Mitigating impacts of climate change in stream food webs

AbstractUnderstanding the effects of changing climates on the processes which support aquatic biodiversity is of critical importance for managing aquatic ecosystems. This research used an experimental approach to determine whether there are potential ecological surprises in terms of threshold relationships between climate and critical aquatic processes. These results were then placed in the context of the potential for riparian replanting to mitigate against these impacts.A review was carried out of climate change experiments in freshwaters, and revealed that the vast majority of studies have failed to take into account predicted increases in the frequency of extreme events (such as heatwaves) on biota. In order to include these components of changes in climate, a methodology was developed for downscaling global circulation models of climate change to generate realistic temperature data to use as an experimental treatment. Stream communities from the field were brought into experimental flumes and warmed according to the predictions of the down-scaled climate change models. Experiments were run for six weeks and responses were measured for basal processes (algal productivity and carbon dynamics) and aquatic invertebrate communities. Basal processes showed relatively small responses to the changed temperature regime, and appear to be relatively resistant for warming on the scale predicted under climate change scenarios for the next century. Aquatic invertebrate communities did show some responses, but these tended to be in terms of changes in size structure withion particular taxa rather than major impacts on patterns of biodiversity.The largest effects were seen for emerging adults of aquatic insects, were all species in the community responded in some way to our 2100 climate change treatment. Responses were species- and sex-specific. Males of all mayfly species emerged faster under 2100 temperatures compared to 1990-2000 temperatures. For the mayfly Ulmerophlebia pipinna (Leptophlebiidae), this implied a change in the sex ratio that could potentially compromise populations and, ultimately, lead to local extinctions. Furthermore, our results show a decrease in the overall community body size (average across taxa) due to a shift from bigger to smaller species.These results are in accord with the ecological rules dealing with the temperature-size relationships (in particular, Bergmann’s rule). Studies of streams in the field revealed that riparian vegetation did cool stream temperatures, and that the presence of riparian vegetation, ideally with extensive vegetation cover across the catchment, did appear to maintain higher diversity and abundance in stream invertebrate communities. Therefore it seems that restoring riparian vegetation does represent an effective means of adaptation to changing climates for temperate south eastern Australian freshwaters.Please cite this report as: Thompson, RM, Beardall, J, Beringer, J, Grace, M, Sardina, P 2013 Mitigating impacts of climate change on stream food webs: impacts of elevated temperature and CO2 on the critical processes underpinning resilience of aquatic ecosystems National Climate Change Adaptation Research Facility, Gold Coast, pp.136.Understanding the effects of changing climates on the processes which support aquatic biodiversity is of critical importance for managing aquatic ecosystems. This research used an experimental approach to determine whether there are potential ecological surprises in terms of threshold relationships between climate and critical aquatic processes. These results were then placed in the context of the potential for riparian replanting to mitigate against these impacts.A review was carried out of climate change experiments in freshwaters, and revealed that the vast majority of studies have failed to take into account predicted increases in the frequency of extreme events (such as heatwaves) on biota. In order to include these components of changes in climate, a methodology was developed for downscaling global circulation models of climate change to generate realistic temperature data to use as an experimental treatment. Stream communities from the field were brought into experimental flumes and warmed according to the predictions of the down-scaled climate change models. Experiments were run for six weeks and responses were measured for basal processes (algal productivity and carbon dynamics) and aquatic invertebrate communities. Basal processes showed relatively small responses to the changed temperature regime, and appear to be relatively resistant for warming on the scale predicted under climate change scenarios for the next century. Aquatic invertebrate communities did show some responses, but these tended to be in terms of changes in size structure withion particular taxa rather than major impacts on patterns of biodiversity.The largest effects were seen for emerging adults of aquatic insects, were all species in the community responded in some way to our 2100 climate change treatment. Responses were species- and sex-specific. Males of all mayfly species emerged faster under 2100 temperatures compared to 1990-2000 temperatures. For the mayfly Ulmerophlebia pipinna (Leptophlebiidae), this implied a change in the sex ratio that could potentially compromise populations and, ultimately, lead to local extinctions. Furthermore, our results show a decrease in the overall community body size (average across taxa) due to a shift from bigger to smaller species.These results are in accord with the ecological rules dealing with the temperature-size relationships (in particular, Bergmann’s rule). Studies of streams in the field revealed that riparian vegetation did cool stream temperatures, and that the presence of riparian vegetation, ideally with extensive vegetation cover across the catchment, did appear to maintain higher diversity and abundance in stream invertebrate communities. Therefore it seems that restoring riparian vegetation does represent an effective means of adaptation to changing climates for temperate south eastern Australian freshwaters

Antivirulence Potential of TR-700 and Clindamycin on Clinical Isolates of \u3cem\u3eStaphylococcus aureus\u3c/em\u3e Producing Phenol-Soluble Modulins

Staphylococcus aureus strains (n = 50) causing complicated skin and skin structure infections produced various levels of phenol-soluble modulin alpha-type (PSMα) peptides; some produced more than twice that produced by the control strain (LAC USA300). TR-700 (oxazolidinone) and clindamycin strongly inhibited PSM production at one-half the MIC but exhibited weak to modest induction at one-fourth and one-eighth the MICs, primarily in low producers. Adequate dosing of these agents is emphasized to minimize the potential for paradoxical induction of virulence

Tigecycline Induction of Phenol-Soluble Modulins by Invasive Methicillin-Resistant \u3cem\u3eStaphylococcus aureus\u3c/em\u3e Strains

We examined the effects of tigecycline on three types of exoproteins, α-type phenol-soluble modulins (PSMα1 to PSMα4), α-hemolysin, and protein A, in 13 methicillin-resistant Staphylococcus aureus isolates compared to those of clindamycin and linezolid. Paradoxical increases in PSMαs occurred in 77% of the isolates with tigecycline at 1/4 and 1/8 MICs and clindamycin at 1/8 MIC compared to only 23% of the isolates with linezolid at 1/8 MIC. Induction was specific to PSMα1 to PSMα4, as protein A and α-hemolysin production was decreased under the same conditions by all of the antibiotics used

An optimality-based model of the dynamic feedbacks between natural vegetation and the water balance

The hypothesis that vegetation adapts optimally to its environment gives rise to a novel framework for modeling the interactions between vegetation dynamics and the catchment water balance that does not rely on prior knowledge about the vegetation at a particular site. We present a new model based on this framework that includes a multilayered physically based catchment water balance model and an ecophysiological gas exchange and photosynthesis model. The model uses optimization algorithms to find those static and dynamic vegetation properties that would maximize the net carbon profit under given environmental conditions. The model was tested at a savanna site near Howard Springs (Northern Territory, Australia) by comparing the modeled fluxes and vegetation properties with long-term observations at the site. The results suggest that optimality may be a useful way of approaching the prediction and estimation of vegetation cover, rooting depth, and fluxes such as transpiration and CO2 assimilation in ungauged basins without model calibration

An optimality-based model of the coupled soil moisture and root dynamics

The main processes determining soil moisture dynamics are infiltration, percolation, evaporation and root water uptake. Modelling soil moisture dynamics therefore requires an interdisciplinary approach that links hydrological, atmospheric and biological processes. Previous approaches treat either root water uptake rates or root distributions and transpiration rates as given, and calculate the soil moisture dynamics based on the theory of flow in unsaturated media. The present study introduces a different approach to linking soil water and vegetation dynamics, based on vegetation optimality. Assuming that plants have evolved mechanisms that minimise costs related to the maintenance of the root system while meeting their demand for water, we develop a model that dynamically adjusts the vertical root distribution in the soil profile to meet this objective. The model was used to compute the soil moisture dynamics, root water uptake and fine root respiration in a tropical savanna over 12 months, and the results were compared with observations at the site and with a model based on a fixed root distribution. The optimality-based model reproduced the main features of the observations such as a shift of roots from the shallow soil in the wet season to the deeper soil in the dry season and substantial root water uptake during the dry season. At the same time, simulated fine root respiration rates never exceeded the upper envelope determined by the observed soil respiration. The model based on a fixed root distribution, in contrast, failed to explain the magnitude of water use during parts of the dry season and largely over-estimated root respiration rates. The observed surface soil moisture dynamics were also better reproduced by the optimality-based model than the model based on a prescribed root distribution. The optimality-based approach has the potential to reduce the number of unknowns in a model (e.g. the vertical root distribution), which makes it a valuable alternative to more empirically-based approaches, especially for simulating possible responses to environmental change

Relational Symbolic Execution

Symbolic execution is a classical program analysis technique used to show that programs satisfy or violate given specifications. In this work we generalize symbolic execution to support program analysis for relational specifications in the form of relational properties - these are properties about two runs of two programs on related inputs, or about two executions of a single program on related inputs. Relational properties are useful to formalize notions in security and privacy, and to reason about program optimizations. We design a relational symbolic execution engine, named RelSym which supports interactive refutation, as well as proving of relational properties for programs written in a language with arrays and for-like loops

Impacts of an extreme cyclone event on landscape-scale savanna fire, productivity and greenhouse gas emissions

North Australian tropical savanna accounts for 12% of the world\u27s total savanna land cover. Accordingly, understanding processes that govern carbon, water and energy exchange within this biome is critical to global carbon and water budgeting. Climate and disturbances drive ecosystem carbon dynamics. Savanna ecosystems of the coastal and sub-coastal of north Australia experience a unique combination of climatic extremes and are in a state of near constant disturbance from fire events (1 in 3 years), storms resulting in windthrow (1 in 5–10 years) and mega-cyclones (1 in 500–1000 years). Critically, these disturbances occur over large areas creating a spatial and temporal mosaic of carbon sources and sinks. We quantify the impact on gross primary productivity (GPP) and fire occurrence from a tropical mega-cyclone, tropical Cyclone Monica (TC Monica), which affected 10 400 km2 of savanna across north Australia, resulting in the mortality and severe structural damage to ~140 million trees. We estimate a net carbon equivalent emission of 43 Tg of CO2-e using the moderate resolution imaging spectroradiometer (MODIS) GPP (MOD17A2) to quantify spatial and temporal patterns pre- and post-TC Monica. GPP was suppressed for four years after the event, equivalent to a loss of GPP of 0.5 Tg C over this period. On-ground fuel loads were estimated to potentially release 51.2 Mt CO2-e, equivalent to ~10% of Australia\u27s accountable greenhouse gas emissions. We present a simple carbon balance to examine the relative importance of frequency versus impact for a number of key disturbance processes such as fire, termite consumption and intense but infrequent mega-cyclones. Our estimates suggested that fire and termite consumption had a larger impact on Net Biome Productivity than infrequent mega-cyclones. We demonstrate the importance of understanding how climate variability and disturbance impacts savanna dynamics in the context of the increasing interest in using savanna landscapes for enhanced carbon sinks in emission offset schemes

Coupling carbon allocation with leaf and root phenology predicts tree-grass partitioning along a savanna rainfall gradient

The relative complexity of the mechanisms underlying savanna ecosystem dynamics, in comparison to other biomes such as temperate and tropical forests, challenges the representation of such dynamics in ecosystem and Earth system models. A realistic representation of processes governing carbon allocation and phenology for the two defining elements of savanna vegetation (namely trees and grasses) may be a key to understanding variations in tree–grass partitioning in time and space across the savanna biome worldwide. Here we present a new approach for modelling coupled phenology and carbon allocation, applied to competing tree and grass plant functional types. The approach accounts for a temporal shift between assimilation and growth, mediated by a labile carbohydrate store. This is combined with a method to maximize long-term net primary production (NPP) by optimally partitioning plant growth between fine roots and (leaves + stem). The computational efficiency of the analytic method used here allows it to be uniquely and readily applied at regional scale, as required, for example, within the framework of a global biogeochemical model. We demonstrate the approach by encoding it in a new simple carbon–water cycle model that we call HAVANA (Hydrology and Vegetation-dynamics Algorithm for Northern Australia), coupled to the existing POP (Population Orders Physiology) model for tree demography and disturbance-mediated heterogeneity. HAVANA-POP is calibrated using monthly remotely sensed fraction of absorbed photosynthetically active radiation (fPAR) and eddy-covariance-based estimates of carbon and water fluxes at five tower sites along the North Australian Tropical Transect (NATT), which is characterized by large gradients in rainfall and wildfire disturbance. The calibrated model replicates observed gradients of fPAR, tree leaf area index, basal area, and foliage projective cover along the NATT. The model behaviour emerges from complex feedbacks between the plant physiology and vegetation dynamics, mediated by shifting above- versus below-ground resources, and not from imposed hypotheses about the controls on tree–grass co-existence. Results support the hypothesis that resource limitation is a stronger determinant of tree cover than disturbance in Australian savannas.The contributions of V. Haverd and P. Briggs were made possible by the support of the Australian Climate Change Science Program. B. Smith acknowledges funding as an OCE Distinguished Visiting Scientist to the CSIRO Oceans & Atmosphere Flagship, Canberr

Recent increases in terrestrial carbon uptake at little cost to the water cycle

Quantifying the responses of the coupled carbon and water cycles to current global warming and rising atmospheric CO2 concentration is crucial for predicting and adapting to climate changes. Here we show that terrestrial carbon uptake (i.e. gross primary production) increased significantly from 1982 to 2011 using a combination of ground-based and remotely sensed land and atmospheric observations. Importantly, we find that the terrestrial carbon uptake increase is not accompanied by a proportional increase in water use (i.e. evapotranspiration) but is largely (about 90%) driven by increased carbon uptake per unit of water use, i.e. water use efficiency. The increased water use efficiency is positively related to rising CO2 concentration and increased canopy leaf area index, and negatively influenced by increased vapour pressure deficits. Our findings suggest that rising atmospheric CO2 concentration has caused a shift in terrestrial water economics of carbon uptake