Influence of Sieve Mesh Size on Relationships between Macroinvertebrate Assemblage and Environmental Variables in Wetlands

Macroinvertebrates are often excluded from wetland monitoring because samples collected using a conventional 500-μm mesh sieve are time consuming to process. To facilitate increased cost-effectiveness of obtaining macroinvertebrate data, influence of sieve mesh size on relationships between macroinvertebrate and environmental variables was evaluated in 27 prairie pothole wetlands. Benthic and water-column samples were washed through sieves with mesh sizes of 6 mm, 4 mm, 2 mm, and 500 μm, and macroinvertebrate numerical densities and taxon richness were quantified. Influence of particulate matter was evaluated by washing invertebrates through sieves before and after removal of this material from samples, and calculating differences in density and taxon richness. Regardless of sieve mesh size and particulate matter abundance, macroinvertebrate taxon richness exclusive of taxa occurring in all wetlands (planorbid snails, oligochaetes, leeches, chironomids) was positively correlated with plant cover, and negatively correlated with turbidity and fish biomass (p ≤ 0.05).Use of a 6-mm mesh sieve reduced sample volume by 35% and processing time by 54% relative to the 500-μm mesh sieve. Results suggest that reliance on taxon richness metrics and a sieve with 6-mm mesh will reduce macroinvertebrate sampling costs while still generating data that reflect wetland condition.