title: A colorimetric DET technique for the high-resolution measurement of two-dimensional alkalinity distributions in sediment porewaters.
abstract: Measurements of porewater alkalinity are fundamental to the study of organic matter mineralization in sediments, which plays an essential role in the global cycles of carbon and nutrients. A new colorimetric diffusive equilibration in thin film (DET) technique is described for measuring two-dimensional total alkalinity distributions in sediment porewaters at high resolution (1-2 mm(2)). Thin polyacrylamide hydrogel layers (0.8 mm) equilibrate with the porewater and, after removal, are immediately laid onto another hydrogel containing formic acid, which reacts with alkalinity-generating species, and the pH-indicator bromophenol blue. The resultant color change is quantified using computer-imaging densitometry. The lower limit of detection is 0.2 meq L(-1) and the upper measurement limit is 8 meq L(-1). Deployment in seagrass colonized sediment revealed high levels of spatial heterogeneity in the porewater alkalinity distribution, with concentrations ranging from 2.28 meq L(-1) in the overlying water to 5.13 meq L(-1) in some parts of the sediment. This is the first time that two-dimensional, high-resolution distributions of porewater alkalinity have been measured.
authors.affiliation: Environmental Futures Research Institute, Griffith School of Environment, Griffith University, Gold Coast Campus, Queensland 4222, Australia. Electronic address: w.bennett@griffith.edu.au.
authors.forename: William W
authors.initials: WW
authors.lastname: Bennett
authors.affiliation: Environmental Futures Research Institute, Griffith School of Environment, Griffith University, Gold Coast Campus, Queensland 4222, Australia.
authors.forename: David T
authors.initials: DT
authors.lastname: Welsh
authors.affiliation: Environmental Futures Research Institute, Griffith School of Environment, Griffith University, Gold Coast Campus, Queensland 4222, Australia.
authors.forename: Antoine
authors.initials: A
authors.lastname: Serriere
authors.affiliation: Environmental Futures Research Institute, Griffith School of Environment, Griffith University, Gold Coast Campus, Queensland 4222, Australia.
authors.forename: Jared G
authors.initials: JG
authors.lastname: Panther
authors.affiliation: Environmental Futures Research Institute, Griffith School of Environment, Griffith University, Gold Coast Campus, Queensland 4222, Australia.
authors.forename: Peter R
authors.initials: PR
authors.lastname: Teasdale
mesh_terms: D000468:Alkalies / Q000032:analysis*; D003124:Colorimetry; D004784:Environmental Monitoring / Q000379:methods*; D019015:Geologic Sediments / Q000737:chemistry*; D057230:Limit of Detection; D011793:Queensland; D014874:Water Pollutants, Chemical / Q000032:analysis*; D035962:Zosteraceae / Q000254:growth & development
chemical_list: D000468:Alkalies; D014874:Water Pollutants, Chemical
keywords: Alkalinity; Biogeochemistry; DET; High-resolution; Porewater; Two-dimensional