VTechWorks Repository :: Browsing by Author "Simmons, George M. Jr."

Browsing by Author "Simmons, George M. Jr."

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Abundance and Size Distribution of Particulate Matter Fractions Near a Caribbean Bank Barrier Reef
Simmons, George M. Jr. (Inter-Research, 1979)
Recent research indicates that corals have the ability to occupy several trophic levels and that particulate matter (PM) appears to play a major role in meeting their daily energy requirements. A study was undertaken to determine the amount and size distribution of PM near a bank barrier reef off the West Indies Laboratory on St. Croix, U.S.V.I. Size distributions were determined by filtration through selected sieves and filters ranging between 250 and 0.45 μm. Results showed that PM was greater in back-reef than fore-reef areas and greater during day than night hours. The PM collected on the smallest filters (0.45μm) remained constant during both sampling periods and could potentially supply 60 % of the daily energy requirements for corals. Inclusion of the PM on the next size filter (8.0 μm) would more than account for their daily energy requirements. The mean PM abundance found in this study (1.1 mg 1^-1) is the same as that reported at another Caribbean laboratory in the West Indies.
Comparisons of Secondary Production, Life History, and Mouthpart Functional Morphology Between Two Populations of the Amphipod Gammarus minus
Haley, Carol J. (Virginia Tech, 1997-01-21)
In this study, features of ecology, behavior, and functional morphology related to feeding activity of two populations of the amphipod Gammarus minus were compared. The two populations occupied different habitats, and I attempted to determine whether differences observed between the two populations were related to habitat. Annual production and life history of the populations were compared and their relationship to factors such as temperature, water-chemistry, and quantity of available organic matter were examined. Mouthpart and foregut morphology were compared between the two populations and between immature and mature amphipods with light and scanning electron microscopy. Measurements of structure were analyzed by linear regression. A behavioral study, comparing feeding of immature and mature G. minus, was conducted in the laboratory. Annual production of G. minus occupying a habitat characterized by the presence of watercress, gravel substrate, and constant temperature (Site 1) was 3.9 g/m² (95% C.I.: 3.2- 4.5), while that in the habitat characterized by leaf detritus and fluctuating temperatures (Site 2) was 1.8 g/m² (95% C.I.: 1.6-2.1). Breeding occurred throughout the year at Site 1, but there was a yearly cycle at Site 2. The greatest numbers of the smallest size classes of amphipod were present at Site 2 when the quantity of ash-free dry mass (AFDM) of wood and bark was greater than AFDM of leaf detritus. Of nine mouthpart and foregut structures studied, three, the number of cuspidate setae on outer plates of maxillipeds, the length of the dactyl on maxilliped palps, and the number of hook setae on the foregut ampullae, were found to be correlated with body length. Of these, rates of increase in maxilliped setae numbers and hook setae numbers were greater for immature than mature animals, and the number of hook setae for a given sized animal was generally greater for animals at Site 1 than Site 2. Animals presented with ground-up leaf material in the laboratory exhibited twenty-one recognizable behaviors. The frequencies of six behaviors were found to be statistically different between immature and mature animals. The differences suggest that immatures may prefer a food type or size other than that provided in the experiment.
Copper Concentrations in Tidal Creeks and Estuaries of the Eastern Shore and the Relationship to Plasticulture and Copper-based Crop Protectants
Klawiter, Kathryn Alyce (Virginia Tech, 1998-02-09)
This project investigates the effect of plasticulture and copper-based crop protectants on water quality on the Eastern Shore of Virginia. Water and sediment copper concentrations in both plasticulture and non-plasticulture containing watersheds were measured to determine the scope of copper in Eastern Shore tidal creeks. Runoff from a variety of land-uses including agricultural, plasticultural, residential and natural areas were collected and measured for copper to determine where copper-containing runoff originates. Copper concentrations in plasticulture impacted tidal creeks were higher than background (0 - 3 ug/L) only in spikes, during or immediately after runoff-producing rainfall events. These spikes registered as high as 263 ug/L total copper, or 127 ug/L dissolved copper. Plasticulture and copper-based crop protectants were affirmed as the cause of these spikes because control watersheds indicated no high copper spikes. Runoff from different land-uses verify that copper is present in high concentrations only in runoff from fields engaged in plasticulture and using copper-based crop protectants. Sediment copper concentrations were found to be within the natural range, but exhibited some variability based on proximity to agricultural copper inputs.
An Ecotoxicological Evaluation of Active Coal Mining, Sedimentation and Acid Mine Drainage in Three Tributaries of the Leading Creek Watershed, Meigs County, Ohio
Latimer, Henry Augustus II (Virginia Tech, 1998-09-21)
Three streams (Parker Run, Little Leading Creek and Thomas Fork) in the Leading Creek watershed, Meigs County, Ohio were impacted by active coal mining, agricultural and abandoned mined land sedimentation and acid mine drainage (AMD), respectively. An ecotoxicological evaluation was performed using physical (water chemistry and sediment depth analyses), toxicological (acute water column, chronic sediment and 35-day in situ toxicity tests) and ecological (benthic macroinvertebrate community sampling) parameters. Persistent acute toxicity (mean 48-hr LC50 of 30.3% to C. dubia) due to low pH (mean of 5.4) and high concentrations of dissolved metals (ex: Al ~ 10 mg/L) were responsible for the significantly depressed benthic macroinvertebrate community sampled in Thomas Fork. Heavy sedimentation (>30 inches), with no associated toxins, significantly decreased both abundance and diversity of benthic macroinvertebrates in Little Leading Creek. High concentrations of sodium (mean of 910 mg/L), TDS (mean of 3,470 mg/L), and periodic acute water column toxicity (mean C. dubia survival of 62% in 100% sample) were most likely responsible for the depressed benthic macroinvertebrate community observed in Parker Run. In ranking the severity of impacts, AMD was first followed by non-toxic sedimentation, and active coal mining ranked last. A catastrophic coal slurry spill significantly impacted the benthic macroinvertebrate community in Parker Run in April 1997. Six sampling stations were established to monitor the recovery of the stream's benthic community and evaluate any impact the active coal mine effluent had on the recovery time of the community. The effluent, characterized by high concentrations of TDS (~4,200 mg/L), significantly hindered benthic macroinvertebrate community recovery in Parker Run. The benthic community at the initial spill site, which was above the active mine effluent, recovered to levels measured at an upstream reference within 4-9 months. Benthic communities impacted by both the slurry spill and the effluent still had not recovered 16 months after the spill. Concentrations of TDS measured in the stream were significantly correlated (r = -0.765 and -0.649 respectively) with both EPT richness and percent C. dubia survival in water column toxicity tests. Laboratory analysis of synthetic coal mine effluent, similar in composition to that of the Parker Run effluent, was performed to determine toxicity thresholds for sodium, sulfate, TDS and conductivity. Acute toxicity thresholds were found for sodium (between 900 and 1,000 mg/L), TDS (4,200 and 6,400 mg/L), and conductivity (5,000 and 6,200 µmhos/cm). It was also determined that any toxic contribution of sulfate in solution with high concentrations of sodium (~1,000 mg/L) and/or TDS (~4,200 __ 6,400 mg/L) was secondary to that of the toxic effect of sodium or TDS in that solution.
The effect of pumped-storage reservoir operation on biological productivity and water quality
Simmons, George M. Jr.; Neff, Stewart E. (Water Resources Research Center, Virginia Polytechnic Institute, 1969)
With the increased utilization of our water resources by a growing population, intelligent management of these resources, giving full consideration to all the relevant factors, becomes essential. Pumped-storage hydroelectric projects have been developed giving primary emphasis to the factors which relate to the generation of electricity. These projects can also provide a means of reducing stream pollution effects through stream flow augmentation and by lessening the effects of thermal stratification...
A finite element model of submarine ground water discharge to tidal estuarine waters
Robinson, Michael A. (Virginia Tech, 1996)
In the research presented here, a new ground water model, FEMCoast, was developed to simulate ground water discharge to the intertidal zone of estuarine systems. This research may be the first attempt to model the ground water discharge process in a tidal estaurine system. The development of FEM Coast was undertaken as no existing ground model was capable of directly simulating the dynamic boundary conditions along the sediment water interface of the intertidal zone. Reproducing the dynamic tidal boundary conditions along the sediment water interface was determined to be essential to replicating the complex salinity gradients observed in the ground water within the intertidal zone. Field data and model results confirmed the presence of a region of ground water where an inverted salinity gradient existed. In this region the concentration of salinity decreased with depth from the ground surface. FEMCoast was also able to reproduce field data on the movement of the near shore water table and ground water discharge rates and patterns. However, the model was not able to replicate the short-term fluctuation in the concentration of salinity within the aquifer due to changes in the concentration of salinity within Cherrystone Inlet. It is believed that the inability to account for the wave action of the tides within the intertidal zone is responsible for this difficulty. The use of FEMCoast integrated with field studies provided a new method to investigate ground water discharge to tidal estuarine systems.
Importance of Submarine Groundwater Discharge (SGWD) and Seawater Cycling to Material Flux across Sediment Water Interfaces in Marine Environments
Simmons, George M. Jr. (Inter-Research, 1992)
The movement of water across sediment/water interfaces is very important to the ecology of aquatic habitats. Submarine groundwater discharge (SGWD) occurs primarily by advective flow and may be due to a variety of factors. In nearshore marine environments, the major factor is probably groundwater flow from upland regions. In oceanic environments, SGWD is probably influenced more by tides and surge action. SGWD, therefore, represents various mixtures of fresh groundwater and seawater. This paper summarizes the first regional study of SGWD and its attendant solutes in shallow estuarine, continental shelf and coral reef habitats, and calls attention to the magnitude of water volumes which appear to be circulating through marine sediments. Data on SGWD from sites in the Florida Keys and on the southeastern continental shelf of the U.S. indicate that water movement across sediment/water interfaces is a common occurrence at least to water depths of 30 to 35 m. Discharge values from the Florida Keys were 8.9 l m-2 d-1 (N congruent-to 344) for depths < 27 m and 5.4 l m-2 d-1 (N congruent-to 261) for depths of ca 27 to 39 m. On the southeastern continental shelf, discharge ranged between ca 6 and 20 l m-2 d-1. One site was found in 20 m depth where there was a persistent negative hydraulic head and a mean influx of seawater to the sediments (ca 10.8 l m-2 d-1). Even though geohydrological models would predict coupling of SGWD with landbased hydraulic heads, definitive lower salinity SGWD could not be detected. The driving force seems to be subtidal pumping and much of the discharge measured was probably recycled seawater. This research also demonstrated that SGWD serves to move dissolved solutes into the water column, and could be an important link in benthic-pelagic coupling in continental shelf ecosystems.
Integrative Bioassessment of Acid Mine Drainage Impacts on the Upper Powell River Watershed, Southwestern Virginia
Soucek, David J. (Virginia Tech, 2001-05-14)
Acid mine drainage (AMD), a result of oxidation of minerals containing reduced forms of sulfur (pyrites, sulfides) upon exposure to water and oxygen, is an environmental problem associated with abandoned mined lands (AML). Numerous studies have documented the impacts of AMD upon aquatic communities within acidified stream reaches; these impacts include reduced taxonomic richness and abundance, and/or a shift from pollution sensitive to pollution tolerant species. This dissertation comprises a number of integrative assessments and experiments conducted to investigate the nature of AMD ecotoxicity in the upper Powell River watershed. Emphasis was placed upon bioassessment methodologies and AMD impacts beyond the zone of pH depression. Major findings and processes developed included: 1) an Ecotoxicological Rating (ETR) system was developed that integrates chemical, toxicological, and ecological data into a single value depicting the relative environmental integrity of a given station within a watershed; 2) water column chemistry rather than sediment toxicity was the major factor causing acute toxicity to aquatic biota in close proximity to AMD discharges; 3) solid ferric hydroxide can cause acute toxicity to standard test organisms in the absence of dissolved iron; 4) Asian clams (Corbicula fluminea) can be used to detect both acutely toxic AMD inputs and nutrient loading in low order streams, and clam responses of survival and growth reflect those of indigenous communities to the two contaminant types; 5) aluminum (Al) in transition from acidic to neutral pH waters can cause acute toxicity to aquatic invertebrates, and may be the cause of impaired benthic macroinvertebrate communities in neutral pH (>7.0) waters downstream of an acidic tributary; 6) in the larger river system (North Fork Powell and Powell mainstem), urban inputs appear to have a greater influence upon aquatic communities than metal loading from AMD impacted tributaries; 7) the use of individual level assessment endpoints, such as Asian clam growth in in situ toxicity tests, eliminates variables that may confound attribution of community level impacts to contaminants; and 8) the near elimination of predatory stoneflies (Plecoptera) downstream of the Stone/Straight Creek tributary to the North Fork Powell River was associated with water column Al concentrations. This research was funded by the Virginia Department of Mines, Minerals, and Energy, Division of Mined Land Reclamation, and by the Powell River Project.
Limnological investigations of a natural, subalpine lake in the early stages of eutrophication: Mountain Lake, Giles County, Virginia
Beaty, Myron H. (Virginia Tech, 1995-04-01)
Comprehensive year-round limnological investigations of Mountain Lake, Virginia were conducted from November 1992 through October 1994. Monthly physical, chemical, and biological measurements suggest that this ecosystem has shifted toward a more eutrophic condition. A trend in whole lake mean annual orthophosphate-phosphorus and inorganic nitrogen increases have occurred over the past decade, although primary productivity, cell densities, and chlorophyll a values indicate no consistent trends. Hypolimnetic oxygen deficits, however, have continued to increase over time, and in October 1994 the first measure of anoxic deep water was observed. Concurrently with the chemical changes, shifts in macrophytes and phytoplankton have occurred. Most notably were reductions in Nitella megacarpa and Dinobryon spp., an increase in Ceratophyllum sp., and a summer dominance of Sphaerocystis schroeteri and Aphanocapsa_ elachista. These two species represent algal classes, Chlorophyceae and Cyanophyceae, which have also increased in relative abundance and seasonal persistence in Mountain Lake. Nutrient addition studies conducted in 1994 indicated limiting concentrations of both phosphorus and inorganic nitrogen during most periods of thermal statification. Significant increases in primary productivity occurred within 48 hrs with the addition of K₂HPO₄ and/or NH₄NO₃ in the pico-, nano-, and microplankton size classes. The smaller size fractions (picoand nanoplankton) responded more strongly to the N enrichment, whereas the microplankton responded more with the P enrichment. In all cases, ammonium-N was the preferred inorganic nitrogen source during these Studies, as suggested from earlier studies of methylamine uptake in this lake. Studies of the importance of various phytoplankton size classes (pico-, nano-, micro-, and macro-) during thermal stratification indicated that the microphytoplankton were the most important size class in cell number, cell diversity, and contributed ~95% of the total primary productivity. The picophytoplankton were second in importance constituting ~5% of total primary productivity, whereas the relatively small numbers of nano- and macrophytoplankton contributed little primary productivity. This finding contrasts to many other oligotrophic ecosystems where the pico- and nanophytoplankton have demonstrated significantly greater importance. Increasing nutrient concentration, increasing hypolimnetic oxygen deficit, and shifting phytoplankton community structure suggest that Mountain Lake is entering the early stages of eutrophication. Continuation of increasing nutrient loads in this natural lake will potentially further shift this ecosystem toward eutrophic conditions.
The macrobenthos of a new reservoir, Lake Anna, Louisa County, Virginia
Voshell, J. Reese Jr. (Virginia Polytechnic Institute and State University, 1976)
The macrobenthos of a new reservoir in central Virginia, Lake Anna, was studied for the first three years after impoundment, 1972-1975. Prior to this, extensive macrobenthic collections had been made in the river destined for impoundment, the North Anna River. The biota of this river had been seriously affected by acid mine drainage for over 100 years. Macrobenthos consists of the organisms living on the bottom or the solid-liquid interface. The occurrence of these organisms is significant, because they are major items in the diet of many fish, and are thus important in the flow of energy through an ecosystem. The basic objectives of this study were to determine the changes in macrobenthic community structure brought about by impoundment, and then to observe the successional changes which occurred in the following years. This information was then compared to a hypothetical model predicting the productivity of new reservoirs. It was discovered that traditional grab sampling was not reliable in new reservoirs because of the abundant submerged terrestrial vegetation. An original sampling method was developed which involved the use of SCUBA to place and retrieve artificial substrate samplers. This SCUBA method was compared to grab sampling, and found to more reliably estimate macrobenthic community structure. Following impoundment, there was an immediate change in macrobenthic community structure. Colonization of the new reservoir occurred very quickly, especially during the first summer period. The acid mine drainage did not affect the distribution of macrobenthos in the new reservoir, probably because of dilution. Identification of over 525,000 organisms revealed that they could be classified into three groups: first colonizers, omnipresent species, and second colonizers. A review of the food habits of these organisms indicated that there were four trophic functional groups: micropredators, macropredators, collector-microgatherers, and collector-microfilterers. The first colonizers consisted of three species, one of which was completely dominant in each of the first three functional groups the first year. The second colonizers consisted of many additional species, several of which shared dominance in each of the same three functional groups the second and third years. The omnipresent group consisted of midge larvae which were dominant in the fourth functional group, collector-microfilterers, in all three years. This information, in conjunction with analysis of the horizontal, vertical, and temporal distribution, indicated that the development of macrobenthic community structure in Lake Anna followed the general trends expected in ecological succession. These trends are increased number of species, increased equitability of species composition, and better organization of distribution. A comparison of the development of macrobenthos in new reservoirs with a model of expected productivity indicated that the abundance of macrobenthos. may also exhibit the same trends as productivity. These trends are an initial increase in productivity for several years, followed by a sharp decline for several years, to be finally followed by a small increase and stabilization. This sequence of events probably requires at least 15 years for macrobenthos.
Mechanisms governing phosphorus retention in streams
D'Angelo, Donna Jean (Virginia Tech, 1990-04-01)
A nutrient is defined as a chemical element necessary for life. In streams, phosphorus is typically one of the most important nutrients and often limits microbial (algae, bacteria, and fungi) growth. As a result, retention of phosphorus within streams largely determines productivity. Factors that influence retention include temperature (Elwood et al. 1981b), velocity (Bencala 1983), and organic matter (Mulholland et al. 1984). Watershed input-output budgets have been commonly used to evaluate nutrient retention characteristics (Borman et al. 1974). These studies provide information about nutrient flux through ecosystems but offer little information about mechanisms governing nutrient dynamics. In contrast, nutrient spiralling, as described by Webster and Patten (1979), provides a method to evaluate retention and the mechanisms governing it. A nutrient spiral is defined as the distance traveled by a nutrient ion as it completes one cycle from dissolved form to particulate form and back to dissolved form. The distance a nutrient ion travels in dissolved form is called the uptake length and typically accounts for > 90% of spiralling length (Newbold et al. 1983). Uptake length is commonly used instead of spiralling length, because unlike spiralling length, uptake length can be measured without the use of radiotracers. Nutrient spiralling, developed in the late 70's and early 80's, is a relatively new concept. Work on spiralling length (or uptake length) has just begun to allude to possible mechanisms of solute retention and the relative importance of these mechanisms (see Solute Working Group 1990 for a review of concepts and methodology). Recent nutrient retention studies have shown phosphorus retention to be affected by both physical (e.g. temperature, velocity) and biological (e.g. microbial activity, organic matter biomass) factors. However, these studies have yielded conflicting information as to the relative importance of these factors. For example, Gregory (1978) and Elwood et al. (1981) demonstrated that uptake was mostly biotic, while Meyer (1979) found that uptake was determined by physical factors in the streams she studied. This contradiction suggests that streams may range from those driven primarily by biological mechanisms to streams driven almost entirely by physical factors with most streams falling somewhere between these extremes. The relative importance of physical and biological factors may vary spatially and temporally within a stream. This study was designed to systematically identify and examine factors that influence nutrient retention. More specifically, the objectives of this study were: 1) Examine microbial colonization and breakdown characteristics of leaves with different amounts of structural rigidity, under different constrainment techniques, to gain insight into how these characteristics may affect nutrient retention. 2) Use artificial streams to separate and identify factors governing nutrient retention by controlling flow and using different amounts and types of leaf material. 3) Evaluate how land-use practices may alter phosphorus retention mechanisms by comparing results of nutrient releases in natural streams draining undisturbed mixed hardwood watersheds with releases in streams draining disturbed watersheds (i.e. watersheds that had been logged and planted in white pine).
Monitoring pesticides in the groundwater and submarine groundwater discharge of the Eastern Shore of Virginia
Hubbard, Thomas W. (Virginia Tech, 1993-07-05)
The purpose of the research was to determine if pesticides were being transported from the place of application by the shallow groundwater and discharged into the Chesapeake Bay and Atlantic Ocean, and quantify the pesticides if they were transported. One reference (undeveloped) and four agricultural sites were tested over a 11 month period from April 1992 to February 1993. Over 500 groundwater samples were analyzed from both shallow wells and seepage meters placed in the Chesapeake Bay and Magothy Bay. The samples were analyzed in accordance to EPA Method 525.1 by solid phase extraction with octadecyl bonded disks followed by gas chromatography. The samples were examined for 5 of the most commonly used pesticides: atrazine, alachlor, carbofuran, cyanazine, and metolachlor. Pesticides were detected in only 16 samples. All the detections were at low concentrations, with only one being over 1 μg/L. The study concluded that if pesticides were being transported by the groundwater, they were below a μg/L (ppb).
Negative photoaxis of mosquito larvae as a potential tool in the rapid bilogical monitoring of aquatic wastes (Diptera: Culicidae)
Knausenberger, Walter Ingolf (Virginia Tech, 1975-02-05)
A little-known approach to toxicity testing--based on negative phototaxis of larval Aedes aegypti--was investigated as a contribution to the search for rapid methods applicable to the field of water pollution control. Zinc and copper were the toxicants tested. All tests were conducted with a standard "synthetic" dilution water. A mosquito colony was established to provide a uniform supply of test larvae. Preliminary tests were performed on the acute toxicity of zinc and copper against A. aegypti larvae, as well as tests on larval growth and development at various concentrations of the metals. For the photomigration toxicity tests, two juxtaposed troughs were used, one containing the test solution, the other a control. Third instar larvae migrated away from a six-watt fluorescent light for two minutes per run. This was repeated at intervals until 50% were unable to migrate 50 cm in 120 sec. Photographs were taken of the larval migrations. From the pictures an empirical criterion was derived (the 40-cm, 60-sec ET₅₀) through a series of graphical interpolations. All inactivation analyses were based on this criterion. From time-inactivation regression lines, exponential toxicity curves were obtained by interpolation. The curves were of an unusual shape, depicting the characteristic nature of the dosage-response. The sensitivity of the inactivation technique was comparable to that of the acute toxicity tests. However, inactivation was far quicker; depending on concentration, it occurred within one to five hours. By all methods used in this study, zinc and copper were judged to be slow-acting and of low overall toxicity. Copper was, however, consistently more toxic than zinc by at least one order of magnitude. The ET₅₀ in 10 ppm Cu⁺⁺ was 147 min.; in 10 ppm Zn⁺⁺, it was 209 min. Some possible improvements in technique were discussed. It was suggested that the photornigration approach to toxicity testing can be of definite practical use to biologists in water pollution control.
A pre-impoundment study of the North Anna River, Virginia
Simmons, George M. Jr. (Water Resources Research Center, Virginia Polytechnic Institute and State University, 1972)
As our population continues to grow, it is evident that there is an increasing demand for more convenience. More convenience implies, in part, a greater demand for electrical energy. As the electrical industry expands to provide a more leisurely life, water power will, by necessity, have to be utilized in one way or another. The harnessing of a potentially available water resource usually results in the damming of a river and subsequent creation of a reservoir. A pre-impoundment study, if considered before plans are finalized, will enable all concerned to view the natural resource before it is modified or changed. The natural resource, in this case a river, can .then be evaluated for its potential as a recreational resource, industrial resource (coolant, raw water supply, diluant, etc.), public water supply, or agricultural resource (irrigation, water source for livestock, digestion and dilution of feedlot runoff, etc.). In the past, little effort has been made to study the total resource potential of a river and then evaluate what is to be gained when a reservoir is created.
A Re-Evaluation of Mountain Lake, Giles County, Virginia: Lake Origins, History and Environmental Systems
Cawley, Jon C. (Virginia Tech, 1999-11-08)
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.
Sediment-water column nutrient exchanges in southern Chesapeake Bay nearshore environments
Reay, William G.; Gallagher, Daniel L.; Simmons, George M. Jr. (Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University, 1993-08)
Using field and modeling methodology, the effects of benthic microcommunities and physical transport mechanisms on sediment nutrient flux were investigated for two nearshore sediment types on Virginia's Eastern Shore. Subtidal sandy mineral sediments were conducive to water transport and influenced by groundwater discharge to a greater degree than less-permeable organic silt-clay sediments. Sediment ammonium and dissolved inorganic phosphorus (DIP) fluxes were strongly dependent on benthic aerobic respiration rates for silt-clay sediments as compared to sandy substrates. In-situ studies showed a significant decrease in ammonium and DIP fluxes as a result of nutrient uptake by benthic microalgal communities. The importance of advective solute transport mechanisms within nearshore sediments was demonstrated by a one-dimensional, steady-state model for a conservative substance. By incorporating dispersive and advective transport mechanisms, model predictability for chloride sediment flux was significantly improved as compared to a diffusion-based model. Model results indicate that velocity-associated transport of solutes, driven by elevated upland hydraulic heads, is significant and can dominate over diffusive flux in sandy sediment. In contrast, silt-clay sediment solute fluxes were dominated by dispersive processes. The importance of sedimentary nutrient flux in a shallow coastal embayment was demonstrated by short water column dissolved inorganic nitrogen (DIN) and DIP turnover times ·with respect to sediment nutrient fluxes, by the significance of ammonium and DIP sediment nutrient fluxes with respect to phytoplankton nutrient assimilation demands, and by the relative importance of benthic respiration with respect to water column primary productivity. To evaluate water quality impacts of groundwater discharge on a larger scale, a surface, groundwater, and in-situ groundwater discharge water quality survey was conducted in a shallow estuarine embayment. Sediment inorganic nitrogen fluxes were elevated adjacent to agricultural fields without benefit of a vegetative buffer. Nitrogen contributions from direct groundwater discharge and groundwater-derived creek contributions appear to be of significant importance in terms of water quality and phytoplankton nitrogen assimilation demands. In summary, this study highlights the importance of nearshore sediments with regard to estuarine nutrient water quality and ecological processes. Neglecting groundwater discharge as a nutrient source and transport mechanism and potential biotic effects occurring at the sediment-water interface may lead to misinterpretation of data and error in water quality strategies.
Sediment-Water Column Oxygen and Nutrient Fluxes in Nearshore Environments of the Lower Delmarva Peninsula, USA
Reay, William G.; Gallagher, Daniel L.; Simmons, George M. Jr. (Inter-Research, 1995)
Sediment-water column exchanges of oxygen, dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) were measured in situ over an annual cycle for sandy and silt-clay sediment types in a shallow Chesapeake Bay (USA) inlet. Benthic oxygen and inorganic nutrient fluxes differed between sediment types. Based on metabolic rate estimates and photosynthetic pigment concentrations, nearshore sandy sediments were more productive than silt-clay sediments. Overall benthic community respiration rates were 872 mu mol m(-2) h(-1) for sandy sediments and 2220 mu mol m(-2) h(-1) for silt-clay sediments. Elevated ammonium and DIP sediment fluxes were associated with silt-clay sediments. Sandy and silt-clay sediment ammonium fluxes ranged from -44 to 358 and -30 to 615 mu mol m(-2) h(-1) respectively, with DIP fluxes ranging from -5.3 to 42.0 and -3.3 to 35.7 mu mol m(-2) h(-1). Negative nutrient flux values denote sediment uptake. Sediment ammonium and DIP fluxes were dependent on benthic aerobic respiration rates for silt-clay sediments. In contrast, sandy sediment ammonium fluxes were less dependent and DIP fluxes showed no relationship to benthic aerobic respiration rates. Ammonium and DIP flux rates were significantly reduced in transparent chambers as compared to opaque chambers indicating the importance of the benthic microalgal community. On an annual basis, sandy sediments could supply 11% of the phosphorus and 6% of the phytoplankton nitrogen requirements based on gross productivity estimates, whereas silt-clay sediments could supply 11 and 14%, respectively. Positive correlations between sandy and silt-clay sediment DIN fluxes and phytoplankton DIN assimilatory demands emphasize the importance and interdependence of sediment heterotrophic and water column autotrophic processes. Short water column DIN and DIP turnover times, on the order of hours, were characteristic of summer conditions when water column nutrient concentrations were low and silt-clay sediment nutrient fluxes high. Conversely, nutrient turnover times on the order of days were characteristic of winter conditions when water column nutrient concentrations were high and sediment nutrient fluxes low.
Structure and function of zooplankton colonization in twelve new experimental ponds
Jenkins, David Glenn (Virginia Tech, 1990-05-05)
This study examined the structural and functional development of zooplankton communities in 12 new experimental ponds for one year and tested four predictions derived from the Random Placement Hypothesis (Coleman 1981). Physico-chemistry, zooplankton colonization dynamics, zooplankton community structure and function were analyzed every two weeks from 5 February 1988 to 10 February 1989. Ponds varied in physico-chemistry at points in time but followed similar patterns during the study year. Ponds were not colonized by zooplankton similarly. Some species occurred in all ponds with about the same timing, but many species exhibited variable timing among ponds or never occurred in more than a few ponds. Colonization curves varied among ponds and through time, and species accrual curves differed in both accrual rates and the numbers of species accrued. Observed colonization curves did not closely match the curve expected according to the Random Placement Hypothesis. Zooplankton community structure also varied among ponds. Multivariate analyses could not discern similar trends in zooplankton community structure among ponds due to the disparity of species trends among ponds. species data were pooled into taxa (Copepoda, Cladocera, Rotifera, ostracoda and Chaoborus) and analyzed. Rotifers dominated zooplankton communities in densities and biomass, and ponds differed in taxa densities and biomasses. Zooplankton community function was more similar among ponds than community structure. Multivariate analyses indicated ponds generally followed similar trajectories in zooplankton community function through the year. Zooplankton did not colonize experimental ponds equally and did not develop similar zooplankton community structure among ponds. Dispersal processes probably limited colonization and development of zooplankton community structure. Zooplankton community function was generally more similar among ponds than community structure, probably due to the functional redundancy of zooplankton species. Implications of these results for experimental pond studies are discussed.
A study of lethality and toxic mechanisms of intermittent chlorination to freshwater fish
Bass, Michael Lawrence (Virginia Tech, 1975-11-02)
Most of the literature concerning chlorine deals with continuous exposure, and is not readily applicable to this intermittent release of chlorine. Brungs(1973) reported that very little work has been done on the effects of intermittent exposure on fish, and that temperature has little or no effect on chlorine toxicity. Since many steam-electric generating plants are on streams with predominantly warmwater fish, it was important to determine the effects of the intermittent release of chlorine on a fish of this type. The toxicity of intermittent chlorination, and the possible interaction with temperature to a warmwater fish, bluegill (Lepomis macrochirus) was investigated with the support of the American Electric Power Corporation. Because relatively little is known about the physiological effects of intermittent chlorination on fish, a study of this problem was performed using the rainbow trout (Salmo irdneri).This species was chosen because of the availability of large mature specimens. the ease of handling- and the considerable amount of physiological background data in the literature. Another part of this study was to investigate the histological changes occurring in the bluegill and rainbow trout that resulted from intermittent chlorination. The data obtained were used to construct an hypothesis concerning the toxic mode of action of chlorine to freshwater fish.
Toxicity of Copper to Mercenaria mercenaria (Hard Clam)
LaBreche, Timothy Merrick Clark (Virginia Tech, 1998-11-05)
Toxicity of copper to larval Mercenaria mercenaria was evaluated with static non-renewal and continuous renewal methods that permitted daily observation of mortality, activity, development, and metamorphosis without subsampling. Clam larvae, 100 - 150 microns, were held for up to two weeks in small, 30 mm, sealed petri plates during static assays with excellent survival of control organisms, low evaporative losses, and relatively low between replicate variability. An eight day LC50 of 12 micrograms / liter for six day old organisms was determined as well as EC50s (active swimming). EC50s at 24 hours were as much as much as seven times lower than LC50s after 24 hours of exposure. Flow - through assays were conducted with a modified petri dish design. Two sections from opposing sides of a 30 mm petri dish were removed and covered with 35 micron polyester screening. This dish (organism dish) was placed in an outer catch dish that captured the effluent toxin as it passed through the screening and routed it to a catch bottle for water quality analysis. The toxicant feed line entered through the catch dish cover and slowly dripped toxin into the organism dish. Water quality in the flow - through assay remained excellent. Survival of control organisms in the flow - through assay was lower than in static assays, but metamorphosis was not delayed as had been observed in static assays. Data variability was low enough that statistical distinctions were made between the effects of copper on metamorphosis. A non-standard "M" shaped survival response was observed in all assays. The responses generating the "M" shaped response in the static petri assay were statistically different from each other. Activity, as judged by swimming, in organisms was not observed to follow the "M" shaped pattern. Instead, it decreased exponentially with increasing copper concentrations. Static experiments with unfed clams, observations of activity, and data from experiments in copper accumulation by algae led to a theory relating the unusual dose response to food consumption and its relationship to the effective dose of copper to which the larval clams were exposed.

Browsing by Author "Simmons, George M. Jr."

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