Wilkins, Leann I. (2009-05). Modeling an endangered species in an urban landscape: fountain darter (Etheostoma fonticola) survival in the Upper San Marcos River, Hays County, Texas. Master's Thesis. Thesis uri icon


  • To accommodate for human population growth along the Texas I-35 corridor,
    land is becoming increasingly urban and decreasingly pervious, modifying the
    infiltration and runoff rates in the Edwards Aquifer, especially to its spring fed Upper
    San Marcos River (USMR). Contaminants like heavy metals and organic chemicals can
    accumulate on impervious surfaces and with runoff, enter into the USMR at potentially
    harmful levels. The objective of this study was to determine how the population of an
    endangered Edwards Aquifer species, the fountain darter (Etheostoma fonticola), might
    respond to potential water quality changes associated with urbanization. I developed a
    stochastic, sex and stage-structured population dynamics simulation model that
    represents the relationships between urbanization, springflow variations, contamination
    levels, and natural history of the fountain darter.
    Future fountain darter population trends (2008-2040) were simulated under 10
    treatments of nine scenarios. A simulation scenario (n=50) corresponded to one of three
    variations of springflow (random, high and low flow) and one of three variations in
    percentage of runoff entering the river (100, 50 or 30). The 10 treatments were
    variations on water quality: uncontaminated (1), contaminated by Cu (2), Zn (3), Cd (4),
    Cr (5), polycyclic aromatic hydrocarbons (PAH) (7), bifenthrin (8), carbaryl (9) and
    dicamba (10) and an additive affect of Cu, Cr, Cd, and Zn (6).
    Simulating ideal conditions, the average darter population from 2008-2040 was
    54155+2969 (mean+SE) individuals. Contaminant treatments that caused a significant (p<0.001) decline in the population by 2040 under 100% runoff conditions were the all
    metal (650 plus/minus 640), Cu (3141 plus/minus 265), PAH (4621 plus/minus 475), Zn (6169 plus/minus 5406), and Cd
    (27987 plus/minus 6751) scenarios. With 50% runoff, the all metals (15740 plus/minus 5455), Cu
    (16815 plus/minus 6263), PAH (19675 plus/minus 995), and Zn (15585 plus/minus 3097) treatments simulated
    significantly lower populations (p less than 0.001). At 30% runoff, Cu (23976 plus/minus 6787), the all
    metal (25853 plus/minus 7404) and PAH (28167 plus/minus 1194) treatments decreased the population
    significantly (p less than 0.001). Over all scenarios, copper, zinc and PAHs caused >50% decline
    in the population. Assuming 100% or 50% of all San Marcos sub-basin runoff is
    directly entering USMR, there could currently be levels of Cu, Zn, and PAHs higher
    than what darters can withstand.

publication date

  • May 2009