Chemical diversity and spatial variability in myriad lakes in Nhecolândia in the Pantanal wetlands of Brazil

Abstract

Nearly 15,000 shallow, saline or freshwater lakes and ponds coexist in close proximity in the Nhecolâ ndia, a 24,000 km 2 subregion of the Pantanal wetland in Brazil. This study aims to understand the origin of such diversity in surface water, which is a key aspect for the wetland services and biodiversity in the region. Both soil observations and water samples were collected at the regional or local scale and supplemented by previously published data sets. Statistical and geostatistical treatments were carried out and completed by discrete watertable monitoring. The results confirmed the absence of a regional pattern in surface-water salinity, and the independence of electrical conductivity values, even for neighboring lakes. Despite great differences in chemical composition, all surface waters in the region belong to the same chemical family, corresponding to several concentration stages of the Taquari River water that supplies the region. The concentration stage depends on the hydrological functioning of each lake, which is itself controlled by the relative importance of low-permeability soils as a barrier to movement of water into or out of the lakes through the subsurface. In this framework, oligosaline ponds, freshwater lakes, and saline lakes work as recharge, flow-through, and discharge wetlands, respectively. The salinity observed in some lakes results from an ongoing process of accumulation and evaporation under relatively humid climatic conditions and poor drainage.

Biogeochemical diversity and hot moments of GHG emissions from shallow alkaline lakes in the Pantanal of Nhecolândia, Brazil

“…2, where the solid lines denote the regional trends of the major ions versus the sodium concentration drawn from the analyses of 147 lakes (Furian et al, 2013). Our results cover 15 a wide range of salinity with Na + concentration from 0.3 to 500 mg L -1 .…”

“…The water chemistry (Fig 2) of the studied lakes covers a large range of alkaline salinity as observed at the regional level by Furian et al (2013). Therefore, from the point of view of mineral chemistry, the lakes are representative of the region and evolve in a sodic-alkaline pathway under the influence of evaporation (Barbiero et al, 2004).…”

“…The co-existence of freshwater and saline lakes occurs mainly in the southern and south western, lowland portions of Nhecolândia. Furian et al (2013) have shown that the presence of salinity in the lakes results from an ongoing process of accumulation and evaporation under relatively 15 humid climate but poor drainage conditions. These authors have determined that the evaporation process and associated mineral precipitations that control dissolved Ca, Mg and K account for at least 86% of the chemical variability in surface waters (n = 147 lakes) based on major ion chemistry.…”

“…were measured by ion chromatography, alkalinity by 0.1N HCl titration, and dissolved organic carbon (DOC) concentrations were determined with a Shimadzu TOC-5000A. In order to compare the collected soil solutions with the regional chemistry presented by Furian et al (2013), the results of the water analysis were plotted into concentration diagrams based on their 25 sodium amount.…”

“…The number of lakes was estimated from 12,000 to 17,500 including 500 to 600 saline-alkaline ones (Costa et al, 2015;Evans and Costa, 2013). Furian et al (2013) have shown that the level of salinity of neighboring lakes are independent and that the co-20 existence of both, saline and freshwater lakes occurs as a result of the distribution of the soil cover that induce a differential hydrological regime. Under the influence of cumulative evaporation over the years, the pH of some saline lakes has reached high values, close to or above 10, resulting in an increasing solubility of the organic matter, with dissolved organic carbon (DOC) values up to 750 mg L -1 (Barbiero et al, 2016;Mariot et al, 2007).…”