Feb 14, 2013

Old growth meets "new" drought

One rain doesn't end a drought,

Especially one that's seven years in the making.

The twin hydrograph above compares the pattern of flooding Corkscrew Swamp Sanctuary for two periods: 1960 to 1975 on the left, i.e. "Then" and the more recent period, i.e. "Now" of 2005-2012 on the right.  During the "Then" period, the tall cypress enjoyed an average hydroperiod of 9 months per year.  Fast forward ahead to the past 7 years and the same cypress are subjected to an average hydroperiod of 4-5 months per year.  Also apparent is the deeper and lengthier incursions into deep drought.  During the "Then" period, the water table only briefly, on average for a month, dropped below the level of the pond apple forest floor -- and even then only shallowly, i.e. about 0.3 ft.  Compare that to the past seven years when, on average, the water table drops below the level of the pond apple forest floor for 4 months per year -- and importantly -- much deeper, as much as over a foot.  What's the result of this changed hydrology?  Peat loss would seem likely and -- considering cypress of such tall stature are usually flooded and or hydric -- it must be stressing the trees, too.

The old worry in Corkscrew was the the wood storks, or more specifically: how to maintain the rate of the  dry season recession for wood storks to forage and nest.  Now the new worry is simply keeping the swamp hydrated ...

To protect the trees.

Meanwhile, vital freshwater spills unwanted out the Lake down the Caloosahatchee.


teeberg said...

Thank you -- very interesting, insightful and scary!

I don't know what to make of the last mention about the unwanted fresh water. Can you explain more about that?

Thanks -- it's fun to read your stuff!

Gohydrology said...

The source of the missing water at Corkscrew definitely warrants a closer a look -- it's some combination of lower aquifer levels, reduced surface water contributions, and rainfall. More important is finding solutions to what we can do to reverse it.

While the loss of water at Corkscrew is not Lake O, it is frustrating from a water stewardship perspective to know Lake water is being wasted to tide when wetlands to the south that once depended on its overflow and ambiently higher water table could use a more steady contribution of headwater flows from the north to sustain hydroperiod at habitat appropriate levels into the spring.