The present paper summarizes observations made on Mountain Lake, Virginia during 1961, 1962, and 1963. It includes data on the annual cycle of physical and chemical events occurring in the lake, and will serve as a point of departure for future, more specialized studies there. Observations made on the profundal bottom fauna of the lake during the same period are also reported. / Master of Science

Seasonal effects on protozoan colonization of polyurethane foam (PF) units were investigated in.an oligotrophic lake, Mountain Lake, Virginia. PF units were placed into the lake's pelagic water to simulate barren habitat islands suitable for colonization by protozoa. The results were interpreted with respect to the MacArthur-Wilson equilibrium theory of island biogeography. Results showed seasonal changes can cause a substantial amount of instability in colonization curves. Within a season, changes in the lake's planktonic species pool were more prominent during the decay of the thermocline than during Fall or Spring overturn and Summer stratification. For different seasons, the relationship between changes in the lake's planktonic species pool and species accrual on PF units was positive, for total species and for ciliate species. For different seasons, the relationship between changes in colonization rate and species accrual was consistent with MacArthur-Wilson theory. In contrast, for different seasons, the relationship between changes in equilibrium number of species and species accrual was inconsistent with MacArthur-Wilson theory, and this places in question the interseasonal predictive value of colonization curves. For some situations where the MacArthur-Wilson equation for insular colonization did not describe adequately the colonization a modified equation was developed. The modified equation was used to account roughly for species which may rapidly colonize and persist in PF unit communities and described adequately more total species colonization curves than the unmodified equation. Moreover, the modified equation was a useful tool for the interpretation of PF unit colonization by protozoa. / Master of Science

The first comprehensive year-round investigation of Mountain Lake, Virginia since 1970-71 was begun in March 1985 and continued through November 1987. Monthly studies suggested that this unique natural lake is undergoing change. Whereas inorganic nitrogen, orthophosphate, Secchi disc transparency, and primary productivity continue to suggest an oligotrophic condition, important limnological changes are indicated by the greater seasonal hypolimnetic oxygen depletion and extractable chlorophyll a which at times approach mesotrophic levels. In addition, the decrease in alkalinity, the increase in sulfate levels, and the increase in pH fluctuations compared to the past, suggest that Mountain Lake is susceptible to damage or change by acid rain and perhaps other perturbations that effect pH alkalinity, or hardness. Changes were also noted in phytoplankton composition. One hundred sixty-three taxa were identified which included 56.4% Chlorophyta, 17.8% Chrysophyta, 13.5% Cyanophyta, 8% Pyrrophyta, 3.7% Cryptophyta, and 0.6% Euglenophyta. Sixty percent of these taxa were new reports for Mountain Lake. Dominant pyrrophytes included Gymnodinium sp. and Peridinium wisconsinense. Dominant chlorophytes included Scenedesmus bijuga, Quadrigula chodatii, and Oocystis pusilla. Important cryptophytes were Cryptomonas erosa var. reflexa, C. pusilla, and C. pyrenoidifera. The most abundant cyanophyte was Aphanocapsa elachista var. conferta. The only diatom (chrysophyte) that ever dominated was Cyclotella meneghiniana. Studies of ammonia uptake by the phytoplankton, using the ammonia analog [¹⁴C]methylamine (MeA), revealed that during thermal stratification, phytoplankton succession was related to rapid ammonia uptake. Each successive phytoplankton community had significantly higher Vmax values for ammonia (methylamine) until midsummer when ammonia-nitrogen levels were at a seasonal low. At that point, the Vmax values dramatically declined and the community became dominated by blue-green algae. When allochthonous inputs of inorganic nitrogen renewed the levels of ammonia-nitrogen, Vmax values increased and the community changed, replacing the blue-green algae. Communities dominated by green algae (Chlorophyta) had higher MeA (and thus ammonia) uptake rates than those dominated by cryptophytes or blue-green algae (Cyanophyta). The effect of various treatments and inhibitors on MeA uptake by the phytoplankton support the conclusion that ammonia uptake is a chemical, light-independent, energy-dependent process. / Ph. D.

The attributes of alewife and gizzard shad as coexistent forage fishes for striped bass (Morone saxatilis), walleye (Stizostedion vitreum vitreum) and largemouth bass (Micropterus salmoides) were evaluated in Smith Mountain Lake, an 8,337 ha hydroelectric impoundment in south-central Virginia. Alewife and gizzard shad larvae exhibited strong spatial segregation which minimized the potential for direct trophic competition and increased feeding opportunities for piscivores. Gizzard shad spawning peaked in June while alewife spawning peaked in July. Daily growth rate of age-0 gizzard shad was 37% greater than for age-0 alewives. Later spawning and slower growth enhanced temporal and morphological availability of alewives to piscivores and reduced the potential for exploitative competition between the clupeids. Distributional analysis indicated that gizzard shad were primarily uplake and littoral while alewives were mostly downlake and pelagic. Alewives co-occurred with striped bass and walleye during the growing season and were crucial in providing forage for these piscivores. Largemouth bass shared a common distribution with gizzard shad and were more trophically dependent than other piscivores on them. Prey supply and predator demand were one year out of phase; gizzard shad and alewife production peaked in the first year of life while their predators' cohort production peaked in the second year. Cohort production analysis indicated that over their lifespan, striped bass prey demand (per 1000 fish) would exceed that of walleye and largemouth bass by 17% and 166%, respectively. Lifespan cohort production patterns and ingestibility limitations on prey assured that most predation pressure in Smith Mountain Lake came from piscivores ages 0-2 and was constrained to alewives ages 0 and 1 and young-of-the-year gizzard shad. Prediction of patterns of consumption of alewife and gizzard shad by piscivores was derived from analyses of morphological and distributional availabilities; these agreed closely with actual diets for most predator-prey location, season and age combinations. The alewife appears to be both compatible with, and complementary to, the gizzard shad as a forage species in Smith Mountain Lake. Suitability of alewives for introductions into other reservoirs will vary with the morphometry and management objectives for those waters. / Ph. D.

This thesis attempted to study the bottom productivity both qualitatively and quantitatively with reference to the distribution of bonthos. The study of the bottom fauna in large reservior lakes is a relatively new field. This work will give more information on an unknown field than previously existed, although its scope is not intend to be exhaustive.

This project included the following goals: 1. To review and assess the geomorphology and lake morphometry of Mountain Lake, Giles County, Virginia with regard to its age and origin. This included production of an updated bathymetric map of Mountain Lake using Sonar imaging of the lake bottom. 2. To evaluate present trophic conditions in the lake waters. This analysis included the first-reported nutrient conditions for input streams to the lake and rainwater. 3. To collect representative "modern" bottom sediment samples and to analyze these sediment samples for sedimentological characteristics, diatoms , and terrestrial pollen. This analysis focussed on present environmental conditions in the lake, and the determination of modern diatom thanatocommunities. 4. To collect complete bottom sediment cores from the lake. Coring was done using a diver-assisted manual coring device designed specifically for this project. 5. To analyze Mountain Lake sediment cores for sedimentology, age determination, and temporal differences in sediment characteristics, diatoms and pollen. This analysis focussed on interpretation and documentation of environmental changes through the lake's history. Primary discharge from the lake presently occurs through a leaky subterranean pathway associated with the deepest, crevice-like portion of the lake. This discharge results in the crevice drain not filling shut with sediment despite its location within the lowest portion of the lake. The lake structure, crevice, and subterranean drain are associated with a regional lineation feature represented in part by the path of Salt Pond Drain and a small input stream ("I-4") to the lake. Initial damming was caused by downdrop of overlying rock. The damming is not complete, and the rate of discharge through time is controlled, in part, by regional tectonic events and by a balance of hydrologic conditions and sedimentation factors. The present lake is generally oligotrophic in nature, with phosphorus representing the major limiting nutrient. Rainfall presently represents the largest source of nutrient to the lake. Present diatom flora in Mountain Lake includes 66 individual taxa, representing 25 genera. Of these, 12 forms or species have not been reported in Virginia inland waters prior to this project. The diatoms reflect the oligotrophic and circumneutral nature of the lake. At least seven diatom thanatocommunities can be defined in the lake, based on taxa, delineated by depth and nutrient conditions. The ratio metric of planktonic to littoral diatoms can be used to estimate past water depths in the lake from bottom sediment. An orange clay layer at 5 cm from the modern sediment/water interface represents human intervention in lake history, namely the hotel and road building in the early 20th Century. The age of the lake is greater than 6000 years. Specific 14C from sediment produced dates of 1860 +100, 4220 +50 and 6160 +70 bp. Within this interval, at least 6 extended periods of low or empty lake level occurred (at approximately 100, 400, 900, 1200, 1800, and 4200 yrs bp). Several of these low intervals are likely to correspond with cool dry conditions co-incident with solar minima events. When the lake has been low or empty, it has tended to develop Sphagnum bog conditions with the low lake surrounded by open or wooded meadows. Terrestrial flora surrounding the lake appears to have remained relatively similar through 6100 years, although red spruce originally accompanied hemlock. / Ph. D.

Located in Giles County, Virginia, Mountain Lake has a documented history of dramatic water level fluctuations. Previous water balance studies have documented that the main cause of water loss is outflow to groundwater. However, the flow paths of water exiting the lake are unknown. This study applied hydrologic, geophysical, and dye tracer methods to examine the pathways for water loss and the possible geologic controls on these flow paths. Continuous lake level monitoring data show seasonal trends of draining and filling over a three year period. Electrical resistivity profiles suggest the presence of a large low-resistivity zone beneath the northern end of the lake. A dye tracer study yielded limited positive results, but dye detection in one stream and within the lake suggest complex flow dynamics. The most likely reasons for the lack of dye recovery include dilution of the dye during lake recovery, seepage of water below monitoring site locations, or formation of a temporary seal in the depressions created by influx of sediment during periods of lake bed exposure. / Master of Science

The Nitella which grows in Mountain Lake, Giles County, Virginia, was investigated and found to be Nitella megacarpa (T.F.A.) em. R.D.W. after N. furcata subsp. megacarpa and not N. flexilis (L.) Ag. as previously reported. Internodal cell length was found to increase with depth, pigment content changed with depth, biomass distribution had decreased since an earlier study, primary productivity was low and was associated with the depth of maximum biomass and pigment content, and the furcations of the branchlets increased in shallower water. / M.S.

The food habits, survival rates, and abundance of four predatory fish species (striped bass, walleye, largemouth bass, smallmouth bass) were determined and combined with information on energetics and growth to quantitatively assess predator-prey interactions in Smith Mountain Lake, a large hydroelectric reservoir in south-central Virginia. A total of 1871 stomachs of the four species was examined from fish collections between April 1983 and December 1984. Food habits of each predatory species were assessed and compared by season using Schoener's (1970) diet overlap index. Significant diet overlap occurred between the pelagic predators (striped bass and walleye) and between the littoral black basses (largemouth bass and smallmouth bass) in all seasons and locations where sufficient stomach samples were collected. Survival and abundance estimates for the four predators were derived from several data sets. First-year survival of striped bass fingerlings averaged 20.8% for an 11-year period (1973 to 1983) and ranged from 3.9% to 54.3%. Average survival of age-0 largemouth bass and smallmouth bass was 53% and 45%, respectively, for the period 1979 to 1983. Species-specific survival rates for predators age 2 and older ranged from 29% to 59%. Of the predators age 1 and older, largemouth bass were the most numerous at an estimated density of 61.2/ha, followed by striped bass at 16.3/ha. Age 1 and older smallmouth bass and walleye were less abundant, at densities of 8.2 and 2.0/ha, respectively. A bioenergetics model was developed for striped bass and, with models developed for walleye and largemouth bass, used to estimate annual consumption of alewives and gizzard shad by the four piscivorous species. Annually, striped bass consumed the greatest amount of adult and young-of-year alewives, whereas largemouth bass ate nearly 70% of the total shad biomass consumed by all predators. A comparison of predator demand to clupeid supply substantiated diet overlap data; namely, that native and introduced predators were compatible in Smith Mountain Lake. The striped bass bioenergetics model was used to make inferences about potential stocking strategies for striped bass based on availability of age-1 and older alewives. A stocking rate of 20-24 fingerlings/ha appears to maximize production of striped bass and minimize potential competitive interactions between striped bass and native black bass in Smith Mountain Lake. / Ph. D.

Phosphorus is often the limiting nutrient of primary productivity in southern Appalachian reservoirs, but its impact on higher trophic levels has not been assessed. Regression analysis was used to examine the relationship between total phosphorus concentrations and estimates of fish standing stock in Smith Mountain Lake (SML) over time and for 22 southern Appalachian reservoirs (SAR) at the same time. ln SML, which had responded to a nutrient reduction program, total phosphorus concentration and fish biomass concurrently declined over an 12-year period; phosphorus concentration accounted for one-third (cove-specific) and two-thirds (whole-Iake) of the annual variation in fish standing stock. Total phosphorus concentration was also the best predictor of fish abundance in SARs, accounting for 84% of the variation in standing stock despite great diversity in reservoir physical, chemical, and biological characteristics. Predictive power was generally higher at lower levels of the food chain (i.e. planktivores, younger fish) than for piscivores. Planktivore response to phosphorus was found to be immediate. Piscivore biomass did not vary significantly with phosphorus, owing in part to poor energy transfer up the food chain and variable management practices. Phosphorus concentration and total fish standing stock appear to have stabilized in SML since 1980. Losses in fish standing stock due to deceased fertility in SML have been partly offset by an increase in coolwater habitat. Aesthetic versus fishery benefits and the complexity of dealing with a longitudinal trophic gradient need to be considered for future management of SML. / Master of Science / incomplete_metadata