Article pubs.acs.org/est
Ecological Effects of Biochar on the Structure and Function of Stream Benthic Communities William H. Clements,*,† Ralph G. Stahl, Jr.,‡ and Richard C. Landis§ †
Department of Fish, Wildlife and Conservation Biology, Colorado State University, Fort Collins, Colorado 80523, United States DuPont Corporate Remediation Group, Chestnut Run Plaza, 974 Centre Road, Wilmington, Delaware 19805, United States § DuPont Engineering and Technology, Chestnut Run Plaza, 974 Centre Road, Wilmington, Delaware 19805, United States ‡
S Supporting Information *
ABSTRACT: The introduction of biochar, activated carbon, and other carbonaceous materials to aquatic ecosystems significantly reduces the toxicity and bioavailability of contaminants. However, previous studies have shown that these materials can have negative effects on aquatic organisms. We conducted field and mesocosm experiments to test the hypothesis that biochar altered the structure and function of stream benthic communities. After 30 d in the field, colonization by stoneflies (Plecoptera) was significantly lower in trays containing biochar compared to the results from the controls. In stream mesocosms, biochar increased macroinvertebrate drift and significantly reduced community metabolism. However, most measures of community composition showed little variation among biochar treatments, and significant responses were limited to a single stonefly species (Capnia confusa). When benthic communities were simultaneously exposed to biochar and Cu, effects were primarily associated with metal exposure. Because it is unlikely that biochar treatments would be employed in uncontaminated areas, these moderately negative effects should be considered within the context of the positive benefits associated with reduced contaminant bioavailability and toxicity. Additional research is necessary to improve our understanding of the mechanisms responsible for biochar effects on benthic communities and to identify the optimal application rates and size fractions that will maximize contaminant sorption but minimize potential negative effects.
■
traits.4 In contrast to these findings, other investigators have shown that the impact of these materials is relatively mild2 and that reduced contaminant bioavailability may outweigh ecological effects.6 In addition to potential toxicological effects of biochar on aquatic organisms, physical alterations in habitat associated with the transport and deposition of these materials are also possible.11 For example, loss of interstitial space as a result of biochar deposition in natural substrate may influence stream benthic communities or affect food resources for some groups. Because most studies of biochar or AC have examined soil or sediment amendments, little is known about these physical alterations or the effects of direct exposure. Finally, although laboratory studies have investigated responses of individual species to biochar, there have been relatively few controlled experiments investigating the effects on natural aquatic communities and ecosystem processes. The application of biochar in floodplains and associated stream banks has been proposed as a remediation procedure by which to address legacy contaminants such as mercury.12 However, because of the potential for release of these materials to aquatic ecosystems8 and the uncertainties associated with their effects on community and ecosystem processes, a better
INTRODUCTION Field and laboratory studies have shown that the introduction of carbonaceous materials such as activated carbon (AC) and biochar can significantly reduce the toxicity and bioavailability of some contaminants.1−3 The addition of these materials to contaminated sediments may provide a cost-effective alternative to more disruptive remediation strategies, such as dredging or capping.4 Despite results demonstrating the effectiveness of carbonaceous amendments at reducing contaminant bioavailability, relatively little is known about the ecotoxicological effects of these materials. With few exceptions,4,5 most of this research has been conducted in terrestrial ecosystem or focused on single species.1,6,7 Consequently, our understanding of longterm effects on aquatic organisms and on ecological processes is limited. Because of the potential for runoff and the leaching of toxic materials from soils amended with biochar, especially when applied to riparian habitats, potential risks to aquatic ecosystems should be evaluated.8 Furthermore, ecotoxicological studies of biochar and AC conducted in aquatic systems have reported conflicting results. In a comprehensive review of biological responses to activated carbon, Janssen and Beckingham6 reported adverse effects in approximately 20% of the 82 laboratory experiments examined, suggesting that the field application of these materials may be premature.9,10 The most common responses observed in these studies were effects on growth, lipid content, behavior, and survival.6 There is also evidence that effects of carbonaceous amendments on benthic communities are species-specific and related to life-history © XXXX American Chemical Society
Received: September 10, 2015 Revised: November 9, 2015 Accepted: November 11, 2015
A
DOI: 10.1021/acs.est.5b04400 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Article
Environmental Science & Technology
communities were removed from the stream, transferred to the SRL in 4 L coolers, and randomly assigned to biochar treatments (three trays per mesocosm). To compare the effects of direct exposure to those associated with chemicals leaching from biochar, we exposed benthic communities in the first mesocosm experiment to two size classes of biochar. After a 24 h acclimation period, the 16 streams were randomly assigned to four treatments (n = 4): control, large biochar (1.0−10.0 mm), small biochar (
