Depth profiles for various water quality parameters at El Potrero (type locality for Prietella phreatophila)

At this locality, two points of access to subterranean waters were explored. Flow was not discernible at either site, and water was not discharging to the surface at either (though it does so during floods at both sites).

  1. Potrero 1 - on the west (?) side of the canyon is what is presumably the type locality of P. phreatophila, in a steeply dipping and narrow fracture which could be penetrated by divers only to a depth of XX m. This site is heavily pumped for wat er for the coal washing plant in nearby Palau. Water quality in this site was taken from the surface only.

  2. Potrero 2 - on the east (?) side of the canyon, and slightly downstream from the presumed type locality (Potrero 1) is a now-covered cave. Upon lifting the steel trap door, one enters a pool of water, followed by a short dry cave, which then drops bac k into water. This is a solution channel, not a fracture like is found across the arroyo at the type locality.

Water quality for El Potrero 2 (east side of the arroyo)at El Potrero, near Melchor Múzquiz, Coahuila. Clic k on any graph for a larger image.
Temperature
temperature bar chart		 Specific conductance
specific conductance throughout course of the dive
pH
pH throughout course of the dive		 Dissolved Oxygen
Dissolved Oxygen throughout course of the dive
Redox Potential
Redox Potential throughout course of the dive		 Time / depth profile of the dive
Time / depth profile of the dive

We thus conclude:

  1. Waters in Potrero 1 and Potrero 2 are distinctly different.
  2. Potrero 2 contains at least 2 water masses: a homogeneous surface layer extending to 3.6 m depth and a transition layer from 3.7 to at least 5.4 m or more. Presumably, if the cave extended to even deeper depths, a homogeneous layer would be encountered below the transition layer as was the case with Rio Frio.
  3. Comparison of how parameters change between shallow and deep water masses in Rio Frio and Potrero 2 show similarities and differences as follows:

    Comparison of Rio Frio cave and El Potrero 2
    Río Frio Potrero 2
    Shallow Deep Shallow Deep
    Temperature Cooler Warmer Warmer Cooler
    pH Higher Lower Higher Lower
    Specific Conductance Lower Higher Lower Higher
    Dissolved Oxygen Lower Higher Higher Lower
    Redox Potential Lower Higher Lower Higher

    Thus, direction of change with depth for pH, specific conductance and redox are the same for the two caves, while temperature and dissolved oxygen move in opposite directions for Rio Frio and Potrero 2.