Organic Matter Decay via Cotton Strips
The following is a very brief synapsis of what organic matter decay is, and why we use cotton strips for this measurement. I’m in the process of making ~170 cotton strips to be taken to Ecuador and used as a part of our study.
Our methods and the following comes from two papers and citations therein (Tiegs et al. 2007, 2013)
To understand how non-native trout farms are affecting streams and the biota, it is best to look at them from various perspectives. That is why our project involves frogs, benthic macroinvertebrates, stream chemistry, and organic matter decay. Organic matter decay is a functional, or process based, analysis of our sample streams and will take place above and below non-native trout farms. Historically, and in most studies, today, leaf litter is used to perform this type of analysis. This involves placing dried and weighed leaf litter into mesh bags. After a designated length of time, the bags are removed, dried, and re-weighed. The object is to determine how much leaf mass was lost, a measure of how effective the stream is at processing organic matter. However, this method has some drawbacks. First, it is very difficult to standardize the leaf litter placed into each bag, let alone across large geographical areas. Second, not all leaf types decompose at the same rate (oak is takes a while compared to beech leaves). Finally, the amount of weight lost due to decay can be tricky to measure. If stream turbulence causes fractionation of the leaves prematurely, leaves may weigh less than would be expected. Alternatively, the buildup of fungi and bacteria on the leaves can cause the leaves to weigh more than expected. To combat this, standardized cotton strip essays have been developed. Using artists’ fabric, strips of cloth are cut the same length and the same width (measured by thread count). These strips are deployed into the streams in a similar manner to leaf-litter bags. They are secured to the bottom of the stream in a riffle, a shallow area with increased water velocity. After 2-4 weeks, they are removed, treated with ethanol to stop decay, dried and prepared for analysis. To determine the level of decay, each cotton strip is placed into a tensiometer (measures tensile strength; cool name, right?) and literally pulled apart. We record the amount of force it takes for the threads to start breaking. The more decay, the easier it is to pull them apart, the lower the force measured. We then adjust the measurements for the temperature of the water (warmer water increases decay rate) and we can compare our sites and streams. Kind of cool and elegant really.
Tiegs S.D., Clapcott J.E., Griffiths N.A. & Boulton A.J. (2013) A standardized cotton-strip assay for measuring organic-matter decomposition in streams. Ecological Indicators 32, 131–139.
Tiegs S.D., Langhans S.D., Tockner K. & Gessner M.O. (2007) Cotton strips as a leaf surrogate to measure decomposition in river floodplain habitats. Journal of the North American Benthological Society 26, 70–77.
Freshly cut, measured and frayed, cable tie added (strip ready to go)
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