SUMMARY: Source decay happens when a source remains reachable but becomes less useful, less current, less relevant, or less trustworthy than its label implies.
Broken links are easy to notice. Decayed sources are harder. They still load. They still carry authority from old use. They may still look appropriate in a list, citation, or headline panel. The problem is not absence. The problem is stale confidence.
Source decay affects search visibility and reader trust at the same time. A site that keeps old references without review begins to tell search engines and readers that freshness is accidental.
Decay Signals
Temporal decay: the source still exists but no longer reflects the current state of the subject.
Context decay: the source is accurate in isolation but no longer supports the point being made.
Authority decay: the source once had standing in the system but has not earned continued trust.
Discovery decay: a source or feed has drifted into formats that search engines, readers, or operators can no longer scan cleanly.
Countermeasure
Give important sources a freshness window, a replacement path, and a removal threshold. Pair this with source rotation so trust is renewed by review instead of preserved by habit.
Operator Rule
A source that is still online is not automatically still useful.
Field assessment: decay is what trust looks like when nobody revisits it.