The Effects of Nutrient and Peat Amendments on Oil Sands Reclamation Wetlands: A Microcosm Study

Abstract

Oil sand mining operations in Alberta, Canada produce large quantities of process water and mature fine tailing (MFT) during the bitumen extraction process. Wet landscape reclamation is one of the reclamation strategies proposed to utilize process water and MFT in the creation of aquatic reclamation environments that are economically and environmentally acceptable.

In the interest of utilizing nutrient enrichment and peat amendment to improve aquatic flora and fauna colonization in new oil sands aquatic reclamation, this microcosm study was designed to assess the phytoplankton and periphyton growth (summer 2008), as well as benthic invertebrate colonization (summer 2009). Peat amendment significantly increased the growth of phytoplankton and periphyton by providing sufficient nutrients (total nitrogen, total phosphorus and dissolved organic carbon) to the system. In reference wetland, benthic invertebrate colonization was significantly increased by utilizing sand as bottom substrate and decreased by MFT/Sand mixture as bottom substrate. In OSPM-affected wetland, benthic invertebrate colonization was not affected by utilizing MFT/Sand as bottom substrate. In comparison to OSPM-affected wetlands, reference wetland had larger number of benthic invertebrate families and higher total abundance.

In this research, experimental microcosms were constructed in three reclamation wetlands with different types of reclamation materials as the bottom substrates (sand, MFT + sand) and amendments (nutrient and/or peat) added to optimize growing conditions for phytoplankton and periphyton, thus creating a biological detrital layer over unfavourable substrates to enhance benthic invertebrate colonization. The growth estimates of phytoplankton and periphyton on MFT + sand without amendment were low in comparison to the control (water only, no substrate). In comparison to sand, MFT + sand had higher growth estimates at OSPM-affected sites, but lower growth estimates at reference site. The growth estimates of phytoplankton and periphyton on MFT + sand were significantly increased with peat amendment. Nutrient (nitrogen and phosphorus) enrichment insignificantly improved the phytoplankton and periphyton growth. Peat amendments elevated the concentrations of nitrogen, phosphorus and dissolved organic carbon in the system and maintained these high concentrations throughout the experiment period. Nutrient enrichment only temporarily (less than 3 weeks) elevated nitrogen and phosphorus levels as the nutrients added were quickly utilized by the system.

Benthic invertebrate colonization was assessed in the following year. Sand treatments had increased total abundance and numbers of families of benthic invertebrate compared to the mature sediments of the reference wetland. In oil sand process material (OSPM)-affected wetlands, sand treatments had slightly lower abundance and fewer numbers of families in comparison to the mature sediments. In comparison to sand treatments, MFT + sand treatments had decreased total abundance in the reference wetland but not in OSPM-affected wetlands that received MFT input during its construction. Peat amendment and nutrient enrichment had no impact on benthic invertebrate total abundance or composition.