Why is the intensity of a pulse different at different sites?

Because pulse wave velocity decreases as arterial diameter decreases, a slight difference in local vasculature can cause inter-site differences not only in pulse transit time but also in its variations.  

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poor water quality affects most estuarine organisms, including commercially important fish and shellfish. the pollutants that have the greatest impact on the health of estuaries include toxic substances like chemicals and heavy metals, nutrient pollution (or eutrophication), and pathogens such as bacteria or viruses.