Reservoir Southern Research Articles

Structure of Littoral-zone Fish Communities in Relation to Habitat, Physical, and Chemical Gradients in a Southern Reservoir

How the distribution and abundance of organisms vary across environmental gradients can reveal factors important in structuring aquatic communities. We sampled the littoral-zone fish community in a large reservoir (Lake Texoma) on the Texas–Oklahoma (U.S.A.) border that has pronounced environmental gradients from up- to downlake and between major tributary arms. Our objective was to evaluate the predictability of the littoral-zone fish-community structure from a suite of environmental variables. A stepwise multiple-regression model, with environmental factors at independent variables, explained 64% of the variation in fish species richness across sample sites. The number of species was positively associated with water-column productivity and total Kjedahl nitrogen, and negatively associated with Secchi depth and benthic productivity. Canonical correspondence analysis, with environmental factors as independent variables, explained 63% of the variation in fish-community structure across sites. Equal proportions of the variation in community structure were explained by variables that have strong gradients within the reservoir (e.g., Secchi depth and water-column productivity) and those that represent local habitat variables (e.g., shoreline aspect and substrate type).

Interspecific Comparisons and the Potential Importance of Nutrient Excretion by Benthic Fishes in a Large Reservoir

Fishes can provide an important link between benthic and pelagic habitats by removing nutrients from sediments and excreting them into the water column. The relative importance of nutrients excreted by fishes to ecosystem productivity may vary among species and with abiotic conditions. I measured excretion rates of three benthic feeding fishes, gizzard shad Dorosoma cepedianum, smallmouth buffalo Ictiobus bubalus, and river carpsucker Carpiodes carpio, to examine the potential contribution of these species to the nutrient budget of a large southern reservoir. All species showed a significant relationship between log excretion rate and log body mass but no differences among species in the slopes or intercepts. For all species combined, the slope of the relationship was less than 1, suggesting a less than proportional increase in excretion rate with size. Using mean standing crop estimates from published cove rotenone surveys in Oklahoma, the nutrient loading to Lake Texoma by these fishes was estimated to be 0.0096 kg · ha−1 · d−1 for phosphorus and 0.3580 kg · ha−1 · d−1 for nitrogen. These values exceeded external nutrient-loading rates from the watershed 12% and 43% of the time for phosphorus and nitrogen, respectively.

Reservoir characteristics and development plan of the Oguni geothermal field, Kyushu, Japan

Geothermal power development at the Oguni field, central Kyushu, is planned to begin in the year 2001 with a double flash system generating 20 MW e. The Oguni reservoir has been delineated by systematic geothermal surveys, well tests and reservoir engineering studies. The fractured reservoir is horizontally layered and divided into northern and southern portions. Both of them have NaCl dominant fluids ranging from 200 to 240°C. The northern reservoir covers a large area including the Takenoyu Fault Zone and has a relatively high permeability (kh≈80–230 darcy-m). By contrast, the southern reservoir covers a relatively small area and has limited transmissivity. The southern reservoir has a higher pressure (1 MPa) than the northern reservoir, indicating little connectivity between them. Based on numerical calculations, as well as the surface topography and environmental aspects, the production and reinjection zones have been separated, and a large part of the necessary fluid will be produced from the northern reservoir along the Takenoyu Fault and a small part will be taken from the southern reservoir. The separated water will be reinjected into the northernmost part of the northern reservoir, in order to prevent a cold sweep problem for production.

Wintering Waterbird Use of Two Aquatic Plant Habitats in a Southern Reservoir

Increasing use of grass carp (Ctenopharyngodou idella) to control aquatie plants in large reservoirs has been a concern of waterbird managers because grass carp reduce biomass and diversity of native aquatic macrophytes and potentially lower habitat quality for birds. Native macrophytes were virtually climinated from Guntersville Reservoir. Alabama after the Tennessee Valley Authority (TVA) released grass carp, but Eurasian: watermilfoil (Myriophyllum spicatum) was unaffected. We revegetated 0.1-ha areas at Guntersville Reservol with native plants, and compared waterbird use and activity in native plant and miltoil habitats during October January to better evaluate effects of these habitat chauges on migrating and wintering waterbirds. We also determined the relative availability of these 2 plant types during fall and early winter. Milfoil and native plant habitats were used predominately by dabbling ducks and American coot (Fulica americana). Waterbirds were absent more often from native vegetation plots (36%) than from milfoil plots (1%) Density of waterbirds was high in native plant habitats in October, but was greater in milfoil habitats from November to January as native plant biomass declined and milfoil remained relatively abundant. Feeding was the predominant activity in most months, and time spent foraging did not differ between plant habitats in 1994-95. In 1993-94, waterfowl loraged more in native plant habitats in October and November, but foraging was greater in milfoil habitats in December and Jamiary. Submersed native plants and milfoil both were important to ducks and coot using Guntersville Reservoir Results suggest that maintaining a diverse aquatic plant community at southern reservoirs is beneficial to migrating and wintering waterbirds.

Relationships between seismic activity and piezometric level changes in the Arax basin (SW Armenia): attempt at a typology of seismically induced piezometric anomalies

We analyze the relationships between seismicity in the Arax basin, and the water level changes of two deep confined fresh water reservoirs, monitored by two wells with hourly records of piezometric levels. The reservoirs are alimented by the northern faulted border of the basin and discharge on the southern border. In the vicinity of the recording wells, the water flow may be considered as stationary on a time scale of months.Tectonic and neotectonic studies indicate that the basin is located in an area where the state of stress varies, with theminimum stress (σ3) oriented horizontally and E-W to NE-SW and the maximum stress (σ1) varying from vertical to horizontal.Analysis and filtering of hydrographs yields cleaned curves where seismically induced piezometric level changes can be identified. The most relevant observations are the following:Each well records events occurring only in the tectonic block where it is located, independently of earthquake magnitude.Ten types of seismically induced piezometric anomalies are identified, each of them resulting from a peculiar reaction of the reservoir to a local change of the strain state induced by the earthquake. The duration of the deformation may either be short (about 1 week) or long (about 2 months).Level changes of the aquifer often postdate earthquakes and are not precursors.We attempt to correlate the state of stress and the anomalous behavior of the piezometric levels in the two wells. Inthe northern reservoir, σ3 is perpendicular to the flow lines, the hydraulic gradient is lower than in the south, the rocks are fractured and the permeability is mainly of a fracture type. Seismic energy and water level changes are well correlated. In the southern reservoir, σ3 and the flow lines are parallel and the water-bearing rocks consist in a continuous medium where the permeability is mainly of a pore type. There is a poor correlation between seismic energy and water level changes.

Hypolimnetic Oxygen Deficits and Anoxic Factors in Garner Lake, a West Tennessee Reservoir

ABSTRACT Oxygen demand and anoxic factor values were calculated for Garner Lake, a 96-ha reservoir in Shelby County, Tennessee during 1994 and 1995. This physically unique reservoir of the West Tennessee Plain physiographic region has a mean depth of 5.5 m and very high total phosphorus concentrations (concentrations often above 100 μg · L−1 and a maximum value of 1510 (μg · L−1). Areal hypolimnetic oxygen deficit (AHOD) values were 234 and 182 mg · m−2 · day−1, and anoxic factors (AF) were 17.7 and 13.0 days · year−1 in 1994 and 1995, respectively. AHOD and AF values predicted from phosphorus and lake morphometry are much higher than observed values. Several causes could explain Garner Lake's lower than expected AHOD and AF values: 1) it is a southern reservoir and may function differently from more northern, dimictic lakes upon which the models are based, 2) it had been fertilized in 1993.

Introduced clupeids in a southern reservoir: more evidence for system-specific reproductive styles

Latitudinal trends in reproductive characteristics are evident for some species of Clupeidae. However, selection for life history styles may operate at the population level. The reproductive cycles of alewifeAlosa pseudoharengus and threadfin shadDorosoma petenense in Dale Hollow Reservoir, Tennessee, were monitored over two spawning seasons on the basis of a gonadosomatic index (GSI). Inshore movements normally associated with spawning migrations were monitored using gill nets in spring 1989. GSI values peaked for both species at least one month earlier in 1989 than in 1988 due to warmer water temperatures earlier in the year. Highest GSI values for female alewife occurred each year when surface water temperatures were about 20° C; threadfin shad GSI values peaked at temperatures of 22°–26° C. Trends in male GSI values in both species were similar to those in females. Alewives were not abundant in warm (> 22° C), shallow water after 1 May 1989, but alewife GSI values remained high after this date, suggesting that elevated inshore temperatures limited alewife reproduction. All aspects of alewife reproduction were comparable to other populations of alewife but did not follow latitudinal trends. Threadfin shad reproductive characteristics were similar to other published accounts. We suggest that thermal regimes and reservoir trophic status are important factors for clupeid reproduction and population-level analysis is suggested when considering reproductive styles. Further, our ability to predict the ecology of introduced species in freshwater systems is impaired when species considered have not coevolved or evolved in marine environments.

Watertightness of chiew larn reservoir, suratthani, Southern Thailand

Chiew Larn reservoir is formed by damming the Khlong Saeng valley which is located in Suratthani, Southern Thailand. The maximum water level and the limestone perviousness are the main problems of this project. At the southern reservoir rim, there is a limestone area that runs from Khlong Saeng to the Khlong Sok valley giving rise to concern about reservoir leakage. To cope with this problem, the hydrogeology of this basin was studied in order to confirm that the underground water table is higher than the reservoir level. Hydrogeological observations, such as the water inventory of the surface creeks and ponds, flourescence test of the underground water including underground water measurement in rotary drill-holes, demonstrated that the underground water table in this area is high enough to prevent the leakage of reservoir water. This conclusion is supported by the high water level recorded in DH-1, at the ground elevation of 176 mMSL, depth 80 m showing that the elevation of the ground water table is at 173 mMSL in April 1973, at the end of the dry season.

Adverse Effects of Water Injection Into Thick Sand Reservoirs Containing Thin, Highly Permeable Lenses

Abstract Engineering studies for pressure maintenance by water injection were completed in 1956on four reservoirs located in the Ovejafield of Eastern Venezuela. Injection into the reservoirs began in Nov., 1957. Severechanneling of injected water occurred in the reservoirs, causing the suspension of water injection. Channeling is attributedto selective encroachment of the injectedwater through thin, highly-permeable sandsections. The J3 sand, OM–100 reservoir, is presented as a case history of the existing problem. Preliminary reservoir data indicatedgood sweep efficiencies and high recoveryby water injection. Flood studies on coresamples yielded recoveries in the 45 to60 per cent range. Predicted recoveries by pressure depletion and pressure maintenancewere 10.5 and 18.1 per cent, respectively. Water injection into the J3 sand wasdiscontinued in Nov., 1960, when it becameapparent that continued injection would be detrimental to ultimate recovery. The volumetric size of the water-encroachedpattern was 30 per cent of total reservoir volume. Channeled water extended into updipwells, and continued injection would extend these channels in an updip direction. The remedial approach to depletionis planned for two phases:wet wells will be produced at increased rates to prevent extension of water encroachment; andgas will be injected into the secondarygas cap for pressure maintenance. Preliminary studies indicate an ultimate recovery of 26 million bbl by gas injection, which represents 14 percent of the oil originally in place. Introduction The Oveja field is located in the southernportion of the Greater Oficina area of Eastern Venezuela. The field was discovered in 1952 with the drilling of a wildcat well, Mundo–1, which has been renamed OM–100. Subsequently, field development included88 wells for drainage of the I J3, L1L andL4 sands. Water encroachment through thin sections of highly permeable sand contained in thicksand deposits has yielded adverse effectsto pressure maintenance by water injectionin all of the afore-mentioned sands. Injection of water into the J3, L1L (southern reservoir)and L4 sands has been discontinued. A fourthinjection project, L1L sand (northern reservoir), is currently being studied for possible discontinuation. Water injection into theI2L–3 sand was never initiated because ofobserved adverse effects in the other reservoirs. The problem of water encroachment, as displayed in the J3 sand, will be considered in this paper. The J3 sand is selected for presentation because the encroachment pattern is more severe than in the other sands. Geological and Reservoir Data Structure The Oveja sand deposits are channel deposits with closure to the south formed by the main Oveja fault. The structureand isopach maps presented in Figs. 1 and2 disclose a 20 dip to the northeast andsand pinch-outs occurring to the east and west. Reservoir boundaries are completedto the north by a southwest-to-northeastmajor fault and the water-oil contact at3,438-ft subsea. Size Surface area overlying the J3 sandcovers 2,216 acres and the average net sandthickness is 44 ft, giving a total reservoir volume of 97,500 acre-ft. Volumetric calculations indicate that the pool originally contained185 million STB of oil, a volume which hasbeen confirmed within a small percentage by material-balance calculations. JPT P. 253^