Biotic Indexes

A biotic index is the counting of invertebrates so to get a score can be made on a river body showing the water quality. To do a biotic index tools needed are dipnets, a tray, a field guide and a paper to record the species found. To do a biotic index three minute kick sample on he river bed. the kicks sample is caught in dip nets and the contents are emptied into a tray and brought one side. Then a table is made like the one bellow.

Biotic Index Example 1
Species Numbers Found
 
0 1-5 6-10 11+
Mayfly Nymphs
yes no no no
Alderfly and Stonefly
yes no no; no
Cased Caddisfly
no yes no no
Freshwater Shrimp
no no yes no
Tubifex Worm
no no yes no
Bloodworm
no no no yes

The table above is a recorded sample of a river showing that the sample contains alot of bloodworm and very few mayfly nymph. This is a good indicator of the water quality of the section of river. which means there is little oxygen water and only invertebrates such as boodworms that have haemoglobin in their blood which enables them to have and advantage to the mayfly by belieng able to survive low oxygen levels in the water. This could be from a sewage outlet entering the river of a river thats heavily silted leaves from over hanging trees which uses up the oxygen through the breakdown by micro organisms such as bacteria.

Biotic Index Example 2
Species Numbers Found
 
0 1-5 6-10 11+
Mayfly Nymphs
no no no yes
Alderfly and Stonefly
no no yes no
Cased Caddisfly
no no yes no
Freshwater Shrimp
no yes no no
Tubifex Worm
no yes no no
Bloodworm
yes no no no

The table above shows that there are lot of mayfly nymphs and a good head of fresh water shrimps, alderfly and caddis which would mean that the water has a really good water qualitiy with high oxygen and maybe fast flow.

So biotic indexes are a really good way to find out the water quality of a stretch of river by the invetebrates that live there. Invertebrates such as mayfly will prefere a higher water quality and the absence of mayfly nymphs could mean poorer water quality. The bugs that are able to live in poorer conditions will be available what ever the water quality and the absence of the invertebrates that prefer a higher water quality can be put in a table creating a biotic index.