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In 1993 concerns were expressed by English Nature that Devon's three largest sand dune systems Braunton Burrows, Northam Burrows and Dawlish Warren were drying out to the detriment of the dune habitat flora and fauna. Research was therefore required to understand how these systems functioned hydrologically, to determine whether they were drying out and if so to recommend sustainable management options aimed at reinstating former water levels, or preventing any further lowering of the water tables. At Braunton water table elevations have been monitored on a monthly basis by the Nature Conservancy, the Nature Conservancy Council and English Nature since 1972. These data were invaluable in describing the spatial and temporal hydrological characteristics and functioning of the groundwater system. Braunton Burrows was the main study site of the research. At both Northam and Dawlish, at the start of the fieldwork programme a dipwell monitoring network was installed and water table elevations were recorded weekly. Hydrological characteristics of each dune system were related to temporal variability in effective precipitation, the tide, the underlying geology and sediment properties. The groundwater system at Braunton was mounded, with effective inputs accumulating over an impermeable basal layer close to mean sea level. The system was very sensitive to seasonal variability in effective precipitation. At the centre of the groundwater mound, during the winter months, the elevation of the water table was 10 in above OD. The groundwater mound was asymmetric, with the highest water table elevations occurring along the eastern margin of the system. The transitional zone from dune sands to marshland, of a lower permeability, was restricting the inland lateral drainage regime and was controlling both the shape and elevation of the water table. At Northam the groundwater system was also mounded and again the shape and elevation of the water table were dependent upon effective precipitation. Unfortunately the monitoring network at Dawlish proved insufficient to describe either the shape or elevation of the groundwater table. Within the smaller systems of Northam and Dawlish variable sediment properties lead to intra-site variability in annual cyclical water table fluctuations. A prominent trend in the long-term water table data for Braunton Burrows was the general overall decline in the elevation of the water table from 1983 to mid 1992. With precipitation as the primary source of groundwater recharge, consecutive years with below average effective precipitation (1983-1992) was undoubtedly the primary cause, but was exacerbated by the drainage improvement works carried out on West Boundary Drain in 1983. Scrub growth, artificial drainage of the golf course and marine erosion were also possibly influencing the groundwater drainage regime. At Northam and Dawlish, without historical data it was not possible to determine if the systems were drying out, however factors influencing annual cyclical water table elevations were identified. Again climate was the key variable controlling the long-term elevation of the water table and undoubtedly the dry spell between 1983 and 1992 would have had repercussions on the elevation of the water table within these two systems. At Northam the drainage ditch network and reduced tidal inundation were the other main factors influencing groundwater levels. At Dawlish the golf course pump drainage system and scrub encroachment were effectively reducing annual groundwater recharge. At Braunton a numerical groundwater flow model was used as a predictive management tool, to assist in the recommendation of sustainable water level management options. A range of commercial groundwater flow models were reviewed and Visual MODFLOW, incorporating the original United States Geological Survey's MODFLOW code, with a fully integrated pre and post processor, was selected as the most suitable model for the Braunton scenario. The modelling exercise had three objectives; to test whether a commercial model such as Visual MODFLOW could be applied successfully to simulate the hydrology of Braunton Burrows; to gain further detail on the hydrological functioning of the system and ultimately if the model was calibrated to test a set of management scenarios to predict the hydro-ecological consequences of introducing new management practices into the system. Having identified the most probable factors influencing water table elevations within each dune system, sustainable hydrological management options were recommended with the aim of raising water levels, or preventing any further decline in water table elevations. The management options afforded nature conservation the highest priority, but also took into consideration the long-term requirements of all the other land user groups.A t Braunton when formulating the managemenrt ecommendationst he modelling predictions were also taken into consideration. Potential areas for future research were also identified. Water level monitoring should continue at all three sites, so that the longer-term impact of any water level management strategies implemented as a result of this research can be evaluated. Also at both Northam and Dawlish a more detailed analysis of the geology and sediment properties would be invaluable in providing a more comprehensive hydrological description of the functioning of the groundwater systems. The Braunton groundwater model could be developed further, addressing and overcoming problems encountered in this study and evaluating a wider range of water level management scenarios. As a result of this research far more is understood about the hydrological functioning of Devon's three largest dune systems and the recommendation of sustainable remedial/restorative water level management options will help to ensure that these ecologically diverse habitats are conserved for future generations. This research has also provided both the applied and theoretical framework to address water resource management problems within small and large scale dune systems around the shores of Great Britain.

Natural radioelements and inert gases in solution in groundwaters have been applied to problems of groundwater flow and age measurement. The 4He content of groundwaters generally increases with age and in the Bunter Sandstone, Nottinghamshire, the 4He contents of groundwaters have been linearly related to 14C ages. In the Lincolnshire Limestone, the He contents of the groundwaters have been used to indicate mixing of recharge water and interstitial water. In the other study areas, 4He and 40Ar in groundwaters have been used as qualitative indicators of age. The 4He contents of core samples have been related to the 4 He contents of the interstitial water and the formation depth. 4He diffusion in confined and non--confined sedimentary structures has been discussed. The amounts of non-radiogenic inert gases dissolved in groundwaters have been used to estimate groundwater recharge temperatures. In the Bunter Sandstone, these have been related to palaeoclimatic history by calibrating with the 14C ages. Estimated recharge temperatures have also been related to seasonal recharge, changes in the altitude of recharge and to variations in the hydrogen and oxygen isotopic ratios. Variation of the 222Rn contents of groundwaters has been used as an indicator of aquifer variability. The relative importance of intergranular and fissure flow and the variation in efficiency of 222Rn release into groundwaters has been investigated. The fraction of 222Rn released from rocks has been determined and the mechanisms by which 222Rn is released from sandstone, limestone and granite rock fragments has been discussed. Variability of the 226Ra contents of groundwaters has been explained in terms of the relative importance of the recoil and etch mechanisms of solution and the solubility of 226Ra salts in groundwaters.

The mechanism of Rn solution in groundwaters has been studied in both laboratory simulations and in field situations. The effect of sporadic and seasonal changes in rainfall patterns on the Rn contents of perennial springs in the Mendip Hills has been investigated. The separate contributions of surface streams, soil zone residence and percolation within the rock formation have been identified. The relative importance of fissure or conduit and percolation flow in the aquifer have been shown to determine the nature of the response of Rn content to rainfall patterns. An examination of the Rn contents of air in limestone caverns has established that intergranular diffusion of Rn from below the rock surface is the primary reason for Rn release into the air space. Rn transport and release from stream inflows is relatively unimportant. Experimental determinations of the Rn diffusion coefficient in rock sections have shown that such intergranular diffusion is much more significant than intragranular diffusion. Laboratory studies of Rn release from fragmented rock samples have been used to determine the efficiency of radon release for different rock types. These studies have also confirmed that intergranular diffusion is an important process by which groundwaters acquire high Rn contents. The Ra content of geothermal groundwaters from Iceland have been determined. The Ra and U contents of calcite deposits from various depths within these geothermal systems are discussed in relation to changes in the Ra geochemistry. Rn contents have also been determined for groundwaters from the Berkshire Chalk and are shown to be dependent upon the extent to which porewater mixing has occurred.

Source: Dissertation Abstracts International, Volume: 34-04, Section: B, page: 1574. / Thesis (Ph.D.)--The Florida State University, 1973.

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Ecologists have studied the responses of pelagic ecosystems to varying levels of nutrient loading and fish predation on many different scales ranging from small experimental enclosures to whole lake systems. There are recurring patterns of response to these two variables, which are generally predictable on the basis of biogeographic, behavioral, morphological, and physioenvironmental ecological principles applied to the life histories stategies of individual species. This study focused on the changes in pelagic trophic structure in response to varying levels of productivity (regulated by nutrient loading rates) and fish densities (determined by stocking densities). Zooplankton life history traits used to explain the community responses to these two variables included: body size at sexual maturity, generation time, reproductive potential, temperature dependant growth rates, morphological adaptions to vertebrate and invertebrate predation, and modes of food acquisition. A small naturally fishless lake in southeastern Alaska was the observational unit of this study conducted over a seven year period from 1980 through 1986. The objectives of this study were to 1) test whether additions of inorganic fertilizer to the lake would increase its capacity to produce coho (Oncorhyncus kisutch) smolts, and 2) describe the structural and functional changes in the pelagic ecosystem in response to varying rates of nutrient loading and zooplanktivore densities. The study design consisted of no treatments during four of the study years, and one year of each of the following treatments: 1) fertilization only, 2) no fertilization and low stocking densities (2,000 fry/ha), and 3) fertilization and high stocking densities (4,000 fry/ha). During nonfertilized years, rainfall was the driving force behind nutrient loading rates. Nutrient loading rates (exclusive of fertilizer additions) displayed a two to three fold magnitude in annual variation over the seven year study period. Changes in nutrient loading during nonfertilized years appeared to regulate pelagic productivity, but in a complex and counter intuitive manner. In contrast to the widely documented positive correlation between chlorophyll concentrations and nutrient loading rates, grazing pressure by zooplankton appeared to be the factor regulating standing crops of phytoplankton. During nonfertilized years, mean summer total chlorophyll was inversely correlated to total zooplankton biomass, and displayed a 2.5 fold magnitude in annual variation. Diaptomus kenia biomass (the primary component of total zooplankton biomass) was low in 1980 following a year with a low amount of summer rainfall (1979), then increased after each year (1980 and 1981) with relatively high amounts of summer rainfall. The positive response of D. kenia to conditions stimulated by high summer rainfall (and high nutrient loading rates) was delayed by their long generation time (one reproductive period per year). D. kenia and total zooplankton biomass peaked in 1982, the year that the least amount of summer rainfall was observed. In contrast to the intuitive perception that nutrient poor conditions are less productive, the highest zooplankton production occurred when nutrient loading rates and phytoplankton concentrations were at their lowest levels. Accelerated nutrient regeneration rates and phytoplankton turnover times were the most probable factors which allowed the high zooplankton production to be maintained under these nutrient poor conditions. Fertilizer treatments increased the mean summer total chlorophyll concentrations four to six fold over the maximum observation (1.03 μg/1) for nonfertilized years. At high nutrient loading rates, the relationship between total chlorophyll and zooplankton biomass switched to a positive correlation. Rapid egg production and short maturation times allowed the cladocerans to most efficiently exploit the food resources stimulated by fertilization. B. longirostris dominated zooplankton biomass during the fertilized stocking period, but was only preyed upon by a small percentage of the fish when larger zooplankters (Holopedium gibberum and Epischura nevadensis) were abundant. Fertilization treatments increased the the coho smolt producing capacity of the lake by about 60 %. / Graduation date: 1991

Acute and chronic toxicity tests for malathion, diazinon, and sherpa and for Cu, Hg, Pb, Zn, Ni, and Fe were conducted. Mortalities and LC50-96 hr values for Barilius vagra and Cyprinus carpio exposed to pesticides were variable. Long-term exposure to pesticides modified morphology and behaviour. The LC50-96 hr values for Cu, Hg, Pb, Zn, Ni, and Fe were low for small fish. Selected metal residues were significantly greater in whole juvenile carp following exposure to sublethal concentrations. Water samples from selected industrial drainages and receiving streams showed abnormal pH and oxygen levels. Selected metals (Fe, Pb, Zn, Cd, Cu, Ni, Hg) were higher in all effluents. Static bioassays of the undiluted industrial effluents from three sites caused 100% mortality in carp during the first 24 hrs and some mortality when effluents were diluted by 50%. A mesh size vulnerability model using the girth retention function for the Mangla Lake Fishery was developed. The impact of variable mesh size on fish harvest was evaluated. Probability of encountering the net was proportional to the distance travelled by fish, and a corrected size distribution improved the use of the model. Harvest of a surplus of large fish could be achieved by: (1) increasing the number of commercial nets in the 65-105 mm mesh size and (2) using a broader range of mesh sizes. Controlling fishing intensity and mesh size regulation over time would provide feedback for subsequent management decisions. Dynamic changes in the population, permissible harvest, number of fingerlings stocked and maintenance of year classes would allow the development of a better management model. Three supplementary feeds from inexpensive ingredients were developed and their relative ability to increase the growth of three indigenous carp (Catla catla, Labeo rohita, and Cirrhinus mrigala) and two exotic carp (Cyprinus carpio and Hypophthalmichthys molitrix) were compared. The growth of indigenous carp was low on all three feeds. All species of fish grew best on feed three. Information is needed on the ecological niches and nutrient requirements of the native carps.

Tracking recovery in disturbed environments requires the consideration of many spatial and temporal scales. A sensitive indicator organism, Hyalella azteca, was used to assess lake recovery at multiple scales in the region of Sudbury, Canada. A 40-lake presence-absence survey was conducted over a period of 23 years to track colonization history and chemical factors that limit this typically ubiquitous organism. A six-lake study was used to investigate the importance of spatially varying watershed characteristics within lakes, which could provide habitat hot spots for colonization during early stages of recovery. An intensive single-lake study examined the effects of local-scale chemistry (e.g., bioavailable metals, waterborne organic matter) and adjacent subcatchment terrestrial features on the availability of suitable habitat for colonizing amphipods. At the regional scale, presence-absence models suggested that colonization probability increased with lake water conductivity and alkalinity. Within lakes, subcatchment confluence sites appeared to be important habitats in the early stages of colonization. Site-specific features, such as macrophyte and woody debris cover, increased and decreased H. azteca abundance, respectively, and yet these relationships were influenced by adjacent terrestrial subcatchment characteristics. For example, with more terrestrial vegetation, the relative increase in abundance due to macrophyte cover was further increased. Within the intensively-studied lake, larger subcatchments with more terrestrially-derived waterborne organic matter had higher abundances of H. azteca. Using H. azteca as an indicator of aquatic ecosystem health, these relationships suggest that as lakes recover, subcatchment confluence sites can be hot-spots for colonization, and their suitability improves with interactions between local habitat characteristics and terrestrial characteristics. / Thesis (Master, Biology) -- Queen's University, 2014-01-31 21:50:26.021

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