Integrating simulation models and statistical models using causal modelling principles to predict aquatic macroinvertebrate responses to climate change.

Climate change is projected to threaten ecological communities through changes in temperature, rainfall, runoff patterns, and mediated changes in other environmental variables. Their combined effects are difficult to comprehend without the mathematical machinery of causal modelling. Using piecewise structural equation modelling, we aim to predict the responses of aquatic macroinvertebrate total abundance and richness to disturbances generated by climate change. Our approach involves integrating an existing hydroclimate-salinity model for the Murray-Darling Basin, Australia, into our recently developed statistical models for macroinvertebrates using long-term monitoring data on macroinvertebrates, water quality, climate, and hydrology, spanning 2,300 km of the Murray River. Our exercise demonstrates the potential of causal modelling for integrating data and models from different sources. As such, optimal use of valuable existing data and merits of previously developed models in the field can be made for exploring the effects of future climate change and management interventions.

Insight into the multi-decadal effects of floods on aquatic macroinvertebrate community structure in the Murray River using distributed lag nonlinear models and counterfactual analysis.

We describe the multi-decadal delayed effects of flood on macroinvertebrate community structure using 33 years of monitoring data on macroinvertebrates, water quality, and climate, and 51 years of hydrological data, spanning 2300 km of the Murray River, Australia. We used distributed lag nonlinear models in a four-step analytical process, including 1) modelling macroinvertebrate community structure, represented as a set of principle coordinate axes, as a function of a lagged hydrologic index and other environmental variables using distance-based redundancy analysis 2) visualizing the patterns of delayed effects of flows on the PCO axes, 3) modelling the abundances of groups of taxa along individual PCO axes, and 4) combining the two sets of models in a counterfactual analysis to predict the community structure under flood and no-flood scenarios to describe the multi-decadal trajectory of the community following a flood. Our findings show an increase in abundance of most taxa of filtering-gathering collectors, scrapers, and shredders in the long term that implicates an influx of organic matter of all sizes, from particulate organic matter to coarse and large woody debris, that serves directly or indirectly as a food resource and/or habitat. Our approach enabled the isolation of a flood impact from the confounding effects of other flow events and environmental variables, overcoming a substantial challenge in ecohydrological studies.

Improving ecological response monitoring of environmental flows.

Environmental flows are now an important restoration technique in flow-degraded rivers, and with the increasing public scrutiny of their effectiveness and value, the importance of undertaking scientifically robust monitoring is now even more critical. Many existing environmental flow monitoring programs have poorly defined objectives, nonjustified indicator choices, weak experimental designs, poor statistical strength, and often focus on outcomes from a single event. These negative attributes make them difficult to learn from. We provide practical recommendations that aim to improve the performance, scientific robustness, and defensibility of environmental flow monitoring programs. We draw on the literature and knowledge gained from working with stakeholders and managers to design, implement, and monitor a range of environmental flow types. We recommend that (1) environmental flow monitoring programs should be implemented within an adaptive management framework; (2) objectives of environmental flow programs should be well defined, attainable, and based on an agreed conceptual understanding of the system; (3) program and intervention targets should be attainable, measurable, and inform program objectives; (4) intervention monitoring programs should improve our understanding of flow-ecological responses and related conceptual models; (5) indicator selection should be based on conceptual models, objectives, and prioritization approaches; (6) appropriate monitoring designs and statistical tools should be used to measure and determine ecological response; (7) responses should be measured within timeframes that are relevant to the indicator(s); (8) watering events should be treated as replicates of a larger experiment; (9) environmental flow outcomes should be reported using a standard suite of metadata. Incorporating these attributes into future monitoring programs should ensure their outcomes are transferable and measured with high scientific credibility.

Assessing the potential for using wetlands as intermediary storages to conjunctively maintain ecological values and support agricultural demands.

Water sharing to meet both agricultural and environmental demands is a critical issue affecting the health of many floodplain river systems around the world. This study explored the potential for using wetlands as temporary off-river storages to conjunctively maintain ecological values and support agricultural demands by assessing the effects of artificial drawdown on wetland aquatic plant communities. An initial experiment was undertaken in outdoor mesocosms in which four different treatments were compared over a 131 day duration: (1) natural drawdown where the water was left to drawdown naturally via evaporation; (2) partial drawdown where approximately half of the volume of water was pumped out after 42 days; (3) stepped drawdown where approximately half of the volume of water pumped out after 42 days, and then the remaining volume of water was pumped out after 117 days; and (4) total drawdown where all of the of water was pumped out after 117 days. A complementary field study was subsequently undertaken where two wetlands were left to drawdown naturally and two were partially drawn down artificially (i.e. had approximately half of their volume removed by pumping). Results from both of these studies indicated that neither aquatic plant abundance nor taxon richness were adversely affected by partial drawdown. Rather, both studies showed that aquatic plant communities subjected to a partial drawdown treatment became more species rich and diverse than communities subjected to a natural drawdown treatment. This suggests that it may be possible to use wetlands as intermediary storages for the dual purposes of maintaining ecological values and supporting agricultural demands.