Coal pit lake closure by river flow through: risks and opportunities

Mark Lund, Melanie Blanchette, Colm Harkin & Paul Irving

Project background

This project (C23025) builds upon the previous ACARP project (C21038) undertaken by the Mine Water and Environment Research (MiWER) Centre in Collie (Western Australia). In project C21038 we identified that nutrients were limiting algal productivity, water quality improvements, and the development of ecosystem values in coal pit lakes. Small catchments commonly associated with pit lakes appeared to limit natural inputs of nutrients – particularly carbon. Terrestrial leaf litter and other coarse organic material stimulated macroinvertebrate biodiversity. There were increases in taxa abundance and richness and algal productivity, in the pit lakes, despite no improvement in overall water quality. The Collie pit lakes are acidic (pH down to 2), with high concentrations of some metals (such as aluminium) and range from fresh to brackish, yet contain little sulphate. The outcomes of the previous ACARP project (C21038) suggest that developing environmental values (e.g., increasing aquatic biodiversity) could be a valid alternative to meeting (often difficult) water quality guidelines for pit lake closure criteria and subsequent relinquishment.

Connecting a pit lake to natural drainage lines could increase the effective catchment size of the lake. The South Branch of the Collie River was diverted around the pit that would eventually form Lake Kepwari. In 2011, the diversion around the lake failed during storm flows, allowing river water to pass through the lake before returning to the river downstream. Downstream water quality parameters were within ANZECC/ARMCANZ (2000) guidelines for the protection of 80% of ecosystem values. Additionally, the flow-through event appeared to have improved the water quality (increased pH) and environmental values (macroinvertebrate biodiversity) of Lake Kepwari. Following the 2011 breech, a three-year trial allowing the lake to be deliberately connected to the seasonal Collie River was approved by Department of Water (WA).

Project objectives

ACARP project C23025 will use this unique trial to assess the impacts of connecting a river to a pit lake, particularly on downstream aquatic ecosystems. This project is also a trial of the concept that increasing effective catchment size has a positive effect on lake ecology.

The seasonal Collie River is degraded by secondary salinization, resulting in occasional highly saline flows. In ACARP project C23025, we will also assess the effects of saline river water on Lake Kepwari.

The main objective of this project is to determine the risks and opportunities associated with diverting a river through a mine pit lake. Specifically, we will:

  1. Determine the downstream effects of pit-lake decant, with a particular focus on environmental and amenity values.
  2. Determine the effects river of inflow on environmental values and water quality within the pit lake. (Essentially a field-scale demonstration of a key finding from C21038 that larger catchments should enhance pit lake water and environmental quality).
    1. Understand the impact of variably saline river water on mixing within a moderately saline pit lake.
  3. Develop a national standard protocol for seasonal river monitoring that could be applied by the coal industry to manage river flow-throughs (either accidental or planned), as a part of mine closure strategy.

Current activities

To commence this project, we have focused on site selection for monitoring the Collie River South. Sites have to be readily accessible, representative of the aquatic habitats of interest, and reflective of the overall nature of the catchment. We have also identified another local flow- through system for inclusion in the monitoring program. This new system is a small stream – topped up by dewatering flows from Griffin Coal operations–that flows through Stockton pit lake. Increasing replication (i.e., 21 sites across two flow-through systems) will enhance our ability to detect the impacts of river flow-through on river and pit-lake systems. In the process we have identified an additional 30 riverine potential sites in the Collie basin that could be useful for future research.

Regular monitoring of Lake Kepwari (as part of the trial conditions) occurs quarterly and we have added a similar monitoring program for Stockton Lake. Currently we have sampled Lake Kepwari five times and Stockton three. Preliminary data from Lake Kepwari indicates that the lake is stratified continually by salinity, enhanced by temperature stratification. Conductivity of the bottom waters is highest in March and June, possibly due to saline groundwater inflows. River inflow between August and October appears to slightly dilute the bottom waters (although the exact mechanism is not currently understood). Importantly, bottom pH is >6 during October, but then appears to return to 4.5 by June probably due to incoming acidity from groundwater. The installation of continuous monitoring gear in both lakes should help clarify the processes responsible for these water quality changes. We have used off-the-shelf monitoring gear that provides detailed insight into physical (stratification) and chemical (light, temperature, conductivity and dissolved oxygen) changes in a very economical package that could be used in any pit lake.

Value-adding

We have also value-added to the ACARP project with Edith Cowan University- funded support for an assessment of the impacts of catchment activities (mining, agriculture) on aquatic microbes in the Collie catchment. In November 2014, we hosted colleagues from Montana State University (USA) with whom we are collaborating on the microbial work. The microbial work is likely to prove highly beneficial to the mining industry by providing an economic way of understanding microbially-mediated environmental processes as well as developing microbes as tools for environmental assessment. In April 2015, we visited our colleagues at Montana State University to discuss and test how methodological differences might influence the microbial analysis.

Knowledge transfer

A paper on approaches to pit lake closure, based on ACARP projects C21038 and C23025 was presented at the International Mine Water Association (IMWA) Conference in Xuzhou, China in 2014. A copy of the paper can be obtained for free from http://imwa.info/docs/imwa_2014/IMWA2014_Lund_720.pdf. Abstracts based on work conducted in C21038 and a poster on our microbial work have been presented at ICARD/IMWA 2015 in Chile. Presentations on previous and current ACARP projects were made to the Hunter Coal Environment Group (NSW) in February 2015.

Figure 1. Section of Melaleuca- dominated river typical of SW Western Australia (Collie River South flowing into Lake Kepwari). Figure 2. Creek flowing into Lake Stockton.

Ecology of black-stripe minnow (Galaxiella nigrostriata, Pisces: Galaxiidae) in remnant populations on the Swan Coastal Plain, Western Australia

Dave M. Galeotti (MiWER), Clint McCullough (MiWER), Mark Lund (MiWER), Mark Gell (KSS)

What habitat requirements does a fish that live in seasonal wetlands have and how does this relate to rehabilitating these wetlands from mining?

The south-west of Western Australia is home to only ten native species of freshwater fish. Of those ten, eight are endemic and two of those species live in seasonal wetlands (most fish live where water is permanent!) One of those species, the black-stripe minnow, Galaxiella nigrostriata, is currently known only to exist in three locations in WA: Melaleuca Park near Perth, Kemerton near Bunbury and between Augusta and Albany. While the ‘southern’ distribution mainly occurs within National Parks, the two remnant populations are not as protected.

My research will look at what factors decide their habitat choice and ultimately what they require to survive. The information gathered will help direct the conservation and rehabilitation of wetlands for this unique species by understanding their ecological requirements. With a continuing. drying climate and further pressures on the wetlands from development and groundwater extraction, research into this fascinating fish is of great importance. Wetlands on the Swan Coastal Plain have a history of being filled, drained and/or degraded for agriculture, mining, urban sprawl and industrial uses. For example, one remnant population is on the project area of a sand mine. Luckily, the mining company is being proactive in their conservation efforts by funding research such as this.

There are four study components to my project: habitat and diet preferences, aestivation requirements and population genetic structure. The first three can be classed as the ecological requirements of the fish and the genetic component stands alone as an overall species management issue. Study results will provide information to help conserve this threatened species, direct wetland rehabilitation requirements on the mine project area and may be used to identify habitats likely to contain ‘new’ populations.

     

Photos: A seasonal wetland that only sometimes contains black-stripe minnow. September (left) and January (right).


Photos::Minnows are thought to aestivate in Koonac crayfish burrows

Funding:

Part of D. Galeotti’s MSc project. Funded by Kemerton Silica Sands

Outputs:

Galeotti, D. M.; McCullough, C. D. & Lund, M. A. (2010). Can meta-population theory explain survival of an aestivating fish species in a seasonal wetland complex? 31st Congress of the International Association of Theoretical and Applied Limnology. Cape Town, South Africa. 12–18 August. Societas Internationalis Limnologiae (SIL). PDF

Galeotti, D. M.; McCullough, C. D. & Lund, M. A. (2009). Can meta-population theory explain survival of an aestivating fish species in a seasonal wetland complex? Australian Society for Limnology 2009 Congress. Alice Springs, Australia. PDF

Galeotti, D. M.; McCullough, C. D. & Lund, M. A. (2010). Black-stripe minnow Galaxiella nigrostriata (Shipway 1953) (Pisces: Galaxiidae), a review and discussion. Journal of the Royal Society of Western Australia 93: 13-20. link

Galeotti, D. M.; McCullough, C. D. & Lund, M. A. (2008). A synthesis of Black-striped Minnow (Pisces, Galaxiidae: Galaxiella nigrostriata) ecological requirements, south-western Australia. Centre for Ecosystem Management Report 2008-12. Edith Cowan University, Perth, Australia. Unpublished report to Kemerton Silica Sand Pty Ltd. PDF

Galeotti, D. M., Castalanelli, M., Groth, D. M., McCullough, C. D. & Lund, M. A. (2014). Genotypic and morphological variation between Galaxiella nigrostriata (Galaxiidae) populations: implications for conservation. Marine and Freshwater Research.

Article on WA Science Network entitled WA’s back-stripe minnow research continues link

Article on ABC News link