Interactions of water and sediment phosphorus in Lake Eymir

Plevneli, Tolga
A detailed study is held in Lake Eymir, a shallow eutrophic lake, investigating the phosphorus concentrations in water and the bottom sediment. Water depth, secchi depth, TSS, sediment soluble total phosphorus, sediment soluble PO4-P, Chl-a , TKN, NH4-N, NO2-N, NO3-N, alkalinity, temperature, pH, conductivity, dissolved oxygen, turbidity and PAR parameters are monitored for 21 months and Principal Component Analysis (PCA) is applied to identify trend of phosphorus concentration in water column. Results indicated that total phosphorus concentrations in water column and sediment at lake bottom are susceptible to changes caused by the variations in other water quality parameters compared to average, surface and mid-depth values. Correlations observed between P and other parameters were the highest in Bottom – 3 data set. In order to model sediment soluble total phosphorus in Lake Eymir, chlorophyll-a, NH3, total phosphorus, PO4-P, temperature, conductivity, pH, turbidity, ΔT and dissolved oxygen are defined as effective parameters. Linear regression models were more successful in predicting sediment soluble phosphorus concentrations compared to non-linear ones. Turbidity is a good tracer for total phosphorus concentrations in Lake Eymir. Temperature is seasonally effective on phosphorus concentrations, and may create stratified water in summer. Stratification causes phosphorus to build up in bottom water layer. Particle size distribution results show that area of sampling point 1 has different characteristics compared to other sampling locations since it is located at the inlet. The exchange of phosphorus from water to sediment is mostly completed within the first 7-8 hours. On average, 30% of the exchange is completed in an hour. It is clearly seen that although sediment layer in the lake is a phosphorus source, it has not reached its phosphorus binding capacity yet. Adsorption isotherm is found to be pseudo-second-order with a coefficient of determination greater than 0.9909 at all sampling points. Sediment phosphorus content has been fractioned into NH4Cl-P, BD-P, NaOH-P and HCl-P in order to identify permanent and bioavailable parts. Fractionation results show that even if the soluble concentrations are low, they are high enough to cause eutrophication problems.