Subsurface hydrochemical precision treatment of a coastal acid sulfate soil

A1 Journal article (refereed)

Internal Authors/Editors

Publication Details

List of Authors: Krister Dalhem, Sten Engblom, Pekka Stén, Peter Österholm
Publisher: Elsevier
Publication year: 2019
Journal: Applied Geochemistry
Journal acronym: APGEO
Volume number: 100
Start page: 352
End page: 362
eISSN: 0883-2927


Some of the most economically valued soils for agricultural use are naturally occurring sulfide rich sediments. However, formation of acid sulfate soils
with sulfuric materials (pH ≤ 4) can occur when sulfidic materials are
exposed to air, which can then result in mobilisation of large amounts
of acid and metals into nearby water bodies. In this study, controlled
drainage, subsurface irrigation and hydrochemical precision treatments
are combined to reduce acidic discharges on a novel project field in
western Finland. The PRECIKEM project field consists of nine identical
hydrologically isolated 1 ha subfields. Each field had a drainage system
consisting of three subsurface drainage pipes (c. 1.3 m deep), a
collector pipe, and a control well enabling manual groundwater table
management. Utilising such drainage installations already common on
farmlands, suspensions of fine-grained (d50 = 2.5 μm) calcium carbonate and/or calcium hydroxide were pumped in to control wells in order to be distributed in to subsoils with sulfuric materials via drainage networks with the aim to: (1) neutralise acidity,
(2) inhibit microbially mediated sulfide oxidation and (3) immobilise
metals. The discharge waters from the fields were monitored during the
project period 2012–2016. As is typical for acid sulfate soils with
sulfuric materials, the discharge waters from the reference fields
(n = 3) that had been treated with water only, had very low pH values
(≤4) and the acidity and concentrations of several metals were up to two
magnitudes higher than the average in Finnish stream waters. Excavation
of selected treated fields revealed the calcium carbonate to have
formed a neutralising coating on the surfaces of hydrologically active macropores
in the soil matrix near the subsurface drainage pipes. This effectively
resulted in a long-term (1–4 years) situation of raised pH, lower
acidity and lower concentrations of several acid sensitive metals, most
prominently a significant decrease (>90%) in Al concentrations. Fe
concentrations in discharge waters were subsequently decreased as the
predominance of Fe shifted toward the schwertmannite and iron oxides
stability phases due to changes in pH/redox conditions. The methods
presented in this work showed favourable steps toward environmentally sustainable agriculture and improving the chemical and ecological status of acid sulfate soil affected coastal waters.


Acidity, Acid sulfate soils, aluminium, Drainage

Last updated on 2019-21-05 at 03:15