Environmental Geochemistry flash cards

Main input into fresh water to terrestrial systems

Rainfall

Pathways of rainfall after landing

Remain at the surface in ponds and puddles and undergo evaporation, Flow across the surface into rivers, lakes or the oceans where again it may be evaporated or seep into groundwater, Infiltrate the surface to become soil moisture where again it may evaporate, flow through the system to seep into lakes or rivers or percolate into the groundwater. Groundwater is eventually returned to the surface by capillary movement.

Percentage of Earth’s water that is fresh

2.5% is freshwater.

Around three-quarters of this freshwater is currently locked away in the planets ice caps

Orographic

Mechanical lifting of moist air over e.g. mountain ranges, or islands

Cyclonic

Frontal (moist air forced up over cold air) and non-frontal (convergence and uplift of air in a low pressure region).

Convectional

Heating of ground surface causes up-currents of thermally unstable air.

Why is chloride the ion chosen to start calculations

It shows little fractionation i.e. is unlikely to have changed as chloride is typically not derived from terrestrial sources and is an uncommon pollutant.

Qualities of geocolloids

Part of the clay fraction (< 2 μm diameter) of soils and sediments, large surface area to mass ratio, charged surface (negative or positive)

Classes of geocolloids

Aluminosilicate clays, hydrous oxides, Soil organic matter

Electrical double layer

One layer is the surface of the geocolloid. The second layer is the layer of ions that are attracted to that charged surface.

Factors that influence geocolloid surface charge

Isomorphous substitution (e.g. aluminosilicate clays), Surface adsorption of ions (e.g. Fe-oxides and humus).

Gouy-Chapman diffuse double layer (GCDDL) theory

The charge decays with increasing distance from the surface in an exponential way

Stern Layer

a zone close to the surface where there is a rapid linear decay in electrical potential indicating that Some counter ions have bonded directly to the surface, reducing the electrical potential and effectively neutralising the electrical charge. (Specific adsorption)

Effect of electrostatic field on aggregation

Large (Diffusion), Small (Aggregate)

Variables that affect the decay constant, Kappa (κ)

Concentration of salt, Valence of the counter ion, Temperature

Causes of soil salination

Terminal lakes, Change in Vegetation cover, Under irrigation, Over irrigation, Marine inundation

‘ion pair’ or ‘outer sphere’

The ions are combined but still separated by all or part of their hydration sphere

’complex ion’ or inner sphere

The ions share a hydration sphere

Exceptions to pure water and solid phases being 1 in equation constant calculation

Excess surface activity, Formation of 'solid solutions', Very dry soils when the activity of water falls below 1.

Ion activity

Free ions in solution undergo intermittent long-range electrostatic interactions (attraction or repulsion) which interferes with the rate at which an ion can take part in associative chemical reactions and therefore the final equilibrium position of those reactions.

Solubility product

Equilibrium constants determined in the presence of a prescribed solid phase at equilibrium (The theoretical constant)

Ion activity products

The measured version of a solubility product, not necessarily determined in the presence of a particular solid, in fact that is what you may be testing for