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The following "what if" scenarios were developed by Martin Christ for the May 28, 2003 meeting to help the NCC clarify understanding of the characteristics of nutrient impairment.

Ground rules

1.         This is only a values clarification exercise, not proposals of specific impairment criteria

2.         This procedure is unlikely to ever be complete.  It should be ended by consensus, when we think there is no more progress to be gained by this exercise

3.         The goal is elucidate both consensus and differences of opinion on impairment

4.         Certain scenarios may be unmeasurable.  Nevertheless, they may be valuable for values clarification.

5.         All scenarios are just hypothetical at this point.

6.         Please add additional scenarios to this list.

Scenarios:  in which of these cases are the streams impaired?

1. Nutrient additions cause biomass of fish in a stream to double, with no change in fish species composition.
2. Nutrient addition cause biomass of fish in a stream to return to levels seen ten years ago, before several farms in the watershed implemented BMPs.
3. Nutrient addition reduces the population of a single darter species to a level such that it cannot survive the ten-year drought.
4. Nutrient addition reduces the population of a single darter species to a level such that it cannot survive the ten-year drought, but the stream can be recolonized from a neighboring stream every year during high water.
5. Nutrient addition reduces the population of native brook trout to a level such that it will not survive the ten-year drought.
6. Nutrient addition causes a community that contained approximately equal numbers of five different species of fish to change.  The new community contains the same number of fish, but 80% belong to one species, and the remaining 20% are evenly divided, 5% for each species.
7. Nutrient addition causes a community that contained approximately equal numbers of five different species of fish to change.  The new community contains four times the number of fish, but 80% belong to one species, and the remaining 20% are evenly divided, 5% for each species.
8. An index for streams that uses the composition of the periphyton community has been devised.  A certain stream has higher phosphorus concentrations than nearby streams, and has a much lower score on the periphyton index.
9. A periphyton index for streams has been devised.  Reliable papers show that scores of 50 are almost always associated with extremely species-poor communities.  A diverse stream had an index of 80 in 1995, 70 in 2000, and 60 in 2005.
10. Because of nutrients, the stream bed in a 100-yard reach has become covered in filamentous algae during spring and summer.  That only began to happen five years ago, but now occurs every year.
11. Nutrients are shown to cause an endangered mussel species to disappear from a stream.
12. Nutrients are shown to cause a non-endangered mussel species to disappear from a stream.
13. A stream has a high nitrate concentration, and several deformed amphibians have been found nearby.