1. Answer A
Temperature provides a snapshot of informationabout the quality of water in the river because it can only beassessed at a specific period in time. The temperature of water inrivers differs depending on the amount of pollutants in it. On theother hand, macro invertebrates provide information of water inrivers over a period of time based on the fact that variousmicroorganisms spend part or whole of their lives in the water. Thisis dependent on oxygen levels in the water which is based on thelevel of pollution. By calculating the complete biotic index, one isable to assess the quality of river through the number of microinvertebrates sampled.
2. Answer B
There are four habitat types mentioned in thevideo namely, riffles, undercut banks, snags and leaf packs in theirreducing biodiversity respectively. Complete biotic index requiresthree samples from three distinct habitats with emphasis on thehabitat with highest diversity. To collect samples from riffles, twosubsamples are taken both upstream and downstream. Upstream sample istaken first starting on the lower end of the river going up whilekicking and rubbing rocks for two minutes to dislodge as manyorganisms as possible into the de-frame net. The sample is then putin the dish pen and rinsed. Downstream sample is taken from up goingdown the river while kicking and rubbing rock for two minutes andthen emptied into dish pen. The two samples make up the rifflesubsample.
Undercut banks subsample is taken by placingthe net from underneath the bank and moving up the overhangingvegetation to dislodge organisms. Twenty jabs are adequate and thesample is emptied into the dish pen. Snag samples are taken byplacing the net underneath the log and moving along it to dislodgeany organisms. Twenty jabs are taken and sample emptied into thedish. Lastly, leaf back sample is taken by placing the net on thedownstream edge and allowing as many leaf packs to enter the net. Thesamples are sorted, counted and biotic index calculated.
3. Answer C
Macro invertebrates are ubiquitous in water andcan be found in water bodies worldwide. They have limited mobility inwater and therefore can be localized easily. These microinvertebrates also spend part or whole of their lives in water andfinally, they utilize oxygen from the water for survival. Theirnumbers in water determines the quality of the water bodies based onthe sensitivity and tolerability to oxygen levels.