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Seasonal Considerations
The numbers and types of invertebrates can change according to the seasons without any relationship to pollution. When analyzing invertebrate data, keep in mind these seasonal considerations:
Spring
- Unusual scouring by high water flows, ice dams or truck loads of snow dumped into rivers may cause a decrease in invertebrate populations.
- Spring invertebrates tend to be easier to see, easier to count and easier to identify because of their low numbers and large size.
Autumn
- Rivers are shallow in the autumn, making it easier for people to wade-in and collect invertebrates.
- Reproduction over the summer gives rise to higher invertebrate populations.
- Invertebrate samples collected in the autumn tend to contain higher numbers of organisms.
- Autumn immature insects are smaller and more difficult to identify.
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