published_or_final_version / Applied Geosciences / Master / Master of Science

Earlier studies indicate that the interaction between heterotrophic bacteria and dissolved organic matter is rather different in rivers and estuaries. The aim of my thesis was to elucidate if bacteria are regulated differently in the Råne river and estuary during a spring situation. Surface water was collected at both locations and a bioassay performed to study limiting substances for bacterial production, proportion bio-available dissolved organic carbon (DOC) in the water and bacterial growth efficiencies (BGE). The Carbon, Nitrogen and Phosperous concentrations were all higher in the estuary than in the river. The bioassay showed that nitrogen-phosphorus limited the bacterial production at both locations, while DOC occurred in excess. The bio-available part of the DOC pool was larger in the estuary (~6%) than in the river (~3%). However, the BGE was much higher in the river (~40%) than in the estuary (~5%), indicating that a larger proportion of the consumed DOC was used for respiration in the estuary. I conclude that heterotrophic bacteria are limited by the same substance, but that the bacterial metabolism is quite differently regulated in the river and in the estuary.

Increasing municipal and regional water demands have reduced freshwater inflows to the Nueces Delta. These flow reductions impair the marsh ecosystem’s functionality. As part of a United States Army Corps of Engineers multi-agency collaboration to restore the Nueces River and its tributaries, we have developed a mass-conservative hydrodynamic model to analyze fate and transport of freshwater and tidal inflows to the Nueces Delta. The model is built upon the LIDAR bathymetric data collected by the Coastal Bend Bays and Estuaries Program (CBBEP). Input data includes tidal, salinity, and wind data obtained from the Texas Coastal Ocean Observation Network (TCOON), pumping data from the Nueces River Authority, precipitation data from NOAA, and river flow from the USGS. The underlying modeling method uses conservative finite-difference/volume discretization on a Cartesian rectangular grid to simulate the movement of water and salt fluxes across the delta. Sub-models to represent the hydraulic influence of flow constrictions (e.g. railroads trestles, culverts) have been developed. The model’s response to forcing from wind, precipitation, and roughness were analyzed. The time to spin up for the model was analyzed and found to be approximately seven days. Preliminary validation of the model was qualitative but the overall trend of the tide coming in appears correct at the monitoring stations analyzed, indicating that the lowest frequency forcing of the tide and wind are correct. The effects of pumping into the delta were investigated under different pumping conditions to reveal the area inundation and impacts on salinity from pumping. / text

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Recollecting Place is the product of an experiential approach to Landscape Architecture. It is at once the re-telling of a place that is expected to be quite foreign to the reader as well as an examination of the method by which landscape architects assume truth of a place. As professionals, we develop a method by which we examine a site, re-tell its truth and then alter it somehow. Recollecting Place is the story of how the teller’s connections with the place in questions offer a version of the truth that can inform the design in a way that is different, and arguably more appropriate than if the site had been investigated by more traditional methods.

Estuaries are productive ecological transition zones between freshwater and marine environments that provide important commercial, recreational, aesthetic and cultural resources. The Avon-Heathcote estuary in Christchurch, New Zealand, is no exception, and its close proximity to different kāinga and Christchurch city has provided cultural, recreational and aesthetic values for centuries, especially Mahinga kai for Tangata Whenua. Tuangi (The New Zealand cockle, Austrovenus stutchuryi) is an important source of Mahinga kai to the iwi Ngai Tahu, but also an important ecological ecosystem engineer that provides internal habitat to parasites and, through its shell production, external habitat (hard substratum) for epibiota species. Several parasites, in particular the metacercariae echinostome parasite Curtuteria australis, depend on Austrovenus as its intermediate host, and these parasites can be considered allogenic engineers because they turn living material (here the host) from one physical state into a second. This is particularly evident in intertidal sedimentary estuaries where parasites, including Curtuteria, can alter the behaviour and fitness of the ecosystem-engineering hosts and thereby alter entire community structures. Similarly, several epibiota species depend on the shell of Austrovenus as a substratum on which to live. This hard substratum is particularly important for epibiota in estuaries that are devoid of rocky reefs, including autogenic ecosystem engineers like common large macroalgae (e.g. Ulva spp.). However, the Avon-Heathcote estuary, like many estuaries around the world, has become nutrient-enriched following sewage wastewater discharges, input from rivers and encroaching urban development, facilitating enhanced growth of algae attached to shells. Following recruitment and rapid growth on the shells, large algal fronds can break off and accumulate into thick mats that may cause anoxia and detrimental effects on many estuarine organisms. The main objective of this thesis is to quantify key linkages between three types of ecosystem engineers; the cockle Austrovenus, its internal parasites and its external epibiota community, including large macroalgae that can detach from the shell and develop into free-living mats. To address these objectives, spatial-temporal field surveys and laboratory and field experiments investigated (i) when and where Austrovenus provide internal habitat to parasites and external habitat to epibiota, and (ii) if and how parasites and epibiota affect survival and positioning of Austrovenus in or on the sediment. It was hypothesized that parasites and epibiota species would be abundant in and on Austrovenus and that their densities would vary across seasons and environmental gradients. It was also expected that parasites would reduce the ability of Austrovenus to bury themselves, so that surface-lying cockles would have higher parasite densities and be more susceptible to predation. Finally, it was hypothesized that a cover of macroalgae would decrease the susceptibility of Austrovenus to predation, but have negative effects on associated epibiota species, and that herbivorous epibiota species, through grazing, could control the abundance of epibiotic Ulva recruits. Seasonal collections of Austrovenus showed that parasite densities varied in different environments within the estuary (mean ranged from 3-129 for buried hosts and 7-187 for surface-selected hosts). However, host parasite loads did not vary between seasons. Parasite infestation was, found to be slightly higher in hosts exposed above the sediment compared to those buried in sediment. However, the test factor host position accounted for < 1% of the total data variability and therefore host position is of relative low ecological importance. Spatial variability in host parasite loads was significantly correlated to host sizes (its width, Rho = 0.72), individual epibiota species (Anthopleura and Elminius, Rho = –0.11 and Rho = 0.1, respectively), percentage coarse ssediment (Rho = 0.55), and less so to salinity (Rho = 0.42) and elevation level (Rho = 0.33), although the latter two variables were not statistically significant. A laboratory experiment did not confirm the expected hypothesis that hosts with high parasites loads had impaired burrowing ability. A 6-week field experiment, where the burrowing ability of the host was manipulated to increase its visibility, showed that hosts with reduced burrowing abilities did not have higher mortality than hosts with normal burring ability. Epibiota species were also highly variable in the estuary. A spatial survey from 15 sites found four encrusting and 11 solitary epibiota species with highly variable densities across sites and seasons. Factors that accounted for epibiota richness and density included host size and seasonality (particularly for macroalgal species), whereas environmental gradients and co-occurrence patterns with different epibiota species explained additional variability for only a few species. Foliose and tubular forms of Ulva spp. were the most abundant epibiota species throughout estuary (on average 2.3 and 1.7 per host, respectively) and were therefore studied in more detail. A 6-week field experiment showed that drift macroalgal mats had little effect on densities of either Austrovenus or epibiota species. Similarly, another field experiment showed that predators had no impact on Austrovenus abundances, irrespective of its size, if Austrovenus was allowed to bury or not, and if it was unconcealed or concealed under macroalgal mats. Finally, a laboratory experiment showed that small meso-grazers, under natural background densities, could not reduce densities or sizes of Ulva recruits on shells or barnacles (attached to Austrovenus shells). This study has shown that a single species of estuarine shell-forming ecosystem engineer provides ubiquitous internal and external habitat for other species throughout an estuary. The study has helped clarify how ecosystem engineers can directly control species abundances (here of parasites and epibiota) but also function as nursery grounds for other important ecosystem engineers (here bloom-forming drift algae). Furthermore, and in contrast to past research, this study did not find strong relationships between parasites and Austrovenus or its epibiota, suggesting that past generalisations about parasite effects may not be applicable within and between all estuaries. Finally, the study documented that drift macroalgae and consumers, in natural background densities, had very little impact on Austrovenus and its epibiota. Previous studies have shown that hosts with high parasite loads are commonly found on the sediment surface. These studies have suggested that this impaired burial ability makes the host more vulnerable to predation (by the parasites final host). However, at the same time, surface-lying host are also more exposed to fouling by epibiota species, which could reduce predation (by the final host) because epibiota may conceal it. However, this thesis found little support for either of these opposing ecological processes; parasite loads did not decrease burial ability, and host exposed the surface were not predated more, irrespective of being concealed or not Clearly, future studies should aim to identify thresholds in space, time, and densities where parasites, macroalgae and consumers have stronger impacts on Austrovenus and each other than shown here.

Recollecting Place is the product of an experiential approach to Landscape Architecture. It is at once the re-telling of a place that is expected to be quite foreign to the reader as well as an examination of the method by which landscape architects assume truth of a place. As professionals, we develop a method by which we examine a site, re-tell its truth and then alter it somehow. Recollecting Place is the story of how the teller’s connections with the place in questions offer a version of the truth that can inform the design in a way that is different, and arguably more appropriate than if the site had been investigated by more traditional methods.

The speciation and particle-water interactions of Ni were investigated in three estuaries with contrasting pollution levels, hydrodynamics and geochemical characteristics. Samples of water and sediments were collected seasonally from the Tamar, Tweed and Mersey Estuaries. The chemical speciation of dissolved Ni was determined by adsorptive cathodic stripping voltammetry (ACSV), and the sorptive behaviour of Ni was studied under simulated estuarine conditions using " Ni coupled to liquid scintillation counting. A relatively high particle reactivity was observed only in the Tamar Estuary, where ACSV-non labile Ni was removed in the low salinity region, followed by addition of ACSV-labile Ni in the mid-estuarine region. The largely conservative behaviour of dissolved Ni in the Tweed Estuary was attributed to the combination of rapid flushing and low suspended particles concentration. In the Mersey Estuary, dissolved Ni (and Co, Zn, Cd and Pb) often showed positive deviations from conservative behaviour, which were attributed to anthropogenic and/or geochemical inputs. The fraction of ACSV-non labile Ni behaved differently in the three estuaries, with a sharp decrease from 90 to 30% from freshwater to seawater in the Tamar, scatter between 30 and 70% in the Tweed, and relatively constant values of 50-70% in the Mersey. These differences are interpreted within the context of different hydrodynamics and geochemistry of the three estuaries. Speciation modelling showed that between 30 and 70% of dissolved Ni in the Tweed, and between 50 and 70% in the Mersey, was bound to a class of strong ligands (log K'NIL = 19.0 ± 0.4 and 18.7 ± 0.5, respectively), which were saturated by the ambient concentrations of Ni throughout the estuaries, suggesting that the ligands are highly specific towards Ni. Irradiation of riverwater samples with UV light (believed to remove dissolved organic matter) significantly enhanced Ni uptake onto estuarine suspended particulate matter, with an increase in the 63Ni distribution coefficients (Kds) of up to 10 fold. Conversely, the addition of synthetic humic acids to UV-treated riverwater decreased significantly the 63Ni Kds. Complexation of Ni by dissolved natural ligands also affected the progression of sorptive reactions, with a system response time (i.e. the time required to achieve 63% of the sorptive equilibrium) between 1.6 and 8.9 hours. The results from this study suggest that the low particle reactivity generally exhibited by Ni during estuarine mixing is due to its ability to complex strongly with dissolved natural ligands (truly dissolved organic or colloidal organic/inorganic), and therefore resist adsorption onto particles.

Food web theory purports to describe properties that are common to all natural communities. Unfortunately, the data upon which the theory is based is fragmentary, and one of the most obvious omissions is that of parasites. The present study attempts to address this problem. The Digenean parasites found in the Ythan in two species of estuarine snail, <i>Littorina littorea</i> and <i>Hydrobia ulvae</i>, were identified, and prevalences were recorded. Field and laboratory experiments were conducted to assess the impact of infection on the mortality, behaviour and fecundity of the snail hosts. The importance of the parasites as predators of the snails in this ecosystem was assessed relative to the impact of other species recorded in the published Ythan food web. The parasites found in 12 species of fish occurring in the Ythan were recorded. In addition, five species of birds taken from Loch Leven, Perthshire, were autopsied, and parasites present were identified. Using this data, along with information available from the literature, the published food webs of the Ythan and Loch Leven systems were augmented with host-parasitic links. The new webs thus created were analysed for five patterns (food chain length, proportion of top, intermediate and basal species, degree of omnivory, linkage density and degree of triangulation). The values for these patterns were compared with those obtained from published webs without parasites, and with the predictions of the cascade model. A revised version of the cascade model, incorporating scale variant linkage density, was found to accurately predict maximum food chain length.