## 2 Materials and Methods
### Estimation of Metabolism  
Meteorological and water variables were measured at 10-min intervals from two buoys (_Estacion de Monitoreo Ambiental Costero, EMAC_) moored approximately in the deepest point of each lake (Figure 2). The physicochemical variables were measured at a 0.5-m depth, including dissolved oxygen (DO), water temperature, water level and electrical conductivity. Meteorological variables were measured at 2.10 m in height on the buoy, including air temperature and wind speed and direction. Data is available on the website www.emac.iado-conicet.gob.ar [50].  
Estimation of the ecosystem metabolism was based on [1], with modifications for saline environments for LS and high wind environments for both lakes [51]. Hourly NEP (\(NEP_{h}\)) (mmol O\({}_{2}\) m\({}^{-3}\) h\({}^{-1}\)) was calculated as the difference between the changes in DO concentration (\(\Delta DO\)) and the fraction between the diffusive oxygen exchange of gas with the atmosphere (\(F\)) and the daily mean water depth (\(z\)) (Table 1). Unlike stratified lakes, we employed the daily mean depth instead of the mixing depth as both lakes are polymicic considering their shallow depth, the flat shape of the basins, and freedom from obstacles and continuous wind action [21; 22; 52]. \(F\) (mmol O\({}_{2}\) m\({}^{-3}\) h\({}^{-1}\)) was calculated as the difference between the DO measured and the concentration of oxygen in equilibrium with the atmosphere (\(DO_{sat}\)), where \(k\) is the coefficient of oxygen exchange at a given temperature (Table 1). This was computed from the Schmidt number (\(Sc\)) and the gas piston velocity (\(k_{660}\)), with a correction for high wind environments, using a half coefficient instead of two-thirds [51]. In this study, the \(Sc\) was calculated at each time step using the DO-specific equation of [53], but using the coefficients for seawater for the LS lake (4) and freshwater for the SG lake (5) (Table 1). The \(k_{660}\) was estimated with a correction for high wind environments based on the equation proposed by [54] as a function of wind speed at 10 m above the lake surface (\(U_{10}\)). As the wind speed at the buoy is measured at 2.10 m above the water (\(U_{2.1}\)), \(U_{10}\) was calculated assuming a neutrally stable boundary layer from the relationship given by [55] and \(a\) is a correction factor (Table 1).  
To obtain GPP, R, and NEP values, NEP occurring during photosynthesis (\(NEP_{d daytime}\)) was estimated as the mean hourly NEP taking place between sunrise and sunset extrapolated over day length [2]. The fraction of the day when there was daylight (_day fraction_) was calculated from latitude and date of measurements in radians (Table 1). We assume that there is no photosynthesis at night and GPP = 0 (therefore R = NEP during the nighttime), and that R during nighttime was equal to R during the daytime. Hourly respiration rates derived from changes in DO concentration during nighttime (\(R_{hr}\)) were extrapolated over a 24-h period to calculate the respiration during the day (\(R_{day}\)). Respiration during the daytime (\(R_{daytime}\)) was calculated from mean \(NEP_{hr}\) during darkness (\(R_{hr}\)) extrapolated over a day length. Finally, as NEP during daytime is the difference between GPP and \(R_{daytime}\), GPP was calculated as the \(NEP_{daytime}\) added to \(R_{daytime}\) (Table 1). All rates were integrated daily (day\({}^{-1}\)).  
Figure 2: Map with isobaths in meters and location of the _Estacion de Monitorco Ambiental Costero_ (_EMAC_) buoy in the: (**a**) La Salada and (**b**) Sauce Grande lakes.