Theses/Dissertations - Biology

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Phytoplankton production in a central Texas reservoir.
(1969) Kimmel, Bruce Lee; Lind, Owen T., 1934-; Baylor University.
Phytoplankton production and other environmental variables were measured from June to November, 1968 to determine factors affecting production and trophic status of the producer community in a shallow, polymictic, central Texas reservoir. The reservoir was highly productive and eutrophic. Net phytoplankton production estimates, derived from data, averaged 390 mg C m“3 day“^, 857 mg C m“2 day”^, and 300 g C m"^ yr~for the impoundment. Light extinction by organic and inorganic turbidity limited phytoplankton production by decreasing the photic depth. Nutrient limitation was of minor importance, although greater production occurred near points of nutrient inflow than in other reservoir areas. Wind-mixing of the reservoir is believed to accelerate its eutrophication by promoting rapid nutrient recirculation, and thus maintaining nutrient availability for primary production. The impoundment is expected to age more rapidly with time as its basin shallows and phytoplankters spend an increasingly larger fraction of their lives in the productive zone.
Uptake and utilization of alanine-1-14C by freshwater algae.
(1969) Campbell, David Bennett; Lind, Owen T., 1934-; Baylor University.
Experiments were conducted x^ith Chlorella pyrenoidosa, Cosmarium formosulum, and Gloeocapsa sp. to determine their relative heterotrophic capacity at various conditions. Cultures were incubated in nutrient media with 0.5 uc DL-alanine-l-^C added at various temperature (10C, 20C, 30C) and illumination (0 ft-c, 2137 ft-c, 8547 ft-c) conditions. A temperature increase resulted in an increase in alanine uptake in Ck pyrenoidosa and C. formosulum. Uptake decreased in Gloeocapsa at 20C but increased at 30C. High light intensity and darkness stimulated uptake in C. pyrenoidosa and C. formosulum and uptake was minimal at 2137 ft-c. Uptake occurred at all illumination conditions with Gloeocapsa, but was maximum at 2137 ft-c. Alanine was incorporated into cytoplasmic protein in C. pyrenoidosa and C.. formosulum but a significant amount was incorporated into protein in Gloeocapsa only at 2137 ft-c. These species were concluded to be facultative heterotrophs.
Pond succession on the Kaibab Plateau, Arizona.
(1969) Kimmel, James Ross; Lind, Owen T., 1934-; Baylor University.
Quantitative data were obtained for a serai comparison of five sinkhole ponds on the Kaibab Plateau, Arizona. Species diversity, community metabolism, primary production, and relative serai rank were assayed. Information theory and non-information theory species diversity indices were used to compare the phyto- and zooplankton, benthos, and emergent vegetation both within and among ponds. Species diversity of these four pond features showed large fluctuations, hence diversity indices afford distinction only between early versus late serai stages. The ponds were divided into early versus late categories based on community metabolism estimates, as calculated by the diel oxygen curve method. Primary production values, derived from diel oxygen curve values, indicate that primary production increases during succession to a certain point, then decreases as the aquatic ecosystem approaches senescence. Methods of estimating serai stage based on measurements of individual characteristics were ineffective, so a systems analysis approach was developed. Species diversity, photosynthesis-respiration ratio, and mean depth wer*e related mathematically to produce a serai ranking value which varies directly with serai stage. Values calculated with this formula correspond well with presumed serai stages of the ponds.
Age and growth of the white crappie, Pomoxis Annularis Rafinesque, in Lake Waco, Texas.
(1969) Chen, Terry Huei-Hsiung; Lind, Owen T., 1934-; Baylor University.
The major collection of white crappie was from 17 July 1967, to 10 April 1968, by traps and gill nets. Other fish were taken by anglers and seines in June 1968. A total of 1142 fish were included in this study. Spawning season for Lake Waco crappie was from late February to early May and was at its peak in March and April. White crappie in Lake Waco may spawn after one year. Growth rate of Lake Waco white crappie was rapid. The average back-calculated total lengths(TL) for Lake Waco crappie for the last 4 years were as follows: 145mm for the first year’s growth, 216mm for the second age group, 271mm for the third age group, and 309mm for the fourth age group. In the white crappie scales started to develop on the caudal peduncle in fish 16mmTL. The first fully scaled fish observed was 31mmTL. The region between the dorsal fin and pectoral fin was the last place to develop scales. The mathematical expression of the length-weight relationship for the white crappie of Lake Waco is: log W = -5.6131 + 3.2954 log L where W= body weight in grams L=total length in millimeters. The body-scale relationship demonstrated a parabolar curve. The equation L=35.506219 + 1.215665 S + 0.000931 s2 fitted the body-scale relationship of Lake Waco white crappie well. Principal food items of white crappie were small fishes (mainly shads, Dorosoma cepedianum and D. petenense), aquatic insects, and small crustaceans. Lymphocystis was only found in the spring, and about 1.7 percent of the fish were infected. Infection by nematode parasites, Camallanus oxycephalus, was observed in the spring and summer, but infected fish showed no signs of weakness.
Some effects of thermal history on the largemouth black bass, Micropterus salmoides (Lacepede), of two central Texas reservoirs receiving power plant effluents.
(1972) Venables, Barney James; Lind, Owen T., 1934-; Baylor University.
Mean annual growth of the first three age classes of largemouth black bass from Tradinghouse Reservoir was near the average growth reported in the literature for southern waters. Largemouth black bass collected from the discharge canals of Tradinghouse Reservoir (which has received power plant effluent for only 2 years) and Lake Creek Reservoir (which has received power plant effluent for 20 years) showed no difference in male or female gonadal development, condition factor, or thyroid activity; however, the largemouth black bass collected from the Tradinghouse Reservoir discharge canal showed signs of decreased physiological activity with respect to the Lake Creek sample. No significant detrimental effects of the power plant effluents were detected.
The ostracode Cypridopsis vidua: physiological response due to thermal stress.
(1973) Wysong, Mark Lee; Lind, Owen T., 1934-; Baylor University.
Upper temperature effects were measured on the mean oxygen consumption, carbon dioxide production, ingestion, assimilation, and egestion rates of the ostracode Cypridopsis vidua. to determine positive or negative effects of temperature stress. Oxygen consumption and carbon dioxide production were near the literature reportings of the Class Ostracoda, with a linear increase with increasing temperatures. Respiratory Quotients were very low. Ingestion and assimilation rates were positively linearly related with temperature to 30C and 25C. respectively, above which each was negatively affected. Assimilation efficiency dropped from 70 percent at 15C to 16 percent at 35C. Ingestion and assimilation rates increased per mg biomass with decreasing size of organism. Active avoidance of 30 and 35C temperatures was observed.
Structure and photosynthetic response to abrupt thermal stress of a periphyton algal community colonized in a power plant discharge canal.
(1976) Lukins, David Alan; Lind, Owen T., 1934-; Baylor University.
Tremendous increases in energy needs have led to construction of many new power plants. Effects of heated power plant effluents on aquatic organisms have not been clearly established, Periphyton community structure was used to assess these effects. Species diversity (H") was used to monitor changes in periphyton algal community structure in the discharge canal of a fossil fuel power plant near Waco, Texas. Diversity decreased closer to the power plant discharge. Minimum diversity was 0,96 in June at the sampling station closest the power plant and maximum diversity was 2.89 at the station farthest from the discharge in March. Diatoms dominated the attached algal flora at all stations in the January and March samples. By May diatoms were being replaced by bluegreens at the sampling station closest the power plant, yet diatoms were still the major group at all stations. By June bluegreens were dominant at the station closest the power plant and were increasing at the other' stations but were not dominant. Primary periphyton production per unit biomass was measured following exposure to abrupt thermal change as encountered during shutdown and startup of a power plant. Production was greatest for samples colonized near the power plant discharge for both 10 C and 30 C experimental temperatures. Maximum primary periphyton production using methods was 0.61 ug C organic matter * hr“*.
The production, nitrogen, and phosphorus dynamics of Elodea sp., Potamogeton sp., and Nitella sp. in Sam Rayburn reservoir, Texas.
(1978) Neely, Robert Kyle; Lind, Owen T., 1934-; Baylor University.
The 1977 annual maximum biomass of Elodea sp., Fota- — 2 mogeton sp., and Nitella sp. was found to be 1013.6 g m~ , 168.4 g m **, and 32?.6 g m~'', respectively. Combined, these plants produce 80,528.16 kg dry wt lake”* year”*. However, this value is only 0.289?5 of phytoplankton production. Production of the macrophytes may have been greater had a a severe draw-down not occurred. The seasonal changes in ash weight and nutrient concentrations did not conform to the typical curves» nor did the seasonal change in biomass conform to the expected sigmoid curve (Westlake, 1965b)* The atypical patterns were due to the effects suffered from the water level change. Nitrogen and phosphorus concentrations in the plant tissues were not found to be indicative of environmental concentrations of nitrogen and phosphorus. This occurrence may have been due to neither nitrogen nor phosphorus of waters or sediments being limiting. Evidence for secretion of phosphorus by Elodea sp. was found. Diffusion gradients of phosphorus were found between the interior and exterior of the Elodea sp. stands.
The effects of phosphorus starvation on phosphate storage, three storage products and cellular organelles of Chlorella pyrenoidosa.
(1983) Ransom, Charlotte B.; Lind, Owen T., 1934-; Baylor University.
The ultrastructure of phosphorus starved, phosphorus restored and total nutrient cells of Chlorella pyrenoidosa was described by i morphometric analysis. The rate of phosphorus incorporation into polyphosphate bodies of phosphorus starved cells was described as a volume fraction of the whole cell volume over a 210 min period. Maximum phosphorus incorporation into polyphosphate bodies of phosphorus starved cells occurred in the first 30 min of exposure to phosphorus. After 180 min exposure, the volume fraction of the polyphosphate bodie's of these cells decreased significantly. Several different trends were observed in the volume fractions of other cellular components. The volume fraction of starch in the chloroplast was significantly larger in the total nutrient cells than in cells of any other treatment. Lipids and pyrenoid volume fractions were significantly higher in phosphorus starved and phosphorus restored cells than in total nutrient cells. Phosphorus starved cells had the smallest volume fraction of vacuoles. Upon exposure to phosphorus, the vacuolar volume fraction increased until it equalled that of total nutrient cells. No significant differences in the volume fractions of the chloroplast, nucleus or mitochondrion were observed for any treatment.
The effect of the form and concentration of nitrogen on geosmin production by an aquatic actinomycete (streptomyces isolate WM1C1).
(1983) Katzif, Samuel D.; Lind, Owen T., 1934-; Baylor University.
Actinomycetes are organisms that produce geosmin which is one of the organic compounds responsible for the earthy (musty) odor in water. This study was designed to isolate an actinomycete, confirm it as a geosmin producer, and determine the effects of the form and concentration of nitrogen on the production of geosmin by the isolate. Five actinomycetes were isolated from the muds of Lake Waco; four were identified as Streptorayces and one as a possible Nocardia sp. or Micromonospora sp., and two Streptomyces spp. were confirmed to be geosmin producers by GC-MS. The effects of nitrogen on one Streptomyces sp. were reported as affecting threshold odor number (R.O.N.), biomass production (mg dry wt), and Specific T.O.N. (T.O.N.-mg dry wt ^). The forms of nitrogen used were NO^-N as KNO^, NH^-N as NH^Cl, and organic nitrogen (ORG-N) as asparagine and the concen- tration range of nitrogen was 0.000 mg'L to 0.600 mg * L. T.O.N. values increased linearly as concentrations of NO^-N and NH^-N increased while ORG-N (0.300 mg'L inhibited geosmin production. Biomass production increased linearly as concentrations of NO^-N and ORG-N increased (0.000 mg*L ^ to 0.600 mg'L"'*") but low concentrations of all three nitrogen forms did not promote significantly larger biomass proudction than the nitrogen-free media. Specific T.O.N. increased as concentrations of NH^-N and NO^-N increased with NH^-N producing significantly higher Specific T.O.N. per flask.
Variation in benthic community structure: the role of the macroenvironment along a downstream gradient.
(1984) Meyerhoff, Richard D.; Lind, Owen T., 1934-; Baylor University.
McKittrick Creek, a discontinuous mountain-desert stream in Guadalupe Mountains National Park, Texas, was sampled at discrete 1 ocations(pools ) to test for differences among biomass, density, species diversity, equitability, and species richness in the benthic macroinvertebrate community. Significant differences occurred among pools for the biotic characteristics of the benthic community along the downstream gradient. Connected pools were more similar to each other than pools separated by dry reaches. The greatest biomass (700-1200 mg dry weight /m ) and species diversity (2.5-3*2) values occurred at the two furthest downstream pools and two furthest upstream pools, while the least biomass (150-600 mg dry weight/m ) and species diversity (2.2-2.14) values occurred at two midstream pools. Equitability (0.65-0.80) and species richness (11.0-7.6) values varied considerably among pools, but were generally greatest in downstream pools. Density values also varied considerably among pools (2500-14000 organisms/m ) with the greatest density at the furthest downstream pool. Variation in macroenvironmental characterist i cs associated with food availability was more important than substrate size and fish predation in determining the benthic community structure of McKittrick Creek. Variance in biomass and density of the benthic community was explained best by differences in quantities of coarse detritus. Pools with greater quantities of coarse detritus had less invertebrate biomass and density. Variance in species diversity and species richness values was explained best by changes in periphyton biomass. Variance in equitability values was not associated with any macroenvironmental characteristics. Although the type of food available (e.g., coarse detritus or periphyton) explained most of the variance among pools for benthic community characteristics, interaction among available food type, substrate size, and predation by fish may actually determine the benthic community structure of some pools.
Phytoplankton productivity of tropical Lake Chapala, Mexico.
(1985) Doyle, Robert D. (Robert Donald); Lind, Owen T., 1934-; Baylor University.
Phytoplankton productivity and other environmental variables were measured for one year (June 1983 - June 1984) at five stations on Lake Chapala, Mexico. Contrary to expectations, productivity in this shallow, tropical lake 14 was low. Phytoplankton productivity, estimated from C data, was 76.4 g C m”^ year”'*' (209 mg C m”^ day”'*'). Phytoplankton productivity at the depth of optimum light intensity averaged 320 mg C m”^ day”'*', and always occured within the top 70 cm of the water column. Light extinction due to' inorganic turbidity was the principal limiting factor of areal phytoplankton productivity. Nutrient limitation was less important, although nitrogen may have become limiting during the dry season. Among stations, areal phytoplankton productivity varied inversely with turbidity and was decidedly seasonal. It was highest during the rainy season (June - September), when the water was most transparent.
The relationship of turbidity and organic matter to bacterial productivity and biomass in a small Texas lake.
(1986) Davalos, Laura; Lind, Owen T., 1934-; Baylor University.
The relationship between water turbidity and bacterial cell synthesis, specific production and bacterial productivity was investigated in a small Texas reservoir. Sampling dates were selected to include a variety of water turbidities. Bacterial cell synthesis calculated from rates 3 7 of H-thymidine incorporation ranged from 1.97X10 to 4.79X10 cell 1 h . Specific production ranged from 0.006 to 0.03 ug C ug C”^ 1“^ h”^. Bacterial production varied between 0.23 and 0.83 ug C l”"*" h”^. Multiple regression analysis showed that turbidity explained 63.6% of the variation in cell synthesis. When combining turbidity with the biomass of the particle-attached bacteria 82% of the changes were explained and 95.6% were explained when combining turbidity, attached cell biomass and total organic carbon. Changes in specific production were determined primarily by the turbidity (r=.76), combining turbidity with dissolved organic carbon the variation explained was 90.3%. The absolute bacterial production changes were not explained by any of the environmental variables measured during the study.
Biological nitrogen fixation in a nitrogen limited tropical lake, Lake Chapala, Mexico.
(1987) Glass, Joan Ann; Lind, Owen T., 1934-; Baylor University.
The objective of my study was to quantify the rate of biological nitrogen fixation in Lake Chapala, Mexico. Lake Chapala is the largest lake in Mexico. It is an ancient, tropical lake which is shaped in an east-west culde-sac with the inflow and outflow at the eastern end. Previous work showed low available nitrogen leading to nitrogen limitation of primary production. These measurements of available nitrogen ranged from undetectable to 1.8 _ - | mg 1 on an east-west gradient of sampling stations throughout the year. Nitrogen levels were lowest at the western end of the lake. Biological nitrogen fixation rates were expected to increase as the ambient nitrogen decreased. However, biological nitrogen fixation, measured by the acetylene reduction technique, was negligible at all stations. A reverse from the expected gradient of nitrogen fixation was found in the water from Lake Chapala when mixed with known nitrogen-fixing cyanobacteria. Greater nitrogen fixation by the added cyanobacteria was found with greater available nitrogen in the water. Also, the rate of nitrogen fixation by the introduced cyanobacteria increased when the water from Lake Chapala was filtered. This increased rate i i i of nitrogen fixation by the introduced cyanobacteria was attributed to the removal of an inhibitor within the water of Lake Chapala, Mexico. The lack of nitrogen fixation in Lake Chapala was attributed to the lack of filamentous cyanobacteria. There are three factors which may have inhibited the growth or functioning of cyanobacteria: 1) The high winds mixing this shallow lake inhibited growth of chains and mat formation of cyanobacteria. 2) Wind-induced turbidity contributed to light inhibition of cyanobacteria in the water column and sediments. 3) Organism on the suspended particulates or chemical compounds adsorbed to the suspended particulates may have been an inhibiting factor.
The role of zooplankton - phytoplankton community interactions in the nutrient dynamics of Lake Chapala, Mexico.
(1988) Trotter, Bruce G.; Lind, Owen T., 1934-; Baylor University.
I investigated ammonia nitrogen (NH^-N) regeneration and grazing by zooplankton and their effects on phytoplankton production and biomass. Two sets of experiments were conducted on samples from Lake Chapala, Mexico from September through December, 1983. One set of experiments was designed to measure zooplankton NH^-N regeneration, and the other set was designed to measure the effects of zooplankton on phytoplankton production, biomass, and production efficiency (P/B). Lake Chapala is a large, shallow, tropical lake with a wet season from late May to September, and a dry season the remainder of the year. I sampled four stations, representing major lake regions, five times each to provide water and organisms for 20 experimental series. Samples were returned to the laboratory for enclosure experiments incubated in a large heated outdoor tank for 3 to 5 days. Polyethylene enclosures retained and/or excluded zooplankton. Six species of cladocerans were found in samples from Lake Chapala, with Ceriodaphnia pulchella as the most abundant. Only two species of copepods occurred, but they were more abundant than the cladocerans. The most frequently encountered species was Diaptomus albuquerquensis at an average density of 31.48 per liter. Zooplankton NH^-N regeneration accounted for 14.5% of ambient NH^-N concentration, for an average turnover time of 7.8 days. Regeneration provided an average of 33.0% of NH^-N uptake by phytoplankton and 93.4% of the estimated nitrogen required for phytoplankton production. Zooplankton NH^-N regeneration significantly contributed to the NH^-N pool but did not supply enough nitrogen to maintain phytoplankton production at all times during the study. Zooplankton NH^-N regeneration was greatest in September when ambient nitrogen concentrations were highest. The effect of zooplankton on phytoplankton production, biomass, and P/B ratio was less clear than the effect of zooplankton in NH^-N regeneration. Few significant differences in phytoplankton production and biomass occurred between experimental and control enclosures. The effect of zooplankton on phytoplankton production and biomass seemed to change seasonally, as NH^-N concentrations declined. The presence of zooplankton improved phytoplankton production efficiency (P/B) in the middle part of the study. The relative change in phytoplankton P/B ratio between experimental and control enclosures increased from September to mid-October and declined thereafter.
The effect of clay minerals on cadmium toxicity to bacterial production.
(1990) Balderson, Russell K.; Lind, Owen T., 1934-; Baylor University.
The effect of clays on cadmium toxicity to bacterial production and specific production was investigated in Lake Brazos, McLennan County, Texas. Bacterial production calculated from ^H-thymidine incorporation rates in samples without added cadmium ranged from 5.3x10"^ to 2.13x10"^ jj.g c 1"1 hr~l. Specific production varied between 8.1x10"® and 3.32x10"4 (Ig C ^lg C"1 hr"*. Cadmium significantly reduced bacterial productivity at low levels (1 mg Cd 1"-*-) . The response was non-linear. Reduction ranged from 79% at 1 mg Cd 1"1 to 98.4% at 20 mg 1"1. Reduction at 5 and 10 mg Cd 1"^ was 62.4% and 65.1%, respectively. Specific production dropped by 70.5% at 1 mg Cd 1"1, 82.2% at 20 mg 1"-*-, 55% at 5 mg l"-'-, and 50.4% at 10 mg Cd 1"1. Added clays increased cadmium toxicity to bacteria. Bacterial production and specific productivity were reduced by 90.7% and 85.9%, respectively, at 1 mg Cd 1"1 in samples amended with 20 mg 1"^ clay. Cadmium toxicity decreased with further additions of clay, approaching that observed in the untreated samples.
Extracellular organic carbon from Eichhornia crassipes (Mart.) Solms: does water hyacinth leak organic carbon?
(1990) Weis, Julie Ann; Lind, Owen T., 1934-
Aquatic macrophytes leak photosynthetically-fixed carbon as dissolved organic molecules. This leakage of organic carbon appears to be an energetically inefficient process. However macrophyte extracellular organic carbon (EOC) may be evidence of a symbiotic association between macrophytes and epiphytic bacteria. Bacteria colonize macrophytes, and EOC is a potential energy source for heterotrophic bacteria. I investigated extracellular release of organic carbon from F, i chhornia eras sipes (Mart.) Solms (water hyacinth), and utilization of that EOC by epiphytic bacteria. I reduced the number of bacteria on water hyacinth roots using a combination of sodium hypochlorite (bleach) and chloramphenicol (antibiotic). Using l^C-labelled CO2, I then compared the percentage of photosynthetically-fixed carbon released from plants having intact epiphytic communities with the percentage released from plants having artificially-reduced epiphytic communities. Water hyacinth roots supported a large and active microbial community. The mean density of epiphytic bacteria was 1.4 x 10 cm in the spring and 1.8 x 10 cm in late summer. Approximately 24% of the bacteria on water hyacinth roots were metabolically active. Water hyacinth released 0.02-0.15% of photoassimilated carbon during a 12-hour light period. Bacterial uptake of EOC did not appear to mask true EOC release, because more EOC was not recovered from plant-epiphyte complexes having reduced epiphytic communities. Leakage of organic carbon from water hyacinth was an insignificant portion of the plant's carbon budget. Thus leakage from water hyacinth is unlikely to represent a significant portion of an aquatic system's total carbon budget. However water hyacinth EOC may have enhanced the development of the plant's epiphytic community. The bacterial population on treated roots grew quickly, almost doubling in 12 hours. In turn, bacteria on water hyacinth roots appeared to stimulate EOC production. When more bacteria were present on water hyacinth roots, more EOC was released from the plant-epiphyte complex.
Bacterial growth on UV-B photolytically produced dissolved organic matter.
(1995) Velarde, Gabriela; Lind, Owen T., 1934-; Baylor University.
The effect of ultraviolet radiation into the Lake Chapala trophic processes was investigated in this study. Responses of bacterial populations to changes in UV radiation exposed water were significantly greater (bacterial biomass increased 57% and cell concentration increased 92%) compared to those populations that were grown in water covered by glass as UV blocker. Measurements for penetration of ultraviolet radiation in the water column of Lake Chapala were made at midday and to a depth of 0.45 m in one of the clearest parts ofthe lake (Station 11). Ten per cent of the UV radiation that reached the surface ofthe lake was still present at 0.2 m of depth. The extinction coefficient was 10.1 m. For a lake with low phytoplankton productivity, the supply of organic carbon via photolysis ofrefractory material may be an important supplement to bacteria in the water column.
How does the material adsorbed onto flood-borne sediment affect lake zooplankton populations?
(1997) Pittman, Helen M.; Lind, Owen T., 1934-; Baylor University.
The effect of materials adsorbed onto flood-borne sediments on Brachionus calyciflorus was investigated in this study. Sediment samples were collected from the North Bosque River and South Bosque River which drain into Lake Waco for five months during flood events and low water flow. Measurements for population parameter changes were made after the rotifer cysts were subjected the materials leached off the floodborne sediment (elutriates). B. calyciflorus population growth and birth rates were inhibited and their death rates were stimulated when subjected to ambient elutriate concentrations containing contaminants from the North Bosque River. Population parameters remained statistically unaltered for the South Bosque River samples.
The effect of the exotic cladoceran Daphnia lumholtzi on the native zooplankton of a central Texas reservoir.
(1997) Fleming, Steven William; Lind, Owen T., 1934-; Baylor University.
Waco reservoir was sampled for one year at five sample sites and six months at two sample sites in an attempt to detect competition between D. lumholtzi and native zooplankton. No competition could be detected. Also monitored were egg bank densities of D. lumholtzi, temperature of water, air and sediment. The seasonality and horizontal distribution of D. lumholtzi was also monitored for Waco reservoir for one year and was monitored in Belton Reservoir for four months. Although no strong correlation existed between D. lumholtzi and water temperature or Secchi depth in Waco reservoir, D. lumholtzi densities in Belton reservoir increased along a up-river transect including increasing water temperature, and reduced Secchi depth.

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