Thesis supervisor: Professor Jaak Truu (University of Tartu), Senior Research Fellow Marika Truu (University of Tartu)
Opponent: Professor Sara Hallin (Swedish University of Agricultural Sciences)
Human activities have increased the amount of reactive nitrogen in ecosystems, causing severe environmental problems. In order to protect aquatic ecosystems from excessive nitrogen, the implementation of treatment wetlands (TWs) is proposed.
Microbial communities play a key role in the nitrogen cycle and hereby it is crucial to understand the relationships between microbial communities and environmental parameters in TWs. Favourable conditions for processes with maximum nitrogen removal and minimum N2O emission should be created in TWs.
In this dissertation, the bacterial community structure and its nitrogen removal potential were characterised in the soils and sediments of a polluted river water treating wetland complex in relation to site-specific characteristics (soil chemical parameters, water regime, and soil type).
Water regime was an important factor in determining the structure of the bacterial communities in the studied TW soils - the communities in the occasionally flooded areas were more diverse and complex than those of the permanently flooded areas.
Genetic potential for denitrification was detected in all the studied soils and this was dependent on the site’s hydrological conditions. Nitrite reduction potential was higher in the permanently flooded zones, while greater potential for N2O reduction was in the bacterial communities of occasionally flooded areas. The proportions of denitrification-related genes were affected by soil chemical parameters. Genetic potential for ANAMMOX and n-damo processes was detected in the soils of the TWs and the most suitable conditions for those bacteria were in the permanently flooded areas.
The results of this study indicate that the bacterial communities of TW soils have the genetic potential for several nitrogen removal processes; nevertheless, denitrification is the main process performing this function and a creation of the occasionally flooded areas would decrease the N2O emission from partial denitrification from the TWs soils.