Regional hydrochemistry of North American carbonate terrains

The chemical variation of water samples drawn from carbonate terrains between southern Canada and northern Mexico is shown to be divisible into, first, variations at the local level due to (1) hydrogeologic conditions (time independent), (2) short‐term fluctuations of hydrologic factors (stochastic in time), and (3) seasonal fluctuations of such factors as temperature, precipitation, and plant growth (systematic in time) and, second, regional climatic effects. These regional climatic effects can be satisfactorily represented by mean annual groundwater temperature variation. The regional variation only emerges clearly if care is taken to compare water samples from the same hydrologic class, in this case, springwater. The partial pressure of carbon dioxide with which a springwater sample is in equilibrium is well represented by log Pco 2 = a + bT , where a is of the order of −3.5 and b is approximately 0.07 with Pco 2 in atmospheres and T in degrees Celsius.