Hi Seriba If there are a lot ...

Hi Seriba If there are a lot of domesticated animals such as goats and cattle, ecoli may not be a good indicator as you may not be able to separate between human and animal faecal contamination, unless you undertake quite complex microbial source tracking. Possibly you may not be interested in separating between animal and human contamination and may only want to see the total faecal contamination. This makes life much easier. As there is not much fertiliser usage, nitrogen also could be a good indicator of contamination. There is no 'magic' statistical method that can give you the answer that you want. I am sorry, I just cannot suggest such a method. What you are trying to do is quite complex. Please have a look at the following paper. http://eprints.qut.edu.au/4016/1/4016.pdf Possibly you can follow a similar procedure, install shallow monitoring wells along the groundwater flow paths to the wetland do some testing of the water collected in the groundwater wells. A simple mathematical calculation should give you an approximate idea of the amount of contamination flowing into the wetland