Geology Department, Universitat Autònoma de Barcelona, E-08193-Bellaterra, Barcelona, Spain.
Àrea de Geodinàmica Externa i Geomorfologia, Universitat de Girona, E-17071 Girona, Spain.
Sci Total Environ. 2021 Jul 15;778:146070. doi: 10.1016/j.scitotenv.2021.146070. Epub 2021 Feb 26.
A historical series of aerial photographs spanning more than 70 years (1945-2018) revealed that natural acid rock drainage (ARD) has experienced an intensification in the Noguera de Vallferrera alpine catchment (Central Pyrenees) due to climate change during the last decade. ARD manifests by the precipitation of whitish aluminum-compounds that strikingly cover the beds of some gullies and streams in high-mountain catchments. The total length of affected streams has increased from ca. 5 km (1945) to more than 35 km (2018). Up to 68 water samples were collected in three main areas to determine the spatial variation in acidity and concentration of dissolved metals, representative of surface and subsurface waters. Concentration of aluminum clearly correlates with acidity of waters. Aluminum precipitation occurs where acidic waters, enriched in metals due ARD related to the oxidation of sulfides, mix with non-acidic waters. In addition to aluminum, other potentially toxic trace metals are present at concentrations well above the quality standards for natural waters. Here, we show that climate warming and the severe droughts recorded in the last decade are the most plausible causes for the observed ARD intensification. This result is supported by a good correlation between the regional ascending rate of the periglacial limits (ca. 46 m-height/decade) and the rising rate of the maximum elevations at which ARD occurs (ca. 45 to 55 m-height/decade). In addition to climatic control, we also show that the local geomorphology is playing a major role. The distribution of periglacial deposits (rock glaciers, protalus ramparts, cones and talus slopes) and deep-seated gravitational slope deformations exert a strong control on the spatial patterns and hydrodynamics of ARD. A better understanding of the phenomenon and the monitoring of its evolution can provide clues on these side effects of climate warming, here and in many other alpine catchments worldwide.
一段跨越 70 多年的历史航空照片系列（1945-2018 年）显示，由于过去十年的气候变化，自然酸性岩石排水（ARD）在诺盖拉·德瓦勒费雷拉高山流域（比利牛斯山脉中部）加剧。ARD 的表现为白色铝化合物的沉淀，这些化合物鲜明地覆盖了高山流域一些沟壑和溪流的床面。受影响溪流的总长度从 1945 年的约 5 公里增加到 2018 年的 35 公里以上。在三个主要区域采集了多达 68 个水样，以确定酸度和溶解金属浓度的空间变化，这些金属代表地表水和地下水。铝浓度与水的酸度明显相关。酸性水，由于与硫化物氧化有关的 ARD 而富含金属，与非酸性水混合时会发生铝沉淀。除了铝之外，其他潜在的有毒痕量金属的浓度也远高于天然水的质量标准。在这里，我们表明气候变暖以及过去十年记录的严重干旱是观察到的 ARD 加剧的最可能原因。这一结果得到了区域冰缘上升率（约 46 米/十年）与 ARD 发生的最大海拔上升率（约 45 至 55 米/十年）之间的良好相关性的支持。除了气候控制之外，我们还表明，当地的地貌形态也起着主要作用。冰缘沉积物（岩冰川、原斜坡堤、锥体和岩屑斜坡）和深层重力边坡变形的分布对 ARD 的空间格局和水动力有着强烈的控制作用。更好地了解这一现象及其演化的监测可以为气候变暖的这些副作用提供线索，无论是在本地还是在世界上许多其他高山流域。
