Impacts of land use and water level fluctuation on soil aggregates and nitrogen and carbon in newly formed reservoir buffer strips

Organic matter distribution patterns and soil aggregate stability (SAS) are critical factors for comprehending the environmental evolution of reservoirs and their surroundings. However, it remains unclear how SAS and aggregate-related N and C respond to external environmental factors (e.g., land use, water level fluctuation) in the newly formed reservoirs' buffer strips. In this work, we examined the impacts of the distance from the watercourse and different land use types on SAS and the patterns of organic matter distribution before and after seasonal water level fluctuations (in April and June 2021) in the Chushandian Reservoir (CR) buffer strips. The research discovered that the mean weight diameter (MWD) and geometric mean diameter (GMD) of soil aggregates varied across land uses, ranking as: woodland > grassland > abandoned cropland. Moreover, both MWD and GMD increased as the distance from the watercourse grew. Based on variation partitioning analysis and partial least squares path modelling results, distance from the watercourse showed less effect on nutrient content and SAS than land uses, and aggregate fractions played a mediating role in this process. Furthermore, the relative contribution of coarse aggregate fractions (macroaggregates, > 0.25 mm) to soil N and C levels was greater than that of fine aggregate fractions (microaggregates, < 0.25 mm). The research findings illustrate that various protection measures should be considered for different land use strategies to enhance SAS and promote the accumulation of N and C associated with aggregates in the CR buffer strips. In addition, these findings can provide valuable references for ecological restoration efforts in regions with comparable situations.