Dec 12, 2011

Hydrologic ax knows no bounds

Corkscrew swamp famously escaped the saw …
That means its giants have roots reaching hundreds of years down.

(And, yes, they are tall too!)

Just using the eyeball test:
This tree looks to be around 500 years old.
But did its hydrograph also remain similarly unscathed?

Here’s a comparison of hydrographs, color coded with regard to statistic categories (i.e., 0th, 10th, 33rd, 50th, 66th, 90th, and 100th percentile) and habitat types (i.e., dry season refugia, pond apple, tall cypress, marl prairie, and pinelands) for the fifteen year period of 1960-1975 and 1990-2005.

Whoa! What caused this hydrograph to change?

The hydrograph looks more or less intact:

Seasonal trends of the summer wet and winter dry area easy to see.

However, decades ago (left) the swamp seemed to show a more predictable pattern: Yes, there were flood and drought seasons, but the darker band between the 33rd and 66th percentile is much tighter (on the left) than what’s seen on the modern day hydrograph (right). Particularly noticeable is the wider range of fluctuation and deeper drop of the modern day (right) spring drydown. Less obvious, but also present (if also counterintuitive, although also explainable), is the modern day’s higher wet-season hump.

I took this panoramic photo
standing at the long-term staff gage
What’s going on?

Climate could be in play. We’ve had some wet summers in that period (1995, 1999, and 2005) plus a big drought during 2000-2001. Also a factor is the landscape around Corkscrew which, unlike the sanctuary, and despite the great success of the Corkscrew Swamp Regional Ecosystem Watershed (CREW) initiative, conservation efforts have tended to focus on low-lying wetlands (i.e., in the adjacent Corkscrew Swamp Regional Ecosystem Watershed) whereas uplands have been converted into agriculture or urbanized.

All things being equal (meteorologically speaking), that leaves less land for the same amount of water; or in other words, higher peaks in the areas that still hold water and lower dry season drops due to the spatial loss of upstream storage.

Boardwalk at Corkscrew Swamp
Hydrology Lesson No. 12:

The next step in wildlands conservation is protecting the hydrograph, too!

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