St Croix River Road Ramblings

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Sunday, November 2, 2008

Sand Carp

I grew up as a Jack Pine Savage in NW Polk County on the edge of the land they call the Sand Barrens. I never new much about the area until I met Doug Johnson, professor at the UW, digging in the clay bank along Trade River on Evergreen Av., 10 years ago. He told me this story: Some 10,000 to 50,000 years ago some glaciers melted and made a huge lake upriver from St. Croix Falls. Each year as the glacier melted, layer after layer of clay washed into the lake and settled to the bottom – to nearly 200 feet thick. Then as the melting slowed, only fine sand filtered in leaving another 20 feet of sand on the lake bottom. This lake, he called Glacial Lake Lindh—or just Lindh, drained when the water cut through the rocks at the Falls of St. Croix.

Professor Johnson said when the surface water drained; it left about 15 feet of water still in the lake bottom saturating the lower three-fourths of the 20 foot sand layer. The dry sand at the top started blowing and made big sand dunes—the big ridges through the Sterling Barrens. With time and lots of rain, the dunes stabilized when prairie grasses and plants moved in. Lightning fires kept the trees burned off. He told me that it is woods now only because there are people who put out the fires and plant trees (the County and the DNR mostly). He says the area is especially interesting to biologists because the underground lake is filled with both water and sand—attracting and evolving some mighty strange animals. Since then I have made a study of some of these unique species and will share a few with you in hopes you will help us preserve them in their special sand barrens lake habitat.

Lots of people drive along the River Road or Evergreen Avenue and the other old roads in the Barrens and see the rows of dirt mounds along the ditches and wonder what is making them. Well, very few people have seen the Sand Carp that is pretty common in Sand Lake Lindh. As the lake slowly dried up, pools of water were left with fish trapped in them—land locked from the St. Croix, but sitting on 15 feet of water soaked sand. Over a few thousand years some carp evolved to live in the sandy slurry of the old lake, eating roots instead of water plants, and creating water filled tunnels in the firmer areas. Their most unique difference is the blow hole (just like a whale) that they use to clear their sinuses of the sand that filters in. Each sneeze leaves a mound of dirt on the ground above. If you are driving along a barrens road, look for the series of 4 to 6 mounds in row, the sure sign of an active Sand Carp.

Sand Carp are tasty. Their fins make an especially delicate soup. You must be careful to take only those who have not been swimming amongst poison ivy roots or your stomach lining may break out with ivy blisters. We catch them by digging a sand pit—a 10 foot hole straight down in the sand near the mounds. The Sand Carp comes swimming and burrowing along in the wet sand and drowns when he fall into the water hole.

The Sand Beaver is a rarer find, but the careful nature watcher can see signs of their work. Like the Sand Carp, they too spend most of their lives below the surface living in the underground creeks, so abundant at the edges of Sand Lake Lindh. Some of these creeks burst forth as springs along Wolf Creek, Trade River and the St. Croix. The Sand Beaver are invaluable to keep the lake from drying out, as their underground dams block many of the outlet springs. You can see their activity when you see a cluster of dead trees. They cut the roots for their dams. They are a nuisance when they mistake your well for a dam leak and plug your well point (many local wells are only 10-20 feet deep taking advantage of the sand filtered lake water). Jack Pine Savages take a rifle shot down their well to scare away the beavers and to blow out the debris.

The Sand Tern is a unique member of the duck family that has adapted to the underground sand filled lake. It burrows deep into the sand hollowing out a small cavern that fills half full of water. There it builds a floating nest with cattail seedheads brought from a nearby swamp, and raises up to a dozen ternlets. The primary difference from the normal Tern and the Sand Tern is the presence of clawed webbed feet and a seining bill. The claws allow the birds to climb from the hole to the outside. The bill is similar to that of a baleen whale (although smaller) who gulps a huge mouthful of water and then spits it out through strainer teeth to keep the small fish, plankton and shrimp. The Sand Tern takes a mouthful of wet sand and then strains out the sand leaving the bugs, algae and krill.

A rare but increasing species is the Sand Alligator. Normally our area is too far north to allow alligators to survive through the winter. However, years of Twin Citians flushing baby alligators purchased on Florida vacations and becoming nasty pets, have let them travel down the Mississippi to Prescott and then up the St. Croix where they enter Sand Lake Lindh through springs and into the interconnected tunnels of the Sand Carp. They prey mostly on Sand Carp and are comfortable in the cold winters far below the frozen surface, hibernating in abandoned Sand Tern caverns (the web of nature is marvelous!). They can be seen sunning themselves along the horse camp on Trade River on a quiet summer afternoon.

Pocket gophers live in the upper dry layer of the lake and in the dunes. A 10 inch rain can raise the lake water table high enough to drown most of them. This had happened only once in the past 50 years, back in June of ’42 when it rained for 4 days straight. A few living at the top of a dune ridge escaped to repopulate the area as the water table gradually dropped. Their biggest predator is the badger from above, the gopher snake from within and the alligators from below.

The 2006 and 2007 dry years have lowered the lake level nearly 2 feet. As a preparation to future dry years predicted by global warming, a few of the Sand Carp are actively evolving their fins as rudimentary legs and taking short sunbathing trips to the surface. I have only seen them near the Sterling tower, where Fox Ridge rises 100 feet about Sand Lake Lindh’s water level.

The next time you travel through the Sterling Sand Barrens, bring a post hole digger, find a low spot between the dunes and dig a hole down to the lake. Spend a half day peering down this window into Sand Lake Lindh. If you don’t see at least one of the sandwater species I have talked about, I will be very disappointed.