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Ponds ecosystems are the most common type of lentic waterbodies in Czech Republic. In the last century, the quality of ponds water has been greatly influenced by intensive management in the catchment and ponds alone. As a result of the increasing concentration of nutrients, ponds lead to eutrophication. This is expressed as extensive primary production of phytoplankton and algal blooms. Decomposition of the accumulated organic matter affects the oxygen regime, pH and distribution of nutrients in the pond. Organic matter plays a key role in physical, chemical and biological processes in the ecosystem. The aim of the work was to describe the dynamics of organic carbon in the eutrophic ponds ecosystem with emphasis on its dissolved part (DOC). This study included evaluation of DOC concentration from 6 pond systems in the Třeboň region from 2010 to 2011 and a comparison with DOC concentrations from 2020. The relationship of DOC concentration to other chemical parameters of water was evaluated. It found that DOC concentration had no significant correlation with other parameters. The concentration of nutrients TN and TP had decreased over the last 10 years, while DOC concentration had increased. More detailed data from 5 ponds from 2008 to 2011 were evaluated in the same way. Optical methods such as absorbance and fluorescence were used to describe DOC dynamics. These methods were used to monitor 10 ponds from Třeboň and České Budějovice regions in 2017?2018. Data were compared between these regions because they differed in conductivity, but it had no differences in DOC concentration and other chemical parameters. The average value of DOC concentration was 14,8 mg l-1. The absorption characteristics of DOM such as spectral slope S275-295 and slope ratio SR suggested an autochthonous source of DOM. Specific absorbance values at 254 nm SUVA254 ranged from 1,4?3,0 l mgC-1 m-1 and indicates autochthonous substances with lower molecular weight and lower content of aromatics. SUVA254 values were higher in the Třeboň region, which indicates that there was a more allochthonous DOM with higher molecular weight and more aromatics in DOM in contrast to the České Budějovice region. Evaluation of seasonal changes in the composition of DOM using optical methods revealed that in the summer there were more autochthonous substances with lower molecular weight and lower aromatics DOM. SR values were negatively correlated to molecular weight and were higher in summer. FI and BIX values indicating autochthonous and microbial source DOM increased in summer. Optical methods were used for the first time to monitor the dynamics of organic matter in ponds. |
