Can pollution severity affect diatom succession in streams and could it matter for stream assessments?

Abstract

While the succession of benthic diatoms on scoured substrata has been widely studied to better understand community recovery from high flow disturbances, how anthropogenic stressors affect this common and dynamic process has received little attention; yet, it could have consequences for bioassessment and subsequent management decisions. Our objectives were to examine if the severity of acid mine drainage (AMD), a stressor of common concern in several countries, affected patterns of community development, diversity, and stream assessment outcomes (based on diatom metrics and indices) when diatoms are sampled during succession. In southeastern Ohio (USA), we deployed unglazed ceramic tiles in three streams along an AMD-impact gradient and in a control stream with no upstream AMD sources, and we sampled diatoms on days 5, 12, 19, 26, and 33. Diatom diversity decreased as AMD severity increased. In more severely AMD-impacted streams, diatom succession was simplified with less community turnover during the 33-day study than the least impacted AMD stream and control stream. Variability in community structure, diversity, and index scores was greatest at the least impacted AMD site. This stream was misclassified during succession by the Diatom Model Affinity index (severely impaired, then unimpaired, then ultimately moderately impaired) and the AMD-Diatom Index of Biotic Integrity (fair condition, then ultimately good condition). The control stream and the two more severely AMD-impacted streams were never misclassified during succession. Severe pollution may reduce niche availability by overriding effects of other environmental gradients important to diatoms (e.g., light and nutrients). The variability at intermediate stressor levels might lead to misclassification and misdirected management decisions if care is not taken to ensure a community has fully recovered from disturbance. © 2013 Taylor and Francis Group, LLC.