Ecological and statistical models to configure flow regime for environment benefit in highly engineered rivers: a case study in the MacKenzie River, Southeast Australia.

Ecological and statistical models were developed using freshwater algal assemblages to assess water quality and ecological health of a regulated river. These models were used to inform configuration of flows to maintain or improve environmental conditions of the waterway whilst meeting consumptive water supply commitments. The flow regime of the MacKenzie River, western Victoria, Australia, has been substantially modified since the construction of a water supply reservoir on its upper reach in 1887. Water is withdrawn at several locations downstream of the reservoir, creating a substantially modified flow regime, impacting key environmental values of the river. To assess the impact of the different flow regimes on river health and ecosystem function, ten sites were repeatedly sampled along the river between February 2012 and April 2014. Physical and chemical characteristics of water, including pH, temperature, turbidity, electrical conductivity, dissolved oxygen, total nitrogen, total phosphorous, cations, and anions, were measured. Biological properties of the algal periphyton communities, including dry mass, ash-free dry mass, chlorophyll-a concentration, and species composition, were also measured. Exploration of the algal assemblage and water chemistry data using the computationally unconstrained ordination technique such as principal component analysis principal component analysis (PCA), correspondence analysis (CA), detrended correspondence analysis (DCA), and canonical correspondence analysis (CCA) indicated two strong gradients in the data sets. Furthermore, the quantitative ecosystem response models have been developed as the prototype tool to assist in the future configuration of flows in this river. The empirical data and models showed the lower reaches of the river to be in poor condition under low flows, but this condition improved under flows of 35 ML/day, as indicated by the reduction in green algae and cyanobacteria and improvement. Finally, the results are presented to tailor discharge and duration of water volume by amalgamation of consumptive and environmental flows to improve the condition of the stream thereby supplementing the flows dedicated to environmental outcomes.

Community structure and ecological responses to hydrological changes in benthic algal assemblages in a regulated river: application of algal metrics and multivariate techniques in river management.

The flow regime of the Wimmera River was substantially modified due to the construction of a water supply reservoir. Samples of diatoms and soft algae and measurements of water quality were analysed at ten sampling sites for 3 years (between February 2012 and November 2014) along the MacKenzie River, a tributary of the Wimmera River, in different seasons and under different flow regimes, to understand the spatial and temporal variation in the relationship between algal communities, water quality and stream condition. Baseline information on algal communities and water quality was collected during base flow conditions, while experiments on the effect of water releases on algal communities were based on flow regime variations (manipulated flow regimes), specifically on the algae community structure, water quality and ecosystem function. Algal species composition changed along the river under different flow regimes and different seasons. Under base flow, Bacillariophyta (diatoms) were more abundant upstream, and filamentous green algae were more abundant downstream. The results showed that the algal composition shifted downstream after water release events. Chlorophyta (green algae), Cyanophyta (blue-green algae) and Chrysophyta gradually increased from upstream to downstream under base flow conditions and before water releases, whereas diatoms were greater upstream and increased downstream after water releases. The results are presented to tailor discharge and duration of the river flows by amalgamation of consumptive and environmental flows to improve the condition of the stream thereby supplementing the flows dedicated to environmental outcomes.

Organic pollutants, heavy metals and toxicity in oil spill impacted salt marsh sediment cores, Staten Island, New York City, USA.

Sediment cores from Staten Island's salt marsh contain multiple historical oil spill events that impact ecological health. Microtox solid phase bioassay indicated moderate to high toxicity. Multiple spikes of TPH (6524 to 9586 mg/kg) and Σ16 PAH (15.5 to 18.9 mg/kg) were co-incident with known oil spills. A high TPH background of 400-700 mg/kg was attributed to diffuse sources. Depth-profiled metals Cu (1243 mg/kg), Zn (1814 mg/kg), Pb (1140 mg/kg), Ni (109 mg/kg), Hg (7 mg/kg), Cd 15 (mg/kg) exceeded sediment quality guidelines confirming adverse biological effects. Changes in Pb206/207 suggested three metal contaminant sources and diatom assemblages responded to two contamination events. Organic and metal contamination in Saw Mill Creek Marsh may harm sensitive biota, we recommend caution in the management of the 20-50 cm sediment interval because disturbance could lead to remobilisation of pre-existing legacy contamination into the waterway.