Response of wetland landscape pattern gradient to human activity intensity in Yellow River Delta

Abstract: The Yellow River Delta, located on the west coast of Laizhou Bay, is the most extensive and youngest wetland in the China's warm temperate zone. It possesses abundant species and numerous new land resources. However, urban construction, reclamation, oil exploitation, tourism development and other human activities in recent years have directly or indirectly impacted the wetland ecosystem pattern, and naturally, the wetland landscape has significantly changed. In view of this phenomenon, most scholars have only studied the influence of single human activity on wetland landscape, lacking holistic grasp and response analysis of wetland landscape pattern under different disturbance intensity. Therefore, based on the theory of landscape ecology and the support of RS (remote sensing), ArcGIS and FRAGSTATS, the wetland landscape type map in the Yellow River Delta influenced by the human activities was constructed using the method of artificial visual interpretation with the 4 remote sensing images (1989, 1999, 2009, 2014), and the cultivated land, industrial and mining land and other land use were selected to reflect the intensity of human activities, which was divided into 10 levels from strong to weak using the natural breaks method. Besides, the change characteristics of wetland landscape pattern in different periods within different transects were analyzed, as well as the gradients response of 4 main types of landscape pattern characteristics to human activity intensity in 2014. The results were as follows: 1) The total area of the Yellow River Delta increased slightly. Natural wetland landscape showed a decreasing trend, of which beach was reduced the most, followed by meadow, and the artificial wetland landscape continued to increase. 2) The landscape transfer was very dramatic, mutual transformation between meadow, beach and other natural wetland landscape turned larger, while that between construction land, mining land and other non-wetland landscape turned smaller. Which was the largest decrease in tidal flat, a decrease of 38 245.35 hm2, followed by a decrease of meadow 37 164.54 hm2. 3) Influenced by human activities and other factors, the fragmentation degree of wetland landscape in the Yellow River Delta was intensified within the 25 years, and the patch type was especially more diversified and was more evenly distributed in the landscape. What was more, the landscape also showed obvious spatial differences in different transects due to human activities. 4) At the landscape level, wetland landscape richness and PD (patch density) increased with the decrease of human activity intensity, and in 2009, the number of patches reached eight thousand; yet SHDI (Shannon diversity index) and SHEI (Shannon evenness index) first ascended and then descended, which was consistent with the intermediate disturbance hypothesis. In addition, landscape aggregation increased, and landscape connectivity also increased, which reached 99.42% to the most extent, while the degree of fragmentation reduced. At the type level, the change of landscape pattern could be well reflected by the 4 main landscape types (reservoir pond, aquafarm, salt pan and unutilized land). Especially, PLAND (percentage of landscape), PD, and LPI (largest patch index) had significant variations with the gradient of human activity intensity, and LSI (landscape shape index) and MPFD (mean patch fractal dimension) changed obviously, which indicated that landscape shape was becoming increasingly complicated. The largest patch index of salt pan reached 26%, when human interfered with salt pan to the most extent. The study also revealed the gradient change of landscape pattern along the intensity of human activities, which could provide a reference for the rational development and sustainable utilization of the Yellow River Delta.