Differences between two methods measuring the decomposition of organic matter in an aquatic system

Abstract

The decomposition of organic matter in aquatic systems is a critical component of ecosystem health and can be used as an indicator of water quality, water chemistry, fish and microorganism community function. The deployment of leaf packs is a common method used to measure the decay rate of organic matter in aquatic systems. Recent studies have begun to use cotton strips as a surrogate for leaf packs, which have been used in the study of organic decomposition in soils. This study aimed to quantify any differences and the relationship between leaf packs and cotton strips, with an additional comparison of caged and uncaged cotton strips. Percentage mass loss per degree day was used to compare leaf packs and cotton strips, and tensile strength was used to determine the difference between caged and uncaged strips. A total of 378 samples (128 for leaf packs, 128 for caged cotton strips and 128 for uncaged cotton strips) were placed in three watersheds, and each watershed had six sites. There were significant differences between leaf packs and cotton strips, and site had the strongest effect, which may reflect confounding factors such as water velocity, temperature, pH, and variability in water chemistry. There was no significant difference between caged and uncaged cotton strips, which indicated that the cage used in the study had no impact on the decomposition of cotton strips. Also, tensile strength was shown as another valid way to determine the decay rate of cotton strips, as a measure of stream function. For future research, the uncaged cotton strips would be the best method, saving both time and labour. Key words: leaf pack, cotton strips, organic matter, decomposition, stream system, percentage mass loss per average degree day, tensile strength