Temporal and spatial patterns of insect emergence from a Lake Michigan coastal wetland

Abstract

Emergence traps were used to sample insects along a transect through a river delta wetland on Green Bay, Lake Michigan in an attempt to document spatial and temporal patterns in insect emergence. Various abiotic factors were also measured to determine which factors influenced these dynamics. Significant decreasing gradients in dissolved oxygen and pH with distance from the river, coupled with trends in sum nitrate (nitrate + nitrite), revealed that riverine water was mixing with wetland water up to 100 m from the wetland-river interface. Annual emerging insect densities decreased exponentially with distance from the river while emerging insect biomass decreased linearly with distance, both of which were significant. Insects were largely comprised of Chironomidae, which represented 7–88% of the insects emerging. Loss of biomass was largely due to emergence of Aeshnidae (0–34%), Libellulidae (0–69%), Coenagrionidae (0–23%), Siphlonuridae (0–63%), and Chironomidae (1–25%). Major Chironomidae emergence events occurred from early spring until early summer and again from late summer to early fall. These events were likely an important source of energy needed for avian egg production, duckling growth, or migratory flights. Spatial and temporal patterns revealed the importance of wetland areas adjacent to the Peshtigo River to emerging insects, as well as to the transient organisms that use them as a food source.