Danube Rivers Morphology and Revitalization - DANUBEPARKS

The river grows and the gradient lessens with few riffles and rapidsTerrestrial organic matter is insignificant in comparison to the volume of water;Energy is supplied by dissolved organic material from upstream reaches; Drifting phytoplankton and zooplankton contribute to the food base as do organicmatter from the floodplain during flood pulses; Increasing turbidity reduces sunlight to the streambed causing a reduction inrooted aquatic plants; Backwaters may exist where turbidity has settled and aquatic plants areabundant; Fish species are omnivores and plankton feeders such as carp, buffalo, suckers,and paddlefish;Sight feeders are limited due to the turbidity (MN DNR, Healthy Rivers).To discuss about the longitudinal connectivity it is good to have some questionat the beginning and to try to find some answers as an understanding way of theconcept.How connected is the river along its length?The longitudinal connectivity implies that stream (in our case river) shouldhave a continuously path from the spring to its mouth. This is the natural case.Is it broken up by dams, weirs or natural obstacles?This longitudinal continuity could be often tainted by natural and artificialcauses. The main artificial causes are: dams for different purposes (water stocking,producing energy etc.). Natural causes are more rare and usually are accidentally(weirs created by thunderstorms by getting down the trees) and not accidentallyweirs created by beavers. Vertical connectivity is represented by the connection between theatmosphere and groundwater. The ability of water to cycle through soil, river, and airas liquid, vapor, or ice is important in storing and replenishing water (Figure 2). Thisexchange is usually visualized as unidirectional–precipitation falling onto land andthen flowing over land or percolating through the ground to the stream. An equallyimportant transfer of water occurs from the streambed itself to surrounding aquifers.Groundwater can contribute to flows in the river at certain times in the year and atcertain locations on the same stream. Streams may either gain or lose water to thesurrounding aquifer depending on their relative elevations. Lowering the water tablethrough groundwater withdrawals may change this dynamic exchange inunanticipated ways (Stream Corridor, FISRWG).The slow movement of water through sediments to the river produces severalecological benefits (Minnesota Department of Natural Resources):