Dep. of Environmental Studies and Sciences, Univ. of Winnipeg, Winnipeg, MB, R3B 2E9, Canada.
Dep. of Chemistry, Univ. of Winnipeg, Winnipeg, MB, R3B 2E9, Canada.
J Environ Qual. 2020 May;49(3):700-711. doi: 10.1002/jeq2.20062. Epub 2020 Mar 30.
Increased phosphorus (P) availability under flooded, anaerobic conditions may accelerate P loss from soils to water bodies. Existing knowledge on P release to floodwater from flooded soils is limited to summer conditions and/or room temperatures. Spring snowmelt runoff, which occurs under cold temperatures with frequent freeze-thaw events, is the dominant mode of P loss from agricultural lands to water bodies in the Canadian Prairies. This research examined the effects of temperature on P dynamics under flooded conditions in a laboratory study using five agricultural soils from Manitoba, Canada. The treatments were (a) freezing for 1 wk at -20 °C, thawing and flooding at 4 ± 1 °C (frozen, cold); (b) flooding unfrozen soil at 4 ± 1 °C (unfrozen, cold); and (c) flooding unfrozen soil at 20 ± 2 °C (warm). Pore water and surface water were collected weekly over 8 wk and analyzed for dissolved reactive phosphorus (DRP), pH, calcium, magnesium, iron (Fe), and manganese (Mn). Soils under warm flooding showed enhanced P release with significantly higher DRP concentrations in pore and surface floodwater compared with cold flooding of frozen and unfrozen soils. The development of anaerobic conditions was slow under cold flooding with only a slight decrease in Eh, whereas under warm flooding Eh declined sharply, favoring reductive dissolution reactions releasing P, Fe, and Mn. Pore water and floodwater DRP concentrations were similar between frozen and unfrozen soil under cold flooding, suggesting that one freeze-thaw event prior to flooding had minimal effect on P release under simulated snowmelt conditions.
在水淹、厌氧条件下，磷（P）的可利用性增加可能会加速土壤中 P 向水体的流失。目前，关于水淹土壤向洪水释放 P 的知识仅限于夏季条件和/或室温。在频繁发生冻融事件的低温下发生的春季融雪径流是加拿大草原农田向水体中 P 流失的主要模式。本研究通过在实验室中使用来自加拿大马尼托巴省的五种农业土壤，研究了温度对水淹条件下 P 动态的影响。处理方法是：(a) 在-20°C 下冷冻 1 周，在 4±1°C（冷冻、低温）下解冻和水淹；(b) 对未冷冻的土壤在 4±1°C（未冷冻、低温）下进行水淹；和 (c) 对未冷冻的土壤在 20±2°C（温暖）下进行水淹。在 8 周的时间内，每周收集一次孔隙水和地表水，并分析溶解反应性磷（DRP）、pH 值、钙、镁、铁（Fe）和锰（Mn）。在温暖的水淹条件下，土壤中 P 的释放得到增强，与冷冻和未冷冻土壤的低温水淹相比，孔隙水和地表洪水的 DRP 浓度明显更高。在低温水淹下，厌氧条件的发展缓慢，Eh 仅略有下降，而在温暖的水淹下，Eh 急剧下降，有利于促进释放 P、Fe 和 Mn 的还原溶解反应。在低温水淹下，冷冻和未冷冻土壤的孔隙水和洪水 DRP 浓度相似，这表明在模拟融雪条件下，一次冻融事件对 P 释放的影响很小。
