Quantifying alkalinity generating processes in a tidally remediating acidic wetland

Scott G. Johnston, Annabelle F. Keene, Edward D. Burton, Richard T. Bush, Leigh A. Sullivan

Research output: Contribution to journalArticle

21 Citations (Scopus)

Abstract

Lime-assisted tidal exchange (LATE) is a new remediation technique that is demonstrably effective at decreasing acidity in coastal acid sulfate soils (CASS). However, the relative magnitude of the major in situ alkalinity generating processes and external alkalinity inputs that dominate neutralization of acidity during LATE have not been quantified. Here, we combine investigations of porewater and solid-phase geochemistry from a remediating CASS wetland to derive first-order estimates of alkalinity generating processes and inputs after 6years of LATE. Quantified inputs include: marine derived HCO 3 - from tidal exchange; hydrated lime additions; and in situ alkalinity from anaerobic metabolism of organic carbon coupled with reduction of iron and sulfate. A progressive increase in tidal inundation led to the development of significant relationships (α=0.01) between topography and both non-sulfidic, solid-phase Fe(II) and solid-phase reduced inorganic sulfur species. These topographic relationships were conjoined with a digital elevation model, enabling up-scaling of alkalinity estimates to a sub-catchment level. Estimates indicate the relative order of importance of alkalinity generating processes and inputs is Fe reduction (50-64%)>tidal exchange (25-42%)>sulfate reduction (7-13%)>>hydrated lime addition (<1%). Accurately attributing the relative contributions due to Fe and SO 4 2- reduction was limited by an inability to distinguish between non-sulfidic, solid-phase Fe(II) generated by microbial dissimilatory reduction of Fe(III) or chemical reduction of Fe(III) by H 2S. Nevertheless, the combined alkalinity contribution of these two electron accepting processes accounts for between 58 and 74% of the total. The majority (>99%) of net alkalinity generation was due to either tides or microbial metabolism. This indicates that the LATE remediation technique is both a cost effective means of decreasing soil acidity and is readily transferable to similar CASS landscapes - provided there is adequate supply of suitable electron donors and sufficient regenerative capacity in the adjacent estuarine/marine tidal HCO 3 - pool.

Original languageEnglish
Pages (from-to)106-116
Number of pages11
JournalChemical Geology
Volume304-305
DOIs
Publication statusPublished - 2012
Externally publishedYes

Fingerprint

Wetlands
Alkalinity
alkalinity
lime
wetland
Sulfates
acid sulfate soil
Acidity
Soils
acidity
Hydrated lime
Remediation
Metabolism
Acids
remediation
metabolism
sulfate
Geochemistry
Tides
neutralization

Cite this

Johnston, Scott G. ; Keene, Annabelle F. ; Burton, Edward D. ; Bush, Richard T. ; Sullivan, Leigh A. / Quantifying alkalinity generating processes in a tidally remediating acidic wetland. In: Chemical Geology. 2012 ; Vol. 304-305. pp. 106-116.
@article{13c88a1c9f93490a89a292d8963d4adf,
title = "Quantifying alkalinity generating processes in a tidally remediating acidic wetland",
abstract = "Lime-assisted tidal exchange (LATE) is a new remediation technique that is demonstrably effective at decreasing acidity in coastal acid sulfate soils (CASS). However, the relative magnitude of the major in situ alkalinity generating processes and external alkalinity inputs that dominate neutralization of acidity during LATE have not been quantified. Here, we combine investigations of porewater and solid-phase geochemistry from a remediating CASS wetland to derive first-order estimates of alkalinity generating processes and inputs after 6years of LATE. Quantified inputs include: marine derived HCO 3 - from tidal exchange; hydrated lime additions; and in situ alkalinity from anaerobic metabolism of organic carbon coupled with reduction of iron and sulfate. A progressive increase in tidal inundation led to the development of significant relationships (α=0.01) between topography and both non-sulfidic, solid-phase Fe(II) and solid-phase reduced inorganic sulfur species. These topographic relationships were conjoined with a digital elevation model, enabling up-scaling of alkalinity estimates to a sub-catchment level. Estimates indicate the relative order of importance of alkalinity generating processes and inputs is Fe reduction (50-64{\%})>tidal exchange (25-42{\%})>sulfate reduction (7-13{\%})>>hydrated lime addition (<1{\%}). Accurately attributing the relative contributions due to Fe and SO 4 2- reduction was limited by an inability to distinguish between non-sulfidic, solid-phase Fe(II) generated by microbial dissimilatory reduction of Fe(III) or chemical reduction of Fe(III) by H 2S. Nevertheless, the combined alkalinity contribution of these two electron accepting processes accounts for between 58 and 74{\%} of the total. The majority (>99{\%}) of net alkalinity generation was due to either tides or microbial metabolism. This indicates that the LATE remediation technique is both a cost effective means of decreasing soil acidity and is readily transferable to similar CASS landscapes - provided there is adequate supply of suitable electron donors and sufficient regenerative capacity in the adjacent estuarine/marine tidal HCO 3 - pool.",
keywords = "Acid sulfate soil, Anaerobic metabolism, Iron reduction, Sulfate reduction, Tidal wetland",
author = "Johnston, {Scott G.} and Keene, {Annabelle F.} and Burton, {Edward D.} and Bush, {Richard T.} and Sullivan, {Leigh A.}",
year = "2012",
doi = "10.1016/j.chemgeo.2012.02.008",
language = "English",
volume = "304-305",
pages = "106--116",
journal = "Chemical Geology (Isotopic Geoscience) Section",
issn = "0009-2541",
publisher = "Elsevier",

}

Quantifying alkalinity generating processes in a tidally remediating acidic wetland. / Johnston, Scott G.; Keene, Annabelle F.; Burton, Edward D.; Bush, Richard T.; Sullivan, Leigh A.

In: Chemical Geology, Vol. 304-305, 2012, p. 106-116.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Quantifying alkalinity generating processes in a tidally remediating acidic wetland

AU - Johnston, Scott G.

AU - Keene, Annabelle F.

AU - Burton, Edward D.

AU - Bush, Richard T.

AU - Sullivan, Leigh A.

PY - 2012

Y1 - 2012

N2 - Lime-assisted tidal exchange (LATE) is a new remediation technique that is demonstrably effective at decreasing acidity in coastal acid sulfate soils (CASS). However, the relative magnitude of the major in situ alkalinity generating processes and external alkalinity inputs that dominate neutralization of acidity during LATE have not been quantified. Here, we combine investigations of porewater and solid-phase geochemistry from a remediating CASS wetland to derive first-order estimates of alkalinity generating processes and inputs after 6years of LATE. Quantified inputs include: marine derived HCO 3 - from tidal exchange; hydrated lime additions; and in situ alkalinity from anaerobic metabolism of organic carbon coupled with reduction of iron and sulfate. A progressive increase in tidal inundation led to the development of significant relationships (α=0.01) between topography and both non-sulfidic, solid-phase Fe(II) and solid-phase reduced inorganic sulfur species. These topographic relationships were conjoined with a digital elevation model, enabling up-scaling of alkalinity estimates to a sub-catchment level. Estimates indicate the relative order of importance of alkalinity generating processes and inputs is Fe reduction (50-64%)>tidal exchange (25-42%)>sulfate reduction (7-13%)>>hydrated lime addition (<1%). Accurately attributing the relative contributions due to Fe and SO 4 2- reduction was limited by an inability to distinguish between non-sulfidic, solid-phase Fe(II) generated by microbial dissimilatory reduction of Fe(III) or chemical reduction of Fe(III) by H 2S. Nevertheless, the combined alkalinity contribution of these two electron accepting processes accounts for between 58 and 74% of the total. The majority (>99%) of net alkalinity generation was due to either tides or microbial metabolism. This indicates that the LATE remediation technique is both a cost effective means of decreasing soil acidity and is readily transferable to similar CASS landscapes - provided there is adequate supply of suitable electron donors and sufficient regenerative capacity in the adjacent estuarine/marine tidal HCO 3 - pool.

AB - Lime-assisted tidal exchange (LATE) is a new remediation technique that is demonstrably effective at decreasing acidity in coastal acid sulfate soils (CASS). However, the relative magnitude of the major in situ alkalinity generating processes and external alkalinity inputs that dominate neutralization of acidity during LATE have not been quantified. Here, we combine investigations of porewater and solid-phase geochemistry from a remediating CASS wetland to derive first-order estimates of alkalinity generating processes and inputs after 6years of LATE. Quantified inputs include: marine derived HCO 3 - from tidal exchange; hydrated lime additions; and in situ alkalinity from anaerobic metabolism of organic carbon coupled with reduction of iron and sulfate. A progressive increase in tidal inundation led to the development of significant relationships (α=0.01) between topography and both non-sulfidic, solid-phase Fe(II) and solid-phase reduced inorganic sulfur species. These topographic relationships were conjoined with a digital elevation model, enabling up-scaling of alkalinity estimates to a sub-catchment level. Estimates indicate the relative order of importance of alkalinity generating processes and inputs is Fe reduction (50-64%)>tidal exchange (25-42%)>sulfate reduction (7-13%)>>hydrated lime addition (<1%). Accurately attributing the relative contributions due to Fe and SO 4 2- reduction was limited by an inability to distinguish between non-sulfidic, solid-phase Fe(II) generated by microbial dissimilatory reduction of Fe(III) or chemical reduction of Fe(III) by H 2S. Nevertheless, the combined alkalinity contribution of these two electron accepting processes accounts for between 58 and 74% of the total. The majority (>99%) of net alkalinity generation was due to either tides or microbial metabolism. This indicates that the LATE remediation technique is both a cost effective means of decreasing soil acidity and is readily transferable to similar CASS landscapes - provided there is adequate supply of suitable electron donors and sufficient regenerative capacity in the adjacent estuarine/marine tidal HCO 3 - pool.

KW - Acid sulfate soil

KW - Anaerobic metabolism

KW - Iron reduction

KW - Sulfate reduction

KW - Tidal wetland

UR - http://www.scopus.com/inward/record.url?scp=84858959955&partnerID=8YFLogxK

U2 - 10.1016/j.chemgeo.2012.02.008

DO - 10.1016/j.chemgeo.2012.02.008

M3 - Article

VL - 304-305

SP - 106

EP - 116

JO - Chemical Geology (Isotopic Geoscience) Section

JF - Chemical Geology (Isotopic Geoscience) Section

SN - 0009-2541

ER -