Impact of peat moss released by a commercial harvesting operation into an estuarine environment on the sand shrimp Crangon septemspinosa

Abstract

Current methods used in harvesting peat in eastern Canada have raised concerns regarding potential impacts of escaped peat particles on aquatic ecosystems. A study was carried out in Mill Creek, an estuarine tributary of the Richibucto River in New Brunswick, where peat originating from a commercial operation has accumulated over several years. The sand shrimp Crangon septemspinosa Say (1818) was selected to determine potential environmental stress related to presence of peat in the sediment because of its close association with the substrate. Despite the introduction of sedimentation ponds at the harvesting site in 1994, peat particles continued to enter and accumulate in Mill Creek between 1997 and 1999. Increases in peat depth ranged from 6 to 31 cm and the volume of surficial (0–15 cm) sediments containing peat increased from 35% in 1997 to 44% in 1998 and 76% in 1999. Beach seine surveys carried out during July to September of 1996–1998 indicated that fewer sand shrimp occurred over substrates having higher (>66%) peat concentration than over sand or mud with lower (<33%) peat concentration. Length of sand shrimp did not vary consistently with peat concentration but sand shrimp caught over substrates containing medium (34–65%) peat concentration displayed lower condition [wet weight at total length (TL)] than conspecifics from substrates of both higher and lower peat concentration in all surveys. In a separate survey, peat was found in the stomachs of sand shrimp caught over substrates composed of high but not low peat concentration. We conclude that present mitigation measures at this site have been ineffective in preventing escape of peat moss into the estuarine environment and that the resulting peat deposition has reduced habitat quality for estuarine macrofauna as reflected in a reduction of the number and condition of sand shrimp.