Holocene sedimentary history of the Silala River (Antofagasta Region, Chile)

Abstract

Assessing past and ongoing climate change in the central Andes is critical for understanding the impact of future environmental changes under anthropogenic warming. Emerging from springs located in Bolivia and flowing into northern Chile's Atacama Desert, the Silala River contains inset, terraced wetland (or in‐stream) deposits that provide a unique opportunity to study the impact of past hydroclimate change in a sensitive groundwater system with a small catchment area. After an initial (late Pleistocene) period of deep incision to form the present ravine, in‐stream wetland fine‐grained deposits formed during three phases of aggradation dated to >8.5–1.9 ka (Unit 1), >0.65–0.2 ka (Unit 2), and <0.2 ka to the recent 20th century (Unit 4). These phases of accumulation were coeval with periods of well‐dated records of elevated groundwater tables throughout northern Chile. Phases of abrupt downcutting occurred due to a lowering of the water table after 1.9 ka and before 0.2 ka. The cycle of erosion and deposition clearly continues to the present as evinced by the very recent (21st century) incision of Unit 4 (>1.5 m in some areas) throughout sectors of the Silala where dried‐out standing vegetation can be seen. Such recent incision may be due to multiple different factors, including recent climate change coupled with intense extraction of groundwater resources by the copper mining industry.This article is categorized under: Human Water > Water Governance Science of Water > Hydrological Processes Science of Water > Water and Environmental Change

The Quebrada Negra wetland study: An approach to understand plant diversity, hydrology, and hydrogeology of high‐Andean wetlands

“…3.1 | Flora of the Quebrada Negra cushion bog Latorre (2019) observed and collected a total of 12 different taxa at the two sampling sites (Table 1). The cushion bog present at Quebrada Negra occupies a narrow portion of the steep valley floor and corresponds to a sloping peatland as described by Squeo et al (2006).…”

“…These are typically groundwater-fed systems, recharged by rainfall and snowmelt, that occupy the bottom portions of steep, narrow ravines (Squeo et al, 2006). The flora of the Quebrada Negra is very similar in composition to the majority of high-Andean cushion bogs in the Antofagasta and Tarapac a regions, although somewhat less diverse than the latter (Latorre, 2019;Villagr an et al, 1999). As with other high-Andean wetlands, these bogs are dominated by cushion plants from the Juncaceae family, in this case Oxychloe andina.…”

“…A survey of the flora from the Quebrada Negra wetland took place on December 29, 2018, in which visual observations were complemented with photographs and Global Positioning System (GPS) measurements (Latorre, 2019). Plant taxa were identified and collected at two different sites (one in the Quebrada Negra wetland area (F1) and one in the riverbank downstream of the wetland (F2); "Flora" sites in Figure 1) and compared to those reported for the Bolivian wetlands (DHI, 2018).…”

Introduction to the Silala River and its hydrology

“…Infiltrated water can evaporate from the soil's unsaturated zone as direct evaporation or plant transpiration (together referred to as evapotranspiration), travel to the river as lateral subsurface flow (i.e., interflow), or percolate and recharge the aquifer. While precipitation and evapotranspiration depend on meteorological conditions, evapotranspiration is also highly influenced by the presence and activity of vegetation, as well as by water availability, which is a function of soil type (Su arez, Sarabia, et al, 2024); whereas infiltration depends on topographical and geological characteristics of the basin Latorre, et al, 2024). The characteristics of the soils and its distribution in the basin are described elsewhere in this special issue (G omez et al, 2024;Y añez-Morroni et al, 2024a).…”

“…EC measurements were also performed in the Putana River wetland (EC-3), which is outside the Silala River basin, but resembles -in terms of vegetation and elevation-the wetlands that are in the headwaters of the Silala River (Su arez, Oportus, et al, 2024). ET a was also measured with the portable chamber method in the native vegetation over the alluvial deposits of the basin (Su arez, Latorre, et al, 2024), as well as in the Quebrada Negra wetland, which is an undisturbed Chilean wetland nearest to the Cajones and Orientales (Bolivian) wetlands (Muñoz & Su arez, 2019;). ET a rates were higher in the monitored wetlands, compared to the measured values in the alluvial deposits of the basin.…”