A modeling approach for calcium carbonate precipitation in a hypersaline environment: A case study from a shallow, alkaline lake

摘要

Carbonates are widespread occurrences in various environmental conditions. Particularly, microbial induced and/or controlled carbonate formations are considered significant archives for recording critical environmental conditions that can be used not only to reconstruct paleo-environments, but also to gain valuable information about evidence of life in environments. Therefore, deciphering carbonate precipitation mechanisms, and the factors controlling these processes, particularly in extreme environments, hold significant insights for industrial applications, and for searching life in extra-terrestrial environments. In the scope of these contexts, we tried to model carbonate precipitation mechanism and possible biological influences in a hypersaline lake, known as an extreme environment in Turkey, in terms of its water chemistry. The aim of this research is to model CaCO3 precipitation in the Acigol Lake, using water quality data from the field, and meteorological data obtained from the Turkish State Meteorological Service for the years 2013 and 2015. To achieve this, AQUATOX model is utilized. The model is calibrated for nine stations of the lake using parameters related to water quality, site characteristics, inflow loadings and lake hydrodynamics. Calibration dataset is obtained from the field measurements and meteorological data, for the year 2013. Model validation is conducted both using experimental data, and field observations, obtained in August, 2015. An integrated modeling approach is undertaken by coupling a geochemical reaction model and a process-based ecosystem model, AQUATOX; using field, experimental and meteorological data. Model results suggest that the amount of CaCO3 precipitation in the system ranges from 35.16 to 128.48 mg L-1 d(-1). Temperature, photosynthesis rate, depth and pH are found to be the most significant variables that govern the biogeochemical processes responsible for CaCO3 precipitation. The model showed a strong relationship between calcite precipitation and certain cyanobacteria species such as Anabaena and Aphanizomenon sp. Results also indicate that the model was successful in representing the relationships between calcite precipitation variations, and phosphate and pH. The Nash-Sutcliffe model efficiency coefficient and NRMSE are found to be 0.93 and 0.29, respectively.