Landscape level characterization of the aquatic biogeochemistry and terrestrial landcover of Cuatro Ciénegas, Coahuila, México

Background/Question/Methods

The Cuatro Ciénegas Basin (CCB) in the Chihuahuan desert in Coahuila, México has the highest level of endemism in North America. This basin is divided into two lobes by the Sierra San Marcos and contains numerous types of water bodies. A whole-basin study of the biogeochemistry of this spring-fed system is much needed to understand hydrological flow paths and their influence on the landscape and biogeochemical properties. Since 2011, physicochemical parameters have been measured and water samples have been collected and analyzed for nutrients, trace metals, and stable oxygen and hydrogen isotopes from 15 springs, pools, and streams. Long-term transects perpendicular to the shoreline of 10 of these water bodies were established to characterize surrounding landcover.

Results/Conclusions

Across CCB, aqueous salinity and conductivity spanned between 0.6-4.1 ppt and 1327-8420 uS. The highest values were found in the easternmost site (Los Gatos), followed by another eastern site, Los Hundidos. pH values ranged from 6.94 to 7.93 with lowest pH values in the western lobe (Churince and Juan Santos), while dissolved salts were lowest in the southeastern part (Santa Tecla and Teclitas). Dissolved organic carbon concentrations ranged over two orders of magnitude (58 – 5307 uM). The lowest concentrations were generally found in northern sites (Rio Mesquites, Mojarral, and Anteojos), while the highest were found in the eastern spring site Rancho las Pozas. Nutrient data also showed some geographic trends, however patterns differed for nitrogen and phosphorus. While total dissolved nitrogen and phosphorus were highest in the eastern lobe, the highest values of each were not found at the same sites. Rancho las Pozas had the highest nitrogen (>500 uM N), while Los Hundidos had the highest phosphorus concentrations (1.0 – 3.2 uM P). Also in these sites, nitrogen to phosphorus (N:P) atomic ratios were 620 and 19, respectively. N:P ratios across CCB ranged from 7 – 997, with a mean of 139. Both the highest (>500) and lowest (<20) N:P ratios were found in the eastern lobe. The dominant landcover across all sites was grasses (53%), followed by barren land (19%) and shrub/scrub (14%). Teclitas contained the most and equally proportional landcover types while Escobedo, an eastern spring site, also included four landcover types but was dominated by grass (87%). A more comprehensive study of the ecosystem properties of CCB will help us understand the biogeochemistry and the ecological complexity of this unique system and aid in its conservation.