Research Summary

Peatlands are specialized wetlands that serve as a source of water laden with biologically significant nutrients used in downstream aquatic ecosystems. These waterlogged, anoxic, and acidic systems slow down decomposition and accumulate large stocks of poorly decomposed organic material, called peat (Landry & Rochefort, 2012). When dried, peat is a desirable growing medium for horticulture. Horticultural peat extraction is an expanding industry in Canada that changes important peatland physical and chemical parameters that can alter the concentration and mobility of nutrients stored in the peat. As water moves through the peat, these compounds can leach into ditches and be transported off site. Elevated concentrations of nutrients in outflow water can increase water quality degradation, elevate water treatment costs, and may cause eutrophication in downstream aquatic ecosystems (Niedermeier & Robinson, 2009; Worrall et al., 2007). Understanding the changes to the physicochemical environment when the peatland is altered can help estimate the potential leaching risk of nutrients available in peat surface soils, and help predict the impact, if any, to downstream aquatic ecosystems.

This study investigates the potential impact of peat extraction activities on the availability of chemical compounds able to leach into surface water and be transported off-site. A systematic, stratified sampling technique was used to conduct transects within undisturbed, extracted, and restored peat fields. Peat temperature, soil moisture, depth of rust, and depth of ice were measured at each location to assess the physicochemical factors influencing nutrient availability in surface peat. Plant Root Simulator (PRS®, Western Ag Innovations) probes were installed at each measurement location to measure available nitrogen over a four week span. During this sampling period, water chemistry was collected at outflow locations from each peat extraction phase to determine if nutrients observed in the peat field were able to leach into the ditch and potentially move off-site.

Peat extraction activities appear to increase surface temperature and nitrogen availability in extracted peatlands. Therefore, extraction fields may be a major source of nitrogen that should be monitored. However, chemistry collected at extracted site outflows showed similar ammonium, pH, and electrical conductivity values to the natural site despite differences observed in the in situ peat. No nitrate was found at any site outflows. This suggests that alterations to the peat chemistry occurring in the peat field are not able to move to the ditch and be exported off site. Assessment of nitrate concentrations at outflow locations from throughout the season show pulses of nitrate associated with large rainfall events at older extracted peatlands.

Understanding what physicochemical properties may be important, and when they may apply, will help land managers assess the relative risk of nutrient leaching depending on what type of peat extraction activity is occurring. However, care should be taken to understand the time of year when samples are collected, as nitrate mobility requires a hydrologic linkage between the peat field and the outflow. This is facilitated by impermeable frozen ground in the spring and heavy rainfall events.

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