T60 New Voices in Geobiology II

Sunday, 22 October 2017
1:30 PM - 5:30 PM
Room 602/603

LONG-RANGE TIME DOMAIN CORRELATION: AN EMERGING BIOGEOCHEMICAL SYSTEM MEASUREMENT ELUCIDATES CHANGES IN DOMINANT GEOCHEMICAL PROCESSES

Paper number: T60-13
Program: Technical Sessions
Time: 4:35 PM – 4:50 PM

Authors

Abstract

Correlation analysis of environmental electrochemical time series is an emerging biogeochemical technique. Analyzing a suite of time series provides insight into the nature of the geochemical environment. Four time series from an oxic-anoxic cyclical bioreactor experiment was analyzed using detrended fluctuation analysis. A sediment suspension from a hyper-eutrophic freshwater marsh was exposed to alternating 7-day periods of purging with air and N2 gas for 74 days1. Differences in strength of temporal scaling in each geochemical setting serve to distinguish individual environments on the basis of electrochemical response. pH, redox potential (Eh), dissolved oxygen (DO), and carbon dioxide (CO2) were measured every 20 min. Scaling exponents for three different geochemical environments: aerobic respiration, NO3- reduction, and mixed Fe(III), Mn2+, SO42- reduction were calculated. Correlation strength ranges from 0 – 2; 0 – 0.5 is anticorrelation, 0.5 is no correlation, and 0.5 – 2 is progressively stronger correlation.

During anoxic-oxic transitions, Eh increases >300 mV and O2 saturation increases to 68.5% within 1 h of N2 – air transition (95% within 5 h). pH increases by 0.3 within 6 h; such that steady state conditions are reestablished within 6 h. This contrasts the observed scaling behavior during aerobic respiration, characterized as follows: very strong correlation of pH (1.74 ± 0.04), and Eh (1.72 ± 0.04), strong correlation of DO (1.35 + 0.04), and moderate correlation of CO2 (0.94 + 0.05). During oxic-anoxic transitions; following N2 influx, O2 is depleted within 2 h, Eh decreases by 100 mV within 1 h, and CO2 levels increase for 6 h then plateau, as does pH. During NO3- reduction, exponents indicate very strong correlation of CO2 (1.68), and strong correlation of pH (1.22) and Eh (1.38), and weak correlation of DO (0.82). Periods of mixed Fe(III), Mn2+, and SO42- reduction are characterized by very strong correlation of pH (1.67 ± 0.02) and Eh (1.77 ± 0.02), uncorrelated DO (0.59 ± 0.01), and moderately correlated CO2 (0.94 ± 0.02). Scaling exponents >1.60 have been linked to active biological cycling of electrolytes. Collectively, the scaling behavior makes it possible to distinguish the three geochemical states.

1Parsons CT, Rezanezhad F, O’Connell DW, Van Cappellen P (2017) Biogeosciences 14, 3585-3602.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-307948

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