Hydrochemical Characteristics Jointly Determine the Transport and Cycling of Soil Carbon, Nitrogen, and Phosphorus in an Arid Chinese Wetland

Salt accumulation gradually changes the cycling of carbon (C), nitrogen (N), and phosphorus (P) and may even transform sinks into sources in arid wetlands. However, it's not clear how hydrochemical characteristics affect the wetland's source or sink function or how they affect C, N, and P cycling in arid regions. To clarify these relationships, we conducted field measurement in arid northern China. We simulated the variations of hydrochemical characteristics and the storage and stoichiometry of C, N, and P using the process‐based DeNitrification‐DeComposition (DNDC) and Hydrus‐1D models. The meteorological and hydrological processes had obvious characteristics of seasonal and interannual changes. The measured evapotranspiration averaged 660.23 and 587.94 mm year−1 in the saltmarsh and riparian wetlands, respectively. The soil showed a clear trend with higher SO42−, Na+, Ca2+, and Cl− fractions in comparison with lower Mg2+, K+, and HCO3− fractions, with the major ion and nutrient concentrations gradually decreasing with increasing depth in the soil. The major ion types had characteristics of Na+‐Ca2+‐SO42−‐Cl− in the saltmarsh wetland and riparian wetland. The storage of total C, N, and P were 372.72 ± 66.52 t C/hm2, 10.92 ± 2.59 t N/hm2, and 17.55 ± 1.54 t P/hm2 in the saltmarsh wetland versus 119.72 ± 27.88 t C/hm2, 4.38 ± 1.24 t N/hm2, and 13.17 ± 1.46 t P/hm2 in the riparian wetland. Therefore, wetland salinization in our study led to increased soil C, N, and P contents and storage and thereby enhanced the sink function of the wetlands. Key Points We simulated the variations of hydrochemical characteristics and the storage and stoichiometry of C, N, and P The model coupled the Hydrus‐1D and DNDC models to solve a drawback of hydrochemical simulation We identified the mechanisms by which hydrochemical characteristics determine the transport and cycling of soil nutrient