Abstract
Anthropogenic perturbations impact aquatic systems causing wide-ranging responses, from assemblage restructuring to assemblage recovery. Previous studies indicate the duration and intensity of disturbances play a role in the dynamics of assemblage recovery. In August 2011, the Pearl River, United States, was subjected to a weak black liquor spill from a paper mill which resulted in substantial loss of fish in a large stretch of the main channel. We quantified resilience and recovery of fish assemblage structure in the impacted area following the event. We compared downstream (impacted) assemblages to upstream (unimpacted) assemblages to determine initial impacts on structure. Additionally, we incorporated historic fish collections (1988–2011) to examine impacts on assemblage structure across broad temporal scales. Based on NMDS, upstream and downstream sites generally showed similar assemblage structure across sample periods with the exception of the 2 months postdischarge, where upstream and downstream sites visually differed. Multivariate analysis of variance (PERMANOVA) indicated significant seasonal variation among samples, but found no significant interaction between impacted and unimpacted assemblages following the discharge event. However, multivariate dispersion (MVDISP) showed greater variance among assemblage structure following the discharge event. These results suggest that 2 months following the disturbance represent a time period of stochasticity in regard to assemblage structure dynamics, and this was followed by rapid recovery. We term this dynamic the “hangover effect” as it represents the time frame from the cessation of the perturbation to the assemblage's return to predisturbance conditions. The availability and proximity of tributaries and upstream refugia, which were not affected by the disturbance, as well as the rapid recovery of abiotic parameters likely played a substantial role in assemblage recovery. This study not only demonstrates rapid recovery in an aquatic system, but further demonstrates the value of continuous, long-term, data collections which enhance our understanding of assemblage dynamics.
Highlights
Pollution of aquatic systems through industrial, municipal, and/or agricultural discharge is well known to negatively impact aquatic communities (Detenbeck et al 1992; Ensign et al 1997; Ryon 2011)
Fish assemblage recovery following these types of perturbations has occurred relatively quickly (Meffe and Sheldon 1990; Peterson and Bayley 1993; Albanese et al 2009), whereas in other situations, it has taken years to return to preperturbation conditions (Detenbeck et al 1992)
Ecology and Evolution published by John Wiley & Sons Ltd
Summary
Pollution of aquatic systems through industrial, municipal, and/or agricultural discharge is well known to negatively impact aquatic communities (Detenbeck et al 1992; Ensign et al 1997; Ryon 2011). These types of disturbances are referred to as “pulse” disturbances (Bender et al 1984), as they rapidly impact species numbers, but are followed by a return to an equilibrium state.
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