FRESHWATER POLLUTION

1. FRESHWATER POLLUTION The Effects of Pollution Caused by Treated Domestic Sewage on a Freshwater Ecosystem

2. 2 Specific Information: The sewage treatment works is in St. Jean du Bleymard. It serves two settlements - St. Jean du Bleymard and Le Bleymard. These two settlements have a combined population of 446 (1999 census). It also receives waste from a small holiday village when it is open in July and August. The total population may then reach 1200 people. The liquid waste from the treatment works is discharged almost continuously in low volumes, and diluted by the river Lot.

3. 3 Map of Study Sites:

4. 4 What is a Pollutant?? A pollutant may be natural or unnatural. Pollutants are not necessarily highly toxic chemical compounds. It is the concentration of the substance that defines it as a pollutant. Domestic sewage is rich in ammonium from urine and faecal matter, phosphates from detergents and particulate matter. By proportion, it is approximately 45% carbohydrate, 45% fat and 10% protein.

5. 5 Sewage Treatment Process: Sewage is stirred by a propeller. This increases its surface area. Air (esp. Oxygen) mixed with the sewage. Liquid and solid separation. Liquid continues onto biological treatment.

6. 6 Biological Treatment: Urea from domestic sewage breaks down into Ammonium (NH4+). Aerobic bacteria carry out oxidation reactions, converting the ammonium ions to nitrate. The reactions: 2NH4+ + 3O2 ? 2NO2-+ 4H+ (Carried out by nitrosomonas) Ammonium is used as food for Nitrosomonas to produce nitrite (NO2-). 2NO2- + O2 ? 2NO3- (Carried out by nitrobacter) Nitrobacter use the Nitrites from the previous reaction and produce Nitrates (NO3-). Both reactions use up Oxygen. Nitrosomonas and nitrobacter occur naturally in watercourses therefore if the treatment process is insufficient, the ammonia will be converted to nitrate and cause Oxygen depletion in the receiving water.

7. 7 Abiotic Hypothesis:

8. 8 Biotic Indicators There are a huge diversity of invertebrates living in rivers. They have a range of tolerances to different water qualities, especially different levels of oxygen concentrations. Therefore there are ‘Indicator Species’ which can help determine the long term quality of the river water. Biological Monitoring Party Score (BMWP) can be used as a biotic index. Invertebrates with a low BMWP can tolerate low levels of Oxygen and are therefore good indicators of poor water quality.

9. 9 Aims: To determine the effects of point source organic pollution from a small rural sewage treatment works on the water quality of an upland stream. To investigate the effects of water quality changes on stream fauna.

10. 10 Objectives: To determine how treated sewage affects the abiotic conditions: Oxygen concentration Temperature pH Ammonium Nitrates Phosphates Dissolved Load To determine the susceptibility of freshwater invertebrates to organic pollution, using indicator species to give an indication of the extent of long term pollution. To determine the effects of pollution on species diversity and abundance.

11. 11 Species we may find!!

12. 12 Stonefly nymph Stonefly nymphs prefer rocky, stony, or gravel bottoms in cool, well-oxygenated, swift-moving streams or small rivers. Any effluent that reduces the oxygen content of the stream quickly kills the nymphs. BMWP = 10

13. 13 Flattened Mayfly Nymph These are only found in very clean water containing lots of oxygen. They absorb oxygen from the water through their gills. They are primary consumers that eat plants and algae. BMWP = 10

14. 14 Cased caddis Fly Larvae Caddisflies use silk (like butterflies) to build cases from gravel, twigs, needles, or sand. Different species build distinct cases, but they often lose them when removed from a stream. BMWP = 8 -10

15. 15 Cranefly Larvae Up to four inches long with a Fleshy, plump, rounded segmented body Its digestive track (internal organs) can be seen moving back and forth as it crawls. No legs and the back end usually has several extensions or finger-like lobes. BMWP = 5

16. 16 Flatworms Flatworms are unsegmented worms with flattened bodies. Their flatness allows them to shelter beneath stones. Being flat increases the area of skin exposed to the water, which improves the flatworm's oxygen uptake. BMWP = 5

17. 17 Freshwater Mite Tiny animals related to spiders. Up to 8mm. They have an oval body and 8 legs. Many are brightly coloured. BMWP = 4

18. 18 Leeches Flat, Worm-like, segmented body. Many are scavengers or feed on other invertebrates. Suckers at both ends are used for attachment, feeding, and locomotion. They swim gracefully and quickly in an up-and-down motion. BMWP = 3

19. 19 Red Midge Larvae (Bloodworms) These are sometimes called 'bloodworms' because of their bright red colour, but they are not worms at all. They are midge larvae. They eat dead organic matter and can tolerate very low oxygen levels. BMWP = 2

20. 20 Tubifex Worms These are thread-like worms that live in the mud on stream bottoms. They are filterfeeders They can tolerate extremely low levels of oxygen and are therefore found in polluted water. BMWP = 1

21. 21 This shows freshwater fauna as indicators of river pollution.