Scoat Tarn and Acid Rain

Scoat Tarn is tucked up in the hills above Wasdale. If you look carefully, it is somewhere in the middle of the picture. It has been used in studies of the amount of acid rain in the environment (look at the data in the latest report http://awmn.defra.gov.uk/resources/annualreports/index.php). So I decided to repeat an experiment I've done before into the effect of acid rain on the growth of cress seeds.
I got 5 half Petri dishes and some cotton wool. I also got some 0.010 Molar Citric Acid (that's effectively really, really weak lemon juice). I then watered the Citric Acid down further so that I was using 5 concentrations of weak acid: 0M (pure water, really) 0.002M, 0.004M, 0.008M, 0.010M (somehow I forgot to set up 0.006M!)
I soaked a piece of cotton wool with each solution and put it into a Petri dish. I then put 20 cress seeds on top of the cotton wool and left them in the same place so that they got the same light and temperature.