Organic Matter Breakdown As a Measure of Stream Health in New Zealand Streams Affected by Acid Mine Drainage


Functional indicators of stream health have the potential to provide insights into stream condition that cannot be gained by traditional structural indices. We examined breakdown of leaves, wood, and cotton cloth strips at 18 sites along a gradient of effects of drainage from coal mines in New Zealand to determine the usefulness of these methods as functional indicators of stream health. The pH varied from 2.7 to neutral across the streams, and the more acidic streams typically had higher concentrations of aluminum, iron, zinc, and other metal ions. Precipitates of metal (mainly iron) hydroxides were present in most streams affected by mine drainage, especially in those with a pH of 4-5. Breakdown rates of all organic matter types were highest in several reference streams with neutral pH and lowest in sites with high rates of metal hydroxide deposition. Breakdown was relatively fast in the most acidic streams (pH < 3), in some cases as fast as at reference sites; these sites also had elevated nutrient concentrations. Shredding invertebrates were absent in litterbags from acidic streams and common at only 2 reference sites; their presence contributed to fast breakdown of leaves in the field and in lab microcosms. Microbial respiration was closely related to breakdown rates of leaves and wood; it was high at neutral and highly acidic streams, but lower at sites with pH 4-5, where metal hydroxides were precipitating onto solid surfaces. In these metal hydroxide-stressed streams, leaf and wood breakdown was slower, and associated biota, including microbes, were more affected than by water chemistry stressors (pH, dissolved metals) associated with mine drainage. Litter breakdown and microbial respiration provide insight into the functioning of streams, yielding different responses than traditional structural measures based on macroinvertebrates, which did not accurately distinguish impacts from acid mine drainage.


Biological Sciences


Foundation for Research, Science and Technology of New Zealand


Funding for this project was provided by the Foundation for Science, Research and Technology of New Zealand (Grant CRLX0401).

Keywords and Phrases

Acid Mine Drainage; Acidic Streams; Dissolved Metals; Ecosystem Functions; High Rate; Litter; Litterbags; Macroinvertebrates; Metal Hydroxide; Microbes; Microbial Respiration; Mine Drainage; Neutral PH; New Zealand; Nutrient Concentrations; Reference Sites; Reference Streams; Solid Surface; Stream Condition; Stream Health; Structural Indices; Structural Measures; Water Chemistry; Aluminum; Bacteria; Biogeochemistry; Biological Materials; Coal Mines; Decomposition; Drainage; Health; Indexing (Materials Working); Metal Ions; Metals; Organic Compounds; Acidity; Coal Mine; Concentration (Composition); Environmental Indicator; Microbial Activity; Nutrient Availability; Organic Matter; PH; Precipitation (Chemistry); Streamwater; Gossypium Hirsutum; Invertebrata

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Article - Journal

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© 2013 Elsevier, All rights reserved.

Publication Date

01 Jan 2013