|Other Abstract||Landscape connectivity is critical to biodiversity conservation and ecosystem stabilization. The Yellow River Delta has the youngest coastal wetland ecosytems with high biodiversity and ecosystem services in the world, which makes it a typical area to study landscape connectivity. In recent years, due to intensive human activities, wetlands in this detla had been significantly fragmented, resulting in the decreasing of
landscape connectivity. Understanding the mechanism of the connectivity changes and effectively identifying the key landscape elements to affect connectivity will provide data support and scientific basis for the wetland conservation and restoration management in the Yellow River Delta.
This study selected 1991 and 2020 as the key time nodes of wetland changes in the Yellow River Delta. We identified coastal reclamation and oil wells, two main drivers of wetland connectivity, and analysed their effcts on wetland connectivity, combining remote sensing, GIS and circuit theory model technologies. Here, we use a framework of wetland source identification, resistance surface construction and corridor extraction to carry out the following work. (1) Based on high-resolution remote sensing images, land use types (3 first-level, 19 second-level and 36 third-level) in 1991 and 2020 were visually interpreted. At the same time, coastal reclamation and oil wells were extracted. (2) Conefor software was used to analyze landscape structure and thus 73 ecological sources were identified according to the “attribute-structure” framework;
(3) The resistance surface was constructed by referring to relevant literature and night light data; (4) The potential ecological corridors and Least Cost Path (LCP) were calculated using Circuitscape to analyze the impacts of reclamation activities and oil wells on landscape connectivity in 1991 and 2020; (5) The “pinch points” and obstacle areas were extracted to analyze their spatial characteristics. Based on our results,
suggestions for conservation and restoration management of wetland landscape connectivity in the Yellow River Delta were put forward.
The results showed that:
(1) The area of natural wetlands decreased by 787.20 km2 from 1991 to 2020,while the areas of constructed wetlands and non-wetlands increased significantly in the Yellow River Delta. Natural wetlands were significantly fragmented except for the protected areas (PAs) in the Yellow River Delta Nature Reserve. The probability of connectivity (PC) of the natural wetlands decreased from 0.1801 to 0.0464.
(2) During the past 30 years, the area of seven major reclamation types increased by 814.26 km2. The reclamation activities were the most prominent in the central and western parts of the Yellow River Delta, where herbaceous swamps and shrub wetlands had been transferred. 8,869 oil wells had been built, mainly in the central and eastern industrial and mining areas and 325 oil wells were built in the PAs. Most of wells were distributed in the shrub wetlands and salt marshes in the northern part of the PAs.
(3) The results of the Circuitscape showed that: Spatial changes in potential ecological corridors and LCP are consistent with those of reclamations and oils well.
In 1991, the potential ecological corridor was wide, but in 2020, the cumulative current density distribution was fragmented, the potential ecological corridor became narrower, and the LCP disappeared or became longer. On the basis of reclamation activities and oil production field construction, the accumulative current density appears the cliff-like patch low value area, the potential ecological corridor becomes crowded, the LCP is obviously lengthened, and a large number of LCPs have been shared by multiple ecological resources; Reclamation activities mainly affected the potential ecological corridors and LCP of shrub wetlands, salt marsh wetlands and mud flat, which showed that the connectivity of coastal wetlands in the east and north of the Yellow River Delta decreased significantly. The oil production field construction
mainly affects the potential ecological corridor and LCP of shrub wetlands, forest wetlands and river, which mainly distributed in the central and southwestern Yellow River Delta.
(4) In 2020, the area of “pinch point” affected by reclamation was 55.71 km2, of which the area of “pinch point” in the PAs was 24.06 km2, accounting for 16.91%. The area of “pinch point” affected by oil production field is 86.56 km2, of which 36.06 km2
is within the PAs, accounting for 25.34%. The obstacle areas are mainly concentrated in the west and southeast of the northern protected area and the central and south of the Yellow River Delta.
(5) Based on the results above, the detailed suggestions on wetland conservationand restoration management in the Yellow River Delta were put forward. We should strictly control the ecological background value and maintain the connectivity of the ecological corridors. At the same time, pinch areas should be given high priority of conservation and the obstacle areas should be given high priority of restoration, respectively.|