Technical Reports Document Library

The purpose of this report is to document the results of all aquatic ecosystem monitoring conducted in 2001 at Comal Springs located in New Braunfels, Texas. The monitoring and report preparation was performed by BIO-WEST, Inc. Pflugerville, Texas.

[Excerpted from the Executive Summary]
…During 2001 the conditions in the Comal ecosystem were representative of a normal-to-wet winter and spring followed by the typical summertime decline. However, unlike summer 2000, a significant rainfall event occurred in late summer (September 2001) and moderate-to-high rainfall conditions occurred throughout the remainder of the fall, including another major event in November 2001. As a result, no critical period samples were triggered by low-flow events in 2001; yet two sampling events were conducted following the periods of intense flooding in which the 24-hour mean discharge in the Comal River reached levels that have occurred less than 0.5% of the time in the recorded hydrograph. In each case sampling was conducted after the ecosystem had returned to normative conditions in order to evaluate the postflooding effects, but not so soon that sampling would be influenced by immediate, ephemeral impacts occurring during the elevated flow conditions. …

Throughout this time period the Comal ecosystem can be characterized as an ecosystem with very high water quality for the chemical and physical variables that were measured…. Aquatic vegetation remained abundant throughout the study period and provided suitable habitat for biological communities…. Fountain darters were collected from each reach sampled reach during each sampling event. The overall size class distribution for the Comal ecosystem represents that of a healthy fish assemblage…

By all indications the densities of giant ramshorn snails (Marisa cornuarietis) observed in the Comal ecosystem during the study period to date (including the 2000 low-flow events) pose no serious threat to the aquatic vegetative community. However, because of the impact that this exotic species can have under heavier densities, close monitoring of this species should continue. The gill parasite that has been reported for the fountain darter was evident in a number of collected fountain darters. …

Within the spring runs and at the springs’ orifices, suitable habitat for the listed invertebrates was observed throughout the study period. Several Comal Springs riffle beetle (Heterelmis comalensis) adults and larvae were collected in the drift nets throughout the year. A major discovery in 2001concerning invertebrates was the extension of the known range for the Comal Springs riffle beetle. …

Suitable habitat for the Comal Springs salamander (Eurycea sp.) was noted in the spring runs and Spring Island area with Comal Springs salamanders observed in each area for each sampling event. …

One conclusion that can be made is that this study is the most comprehensive biological evaluation that has ever been conducted on the Comal ecosystem.