Differences in microbial community structure and nitrogen cycling in natural and drained tropical peatland soils

Funding Information: This was supported by the Estonian Research Council (grant IUT2-16); and the EU through the European Regional Development Fund through Centre of Excellence EcolChange and the European Social Fund (Doctoral School of Earth Sciences and Ecology). We would like to thank the PhD students participating in the field works.Peer reviewedPublisher PD

Soil Bacterial and Archaeal Communities and Their Potential to Perform N-Cycling Processes in Soils of Boreal Forests Growing on Well-Drained Peat

Funding Information: This study was supported by the Estonian Forest Management Centre, the Estonian Research Council grants PRG548, PRG916, and PRG352, WaterJPI-JC-2018_13 project, and Centres of Excellence Environ and EcolChange.Peer reviewedPublisher PD

Vabaveelise tehismärgalakompleksi bakterikoosluse struktuur ja selle lämmastikuärastuse geneetiline potentsiaal

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Inimtegevuse tulemusena on kordades suurenenud bioloogiliselt kättesaadava lämmastiku hulk eri ökosüsteemides, mis omakorda on põhjustanud ulatuslikke keskkonnaprobleeme. Üks võimalus veeökosüsteemide kaitsmiseks liigsete toitainete eest on tehismärgalade (TM) rajamine. Mikroobikooslustel on TMide lämmastikuringes võtmeroll ning seetõttu on oluline mõista seoseid mikroobikoosluste ja keskkonnaparameetrite vahel nimetatud ökosüsteemides. TMi tuleks luua sobilikud tingimused eelkõige sellistele bioloogilistele protsessidele, mis tagaks maksimaalse lämmastikuärastuse minimaalse kasvuhoonegaasi N2O emissiooniga. Käesolevas töös uuriti reostunud jõevett puhastava TMide kompleksi muldade ja setete bakterikoosluse struktuuri, hinnati selle lämmastikuärastuse geneetilist potentsiaali ning analüüsiti nende näitajate seoseid keskkonnaparameetritega (keemilised parameetrid, veerežiim ja pinnasetüüp). Töö tulemused näitasid, et veerežiim on oluline faktor mulla bakterikoosluste struktuuri kujunemisel. Ajutiselt üleujutatud alade bakterikooslused olid võrreldes püsivalt üleujutatud alade kooslustega mitmekesisemad ja ühtlasema bakteriliikide jaotusega. Uuritud muldade bakterikoosluste denitrifikatsiooni potentsiaal sõltus hüdroloogilistest tingimustest vastavas TMi osas. Suurim nitriti redutseerimise potentsiaal esines püsivalt üleujutatud alade bakterikooslustes, kuid suurim N2O redutseerimise potentsiaal ilmnes ajutiselt üleujutatud alade kooslustes. Mulla keemiline koostis mõjutas denitrifikatsiooniga seotud geenide osakaalusid TMide muldade bakterikooslustes. TMide muldades tuvastatud ANAMMOXi ja n-damo protsesse läbiviivate bakterite osakaalud olid suuremad püsivalt üleujutatud alade bakterikooslustes. Antud töö tulemustest võib järeldada, et ehkki lämmastiku eemaldamine TMide muldadest toimub väga erinevate protsesside vahendusel, on denitrifikatsioon peamine seda funktsiooni läbiviiv protsess ning ajutiselt üleujutatud alade loomine võimaldaks vähendada osalisest denitrifikatsioonist pärinevat N2O emissiooni TMide muldadest.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

Characterization of algal and microbial community growth in a wastewater treating batch photo-bioreactor inoculated with lake water

Microalgae grown in photo-bioreactors can be a valuable source of biomass, especially when combined with wastewater treatment. While most published research has studied pure cultures, the consortia of algae and bacteria from wastewater have more complex community dynamics which affect both the biomass production and pollutant removal. In this paper we investigate the dynamics of algal and bacterial growth in wastewater treating batch photo-bioreactors. The photo-bioreactors were inoculated with water from a nearby lake. Lake water was obtained in August, November and December in order to add native algal species and study the effects of the season. The photo-bioreactors inoculated with lake water obtained in August and November produced more biomass and grew faster than those that only contained the algae from wastewater. The results indicated a rapid decline in bacterial abundance before algae began to multiply in reactors supplemented with lake water in November and December. The reactors were also successful in removing nitrogen and phosphorous from wastewater.Additional funding from SVU (12-123), Purac and Mälarenergi, and by grant IUT2-16 of the Ministry of Education and Research of the Republic of Estonia (J. Truu, M. Truu, T. Ligi).</p

Dynamics of Bacterial Community Abundance and Structure in Horizontal Subsurface Flow Wetland Mesocosms Treating Municipal Wastewater

Dynamics of bacterial community abundance and structure of a newly established horizontal subsurface flow (HSSF) pilot-scale wetland were studied using high-throughput sequencing and quantitative polymerase chain reaction (PCR) methods. Bacterial community abundance increased rapidly within one month and stabilised thereafter in three replicate HSSF constructed wetland (CW) mesocosms. The most dominant phylum was Proteobacteria, followed by Bacteroidetes in wetland media biofilms and Firmicutes in influent wastewater. CW bacterial community diversity increased over time and was positively related to the wastewater treatment efficiency. Increase in the abundance of total bacteria in the community was accompanied with the abundance of denitrifying bacteria that promoted nitrate and nitrite removal from the wastewater. During the 150-day study period, similar patterns of bacterial community successions were observed in replicate HSSF CW mesocosms. The data indicate that successions in the bacterial community in HSSF CW are shaped by biotic interactions, with a significant contribution made by external abiotic factors such as influent chemical parameters. Network analysis of the bacterial community revealed that organic matter and nitrogen removal in HSSF CW could be, in large part, allocated to a small subset of tightly interconnected bacterial species. The diversity of bacterial community and abundance of denitrifiers were good predictors of the removal efficiency of ammonia, nitrate and total organic C in HSSF CW mesocosms, while the removal of the seven-day biochemical oxygen demand (BOD7) was best predicted by the abundance of a small set of bacterial phylotypes. The results suggest that nitrogen removal in HSSF CW consist of two main pathways. The first is heterotrophic nitrification, which is coupled with aerobic denitrification and mediated by mixotrophic nitrite-oxidizers. The second pathway is anaerobic denitrification, which leads to gaseous intermediates and loss of nitrogen as N2