| Question 1: ________ compounds are usually found as relatively insoluble phosphates in river water and, except in some exceptional circumstances, the origin is from agriculture of human sewage. | |||
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| Question 2: A mixing zone may be very large and extend for many miles as in the case of the ________ and Missouri rivers in the United States and the River Clwyd and River Elwy in North Wales. | |||
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| Question 3: Coupled with the release of oxygen in photosynthesis is the creation of bi-carbonate ions which cause a steep rise in pH and this is matched in darkness as ________ is released through respiration which substantially lowers the pH. | |||
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| Question 4: A river flowing across very ancient ________ schists is likely to have dissolved very little from the rocks and maybe similar to de-ionised water at least in the headwaters. | |||
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| Question 5: Some organic constituents such as synthetic ________, pesticides, pthalates have direct metabolic effects on aquatic biota and even on humans drinking water taken from the river. | |||
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| Question 6: Ammonium ions also have a toxic effect , especially on ________. | |||
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| Question 7: Conversely a river flowing through chalk hills, and especially if its source is in the chalk, will have a high concentration of carbonates and bicarbonates of ________ and possibly Magnesium. | |||
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| Question 8: Some lead and copper mining also encounters ores containing ________ which may then be released into local rivers. | |||
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| Question 9: As a consequence the majority of ground-water data comes from samples taken from springs, wells, water supply bore-holes and in natural ________. | |||
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| Question 10: ________ is very toxic even at very low concentrations but leaves no visible of its contamination. | |||
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