Spatiotemporal Variations of Temperature, Oxygen, and Salinity in a Typical Constructed Wetland for Source Water Protection in a Plain River Network

ABSTRACT

Pond–wetland–reservoir complexes serve as critical buffers in the pretreatment of micro‐polluted source water, yet their spatiotemporal hydrochemical dynamics—and the ecological implications thereof—remain poorly quantified across functional units. This study characterizes the seasonal and diurnal variability of water temperature (WT), dissolved oxygen (DO), and electrical conductivity (EC) in a multi‐stage source‐water constructed wetland (Yanlong Lake, Yancheng, eastern China) by integrating seven published studies (2013–2019) with two high‐density in situ spring monitoring campaigns (116 sites, 2023). Results suggest that high‐temperature seasons amplify inter‐unit thermal heterogeneity (maximum ΔWT up to 1.5°C), whereas the emergent vegetation zone appears to attenuate both seasonal and diurnal temperature fluctuations—exhibiting seasonal amplitude (DifMaxMin) below ~21°C, suggesting an indicative thermal‐buffering threshold in this system. The wetland maintained a net oxygenation effect throughout the year, elevating yearly mean DO concentration and saturation by ~74% relative to source water, with the strongest enrichment occurring during winter and spring. Electrical conductivity showed a progressive upstream‐to‐downstream increase during spring, with littoral margins of the submerged and deep‐water zones emerging as ionic accumulation hot spots. On the diurnal scale, the distributary channels of the emergent zone remained near‐isothermal (~20°C–21°C) and relatively resistant to atmospheric forcing, whereas littoral zones behaved as temperature‐sensitive hot spots with pronounced DO supersaturation and elevated EC. We introduce the concepts of “thermal‐buffer zones” and “temperature‐sensitive zones” to characterize wetland thermal heterogeneity and discuss the implications of the ~21°C threshold for biogeochemical processes and algal ecology. These findings advance understanding of eco‐hydrochemical coupling in constructed wetlands and may inform climate‐adaptive wetland design and source‐water quality management.