Water Quality and Macroinvertebrate Community Structure of Mining Lakes and Ponds across New Zealand

Abstract

Mining operations often create standing water bodies ranging from small ponds to large lakes, which form in a variety of structures such as remnant pits, strip-mine ponds, and water treatment structures that may be subjected to acid mine drainage (AMD) generation. The structure and chemistry of these systems can be quite variable, and little is known about their biotic communities in New Zealand and how they respond to active mining, mine abandonment and rehabilitation. This study examines the water chemistry, physical habitat and macroinvertebrate community composition of mine lakes and ponds encompassing a variety of mining types, geography, age, and rehabilitation settings across New Zealand. Physicochemical parameters across mining lakes showed an association between metals and sulphate, and between phosphorus and nitrogen, suggesting two main types of influences: mining activity (AMD) and elevated nutrient inputs from agricultural catchments, respectively. Both mining activities and agricultural practises may enhance concentrations of some toxic metals such as Cd and As in these systems. The degree and type of impact would depend on the different regional setting in which each lake is embedded including underlying geology, catchment land cover, aging, and rehabilitation status. Results based on both field and laboratory observations suggest that metal concentrations alone do not determine taxa richness and diversity in mining lakes. However, when combined with low pH (<4) their synergistic impacts greatly affected invertebrate communities, leading to low taxa richness and diversity, and communities dominated by collector chironomids, Oribatida, Hemiptera, and predator beetles, and very low abundance of zooplankton. Lakes subject to severe eutrophication also showed a great impact on macroinvertebrate communities, which may indirectly relate to the high turbidity that typically diminishes light availability for macrophyte growth, causing loss of habitat and food source for many species. Communities in highly eutrophic lakes were dominated by chironomids, shrimps, mites, and Oligochaeta. Physical habitat parameters such as submerged macrophytes, tall grasses and substrate index showed a positive influence on taxa richness. Particularly, submerged macrophyte appear to be a particularly good driver for the abundance of scraper and piercer. Restoration of mining lakes in New Zealand should firstly focus on the enhancement and maintenance of good water quality in terms of pH and trace metal concentrations over time. However, suitable physical habitat rehabilitation –considering both littoral and riparian zones– as well as damping of surrounding land cover pressures are fundamental factors that should not be neglected when planning self-sustaining rehabilitation.