1. Microbial Community Analysis of a Floating Island System in a Stormwater Wet Detention Basin
Danielle Winter, Dessy Owiti, François Birgand, Terrence Gardner, and Bryan Maxwell
Methods `
Introduction
Floating Islands: An Emerging Water Quality Tool
Weekly Discrete Sampling
Vegetated Mats
Methods of Treatment
Chemical analysis: surface water sample & sediment
Microbial community analysis: solution from mats, root wash from composite root sample, and sediment
Microbial assimilation
Nutrient treatment
Nitrogen
Phosphorus
Filtration and sedimentation of suspended solids
Increases in dissolved oxygen
Reduction in water temperature
Pathogen treatment
Improved aesthetic
Provision of habitat and nutrition
Treatment of heavy metals
Improved microbial diversity
Reduced biochemical oxygen demand (BOD)
Predation within microbial communities
Filtration and sedimentation via root systems
Mats Only
Control
Treatment by Floating Islands
Sample of water within mats and of attached biofilms
Example of an Established Island
Microbial mineralization
Plant uptake (phytoremediation)
Island Prototype Utilized for Sampling
Objectives of this Study
Microbial dissimilatory reductions
Adsorption to plant roots and matting
Characterize microbial community structure in a floating island system to better understand treatment mechanisms and capabilities of these systems.
Analyze coincidence of changes in the wet detention basin environment and changes in microbial community structure.
Investigate spatial and temporal variations in microbial communities in floating island systems.
Develop reliable, replicable methods for sampling microbes in floating island systems.
Chelation of metals via organic compounds extruded by plants
Composite root sample from 3 plant species
Sample of surface water
Sample from upper layer of sediment
Visual of the Sampling Scheme
Results `
PCA Analysis
Microbial Community Analyses
Mat environment appears to strongly influences all FAME indicators. Potential explanations:
Aerobic and anaerobic conditions in mats
Substrate quality
Surfaces available for attachment
Efficacies of different sampling techniques
Presence of a distinct cluster for each sampling location suggests unique community structures.
Bacterial signals are dominated by gram-positive bacteria
Resistant to environmental change
Few are pathogenic
FAME Analysis
Analyzed Fatty Acids
Correlations among Biomarkers (p<0.05)
FAME (fatty acid methyl ester) analysis involves extracting fatty acids from living and dead cells.
Certain fatty acids are specific to cell membranes of certain organisms [See Table].
Analyses performed with an Agilent 780B Gas Chromatography system.
FAME Results
Many positive correlations among and between fungi and bacteria across locations may suggest overlap of favored environmental conditions and/or mutualistic relationships (PCA analysis also suggests this).
Fungal biomarkers 16:0, 18:2ω6, 18:1ω6 may have an overlap of favored environmental conditions and/or mutualistic relationships.
18:3ω6 appears to behave differently from other fungal biomarkers, warranting further investigation to ascertain if this biomarker can identify constituents of the fungal community at a higher resolution.
*17:1ω6, 20:0, 16:0, 18:1ω5, i19:0, and a19:0 not included
Gram-negative bacteria and actinomycetes biomarkers may overlap in favored environmental conditions and/or respond similarly to certain sampling methods.
Actinomyces (genus of actinomycetes)= facultative anaerobes
Gram-negative signals (cy17:0 & cy19:0) = anaerobes
Correlations with Environmental Conditions (p<0.05)
Sediment appears to provide the most conducive environment for biomarkers of
Bacteria (except for 17:1ω6 and i19:0)
Fungi
Actinomycetes
Roots likely provide
Root zone and mat samples tended to exhibit more variability.
Dynamic communities
Shorter establishment period
Ineffective sampling methods
Fungal biomarkers were observed in all locations and in substantial concentrations, indicating potential for floating islands to degrade a variety of organic compounds, such as PAHs, EDCs, and pesticides.
Sulfate-reducing bacteria (17:1ω6) were observed in all three locations, suggesting potential for floating islands to treat sulfate, other oxidized forms of sulfur, and hydrocarbons.
If the most robust microbial community is in sediment, sedimentation is a key treatment mechanism of floating islands. (this should be a conclusion!)
Figure F-1
Many correlations between water properties and sediment biomarkers may suggest significant exchange between the water column and upper sediment layers.
Figure F-2
Only a few correlations were found between chemical properties of the wet detention basin environment and the mat and root zone environments. This result is likely related to elevated variability of FAME results at these locations.
Figure F-3
Figure F-4
Future Work
Conclusions
Continuation of microbial community composition monitoring for a full year.
Monitoring of chlorophyll-a concentrations for a full year.
Deep sequencing of microbes in pond sediment prior to floating island installation and after one year of floating island treatment.