Decomposition Rate and Community Structure of Leaf-packs in an Urban and Rural Stream in Southwestern Missouri

Abstract

Previous studies demonstrated significantly lower diversity and density of aquatic invertebrates in a southwestern Missouri urban stream, Turkey Creek, below a large mall in comparison to above mall sites and a rural stream, Jones Creek. Such invertebrate declines might affect leaf decomposition rates in these streams. We estimated decomposition rate and macro-invertebrate community structure using experimental leaf-packs composed of freshly dried red elm leaves. Thirty-six leaf-packs housed in polyester mesh (2 by 4 mm) bags were anchored in riffles at the three sites. Bags were recovered after 15 and 36 days, invertebrates were removed and identified, and leaf residue air dried. Decay rates as fraction lost/day after 15 days were 4.20%/day Turkey Creek above mall, 4.43%/day Turkey Creek below mall, and 4.45%/day at Jones Creek. After 36 days decay rates were 2.14%/day Turkey Creek above mall, 2.15% Turkey Creek below mall, and 2.36%/day Jones Creek. Rates were not significantly different between sites (ANOVA, P = 0.55 at 15 days and P = 0.23 at 36 days). Decay constants calculated by regressing % dry mass remaining and days in stream were −0.040/day for both Turkey Creek above and below mall and −0.056/day for Jones Creek. Shredders were primarily represented by the cranefly larvae Tipula abdominalis in both TC sites and by T abdominalis and the isopod Lirceus hoppinae in JC. Collector-gatherers, primarily net-spinning caddisflies Cheumatopsyche, Ceratopsyche, and Chimarra, as well as the dipteran family Chironomidae, numerically dominated leaf-packs. Leaf decomposition may be more related other factors, physical fragmentation, microbial processes, and seasonal differences in leaf abundance, than shredding in these streams. Dominance of collector-gatherers appears to indicate leaf-packs serve primarily as habitat and not a direct energy source for many stream macroinvertebrates.