稻田-大气氨交换通量特征、影响机制与模拟模型研究

Atomspheric ammonia is one of the major precursors for aerosol, and can also cause soil and water eutrophication when dry and wet deposited as with its derivatives. Ammonia volatilization occurs when nitrogen fertilizers are applied in paddy fields, but little is known about the characteristics and mechanisms of the bi-directional ammonia exchange between paddy field and atmosphere. In this proposed project, the micrometeorological gradient method is used to measure the ammonia exchange fluxes between paddy field and atmosphere under tranditional and optimized nitrogen fertilizer application rates in the doubling rice cropping system in South China, with the objectives to find out the pattern of ammonia flux in multi-time scales (daily, rice season, annual), to quantify the emission, deposition and net fluxes of ammonia, and to illustrate the mechanisms influencing ammonia exchange as affected by nitrogen fertilizer application and environmental factors. The meteorological variables, plant physiological variables that related to ammonia exchange, NH4+ and H+ concentrations in floodwater or soil solution, and atmospheric acidic gases concentrations are measured synchronously during the flux monitoring, and the key parameters are identified using sensitive analysis and locally parameterized for the the two- layer resistance schemes for bi-directional ammonia exchange, which are developed in American and European countries. After verified by the measured flux data, the revised model can be used for estimating the ammonia exchange flux between paddy field and atmosphere in China. The achievement of this study will provide scientific foundation for clarifying the sources and sinks of ammonia and for making strategy of ammonia emission abatement, and an important modeling tool for fluxes estimate in nitrogen cycling research and air quality modeling in paddy fields.

氨气是生成气溶胶的重要前体物质，其本身和它的衍生物的干湿沉降会导致土壤、水体富营养化。稻田施用氮肥会引起氨挥发，但有关稻田-大气氨双向交换的特征及机理还不明确。本研究以南方双季稻田为研究对象，采用微气象学梯度法原位观测传统和优化施氮水平下稻田-大气氨交换通量，揭示氨通量在微观和宏观时间尺度上的变异规律，定量生长季及周年氨挥发、沉降和净通量，阐明施氮肥及环境因子对氨通量的影响机制。同步观测包括气象因子、与氨交换相关作物生理因子、田面水或土壤溶液中NH4+和H+浓度、大气酸性气体浓度等建模所需参数，以欧美地区的双层阻力地气氨交换通量模型为基础，通过敏感性分析，对模型关键参数进行识别并本地化，采用实测数据对新建模型进行检验，建立稻田-大气氨交换通量模型。项目的实施可为探明稻田区域氨的来源及归趋和制定氨减排策略提供科学依据，也将为稻田区域氮循环通量估算及空气质量模拟提供重要的模型工具。

氨气是生成气溶胶的重要前体物质，其本身和它的衍生物的干湿沉降会导致土壤、水体富营养化。稻田施用氮肥会引起氨挥发，但有关稻田-大气氨双向交换的特征及机理还不明确。本研究以南方双季稻田为研究对象，采用微气象学梯度法原位观测传统和优化施氮水平下稻田-大气氨交换通量，揭示氨通量在微观和宏观时间尺度上的变异规律，定量生长季及周年氨挥发、沉降和净通量，阐明施氮肥及环境因子对氨通量的影响机制。同步观测包括气象因子、与氨交换相关作物生理因子、田面水或土壤溶液中NH4+和H+浓度、大气酸性气体浓度等建模所需参数。以欧美地区的双层阻力地气氨交换通量模型为基础，通过敏感性分析，对模型关键参数进行识别并本地化，采用实测数据对新建模型进行检验，建立了稻田-大气氨交换通量模型。研究发现，亚热带典型稻区大气中NH3-N、大气颗粒物PM10中铵氮以及雨水中铵氮年平均浓度分别为5.7 μg·m-3、12.8 μg·m-3和0.8 mg·L-1，氨/铵氮沉降量分别为3.5 kg·ha-1·a-1、5.6 kg·ha-1·a-1和9.1 kg·ha-1·a-1。2013-2016年稻田氨气净交换通量在32-48 kg·ha-1·a-1。其中早稻季氨气排放通量为15-16 kg·ha-1，晚稻季氨气排放量为21-35 kg·ha-1。稻田施氮肥显著提高NH3排放，早、晚稻季氨气排放量平均占施肥量的15%和11%。在年尺度上NH3-N浓度与气温表现出显著正相关；颗粒态铵氮浓度与NH3-N浓度无显著相关，表明研究区NH3-N浓度不是形成颗粒态铵氮污染的主要限制因子；雨水中铵氮浓度主要与颗粒态铵氮浓度成正相关，与降雨量成负相关。在日尺度上氨气浓度与空气温度，风速成正相关，与空气相对湿度成负相关。氨交换通量与冠层NH3浓度、田面水铵态氮浓度、土壤铵态氮浓度、气温、风速成显著正相关。本项目结果为探明稻田区域氨/铵的来源及归趋和制定氨/铵减排策略提供科学依据，也将为稻田区域氮循环通量估算及空气质量模拟提供重要的模型工具。