Question
We recently had a tree removal service cut down 2 pecan trees and 5 water oaks, all about 60-70 years old. they ground the stumps and it had rained hard that day and left all the mulch on top. the second day we started smelling a horrible smell like sewage. we  called a plumber everything was all ok. we uncovered the stumps to find a lot of this stinky murky water. someone told me the dept. of environmental quality calls it black water, because it ferments on the newly ground stump and under the newly ground mulch. is this true? how can you fix it? it is only on my pecan tree stumps should i be concerned about all the other new stumps they put mulch over?

Answer
The root system is still alive and in the spring the roots "job" is to pump water that contains food and minerals to the leaf buds so they will have enough energy to leaf out. With the tree cut the roots are still pumping this water and this is the smell you are getting. This will stop soon. This happens with some tree species if they are cut in the early spring. You can put powdered lime on the stump surface that this will help neutralize the acid smell. Lime can be found at any nursery and is not expensive. Just cover the stump surface with about a 1/4 inch of the lime.
I would expect the oaks to do the same except they might not smell as strong as the pecan due to the different acid makeup of the trees system. Each tree wood has a different smell depending on the chemicals in the wood.