Mesocosm and Microcosm Bioassays to Examine Effects of Mine-Influenced Sediments on the Growth of Wild Rice (Zizania palustris L.)

Wild rice (WR; Zizania palustris L.) growth response to sediment obtained from Rat River Bay (RRB; control site), Cleaver Lake (CL; legacy zinc-copper mine influenced), and Unnamed Lake (UL; active gold mine influenced) was evaluated by two bioassay systems: (1) a mesocosm-scale bioassay and (2) an accelerated-growth microcosm-scale bioassay. Following an entire growing season of 7 weeks, WR developed to near reproductive maturity, with similar observations using both systems. WR height (HT), dry weight biomass (DWB), and seed production (SP) were statistically higher in RRB than both CL and UL sediment-grown plants. Significant differences were not identified between mesocosm:microcosm ratios for DWB or SP; HT ratios were significant. Wild rice HT, DWB, and SP were statistically lower for CL and UL sediment-grown plants; however, visual differences in growth between sediments were documented mid-season. By the end of the season, ammonia-nitrogen (N) was below detection in CL and UL sediment and decreased by 93% in RRB sediment. Responses of WR to these sediment exposures appeared to be more influenced by ammonia-N concentration than other sediment constituents. Based on data obtained during this study, the microcosm-scale bioassay accurately represented the mesocosm-scale bioassay in terms of WR DWB and SP, both of which were visually recognized. Use of this microcosm-scale bioassay to obtain accurate representations of WR responses to site-specific sediment, or water, exposures can save industry and critical water resource managers time, money, and overall resources.

Automated summary

Wild rice growth response to sediment from different sources varies, mainly influenced by ammonia-N concentration. The microcosm-scale bioassay accurately represents the mesocosm-scale bioassay, offering the potential to save time, money, and resources.