Great Seneca Creek Record

Paved watersheds lose sensitive animals

Context Nationally, sensitive animals fall from 40% of groups found in near-natural watersheds to 22% where a quarter or more is paved.

12.8%of the chapter's watershed paved or roofed (2019)
28%of it forest

Stream ecologists call this the urban stream syndrome: the more of a watershed is paved or roofed, the faster rain runs off it, carrying heat, salt and sediment, and the fewer pollution-sensitive animals live downstream.

Two watersheds after the same stormForestedPavedRain soaks inand seeps slowly to the streamRain runs off into storm drainsand reaches the stream in minutesWatersheds 0–2% paved: sensitive animals are40% of the groups foundWatersheds 25% + paved: sensitive animals are22% of the groups foundAbove the chapter's sites: 12.8% paved or roofeddeveloped 46%forest 28%farm and hay 22%
Illustration of two watersheds; the figures under each come from the national surveys, the bar from EPA StreamCat (NLCD 2019).
All usable biological surveys with watershed land cover (EPA StreamCat, NLCD 2019). Observed averages, not model output.

The watershed above the chapter's sites is 12.8% paved and roofed, in the band where losses usually start to show. Paving there grew only from 11.8% to 12.8% between 2001 and 2019 (StreamCat), so the next step is to look for local causes that land-cover maps miss: construction, stormwater outfalls, sewer leaks or a spill.

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