Cremation
Cremation. The body is converted into Carbon dioxide and water vapour, which rejoin the atmosphere, plus carbon ash mixed with a few other nutrients which can be sprinkled on the soil and will fertilise the plants. Nothing is lost.
You will presumably have machinery in place to balance the levels of carbon dioxide and oxygen if your vegetation isn't up to the job.
Expect about 1.1kg per hour
Assuming a population of 10,000 and an average lifespan of 80 years, you can expect one death every 2.9 days or so. An average North American adult human is 80kg. That's 1.1kg per hour, most of which will be water. This is a very moderate amount of carbon dioxide for a good size biosphere to soak up.