Our two summer students started on Monday so I got them straight into the nitty-gritty of invertebrate sampling.
This weeks sample came from the River Livet just above the confluence with the Tervie. Polly and Michael spent the afternoon picked through the sample and the next two days on and off identifying them. 1146 individual specimens were identified, typical of the number found in the Spey mainstem samples although the make up of the population was different.
The season of the year is important for invertebrate sampling. Some of the early mayflies and caddis will already have hatched so that needs to be borne in mind when analysing the results. On the other hand there were a few Blue winged olive nymphs (Emphemerillidae) present. They overwinter as eggs and appear as nymphs in the spring before maturing quickly in the summer with the hatch over by October.
The photo below shows the sample sorted into the different groups before identifying and counting.
As can be seen from the photo the sample was dominated by mayfly and stonefly. 88% of the mayflies were baetids with a few heptagenids and the above mentioned emphemerllidae. There were almost 400 stoneflies although most were Leuctridae (Needle flies). There was only one of the large stoneflies – quite a lot less than found in the Spey samples although they are hatching at the moment. 60 caddis were recorded, again a great deal less than the 667 found at Castle Grant. None of the cased caddis were of the highest scoring species in the BMWP scoring system.
There were no shrimps nor snails, but in amongst the assorted tray were 38 Pediciidae larvae (Hairy Eyed Cranefly!)
So an interesting sample. I would have said there was evidence of some form of impact. The absence of large stoneflies and the high scoring caddis species, which were abundant in the Spey samples hints at organic enrichment. We need to take a sample from further up for comparison; what we found may be all the Livet supports, but I doubt it.
Polly and Michael showed considerable interest in this subject, they may regret it!