: Effects of extreme floods on macroinvertebrate assemblages in tributaries to the Mohawk River.

MIRIAN CALDERON; ALEXANDER SMITH; BARRY BALDIGO; TED ENDRENY

Schenectady, New York

Simposio; Mohawk Watershed Symposium.; 2015

Union College

The increase in the occurrence of hurricanes in the US, and the following flooding, raises the need for a better understanding of their ecological consequences in our aquatic ecosystems. Floods constitute a major disturbance to streams, causing changes in ecosystem, community or population structure through the modification of their habitats. Macroinvertebrates are particularly susceptible to changes of flow, and although some communities have co-evolved with the stream geomorphology and are relatively resilient to extreme hydrologic events, macroinvertebrates have showed mixed responses to changes in peak flow,mean discharge, baseflow or hourly flow. In general, invertebrate communities often exhibit low resistance to extreme floods and the threshold at which flow alteration causes negative impact is still unknown.In August 2011, remains of Hurricane Irene hit New York State, bringing torrential rainfall. River flooding records were broken in several tributaries of the Mohawk River basin, making this event one of the most devastating ever recorded in the Mohawk Watershed. After the storm retreated, mitigation plans included channelization and sinuosity reduction in some of the affected streams.The objective of this study was to increase the understanding of the impacts of extreme floods on benthic macroinvertebrate communities and determine how flood magnitude and flood-remediation efforts help either to resist adverse effects or recovery (increase resilience or resistance) from extreme hydrologic events. Macroinvertebrates data were collected in 13 sites along the Mohawk River Basin in August 2011, as part of the DEC-NYS Rotating Integrated Basin Studies (RIBS). In October 2011, six weeks after the floods, a second set of samples were taken at the same sites in order to assess the flood impacts. New data sets were collected in July and October 2014. The metrics used to estimate the effect of the flood include: taxa richness, EPT richness, Hilsenhoff?s Biotic Index (HBI), Percent Model Affinity (PMA), Nutrient Biotic Index-Phosphorus and Biological Assessment Profile (BAP). StreamStats Program for New York State was used to estimate peak discharges, Annual Exceedence Probabilities (AEP) and Recurrence Intervals (RI) of the storm at the ungagged sites.This study aims to increase the understanding of the damages caused by floods, and provide substantial evidence about the recovery of these natural systems.