Leaf-Nets (LN): A New Quantitative Method for Sampling Macroinvertebrates in Non-Wadeable Streams and Rivers

Abstract

The ecological knowledge of large rivers is still scarce or highly fragmented mainly because of complex, laborious and expensive procedures to collect informative samples from the benthic biota. Standard sampling protocols for macroinvertebrates were mainly developed and calibrated for wadeable streams, while a number of heterogeneous non-standard sampling procedures are available for large rivers. We propose the new, easy-to-build and cost-effective leaf-nets (LN) method to quantitatively sample benthic invertebrates in non-wadeable waterways. The LN method uses Phragmites australis leaves as substrate and combines the characteristics of the leaf-bags and the Hester–Dendy (HD) multiplates methods. We compared the effectiveness of the LN and HD methods in a near-pristine and in an impacted stream-reach (downstream an aquaculture plant) of a non-wadeable second-order stream of Central Apennines (Italy). Twenty-five of the 34 cumulatively collected macroinvertebrate taxa were common to both methods, while seven taxa were found only on LN and two only on HD. Taxonomic richness and total macroinvertebrate abundance were higher for LN assemblages. Number of Ephemeroptera, Plecoptera and Trichoptera taxa (EPT) also tended to be higher on LN. Assemblage composition was different on LN and HD. Both methods documented a significant decrease in EPT taxa and a concomitant increase in the total abundance of more pollution-tolerant taxa in the impacted stream-reach, but the LN method was more sensitive to impact-associated changes in macroinvertebrate assemblage structure. In contrast to the hardboard plates of HD, the assembled leaves of the LN may act as a direct or indirect food source and may better mimic the texture and composition of more heterogeneous natural substrates thus favouring the migration–colonization process from both bottom and littoral benthic invertebrates. The sampling efficiency, cost effectiveness and simplicity warrant the routine use of the new LN method in large-river ecological assessment. Copyright © 2015 John Wiley & Sons, Ltd.