Wednesday, April 6, 2011

Fish Kill observed at Odana Pond, vultures feast

Spring runoff from urban areas is so salty that it's toxic to fish.

On April 1, six carp were found dead next to one of the ponds in Odana Hills Golf Course. Eleven vultures were loitering about, having finished with all the carp reachable from shore (vultures don't swim).

A likely cause of death for the carp was the "first flush" of spring. That's when all the dirt and salt spread during winter runs off from the streets and parking lots. From there the filth runs into our stormsewers, streams, and lakes.

The large Odana Pond, visible from the beltline, is the first destination for much of the runoff from the west side. From there, the water has had three alternate paths.
  • The historic path was to filter through a ridge of sand dunes along the east edge of the golf course. Originally, there was no surface outlet for the pond. The Odana basin, including lower parts of the golf course, was a wetland.
  • Then the City partially drained the wetlands, by creating a storm sewer outlet to the East, through a pipe under the dunes. The big Odana Pond flows east by a short creek to two smaller ponds, and then to the storm sewer.
  • Finally, Madison Gas and Electric created a third pathway for water from Odana Pond. They pump about 50 million gallons a year into the sand. This two-million-dollar facility represents a mitigation deal with DNR to compensate for water the West Campus CoGen plant withdraws from Lake Mendota.
Yes, MG&E pumps this same water that killed the fish... 50 million gallons of it a year... into the groundwater. Into your drinking water.

Now, it turns out, their permit to discharge this water has expired. They have applied to renew it. But, it turns out that test wells near where the dirty water is being pumped into the ground, have revealed high levels of salt, above levels which require DNR and MG&E to take preventative action.

But the plan they have come up with continues the pumping, for at least an hour a day even during the highest salt levels of spring, and so will be inadequate to solve the salt problem.

Vultures enjoy a  picnic at the golf course.

 Since many Madisonians will be drinking that same water as those fish, when it reaches the aquifer, the vultures might as well hang around.

# # #

* Kurt Welke of the DNR said fish kills are common this time of year. He attributed the cause to low oxygen levels, brought on by the heavy snow cover of last winter, which inhibited oxygen production by algae, plus depletion of oxygen from decomposition of organic matter. But since salt is also toxic to fish, and because this kill occurred during the salt flush period, the fish kill may have been due to salt, or to both causes together.

Update: The chloride concentration in upper Odana Pond on 3/31 was 2100 mg/l.   The above photos are from 4/1.  Source: MG&E sampling.   Carp are somewhat salt tolerant, but together with low oxygen and other pollutants, salt must have added to the lethal stress.

No comments:

Post a Comment