title: Using geochemical indicators to distinguish high biogeochemical activity in floodplain soils and sediments.
abstract: A better understanding of how microbial communities interact with their surroundings in physically and chemically heterogeneous subsurface environments will lead to improved quantification of biogeochemical reactions and associated nutrient cycling. This study develops a methodology to predict potential elevated rates of biogeochemical activity (microbial "hotspots") in subsurface environments by correlating microbial DNA and aspects of the community structure with the spatial distribution of geochemical indicators in subsurface sediments. Multiple linear regression models of simulated precipitation leachate, HCl and hydroxylamine extractable iron and manganese, total organic carbon (TOC), and microbial community structure were used to identify sample characteristics indicative of biogeochemical hotspots within fluvially-derived aquifer sediments and overlying soils. The method has been applied to (a) alluvial materials collected at a former uranium mill site near Rifle, Colorado and (b) relatively undisturbed floodplain deposits (soils and sediments) collected along the East River near Crested Butte, Colorado. At Rifle, 16 alluvial samples were taken from 8 sediment cores, and at the East River, 46 soil/sediment samples were collected across and perpendicular to 3 active meanders and an oxbow meander. Regression models using TOC and TOC combined with extractable iron and manganese results were determined to be the best fitting statistical models of microbial DNA (via 16S rRNA gene analysis). Fitting these models to observations in both contaminated and natural floodplain deposits, and their associated alluvial aquifers, demonstrates the broad applicability of the geochemical indicator based approach.
authors.affiliation: Hydrologic Sciences and Engineering Program, Colorado School of Mines, 1500 Illinois St., Golden, CO 80401, United States.
authors.forename: Amy
authors.initials: A
authors.lastname: Kenwell
authors.affiliation: Hydrologic Sciences and Engineering Program, Colorado School of Mines, 1500 Illinois St., Golden, CO 80401, United States. Electronic address: asitchle@mines.edu.
authors.forename: Alexis
authors.initials: A
authors.lastname: Navarre-Sitchler
authors.affiliation: Hydrologic Sciences and Engineering Program, Colorado School of Mines, 1500 Illinois St., Golden, CO 80401, United States.
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Prugue
authors.affiliation: Department of Civil and Environmental Engineering, Colorado School of Mines, 1500 Illinois St., Golden, CO 80401, United States.
authors.forename: John R
authors.initials: JR
authors.lastname: Spear
authors.affiliation: Department of Applied Mathematics and Statistics, Colorado School of Mines, 1500 Illinois St., Golden, CO 80401, United States.
authors.forename: Amanda S
authors.initials: AS
authors.lastname: Hering
authors.affiliation: Hydrologic Sciences and Engineering Program, Colorado School of Mines, 1500 Illinois St., Golden, CO 80401, United States.
authors.forename: Reed M
authors.initials: RM
authors.lastname: Maxwell
authors.affiliation: Desert Research Institute, Division of Hydrologic Sciences, 2215 Raggio Parkway, Reno, NV 89512, United States.
authors.forename: Rosemary W H
authors.initials: RW
authors.lastname: Carroll
authors.affiliation: Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States.
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Williams
mesh_terms: D001419:Bacteria / Q000302:isolation & purification; D003120:Colorado; D000074062:Environmental Biomarkers; D019015:Geologic Sediments / Q000737:chemistry* / Q000382:microbiology*; D012329:RNA, Bacterial / Q000032:analysis; D012336:RNA, Ribosomal, 16S / Q000032:analysis; D012044:Regression Analysis; D045483:Rivers / Q000737:chemistry / Q000382:microbiology; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology; D014874:Water Pollutants, Chemical / Q000032:analysis
chemical_list: D000074062:Environmental Biomarkers; D012329:RNA, Bacterial; D012336:RNA, Ribosomal, 16S; D012987:Soil; D014874:Water Pollutants, Chemical
keywords: Extractable metals; Floodplain geochemistry; Microbial DNA