Temporal and spatial changes in diatom community structure with the effects of environmental parameters, and ecological status assessment by diatom indices in three shallow lakes (Sakarya, Turkey)

Abstract

Lakes can be monitored using benthic diatoms as proposed by Water Framework Directive. In recent years, in addition to the indices developed for rivers, the indices developed for lakes have been also used. The relationship between environmental parameters and diatom assemblages was investigated monthly to understand temporal and spatial changes in diatom community structure, and to specify the ecological status of the three lakes between May 2015 and April 2016. Based on the Redundancy Analysis (RDA) result, main environmental parameters (orthophosphate, total phosphorus, specific conductance, soluble silica, water transparency, nitrate-nitrogen, and pH) strongly affected the temporal and spatial distribution of diatom assemblages. Shannon diversity index, evenness, and species richness were measured, however, they were not effective in explaining the water quality. The ecological status assessment of the lakes was also performed by using Trophic Index Turkey (TIT), Trophic Diatom Index for Lakes (TDIL), and Specific Pollution Sensitivity Index (IPS). Based on the results of three indices, TIT gave more consistent results with environmental parameters and indicator species and is more sensitive to changes in the trophic status of lakes over time. According to TIT, Lake Little Akgol had a poor ecological condition, while the water qualities of Lake Taskisigi and Lake Poyrazlar were determined as moderate. Due to the sensitivity of the changes in the diatom community structure with the effect of environmental parameters during one year, TIT is an effective tool to assist in the ecological assessment of three natural lakes within the borders of Sakarya province in the north of Turkey.