Response of aquatic macroinvertebrates to early-spring drawdown in nodding smartweed marshes

Abstract

Effects of early-spring water-level reduction on aquatic macroinvertebrate populations were studied in four nodding smartweed (Polygonum lapathifolium L.) marshes in northwest Ohio. Water depths in two marshes were maintained at normal (>40 cm) overwinter levels then were reduced in early April each year to approximately 50% (20 cm) of over-winter depth. Water levels in two other marshes were allowed to fluctuate naturally throughout the study period. Aquatic invertebrate density and biomass were sampled from late March through mid-Junc in the water column, in the benthos, and on the surfaces of nodding smartweed plants. Invertebrate levels (activity, density, and biomass) in the water column were higher (P<0.05) in shallow marshes than in deep marshes. Benthic invertebrate levels in all marshes were low compared to invertebrate levels in the water column. Water-level reduction in smartweed marshes did not significantly increase benthic or periphytic invertebrate levels in shallow marshes over those in deep marshes.