|MadSci Network: Environment|
The effect of eutrophication is first of all the addition of organic nutrients into the freshwater system. When the food supply goes up, so does the number of organisms present, with most of the increase due to bacterial reproduction. Bacteria reproduce very rapidly and can respond more quickly than most other organisms to the input of nutrients.
So, nutrient levels go up and so do the number of organisms present, but the overall rate at which oxygen enters the system will remain about the same. Therefore, there is less oxygen to go round and those organisms which require high levels of O2 will die.
The effects of eutrophication vary according to where you are. You are in a lowland area where the effects are a little less pronounced. The addition of fertiliser often stimulates the production of algae. When the algae dies towards the end of the summer, the bacteria multiply and deprive other organisms of water. I would suggest you try speaking to the biologist at your local water board. They may be monitoring the areas you are studying and may even provide you with some biological data. You might try asking them for some BMWP scores if they use that system.
I would strongly suggest you read the following book which you can order through your local public library:
Ecology of Fresh Waters : Man and Medium, Past to Future by Brian Moss, Paperback 3rd edition (September 1998) Blackwell Science Inc;
See my other responses:
Re: what is a biomarker? Insects as drosophila can be used as biomarkers?
Re: How does organic pollution effect on freshwater strean invertebrate
Try the links in the MadSci Library for more information on Environment .