DOI: 10.5061/dryad.r4xgxd2nn
title: Data from: Drought disrupts atmospheric carbon uptake in a Mediterranean saline lake

description: Saline inland lakes play a key role in the global carbon cycle, acting as
 dynamic zones for atmospheric carbon exchange and storage. Given the
 global decline of saline lakes and the expected increase of periods of
 drought in a climate change scenario, changes in their potential capacity
 to uptake or emit atmospheric carbon are expected. Here, we conducted
 continuous measurements of CO2 and CH4 fluxes at the ecosystem scale in a
 saline endorheic lake of the Mediterranean region over nearly 2 years. Our
 focus was on determining net CO2 and CH4 exchanges with the atmosphere
 under both dry and flooded conditions, using the eddy covariance (EC)
 method. We coupled greenhouse gas flux measurements with water storage and
 analyzed meteorological variables like air temperature and radiation,
 known to influence carbon fluxes in lakes. This extensive data integration
 enabled the projection of the net carbon flux over time, accounting for
 both dry and wet periods on an interannual scale. We found that the system
 acts as a significant carbon sink by atmospheric CO2 uptake in
 wet conditions, with uptake ceasing in periods of drought. Moreover,
 increased air temperatures during wet phases slightly decrease the CO2
 uptake efficiency. Regarding CH4, we measured uptake rates that exceeded
 those of well-aerated soils such as forest soils or grasslands.
 Additionally, we observed that CH4 uptake during dry periods was nearly
 double that of wet periods. However, the absence of continuous data
 prevented us from correlating CH4 uptake processes with potential
 environmental predictors. Our study challenges the widespread notion that
 wetlands are universally greenhouse gas emitters, highlighting the
 significant role that endorheic saline lakes can play as natural sink of
 atmospheric carbon. However, our work also underscores the vulnerability
 of these ecosystem services in the current climate change scenario, where
 drought episodes are expected to become more frequent and intense in the
 coming years.
description: We carried out continuous and interannual measurements of
 CO<sub>2</sub> and CH<sub>4 </sub>fluxes at the
 ecosystem level in the saline lake Fuente de Piedra using the Eddy
 Covariance (EC) method. <strong>-Study site:
 </strong>Fuente de Piedra is a shallow, saline lake in an endorheic
 basin in Málaga, Andalusia, Spain, covering approximately 17 km² with a
 maximum depth of 1.5 meters. Designated as a Ramsar site in 1983, it
 benefits from extensive historical data on water storage and
 meteorological conditions. Salinity levels in the lake, influenced by the
 hydrological cycle, vary from oligosaline to hypersaline, with groundwater
 inflow, streams, and surface runoff contributing to its water, while
 sediment samples show homogeneity in organic carbon, nitrogen, and the C
 ratio. <strong>-Field measurements of greenhouse
 gas fluxes and meteorological drivers: </strong>We used the eddy
 covariance method to measure CO2, CH4, and energy exchanges every 30
 minutes from August 2021 to May 2023, including two dry summer periods. In
 addition to gas measurements, we recorded various environmental and soil
 state variables every 10 seconds, averaging them every 30 minutes using a
 data logger. These measurements included photosynthetic photon flux
 density, air temperature, relative humidity, net radiation, and soil heat
 flow, with sensors placed at specific heights and depths to capture
 representative data. Furthermore, groundwater level, daily precipitation,
 air temperature, and incident solar radiation were monitored using a
 piezometer and meteorological station near the lake, with equipment
 maintained bi-weekly. -<strong>Greenhouse gas
 flux data processing, quality control and partitioning:
 </strong>Greenhouse gas flux data were processed and quality
 controlled using EddyPro® software, following international standards,
 including tilt correction, time lag compensation, and spectral
 corrections. High-quality flux data were selected based on quality check
 flags and sensor cleanliness, with footprint modeling applied to exclude
 data influenced by the adjacent terrestrial environment, resulting in 18%
 and 8% good quality daytime data for CO2 and CH4, respectively, and energy
 balance closure of 76%. <strong>-Predicting
 </strong><strong>greenhouse gas fluxes as responses to
 meteorological drivers: </strong>We examined the relationship
 between CO<sub>2</sub> and CH<sub>4</sub> fluxes
 and meteorological drivers. Using half-hourly flux data, we calculated
 24-hour integrated values and selected dates with over 50% of the
 anticipated data points to represent daily patterns accurately. A linear
 regression with forward model selection, evaluated by the Akaike
 Information Criterion (AIC), identified the most effective model, and the
 influence of predictors was analyzed using the slope coefficients with a
 significance level of alpha = 0.05.
description: # Data from: Drought disrupts atmospheric carbon uptake in a Mediterranean
 saline lake
 [https://doi.org/10.5061/dryad.r4xgxd2nn](https://doi.org/10.5061/dryad.r4xgxd2nn) Inland saline lakes are crucial in the global carbon cycle, but increased droughts may alter their carbon exchange capacity. We measured CO2 and CH4 fluxes in a Mediterranean saline lake using the Eddy Covariance method under dry and wet conditions. We found the lake acts as a carbon sink during wet periods but not during droughts. These results highlight the importance of saline lakes in carbon sequestration and their vulnerability to climate change-induced droughts. ## Description of the data and file structure The attached files contain the data and R code to replicate the analyses and figures presented in the paper, including those from the Supplementary Material. Note that missing values in all data files have been filled as NA or they are kept as empty cells. **CODE (1 FILE)** * **code.R:** R script to replicate analyses and figures in the paper and Supplementary Material. **DATA (5 files in total)** * **fluxes.csv**: comprises raw data on carbon dioxide and methane fluxes: * Columns:  date_time: date and time in format "year-month-day hour:min:sec". date: date in format "year-month-day". CO2: carbon dioxide flux in mol/m2 s. CH4: methane flux in mol/m2 s. * **GWL.csv**: comprises groundwater level information for the study period . * Columns:  FECHA: date in format "year.month.day". GWL (cm): groundwater level (cm above surface). * **GWL_1993_2023.xlsx**: comprises groundwater level information between 1993 and 2023. * Columns:  FECHA: date in format "year.month.day". NIVEL (cm): groundwater level (cm above surface). * **Rain_Ta .csv**: comprises rain and temperature data. * Columns:  date_time: date and time in format "year-month-day hour:min:sec". date: date in format "year-month-day". time (cm): time in format "hour:min:sec". PPT: precipitation in mm/day. Ta= temperature (Celsius degree). * **Sierra_Yeguas.csv**: comprises incident radiation, minimum, mean and maximum temperature measured at daily resolution in the station installed in Sierra de las Yeguas. * Columns:  date_time: date and time in format "year-month-day hour:min:sec". maxTa: maximum daily temperature (Celsius degree). minTa: minimum daily temperature (Celsius degree). meanTa: mean daily temperature (Celsius degree). rad: incident solar radiation (MJ /m day). **SITE IMAGES (2 FILES)** * **dry.jpeg:** aerial photography of the study site during the dry period. * **wet.jpeg:** aerial photography of the study site during the wet period.