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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Net ecosystem metabolism in Texas shallow water estuaries an indicator of freshwater inflow effects, scales of variability, and changes due to climate change and watershed development /

Russell, Marc James, January 1900 (has links) (PDF)
Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.
12

The bacterial sulfur cycle of intertidal sediment in a Pacific estuary

Minter, David John, 1954- 06 1900 (has links)
x, 120 leaves : ill. ; 28 cm Typescript Thesis (Ph.D.)--University of Oregon Includes vita and abstract Bibliography: leaves 113-120 Another copy on microfilm is located in Archives University of Oregon theses, Dept. of Biology, Ph.D., 1982
13

Behavioural responses of the shore crab Carcinus maenus to salinity variation

Mcgaw, Iain James January 1991 (has links)
Behavioural responses of the colour forms of Carcinus maenas to salinity variation were investigated, and related to their physiology and distribution in an estuary. Red males, characterised by a thicker carapace were unable to survive in as low salinities as green males; this was reflected in their poorer osmoregulatory capabilities. Haemolymph osmolality and ion concentrations of red crabs decreased at a faster rate and reached lower levels than in green crabs. Haemolymph osmolality and choice behaviour did not vary with size. In the tidally mixed estuary male and female crabs occurred in roughly similar proportions. Most were green and generally smaller than their open shore counterparts. Migration out of the estuary in winter was reversed in late spring. Differences in salinity tolerance of red and green crabs were reflected in salinity preference behaviour. Green crabs persisted longer in the lowest range of salinities tested, especially if a shelter was available. Prior acclimation affected the timing of choice behaviour; the lower the salinity of acclimation the faster the time of exit from the lowest range of salinities tested, and vice versa. Estuarine green crabs exhibited endogenous locomotor activity of circatidal periodicity and were less responsive to episodes of low salinity than open shore red and green crabs. Constant low salinity initiated a rhythm of circatidal periodicity in arhythmic red and green crabs; red crabs reacted faster and were more active upon salinity change than green crabs. The amount of locomotor activity induced after prior acclimation was similar within each acclimation salinity tested. Carcinus detected salinity variation by responding to the concentrations of Na and Cl in seawater, and was able to differentiate between salinities separated by as little as 0.5ppt., - General physiological changes appear to occur before behavioural responses are mediated; they probably act as cues for the behavioural responses, which appear not to be triggered by specific receptors. Behavioural and physiological responses combing to enhance, the survivability of crabs in changing salinities.
14

A preliminary assessment linking altered catchment land-cover to the health of four temporarily open/closed South African estuaries

Masefield, Vincent Antony January 2014 (has links)
Estuaries worldwide are being subjected to various degrees of catchment degradation, which is having severe consequences on the integrity of these aquatic ecosystems and their ability to function properly. This thesis investigated the relationship between catchment land-cover and estuarine health in four temporarily open/closed estuarine systems (TOCEs) in South Africa, namely the Groot Brak, East Kleinemonde, Mdloti and Tongati. GIS techniques were employed to delineate catchments, lower sections of catchments, 1 km and 100 m buffer zones, and to quantify the extent of land-cover classes present within these delineations. Anthropogenic activities outlined by the Department of Water Affairs and Forestry (DWAF) Resource Directed Measures (RDM) studies and their associated land-cover classes were described. The possible links between catchment and buffer zone land-cover class composition and health of the estuaries were explored. Results indicated that there was a relationship between catchment and estuarine health within the Coastal Protection Zone (CPZ) (1 km and 100 m) buffers, but not at a broader catchment level. Out of natural, urban built-up and cultivation land-cover classes, natural land was determined to be the best predictor of estuarine health within the CPZs. A method of rapidly assessing South African TOCE condition was applied and could be used to prioritise these estuaries for rehabilitation and/or conservation.
15

An analysis of factors controlling the distribution of zooplankton in the Knysna estuary, South Africa

Veldhuis, Helen Anne January 1987 (has links)
The Knysna estuary system, on the south coast of South Africa, was sampled for zooplankton over period of one year. All species were recorded and an attempt was made at relating the distribution of populations to physical factors within the estuary. Over 50 species were identified. Pseudodiaptomus hessei, Acartia(Paracartia) longipatella and A.(Acartiella) natalensis were the dominant copepods in the upper estuary. Paracalanus spp. were dominant near the mouth. Zooplankton distribution was found to be related to tidal exchange. The zooplankton displayed a seasonal cycle of abundance, with maximum numbers occuring during summer. P. hessei displayed no pronounced seasonal cycle in abundance. Its abundance was strongly related to freshwater inflow. Seasonal succession was evident between A. natalensis, the summer dominant, and A. longipatella, the winter dominant. The controlling factors for this cyclical dominance were not clear. Diel vertical migration behaviour was shown to various degrees by virtually all zooplankton populations. The stimulus for this behaviour could not be definitely identified.
16

Physical hydrography and nutrient nitrogen budget of Auke Bay, Alaska

Kirk, Deborah Kathleen 02 June 1972 (has links)
Physical sources of nutrient nitrogen for the Auke Bay, Alaska estuarine ecosystem were investigated. These sources included vertical dispersion, advection, and fresh water sources. Hydrographic circulation patterns for the bay, and a nutrient budget for the surface mixed layer were developed. Measurements of temperature, salinity, currents, wind velocity, rainfall and runoff from the major streams and river influencing Auke Bay were made during the spring and summer of 1971. initial hydrographic and nutrient data (total available nitrogen and nitrate) from early spring were taken during a cruise of R/V Cayuse. Nutrient concentration of nitrate and ammonia in Auke Bay and the fresh water sources entering Auke Bay were measured on a weekly basis from July to September. Vertical mixing rates of 0.42 cubic meters per day were calculated for those times wind mixing did not occur. Mixing rates of 1.2 cubic meters/day were calculated for wind mixed conditions. Vertical dispersion through the pycnocline provided the major source of nutrients for summer phytoplankton production. Fresh water sources provided negligible amounts of nutrients. Average vertical transport of nitrate and ammonia when wind mixing did not occur were 0.5 mg-at/m²/day and 0.3 mg-at/m²/day respectively. During wind mixing, 3.0 mg-at/m²/day for nitrate and 2.0 mg-at/m²/day for ammonia were supplied to the mixed layer. Estimate productivity based on these calculations ranges from an average 100 mgC/m²/day during non wind mixed conditions to 600 mgC/m²/day during wind mixed conditions. / Graduation date: 1973
17

Dynamics of early stage fishes associated with selected warm temperate estuaries in South Africa /

Strydom, Nadine Amelia. January 2002 (has links)
Thesis (Ph. D. (Ichthyology))--Rhodes University, 2002.
18

Effects of organic carbon loading on coupled nitrification/denitrification in estuarine sediments

Jarvis, Brandon Michael. January 2008 (has links)
Thesis (M.S.)--University of West Florida, 2008. / Title from title page of source document. Document formatted into pages; contains 88 pages. Includes bibliographical references.
19

Biogeochemical cycling in estuarine environments of the central California coast

Beck, Nicole G. January 2001 (has links)
Thesis (Ph. D.)--University of California, Santa Cruz, 2001. / Includes bibliographical references (leaves 167-174).
20

The effect of salinity and ammonia on nitirifier function and distribution in estuarine sediments

Gilmour, Fiona Louise. January 2009 (has links)
Thesis (Ph.D.)--Aberdeen University, 2009. / Title from web page (viewed on Feb. 18, 2010). Includes bibliographical references.

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