Integrative Natural History of Indiana Dunes State Park, Part 21: Water Like Liquid Shoe Polish | Indiana, USA
If you stand on the beach of Indiana Dunes State Park at certain times of the year, you'll see feeder streams pouring what looks like dark-brown shoe polish into the blue waters of Lake Michigan. Is this a toxic-waste spill from some leaking landfill or environmentally evil factory?
Nope. It's a natural process that long predates this rustbelt region's industrialization.
The culprit here is the Dunes' oak-dominated tree population. On the towering lakefront dunes themselves, where the soil is a very sandy Entisol, savanna-forming Black Oaks (Quercus velutina) prevail. Their bark and foliage have the highest tannic-acid content of all their genus. Water percolating through their fallen leaves is the chief agent in temporaily dyeing the lake the disconcerting color mentioned above.
But even in the quiet waters of the park's back-of-the-dunes swamp one can spot places where the tannic-acid concentration has built up dramatically.
Here, for instance, you can see it quite clearly, despite the reflection of tree tops and sky. The lighter-brown zones indicate the submerged mat of last year's Pin Oak (Quercus palustris) leaves. Those leaves may be somewhat lower in tannins than the Black Oaks', but they still have enough of the brown stuff to leach it out very noticeably.
In this photo, the dark acidic soup can best be seen at lower right, in the maroon-fringed band of black. If you stick a clear-glass sampling bottle in there, as I have, you'll collect what what could be easily mistaken for Coke or Pepsi. Or yes, for liquid shoe polish.
The other photos and descriptions of this series can be found in my Integrative Natural History of Indiana Dunes State Park album.
Integrative Natural History of Indiana Dunes State Park, Part 21: Water Like Liquid Shoe Polish | Indiana, USA
If you stand on the beach of Indiana Dunes State Park at certain times of the year, you'll see feeder streams pouring what looks like dark-brown shoe polish into the blue waters of Lake Michigan. Is this a toxic-waste spill from some leaking landfill or environmentally evil factory?
Nope. It's a natural process that long predates this rustbelt region's industrialization.
The culprit here is the Dunes' oak-dominated tree population. On the towering lakefront dunes themselves, where the soil is a very sandy Entisol, savanna-forming Black Oaks (Quercus velutina) prevail. Their bark and foliage have the highest tannic-acid content of all their genus. Water percolating through their fallen leaves is the chief agent in temporaily dyeing the lake the disconcerting color mentioned above.
But even in the quiet waters of the park's back-of-the-dunes swamp one can spot places where the tannic-acid concentration has built up dramatically.
Here, for instance, you can see it quite clearly, despite the reflection of tree tops and sky. The lighter-brown zones indicate the submerged mat of last year's Pin Oak (Quercus palustris) leaves. Those leaves may be somewhat lower in tannins than the Black Oaks', but they still have enough of the brown stuff to leach it out very noticeably.
In this photo, the dark acidic soup can best be seen at lower right, in the maroon-fringed band of black. If you stick a clear-glass sampling bottle in there, as I have, you'll collect what what could be easily mistaken for Coke or Pepsi. Or yes, for liquid shoe polish.
The other photos and descriptions of this series can be found in my Integrative Natural History of Indiana Dunes State Park album.