 to 2020,the intensity of marine heatwaves in China’s offshore waters shows an overall upward trend,and the pressure of marine heatwaves on marine ecosystems will continue to increase.In recent years,the regions with a relatively high intensity of marine heatwaves are mainly distributed in the Bohai Bay,Laizhou Bay,Lianyungang,and Rizhao coastal waters,as well as the waters on the west side of Taiwan.From 1993 to 2020,the sea level anomaly in China’s offshore waters shows an overall upward trend.The sea areas with relatively high sea level height anomalies are mainly distributed in the Bohai Sea,Lianyungang and Rizhao coastal waters,Hangzhou Bay,Xiamen Bay,and Beibu Bay.From 1982 to 2020,the average aragonite saturation in China’s offshore waters shows a downward trend as a whole,and the ocean acidification level shows an upward trend.Among them,the aragonite saturation in the Bohai Sea shows a significant downward trend,and the degree of ocean acidification is significantly intensified.(2)Evaluation of cumulative pressure exposures of marine human activities of China’s offshore waters.The value ranges of cumulative pressure exposures of marine human activities of China’s offshore waters at the three-time nodes in 2010,2015 and 2020 are 1.3-10.16,1.06-9.53,and 0.99-9.63.The proportions of China’s offshore waters with low exposure,medium exposure,high exposure and extreme exposure are 40.18%,31.98%,22.46%,and 5.38%.The cumulative pressure exposures of marine human activities show the spatial distribution characteristics that the nearshore is higher than the outer sea and decrease with increasing distance from shore.The areas with high cumulative pressure exposures of marine human activities are mainly distributed in the coastal estuaries and bays,as well as the waters near important port cities.The average cumulative pressure exposures of marine human activities at the three-time points in 2010,2015,and 2020 are 1.32,1.35,and 1.28.The cumulative pressure exposures of marine human activities increase first and then decrease,and show a downward trend as a whole.In the node period of 2015-2020,the cumulative pressure exposures of marine human activities in the Bohai Sea area show a downward trend,especially on the nearshore zones.The three marine ecosystems with the highest cumulative pressure exposures in China’s offshore waters are salt marshes,coasts and,seagrass.The five major bays from high to low are Bohai Bay,Liaodong Bay,Laizhou Bay,Hangzhou Bay,and Beibu Bay.(3)Evaluation of the cumulative pressure effects of China’s offshore marine ecosystems.The value ranges of the cumulative pressure impacts of China’s offshore marine ecosystems at the three-time nodes in 2010,2015,and 2020 are 0-78.18,0-81.67,and 0-78.88.The proportions of China’s offshore marine ecosystems with the level of low pressure,medium pressure,high pressure and extreme high pressure are 37.30%,38.52%,20.01%,and 4.17%.On the spatial scale,the cumulative pressure impacts of China’s offshore marine ecosystems are higher in the nearshore than in the open sea,and decreases from the nearshore to the open sea.The average cumulative pressure impacts of China’s offshore marine ecosystems at the three-time nodes in 2010,2015,and 2020 are 2.97,3.29,and 3.09.The cumulative pressure impacts of China’s offshore marine ecosystems first increase and then decrease,and the overall trend is upward.On the whole,the areas with an obvious increase in cumulative pressure impacts of China’s offshore marine ecosystems are mainly distributed in the sea area about 10 km away from the coastline,especially in the sea areas near the west coast of Zhejiang,Fujian,Guangdong,Guangxi,and Hainan.The three marine ecosystems with the highest cumulative pressure impacts of China’s offshore waters are salt marshes,coasts,and mangroves.The five major bays from high to low are Bohai Bay,Liaodong Bay,Laizhou Bay,Hangzhou Bay,and Beibu Bay.(4)The composition of human activity stressors.The three stressors that have the greatest impact on China’s offshore marine ecosystems are marine heatwaves(29.42%),coastal ports(21.81%),sea level anomaly(17.97%).For China’s three major coastal"blue carbon" ecosystems,salt marshes:coastal ports(21.40%),sea level anomaly(11.67%),and inorganic chemical pollution(11.34%);Seagrass beds:coastal ports(30.93%),sea level anomaly(15.90%),marine heatwaves(10.33%);Mangroves:coastal ports(21.34%),sea level anomaly(13.72%),organic chemical pollution(10.41%).Generally speaking,the climate change factor is the most powerful pressure affecting China’s offshore marine ecosystems.For China’s five major bays,Liaodong Bay:coastal ports(38.73%),sea level anomaly(17.59%),ocean acidification(7.96%);Bohai Bay:coastal ports(39.25%),sea level anomaly(19.11%),maritime traffic(9.40%);Laizhou Bay:coastal ports(36.73%),sea level anomaly(19.52%),phytoplankton biomass(7.45%);Hangzhou Bay:coastal ports(42.77%),sea level anomaly(14.60%),phytoplankton biomass(6.06%);Beibu Bay:coastal ports(40.67%),sea level anomaly(16.82%),marine heatwaves(13.35%).The biggest pressure faced by the marine ecosystems of the five bays is the coastal ports,followed by the sea level anomaly and marine heatwaves in the factors of climate change.For Laizhou Bay and Hangzhou Bay,the pressures on the ecological environment caused by eutrophication and nutrient imbalance are relatively large.(5)In view of the various pressures and threats faced by China’s offshore marine ecosystems,the Nature-Based Solutions can help meet the urgent needs to improve coastal resilience and are also important in addressing climate change risks,protecting and restoring ecosystem integrity,and optimizing landscape patterns.Also,it plays an important role in improving the service functions of marine ecosystems and realizing the value of ecological products.It can effectively solve various social challenges,and contribute to the realization of the United Nations "Marine Sustainable Development Goals(SDG 14)" and the United Nations "Decade of Ocean Science for Sustainable Development(2021-2030)" and improve human well-being and biodiversity.