**4.1 Removing suspended particles**

As suspension feeders, Unionids can remove large amounts of phytoplankton, bacteria, and inorganic nutrients from the water column, enhancing water clarity and quality (Strayer et al., 1999). When present in large numbers, they can filter an amount of water equal to or greater than that of daily stream discharge. In a study conducted in the River Spree in Germany, Welker and Walz (1998) found that freshwater mussels created a zone of "biological oligitrophication" by decreasing phytoplankton and phosphorus in the water column. Unionids can also play other important roles in nutrient cycling, such as removing pelagic nutrient resources and depositing them into nearby sediments as faeces or psuedofaeces (Roditi et al., 1997; Spooner and Vaughn, 2006). Mussels also influence nutrient cycling by serving as nutrient sinks in growing populations, or as nutrient sources in declining ones (Vaughn and Hakencamp, 2001).
