Jon Knight

Wetlands and Mosquitoes: a review

This review brings together information on mosquitoes, the diseases they transmit and the wetlands that provide habitats for the immature stages (eggs and larvae). Wetland values are mentioned, though the main literature on this does not generally overlap the mosquito issue. Mosquito management is overviewed to include: the use of larvicides, source reduction in intertidal wetlands and management in freshwater systems. There is not a great deal of information on mosquitoes and freshwater systems, except for constructed wetlands and they are considered separately. We then consider restoration mainly in the context of wetlands that have been the subject of habitat modification for mosquito control. Land use and climate change, as they affect mosquitoes and the diseases they transmit, are also reviewed, as this will affect wetlands via management activities. Finally the review addresses the critical issue of balancing health, both human and environmental, in an adaptive framework. It concludes that there is a need to ensure that both mosquito and wetland management communicate and integrate to sustain wetland and human health.

Correlations between the satellite-derived seasonal cycles of phytoplankton biomass and aerosol optical depth in the Southern Ocean: Evidence for the influence of sea ice

The relationship between the production of dimethylsulfide (DMS) in the upper ocean and atmospheric sulfate aerosols has been confirmed through local shipboard measurements, and global modeling studies alike. In order to examine whether such a connection may be recoverable in the satellite record, we have analyzed the correlation between mean surface chlorophyll (CHL) and aerosol optical depth (AOD) in the Southern Ocean, where the marine atmosphere is relatively remote from anthropogenic and continental influences. We carried out the analysis in 5-degree zonal bands between 50°S and 70°S, for the period (1997-2004), and in smaller meridional sectors in the Eastern Antarctic, Ross and Weddell seas. Seasonality is moderate to strong in both CHL and AOD signatures throughout the study regions. Coherence in the CHL and AOD time series is strong in the band between 50°S and 60°S, however this synchrony is absent in the sea-ice zone (SIZ) south of 60°S. Marked interannual variability in CHL occurs south of 60°S, presumably related to variability in sea-ice production during the previous winter. We find a clear latitudinal difference in the cross correlation between CHL and AOD, with the AOD peak preceding the CHL bloom by up to 6 weeks in the SIZ. This suggests that substantial trace gas emissions (aerosol precursors) are being produced over the SIZ in spring (October-December) as sea ice melts. This hypothesis is supported by field data that record extremely high levels of sulfur species in sea ice, surface seawater, and the overlying atmosphere during ice melt.

Habitat characteristics and eggshell distribution of the salt marsh mosquito, Aedes vigilax, in marshes in subtropical Eastern Australia.

Abstract Research at 10 locations in coastal subtropical Queensland, Australia, has shown that salt marshes contained heterogeneous distributions of eggshells of the pest and vector mosquito Aedes vigilax (Skuse) (Diptera:Culicidae). The eggshell distribution was related to specific vegetation assemblages, with a mix of the grass, Sporobolus virginicus (L.) Kunth (Poales: Poaceae), and the beaded glasswort, Sarcocornia quinqueflora (Bunge ex (Ung.-Stern) A.J. Scott (Caryophyllales: Chenopodiaceae), as significantly higher in eggshells than any other vegetation. There were also high numbers in the mix of S. virginicus with the arrowgrass, Triglochin striata Ruiz & Pavón (Alismatales: Juncaginaceae). Both mixed types are found in relatively wetter areas, despite very few eggshells being found generally in the low marsh. Most sites contained S. virginicus and eggshell locations were variable for this species alone. This was probably related to its life form variability in response to salinity and location on the marsh. Location on the marsh was important for eggshell distribution with most eggshells around the edges of pools and depressions, followed by, but to a significantly lesser extent, the marsh surface. Eggshells were fewest in the low marsh. Partition analysis resulted in a tree that simplified and summarised the factors important for eggshell distribution confirming the individual analyses. The potential effects of climate, sea level and other change are also briefly discussed in the context of likely changes to land cover and relative location on the marsh. For example, increased sea level may lead to low marsh conditions extending into higher marsh area with implications for oviposition and numbers of eggshells.

Oviposition and larval habitat preferences of the saltwater mosquito, Aedes vigilax, in a subtropical mangrove forest in Queensland, Australia

Abstract Our aim was to investigate the oviposition and larval habitats of the saltwater mosquito Aedes vigilax (Skuse) (Diptera: Culicidae) in a mangrove forest system in subtropical Queensland, Australia. Eggshells (indicators of oviposition) and larvae were sampled in three habitat classes that were depicted in a schematic model. Two classes were in depressions or basins, either with hummocks or dense pneumatophore substrates, both of which retained water after tidal flooding. The third class was in freely flushed mangroves that corresponded with more frequent tidal connections than the depression classes. ANOVA and Tukey-Kramer tests were used to analyze the data. The null hypotheses were rejected: the hummock class was a significant habitat based on both eggshell and larval data. The conclusion was that mosquito production in the mangrove system was distributed unevenly between habitat classes, and that the hummock class had conditions suited to the requirements of the immature stages of Ae. vigilax. This research has the potential to inform mosquito management strategies by focusing treatment on the problem habitats and underpinning habitat modifications including reducing water retention in the basins.

A review of the role of fish as biological control agents of disease vector mosquitoes in mangrove forests: reducing human health risks while reducing environmental risk

The saltwater mosquito, Aedes vigilax, is prolific in coastal wetlands including mangroves and saltmarshes. Ae. vigilax is a vector for arboviruses such as Ross River and Barmah Forest viruses, with significant consequences for human health and economic productivity. In Australia the dominant form of mosquito control is chemicals. For mangroves, this is because there is a critical lack of knowledge supporting alternative approaches, such as environmental modification or biological control using larvivorous fish. This review examines the potential of fish as biological agents for the control of mosquito larvae in mangroves. We consider two key aspects: how larvivorous fish use mangroves; and can larvivorous fish reduce larval mosquito populations sufficiently to provide effective mosquito control? The link between fish and mangroves is reasonably well established, where mangroves act as refuge habitat for small and juvenile fish. Also, research has established that fish can be significant predators of mosquitoes, and therefore may be effective control agents. However, studies of fish activity within mangroves are limited to study of the fringe of the mangroves and not the internal structure of mangrove basins and as a result, fish populations within these areas remain unstudied. Also, until recently there was little appreciation of the mangrove-mosquito habitat relationship and, as a consequence, the importance of the mangrove basin as the key mosquito habitat has also been overlooked in the literature. Similarly, the predator/prey relationships between fish and mosquitoes within mangrove basin environments also remain unstudied, and therefore the importance of fish for mosquito management in mangrove basins is not known. There are substantial knowledge gaps regarding the potential of fish in controlling larval mosquitoes in mangroves. The gaps include: understanding of how larvivorous fish use mangrove basins; the nature of the fish-mosquito predator/prey relationship in mangrove basins; and whether larvivorous fish are effective as a mosquito control option in mangroves.

A conceptual model for integrating physical geography research and coastal wetland management, with an Australian example

We have developed a conceptual model to assist integration between physical geographical sciences, institutional frameworks and management in the context of coastal wetlands. Wetlands are key interconnected systems that will respond early to climate change and especially to associated sea-level changes. A major constraint on management of wetlands is the lack of congruence between the ecosystems and the institutional frameworks that govern their management: connectivity in coastal systems is overlain by institutional fragmentation. We introduce a model that facilitates integration of physical geographical (biophysical) information into the legislative, planning, policy and management process. It consists of interconnected parallel subprojects in science and in planning with strong cross-links with stakeholders at all levels, founded on long-term and trusting relationships. We also show progress that has been made in applying the model, with an Australian example. It is concluded that the approach has potential to move towards the goal of sustainable management but that it urgently needs to evolve, so as to meet the challenges of climate and associated changes.

Managing salt marshes for mosquito control: impacts of runnelling, open marsh water managment and grid ditching in sub-tropical Australia

Three salt marsh sites in south-east Queensland, Australia, have been modified for mosquito control. The problem species is Ochlerotatus vigilax, a vector of Ross River virus that is an epidemic polyarthritic disease. All sites have similar vegetation and tidal influences. Each site has a different form of modification to manage the mosquitoes: runnelling, Open Marsh Water Management (OMWM) and grid-ditching. Results are compared of a treatment and control experimental design, similar for each site, but analysed separately for each site, and over the same 3-year time period. Environmental variables monitored included: for the water table, the depth, salinity and pH; for the substrate, its moisture, salinity and pH; for the vegetation, the size and density of the dominant grass (Sporobolus virginicus) and the number of mangrove (Avicennia marina) pneumatophores. Crab activity was indicated by crab hole numbers.ANOVA analyses, comparing treatment and control at each site, indicated that runnelling had the least significant impact on the environmental variables, whereas most impacts were at the grid-ditched site. Of the 10 variables included here, 5 were affected by runnelling, 7 by OMWM and 9 by grid-ditching. Statistically significant results are summarised, compared to the relevant controls, as follows:Water table: the level was significantly higher near ditches in the grid-ditched site; pH was higher at the treatment in the OMWM site but was lower in the grid-ditched site; salinity was significantly lower in the runnelled and in part of the grid-ditched marsh.Substrate: the moisture was higher at both the OMWM and grid-ditched sites; pH was higher in the OMWM treatment but lower in the grid-ditched marsh; salinity was significantly lower at the runnelled and grid-ditched sites, but was higher near the ditch at the OMWM site.Vegetation and crabs: The grass Sporobolus virginicus was less dense in the treatments in both the OMWM and grid-ditched sites, but was taller in the runnelled site and in part of the grid-ditched site. There were fewer mangrove pneumatophores in the runnelled area, but more in the OMWM one. There was more crab activity in both the runnelled and OMWM sites.It was concluded that runnelling has least impact and that grid-ditching has the most, but that none of these appears to have destroyed the marsh environment.

Unprecedented wind erosion and perturbation of surface geochemistry marks the Anthropocene in Australia

Australia, the last continent to undergo industrial development, is an ideal environment in which to quantify the magnitude of human-induced environmental change during the Anthropocene because its entire agricultural and industrial history has occurred within this period. Analysis of an alpine peat mire showed that rapid industrial and agricultural development (both pastoral and cropping) over the past 200 years has resulted in significant environmental change in Australia. Beginning in the 1880s, rates of wind erosion and metal enrichment were up to 10 and 30 times that of background natural conditions, respectively. Increased dust deposition and an expansion in dust source areas were found to map the progression of European farming across the continent, while dust deposition pulses in the mire matched known land degradation events. After 1990 dust deposition decreased, returning to pre-1880 rates. This was attributed to three factors: net soil loss following more than a century of agricultural activity, increased environmental awareness and soil conservation, and changing windiness. Metal enrichment in the mire reached approximately 2 times natural background accumulation rates by the 1980s as Australias mining industry expanded. However, metal enrichment continued to increase after the 1980s reaching an average of ~5 times background rates by 2006 and reflecting increased mineral resource development in Australia. Collectively, the results show that changes to Australias geochemical and sedimentary systems, as a result of agricultural and industrial development, have profoundly changed the Australian environment during the past two centuries. Key Points The 2.5 up increase in wind erosion since agricultural development Average of 5 times increase in metal enrichment since 1880 Two phases of the Anthropocene are identifiable

Bounding Neighbourhoods: How Do Residents Do It?

Abstract The ‘neighbourhood’ holds an iconic position in planning, yet there has been longstanding empirical criticism and debates about both the use and intellectual underpinnings of the concept. Despite this, it continues to provide a focus for local area planning, local policy interventions and urban design approaches, including in new urbanism. Neighbourhoods may be given physical dimensions so the boundaries that distinguish what is within and what is outside each neighbourhood can be defined. This paper asks what we can learn about such localities through a better understanding of how residents themselves actually identify these boundaries. It derives a series of questions that are addressed through analysis of resident perceptions of neighbourhood boundaries in an inner-city fringe suburb in Brisbane, Australia. The research confirmed many previous concerns about defining neighbourhood boundaries and that many residents were uncertain of the physical boundaries of their neighbourhoods.

Managing mosquitoes without destroying wetlands: an eastern Australian approach

Recognising both the importance of intertidal wetlands and their role in mosquito-borne disease we discuss wise management to conserve wetland values and to reduce vector borne disease health risks. First we summarise the mosquito-borne diseases associated with intertidal wetlands in sub-tropical and tropical Australia. We consider the Ramsar Strategic Plan, its reflection in some key Australian statutes and the relationship between environment-focussed legislation and health legislation. This is followed by a brief overview of mosquito control and its impact on human health. Using a salt marsh example of an integrated process, we describe the development of what was, in the 1980s in Australia, a novel method of habitat modification (runnelling) for mosquito control. Runnelling modifies the tidal water flow on salt marshes, reducing mosquito larval numbers and minimising environmental impacts. The approach is related to two of the Ramsar goals (wise use and institutional capacity and effectiveness). We then describe the extension of its rationale to a complex mangrove system. Finally, with a concept model, we consider the convergence between minimal habitat modification for wetland conservation and human health protection using an interdisicplinary approach involving multiple stakeholders.