HNA Summary Report
Existing Conditions
Connectivity, Fragmentation, and Diversity

Stability implies that dams had little effect on the plan form outline and amount of open water area. Decreases in water area are attributable to several geomorphic processes including: loss of contiguous backwaters, filling of isolated backwaters, loss of secondary channels, filling between wing dams, and delta formation. Increases in water area are apparent where dam impacts inundated significant amounts of low elevation floodplain in lower pool areas.

Connectivity of UMRS aquatic habitats has also been modified by dams that block fish migration on the mainstem rivers and up into tributaries. Flood control and hydroelectric dams block access to over one-half of the length of tributary streams and rivers. Fish use tributaries for spawning and to seek refuge from harsh flow or water quality conditions on the main river. Upper Mississippi River System navigation dams are used to maintain low flow navigation, so the dams were constructed to allow high flows to pass freely through the dams with all gates open. Locks and dams 1 and 19 present nearly complete barriers to upriver fish migration because they are also hydroelectric dams with high fixed crests. The other dams are open from 1 to 30 percent of the time, which provides some opportunity for upriver fish passage (Fig. 16).

Fragmentation
Natural habitats are highly connected south of Minneapolis to Clinton, Iowa, because there is abundant public land (Fig. 17). However, discontinuity in the distribution of public lands and levees (Fig. 18) has resulted in significant habitat fragmentation south of Rock Island and along the lower Illinois River (Fig. 19). The riparian forest remains fairly contiguous in a narrow band along the longitudinal gradient of the rivers, but large tracts of other native floodplain terrestrial communities only remain as remnants in the national wildlife and fish refuges and state conservation areas.

Diversity
Habitat diversity is a measure of the different types of habitats, their size, and their relative abundance in a defined area. Habitat diversity can be calculated for both land cover and geomorphic areas. Land cover diversity is highest along Minnesota, Wisconsin, and northern parts of Illinois and Iowa (Fig. 20). Pools 1 to 4, 14 to 19, and the Illinois River have moderate diversity. Pools 1 and 15 are highly urbanized, Pool 18 and Alton Pool are highly agricultural and have incomplete data. Pool 20 and southward have the lowest Agriculture is an obvious low diversity environment but even natural communities such as this sedge marsh can have few species. A more diverse marsh supports many different types of herbaceous and woody plants. diversity scores. These lower reaches are highly developed for agriculture. Geomorphic area diversity follows a pattern very similar to land cover diversity.