The Transport and Hydrological Response of Simulated Wastewater from a Continuous Point Source in a Northern Ribbed Fen

English Abstract:

To minimize the discharge of wastewater contaminants from remote northern communities and mining operations, fen peatlands in sub-arctic regions are used for tertiary wastewater treatment to detain, transform, and remove these contaminants. However, there is a limited understanding of contaminant transport in fen peatlands, particularly in sub-arctic Canada. To better characterize contaminant transport in these systems, approximately 44 m³ day^-1 of simulated wastewater (concentrated custom-blend fertilizer and Cl^- diluted with water) was pumped into a small 0.5 ha sub-arctic northern ribbed fen continuously for 47 days (July 15^th –August 31^st 2015). Electrical conductivity (EC) of 3 similar northern ribbed fens varied between 15 (min) and 88 (max) μm cm^-1 over the study period (May – September 2015). Water table quickly increased (~0.16 m in 6 days) nearest the point source (8 m down-gradient), resulting in rapid solute transport, as measured by electrical conductivity (EC) (20 to140 μm cm^-1 in 11 days). This rapid transport was due to the large increase of hydraulic conductivity (~2 to180 m day^-1) as the water table rose. More gradual increases in water table (0.18 m in 13 days) and EC (140 μm cm^-1 in 15 days) were observed farther (~50 m) from the point source; this delay was likely due to increased total storage capacity rather than differences in hydraulic conductivity. After 34 days the water table had risen on average 0.16 m across the site, but EC (113 μm cm^-1 in 25 days) was limited to a final distance of 119 m. Northern ribbed fens have a large capacity to detain wastewater as illustrated by the conservative solute plume only travelling 49 % of the total site length (notwithstanding the large increase in hydraulic conductivity as the water table rose) and have the potential to significantly decrease wastewater contamination in northern aquatic environments.