Porewater

Porewater is the water that occupies the void spaces between solid particles in soils, sediments, or rocks. In many environmental settings it is distinct from the bulk groundwater or surface water because it is enriched by dissolution from solids and by limited exchange with the overlying water. It plays a key role in nutrient cycling and contaminant transport.

Porewater contains dissolved ions such as Na+, K+, Ca2+, Mg2+, Cl-, NO3-, NH4+, SO4^2-, HCO3-, as well as dissolved gases like O2, CO2, CH4, and varying pH and redox potential. The chemistry often varies with depth due to redox reactions; oxic zones near the surface may transition to microaerophilic, then nitrate-reducing, iron-reducing, sulfate-reducing, and methanogenic zones in reducing sediments. In organic-rich sediments, porewater can become depleted in oxygen and nitrate while accumulating reduced species and methane.

Porewater is studied by extracting water from the pores using centrifugation, squeezing, or suction samplers, coring with rhizon samplers, or measuring in situ with microsensors and microelectrodes. Analyses determine major ions, nutrients, dissolved organic carbon, trace metals, and dissolved gases.

The porewater chemistry drives diagenetic transformations, metal mobility, and the exchange of solutes with groundwater or overlying water. It controls nutrient availability for plants and microorganisms in soils and wetlands, and governs the mobility of contaminants in contaminated sites.