Comparison and application of spatial pattern measurement methods for water surface of dike-pond

Dike-pond is a landscape system where water and land areas are integrated through ecological and agricultural processes. This type of system is commonly found in the low-lying river delta of China's eastern coast. The water surface of the dike-pond plays an important role in the local economic development and ecological services. However, the use of existing landscape metrics to depict the spatial pattern of the water surface of the dike-pond has not been fully studied. This research aims to fill the gap by comparing a range of such metrics through a case study based on the Xingtan Township of Foshan City, China. We divide the dike-ponds in the study areas into two types: regular and irregular, which represent after and before dike-pond consolidation project respectively. We then test 16 landscape metrics using six cases of compact or scatter pattern. The metric that can distinguish various cases is applied to measure the water pattern of the dike-pond in the study area. Our comparison results suggest that the metric called Weighted Aggregation and Closeness (WAC) is the only one that can accurately capture all the water patterns exhibited in our study area. Among other 15 metrics, Mean Patch Fractal Dimension (MPFD), Area Weighted Mean Patch Fractal Dimension (AWMPFD), Mean Patch Size (MPS), Number of Patches (NumP), and Total Landscape Area (TLA), poorly perceive the pattern difference of the same pond types. And the metrics including Area-Perimeter ratio (AP), Perimeter-Area ratio (PA), Total Edge (TE), Mean Shape Index (MSI), Area Weighted Mean Shape Index (AWMSI), Mean Patch Edge (MPE), and Median Patch Size (MedPS) give measurement results that are contrary to the water pattern. Our application results show that the average WAC value of the regular pond is 40.18% higher than that of the irregular ponds. All the regular ponds have WAC values above 0.20, of which 66.76% are greater than 0.25. Only 4% of the irregular ponds have WAC values above 0.30, but 77.22% of them have WAC values lower than 0.25. These indicate that the pattern of the regular pond is more compact than that of the irregular pond. This is because the regular ponds are formed by large-scale consolidation projects, so they are gridded and closed to each other; the irregular ponds are randomly formed by the individual farmers and scattered around the edge area of the town and the regular ponds. The compact water pattern is beneficial to the dike-pond economy by providing a large proportion for aquaculture and exhibiting agglomeration effects, while the scatter water pattern is beneficial to the dike-pond ecology by promoting the land-water interaction. We note that the pattern difference of the regular pond is not obvious in the study area since the consolidation projects are standardized and uniform. There are more spatial differences of the water pattern of the irregular pond. The WAC values of such type in the central of the study area is 15% higher than that in the northern and southern, due to the central ponds have not been consolidated. These findings are useful to reveal the relationships of spatial pattern with the economic and ecological benefits of the dike-pond. Furthermore, WAC is not only effective for measuring the water pattern of the dike-pond, but also for other patterns with disconnected features.