Investigating the influence of integrated landscape connectivity on water dissolved organic carbon variations in farm pond catchments of subtropical southern China

The landscape connectivity in farm pond catchments leads to complex hydrologic and biogeochemical processes, which is important to the carbon cycle of the watershed. However, little attention has been paid to analyzing the influence of landscape connectivity on water dissolved organic carbon (DOC) content in farm pond catchments. In this study, we developed an integrated landscape connectivity framework that encompasses landscape connectivity metrics, graph theory connectivity indices, and spatial distance. And the graph theory connectivity indices were constructed based on the modified resistance surface using a function that integrated landscape development intensity, slope, and livestock density. Using DOC content data from 86 farm ponds monitored between June 2017 and May 2018. The results demonstrated that the average water DOC content in farm ponds was higher during the dry season (5.35 +/- 2.03 mg/L) compared to the wet season (4.27 +/- 1.40 mg/L). The individual effects of landscape connectivity metrics and graph theory connectivity indices on DOC content were more prominent during the dry season, while the spatial distance had a more significant influence in the wet season. The interactive effects of determinant variables had a more substantial influence on pond water DOC content than their individual effects during both wet and dry seasons. The interactive effect variation ratio (IEVR) of all variables was positive in both seasons (0.143-0.777). Combining landscape connectivity metrics, graph theory connectivity indices, and spatial distance (22.0-24.3%) improved the interpretation of DOC content in comparison to using separate (0.4-12.1%) or paired variables (0.3-19.3%). Our findings suggest that integrated landscape connectivity is necessary to further understand the role of ponds in the organic carbon cycling of surface water. These strategies should not only focus on landscape connectivity metrics, but also consider the influences of graph theory connectivity indices and spatial distance in farm pond catchments.