Using stable isotopes ¹⁸O and ²H of lake water and biogeochemical analysis to identify factors affecting water quality in four estuarine Amazonian shallow lakes

Stable isotopes analyses of oxygen and hydrogen of lake water were used to estimate the effect of evaporation (E) on the water quality of four shallow lakes in the Amapá State coast—Amazon/Brazil. These lakes, with different size and hydrologic conditions, were sampled during the course of the 2015/2016 El-Niño (record-breaking warming/drought in the Amazon rainforest). Hydrometeorological and water quality parameters were simultaneously performed to the isotopic sampling. The results showed that the evaporation process and the water quality can be explained by climate season and distances from the Atlantic Ocean. Lake evaporation losses ranged from ≈0–22% during the wet season in April/2016 and ≈35.7% during the dry season in November/2015. As expected, the evaporation of lake water was greater during the dry season, but it was higher for lakes farther away from the Atlantic Ocean compared with more coastal lakes due to tidal preponderance and the influence of major river channels. The more inland estuarine lakes showed a lower level of salinity (0.00–0.03 ppt) compared with those closer to the Atlantic Ocean (0.01–0.08 ppt). The El Niño phenomenon, with a lower precipitation in the Amazon basin, may initiate salinization of lakes closer to the Atlantic Ocean. Furthermore, strong mean seasonal variations of evaporation (0.06 ≤ E ≤ 0.22) and other hydrologic parameters were observed (precipitation, water temperature, and water depth), with significant effects on the water quality such as salinity, dissolved oxygen, chlorophyll (p <.05). We conclude that the occurrence of the extreme climatic events can disrupt the biogeochemical and hydrological balance of these aquatic ecosystems and salinization of lakes closer to the Atlantic Ocean.