No description available.

Intermittent breaching of sand barriers at temporary open estuaries plays a key role in the functioning of these systems. Breaching events lead to large and rapid changes in the physico-chemical environment which in turn triggers major biological responses. The breaching process can cause significant morphological changes as strong breach outflows can scour large quantities of accumulated sediments from an estuary. Simple laboratory experiments are reported that investigate the temporal evolution of the breach and the scaling of the breach characteristics namely the breach width W, volume Vb, formation time Tf and peak outflow Qp. The experiments were specifically designed to investigate the influence of the outflow volume S, the hydraulic head H and the barrier breadth B on the breach characteristics. The breach width W was found to be proportional to S1/3, whilst the breach volume Vb was found to be proportional to HBS1/ 3. The breach formation time Tf was found to be proportional to (g/S1/3)-1/2 (H/S1/3)-3/2 (B/S1/3)1 and the peak outflow Qp was found to be proportional to (gS5/3)1/2 (H/S1/3)3/2 (B/S1/3)-1. These scalings are also shown to be consistent with observed breach characteristics for actual estuaries and earth dam failures where outflow volumes are typically six orders of magnitude larger than for the models. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2007.

Floodgates were constructed in 1971 on the main creek draining Hexham Swamp, a large wetland on the floodplain of the lower Hunter River, New South Wales. Substantial changes in vegetation have occurred in Hexham Swamp subsequent to the construction of the floodgates. Previous areas of mangroves and saltmarsh have been reduced (180ha to 11ha, and 681ha to 58ha, respectively), and Phragmites australis has expanded (170ha to 1005ha). Much of the mangrove loss (ca. 130ha) was a result of clearing, and the remainder has gradually died off. The factors contributing to the dieback are likely to be a combination of drying of the soil, root competition and, at times, waterlogging. Field sampling as well as microcosm and reciprocal transplant experiments involving key species, Sarcocornia quinqueflora, Sporobolus virginicus, Paspalum vaginatum and Phragmites australis, suggest that a reduction in soil salinity has been an important factor in initiating successional change from saltmarsh to Phragmites reedswamp. The data also suggest that increased waterlogging has been an important factor in initiating vegetation change. This apparently paradoxical result (floodgates and associated drainage generally result in drying of wetlands) is likely to have resulted from occlusion of drainage lines (by sediment and reeds) and is, therefore, likely to be a condition that developed gradually. That is, the initial effect of the floodgates is expected to have been a drying of the swamp, followed over time by an increasing wetness. An examination of vegetation changes after removal of cattle from part of Hexham Swamp, suggests that grazing had little effect on species composition of vegetation or rate of expansion of Phragmites australis. However, grazing does affect vegetation structure (height and density), possibly favours some coloniser species (e.g. Sarcocornia quinqueflora) in particular environmental conditions, and possibly inhibits establishment of Phragmites australis.

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

No description available.

Estuarine phytoplankton growth is often controlled by nitrogen availability. In addition to overall nitrogen loads, nitrogen form (organic vs. inorganic) is an important factor affecting estuarine phytoplankton growth and community composition. Recent studies have shown that in addition to nitrogen availability, trophic cascades and relaxation of grazing pressure may also be important for phytoplankton bloom formation in estuaries. With a goal of better understanding how nitrogen availability and grazing pressure interact to control estuarine phytoplankton growth and community composition, we examined the individualistic as well as the combined effects of nitrogen (varying availability and form) and grazing pressure on estuarine phytoplankton growth and community composition in the Neuse River Estuary, North Carolina, USA. During each of three sampling events (June 2011, August 2011, March 2012) natural phytoplankton assemblages were manipulated with added nitrogen (as urea or nitrate) and reduced grazing pressure (by filtering out zooplankton grazers). Treatments were incubated for 48 hours in an experimental pond, and subsamples taken daily to assess phytoplankton growth responses to treatments through chlorophyll a, diagnostic photopigments and cell enumerations. The effects of nitrogen additions and reduced grazing pressure varied throughout the events. In June, only nitrogen addition stimulated phytoplankton community growth (chlorophyll a), while in August, only grazing reduction had a significant impact on community growth. Neither treatment had a significant effect on community growth in March, as the phytoplankton community faced phosphorus-limitation and decreased grazing pressure associated with cooler winter/spring temperatures. While both treatments did not continuously effect overall phytoplankton growth throughout all experiments, there were always effects seen in some diagnostic photopigments, indicating varying taxa-specific responses to treatments throughout the year, which can be explained by shifts in phytoplankton community composition and environmental factors. These results demonstrate the importance of both bottom-up (nutrient availability and form) and top-down (grazing) controls in a temperate, eutrophic estuary. Results also hint at the potential for other factors (i.e. light and phosphorus-limitation) to play a role in phytoplankton growth as well. Phytoplankton growth, biomass and community dynamics are relevant indicators of environmental change and this study highlights the need to consider the potential interactive effects of controlling factors for proper management of estuarine ecosystems.

No description available.

No description available.

Estuaries support productive and diverse ecosystems, based on the abundant food and diverse habitats. However with increasing human pressures, many estuaries along the coastline of Australia have become degraded. The primary objective of this study was to investigate the effects of estuarine metal contaminants on the physiology, and the subsequent accumulation, in the smooth toadfish, Tetractenos glaber, and their prey items in estuaries in the Sydney region, south eastern Australia. Toadfish and sediments were collected during three seasonal sampling periods (June 2002, September 2002 and January 2003) in four estuaries in the Sydney region (Port Hacking River, Cowan Creek, Parramatta River and Lake Macquarie). Sediment and toadfish tissue metal concentrations varied both spatially and temporally, with highest concentrations exhibited in the metal contaminated estuaries (Lake Macquarie and Parramatta River) during spring 2002 and summer 2003. Toadfish accumulated metals in different tissue, however field experiments were limited in determining the main pathways of accumulation. Controlled laboratory kinetic experiments using radioisotopes of 109Cd and 75Se, indicated that differences in the relative contributions of water and food in the accumulation of these metals are generally governed by the physiology of the toadfish and the type of prey eaten. The distribution of metals in fish organs is important for better understanding metal kinetics and their subsequent toxicity. Toadfish exposed to 109Cd in both water or food showed a shift in distribution from gut lining at the end of the uptake phase to the excretory organs, such as liver, by the end of the loss phase, suggesting that the main uptake pathway for water exposure was via the gut and not the gills, due to fish drinking large amounts of water to maintain osmoregulation. There was no appreciable shift in the distribution of 75Se from the uptake or loss phases, being mostly associated with the excretory organs (gills, liver and kidneys). Further investigation into the accumulation of metals in toadfish prey items revealed that differences in uptake and loss of 109Cd and 75Se were influenced by their aqueous speciation, as well as differences in animal physiology, sequestration, storage and excitation mechanisms. The uptake rates and CFs of 109Cd and 75Se were highest, and the biological half-lives the longest, in pygmy mussels, ghost shrimps and polychaetes relative to the semaphore and soldier crabs. Elevated metal concentrations in certain toadfish tissues from the four estuaries were linked to reduced lipid concentrations and increased protein concentrations, which may be detrimental for growth, reproductive output and survivorship of the fish. A closer investigation into the nutritional value and metal concentrations of toadfish prey items in a selected metal contaminated estuary (Parramatta River) revealed that toadfish from the more contaminated sites within the estuary may grow faster due to higher nutritional value of prey items on a local scale, however on a larger spatial scale, this was not evident. Further investigation is required to determine whether larger toadfish size can be attributed to physiological acclimation or genetic resistance through generations of continuous metal exposure. Many studies have assessed metal concentrations in water, sediments and biota in the field, however few studies have combined both field and laboratory experiments to examine the effects of metals on fish physiology and reproduction, and metal transfer pathways in aquatic biota. This study has contributed to a better understanding of metal accumulation and its physiological effects in estuarine biota and highlights the high spatial and temporal variability in responses of organisms to environmental metal pollution.

Estuaries support productive and diverse ecosystems, based on the abundant food and diverse habitats. However with increasing human pressures, many estuaries along the coastline of Australia have become degraded. The primary objective of this study was to investigate the effects of estuarine metal contaminants on the physiology, and the subsequent accumulation, in the smooth toadfish, Tetractenos glaber, and their prey items in estuaries in the Sydney region, south eastern Australia. Toadfish and sediments were collected during three seasonal sampling periods (June 2002, September 2002 and January 2003) in four estuaries in the Sydney region (Port Hacking River, Cowan Creek, Parramatta River and Lake Macquarie). Sediment and toadfish tissue metal concentrations varied both spatially and temporally, with highest concentrations exhibited in the metal contaminated estuaries (Lake Macquarie and Parramatta River) during spring 2002 and summer 2003. Toadfish accumulated metals in different tissue, however field experiments were limited in determining the main pathways of accumulation. Controlled laboratory kinetic experiments using radioisotopes of 109Cd and 75Se, indicated that differences in the relative contributions of water and food in the accumulation of these metals are generally governed by the physiology of the toadfish and the type of prey eaten. The distribution of metals in fish organs is important for better understanding metal kinetics and their subsequent toxicity. Toadfish exposed to 109Cd in both water or food showed a shift in distribution from gut lining at the end of the uptake phase to the excretory organs, such as liver, by the end of the loss phase, suggesting that the main uptake pathway for water exposure was via the gut and not the gills, due to fish drinking large amounts of water to maintain osmoregulation. There was no appreciable shift in the distribution of 75Se from the uptake or loss phases, being mostly associated with the excretory organs (gills, liver and kidneys). Further investigation into the accumulation of metals in toadfish prey items revealed that differences in uptake and loss of 109Cd and 75Se were influenced by their aqueous speciation, as well as differences in animal physiology, sequestration, storage and excitation mechanisms. The uptake rates and CFs of 109Cd and 75Se were highest, and the biological half-lives the longest, in pygmy mussels, ghost shrimps and polychaetes relative to the semaphore and soldier crabs. Elevated metal concentrations in certain toadfish tissues from the four estuaries were linked to reduced lipid concentrations and increased protein concentrations, which may be detrimental for growth, reproductive output and survivorship of the fish. A closer investigation into the nutritional value and metal concentrations of toadfish prey items in a selected metal contaminated estuary (Parramatta River) revealed that toadfish from the more contaminated sites within the estuary may grow faster due to higher nutritional value of prey items on a local scale, however on a larger spatial scale, this was not evident. Further investigation is required to determine whether larger toadfish size can be attributed to physiological acclimation or genetic resistance through generations of continuous metal exposure. Many studies have assessed metal concentrations in water, sediments and biota in the field, however few studies have combined both field and laboratory experiments to examine the effects of metals on fish physiology and reproduction, and metal transfer pathways in aquatic biota. This study has contributed to a better understanding of metal accumulation and its physiological effects in estuarine biota and highlights the high spatial and temporal variability in responses of organisms to environmental metal pollution.