Chemical speciation in semiarid environments – a review

Authors: ROSSI, COLE - Bureau Of Land Management; HEIL, DEAN - Consultant; Weltz, Mark; Nouwakpo, Sayjro

Submitted to: Journal of Plant Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/9/2019
Publication Date: 9/2/2019
Citation: Rossi, C.G., Heil, D., Weltz, M.A., Nouwakpo, S.K. 2019. Chemical speciation in semiarid environments – a review. Journal of Plant Research. 3(2):305-315. https://doi.org/10.26545/ajpr.2019.b00038x.
DOI: https://doi.org/10.26545/ajpr.2019.b00038x

Interpretive Summary: In semiarid environments, the major cations in soil and surface waters are ionic calcium, magnesium, sodium and potassium (Ca2+, Mg2+, Na+, and K+), and the major anions are chlorite, sulfate, bicarbonate, and carbonate (Cl-, SO 2-, HCO -, and CO 2-), respectively. However, watersheds impacted by fertilization, feedlots, or domestic waste water can also contain elevated levels of nitrate (NO -)and phosphate (PO 3-), mainly in the form of HPO 2- and H PO -. The formation of complexes between all cations and anions needs to be evaluated. Use of Geochemical speciation programs allow to solve for all components present in the system. As an example, the composition of water in semiarid environments is strongly influenced by the dissolution and precipitation of minerals. Geochemical speciation programs as such include a data base of reactions and equilibrium constants for minerals. Depending on the model application and knowledge of the environment being modeled, the user may make choices such as specifying that a specified amount of a given mineral is initially present, or the solution phase is always in equilibrium with a certain mineral. The user may also choose to allow or disallow certain minerals which may not be present initially to precipitate if super-saturation is reached. To start from chemical speciation and have it be meaningful and useful in today's changing world of environmental health and the impact of water quality on all living organisms as well as the storage in our aquifers, learning the basics is truly just the beginning.

Technical Abstract: In semiarid environments, the major cations in soil and surface waters are ionic calcium, magnesium, sodium and potassium (Ca2+, Mg2+, Na+, and K+), and the major anions are chlorite, sulfate, bicarbonate, and carbonate (Cl-, SO 2-, HCO -, and CO 2-), respectively. However, watersheds impacted by fertilization, feedlots, or domestic waste water can also contain elevated levels of nitrate (NO -)and phosphate (PO 3-), mainly in the form of HPO 2- and H PO -. The formation of complexes between all cations and anions needs to be evaluated. Use of Geochemical speciation programs allow to solve for all components present in the system. As an example, the composition of water in semiarid environments is strongly influenced by the dissolution and precipitation of minerals. Geochemical speciation programs as such include a data base of reactions and equilibrium constants for minerals. Depending on the model application and knowledge of the environment being modeled, the user may make choices such as specifying that a specified amount of a given mineral is initially present, or the solution phase is always in equilibrium with a certain mineral. The user may also choose to allow or disallow certain minerals which may not be present initially to precipitate if super-saturation is reached. To start from chemical speciation and have it be meaningful and useful in today's changing world of environmental health and the impact of water quality on all living organisms as well as the storage in our aquifers, learning the basics is truly just the beginning.