Recovery of community structure and leaf processing in a headwater stream following use of a wetland passive treatment system to abate copper pollution

Abstract

A wetland passive treatment system (PTS) was used to treat mine effluent flowing into East Prong Creek, Virginia. Prior to treatment, copper concentrations in the stream ranged from 8.9 to 32.0 μg/L at the impacted sites and from 0.1 to 7.7 μg/L at the reference site. In kick samples, insect abundance (n) and the number of taxa (#) were reduced at the impacted sites (n = 31, 22, 33, 24 and # = 190, 246, 266, 345, at sites 2 - 5, respectively) relative to the reference site (n = 52, # = 973). Red maple (Acer rubrum) leaves broke down twice as fast at the reference site (k = -0.029) than at sites receiving the untreated effluent (k = -0.016, -0.013, -0.013, -0.013 at sites 2 - 5, respectively). In benthic samples and leaf packs, abundances of all functional groups were reduced at the impacted sites relative to the reference site. In terms of abundance, scrapers and predators were most and least affected by copper, respectively.

Following treatment, copper concentrations at the impacted sites in East Prong Creek ranged from 0.1 to 14 μg/L. The wetland PTS was most effective at reducing metal concentrations in the effluent from July to December, when dissolved oxygen concentrations in and flow through the wetland cells were low.

Functional recovery preceded recovery of community structure by at least six months. Decomposition rates were similar at all sites in Fall 1994, after six months of treatment (k = -0.012, -0.011, -0.011, -0.012, -0.012) at sites 1 - 5, respectively). Recovery of community structure was not complete after 1 year of treatment. Abundance of collector-filterers and predators recovered quickly following treatment, while recovery of collector-gatherers and shredders was slower.