Seasonal water regimes and leaf litter processing in a wetland on the Swan Coastal Plain

The effect of seasonal or permanent inundation on the processing of leaf litter from two competing emergent macrophytes Baumea articulata and Typha orientalis was examined at Lake Jandabup, a seasonal wetland on the Swan Coastal Plain. The loss of organic matter from leaf packs was used to quantify leaf litter processing. The contributions made by microorganisms and macroinvertebrates in processing were also assessed. Leaf packs exposed to seasonal inundation (defined as those areas exposed to alternate wetting and drying) had significantly higher losses of organic matter after six months than those permanently inundated for the same period. The presence of stratified water column in the permanently inundated sites in summer, resulting in reduced oxygen levels at the bottom or the water column appears to be the driving force behind the low amounts of organic matter loss from leaf packs in this environment. These results are supported by the presence of peaty soils in the permanently inundated sites and not in those seasonally inundated, indicating that this pattern of leaf litter processing has been occurring for some time. The reflooding of seasonally inundated sites resulted in these leaf packs having the highest microbial biomass and therefore become a preferred food source for invertebrates. Losses of organic matter from leaf packs also highlighted the difference in the amounts of organic matter loss between the two species, with Baumea losing significantly more. The classification into groups of macroinvertebrates found in leaf packs using TWINSPAN resulted in a separation of the permanently inundated sites into distinct invertebrate communities, with no preference for Haumea or typha leaf packs found in established vegetation communities. The resulting differences in functioal feeding group representation between vegetation communities may in part be responsible for differences in the amounts of leaf litter processing. The results from this study indicate that changes to the current seasonal wet/dry hydrological regime experienced by the littoral community at Lake Jandabup will alter the proportions of organic matter available for processing within the wetlan

Origin and fate of organic matter in South-West Australian wetlands

The development and local distribution of organic soils in Australia have been poorly documented. Within Western Australia, conditions conducive to the accumulation of organic matter are geographically restricted and generally occur in coastal and/or forested landscapes. An extensive system of wetlands with peal soils occurs in the Muir-Unicup region in the far south west of Western Australia. Bokarup Swamp, Kodjinup Swamp and Noobijup Lake are representative of the wetlands occurring in this region. They arc shallow

The response of aquatic communities to water quality, land use, flow variability and extraction in an unregulated Australian coastal river

Stream ecosystems are greatly influenced by their catchments through the contribution of water and nutrients. While nutrients are an essential component in driving biological stream functions and processes, the continuing impact of changing land use and diffuse inputs has increased nutrient loads within most aquatic environments around the world. These increasing nutrient loads have resulted in artificial or cultural eutrophication, impairing water quality and aquatic ecosystem function. It is hypothesised in this thesis that catchment properties and agricultural land use increase total nutrient concentrations within the Manning River system on the north coast of New South Wales, Australia. Increases in nutrient concentrations, coupled with reduced flows, will have ecological impacts through increases in primary productivity and algal biomass. To assess how land use and river discharge influences biogeochemical processes, this study measured water quality under various flow conditions and assessed the responses of biota to flow and water quality changes. Regionally-derived nutrient thresholds were identified, as was the influence of discharge on in-stream nutrient concentrations and ratios. Nutrient enrichment experiments, nocturnal water quality investigations and assessments of macroinvertebrate community structure responses were also undertaken to better understand ecosystem functioning

A Framework for Determining Environmental Water Requirements for Alluvial Aquifer Ecosystems

Demand for groundwater is accelerating in Australia and globally. The development of guidelines to ensure ecologically sustainable use of groundwater lags behind this demand, although the broad policy and planning base for environmental water requirements is in place in Australia. Environmental water requirements in aquifers are the groundwater regimes needed to maintain or restore ecological processes and conserve biodiversity. The existing framework for environmental allocations for aquifers requires identification of groundwater dependent ecosystems and estimation of their water requirements in terms of: level (in unconfined aquifers) or pressure (in confined aquifers), discharge flux, and water quality. Of all groundwater dependent ecosystems, aquifer ecosystems are entirely groundwater dependent, but details of their biota, ecosystem processes and water requirements are the least known. This study applied the framework for determining environmental water requirements of aquifer ecosystems in a case study of the Peel Valley Alluvium, an alluvial aquifer connected to the regulated Peel River in the north-east Murray-Darling Basin, New South Wales, Australia. Eleven groundwater monitoring bores were sampled to determine whether structural indicators (abundance and taxonomic richness) of the groundwater invertebrate assemblage composition were correlated with aspects of the groundwater regime. Stygofauna (groundwater invertebrates) and physico-chemical variables were sampled quarterly in these bores from July 2006 to October 2007. Data loggers in 10 of the bores recorded groundwater level and temperature hourly for this period. Long-term stream gauge and groundwater level data were used to investigate the relationship between streamflow and groundwater regime, and to assess the degree of hydrological alteration in the river and alluvium after river regulation... A revised framework for determining environmental water requirements in alluvial aquifers is proposed which takes account of the organising principle of connectivity in delivering a compound disturbance regime, and recognizes the significance of scale and of cross-scale linkages between components of the disturbance regime. Given the current limits of distributional and taxonomic knowledge, the structural indicators of faunal assemblage composition appear inadequate to identify environmental water requirements for alluvial aquifers. The conjunctive use of functional indicators of ecosystem processes is recommended. Field-testing and further development of the framework will contribute to sustainable groundwater management, but realization of this goal relies on the collaboration of researchers, policy makers and knowledge brokers

Environmental Determinants of Malaria Transmission in Agricultural Communities Around Large Dams in Ethiopia

Dams are key to ensuring food security and promoting economic growth in sub-Saharan Africa. However, the potential adverse public health impacts of dams, such as malaria, could undermine their intended benefits. Understanding the influence of dams on the distribution of malaria transmission in different ecological settings is thus crucial to devise tailor-made malaria control tools. This study assessed the impact of dams on malaria transmission at different eco-epidemiological settings, and evaluates the potential of optimized dam management for malaria control. To determine levels of malaria transmission around dams at different ecological settings, entomological and epidemiological surveys were conducted at three Ethiopian dams located in lowland, midland and highland areas. Larval and adult anopheline mosquitoes were collected from dam and non-dam (control) villages between October 2013 and July 2014. Female anophelines were tested for malaria sporozoite infection and blood meal sources. Five years of monthly malaria case data (2010-2014) were also analyzed. Mean monthly malaria incidence was two- and ten-fold higher at the lowland dam than at the midland and highland dams, respectively. Shoreline puddles and irrigation canals were consistently the major mosquito breeding habitats. Densities of larval and adult anophelines were also highest at the lowland dam village, followed by the midland and highland dam villages. Anopheles arabiensis was the predominant malaria vector species, followed by An. pharoensis and An. funestus sensu lato (s.l.) which were largely collected from lowland and midland dam villages. The annual Entomological Inoculation Rate (EIR) of An. arabiensis, An. funestus s.l. and An. pharoensis at the lowland dam village was 157.7, 54.6 and 48.6 infective bites per person per year, respectively. The annual EIR of An. arabiensis and An. pharoensis was 5.4 and 3.1 times higher at the lowland dam village than at the midland dam village. These data indicate that increased malaria associated with dams is higher in the lowland than midland and highland ecological settings. Factors linked to malaria transmission around the study dams were examined using environmental (elevation, distance from the reservoir shoreline, Normalized Difference Vegetation Index (NDVI), monthly average reservoir water level and monthly changes in water level) and meteorological (precipitation, and minimum and maximum temperature) data. Multiple regression analysis demonstrated that village distance from reservoir shoreline (lagged by 1 month) was negatively associated with malaria incidence around all three dams, while average monthly reservoir water level (lagged by 2 months) and monthly precipitation (lagged by 1 or 2 months) were positively associated with malaria incidence only at the lowland and midland dams. Similarly, minimum air temperature and monthly change in reservoir water level when lagged by 2 months were positively associated with malaria incidence at the highland dam. Maximum temperature did not show any correlation with malaria incidence at any of the study dams. These results suggest that reservoir factors (monthly average reservoir water level and reservoir water level change) were important predictors of malaria incidence. Different water level drawdown rates were tested in an experimental field setting to evaluate the potential of using reservoir water level management for larval mosquito control. Twelve experimental dams were constructed on the foreshore of the midland Koka Dam, and grouped into one of four daily water drawdown treatments: 0 (control), 10, 15 and 20 mm.day-1. Larval sampling was conducted weekly during the main transmission season (October to November 2013) and subsequent dry season (February to March 2014). Mean weekly larval density was highest in the control experimental dams throughout the study, and decreased significantly with increasing water drawdown rates in both seasons. The results indicate that faster water level drawdown rates help reduce larval vector abundance around dams. The results of the experimental work were then used to evaluate the potential of water level management for malaria control at the reservoir-scale. Digital elevation models were constructed for the three study dams to estimate reservoir parameters (surface area and perimeter of wetted shoreline) at different reservoir capacities (70, 75, 80, 85, 90, 95 and 100% full capacity). Water level drawdown rates of 10, 15 and 20 mm.day-1 were applied and larval abundance, entomological inoculation rate (EIR) and malaria prevalence were estimated for each reservoir capacity scenario. At the lowland dam, larval abundance increased with increasing reservoir volume and wetted shoreline area, although the opposite pattern was observed at the midland and highland dams due to differences in reservoir topography. Estimated EIR, malaria prevalence, malaria treatment and economic costs generally decreased when water level drawdown rate increased from 10 to 15 and 20 mm.day-1. The results indicate that increasing water level drawdown rate will reduce malaria transmission and the associated economic impacts around dams during the main transmission season. Findings of the present study highlight that by regulating the persistence of shallow shoreline breeding habitats, reservoir water level management could serve as a potential malaria vector control tool around African dams. This study underscores the benefits of optimized dam management by incorporating malaria vector control into reservoir management practices. Mosquito larval control using reservoir water level manipulation could therefore supplement the existing vector control measures to dramatically reduce malaria around dams. Future research should assess the practicability of dam management for malaria control in diverse African settings, including the social and economic costs of optimized dam operations on hydropower generation and downstream agriculture

Restoring vertical connectivity in rivers: geomorphic, hydrologic and biogeochemical responses to log sills in the Williams and Hunter Rivers, NSW, Australia

In alluvial rivers, groundwater and stream water are intimately connected via the saturated sediments lying below and beside the river channel, termed the 'hyporheic zone'. This zone is a spatially and temporally dynamic mosaic of biogeochemically distinct patches that are connected by multiple, hierarchical hydrological flowpaths that also vary in space and time. Active and diverse hyporheic zones promote resilience and resistance in rivers through thermal buffering, retention of water, solutes and organic matter, biogeochemical filtration, nutrient cycling, and biological production that occur within these ecotones between alluvial rivers and true groundwaters. However, alluvial river systems are among the most endangered ecosystems in the world, and in many the spatial and temporal configuration of hyporheic exchange has been impaired by human activities. Efforts to restore hyporheic zones are increasingly common. Typically, these projects have sought to reinstate geomorphic complexity through augmenting coarse sediment or installing wooden structures such as log sills. Most of these attempts have been on low-order reaches and focused at fine-scales (e.g. a single riffle). This thesis describes the first large-scale field experiment to assess the restoration outcomes and ecological success of large, engineered, multi-log structures such as those typically deployed by catchment managers. My study derived a conceptual model from the literature that hypothesized the mechanisms by which a log sill anchored within a riffle would increase hyporheic exchange and influence nutrient processing. I then tested these hypotheses using two log sills placed in each of two gravel-bed rivers, the Hunter River and the Williams River, New South Wales, Australia

Modeling reservoir management for malaria control in Ethiopia

This study investigated how changes in reservoir water level affect mosquito abundance and malaria transmission in Ethiopia. Digital elevation models of three Ethiopian dams at lowland, midland and highland elevations were used to quantify water surface area and wetted shoreline at different reservoir water levels (70, 75, 80, 85, 90, 95 and 100% full capacity) to estimate surface area of potential mosquito breeding habitat. Reservoir water level drawdown rates of 10, 15 and 20 mm.day-1 were applied as scenarios to model larval abundance, entomological inoculation rate (EIR) and malaria prevalence at each dam. Malaria treatment cost and economic cost in terms of lost working days were calculated for each water level scenario and dam. At the lowland dam, increased larval abundances were associated with increasing reservoir water level and wetted shoreline area. In contrast, both larval abundances and area of wetted shoreline declined with increasing reservoir water level at the midland and highland dams. Estimated EIR, malaria prevalence, malaria treatment cost and economic cost generally decreased when the water level drawdown rate increased from 10 to 15 and 20 mm.day-1 irrespective of reservoir water level. Given the expansion of dam construction in sub-Saharan Africa, incorporating malaria control measures such as manipulating drawdown rates into reservoir management has the potential to reduce the malaria burden and health care costs in communities near reservoirs

Predicting the Effects of Restoring Tidal Connectivity on the Vegetation of Fresh and Oligohaline Wetlands: Clarence River Floodplain, Northern NSW

Tidal wetlands are decreasing in number and extent worldwide due to the effects of drains and tidal barriers. These disrupt salinity gradients, reduce the depth, duration and frequency of inundation, prevent exchange of organic and inorganic materials, and interrupt movement of aquatic biota and propagules. Common effects include reductions in bird and fish populations, invasion by terrestrial and freshwater macrophytes, sediment subsidence caused by peat degradation, and activation of acid sulfate soils leading to land degradation and water quality problems. Active management of floodgates has been proposed to restore tidal exchange to waterways and wetlands of the Clarence River floodplain, on the north coast of New South Wales, Australia. Predicting the potential effects of tidal restoration on macrophyte communities is of high priority, particularly for wetlands in the fresher half of the estuarine salinity gradient. The vegetation at these sites provides important foraging and nesting habitat for rare waterbirds and a valuable pasture resource. Our ability to predict the effects of increased tidal connectivity on macrophyte communities in these wetlands is limited. Previous research in Australia has focused on saltmarsh species found in saline habitats and few data are available on the salinity and inundation tolerance ranges of macrophytes found further upstream. Existing models for predicting the effects of tidal restoration on macrophyte community composition are generally inapplicable to these communities because of the need for reference data, either from natural tidal wetlands located nearby or from surveys carried out at rehabilitation sites prior to drainage and tidal restriction. Neither of these are available for wetlands on the Clarence River floodplain. An extensive survey was used to determine distributions of macrophyte species in floodgate-affected wetlands along the Clarence River floodplain, and to relate these distributions to environmental variables, including salinity, relative elevation, acidity, water management and grazing intensity. Strong significant correlations were found between community composition and both site salinity and water depth, indicating the potential value of these variables as predictors of species occurrence

Conidial Morphogenesis and Septin-Mediated Plant Infection Require Smo1, a Ras GTPase-Activating Protein in Magnaporthe oryzae

The pathogenic life cycle of the rice blast fungus Magnaporthe oryzae involves a series of morphogenetic changes, essential for its ability to cause disease. The smo mutation was identified > 25 years ago, and affects the shape and development of diverse cell types in M. oryzae, including conidia, appressoria, and asci. All attempts to clone the SMO1 gene by map-based cloning or complementation have failed over many years. Here, we report the identification of SMO1 by a combination of bulk segregant analysis and comparative genome analysis. SMO1 encodes a GTPase-activating protein, which regulates Ras signaling during infection-related development. Targeted deletion of SMO1 results in abnormal, nonadherent conidia, impaired in their production of spore tip mucilage. Smo1 mutants also develop smaller appressoria, with a severely reduced capacity to infect rice plants. SMO1 is necessary for the organization of microtubules and for septin-dependent remodeling of the F-actin cytoskeleton at the appressorium pore. Smol physically interacts with components of the Ras2 signaling complex, and a range of other signaling and cytoskeletal components, including the four core septins. SMO1 is therefore necessary for the regulation of RAS activation required for conidial morphogenesis and septin-mediated plant infection

A sensor kinase controls turgor-driven plant infection by the rice blast fungus

The blast fungus Magnaporthe oryzae gains entry to its host plant by means of a specialized pressure-generating infection cell called an appressorium, which physically ruptures the leaf cuticle. Turgor is applied as an enormous invasive force by septin-mediated reorganization of the cytoskeleton and actin-dependent protrusion of a rigid penetration hypha. However, the molecular mechanisms that regulate the generation of turgor pressure during appressorium-mediated infection of plants remain poorly understood. Here we show that a turgor-sensing histidine–aspartate kinase, Sln1, enables the appressorium to sense when a critical turgor threshold has been reached and thereby facilitates host penetration. We found that the Sln1 sensor localizes to the appressorium pore in a pressure-dependent manner, which is consistent with the predictions of a mathematical model for plant infection. A Δsln1 mutant generates excess intracellular appressorium turgor, produces hyper-melanized non-functional appressoria and does not organize the septins and polarity determinants that are required for leaf infection. Sln1 acts in parallel with the protein kinase C cell-integrity pathway as a regulator of cAMP-dependent signalling by protein kinase A. Pkc1 phosphorylates the NADPH oxidase regulator NoxR and, collectively, these signalling pathways modulate appressorium turgor and trigger the generation of invasive force to cause blast disease