Desert Dessert in Natural History

By Valeria Souza

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Churince is Basically Dead

Churince System Status aquatic fauna. by Evan Carson, August 20, 2011

Water Levels

Degradation of the system has proceeded rapidly since the February-March 2011 trip. The most obvious change is profound drying of the lower third to half of the system (Table 1). In addition, there has been complete drying of the large Northeast Marsh (represented by CHU06 of Carson, 2005), which, prior to this year, has never occurred in recorded history from 1998- present. The closely associated CHU05 was also dry and the peripheral habitat of CHU07 was reduced to two remnant pools. These latter two sites are peripheral habitats of Laguna Intermedia and formerly received direct flow from the Northeast Marsh (CHU06). Similar to the Northeast Marsh (CHU06), the lower system peripheral site CHU12 (Carson, 2005) was completely dry, which has also never occurred in recorded history from 1998- present. Although water was maintained in the nearby, downstream pool of CHU13, water level was declining rapidly (several cm in a week) downstream at CHU 14 and the final downstream pool (within the Rio Churince) at site CHU15 was almost completely desiccated. Laguna Grande and most of the lower Rio Churince, aside from small, isolated pools, was completely dry. Remaining hydrated stretches of the Rio Churince had little to no flow in the lower system.

From CHU11 to the headspring at CHU01, water was present, but the levels were lower than in February-March and declining. In particular, Laguna Intermedia was substantially lower than in February-March (10 cm reduction). This in part reflects normal changes in seasonal balances of spring-flow and evaporation rates, but the water levels were visibly lower than previously experienced by this researcher. The upper system was essentially stagnant, with much reduced flow from normal conditions and consequent development of flocculent surface mats, alga blooms in the rio, and significant reduction of breeding and feeding habitat.

Physicochemistry

No records of physicochemistry were obtained in Feb-Mar. 2011, but ones obtained in May 2011 demonstrate the severity of change in the system from its normal state. Specific conductance (a proxy for salinity) in the headspring was increased by ~10 % relative to pre-crash levels recorded by this researcher on numerous trips in winter, spring, and summer from 1998-2003. Below the headspring, salinity increases throughout most of the system, including all of the Rio Churince, were 50% or greater relative to pre-crash levels.Increased salinity potentially results from reduced of input of freshwater from the deep aquifer, reductions in lower salinity, shallower parts of the aquifer (tapped first by irrigation efforts), lower pressure and longer transport time to the headspring (in effect increase time available to saturate water with salts prior to emergence at the headspring), or some combination of these factors.

Changes in Faunal Distributions and Abundances

For the three snail species for which long-term records are available (Mexipyrgus churinceanus, Mexithauma quadripaludium, andNymphophilus minckleyi), abundances have been dramatically reduced so as to be virtually absent. Only Nymphophilus minckleyiwas observed alive on this trip, despite considerable effort to capture all three species from the headspring and the Rio Churince, and N. minckleyi and M. churinceanus from Laguna Intermedia.Mexipyrgus and Mexithauma appear functionally extirpated from the system, though N. minckleyi appears to be maintaining a small but viable population. The latter is the most hardy of the three species, so this is not surprising.

As in Feb-Mar. 2011, numbers of the endemic cichlid, Herichthys minckleyi, appear reduced in Poza Churince and the upper Rio Churince. What remains unknown is the composition of the feeding morphs. With high snail abundance in the past but few present today, it is predicted that the molluscivore form of H. minckleyi has or will experience significant population reduction or elimination. Abundances of the detritivorous and piscivorous forms are unknown, with the latter perhaps reduced due to competition with the introduced jewel cichlid Hemichromis guttatus. Hemichromis guttatus remains abundant in much of the remaining Rio Churince system, and is highly abundant in Poza Churince. Abundance of C. bifasciatus in Poza Churince is much reduced from the time prior to system degradation. The Mexican tetra Astyanax mexicanus andendemic Gambusia longispinis appear to have been extirpated from the system altogether. The distribution and abundance of Cyprinella xanthicara* and Dionda sp. have been sharply reduced since Feb-Mar 2011, as there is little typical habitat remaining in lower reaches of the system.

*In October 2011, no C. xanthicara were observed despite considerable effort to verify persistence. It is possible the species remains present at a critically low abundance for the time being, at least.

More environmentally hardy species have also been reduced in population size and shifted in geographic distribution in the system.Cyprinodon atrorus has been forced to move upstream into areas formerly occupied by other species, as lower reaches have dried and upper reach habitats have changed to become more environmentally typical of habitats preferred by this species. Nonetheless, the majority of this species habitat has dried and population sizes have declined sharply. Similarly, the abundance and distribution of Cyprinodon bifasciatus has been significantly reduced, such that the species is apparently restricted to Poza Churince. Consequent to the changes in abundance and distribution of C. atrorus and C. bifasciatus, the hybrid zone between these species has essentially disappeared because the two species no longer overlap extensively in range and number in the middle-lower system.

It is critical that water levels be monitored and change quantified. Also, it is urgent to verify that water extraction in the Hundido Valley has indeed ceased. The Becerra canal needs to be taken out of operation or, at a minimum, severely reduced in flow capacity. Finally, water levels and physicochemistry must begin being monitored in Becerra, Juan Santos, and the headwaters of the Rio Mesquites in order to identify sudden or beginning changes in the viability of these systems. Degradation of the system has accelerated since the May 2011 trip. The most obvious change is reduction and fragmentation of Laguna Intermedia. This system is now very shallow and consists of several rapidly desiccating pools. The most well developed stromatolite fields in the Churince system are now exposed and dry. Downstream of Laguna Intermedia, the Rio Churince has become a series of stagnant, desiccating pools down to CHU11 of Carson (2005). For all purposes, reaches below Laguna Intermedia are lost, and Laguna Intermedia itself is in ecological collapse. Upstream of Laguna Intermedia, the system remains largely stagnant, with much reduced fish and other faunal populations. Algal development and reduction of feeding and breeding habitat is severe in the upper Rio Churince. Poza Churince appears lower than in May, but this could be due to seasonal increases in evaporation rate.

It appears faunal extirpations in this system are occurring and increasing in extent. The endemic Gambusia longispinis is almost certainly extirpated from this system and the native Mexican tetra (Astyanax mexicanus) appears extirpated, as well. Hydrobiid snail endemics, particularly Mexipyrgus and Mexithauma, are close to or already are extirpated from this system. Unfortunately, Poza Churince is the type locality for Mexipyrgus churinceanus. Concerns are also growing that Cyprinella xanthicara has been lost form the system or is close to that point. However, most species are in great danger of being lost from this system, unless higher water flows return very soon. Although Cyprinodon atrorus is well adapted to live in severe habitats, most of the habitats typical of this species are now completely dry. Cyprinodon bifasciatus has suffered drastic population size reductions in its typical habitat (Poza Churince, Upper Rio Churince) and is now absent from Laguna Intermedia. Peripheral habitats in the upper Rio Churince system still maintainDionda sp., Gambusia marshi, Cyprinodon atrorus, Cyprinodon bifasciatus, and Cyprinodon hybrids. As such, these areas are oddly ideal for testing hypotheses of ancient stabilization of hybrid lineages in the basin that arose after regional drying over the last 10,000 or more years.

At this point, the Churince system is essentially a dead system, at least relative to its former condition. It is imperative to return Poza de la Becerra to a vibrant and healthy spring, and revive its associated marsh system and most importantly its outflow, the Rio Garabatal. It is also critical to end unsustainable water extraction in the Hundido Valley, which likely means closing all existing wells and ending water extraction in that basin. I have observed change in Churince of the last 13 years and have an intimate knowledge of the history of Cuatro Ciénegas. Without immediate restoration of Becerra/Rio Garabatal and closure of the wells in the Hundido Valley, the Churince system will almost certainly dry completely within a few years at most. The entire western basin is likely to follow, and when and if this extends the to the headwaters of the Rio Mesquites, the basin will have lost the vast majority of its unique habitats and species, as well as the economic opportunity for its people. Arresting water extraction may already be too little, too late.

Contact information:

Evan W. Carson

Dept. of Biology

University of New Mexico,

MSC03 2020

1 University of New Mexico Way

Albuquerque, New Mexico, 87131-0001

Email: evan.carson@gmail.com or carson1@unm.edu

Website: http://www.evanwcarson.com