Scott Rayburg

Spatial variability of the soil seed bank in a heterogeneous ephemeral wetland system in semi-arid Australia

Soil seed banks are an important component of plant community diversity in ephemeral wetlands, allowing many species to persist through unpredictable periods of flood and drought. Spatial variation of extant vegetation in such habitats commonly reflects patterns of flood history and often varies predictably between broadly differing hydro-geomorphic habitat types. Here we investigate whether spatial variation of soil seed banks is similarly controlled by fluvial processes at this scale. Results are presented from a seedling emergence trial using samples collected from a range of habitat types, and at different scales within these, in the ephemeral Narran Lakes system in semi-arid Australia. Composition and structure of soil seed banks varied significantly between habitat types reflecting broad differences in flood frequency. As predicted, germinable seed abundance was found to be highest in intermediately flooded habitats. Variability in soil seed bank composition at a local scale was also found to be influenced by hydrology with greater spatial heterogeneity evident in the river channel as well as amongst the least frequently inundated riparian and floodplain habitats.

The influence of local land use on the water quality of urban rivers

Urban river flows are often highly variable and extremely polluted, which limits their potential for recreational use and as habitat for terrestrial and aquatic organisms. This study investigates how different urban landuses are reflected in the water quality of a specific river. To accomplish this, the study adopts a longitudinal approach and assesses water quality at multiple points along a single system that has three distinct land uses: 1) rural and agricultural; 2) residential; and 3) industrial. The study shows that water quality is relatively good in the rural and agricultural region, shows signs of impairment in the residential region, and becomes heavily impaired in the industrial region-despite having very similar stream side environments (good riparian vegetation cover and a floodway reserve) for its entire length. This study identifies which portions of the catchment are most responsible for non-point source pollution in urban rivers and therefore can be used to target remediation strategies to help improve the overall quality of these systems.

Winter urban heat island magnitudes of major Australian cities

This study seeks to determine the relative magnitude of the Urban Heat Island (UHI) effect in five major Australian cities during the winter season. To achieve this, the study considers three weather stations in each city: one in a high density urban area, one in a medium density urban area and one in a nearby very low density urban/rural area. For each station, temperature data were collected every 30 minutes over a three day period. The data where then plotted and maximum, minimum, and average temperature differences (and the times of those differences) were recorded. The data show that all of the cities investigated showed a strong winter heat island effect with the magnitude ranging from about 3o C up to 8o C. The largest temperature differences typically occurred near dawn (about 6 am) and overnight. It was also observed that during the day, the high and moderate density urban areas could have temperatures either higher or lower than the rural areas, a condition consistent with other global observations of the UHI effect.

The cooling effect of a medium sized park on an urban environment

The Urban Heat Island (UHI) effect can best be described as an increase in the temperature of urban areas relative to their surroundings. This effect can exceed 5oC in places. This study investigates how vegetation, in particular urban parklands, can be used to reduce the intensity of the UHI effect. To achieve this, the study uses a ground based approach relying on high spatial and temporal resolution temperature measurements using both a hand-held weather meter and a hand-held thermal laser-gun. The study focusses on one medium sized park in Melbourne, Australia and samples air temperatures (at 5 cm and 1.5 m above the ground) and land surface temperature profiles six times a day over one month starting within the park and extending to approximately 1 km outside of the park. The study shows that the park has a significant cooling effect for a distance of up to 860 m from its boundaries and that this is most significant in the early morning. The study also shows that land surface temperatures are more sensitive to park cooling effects than are air temperatures.

Designing urban rivers to maximise their geomorphic and ecologic diversity

River geomorphic complexity is vital to support abundant and diverse ecological assemblages in river environments. With the ever increasing population of global cities, and the consequent spread of urbanized land, pressures on engineers and land planners to modify and control urban rivers channels could be detrimental to their ecological diversity. This research project provides an analysis of the geomorphic complexity and heterogeneity of an urban stream. The study compares different sections of Orphan School Creek in western Sydney, Australia to investigate how channelization and/or alternations in riparian vegetation impact on geomorphic heterogeneity. The sections of Orphan School Creek examined range from freely meandering to fully concrete channelized reaches. The results of this research project clearly show that urbanization has detrimental effects on the geomorphic complexity of urban streams, due to both catchment urbanization and channelization. Through the analysis of Orphan School Creek it was concluded that channelization reduces river geomorphic complexity, with concrete channels providing little or no geomorphic complexity or diversity. However, if managed and/or designed with a view towards optimising geomorphic complexity, urban rivers can attain meaningful ecological benefits while still being controlled to prevent damage to the urban environment from flooding and/or erosion.

CONVERSION OF A DECOMMISSIONED OXIDATION LAGOON INTO A FUNCTIONAL WETLAND

This study proposes an ecologically valuable reuse for a decommissioned oxidation lagoon at the Altona Treatment Plant in Victoria, Australia, which could be replicated elsewhere. Previous design attempts for this project had failed due to the potential risk they posed to both the surrounding environment and the Treatment Plant itself. Therefore one of the objectives was to undertake multiple assessments to mitigate these risks. The most important of these, and the focus of this paper, was the determination of the optimal source and quantity of water needed to sustain the wetland. Potential water sources included: water from a nearby estuarine swamp; treated class C or class A effluent from the treatment plant; and rainfall-fed runoff from the treatment plant site. Through an analysis of cost and quality of the available water sources, it was determined that locally captured rainfall-fed runoff with Class-A recycled water as a backup supply was the most feasible. In addition, hydrologic modelling revealed that this source could maintain flow in the wetland year round, even in drought years.