东北黑土区垄作农田融雪侵蚀过程中氮磷迁移转化机制研究

Snowmelt erosion is the dominant driving force of agricultural nonpoint source pollution in the snowmelt period, especially nitrogen and phosphorus , and the ridge tillage farmland in northeast black soil region is the main source of nonpoint source pollution. However, the migration of nitrogen and phosphorus in the snowmelt period and the accumulation of nitrogen and phosphorus in the cold season were not clear, the sources of nitrogen and phosphorus from the snowmelt runoff or sediment were not sure, and studies about transformation and migration of nitrogen and phosphorus in ridge tillage farmland were rare. In this study, the ridge tillage farmland in the northeast black soil region will be selected as the objects, subsidence of nitrogen and phosphorus in snow will be determined by observing to analyze the accumulation of nitrogen and phosphorus. The transformation of nitrogen and phosphorus under seasonal freeze-thaw and snow cover will be studied by situ observation of nitrogen, phosphorus, water content, soil aggregates, organic matter and other indicators. Snowmelt water infiltration and change of soil nitrogen and phosphorus will be cleared by observing snowmelt process and releasing of nitrogen and phosphorus. The migration mechanism of dissolved nitrogen and phosphorus in snowmelt runoff and adsorbed nitrogen and phosphorus during snowmelt erosion in different slope and ridge tillage farmland will be clarified. And the model of snow-snowmelt-snowmelt runoff-snowmelt erosion and accumulation-transformation-migration-deposition of nitrogen and phosphorus of the ridge tillage farmland in the northeast black soil region will be constructed. This will be useful to prediction and prevention of non-point source pollution of the ridge tillage farmland in the snowmelt period, and this will be the basis theories for ecological environment improvement in seasonal snow area.

融雪侵蚀是融雪期农业非点源污染物氮磷迁移的主要驱动力，垄作农田是东北黑土区融雪期氮磷迁移的主要来源。目前，融雪期氮磷迁移过程和寒季氮磷累积规律尚不明确，融雪径流和侵蚀泥沙中氮磷来源还不能准确判断，也基本未开展垄作农田寒季氮磷累积转化迁移规律的研究。本项目以东北黑土区垄作农田为研究对象，拟在积雪特征观测基础上，确定新雪和积雪中氮磷沉降量，阐明雪中氮磷累积规律；通过原位观测土壤中氮磷含量、含水量、团聚体等指标，揭示季节性冻融作用与积雪覆盖影响下土壤氮磷转化规律；通过观测融雪过程及氮磷释放特征，明确融雪水入渗和土壤氮磷含量变化过程，阐明垄作农田不同坡向、不同垄向融雪径流溶解态氮磷和侵蚀泥沙吸附态氮磷迁移机制，从而建立东北黑土区垄作农田积雪-融雪-融雪径流-融雪侵蚀与氮磷累积-转化-迁移-沉积关系模型，为准确预测和防治垄作农田融雪期非点源污染提供科学依据，为改善季节性积雪区生态环境奠定理论基础。

融雪侵蚀是融雪期东北黑土区垄作农田非点源污染物氮磷迁移的主要驱动力，通过研究积雪与氮磷累积过程、冻融作用和积雪覆盖对表土氮磷转化规律影响、融雪与氮磷释放过程、融雪侵蚀对氮磷迁移规律影响、冻融坡面水动力、生物炭施加对融雪期土壤氮磷的影响等内容，揭示了降雪与积雪过程中氮磷累积规律和节性冻融作用与积雪覆盖条件下氮磷转化规律，明确了氮磷随融雪水入渗土壤的过程和融雪期氮磷迁移过程，确定了冻融坡面土壤剥蚀率的主要影响因子和冻融坡面土壤剥蚀率预测模型，探讨了生物炭还田对融雪期土壤养分的影响。结果表明：积雪期主要为11月至2月，通过Hysplit气团后向轨迹分析表明研究地积雪期主要受西北风影响，大气气团主要来自于内陆地区；积雪化学离子含量远大于新雪，积雪对化学离子起到了贮藏作用，积雪总氮表层含量最高，积雪总磷主要集中在底层；土壤0、5、10 cm处温度与雪深相关性均未达到显著水平，整个积雪过程中土壤温度多处于0 ℃之下，并未对积雪消融产生显著影响；季节性冻融过程中，各层土壤氮磷含量差异显著，整体表现为随着土层增加磷含量减少，而氮含量表层最高，表层0-10cm磷含量和0-5cm氮含量显著高于深层10-20cm；积雪消融主要集中在融雪期每日11:00-16:00之间，一般融雪2-6天，阴坡滞后一周左右，雪深与提前4 h气温相关程度最高；融雪径流中氮磷离子含量与径流量正相关，离子含量大小为NO3->PO43-> NH4+>NO2-，径流中离子含量远大于积雪和新雪；BP神经网络预测冻融坡面土壤剥蚀率误差小；生物炭施加量对融雪期有效养分质量分数有极显著影响，融雪前期生物炭主要通过影响积雪融化速度和增加土壤持水能力，来减少土壤有效养分损失。上述探索性研究成果补充了我国有关融雪侵蚀过程中氮磷迁移研究方面的不足，为准确预测和防治农田融雪期非点源污染提供科学依据，有助于进一步揭示季节性积雪区耕地土壤侵蚀机制及其生态环境效应。