Zooplankton dynamics from inundation to drying in a complex ephemeral floodplain-wetland

Ecological responses to wetting and drying in dryland river floodplain systems are often described in terms of “boom” and “bust”. We suggest that patterns in floodplain species abundances and assemblage structures will be closely linked to the changes in spatial habitat heterogeneity that accompany flooding and drying phases. This study examined the responses of zooplankton through a wetting and drying cycle in a complex floodplain-wetland system in semi-arid Australia, the Narran Lakes. We illustrate the complexity of the zooplankton “boom” and “bust” response. Total densities of zooplankton varied considerably over time and patterns were very dissimilar between sites with abundances varying from <30 animals/L to over 4000 animals/L. We detected different patterns in the proportion of variance in abundances of the broad taxonomic groups (rotifers, cladocerans, ostracods, calanoid copepods, cyclopoid copepods and nauplii) explained by time and space. Site explained the highest proportion of variation in cladoceran and ostracod abundances,whereas variance in calanoid abundances was explained predominantly by time since inundation. Variation in the abundances of the remaining groups was explained largely by the site by time interaction. Zooplankton assemblages were observed to diverge during drying with highest between-site dissimilarities in assemblage structure occurring during the later stages of drying. Such high spatial and temporal variability in zooplankton abundances and community composition could have important consequences for consumers such as fish and some wetland birds that utilize these ephemeral systems for feeding and breeding while they are inundated.

Adaptation planning for coastal inundation and erosion at the local level : a knowledge systems perspective

Scientific projections for climate change induced sea level rise highlight the potential for serious consequences in low lying coastal areas, through impacts upon: built infrastructure; beneficial uses; and ecological values. An area of particular concern relates to the ways in which issues associated with land may be subject to future inundation and, or, erosion. Responding to such issues is complex and challenging, requiring consideration of multiple sources of evidence (with varying levels of certainty), diverse organisational settings and priorities, and multiple perspectives on what the evidence means. Further, limited attention has been directed towards exploring the knowledge dynamics associated with coastal adaption planning. In this paper we explore the knowledge dynamics associated with coastal adaption planning, in order to highlight the inter-organisational and inter-personal challenges involved. We do so by drawing on the views expressed in semi structured interviews by stakeholders with an interest in coastal climate change. The particular focus is on exploring how different actors perceive coastal adaption planning process, and the tensions, challenges, and implications associated with, and arising from, the way in which coastal adaptation knowledge is exchanged.

Negotiating local decision making to manage coastal inundation : certainty, precedence, precaution and practicality

Scientific projections for climate change induced sea level rise highlight the potential for serious consequences in low lying coastal areas, through impacts upon: built infrastructure; beneficial uses; and ecological values. An area of particular concern relates to the ways in which local decision makers work through the issues associated with new development proposals on land that may be subject to future inundation, whether permanent or temporary. In making such issues, local authorities need to consider multiple sources of evidence, and multiple perspectives on what the evidence means. In this paper we examine decision making about coastal development in south west Victoria to explore how such issues are worked through, in terms of the responsibilities of different actors, and the tensions, challenges, and implications associated with, and arising from, the way in which various actors participate in, and negotiate their way through, decision making processes. In doing so, our particular focus is on the way in which different actor types engage with and interpret particular pieces of information (e.g. estimates of sea level rise and LSIO information) which are central to the decision making process. While the focus is on local decision making in south west Victoria, the insights generated may have broader relevance.

Seasonal and diet comparisons of the diets of four dominant fish species within the main channel and flood-zone of a small intermittently open estuary in south-eastern Australia

The diets of four highly-abundant, dominant fish species within the Surrey River, a small intermittently open estuary in south-east Australia, were examined from specimens collected between July 2004 and June 2005. These four, similar-sized species (Atherinosoma microstoma, Galaxias maculatus, Philypnodon grandiceps and Pseudogobius olorum) have limited ability to spatially segregate along the length of the estuary owing to its small size relative to other estuarine habitats. All four species fed on a variety of prey items including crustaceans, insects and detritus. Despite this parity, the four species were demonstrated to occupy differing dietary niches that were concluded to be responsible for reducing interspecific feeding competition. Seasonal variations in the diets were observed for A. microstoma and Philypnodon grandiceps, with these species also exhibiting contrasting diel feeding behaviours. The closure of the estuary mouth led to the flooding of its margins, resulting in an increase in the size of the estuary and providing alternative food resources for the fish to exploit. It appears the inundation of the flood-zone facilitated further significant divergence in the diets of the fish and is likely to be of high ecological value to the estuary.

Presence of fish on the shallow flooded margins of a small intermittently open estuary in South Eastern Australia under variable flooding regimes

Shallow water habitats within estuarine systems are believed to be important areas for small fish. While a wide variety of shallow habitats have been studied, the land that becomes inundated by the damming effect after the closure of intermittently open mouths has previously been overlooked. Fish were sampled monthly from both the main channel and flood zone of an intermittently open estuary between July 2004 and June 2005 using minifyke nets during the day and at night. A total of 7,787 fish were collected during the study representing 13 species and 11 families. Philypnodon grandiceps was the most abundant species and, together with Atherinosoma microstoma, Pseudogobius olorum, and Galaxias maculatus, made up 94% of the total catch. Inundation of the flood zone occurred in two discrete forms associated with mouth condition, which consisted of sporadic flooding while the mouth was open, to long-term flooding for 6 months after its closure. Large numbers of fish were captured on the flood zone, which included nine species; however, A. microstoma dominated the catch. A distinct shift in the flood zone fish assemblage occurred between the two mouth conditions, which is likely associated with changes in hydro-period and food availability of the flood zone and physico-chemical parameters in the main channel. There was no longitudinal variation in the fish assemblage in both the main channel and flood zone; similarly, the diel period was found to have little effect on the fish assemblage. The total catch per unit effort did not vary across seasons and suggests that fish abundance within the estuary is stable throughout the year. Unlike other estuarine systems where shallow water fish assemblages may be structured by variations in tide and elevation within the Surrey, freshwater inflow and, more importantly, mouth condition appear to have the greatest influence in composition of the shallow water flood zone fish assemblage of intermittently open estuaries.

Impact of saltmarsh disturbance on seed quality of Sarcocornia (Sarcocornia quinqueflora), a food plant of an endangered Australian parrot

The article presents a study which evaluates the impact of saltmarsh perturbation on seed quality of Sarcocornia which is a food for the endangered Orange-bellied parrot in Australia. It notes the significant impact of grazing on the energy and availability of Sarcocornia seeds in saltmarshes and indicates that graze-free saltmarshes with regular inundation provide the highest potential for Sarcocornia seed availability. Further, the substantial factor of soil characteristics and salinity of flood water and inundation on the seed production of Sarcocornia is also discussed.

Changes in organic-matter dynamics and physicochemistry, associated with riparian vegetation loss and river regulation in floodplain wetlands of the Murray River, Australia

Extensive clearing of floodplain forests potentially reduces organic matter available to floodplain wetlands. Furthermore, on rivers regulated to provide irrigation water in summer, floodplain wetlands that were previously inundated in spring, now flood in summer/autumn. In the Murray–Darling Basin, Australia, this has changed the timing of organic matter entering the aquatic phase, since leaf fall peaks in summer. Field surveys and mesocosm experiments on floodplain wetlands on the River Murray revealed faster processing rates of leaves in summer/autumn than spring, and no difference between cleared and forested wetlands. Temperature and leaf carbon : nitrogen ratio could not explain these differences, and instead, changes to leaf chemistry associated with ‘terrestrial ageing’ between peak leaf fall in summer and inundation in spring is more likely. The results indicated that the reduction of input of organic matter through riparian tree clearing and changing the timing of inundation interact to alter organic-matter standing stocks and rates of decomposition in floodplain wetlands. Restoring both natural timing of high flows and riparian vegetation might be required for recovery of these wetlands.

A new approach to determining environmental flow requirements : sustaining the natural values of floodplains of the southern Murray-Darling Basin

Large overbank flood events play an important role in maintaining largescale ecological processes and connectivity along and across the floodplains and between the rivers and their floodplains in the southern Murray-Darling Basin. However, the regulation of rivers means that extensive overbank flooding can only occur in the rare circumstance of extreme flood events. Recent environmental water allocations have focussed on the largest floodplain blocks (‘icon’ sites) and a small set of specific values (e.g. colonial nesting waterbirds), as well as on trialling fine-scale manipulation of infrastructure (e.g. pumping) to water relatively small areas. There has been no comprehensive systematic assessment of the entire floodplain and its wider set of flood-dependent natural assets (such as ecosystems and species; herein referred to as ‘natural values’) to maximise the effectiveness of environmental water use and to catalogue values likely to be lost. This paper describes an assessment of some 220 000 ha found to support flood-dependent natural values in Victoria. We mapped the geographic distribution and estimated components of the flooding requirements (natural flooding frequency, and maximum period without flooding and minimum duration of each flooding event before significant deterioration) for each natural value. Using an example of one stretch of the River Murray, we show how the resultant spatial data can be used with floodplain inundation modelling to compare the outcomes of real or planned environmental watering events; potentially providing tools for management agencies to conserve a wider range of floodplain values than is currently the case. That is, water managers and the public can see what ecosystems and threatened species are intended to be maintained by environmental watering and what values are intended to be abandoned across the whole floodplain, rather than just seeing the small subset of values and ‘icon’ sites that are intended to be maintained. Examples are provided to illustrate how information about the location, water requirements and extent covered by potential floods for specific values can be used to build adaptive watering strategies for areas as large as the whole floodplain.

The use of public transport in coastal Australia : modes of travel to work and greenhouse emissions

Commuting to work is one of the most important and regular routines of transportation in towns and cities. From a geographic perspective, the length of people’s commute is influenced, to some degree, by the spatial separation of their home and workplace and the transport infrastructure. The rise of car ownership in Australia from the 1950s to the present was accompanied by a considerable decrease of public transport use. Currently there is an average of 1.4 persons per car in Australia, and private cars are involved in approximately 90% of the trips, and public transportation in only 10%. Increased personal mobility has fuelled the trend of decentralised housing development, mostly without a clear planning for local employment, or alternative means of transportation. Transport sector accounts for 14% of Australia’s net greenhouse gas emissions. Without further policy action, Australia’s emissions are projected to continue to increase. The Australian Federal Government and the new Department of Climate Change have recently published a set of maps showing that rising seas would submerge large parts of Victoria coastal region. Such event would lead to major disruption in planned urban growth areas in the next 50 years with broad scale inundation of dwellings, facilities and road networks. The Greater Geelong Region has well established infrastructure as a major urban centre and tourist destination and hence attracted the attention of federal and state governments in their quest for further development and population growth. As a result of its natural beauty and ecological sensitivity, scenarios for growth in the region are currently under scrutiny from local government as well as development agencies, scientists, and planners. This paper is part of a broad research in the relationship between transportation system, urban form, trip demand, and emissions, as a paramount in addressing the challenges presented by urban growth. Progressing from previous work focused on private cars, this present paper investigates the use of public transport as a mode for commuting in the Greater Geelong Region. Using a GIS based interaction model, it characterises the current use of the existing public transportation system, and also builds a scenario of increased use of the existing public transportation system, estimating potencial reductions in CO2 emissions. This study provides an improved understanding of the extent to which choices of transport mode and travel activity patterns, affect emissions in the context of regional networks. The results indicate that emissions from commuting by public transportation are significantly lower than those from commuting by private car, and emphasise that there are opportunities for large abatment in the greenhouse emissions from the transportation sector related to efforts in increasing the use of existing public transportation system.

Aplicacao do geoprocessamento no estudo da impermeabilidade urbana

The environmental impact of urbanization due to the surface impervious growing and inadequacy of urban occupation induces to a significant increase of inundation events in every urban center. Hence, this paper focuses the concept of impervious surface as an indicator of environment impact, expressed through the changing of pervious areas in impervious areas by paving cover or building occupation. It is taken as a case study 13 areas pertaining to Canoas City, Rio Grande do Sul – Metropolitan area of Porto Alegre, Brazil. The main goal of the methodology process is to achieve information about types of land cover for studying the association with urban impermeability level. Therefore, the manipulation of municipal digital cartographic base of Canoas City with aerial photographs, through the geoprocessing applied in geographic information system toolbox (GIS), allows this research to produce data about of urban impervious areas generation. These results could help the urban settlement planning to reduce the impervious cover and the hydrological impact in its implementation.

Disturbance and the role of refuges in mediterranean climate streams

Refuges protect plant and animal populations from disturbance. Knowledge of refuges from disturbance in mediterranean climate rivers (med-rivers) has increased the last decade. We review disturbance processes and their relationship to refuges in streams in mediterranean climate regions (med-regions). Med-river fauna show high endemicity and their populations are often exposed to disturbance; hence the critical importance of refuges during (both seasonal and supraseasonal) disturbances. Disturbance pressures are increasing in med-regions, in particular from climatic change, salinisation, sedimentation, water extraction, hydropower generation, supraseasonal drought, and wildfire. Med-rivers show annual cycles of constrained precipitation and predictable seasonal drying, causing the biota to depend on seasonal refuges, in particular, those that are spatially predictable. This creates a spatial and temporal mosaic of inundation that determines habitat extent and refuge function. Refuges of sufficient size and duration to maintain populations, such as perennially flowing reaches, sustain biodiversity and may harbour relict populations, particularly during increasing aridification, where little other suitable habitat remains in landscapes. Therefore, disturbances that threaten perennial flows potentially cascade disproportionately to reduce regional scale biodiversity in med-regions. Conservation approaches for med-river systems need to conserve both refuges and refuge connectivity, reduce the impact of anthropogenic disturbances and sustain predictable, seasonal flow patterns.

Freshwater influences on hydrology and seagrass dynamics of intermittent estuaries

Many temperate estuaries have intermittently open and closed mouths, a feature that is often related to intermittent freshwater input. These systems, often overlooked due to their small size, can have large hydrological variability over medium-term time scales.

This variability presents potential difficulties for estuarine species particularly where anthropogenic alterations to freshwater flows can cause large deviations from natural patterns of tidal influence and inundation of habitat.

Influences of natural and hydrological variability on seagrasses were examined in two central Victorian estuaries with anthropogenically-modified but naturally-intermittent freshwater flows and mouth openings. Comparisons were focused on differences between an estuary with artificially-augmented freshwater inflow and an adjacent system, in which the volume and timing of inflows were altered by a reservoir. Eight additional estuaries in the region were also used to provide a context for these two main sites.

Hydrological changes during the three-year field component were affected by the ending of a drought and then a major flood a year later as well as by ongoing anthropogenic flow reduction and augmentation. These influences on hydrology were associated with an initially high seagrass coverage that was substantially reduced and showed signs of recovery only in the system that was affected by lower inflows. Such influences and responses also changed seasonally but to a much lesser extent than the responses to stochastic climatic events.

Natural flows were intermittent and varied substantially between years. Flooding flows represented up to 89% of the long-term annual average flow. Water quality was broadly typical of the region, with the exception of low pH in some tributaries, especially those of Anglesea estuary. Anthropogenic changes to flow were most evident at times of low natural flows and resulted in longer and more frequent periods of zero inflow to Painkalac estuary and a continual base flow to Anglesea. This base flow, from ponds containing coal ash, neutralised waters flowing from upstream and increased conductivity, except at times of high natural flow.

A three-state conceptual model of the magnitude and variability of water levels, based largely on the degree of tidal influence was identified and quantitatively assessed for the two estuaries that were the main focus of the study. These states in turn had a large influence on the area and inundation of benthic habitat. Floods tended to open the mouths of estuaries, which then remained tidal given sufficient flow to overcome sedimentary processes at the mouths. Low and zero inflow was a precondition for closure of the mouths of the estuaries. When closed, differences in inflow resulted in different endpoints in salinity patterns. From an initial pattern similar to a classic ‘salt wedge’, Painkalac estuary, with reduced inflow, quickly destratified and gradually became more saline, at times hypersaline. Anglesea estuary, with augmented flow, tended to remain stratified for longer until becoming completely fresh, given a long enough period of closure.

Episodic changes in the water quality of the estuaries were associated with different components of the freshwater flow regimes. At high flows, fresh waters of low pH with a high metal load entered Anglesea estuary. Except during the largest flood, when the estuary was completely flushed, this water was neutralised at the halocline and resulting in precipitation of metals. High flows into Painkalac were associated with elevated concentrations of clay-sourced suspended solids. During a closed period, with zero flow, a release of sediment-bound nutrients triggered by anoxia was observed in Painkalac, followed by an algal bloom.

The large decline in seagrass extent that was observed in both estuaries was closely related to floods and the subsequent reductions in potential habitat associated with the tidal states that followed. Analysis of historical patterns of extent against rainfall records suggested that periods of drought and extended mouth closures were related to establishment and expansion of beds. This model was similar to that described for South African estuaries and contrasted with more-seasonal patterns reported for local marine embayments.

Rates of in situ decomposition of seagrass detritus showed a mix of seasonal and disturbance-driven patterns of change, depending on estuary. Variability of these rates on a scale of 100s of metres was typically not significant, but there were a few episodes that were highly significant. A negative correlation between decomposition rate and seagrass extent was also observed. A novel technique for assessing cellulose decomposition potential in sediment, adapted from soil science, proved to be a useful tool for estuarine research. Results from this component of the study highlighted both small-scale variability that was inconsistent through time, and also stable differences in decomposition potential between depths and estuaries that were consistent with differences in hydrological state and salinity.

Given the relative lack of knowledge about processes in intermittent estuaries, particularly those relating to changes in freshwater inflow, results from this study will be of value both locally and for similar systems elsewhere. Locally, it is likely that flow regimes to both Anglesea and Painkalac estuaries will be reduced, following closure of the mine power station at Anglesea and due to increased demand from the reservoir above Painkalac. There is potential to manage flows from each of these sources to minimise downstream effects. Regionally, and globally, there are many intermittent estuaries in areas with Mediterranean-type climates. It has been predicted that the climates of these regions will become drier but with an increase in intensity of storm events, both of which have ramifications for flow regimes to estuaries. It is hoped that results of this study will contribute to more informed management of intermittent estuaries in the context of these likely changes.

Loss of 'blue carbon' from coastal salt marshes following habitat disturbance

Increased recognition of the global importance of salt marshes as 'blue carbon' (C) sinks has led to concern that salt marshes could release large amounts of stored C into the atmosphere (as CO2) if they continue undergoing disturbance, thereby accelerating climate change. Empirical evidence of C release following salt marsh habitat loss due to disturbance is rare, yet such information is essential for inclusion of salt marshes in greenhouse gas emission reduction and offset schemes. Here we investigated the stability of salt marsh (Spartinaalterniflora) sediment C levels following seagrass (Thallasiatestudinum) wrack accumulation; a form of disturbance common throughout the world that removes large areas of plant biomass in salt marshes. At our study site (St Joseph Bay, Florida, USA), we recorded 296 patches (7.5 ± 2.3 m(2) mean area ± SE) of vegetation loss (aged 3-12 months) in a salt marsh meadow the size of a soccer field (7 275 m(2)). Within these disturbed patches, levels of organic C in the subsurface zone (1-5 cm depth) were ~30% lower than the surrounding undisturbed meadow. Subsequent analyses showed that the decline in subsurface C levels in disturbed patches was due to loss of below-ground plant (salt marsh) biomass, which otherwise forms the main component of the long-term 'refractory' C stock. We conclude that disturbance to salt marsh habitat due to wrack accumulation can cause significant release of below-ground C; which could shift salt marshes from C sinks to C sources, depending on the intensity and scale of disturbance. This mechanism of C release is likely to increase in the future due to sea level rise; which could increase wrack production due to increasing storminess, and will facilitate delivery of wrack into salt marsh zones due to higher and more frequent inundation.

Exposure mediates transitions between bare and vegetated states in temperate mangrove ecosystems

The resilience of mangroves is dependent on their regeneration capacity. Patchy mid-19th century clearing dramatically affected this capacity, creating stable vegetated and unvegetated states in a fragmented temperate mangrove ecosystem. Mechanisms of mediation between states were tested by monitoring the survival and growth of planted mangrove seedlings and propagules on formerly forested bare mudflats and inside patches of existing forest. Survival (1 to 76%) and growth (-0.83 to 10.45 mm mo-1 increase in plant height) of seedlings was affected by (1) differing levels of exposure found at varying proximities to remnant forest and (2) differing inundation regimes both within and between sites that were randomly selected from locations that varied in aspect relative to prevailing winds. Increases in hydrodynamic energy within and between sites corresponded to a decrease in survival that was much more pronounced at locations that were exposed to prevailing winds. Growth rates were also generally lower at sites in exposed locations, but inundation regime was a more important determinant within sites, where growth was reduced at lower heights on the shore. Results suggest that stability of the bare mudflat state (caused by historical clearance of the mangrove forest) is dependent on level of exposure to hydrodynamic energy, and a return to a forested state is more likely where this exposure is lower. These results have implications for planning and implementing mangrove restoration projects and illustrate the role that physical factors can play in determining the resilience of disturbed temperate mangrove ecosystems.