Impact of rising seawater levels and subsequent flooding on microbial community function in terrestrial soils

Browett, Lewis Callum (2022) Impact of rising seawater levels and subsequent flooding on microbial community function in terrestrial soils. Masters by Research thesis (MSc), Manchester Metropolitan University.

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Abstract

Storm surges, flooding, and the encroaching of seawater onto agricultural land is predicted to increase with climate change fundamentally altering soil properties. It is therefore important to understand the knock-on effect seawater flooding may have on the microbial community and its functioning. This study uses a mesocosm approach to simulate the flooding of terrestrial soil and monitor 1) changes in soil environmental parameters (pH, metal concentration, conductivity), 2) microbial functioning (metabolic activity and degradative enzymes), and 3) microbial community composition (16S sequencing). The system chosen was a naturally occurring saltmarsh-terrestrial pasture gradient where three sites were sampled: Low and High elevation Saltmarsh and agricultural pastureland, incorporating a legacy of differing levels of seawater ingress and exposure. The hypotheses tested in this study were that (1) resistance of microbial community functioning and structure to not be altered during seawater flooding is a factor of pre-adaptation to the stress, and (2) this adaptation will result in communities resilient to flooding, returning to previous state prior to flooding. Soil mesocosms, established from soil taken at the sample sites, were exposed to seawater flooding for durations of 0, 1, 96- and 192-hours submersion. This equated to 72 mesocosms sampled both immediately after the flooding, and after a 14 day “recovery” period. The physicochemical properties significantly increased with seawater flooding in pasture, but not saltmarsh soils. Whilst metabolic activity decreased in all sites post flooding, the saltmarsh communities were more resilient to seawater inundation, and recovered at a faster rate to levels pre flooding. Communities from saltmarsh sites also had a higher resistance to flooding retaining enzymatic function following prolonged exposure. These results suggest that communities previously exposed to flooding have increased resistance / resilience to seawater inundation, and those that do not are significantly impacted even after short flooding durations.