Some considerations about 30 years records of physical-chemical parameters from Lake Masaya.

Abstract

From a historical record of the CIRA/UNAN-Managua between 1988 and 2013, data from 33 selected physical-chemical variables of Lake Masaya were synthesized and analyzed to update a detailed description of their natural ranges and their relationships, as well as an identification of the greater dispersion parameters, both in terms of its natural variability and its stability in the water column.  In comparison with the first set of data reported by the 1970s, the Lake has experienced a slight reduction (>1%) of Cl^-, Ca²⁺, total hardness, and pH, also a significant reduction (>35%) in NO₃^2-, B, and total PO₄^3-, at the same time as a considerable increase (>9%) of HCO₃^-, Mg²⁺, Na⁺, and K⁺, again a significant increase (>40%) in CO₃^2-, F^-, a particularly high (>400%) increase in SiO₂ and NO₂^-, being influential on the EC both the HCO₃^-, Na⁺ and NO₂^-.  Likewise, the COD/BOD₅ ratio has increased by almost 70% and the proportion of Ca²⁺ in relation to other cations has decreased.  Finally, the results suggest that HCO₃^-, Na⁺, CO₃^2-, K⁺, total phosphorus, total alkalinity, BOD₅, temperature, EC and pH are the variables that could best explain the physical-chemical conditions in this lake. It was also noted that the trophic status of the Lake has been alternating between eutrophic and hypereutrophic which implies the urgency in  developing efforts to restore the Lake.

Key words: Lake Masaya, physico-chemical parameters, natural variability.