The Louisiana (LA) shelf is chronically affected by seasonal hypoxia that has been shown to be spatially expanding and growing progressively more severe. Hypoxic conditions on the shelf have been closely linked to the large quantities of nutrients delivered to the Gulf of Mexico via the Mississippi River. Multiple geochemical proxies on a suite of sediment cores from the LA shelf provide a record of environmental change that parallels the onset of hypoxic conditions over the last century and prior to anthropogenic influences. The sedimentary record for the last century shows a shift from terrestrial to algal sources to the sediments, as well as a trend of increasingly enriched nitrogen isotopes, which is probably caused by a combination of large amounts of denitrification, either within the Mississippi watershed or on the continental shelf, increased primary productivity, compounded with relatively minor increases of enriched nitrogen source inputs. The current chronic hypoxia, especially since the early 1970's, is exacerbated by anthropogenic nutrient loading from the Mississippi River basin, but other processes must be responsible in the past. In the historic record, several episodic low-oxygen events are defined by forminiferal assemblages and shifts in the geochemical records. Geochemistry of three sediment cores from the Louisiana (LA) shelf indicates that these historic events are likely caused by increased inputs of terrestrially-derived organic matter during peaks in Mississippi River discharge. These results suggest that low-oxygen conditions may be a natural, aperiodic phenomenon on the LA shelf, and that the current seasonally severe hypoxia resulted from the excess anthropogenic nutrient input.

Earthworking activities have the potential to accelerate soil erosion through vegetation clearance and soil compaction processes. The eroded sediment can have many detrimental effects on receiving aquatic environments, and thus its discharge is controlled under the Resource Management Act, 1991. Two chemically dosed sediment retentions ponds at the SH20 extension project in Mount Roskill, Auckland were investigated, and the impact of the discharge of one of these ponds on a receiving waterbody was assessed using the Stream Ecological Valuation (SEV) method. Rainfall and suspended solid data was collected for a nine month period between November 2006 and August 2007, although sampling did not commence at one of the ponds until March 2007. Two SEV samples were undertaken within the receiving waterbody; one in November 2006 and the other in November 2007 to assess environmental changes resulting from the sediment retention pond discharge. The suspended solids results measured within the sediment retention ponds during this study were much lower than those reported by other studies on earthwork sites. This is believed to be due to the effective implementation of sediment and erosion control measures onsite. The Somerset Road pond was very effective at removing suspended solids throughout the sampling period, with the majority of suspended solid removal occurring in the forebay as it typically did not become full enough to overflow into the main pond. When the forebay was full of water, the PAC dosing system resulted in large reductions in suspended solid levels over a short horizontal distance within the forebay. A smaller amount of suspended solid reduction was achieved in the main pond, predominately through dilution, with the major function of the main pond being additional storage capacity for runoff. Discharge from the Somerset Road Pond was not continuous due to low water levels in the main pond. However, when discharge did occur, the suspended solids levels were very low compared with other studies investigating sediment retention pond discharge. The Richardson Road pond was less effective at removing suspended solids due to the flow regime within the forebay. There were two runoff channels entering the forebay, as well as a continual flow of groundwater. Only one of the runoff channels was directly dosed with PAC, and as the water level in the forebay was typically at, or just below, the level spreader at all times, there was a decreased potential for the PAC to become evenly distributed through the forebay and achieve dosing of all runoff. Furthermore, the main pond discharged continuously during the study period, resulting in reduced residence times of runoff within the pond system. Nonetheless, the discharge from the main pond was much lower than other studies, implying suspended solid reduction was being achieved. The SEV method indicated that the receiving environment was already degraded due to modifications to the riparian vegetation, increased dissolved oxygen demand, and moderate bank erosion. This was reflected in the macroinvertebrate population, with only pollution tolerant taxa being collected, thus limiting the use of macroinvertebrates as an assessment tool in this study. However, the SEV method, which assesses a wide range of ecological functions, implied that very little environmental change occurred as a result of the sediment retention pond discharge. A small increase in deposited sediment was observed on the stream bed, however indications are that deposited sediment is rapidly washed away once earthworks are completed. Thus this deposited sediment may not have a permanent impact within the receiving environment.

The primary aim of this study was to investigate the sedimentation processes within Buffalo Bay, particularly within and adjacent to the Whitianga tidal inlet, in order to ascertain reasons for the shoaling at both the inlet, and the identified shallow zone around Pandora Rock. Comparison of historic bathymetries suggests the ebb delta and ebb discharge channel of the Whitianga tidal inlet are rapidly accreting and the ebb tidal discharge channel is gradually migrating northeast towards Whakapenui Point. Accretion rates of up to 25 cm y-1 were calculated in the ebb delta and inlet discharge channel area between 1979 and 1995 and aerial photo comparisons suggest the ebb delta area had increased by 400 % between 1990 and 2002. Results of the hydrodynamic and sediment transport modelling suggest the rapid accretion in the ebb delta vicinity is likely to be caused by a combination of catchment estuary inputs, which are deposited on the ebb tide as the ebb flow decelerates over the ebb delta, and inputs that have been moved south along Buffalo Beach by flood currents and an eddy that forms landward of the ebb tidal discharge. Residual tidal velocities further suggest a deposition zone in the ebb delta vicinity resulting from opposing currents and the deceleration of currents. Hydrodynamic modelling results indicate the isolated shallow zone around Pandora rock appears to be caused by a transient eddy in the southern section of Buffalo Bay. The eddy is formed by the ebb tidal discharge from the inlet. Accretion probably occurs in the centre of the eddy which moves north as the ebb tide progresses. Results obtained from a current meter and sediment trap deployed in northern Buffalo Bay suggest suspended sediment transport is minimal in northern Buffalo Bay, only occurring with large wave activity. Results of the hydrodynamic and sediment transport modelling further demonstrate that this area experiences low flow velocities, and has little interaction with the rest of Buffalo Bay. The minimal sediment input to this area, combined with the occasional erosion of the seafloor, primarily by wave activity, is thought to have resulted in long term erosion of northwestern Buffalo Bay between 1938 and 1979. Although the beach and nearshore is eroding, it is likely the addition of sediment would act to stabilise this section of eroding beach. Renourishment material could be provided by the ebb delta, the southern tip of Buffalo Bay or the isolated sandbar northeast of the inlet entrance.

Emergent spatial signals which may be interpreted in the context of fluvial sediment transport processes are detected through the use of reflectance spectroscopy in the sand-sized sediments of the Towamba River, southeastern New South Wales. Reflectance spectroscopy of sufficiently fine spectral resolution represents a technique for mineral composition analysis which is complementary to X-ray diffraction, with advantages in terms of ease of sample preparation and rapidity of measurement. Instrumentation is available allowing high-quality spectrum acquisition in the field and from airborne and satellite-borne instruments. The former allows mineral analyses to more easily be incorporated into sediment tracing studies as an additional variable. The latter offers large scale, repeatable areal coverage of a dynamic system in which sediments are exposed to the sky. The Towamba River drains a catchment of c. 1000 km [square] in extensively altered granitic terrain along the south coast of New South Wales, and carries significant quantities of sand-sized sediment through much of the system. Pervasive but spatially variable chlorite, epidote, and sericite have been described in local and neighbouring terrain. These are spectrally active in the SWIR wavelength region in which the PIMA portable spectrometer operates. The airborne HyMap instrument is sensitive through this range as well as through the visible and near-infrared regions. Conventionally such channel sediments would represent a single class in the context of the broader landscape, and comparatively they represent a domain of restricted variance. In this study of samples of sediment were collected for analysis with the PIMA, the results of which supported the efficacy of such an exercise in a conventional tracing context and supported analysis of HyMap imagery. Although issues related to reduction of HyMap-detected radiance to reflectance prevented effective analysis of the shorter wavelengths sensitive to the presence of ferrous and ferric iron, the consideration of absorption feature depths and the application of a matched filtering operator revealed gross-scale spatial patterns which were interpreted as two populations of sand in the main channel. This interpretation is consistent with bank erosion occurring during two very large magnitude flow events in the 1970s, with minor ongoing perturbation of the sediment signal in the main channel by the contribution of sediment from tributaries. The presence of a definite spatial signal having been established, routes for further investigation are suggested. A noisy signal hypothesised on the basis of imagery may be used to better direct a field sampling program for a conventional sediment tracing study. The signal to noise ratio may be improved for example through calibration of radiance to reflectance and removal of atmospheric interference and improved field sampling schemes, after which more rigorous, quantitative exercises such as geostatistical ???field??? trial or spatial series analysis may be performed. Connections to process through sediment transport models are enabled through the use of GIS.

Eutrophication is a global problem affecting many inland and estuarine waters. Many wetlands on the Swan Coast Plain, in Western Australia, have undergone increasing nutrient enrichment since European settlement of the region in the 1850’s. Problems such as algal blooms and nuisance swarms of non-biting midges (Diptera; Chironomidae) are the consequence of nutrient enrichment in many of these wetlands. The restoration of these degraded wetlands, especially with respect to reducing nutrient enrichment, requires a range of comprehensive and effective techniques including catchment management, diversion or treatment of surface inputs and treatment of enriched sediments. Nitrogen and phosphorus, especially phosphorus, are not the only factors controlling algal biomass in water bodies, but they are the only elements that can be removed efficiently and economically. Internal P cycling from wetland sediments can initiate and sustain eutrophication and related algal blooms and nuisance midge problems even after external sources are diverted or reduced. The aim of this study was to identify an effective material to reduce sediment phosphorus release and thereby the phosphorus concentration of the water column. It was also important to determine the impact of the selected amendment material on phytoplankton and larval midge (chironomid) communities. A range of experiments at increasing scales, from bench-top, to microcosm to outdoor mesocosm experiments were designed to test three hypotheses: 1) Materials which have a high P sorption capacity, over a wide range of P solution concentrations, and low P release rate, are potentially suitable agents to reduce P in wetlands with enriched sediments by inactivating sediment P; 2) A reduction in the abundance of cyanobacteria caused by increasing the N:P ratio of an aquatic ecosystem results in a reduction in the density of nuisance species of Chironomidae. 3) Successful amendment of enriched sediments reduces P in the water column thereby reducing the total phytoplankton biomass and the related density of nuisance species of Chironomidae. The adsorption and desorption experiments were carried out under a range of pH values and P concentrations, with a number of materials including fly ash, red mud, precipitated calcium carbonate, crushed limestone and lime to determine the maximum adsorption capacity and affinity of these materials. A rang of P concentrations (0-1000 µg/L) simulated the P concentration of the water column in a range of wetlands of differing trophic status. Poor fits to the Langmuir equation occurred with both red mud and fly ash due to their high P content. A good fit occurred with lime, with a high P removal rate (90%-96%) over the same range. Fly ash and red mud were eliminated from further investigation due to the possibility that they might release phosphorus rather than absorb when P concentrations in surrounding environment were less than 300 µg/L or 200 µg/L respectively (concentrations which can occur in eutrophic systems). Among the three lime-based, redox-insensitive materials tested in the second mesocosm experiments, precipitated calcium carbonate (PCC) possessed the highest maximum adsorption capacity and lowest desorption rate under a range of pH values (6.2, 7.2 and 10) and P concentrations (0-12 000 µg/L), followed by crushed limestone and lime. The different maximum absorption capacities of the three materials appears to be mainly attributed to their particle size (surface area). Lime was chosen as the amendment material for further investigation because it was the only one of the three available in sufficient quantities within the timeframe of this study. Microcosm experiments showed that lime was effective in reducing sediment P release from intact sediment cores, and the ratio of TN:TP in the treatment cores increased over time compared to the control cores (in which TN: TP decreased slightly). In the first mesocosm experiment a significantly higher density of larval midges was found in the treatments than in the controls. The treatments were aimed to increase N:P ratio in the systems to reduce cyanobacteria and, subsequently, larval midge densities. However even though cyanobacteria were eliminated from the treatments, the nitrogen addition appeared to result in higher phytoplankton biomass overall, which fuelled an increase in larval midge densities. In the second mesocosm experiment, the addition of lime to enriched sediments resulted in a reduction in P in the water column. This reduction was accompanied by a reduction in total phytoplankton biomass, the absence of cyanobacteria, and a less abundant and more species - diverse chironomid fauna in the treatment mesocosms. Sediment P fractionation undertaken for both the microcosm and mesocosm experiments showed that most of the phosphorus adsorbed by lime was in the labile fraction (NH3Cl extractable P and NaOH extractable P). Phosphorus in the HCl extractable fraction was also found to be higher in the treatments due to the presence of inert mineral P in the lime than the formation of new hydroxyapatite from adsorbed P. The two mesocosm experiments suggested that larval midges were non-selective feeders, responding to total phytoplankton biomass, rather than the presence of cyanobacteria. Dissolved oxygen and predation also influenced larval midge densities. In summary, although lime appeared to be a useful material for reducing P release from enriched sediments under controlled laboratory conditions, the effect under field conditions was not as definitive. Further work is required to more fully determine the conditions under which sediment remediation may be used as a means of controlling sediment P release and associated high densities of larval chironomids.

The impact of carp on a rhizomatous macrophyte was examined in two consecutive years using three outdoor aquaculture ponds with naturally established beds of Potamogeton tricarinatus. Each pond was divided with wire fencing to form a carp (500 kg ha-1) and control treatment. After 6 weeks, plant biomass had declined to the same extent in the carp and control treatments, indicating that direct physical disturbance by carp was not reducing the biomass of P. tricarinatus. In a second experiment, carp were added to two of the same ponds when plants were regenerating after a 9-11 month drying period. After 8 weeks, P. tricarinatus biomass in the carp treatments was between one half and one tenth of the biomass in the control treatments and one control treatment supported more Najas tenuifolia than the paired carp treatment. The lower biomass of Potamogeton in the carp treatments was a result of fewer shoots and less growth per shoot. Rhizomes had been undermined in the carp treatment with less than 1% of plants growing from rhizome compared to 36% in the control treatment. Accumulation of sediment into traps was significantly higher in the carp treatments (2.5 to 77.5 times more than the control). On average, carp resuspended 662 kg dry sediment ha-1 for each 100 kg ha-1 of carp or 6.6 times their wet weight biomass in dry sediments each day. Some implications of high sediment resuspension are discussed. The research demonstrates that well anchored macrophyte species can show tolerance to the physical disturbance associated with carp benthic feeding, however, these same species are vulnerable during regenerating and recruitment stages. It is suggested that anchorage is the most important factor for determining plant tolerance to carp. The implications for aquatic plant and riverine management are discussed, including the importance of excluding carp from newly flooded wetlands and the role of carp in determining alternative stable states.

Thesis (M. Phil.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

<p>The amount of various phosphorus (P) fractions in the sediment and the relationship between the amount of P and sediment particle size were investigated in a constructed wetland southwest of Linköping. Furthermore, the possible correlation between clay content in the sediment and distance from the inlet was investigated. Sediment samples were collected along three transects from the inlet to the outlet, with six samples in each transect. In order to measure the soluble P, an NH4Cl extraction was done. This was also analysed for total soluble P after oxidation with peroxodisulphate. The sediment was also analysed for total-P and organic P by drying, dispersion in a mortar and sieving followed by boiling in HCl. Analysis of phosphate-P in all extracts was done with an acid molybdate solution and ascorbic acid, forming a blue complex that was measured spectrophotometrically. There was no significant relationship between soluble P or soluble total-P and the proportion of clay in the sediment samples. This was also the case for total-P and organic-P. Generally, the levels of phosphorus in the sediment were low, which may result from too deep sediment samples, causing the settled P-rich sediment to be diluted by the terrestrial soil underneath the wetland. There was a low proportion of clay in the sediment (4 – 18 %), which made it difficult to detect any correlation with soluble-P content. When omitting the samples at the inlet (which were more influenced by vegetation than the others), a significant positive correlation between percentage of clay and distance from the inlet was detected, suggesting that clay particles were settling in the wetland.</p>

Graduation date: 1998

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Science, 1982. / Supervised by Erik Mollo-Christensen. Vita. Includes bibliographical references (leaves 217-223).