微塑料对农田土壤结构及有机质动力学过程的影响

Micro-plastics (MPs) are commonly defined as particles or fibers with a diameter < 5 mm consisting of polymers. The presence of micro-plastics in the environment is a problem of growing concern. While it is widely acknowledged that MPs in the ocean are a serious issue with potentially negative effects on marine organisms, information about MPs storage，transport and impact in agricultural soil is fragmentary. The MPs in agricultural soil originate from fragmentation of larger plastic litter in the agricultural production and routine applications of sewage sludge. In the basin of the Dian Lake, southwestern China, the conventional paddy fields have been instead by intensive vegetable fields under plastic-greenhouses for more than 20 years, which have been subjected to long-term plastic shedding, sewage sludge application and wastewater irrigation. These practices would result in serious MPs accumulation in soils, and the risk of MPs released from soil to the Dian Lake has also be apparent in the meanwhile. Thus, knowledge about the occurrence and consequence of MPs in soils will allow us to sustainably manage the agricultural system and minimize the damage of MPs on soil health. In order to improve the understanding about the effects of MPs on agricultural soils quality and its productivity in the Dian Lake's basin, the objectives of this study are (1) to determine the source, occurrence and distribution of MPs in soils under an intensive vegetable cropping system, and (2) to determine the effects of MPs on soil organic matter dynamics and aggregate formation. The results will advance our currently limited understanding of the occurrence and influence of MPs in agricultural soils. We also expect the results of this project would support the management practices to improve the stability of the agroecological system and environmental health in the Dian Lake's basin.

土壤中微塑料的巨量累积不仅危害农田土壤质量，而且也对区域乃至全球环境造成不利影响。滇池湖盆区农田广泛使用农膜和污泥的历史已近30年，但目前对土壤中微塑料的来源、累积特征及环境影响却所知甚微。针对该问题，本课题通过以小流域为单元实施野外定位研究和室内模拟研究相结合的方式，试图达到明确农田土壤中微塑料主要来源和探明保持农田土壤质量的微塑料数量阈值的目的。本项目首先从土壤、有机肥（包括污泥）、灌排水及河道沉积物中微塑料的形态、大小、数量及分布位置的研究入手，揭示滇池南部柴河小流域内不同农田土壤中微塑料的主要来源、累积特征和流失状况；其次通过开展微塑料与不同质地及有机质含量土壤的共培养试验，深度剖析微塑料类型及数量影响土壤有机质动力学过程与团聚体形成的作用机制，明晰土壤微塑料富集数量与土壤物理质量变动之间的关系。研究结果以期为保持滇池湖盆区农田土壤健康和环境友好提供合理的理论指导和技术支持。

土壤中微塑料的巨量累积不仅危害农田土壤质量，而且也对区域乃至全球环境造成不利影响。滇池湖盆区农田广泛使用农膜和污泥的历史已近30年，但目前对土壤中微塑料的来源、累积特征及环境影响却所知甚微。针对该问题，本课题通过以小流域为单元实施野外定位研究和室内模拟研究相结合的方式，试图达到明确农田土壤中微塑料主要来源和探明保持农田土壤质量的微塑料数量阈值的目的。研究结果显示：滇池南部流域农田表层土壤微塑料颗粒的浓度范围平均为18760颗粒kg-1，92%的微塑料为纤维状，72%的微塑料颗粒分布在土壤团聚体中，灌溉和施用污泥可能是导致滇池南部流域农田土壤微塑料累积的重要因素；通过培养试验发现，随着聚酯微纤维添加浓度升高土壤中天然有机质的累积在减少，并且降低了土壤水稳性大团聚体（>2mm）中有机碳的含量，聚酯微纤维表面可能是促进土壤中有机质降解的热点区域；田间试验和培养试验研究发现聚酯微纤维明显改变了土壤中孔隙的分布特征，但对土壤容重和饱和导水率无显著影响，同时聚酯微纤维对土壤结构稳定性的影响还存在较大的不确定性。研究结果反映出聚酯微纤维可能是通过改变特定的土壤物理性质，从而对土壤微生物群落及其功能产生影响。总体而言，本项目研究结果为微塑料在农田土壤中的累积提供了有价值的证据，同时也为微塑料对土壤物理性质、有机碳动力学和微生物群落的影响提供了有价值的见解。由于微塑料是人为污染物，随着微塑料在土壤中的积累越来越多，更好地了解微塑料表面的生化过程及其与矿质土粒的相互作用，对于管控农田土壤微塑料污染和保护耕地健康至关重要。