Effects Of Human Activity Intensity On Hydrological Connectivity Of Coastal Wetlands In The Yellow River Delta

The abundant coastal wetland resources in the Yellow River Delta have provided favorable conditions for the development of local industry,mining,aquaculture,salt and agriculture.Increasingly frequent human activities have seriously interfered with the land use/cover,landscape pattern and wetland hydrological connectivity in this region.In order to explore the impact of human activity intensity on the hydrological connectivity of the coastal wetland of the Yellow River Delta,this paper adopted ArcGIS spatial analysis technology,field investigation and laboratory analysis to explore and analyze the spatio-temporal changes of land use/cover and hydrological connectivity of the coastal wetland of the Yellow River Delta from 1991 to 2021.On this basis,the index system of human activity intensity and the evaluation index system of hydrological connectivity were constructed to explore the relationship between human activity intensity and the hydrological connectivity of coastal wetlands of the Yellow River Delta,as well as the environmental effects caused by the obstruction of hydrological connectivity.The research results are as follows:(1)From 1991 to 2021,the spatial pattern of human activity intensity in the coastal wetland of the Yellow River Delta extended from the interior of the region to the edge.The area of natural wetland decreased by 835.42 km~2,the area of constructed wetland and non-wetland increased by 366.49 km~2 and 450.51 km~2,respectively.The average annual change rates(K)of natural wetland,constructed wetland and non-wetland area were-1.52%,15.17%and 1.95%,respectively.The comprehensive land use dynamic attitude in the study area showed an"M"shaped fluctuation trend,and the land use change was significant during 1996-2001 and 2011-2016.Human activities during this period had a significant impact on the land use types of coastal wetlands in the Yellow River Delta.From 1991 to 2021,the human activity intensity index(HAILS)increased from 7.93%to 18.84%.The disturbance and impact of human activities on the study area,such as farmland reclamation,aquaculture,salt pan development and oil field construction,became more and more serious over time,and the land use/cover type changed accordingly.During the study period,the corresponding land use types of areas with high human activity intensity were residential areas,industrial and mining areas,aquaculture ponds,salt pans and cultivated land.(2)From 1991 to 2021,the spatial distribution of tidal gullies in the coastal wetlands of the Yellow River Delta has changed significantly,and tidal gullies are distributed in the north and south sides of the lower Yellow River and the estuary.The tidal flat in this region is widely spread,and the influence of human activities is very weak.Tidal gullies constantly develop and evolve under the natural state,especially in the south bank of the Yellow River.Therefore,the nodes are highly connected and the network connectivity is good.The number and length of tidal crevices showed a"W"shaped fluctuation,the frequency of tidal crevices was smaller in the early period and larger in the late period,and the density of tidal crevices showed a fluctuation characteristic of decreasing and increasing.The mean of network connectivity(α)was0.32,the mean of node connectivity(β)was 1.62,and the mean of network connectivity(γ)was 0.55.All the indexes were small,and the hydrological connectivity was weak.The development and evolution of tidal gully had fractal characteristics,but the network connectivity of tidal gully was relatively low.During the study period,the water patch area in the study area basically showed an increasing trend,and the hydrological connectivity index(IIC andPC)showed the same trend.Taking 2011 as the cut-off point,it first decreased and then increased,and reached the maximum value in 2021,which were 0.40 and 0.57 respectively.Based on dIIC index and dPC index,the distribution of important wetland patches in the Yellow River Delta was consistent,and the importance level of water patches in the Yellow River estuary management station area was high.(3)From 1991 to 2011,there was a significant negative correlation between HAILS andIIC at the 1%level,and the correlation coefficient r was-0.962;the correlation coefficient r between HAILS andPC was-0.812;the correlation coefficient r was a significant positive correlation between IIC andPC at the 5%level,and the correlation coefficient R was 0.898.With the increasing intensification and intensity of human activities,the structural connectivity and functional connectivity of hydrological connectivity in the study area decreased significantly,and their changes were consistent and synchronized.From 2011 to 2021,HAILS increased significantly and then slightly decreased,while IIC andPC kept increasing.The reason is that the implementation of wetland ecosystem restoration project in the Yellow River Delta has effectively restored wetland hydrological connectivity,so the hydrological connectivity index has increased.(4)The distribution of heavy metals,petroleum hydrocarbons and antibiotics in soil varies with different land use types in the Yellow River Delta coastal wetland.In terms of heavy metals,the content of heavy metals in soil surface was lower than the national standard and the soil background value of Shandong Province except for Cd element.There is a strong correlation between Cu and Cr and Zn at the 1%level.The enrichment coefficients of Cr,Cu,Zn and Pb are all less than or equal to 1,and there is trace enrichment.The enrichment coefficients of Cr and Pb in aquaculture ponds and Zn in cultivated land were about 1,which were derived from crustal weathering.Cd was relatively enriched in roads,cultivated land,aquaculture ponds and natural wetlands and was affected by human activities.Except for Cd in cultivated land,the risk levels of five heavy metals in other land use types were slight.In addition,the potential ecological risks of the five heavy metals were slight in each land use type.From the perspective of petroleum hydrocarbon,soil samples on both sides of dams and roads contain very high content,and the construction of linear facilities seriously hinders the hydrologic communication on both sides,resulting in continuous accumulation of pollutants in wetland soil.In terms of antibiotics,antibiotics produced by human activities have not caused serious pollution to wetland soil,and only the types and contents of antibiotics have been tested in cultivated land and aquaculture ponds.The antibiotics contained in cultivated land soil are norfloxacin,ciprofloxacin and chloramphenicol.Under different soil depths,the contents of antibiotics contained in aquaculture ponds are oxytetracycline and chloramphenicol.The amount of oxytetracycline decreased with soil depth,and chloramphenicol was detected only in surface samples.