Flooding forested groundwater recharge areas modifies microbial communities from top soil to groundwater table

The response of microbial communities to environmental factors in bank soil and river sediment: A case study along the mainstream of the Yangtze River

Microbial communities, which are crucial for ecosystem function and sustainability, are under environmental pressure. Using phospholipid fatty acids (PLFAs) as a measure of microbial biomass and community structure, the responses of microorganisms to environmental drivers were studied in bank soil and sediment alongside the Yangtze River in China. Thirty-eight sites were investigated over a length of 5500 km, ranging from the plateau to the estuary. Redundancy analysis revealed that microbial community composition in the bank soil was affected by MP (7.8%), geography (19.2%), and physicochemical properties (23.1%), while in the sediment, relevant factors were MP additives (12.8%), metals (21.1%), and physicochemical properties (23.3%). Variations in climate conditions along the course of the river had no effect on the microbial communities in the two habitats. Linear discriminant analysis of the PLFAs profiles showed changes in microbial community composition due to land use (forest, grass, cropland and built land), site class (up-, mid- and downstream) and MPs pollution level in both bank soil and sediment. The increased Gram-positive to negative bacteria (g+/g-) ratio and decreased iso-to anteiso-fatty acid (i/a) ratio indicated greater stress, such as caused by MP pollution (g+/g-: 12.6 to 19.3; i/a: 1.9 to 1.6). In bank soil, total microbial biomass was influenced by urbanization rate and nutrient availability. Specifically, total carbon (TC), total phosphorus (TP), and ammonium nitrogen (NH4+-N) had a positive impact, while inorganic phosphorus (IP), total potassium (TK) and nitrate nitrogen (NO3--N) had a negative impact. In contrast, in sediment only TC had a negative effect on biomass. This study applied PLFA to explore microbial communities and structures responses to environmental drivers in riverine habitats, revealing that anthropogenic factors (e.g. MP pollution and nutrient enrichment) alter microbial communities with urbanization.

Are dominant microbial sub-surface communities affected by water quality and soil characteristics?

Subsurface microorganisms must deal with quite extreme environmental conditions. The lack of light, oxygen, and potentially nutrients are the main environmental stresses faced by subsurface microbial communities. Likewise, environmental disruptions providing an unbalanced positive input of nutrients force microorganisms to adapt to varying conditions, visible in the changes in microbial community diversity. In order to test microbial community adaptation to environmental changes, we performed a study in a surface Managed Aquifer Recharge facility, consisting of a settlement basin (two-day residence time) and an infiltration pond. Data on groundwater hydrochemistry, soil texture, and microbial characterization was compiled from surface water, groundwater, and soil samples at two distinct recharge operation conditions. Multivariate statistics by means of Principal Component Analysis (PCA) was the technique used to map the relevant dimensionality reduced combinations of input variables that properly describe the system behavior. The methodology selected allows including variables of different nature and displaying very different range values. Strong differences in the microbial assemblage under recharge conditions were found, coupled to hydrochemistry and grain-size distribution variables. Also, some microbial groups displayed correlations with either carbon or nitrogen cycles, especially showing abundant populations of denitrifying bacteria in groundwater. A significant correlation was found between Methylotenera mobilis and the concentrations of NO₃ and SO₄, and also between Vogesella indigofera and the presence of DOC in the infiltrating water. Also, microbial communities present at the bottom of the pond correlated with representative descriptors of soil grain size distribution.

Depth, soil type, water table, and site effects on microbial community composition in sediments of pesticide-contaminated aquifer

Microbial community compositions in pesticide-contaminated aquifers have not been studied, although such information is important for remediation and maintaining freshwater sources clean under changing climate. Therefore, phospholipid (PLFAs), glycolipid (GLFAs), and neutral lipid (NLFAs) fatty acids were determined from sand and clay sediments at depths of 0.3-24.8 m, all contaminated with triazines and dichlobenil/2,6-dichlorobenzamide. The portion of fungi and Gram-negative bacteria at 0.3 m was greater than at 0.8 m, where the percentage of Gram-positive bacteria, actinobacteria, and sulfate-reducing bacteria (SRB) increased. In deeper sediments, microbial biomass, activity, and diversity decreased. Clay sediments seemed to serve as a reservoir for slow pesticide elution to groundwater, and their biomarker portion for all bacteria except actinobacteria was greater than in sand sediments. The slow pesticide dissipation seemed to occur in the main groundwater flow zone, resulting in nitrogen release simultaneously with organic matter elution from gardening and bank filtration. As a result, microbial biomass, activity, and diversity were increased. This shift in conditions towards that in surface soil may be appropriate for enhanced natural attenuation of pesticides in groundwater sources.

Dissolved organic carbon influences microbial community composition and diversity in managed aquifer recharge systems

This study explores microbial community structure in managed aquifer recharge (MAR) systems across both laboratory and field scales. Two field sites, the Taif River (Taif, Saudi Arabia) and South Platte River (Colorado), were selected as geographically distinct MAR systems. Samples derived from unsaturated riverbed, saturated-shallow-infiltration (depth, 1 to 2 cm), and intermediate-infiltration (depth, 10 to 50 cm) zones were collected. Complementary laboratory-scale sediment columns representing low (0.6 mg/liter) and moderate (5 mg/liter) dissolved organic carbon (DOC) concentrations were used to further query the influence of DOC and depth on microbial assemblages. Microbial density was positively correlated with the DOC concentration, while diversity was negatively correlated at both the laboratory and field scales. Microbial communities derived from analogous sampling zones in each river were not phylogenetically significantly different on phylum, class, genus, and species levels, as determined by 16S rRNA gene pyrosequencing, suggesting that geography and season exerted less sway than aqueous geochemical properties. When field-scale communities derived from the Taif and South Platte River sediments were grouped together, principal coordinate analysis revealed distinct clusters with regard to the three sample zones (unsaturated, shallow, and intermediate saturated) and, further, with respect to DOC concentration. An analogous trend as a function of depth and corresponding DOC loss was observed in column studies. Canonical correspondence analysis suggests that microbial classes Betaproteobacteria and Gammaproteobacteria are positively correlated with DOC concentration. Our combined analyses at both the laboratory and field scales suggest that DOC may exert a strong influence on microbial community composition and diversity in MAR saturated zones.