This chapter discusses human disturbances to watersheds, streams and riparian buffers. The harms include the typical channeling of the urban stream syndrome, higher stream temperatures, and a loss of stream organisms and ecosystem services. Imperviousness most consistently reduces stream biodiversity, with up to 40-50% of stream taxa lost in watersheds with 15-20% imperviousness. The reduction is particularly apparent in large watersheds, which generally experiences at least some urban development. The chapter mentions that a set of species classified as sensitive are particularly affected, and they serve as indicator species for stream health, yet other aquatic invertebrate species thrive under urbanization. This chapter shows that while urbanization always demonstrates harm to streams, agricultural land use presents a more mixed picture. In the midwestern U.S., row crops can lead to significant species loss compared to pastures, and the losses can be as great as 50% moving from 0% to 100% agricultural land use. However, eastern U.S. agriculture affects stream biodiversity much less than imperviousness, and in the southeast, agriculture has a relatively insignificant effect while urban land use presents serious harm.
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