**5.3 Flow alteration**

Restriction or alteration of flow patterns is another major cause of mussel biodiversity loss. The construction of dams restricts the timing, frequency, and magnitude of natural flow regimes, and affects mussels by altering the stability of the substrate, the type and amount of particulate organic matter (an important food source for mussels), the temperature of the water, and water quality (Poff et al., 2007). Studies have shown decreased mussel populations below large dams, with populations increasing with increased distance downstream from dams and with increasing flow stability (Strayer, 1993; Vaughn and Taylor, 1999). Altered flow regimes after dam construction have been implicated in the extinction of several mussel species, and have resulted in the local extirpation of many more (Layzer et al., 1993). Dams also impair recruitment of juveniles by restricting access to host fish and dispersal of glochidia (Watters, 1999). Urbanization of catchment basins can also alter flow regimes by increasing the amount of impervious cover and channelizing storm runoff, causing higher, faster, and more frequent erosive storm flow events (Walsh et al., 2005). Direct withdrawals of surface and ground water for human consumption can also reduce available habitat, increase water temperatures, and impair mussels' ability to feed, respire, and reproduce (Golladay et al., 2004; Hastie et al., 2003).
