| Coastal wetland is an ecological transition zone where the land and sea meet.It is an important habitat for waterbirds and the most intense area of human activity in the coastal zone.However,due to the impact of coastal ecological engineering,the natural tidal process has been lost inside,and the habitats have gradually shown trnds such as desalination,terrestrialization and rapid pattern evolution.Problems such as area reduction and quality degradation have emerged,and scientific management and control measures are urgently needed to mitigate the negative effects of coastal ecological engineering.Therefore,in view of the threats and challenges facing by waterbird habitats under the impact of coastal ecological engineering,we explore the impact of coastal ecological engineering on waterbird habitats and populations,and provide scientific management for habitats that require manual control,which has important guiding significance for the coastal waterbird habitats' protection and restoration.This study took waterbird habitats as the study objects:(1)aiming at the impact of coastal ecological engineering on waterbird habitats,East Hengsha shoal was selected as the typical study area.Through field surveys,remote sensing image and data statistical analysis the impact of coastal projects on waterbird habitats and populations in the past decade was analyzed,and the correlation between habitat factors and population of Anseriformes was clarified to provide the scientific and theoretical basis for the comprehensive management of waterbird habitats;(2)For the Chongming Dongtan Spartina alterniflora control and waterbird habitats optimization project area(hereinafter referred to as the ecological restoration area),centered on the two ecological elements that are closely related to the quality of waterbirds' habitats: vegetation and hydrology,through the "water-salt" two factors control experiment,the study analyzed the impact of water level and salinity variation on wetland plants after the costal ecological engineering,quantified the water level and salinity survival threshold of plants,and put forward the plant control technology.On this basis,considering the hydrological processes such as rainfall,water surface evaporation,plant evapotranspiration and soil infiltration,the ecological water demand was calculated and the hydrological regulation scheme was formulated.The plant control technology and hydrological regulation scheme were integrated into the scientific,reasonable and implementable comprehensive managements for waterbird habitats.The main results and conclusions are as follows:1.The impact of coastal ecological engineering on waterbird habitats andpopulations.The costal ecological engineering has changed the waterbird habitats and populations significantly in the East Hengsha shoal.With the advance of the project,the natural tidal flat showed a dynamic change trend,the area of the bare flat was reduced,but the vegetation coverage was increasing;With the supply of sediment,a large area of wetland had been created in the silting-promoting area.The plants grew and propagated rapidly,and the proportion of water had decreased.The land-forming area gradually succeeded to freshwater ecosystem,the dominant plant species Phragmites australis had been replaced by Typha angustifolia,and a large number of submerged plants appeared in the water.With the change of habitat in East Hengsha shoal,Anseriformes gradually moved from the land-forming area and natural tidal flat to the silting-promoting area.The main factor affected the quantity of Anseriformes in the natural tidal flat was the area of Scirpus mariqueter / Scirpus triqueter.The main influencing factors of the silting-promoting area were the emergent plant area,NDVI and non-vegetation covered water area;the main influencing factor of the land-forming area was the submerged plant area.In conclusion,the ecological engineering wetland should have open water,adequate food supply and relatively low vegetation coverage.2.Plant control technology for waterbird habitats in coastal ecologicalengineering area.Due to the loss of natural tidal process,the water level of the ecological restoration area was relatively stable,and the salinity of water reduced gradually.In recent years,the area of Scirpus mariqueter decreased,and it was gradually replaced by Typha angustifolia.The results showed that the suitable environment conditions for the growth and reproduction of Scirpus mariqueter and Phragmites australis were 0~5‰,0~10 cm and 0~10‰,0~20 cm respectively.Typha angustifolia was suitable for living in low salinity(0~5‰)and high water level(50 cm),the main limiting factor for its growth was the high water salinity.In lower water level condition,the increase of water level can promote the growth of plant height and biomass,but excessive water level and salinity would play a limiting role.The maximum survival salinity and water level threshold of Scirpus mariqueter in stable condition(11.9~16.6‰;8.7~23.8 cm)were significantly lower than that of natural environment;The Phragmites australis maximum survival salinity threshold of stable condition(14.7~18.3‰)was higher than that of natural environment.However,when the salinity was more than 10‰,the Phragmites australis maximum survival threshold in stable condition(41.5~53.3 cm)was significantly higher than that of natural environment.Based on the above results,the ecological restoration area can maintain the low water level and salinity conditions in spring;raise a certain water level to promote the growth of plant height of protected plant species in summer;maintain low water level and salinity to ensure the propagation process of plants during plant propagation period.In addition,it can be combined with the auxiliary measures of artificial cutting to control the freshwater plant Typha angustifolia.3.Hydrological regulation technology for waterbird habitats in coastalecological engineering area.According to the calculation of ecological water demand on the principle of water balance,the ecological water demand of ecological restoration area(habitat types of Anseriformes)had obvious seasonal change and spatial distribution characteristic.The ecological water demand under the water level demand target of Anseriformes was relatively smaller in May,summer(7~8)and autumn(9~11),and was larger from winter to early spring.C1 N was a large area of water,so needed the largest water demand;C4 was the Scirpus mariqueter shoal,so the water demand was small.Generally speaking,the open water region need to increase the water level in winter to early spring ensure the habitat demand of Anseriformes.In the reed zone,the high salinity water in autumn can be used to control the water desalination.Dynamic monitoring and management should also be strengthened to achieve the reasonable and scientific hydrological regulation.4.Comprehensive control managements of waterbird habitats in coastalecological engineering area.Under the comprehensive management goal,the water transfer in the low water level areas were concentrated in March and Step,while that in other areas were concentrated in March,June and November.The suitable water level can also be achieved by regional water transfer in the secondary habitats.Due to the low water level demand in spring,regional drainage was concentrated in March.In the future management of ecological restoration area,on the premise of ensuring ecological water demand,it is necessary to comprehensively consider the rationality and suitability of habitats,highlight the key points for protection;strengthen environmental monitoring and protection,and make efficient use of water resources;strengthen publicity and education with typical cases of waterbird habitats as the goal to achieve the sustainable development of waterbird habitats.In summary,if the coastal ecological project lack reasonable control,the waterbird habitats would gradually be replaced by freshwater and terrestrial ecosystems,and change the wetland pattern,thereby affecting the quality and stability of waterbird habitats.It is suggested that reasonable plant management and hydrological regulation can be used to maintain the appropriate plant,bare flat and water area ratio and sufficient food sources to achieve suitable and sustainable habitats development and mitigate the negative impact of coastal engineering. |
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