Mar 1, 2011

Swamp has four seasons (not two)

The swamp has two season’s, right?


Meteorologically speaking, yes –

The wet season runs from late May into October and the dry season from November into May.

Hydrograph showing drop of water stage through the swamp's major habitat types

But terrestrially speaking, as water is manifested “on the ground,” I describe the swamp’s water cycle as consisting of four seasons instead.

  • Soaking in season. The early part of May is usually the crunchiest time of the year to walk through the swamp: water is absent except in the deepest pools. By month’s end the wet season will have started, followed by June – the rainiest month of the year; yet only rarely do waters peak this early. Late May through June is usually a “soaking in” season for the preserve.
  • Sheetflow season. The onset of summer, lasting into early fall, coincides with an extensive but ephemeral sheet of shallow flowing water in the swamp. Its flowing aspect is achieved when waters rise to the base of the hydric pinelands (i.e., a depth of 20 inches in the pond apple swamps) and higher. The depth, spatial extent and flow rate of sheetflow typically peak between late August and early October.
  • Hydrologic Interregnum. Starting with the demise of sheetflow in mid fall and lasting through winter is the hydrologic interregnum. This is an approximate five month period in which “wet season” water is still present on the ground, but atmospherically the “dry season” has set in, thus initiating the slow demise of the swamp’s expansive sheet of surface water. The duration of surface water in any one spot is largely habitat dependant, but may also be sustained by winter rains, particularly during El Niño years. Pinelands go dry first, followed by marl prairies which eventually leads to a retreat of waters into the tall cypress and pond apple swamp.
  • Spring drought. The swamp ebbs to its low water mark in April and May due to the cumulative effect of months with little rain and increasing rates of evapotranspiration (rising temperatures, expanding hours of daylight, and plant transpiration). During this period, surface water is practically absent from the swamp other than smallish (typically less than an acre) and isolated pools called dry season refugia.

This year the water cycle clock is running ahead of schedule:

March has barely begun and the spring drought is already underway.

Chart displaying difference between the swamp's meteorologic and terrestrial seasons


Next up to go dry?

Smallish shallow pools of stagnant water are still hanging on in the swamp’s deepest holes – known locally as dry season refugia – but it won't be before long that they go dry too.


That's when the heart of the spring drought officially begins.

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