Stephen John Mackay

Development and Application of a Predictive Model of Freshwater Fish Assemblage Composition to Evaluate River Health in Eastern Australia

Multivariate predictive models are widely used tools for assessment of aquatic ecosystem health and models have been successfully developed for the prediction and assessment of aquatic macroinvertebrates, diatoms, local stream habitat features and fish. We evaluated the ability of a modelling method based on the River InVertebrate Prediction and Classification System (RIVPACS) to accurately predict freshwater fish assemblage composition and assess aquatic ecosystem health in rivers and streams of south-eastern Queensland, Australia. The predictive model was developed, validated and tested in a region of comparatively high environmental variability due to the unpredictable nature of rainfall and river discharge. The model was concluded to provide sufficiently accurate and precise predictions of species composition and was sensitive enough to distinguish test sites impacted by several common types of human disturbance (particularly impacts associated with catchment land use and associated local riparian, in-stream habitat and water quality degradation). The total number of fish species available for prediction was low in comparison to similar applications of multivariate predictive models based on other indicator groups, yet the accuracy and precision of our model was comparable to outcomes from such studies. In addition, our model developed for sites sampled on one occasion and in one season only (winter), was able to accurately predict fish assemblage composition at sites sampled during other seasons and years, provided that they were not subject to unusually extreme environmental conditions (e.g. extended periods of low flow that restricted fish movement or resulted in habitat desiccation and local fish extinctions).

Spatial variation in the distribution and abundance of submersed macrophytes in an Australian subtropical river

Spatial variation in the distribution and abundance of submersed macrophytes in the Mary River, a subtropical Australian river, was examined at 29 sites on four occasions (116 samples) over a 1 year period. Thirteen submersed macrophyte taxa representing seven families were recorded during the study period. Submersed macrophyte cover was generally patchy and mean quadrat cover per sample was below 7% for every recorded taxon. Classification and ordination identified four distinct groups characterised by differences in submersed macrophyte abundance and associated environmental variables. Three of the four groups were characterised by different abundances of three core taxa, Myriophyllum verrucosum, Vallisneria nana and Potamogeton crispus. The distribution of the four sample groups within the Mary River catchment was associated with two environmental gradients, the first gradient representing discharge intensity, discharge variability and total Kjeldahl nitrogen (TKN) concentration and the second gradient representing discharge intensity, substrate composition, riparian canopy cover and total phosphorus (TP) concentration. Both environmental gradients were constrained by geomorphology at the catchment as well as the reach scale. Our findings are consistent with a general conceptual model that highlights the importance of major environmental gradients in structuring submersed macrophyte assemblages.

Fish assemblages in subtropical rivers: low-flow hydrology dominates hydro-ecological relationships

Abstract Effective environmental flow management depends on identification of ecologically-relevant flow attributes to maintain or restore flows in the context of other natural and human influences on stream ecosystems. This study in subtropical eastern Australia identified associations of fish with climatic and flow gradients, catchment topography, reach geology, habitat structure and land use across 20 catchments. Land-use patterns and associated stressors accounted for very little variation in fish assemblage structure. Of the 35 fish species analysed, 24 were strongly associated with gradients in mean daily flows and their variability, baseflow, number of zero-flow days and high-flow pulses, magnitude of the 1-year annual return interval flood and the constancy and predictability of monthly flows. The finding that 22 species (benthic and pelagic) were associated with gradients of antecedent low-flow hydrology indicates that these species (or functional trait groups) should be the focus of further analysis to explore hydro-ecological relationships in systems with regulated flow regimes. Editor Z.W. Kundzewicz; Guest editor M. Acreman Citation Arthington, A.H., Rolls, R.J., Sternberg, D., Mackay, S.J., and James, C.S., 2014. Fish assemblages in subtropical rivers: low-flow hydrology dominates hydro-ecological relationships. Hydrological Sciences Journal, 59 (3–4), 594–604.

Does stream flow structure woody riparian vegetation in subtropical catchments

Abstract The primary objective of this study was to test the relevance of hydrological classification and class differences to the characteristics of woody riparian vegetation in a subtropical landscape in Queensland, Australia. We followed classification procedures of the environmental flow framework ELOHA – Ecological Limits of Hydrologic Alteration. Riparian surveys at 44 sites distributed across five flow classes recorded 191 woody riparian species and 15, 500 individuals. There were differences among flow classes for riparian species richness, total abundance, and abundance of regenerating native trees and shrubs. There were also significant class differences in the occurrence of three common tree species, and 21 indicator species (mostly native taxa) further distinguished the vegetation characteristics of each flow class. We investigated the influence of key drivers of riparian vegetation structure (climate, depth to water table, stream‐specific power, substrate type, degree of hydrologic alteration, and land use) on riparian vegetation. Patterns were explained largely by climate, particularly annual rainfall and temperature. Strong covarying drivers (hydrology and climate) prevented us from isolating the independent influences of these drivers on riparian assemblage structure. The prevalence of species considered typically rheophytic in some flow classes implies a more substantial role for flow in these classes but needs further testing. No relationships were found between land use and riparian vegetation composition and structure. This study demonstrates the relevance of flow classification to the structure of riparian vegetation in a subtropical landscape, and the influence of covarying drivers on riparian patterns. Management of environmental flows to influence riparian vegetation assemblages would likely have most potential in sites dominated by rheophytic species where hydrological influences override other controls. In contrast, where vegetation assemblages are dominated by a diverse array of typical rainforest species, and other factors including broad‐scale climatic gradients and topographic variables have greater influence than hydrology, riparian vegetation is likely to be less responsive to environmental flow management.