Stoichiometric insights into sediment carbon, nitrogen, and phosphorus deposition in small forest reservoirs in southeast China under forest conversion and climate change

Abstract

Forest reservoirs play a critical role in climate regulation, ecological balance, and the maintenance of the hydrological cycle. Stoichiometry is a fundamental ecosystem characteristic that offers essential insights into the fates of carbon (C), nitrogen (N), and phosphorus (P) deposits in sediments. However, studies investigating nutrient deposition patterns in forest reservoirs using C/N/P stoichiometry are scarce. Herein, we analyzed two sediment cores from forest reservoirs in southeast China and used ¹³⁷Cs and ²¹⁰Pb_ex chronologies to assess nutrient deposition over the past 40 years. The mean sediment C, N, and P accumulation rates were 89.30 ± 27.47, 7.50 ± 1.79, and 1.94 ± 0.32 g·m⁻²·a^-1, respectively. Redundancy analysis indicated that soil erosion and sediment grain size significantly affected the nutrient deposition and stoichiometric ratios. Forest conversion and extreme rainfall events increase soil erosion and nutrient deposition in the sediments. Mining activities exacerbate sediment coarsening and nutrient deposition, thereby elevating the C/N/P stoichiometric ratios. Conversely, afforestation efforts and the construction of flood levees intercept coarse particles and organic matter, thereby reducing C and N deposition and the C/N/P stoichiometric ratios. The C/P and N/P ratios dynamically reflected the patterns of C and N deposition. These results provide novel insights into the dynamic feedback mechanisms of stoichiometry on C, N, and P deposition in forest reservoir sediments against a backdrop of increasing forest conversion and frequent climatic anomalies. Future research should focus on afforestation and flood levee construction, which are effective in mitigating the negative effects of forest conversion on soil erosion.