# Reconstruction of Ancient Lake after Peat Excavation--A Case Study about Water Quality
## 4 Discussion
### Physico-Chemical Parameters of Water  
The concentration of nitrites and the value of BOD-5 were high in the post-peat reservoir, however, they did not exceed the limits for carps (Table 4). In autumn 2012, in part A, an increase in BOD-5 was recorded (9 mg O2/L), which indicated a high load of organic matter. In the other periods, biochemical oxygen demand did not exceed 6 mg O2/L, which was admissible for inland waters being the habitat of fish population (especially cypriinds), even under natural conditions. Differences between the annual averages of the studied parameters were calculated and used in further analyses (Table 1). Figure 4 presents the results of canonical variate analysis presenting study objects (part A in years 2012-2014 and part B in years 2013-2014) in relation to the selected physico-chemical elements, characterizing the trophic state of water. Particular points represent the physicochemical characteristics of the objects studied; part A in 2012-2014 and part B in 2013-2014, expressed by the indices describing the trophic state of water. Points representing the water quality parameters show that the variability in this experiment was mainly related to conductivity, which was relatively high in parts A and B (2013), and part B in 2013. Among the water quality parameters studied, the greatest variation was observed for conductivity, which was relatively high in parts A and B in 2013, and only in part B in 2014. However, in 2014, the reservoir, and especially part B, was characterized by low conductivity relative to the other measurements. This means that after the connection of both parts during autumn 2014, the reservoir started to stabilize in terms of salinity, as conductivity was decreasing in both parts (Table 5). Based on the results of the analysis of canonical variables, it can be seen that oxygen, BOD-5 and pH reaction were characterized by a lack of variability between parts of the reservoir in years according to conductivity variability. After limiting the analysis of canonical variables by excluding conductivity (Figure 5), it can be noted that variability is also associated with BOD-5. Part A of the reservoir in 2012 was characterized by the highest values of BOD-5 during the whole research period and showed the lowest value in 2013. In 2013, the reservoir had the lowest BOD-5 values in both parts. Significant variability was also noted in the oxygen content in the water. The highest oxygen concentration was recorded in 2013 in part A, and the lowest in 2014 in both parts. Throughout the period of study, the pH value (about 8.05) of water in the reservoir was almost stable. It can be noted that, in 2002, the values of the parameters mentioned above were the most different from the other results. It was observed that the values of selected physico-chemical factors were most similar to each other for parts A and B of the reservoir in the year 2014. This means that reservoir stabilized as a whole. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Experimental** & & & & & & & & **Total** \\
**Objects** & **Conductivity** & **Oxygen** & **BOD-5** & **Reaction** & **Ammonium** & **Nitrites** & **Nitrates** & **Nitrogen** \\ \hline  & mS/cm & mg O\({}_{2}\)/L & mg O\({}_{2}\)/L & - & mg NH\({}_{4}\)/L & mg NO\({}_{2}\)/L & mg NO\({}_{3}\)/L & mg N/L \\ \hline A\_2012 & 35.70 & 0.045 & 1.425 & 0.015 & 0.020 & 0.016 & 0.305 & 0.714 \\ A\_2013 & 33.45 & 1.020 & \(-0.738\) & \(-0.022\) & \(-0.111\) & 0.002 & 0.665 & \(-0.344\) \\ A\_2014 & \(-4.05\) & \(-0.505\) & \(-0.163\) & 0.003 & 0.080 & \(-0.011\) & \(-0.416\) & \(-0.122\) \\ B\_2013 & 18.70 & \(-0.155\) & \(-0.463\) & \(-0.022\) & \(-0.083\) & 0.006 & \(-0.026\) & \(-0.802\) \\ B\_2014 & \(-83.80\) & \(-0.405\) & \(-0.062\) & 0.027 & 0.094 & \(-0.013\) & \(-0.528\) & 0.554 \\ General mean & 667.55 & 8.955 & 3.863 & 8.048 & 0.246 & 0.027 & 0.763 & 2.457 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Differences between the distinguished experimental objects and the general mean values.