Department of Earth Sciences & Research Center on Natural Resources, Health and the Environment. University of Huelva, Campus "El Carmen", 21071, Huelva, Spain.
Department of Earth Sciences & Research Center on Natural Resources, Health and the Environment. University of Huelva, Campus "El Carmen", 21071, Huelva, Spain.
Water Res. 2023 Apr 15;233:119791. doi: 10.1016/j.watres.2023.119791. Epub 2023 Feb 24.
This study evaluates for the first time the impact of a large wildfire on the hydrogeochemistry of a deeply AMD-affected river at the beginning of the wet season. To accomplish this, a high-resolution water monitoring campaign was performed within the basin coinciding with the first rainfalls after summer. Unlike similar events recorded in AMD-affected areas, where dramatic increases in most dissolved element concentrations, and decreases in pH values are observed as a result of evaporitic salts flushing and the transport of sulfide oxidation products from mine sites, a slight increase in pH values (from 2.32 to 2.88) and decrease in element concentrations (e.g.; Fe: 443 to 205 mg/L; Al: 1805 to 1059 mg/L; sulfate: 22.8 to 13.3 g/L) was observed with the first rainfalls after the fire. The washout of wildfire-ash deposited in the riverbanks and the drainage area, constituted by alkaline mineral phases, seems to have counterbalanced the usual behavior and patterns of the river hydrogeochemistry during autumn. Geochemical results indicate that a preferential dissolution occurs during ash washout (K > Ca > Na), with a quick release of K followed by an intense dissolution of Ca and Na. On the other hand, in unburnt zones parameters and concentrations vary to a lesser extent than burnt areas, being the washout of evaporitic salts the dominant process. With subsequent rainfalls ash plays a minor role on the river hydrochemistry. Elemental ratios (Fe/SO and Ca/Mg) and geochemical tracers in both ash (K, Ca and Na) and AMD (S) were used to prove the importance of ash washout as the dominant geochemical process during the study period. Geochemical and mineralogical evidences point to intense schwertmannite precipitation as the main driver of reduction in metal pollution. The results of this study shed light on the response of AMD-polluted rivers to certain climate change effects, since climate models predict an increase in the number and intensity of wildfires and torrential rain events, especially in Mediterranean climates.
本研究首次评估了雨季初期一场大型森林火灾对深度受 AMD 影响河流水文学的影响。为此，在夏季后首次降雨期间，在流域内进行了高分辨率的水监测活动。与受 AMD 影响地区记录的类似事件不同，这些事件通常会由于蒸发盐的冲洗以及矿场硫化物氧化产物的运输而导致大多数溶解元素浓度急剧增加和 pH 值降低，但在火灾后的第一次降雨中，观察到 pH 值略有升高（从 2.32 升高到 2.88），元素浓度降低（例如，Fe：443 降至 205 mg/L；Al：1805 降至 1059 mg/L；硫酸盐：22.8 降至 13.3 g/L）。河流水文学在秋季的通常行为和模式似乎被火后河岸和排水区中沉积的野火灰的冲刷所抵消。地球化学结果表明，在灰分冲刷过程中发生了优先溶解（K > Ca > Na），K 迅速释放，随后 Ca 和 Na 强烈溶解。另一方面，在未燃烧区域，参数和浓度的变化程度小于燃烧区域，蒸发盐的冲刷是主要过程。随着后续降雨，灰分对河流水化学的作用较小。在灰分（K、Ca 和 Na）和 AMD（S）中，元素比值（Fe/SO 和 Ca/Mg）和地球化学示踪剂用于证明灰分冲刷在研究期间是主要地球化学过程的重要性。地球化学和矿物学证据表明，强烈的水铁矿沉淀是降低金属污染的主要驱动因素。本研究的结果揭示了 AMD 污染河流对某些气候变化影响的响应，因为气候模型预测野火和暴雨事件的数量和强度会增加，特别是在地中海气候中。
