A very good start.

Some suggestions...

I would recommend completing webmaster, pub date, last build date, copyrite (even if Creative Commons).  Length is not explicit but useful attribute to have filled - some really good RSS feed applications can fill in the information automatically.  Most of the automation in RSS feed generation is usually a cost item...but I still search for open source and free...

In addition a UTF-8 encoding would be more universal.

The following code has been cleaned but not substantially modified:

<?xml version="1.0" encoding="iso-8859-1"?>
<rss version="2.0">
  <channel>
        <title>The Unofficial Landing Podcast</title>
        <description>This is the unofficial podcast for the Landing community at Athabasca University.</description>
        <link>https://landing.athabascau.ca/</link>
        <language>en-us</language>
        <copyright> by </copyright>
        <lastBuildDate>,    :: </lastBuildDate>
        <pubDate>,    :: </pubDate>
        <docs>http://blogs.law.harvard.edu/tech/rss</docs>
        <webMaster></webMaster>
    <item>
    <title>Episode One: Whither the Landing, scholarship deadlines, and how to support the AU library.</title>
    <link>https://landing.athabascau.ca</link>
    <description></description>
    <enclosure url="https://landing.athabascau.ca/pg/file/read/85344/the-unofficial-landing-podcast-episode-one" length="" type="audio/mpeg" />
    <source url="https://landing.athabascau.ca/pg/file/read/85344/the-unofficial-landing-podcast-episode-one">Hear the preview here</source>
    <category>Podcasts</category>
    <pubDate>,    :: </pubDate>
    </item>
</channel>
</rss>

- Steve Swettenham