Seasonal Synchrony Inflates Spatial Dependence in Water-Quality Markov Chains: Evidence from a Fine-Scale Agricultural Wetland

Spatial Markov chains are increasingly used to infer spatial dependence among water-quality monitoring sites, usually from raw records retaining the common seasonal signal. We tested whether that dependence reflects interaction between sites or synchrony to a shared seasonal driver. Classic and spatial Markov chains were applied to full-year monthly water-quality index (WQI) records from eight connected sites in a Taihu-basin agricultural wetland (2023–2025, 288 site-months). On raw data, a site’s transitions depended significantly on its neighbours’ state (p = 0.038), but the own-versus-neighbour state table was near-degenerate, 22