Video summarizing Ph.D. dissertation for a non-specialist audience. / Civil and Environmental Engineering / College of Engineering

The Maketu Estuary is a shallow intertidal estuary (2.3 km2) located in the Bay of Plenty, North Island, New Zealand. The Kaituna River contributes the largest freshwater flow into the estuary through control gates. Lake Rotoiti and indirectly Lake Rotorua supply the base flow to the Kaituna River, with tributaries along the 50 km reach also significantly contributing to the flow. Water quality within the river is affected by elevated nutrients, faecal coliforms, high oxygen demand and algae concentrations derived from the lakes as well as contributions from tributaries and industrial and urban discharge. Through the use of a coupled hydrodynamic-biogeochemical numerical model ELCOM-CAEDYM, this study aims to examine the nutrient, phytoplankton and hydrodynamics of the Maketu Estuary and lower Kaituna River. Water quality and hydrodynamic measurements were sourced from Environment Bay of Plenty's data archives as well as a number of instrument deployments to collect water velocity, tidal elevation and salinity and temperature measurements during the course of this study. Included in the field work was a survey of the lower river and estuary bathymetry. Model simulations predicted that the maximum residence time in the Maketu Estuary is 1.5 days, occurring in the inner western region. Residence time in the lower river (mouth to 8.5 km upstream) is in the order of hours although some variations were predicted near the river mouth. Growth rates of four phytoplankton groups where assessed over a 15 day period in January 2004. In the Kaituna River ELCOM-CAEDYM predicted that the community growth rates were small with the exception of a slight increase in biomass of the two freshwater groups in a semi-detached river bend. The increase in the loop was correlated with an increase of residence time. In the estuary, marine diatoms showed the highest growth rates in the western region which is expected to relate to retention time and available nutrients. Dinoflagellates showed the smallest variation in predicted growth rates, most likely due to their broad salinity tolerance. The two freshwater species showed a reduction in abundance when mixed with marine water. A principle limiting factor to phytoplankton growth in both the river and estuary is the low residence time. A number of scenarios were simulated in the river and estuary by altering the forcing conditions in the model. A simulation of the increased nutrient load associated with the Rotoiti diversion wall revealed that phytoplankton growth in the river and estuary will not be significantly affected. Because of the close proximity of the control gates to the river mouth, a proportion of water drawn through the structure can be marine. By opening the old river channel, model simulations predicted that a reduction in salinity would be possible, however the outcome of complete freshwater is probably not achievable. Increasing the discharge volume from the river into the estuary was also simulated. The results indicated that increasing the freshwater inflow at Fords Cut would reduce the salinity in the estuary while increasing the net (residual) flow towards the estuary mouth. Increasing the flow would also result in a greater range of salinity in regions of the estuary. Changing the inflow location to the historic Papahikahawai Channel also affected the salinity in the estuary. The most significant effect of an inflow at this location was a reduction of the residual currents in the western region of the estuary.

Thesis (M.S.), Natural Resources (Water Science), University of Wisconsin--Stevens Point, 2002. / Includes bibliographical references (leaves 37-38).

Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

Hydraulic retention time (HRT) might contribute to the substantial variation in phosphorus-chlorphyll and chlorophyll-zooplankton models because rapid flushing might depress plankton development. However, for a world-wide data set. HRT was not correlated with chlorophyll. Total phosphorus had no effect on chlorphyll when hypereutrophic sites were considered separately, but chlorophyll was negatively related to HRT. Short term HRT, averaged over periods up to one month, was not correlated with chlorophyll, or zooplankton biomass, in seven impoundments on the St. Lawrence and Ottawa Rivers. The size distribution of algae was not affected by HRT. The proportion of rotifer to total zooplankton biomass was positively related to HRT, but this trend disappeared when nauplius biomass was removed from the total. These results indicate that rapid flushing does not necessarily reduce planktonic biomass and that short term HRT is not useful for the prediction and management of planktonic biomass in these systems.

Freshwater ecosystems reflect the condition of their surrounding landscape, and thus are particularly vulnerable to anthropogenic stressors associated with human land-use. One of the most prevalent stressors on stream ecosystems in agricultural regions, such as the Canterbury Plains of New Zealand, is eutrophication, or increased primary productivity. The aim of this thesis was to investigate effects of eutrophication on stream communities, specifically food web structure and ecosystem function. From a food web perspective, eutrophication is a shift in the form and amount of available energy from externally-produced (allochthonous) to internal (autochthonous) basal resources. Such shifts are frequently associated with land-use intensification, due to riparian vegetation removal and increased nutrient inputs, both of which enhance autochthonous production. A field survey across a gradient of eutrophication showed that eutrophic stream food webs are largely autochthonously-based and often contain large numbers of defended primary consumers, which form trophic bottlenecks and prevent energy from reaching higher trophic levels. Consequently, while there is more total energy available, less of that energy is in a usable form for stream food webs. Moreover, I found that eutrophic streams are largely composed of generalist consumers, which shift their diets to refocus on autochthonous resources with increasing productivity. Given that eutrophication causes food web resources to become more homogenous and was a primary driver of food web change, I tested whether reintroducing allochthonous subsidies would alter or reverse the negative effects of eutrophication. To do this I conducted a short-term community assembly experiment and a year-long population biomass accrual study. I found that the simplified, generalist-dominated communities in eutrophic streams did not respond to changes in resource diversity as predicted by food web theories, which are based on more diverse food webs. After restoration of allochthonous subsidies, defended generalist taxa continued to dominate the invertebrate communities. However, while restoring allochthonous subsidies did not mitigate the numerical dominance of defended consumers, the biomass accrual of other, previously excluded desirable taxa, such as mayflies and predatory invertebrates, increased following resource additions. This indicates that more energy reached the top of the food web, suggesting that resource additions alleviated trophic bottlenecks. Overall, my findings have advanced current knowledge about key mechanisms driving food web responses to both anthropogenic stress and to restoration efforts, which can be applied to improve management and restoration of stream ecosystems.

No description available.

Abstract available in PDF file. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1982.

The use of δ18O- PO4 analysis was assessed for the Grand River, a highly impacted river in Southern Ontario that receives inputs from 30 WWTPs. Significant nutrient inputs within the watershed have led to prolific aquatic plant growth, particularly within the central Grand River where this study is focused. Two of the largest WWTPs in the watershed fall within this region and these plants are in close proximity to each other (approximately 20 km apart). Various laboratory tests were carried out to assess the suitability of several DOM removal methods on Grand River water and WWTP effluent prior to mass spectrometric analysis with varying results. Sample analysis showed all river sites to possess δ18O- PO4 values that were elevated relative to equilibrium. These sites are not equilibrium-controlled and, instead, possess δ18O- PO4 signatures controlled by either source inputs, or isotopic fractionation. The second WWTP was shown to deliver PO43- that was elevated relative to equilibrium. WWTP effluent in this study displayed a large δ18O -PO4 range, ranging from 10.4 to 22.9‰. Most of the variation in isotopic composition was found at the second plant, which had high soluble reactive phosphorus (SRP) and a range of 12.5 to 22.8‰ (n = 3). The first plant showed little variation with much lower SRP and a mean value of 11.4 (SD ± 1.0‰, n = 2). The elevated δ18O- PO4 signatures collected from the second WWTP suggest that this plant is supplying the Grand River with isotopically distinct PO43-. This could be used as a way to establish the effect of the second WWTP on the downstream PO43- pool. Phosphate uptake and release by the epilithon and seston were measured using 32P-PO4 additions in recirculating beaker experiments. Two sites, one downstream of the first WWTP and one below the second WWTP, were assessed for gross and net PO43- uptake rates. The gross uptake rates at both sites were low (0.04 to 0.10 µg P cm-2 h-1), with long turnover times for the dissolved phosphate pool (12 to 40 h). Long uptake lengths (30 to 144 km) were measured, indicating low nutrient retention capabilities downstream of the two WWTPs. These significant P contributions appear to have large-scale effects on the river’s P-kinetics, limiting its ability to act as a net nutrient sink even in the more productive summer months. The biomass response below the WWTPs is insufficient to compensate for the elevated PO43- concentrations and low rates of PO43- uptake. Due to the limited use of δ18O -PO4 analysis in river systems, no model exists for predicting the response of δ18O -PO4 with distance downstream of a point source. Coupling rates of PO43- uptake and release with the effluent δ18O -PO4 values provides such a model and generates guidance for future use of this method in lotic environments. WWTP “plume chases” were previously carried out in the Grand River, and involved measuring SRP at several sites downstream of the WWTP discharge points. SRP was used as a proxy for PO43- concentration in this study, and is operationally defined by what passes through a 0.20-µm membrane filter and is molybdate reactive. Best-fit estimates of PO43- uptake and release were determined using these plume chase events. The rates calculated using the 32P-PO4 uptake and release beaker experiments were up to 50 times lower than the best-fit parameters. This exercise illustrates the unsuitability of relaying estimates of P kinetics collected through beaker experiments to an ecosystem level. Model predictions for the river reach below the second WWTP show that effluent δ18O -PO4 signatures should be observable many kilometres from the plant. Because of the unique mean isotopic composition observed for the second WWTP, sampling could occur at a variety of locations downstream to observe the effect of this plant on the river. The river reach below the first WWTP reduces the incoming P loads much quicker than the second reach, which is in part due to the much lower effluent SRP released by the first plant. It is still possible to isolate effluent derived δ18O-PO4 values downstream of this plant. The return to equilibrium is projected to occur several kilometers from the first plant’s confluence, suggesting the applicability of this method in both stream reaches. It would appear δ18O -PO4 could be a valuable tool for eliciting information on P cycling in effluent-impacted river ecosystems, with the Grand River possessing elevated but seemingly typical uptake lengths amongst eutrophic streams.

No description available.