Fiona Dyer

Environmental flows for natural, hybrid, and novel riverine ecosystems in a changing world

The term “environmental flows” describes the quantities, quality, and patterns of water flows required to sustain freshwater and estuarine ecosystems and the ecosystem services they provide. Environmental flows may be achieved in a number of different ways, most of which are based on either (1) limiting alterations from the natural flow baseline to maintain biodiversity and ecological integrity or (2) designing flow regimes to achieve specific ecological and ecosystem service outcomes. We argue that the former practice is more applicable to natural and semi-natural rivers where the primary objective and opportunity is ecological conservation. The latter “designer” approach is better suited to modified and managed rivers where return to natural conditions is no longer feasible and the objective is to maximize natural capital as well as support economic growth, recreation, or cultural history. This permits elements of ecosystem design and adaptation to environmental change. In a future characterized by altered climates and intensive regulation, where hybrid and novel aquatic ecosystems predominate, the designer approach may be the only feasible option. This conclusion stems from a lack of natural ecosystems from which to draw analogs and the need to support broader socioeconomic benefits and valuable configurations of natural and social capital.

Identifying the influence of channel morphology on physical habitat availability for native fish: application to the two-spined blackfish (Gadopsis bispinosus) in the Cotter River, Australia

The impact of channel morphology and flow on physical habitat availability for the two-spined blackfish (Gadopsis bispinosus) was assessed in the Cotter River, ACT, Australia. Physical habitat requirements for three life stages were identified based on previous field sampling in the Cotter River. Two sites were selected with contrasting channel morphology: Spur Hole, with a moderate gradient and runs and glides, and Vanity’s Crossing, with a steeper gradient, rapids, and fast-flowing pools. Physical Habitat Simulation System (PHABSIM) was used to simulate the flow v. physical habitat availability relationship for each life stage at both sites. Clear differences were apparent between sites, with Spur Hole characterised by increasing habitat with increasing flow and Vanity’s Crossing showing the opposite relationship. The nature of the channel morphology determined this difference, with Spur Hole characterised by marginal zones becoming inundated at higher flows and providing additional suitable physical habitat as discharge increases. Vanity’s Crossing does not contain similar marginal zones. Further analysis demonstrated that high water velocity was the most important factor limiting physical habitat availability at both sites. This approach demonstrates the importance of channel morphology in determining physical habitat availability and an alternative use of PHABSIM to highlight limiting factors for target species.

Effects of spatial and temporal variation in hydraulic conditions on metabolism in cobble biofilm communities in an Australian upland stream

Abstract Mesoscale spatial (centimeters–meters) and temporal (days–weeks) flow variability plays an important role in stream ecosystem structure and function. The structural effects of flow variability have been widely tested but its influence on ecosystem processes is less well understood. Our study examined the influence of mesoscale flow variability on cobble biofilm metabolism in an Australian regulated upland stream that had been subjected to severe catchment disturbance as a result of extensive fire 10 mo before the study. Rates of primary production and respiration were calculated from changes in dissolved O2 over 24 h in benthic chambers containing stream cobbles sampled before and after high-discharge events in areas with differing surface-flow types. Overall, cobble biofilm communities were strongly autotrophic (primary production » respiration), probably because of reduced shading and increased nutrient influx caused by the recent fire. Differences in production and respiration before and after individual high-discharge events were inconsistent and, therefore, not statistically significant. The effect of high discharge on respiration was greater when high-discharge events were preceded by long periods of low discharge, but the number of events sampled was limited and this result could not be tested statistically. Rates of respiration and concentrations of organic material, chlorophyll a, and pheophytin a also varied spatially, and these variables were affected more by mesoscale variation in hydraulic conditions than by reach-scale variation in hydraulic conditions. Our results suggest that flow management has the potential to alter benthic metabolism.

Contribution of national bioassessment approaches for assessing ecological water security: an AUSRIVAS case study

River managers in Australia are managing in the face of extremes to provide security of water supply for people, production and the environment. Balancing the water requirements of people, environments and economies requires that water security is viewed holistically, not just in terms of the water available for human consumption. Common definitions of water security focus on the needs of both humans and ecosystems for purposes such as drinking, agriculture and industrial use, and to maintain ecological values. Information about achieving water security for the environment or ecological purposes can be a challenge to interpret because the watering requirements of key ecological processes or assets are not well understood, and the links between ecological and human values are often not obvious to water users. Yet the concepts surrounding river health are inherently linked to holistic concepts of water security. The measurement of aquatic biota provides a valuable tool for managers to understand progress toward achieving ecological water security objectives. This paper provides a comprehensive review of the reference condition approach to river health assessment, using the development of the Australian River Assessment System (AUSRIVAS) as a case study. We make the link between the biological assessment of river health and assessment of ecological water security, and suggest that such an approach provides a way of reporting that is relevant to the contribution made by ecosystems to water security. The reference condition approach, which is the condition representative of minimally disturbed sites organized by selected physical, chemical, and biological characteristics, is most important for assessing ecological water security objectives.

Adaptation of water resources systems to changing society and environment: a statement by the International Association of Hydrological Sciences

ABSTRACT We explore how to address the challenges of adaptation of water resources systems under changing conditions by supporting flexible, resilient and low-regret solutions, coupled with on-going monitoring and evaluation. This will require improved understanding of the linkages between biophysical and social aspects in order to better anticipate the possible future co-evolution of water systems and society. We also present a call to enhance the dialogue and foster the actions of governments, the international scientific community, research funding agencies and additional stakeholders in order to develop effective solutions to support water resources systems adaptation. Finally, we call the scientific community to a renewed and unified effort to deliver an innovative message to stakeholders. Water science is essential to resolve the water crisis, but the effectiveness of solutions depends, inter alia, on the capability of scientists to deliver a new, coherent and technical vision for the future development of water systems. EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR not assigned

Discretization of continuous predictor variables in Bayesian networks

Bayesian networks (BNs) are a popular tool in natural resource management but are limited when dealing with ecological assemblage data and when discretizing continuous variables. We present a method that addresses these challenges using a BN model developed for the Upper Murrumbidgee River Catchment (south-eastern Australia). A selection process was conducted to choose the taxa from the whole macroinvertebrate assemblage that were incorporated in the BN as endpoints. Furthermore, two different approaches to the discretization of continuous predictor variables for the BN were compared. One approach used Threshold Indicator Taxa Analysis (TITAN) which estimates the thresholds based on the biological community. The other approach used was the expert opinion. The TITAN-based discretizations provided comparable predictions to expert opinion-based discretizations but in combining statistical rigor and ecological relevance, offer a novel and objective approach to the discretization. The TITAN-based method may be used together with expert opinion. We propose the empirical estimation of thresholds to discretize continuous predictor variables within Bayesian networks.We used a case study to illustrate it.Predefined criteria were used to select five macroinvertebrate taxa that were incorporated in the BN as endpoints.Continuous predictor variables were discretized using Threshold Indicator Taxa Analysis (TITAN).TITAN-based discretizations provided comparable predictions to expert opinion-based discretizations.

The imperative need for nationally coordinated bioassessment of rivers and streams

Declining water quality and ecological condition is a typical trend for rivers and streams worldwide as human demands for water resources increase. Managing these natural resources sustainably is a key responsibility of governments. Effective water management policies require information derived from long-term monitoring and evaluation. Biological monitoring and assessment are critical for management because bioassessment integrates the biological, physical and chemical features of a waterbody. Investment in nationally coordinated riverine bioassessment in Australia has almost ceased and the foci of management questions are on more localised assessments. However, rivers often span political and administrative boundaries, and their condition may be best protected and managed under national policies, supported by a coordinated national bioassessment framework. We argue that a nationally coordinated program for the bioassessment of riverine health is an essential element of sustainable management of a nation’s water resources. We outline new techniques and research needed to streamline current arrangements to meet present-day and emerging challenges for coordinating and integrating local, regional and national bioassessment activities. This paper draws on international experience in riverine bioassessment to identify attributes of successful broad-scale bioassessment programs and strategies needed to modernise freshwater bioassessment in Australia and re-establish national broad-scale focus.

Who's your mama? Riverine hybridisation of threatened freshwater trout cod and murray cod

Rates of hybridization and introgression are increasing dramatically worldwide because of translocations, restocking of organisms and habitat modifications; thus, determining whether hybridization is occuring after reintroducing extirpated congeneric species is commensurately important for conservation. Restocking programs are sometimes criticized because of the genetic consequences of hatchery-bred fish breeding with wild populations. These concerns are important to conservation restocking programs, including those from the Australian freshwater fish family, Percichthyidae. Two of the better known Australian Percichthyidae are the Murray Cod, Maccullochella peelii and Trout Cod, Maccullochella macquariensis which were formerly widespread over the Murray Darling Basin. In much of the Murrumbidgee River, Trout Cod and Murray Cod were sympatric until the late 1970s when Trout Cod were extirpated. Here we use genetic single nucleotide polymorphism (SNP) data together with mitochondrial sequences to examine hybridization and introgression between Murray Cod and Trout Cod in the upper Murrumbidgee River and consider implications for restocking programs. We have confirmed restocked riverine Trout Cod reproducing, but only as inter-specific matings, in the wild. We detected hybrid Trout Cod–Murray Cod in the Upper Murrumbidgee, recording the first hybrid larvae in the wild. Although hybrid larvae, juveniles and adults have been recorded in hatcheries and impoundments, and hybrid adults have been recorded in rivers previously, this is the first time fertile F1 have been recorded in a wild riverine population. The F1 backcrosses with Murray cod have also been found to be fertile. All backcrosses noted were with pure Murray Cod. Such introgression has not been recorded previously in these two species, and the imbalance in hybridization direction may have important implications for restocking programs.

Why groundwater matters: an introduction for policy-makers and managers

ABSTRACT In many parts of the world the combined pressures of population growth and a drying climate have resulted in the proliferation of water focused policies which aim to increase the resilience of socio-ecological systems. Until recently, these policies often reflected surface water centric views of water resources, with groundwater receiving scant attention. In this paper we provide an introduction to the importance of groundwater for water-dependent socio-ecological systems and why it needs to be better incorporated into environmental water management policies. Specifically we highlight the key role of groundwater in buffering the environment and socio-economic activities against drought. We also outline some of the key challenges that face policy-makers and managers implementing groundwater management policies. These include dealing with groundwater resources that are spatially and temporally mismatched with surface water resources; transboundary governance issues; challenges between focusing on either preventative or restorative actions and most importantly limited knowledge about groundwater resources and groundwater–ecology relationships. We hope that the information in this paper will assist in the development of sustainable surface-groundwater water management policies, as well as highlight important challenges that should be considered before implementing groundwater related policies.

Groundwater salinization intensifies drought impacts in forests and reduces refuge capacity

1. Shallow groundwater aquifers regularly support drought refuges for water-dependent ecosystems. However, many aquifers are impacted by over-extraction and pollution, potentially degrading their ability to support groundwater-fed drought refuges. 2. We investigated the response of groundwater-connected riverine forests to a drought considered equivalent in intensity to those predicted under severe climate change for 2030. The drought’s impact was investigated in an area where shallow groundwater resources are heavily exploited and polluted by salinization. 3. We used remotely sensed vegetation productivity (enhanced vegetation index) data from a long-term data set (2000–2011) at 475 riverine forest sites in the Campaspe catchment, southeastern Australia. Generalized additive mixed models and boosted regression trees were used to model the relationship between groundwater and other environmental covariates with forest change during drought. 4. Models explained up to 44% of the variation in forest change during drought. Forests underwent the greatest declines in areas of high salinity (>6000 lS cm-1) associated with shallow groundwater depths (0–5 m). Conversely, forests in areas of lowest salinity (<2000 lS cm-1) and groundwater depths of more than 7-5 m showed the least decline during drought. 5. In landscapes where groundwater quality is not compromised, previous studies have shown that shallow groundwater provides important drought refuges and refugia. Here, we show that when groundwater salinization has occurred, forests connected to shallow groundwater are more vulnerable to drought. In effect, salinization reduces the capacity of groundwater-connected habitats to function as drought refuges. 6. Synthesis and applications. Currently, there is an emphasis on managing environmental flows to support freshwater ecosystems and associated forests under water stress. However, delivery of environmental water is restricted to areas within a linear stream network and there is often limited capacity to deliver environmental flows during drought. Alternatively, a focus on drought refuges and refugia and processes important for maintaining groundwater quality (e.g. catchment revegetation to reduce shallow groundwater salinization) may better allow drought effects to be managed across a catchment, without directly focusing on highly contested surface water resources.