Intensive Survey of the Guadalupe River Segment 1806

increase in the importance of pollution-tolerant species that feed on FPOM,
and the standing crop was not elevated, in contrast to what would be
expected in the presence of organic pollution.
Changes in species composition and community trophic structure observed
through the reservoir were attributed to natural, longitudinal succession
rather than the effects of artificial organic enrichment. Overall biological
stability in the reservoir, as indicated by macrobenthic community structure,
was judged to be good.
The river 200 m below Flat Rock Dam, 1806.0223 (Station J), exhibited the
highest diversity and equitability and the second highest species richness in
the study, and clean water mayflies were well represented (9 species; 14.1%
of the community), indicating stable environmental conditions. Community
structure resembled that below Ingram Lake Dam, in that both stations had
large standing crops, with FPOM comprising the primary food material as
indicated by community trophic structure. These common characteristics
apparently result from influences of the small mainstream reservoirs
immediately upstream from each station. However, decreased importance of
filterers together v/ith increased importance of gatherers indicated that a
greater portion of the FPOM was in sedimented rather than suspended form
below Flat Rock Dam. Also, grazers were considerably more important below
Flat Rock Dam, indicating a greater prevalence of periphyton, perhaps due in
part to nutrient inputs from the City of Kerrville.
The macrobenthic community at Wharton Road, 1806.0220 (Station K), was also
stable as indicated by very high species richness, diversity, and equitability,
and strong representation by mayflies (9 species; 14.6% of the community).
A considerable shift in community trophic structure, with FPOM feeders
decreasing and grazers increasing in importance, reflected a continuing
longitudinal trend toward increasing prevalence of periphyton as the primary
food source. This further suggests slightly elevated primary production,
possibly as a result of periodic discharges of nutrients from Kerrville.
Tributary Water Ouality
Dissolved oxygen was 8.1 mg/L in Johnson Creek (Station R) and 9.7 in
Cypress Creek (Station V) when monitored (Table 8). All of the dissolved
oxygen levels from the three stations on Third Creek (Stations S, T, and U)
remained above 7.0 mg/L and the narrow ranges between minima and maximum
levels indicates stability in water quality. Levels of pH at the three
tributary streams were similar to those of the mainstream Guadalupe River
stations and water temperature was less than 22°C.
CBOD5 and CBOD2q levels were very low in Johnson and Cypress Creeks
(< 1.0 mg/L), but were slightly elevated in Third Creek (Table 9). Levels
for these two parameters were highest at the uppermost station on Third
Creek (Station S). In fact they were the highest of any measured on the
survey. Other parameters at this station that were also the highest measured
on the survey include orthophosphorus (0.09 mg/L), total phosphorus (0.18
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