Mohanad Abdelgadir defends his thesis Aquatic ecosystem function and environmental change across spatial scales

Mohanad Abdelgadir

Doctoral thesis: Aquatic ecosystem function and environmental change across spatial scales Länk till annan webbplats.

Subject: Environmental Science
Research Area: Environmental Studies
Graduate School: School of Natural Sciences, Technology and Environmental Studies, BEEGS
Faculty Examiner: Markus Meier, Professor in Physical Oceanography at Rostock University, Germany; Leibniz Institute for Baltic Sea Research, Warnemünde, Germany
Language: English

Abstract

Microbial communities comprise immense diversity, mediating numerous ecosystem functions such as nitrogen transformation in aquatic ecosystems. Yet, how microbial communities and ecosystem functions respond to changes in environmental conditions at different spatial scales in aquatic habitats is not fully understood. This thesis investigates the effect of changes in environmental conditions at different spatial scales on Baltic Sea microbial diversity and nitrogen transformation, specifically denitrification, with a focus on biodiversity-ecosystem function relationship. Two spatial scale settings were examined. A small spatial scale setting was examined with experimental mesocosms of benthic sediment of different salinity and dissolved oxygen levels and at different spatial arrangements, and an incubation experiment conducted with benthic sediments from two different aquatic habitats enriched with 15N nitrate isotope. Microbial diversity, denitrification gene transcript abundances, and potential denitrification rate were analyzed. At a large spatial scale of the Baltic Sea benthic and coastal seascape, a metadata-based modeling approach was employed to investigate how current environmental conditions and future climatic change scenarios affect the predicted spatial distribution of key taxa of denitrifiers and nitrogen-fixing filamentous cyanobacteria. Results showed that salinity and dissolved oxygen levels significantly influenced denitrification capacity, according to analyses of transcript abundances of nirS and nosZ genes, which was mainly driven by habitat environmental conditions rather than habitat spatial arrangement. Bacterial community composition in experimental mesocosms was significantly affected by salinity.
Findings from the small scale mesocosms experiments indicate that salinity can be an important driver of microbial denitrification capacity and affect microbial diversity in studied mesocosms. At large coastal and seascape scales, multi-realm environmental variables from both marine and terrestrial domains had significant impacts on the predicted distribution of the studied microbial taxa. The predicted distribution under different global warming trajectories indicated that rising temperatures in year 2050 and 2100 risk reducing the current bio-climatically suitable areas of the studied denitrifiers and filamentous cyanobacteria across the Baltic Sea. The studies with experimental mesocosms and modeling approaches presented in this thesis contribute knowledge and novel predictions on the spatial response of ecosystem function and microbial communities to ongoing and future environmental changes in the Baltic Sea.