Chemistry and karst

Povzetek

The processes of initiation and development of characteristic surface karst landforms and underground caves are nearly all chemical processes. This paper reviews the advances in understanding of karst chemistry over the past 60 years. The equilibrium chemistry of carbonate and sulfate dissolution and deposition is well established with accurate values for the necessary constants. The equations for bulk kinetics are known well enough for accurate modeling of speleogenetic processes but much is being learned about atomic scale mechanisms. The chemistry of karst waters, expressed as parameters such as total dissolved carbonates, saturation index, and equilibrium carbon dioxide pressure are useful tools for probing the internal characteristics of karst aquifers. Continuous records of chemical parameters (chemographs) taken from springs and other karst waters mapped onto discharge hydrographs reveal details of the internal flow system. The chemistry of speleothem deposition is well understood at the level of bulk processes but much has been learned of the surface chemistry on an atomic scale by use of the atomic force microscope. Least well understood is the chemistry of hypogenetic karst. The main chemical reactions are known but equilibrium modeling could be improved and reaction kinetics are largely unknown.

Kemija in Kras
Procesi začetka in razvoja značilnih površinskih kraških oblik in podzemnih jam imajo skoraj vsi razlog v kemiji. Prispevek je pregled napredka v razumevanju kraške kemije v zadnjih 60 letih. Kemijsko ravnotežje raztapljanja in odlaganja karbonatov in sulfatov je dobro poznano, kjer natančno poznamo vse potrebne ravnotežne konstante. Tudi kinetika raztapljanja na makroskopski ravni je dovolj dobro poznana, da lahko modeliramo procese speleogeneze. Osnovne mehanizme raztapljanja na atomski ravni še vedno spoznavamo. Kemija kraških vodah, izražena v parametrih, kot so vsebnost raztopljenih karbonatov, indeks nasičenosti in ravnovesje tlaka ogljikovega dioksida, je danes uporabno orodje za raziskovanje značilnosti kraških vodonosnikov. Zvezno beleženje kemičnih parametrov na kraških izvirih in drugih kraških vodah (kemogrami) skupaj s pretočnimi hidrogrami razkrivajo podrobnosti o podzemnem sistemu pretakanja voda. Tudi kemizem odlaganja sige na makroskopski ravni dobro razumemo, raziskave z mikroskopi na atomsko silo (AFM) pa nam omogočajo nova spoznanja o procesih na atomski ravni. Še najmanj je razumljena kemija hipogenega krasa. Glavne reakcije so znane, vendar je že modeliranje ravnotežja pomanjkljivo, še manj pa vemo o kemijski kinetiki.