Heat and dissolved oxygen exchanges between the sediment and water column in a shallow salty lagoon

Abstract

Dissolved oxygen (DO) and heat exchanges across the water-sediment interface (WSI) of a shallow lagoon are controlled by processes occurring on both sides of the WSI, particularly volumetric source and sink on the sediment side and turbulent transport on the waterside. This article presents and analyzes measurements of DO (J s ) and heat (H g ) fluxes across the WSI in the extremely shallow lagoon of Salar del Huasco (20.274°S, 68.883°W, 3800 m above sea level), where volumetric source of DO and heat exists in the sediment layer, related to benthic primary production and absorption of solar radiation, respectively. Microprofiles of temperature and DO were measured, and they were used for measuring J s and H g , and volumetric source/sink terms in the sediments. This information was used to propose and validate the simple theoretical framework to predict both the magnitude and direction of J s and H g . On the one hand, J s can be predicted with a simple algebraic expression, where the diffusional mass transfer coefficient defines the magnitude of J s while the direction is controlled by the balance between DO production and consumption in the sediments. On the other hand, solar radiation is absorbed in the upper sediments, and this heat diffuses toward the water column and the sediments. The heat flux toward the water column also induces unstable convection that promotes vertical transport across the WSI. The theoretical framework proposed here will help to understand DO and heat budgets of shallow aquatic systems in which solar radiation reaches the WSI.

Bacterial Active Community Cycling in Response to Solar Radiation and Their Influence on Nutrient Changes in a High-Altitude Wetland

“…The microbial community found at the Salar del Huasco, a high-altitude (>3,800 m asl) wetland located in the Chilean Altiplano, is exposed to a range of extreme conditions. This includes total solar irradiance reaching levels of up to 1,000 W m -2 (Aceituno, 1997; de la Fuente, 2014), the effect of which are intensified in these ecosystem due to low atmospheric concentrations of ozone and water vapor, and high ground reflectivity (albedo), but which can be countered by aerosol dust, in this arid desert ecosystem (Cordero et al, 2013, 2016). Salar de Huasco is subject to extreme shifts in temperature through the day (can range from -15 to 20°C) and high evaporation rates, which result in a negative water balance (e.g., precipitation rates of 50–300 mm y -1 versus evaporation rates of 600–1200 mm y -1 (Risacher et al, 2003; de a Fuente and Niño, 2010; de la Fuente, 2014).…”

“…This includes total solar irradiance reaching levels of up to 1,000 W m -2 (Aceituno, 1997; de la Fuente, 2014), the effect of which are intensified in these ecosystem due to low atmospheric concentrations of ozone and water vapor, and high ground reflectivity (albedo), but which can be countered by aerosol dust, in this arid desert ecosystem (Cordero et al, 2013, 2016). Salar de Huasco is subject to extreme shifts in temperature through the day (can range from -15 to 20°C) and high evaporation rates, which result in a negative water balance (e.g., precipitation rates of 50–300 mm y -1 versus evaporation rates of 600–1200 mm y -1 (Risacher et al, 2003; de a Fuente and Niño, 2010; de la Fuente, 2014). The Salar de Huasco is largely groundwater fed, and upwells via a limited number of springs, which generate a wetland habitat, characterized by complex pond and pool systems surrounded by vascular plants forming peatland, locally referred to as bofedales” with the water flowing into a permanent shallow lake (de a Fuente and Niño, 2010).…”

Modeling the influence of benthic primary production on oxygen transport through the water–sediment interface

“…10 shows predicted values of the dimensionless J/(S 1 C W ) 1/2 and C s as a function of k * = kC W /(S 1 C W ) 1/2 . Here, (S 1 C W ) 1/2 is the maximum DO flux consumed in homogeneous sediment for the limit k * → ∞ (Nakamura and Stefan, 1994;de la Fuente, 2014). For any value of P, J rapidly increases with k * (Fig.…”

“…The central depressions of closed basins in the elevated plateaus of Chile, Argentina, Perú and Bolivia are characterized by landscapes formed by a crust of salt resulting from the evaporation of water in saline lakes (Risacher et al, 2003;de la Fuente and Niño, 2010;de la Fuente, 2014). These ecosystems, locally known salares, contain small and extremely shallow lagoons of a few centimeters deep, which are formed by inflows of groundwater that upwell at the perimeter of the salares and completely evaporate (Kampf et al, 2005;de la Fuente and Niño, 2010).…”

“…This DO flux explains the generation of anoxic conditions in water lagoons, with the corresponding changes in chemical balances and water quality (Wetzel, 2001). By including benthic primary production, de la Fuente (2014) showed that the DO flux across the WSI (hereinafter called J) can be positive (toward the water column) or negative (toward the sediments) depending on the rates of DO production and consumption in the sediments and the DO concentration in the water column. However, de la Fuente (2014) considered homogeneous conditions in the sediments, and this assumption requires further analysis and validation.…”