Ecological Stoichiometry of Carbon, Nitrogen and Phosphorus in Deep Sediments within the Critical Zone of South Dongting Lake Wetland, China

This study investigates the ecological stoichiometric characteristics and driving factors of carbon (C), nitrogen (N), and phosphorus (P) in deep sediments within the critical zone of South Dongting Lake Wetland. Correlation analysis, partial least squares structural equation modeling (PLS-SEM), and gradient boosted decision tree (GBDT) algorithm were employed for this investigation. The results showed that the mean values of the total carbon (TC), soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP) contents in sediments are 9.0, 7.3, 0.9, and 0.5 g kg^− 1, respectively. Sediment C, N, and P contents tended to decrease with increasing burial depth (H). The mean ratios of C/N, C/P, and N/P in sediments were 10.5, 46.5, and 5.1, respectively, notably lower than the averages in wetland soils across China. Lower C/N and C/P ratios indicate that the decomposition rate of organic matter is relatively fast and organic P is prone to mineralization in sediments. Additionally, the lower N/P ratio implies N limitation within the sediments. The TC, SOC, TN, and TP exhibited significant negative correlations with both H and redox potential (Eh), while showing positive associations with water content (W). Moreover, these factors influence ecological stoichiometric ratios (ESR) by directly affecting C, N, and P contents in sediments. The GBDT modelling revealed that TN primarily influenced C/N ratios, while TP predominantly controlled C/P and N/P ratios. The contents of C, N, and P, as well as their ESR in deep sediments of wetland are mainly controlled by H, Eh, and W.