Exploratory study of suspended sediment concentrations downstream of harvested peat bogs

Abstract

Peat bog harvesting is an important industry in many countries, including Canada. To harvest peat, bogs are drained and drainage water is evacuated towards neighboring rivers, estuaries or coastal waters. High suspended sediment concentrations (SSC) were found in the drainage water at one particular site during the 2001-2002 spring seasons in New Brunswick (Canada). The main objective of this study was to verify this observation at other sites, compare SSC levels leaving harvested peat bogs with those leaving an unharvested bog, and to determine if high SSC events happen only in Spring or all year round. Suspended sediment concentrations were monitored downstream of three harvested peat bogs and an unharvested reference bog located in New Brunswick during the ice free seasons of 2003-2004. On average, SSC at the harvested sites exceeded 25 mg/l, which is the recommended daily maximum concentration, 72% of the time, while the same concentration was exceeded 30% of the time at the unharvested sites. SSC were found to be significantly higher at harvested sites than at the reference sites for all seasons. The highest SSC medians were recorded in the Fall but SSC was elevated in all seasons. High SSC levels in receiving waters may be caused by field ditching activities and insufficient sediment controls. Findings suggest the NB Peat Harvesting 25 mg/l SSC guideline should be reviewed.

An Evaluation of Mitigation Measures to Reduce Impacts of Peat Harvesting on the Aquatic Habitat of the East Branch Portage River, New Brunswick, Canada

“…Other studies have shown that the 25 mg/L guideline can be exceeded more than 60% of the time in some harvested peatlands (e.g., Pavey et al, 2007). In this study, 25 mg/L was exceeded 36% of the time at the most impacted location (Site 2) in 2007 (entire time series considered).…”

“…were expressed as DC voltages and were converted to SSC (mg/L) using calibration curves. The calibration for each OBS was performed using the methodology described by Pavey et al (2007). In addition, hourly flow measurements were recorded at Site 1.…”

“…The water quality station at Site 1 was operational two years prior to drainage of the exploited area (Phase 1;2005-2006. All three stations were operational during the initial peatland development (Phase 2;2007). Daily operations at the peatland were recorded by the developer.…”

“…Such impacts include peatland drainage to increase forest and agricultural productivity (Coulson et al, 1990;Minkkinen and Laine, 1998) and commercial peat harvesting Pavey et al, 2007). In Canada, most of the peat produced is extracted using the vacuum harvesting method (Daigle et al, 2001).…”

“…In some cases, drainage water with high sediment loads has been shown to have detrimental impacts on aquatic ecosystems (Ouellette et al, 2006). In studies of three New Brunswick harvested peatlands, the current provincial guideline of 25 mg/L for suspended sediment concentration (Thibault, 1998) was exceeded more than 60% of the time during three ice-free seasons Pavey et al, 2007).…”