biological consequences of water pollution by sewage

Question 1

what is the cause of toxic chemicals (pesticides and herbicides)?

Answer 1

sprayed on crops to prevent damage from insects and growth of weeds
runoff occurs from agricultural land if these toxic chemicals are applied in too high a concentration, causing them to enter watercourses

Question 2

how do toxic chemicals (pesticides and herbicides) affect biodiversity?

Answer 2

these chemicals cannot be broken down by organisms
they can be absorbed by aquatic plants and build up in the tissues of these organisms over time

Question 3

what is bioaccumulation?

Answer 3

these chemicals being absorbed by aquatic plants/ invertabraes and building up in the tissues of these organisms over time

Question 4

what is biomagnification?

Answer 4

increasing levels of the chemicals build up in the organisms, can eventually build up to dangerous toxic levels in predators leading to death or failure to breed

Question 5

what is the cause of untreated sewage?

Answer 5

lack of sewage treatment plants in inhabited areas (due to poor infrastructure or lack of money) meaning sewage runs/ is pumped into watercourses

Question 6

what is eutrophication?

Answer 6

sewage provides a good source of food for bacteria which increase rapidly, depleting the oxygen dissolved in the water (as they respire anaerobically)
this lack of oxygen results in the death of aquatic organisms (fish)

Question 7

what is the cause of runoff?

Answer 7

occurs from agricultural land if fertilisers are applied in too high a concentration, causing fertilisers to enter watercourses

Question 8

what is the effect of runoff?

Answer 8

the fertilisier causes increased growth of algae and water plants
resulting “algal bloom” blocks sunlight so water plants on the bottom start to die- so does the algae when competition for nutrients becomes too intense
dead plants and algae are a good source of food for bacteria
leads to eutrophication and the death of many aquatic organisms