Blog Post 8: Tables and Graphs

Soil samples and percent of frond yellowing on  Polystichum munitum and Pteridium aquilinum from randomly selected samples were collected within the surrounding area of the Alfred Howe Greenway trail. Soil samples were later measured for their pH, nitrogen, phosphorous, and potash content using the Rapitest 1601 Soil Test Kit. The following graph summarises collected field data for topsoil samples, illustrating soil type (sandy, loam, clay) and nitrogen content in relation to where the sample was collected along the length of the trail:

Some difficulties were encountered when aggregating data at some soil sample locations, with (1) underground root systems preventing the ability to collect the soil sample from the required depth (4”) or (2) inability to reach the location, such as the case in the presence of very dense vegetation or a steep change in slope elevation. In the case of these difficulties, the nearest accessible soil sample was collected.

No major difficulties were encountered when performing soil tests, however, due to the waiting periods required in waiting for the soil to settle (30 min. to 24 hours) and for colour to develop when conducting the sample test (10 min. for nitrogen, phosphorus, and potash) (Photo 1), soil testing was conducted on several separate days. However, all soil tests were conducted during the day, ensuring sufficient daylight was available for measuring each sample.

Photo 1: (Left) clear solution  of soil sample L1S2 after soil settling (60 minutes). (Right) Nitrogen colour determination (N3 = sufficient) of soil sample L1S2 at 10 minute mark.

When the final results for the nitrogen tests were summarised (Fig. 1), it was surprising to observe that nitrogen levels were lower on average in the remediated landfill area in contrast to the historically forested area, since it was predicted that any landfill waste still buried in the ground could induce biogas release, primarily in the form of methane and carbon dioxide, significantly altering the soil quality from that of a natural habitat, allowing nitrifying bacteria to flourish, leading to higher nitrogen levels (Isaka et. al., 2007).

A landfill cover is reported to be encompassing at least a portion of the remediated landfill, with its aboveground edge observed in a previous blog post entry (Blog Post 6, Photo 2). Perhaps the landfill cover is preventing soil contaminated with landfill content from permeating to the collected topsoil, leading to the recorded low levels of nitrogen (Kightley et. al., 1995) . An alternative explanation could be that denitrification is actually occurring at greater rates in the landfill area, resulting in lower nitrogen levels (Burton and Watson-Craik, 1998).