{"id":2777,"date":"2019-01-23T16:45:36","date_gmt":"2019-01-23T15:45:36","guid":{"rendered":"http:\/\/life.npsumava.cz\/o-vode-a-mokradech\/o-rekach\/"},"modified":"2020-01-24T13:58:47","modified_gmt":"2020-01-24T12:58:47","slug":"about-watercourses","status":"publish","type":"page","link":"https:\/\/life.npsumava.cz\/en\/water-and-wetlands\/about-watercourses\/","title":{"rendered":"About watercourses"},"content":{"rendered":"

Water resembles man in many ways \u2013 for instance, it seeks the easiest path, and you would have to force it to go uphill. And because water repeats the easy paths over and over, it gives rise to springs, streams, creeks, rivers, major rivers. Sometimes they gain too much energy flowing from the mountains and gnaw out new courses, sink in the substrate \u2013 and lo and behold, there\u2019s a valley! Their energy comes from the sun \u2013 sea water returns to the spring areas in the mountains or other, mostly cold areas in the form of water vapour that cools down, condenses, and falls down as rain.<\/strong><\/p>\n

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Life of a river
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Rocky mountain creek<\/p><\/div>\n

A spring can be a well-groomed fountain, but more often it is a wetland from which one or more small rivulets flow out; springs on the bottom of natural or artificial lakes are no exceptions. Several rivulets merge to form a stream, which then usually gets a name. In the initial stage of their lives, rivers tend to be fierce \u2013 taking away more than they deposit, washing away stones, gravel, and bit by bit whole mountains. With kilometres of length and metres of width, the pace slackens. And the river bed undulates \u2013 the river extracts material on the impact side (and forms deep pools where you might find pike lurking, but also high, undercut banks), while on the opposite side, material tends to deposit and form sand banks. Straight sections between the bends often comprise rapids or shallow parts with rushing water \u2013 ford crossings. Braided rivers on hillsides (like, for example, the Be\u010dva River in Moravia) do not tend to undulate much \u2013 during floods, they create a bed even several dozen metres wide, while flowing in several beds, often divided by gravel drifts, under normal discharges.<\/p>\n

Unless a river is deprived of its name by a stronger one at a confluence, it continues its course \u2013 as a lowland river. An elderly lady, carrying water much more slowly, who prefers indirect routes and sometimes forks the channels in a way similar to the Amazon \u2013 a river arm here, a fourth parallel through-flow channel there, and the main stream is almost invisible under the nettles and thriving vegetation. The best example of this is the Litovelsk\u00e9 Pomorav\u00ed Protected Landscape Area. When a meander bends too much, the thin neck breaks when a flood comes, the river straightens, and the meander, now an oxbow, slowly silts up and overgrows. In these parts, the river mostly carries fine sands and clays, and deposits them, sometimes bringing so much of them that it then flow on its own sediments \u2013 in fact, raises the bed above the surrounding terrain. In \u0160umava, nice meanders can be found on the Vltava in a section called Vltavsk\u00fd luh (Vltava Flood Plain) \u2013 far from being a lowland river, the Vltava nonetheless beautifully meanders under the Soumarsk\u00fd Bridge at an altitude exceeding 750 metres and behaves like a river that is close to entering the sea. But being located in cold mountains and surrounded by peat bogs, the Vltava most of all resembles lowland rivers of the far north.<\/p>\n

\"Meandring<\/a>

Meandring Vltava River<\/p><\/div>\n

Life in a river
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Water is full of life (unless we percolate it with chlorine). River life changes with the water temperature and the amount of light and oxygen. The upper course contains crystal clear water \u2013 low in nutrients, cold, and well-oxygenated. The middle course tends to be warmer, with less light towards the bottom, and a medium level of oxygen. And the slow, warm, meandering river in the lowlands is very low in oxygen, but nutrients are at maximum (nitrates washed away from cultivated fields are \u201cextra\u201d). All of this changes life in the river, both flora and fauna.<\/p>\n

In the wells and deep springs, tiny creatures, colourless and without eyes, patiently wait in the cold water for a bite \u2013 edible stuff sometimes fall into a spring. Springs, those exposed to sun, are home to freshwater snails (e.g. Bythinella austriaca<\/em>) and common water moss. Spring basins and rivulets, too small for a trout to turn around in, are ideal for freshwater shrimp (agile crustaceans, about one centimetre long), Turbellaria<\/em> flatworms living pressed against the stones, and horsehair worms, more than ten centimetres long and yes, resembling horsehair.<\/p>\n

When a rivulet can be called a stream, you will most probably see trout, European bullheads (\u201cwater dragons\u201d), and the marvelous, cyclostomatous European brook lamprey, a fish that spends most of its life as a larva \u2013 ammocoete \u2013 buried in fine sediments, filter feeding with its round mouth. Adults only live for several days or weeks \u2013 they simply deposit eggs, create a new generation, and die. The lamprey larvae enjoy a longer life, usually four to five years in our streams.<\/p>\n

Streams and rivers also provide a habitat to land invertebrates who spend most of their lives as aquatic larvae. Mayflies are not short-lived, though the saying claims otherwise \u2013 their larvae live for several years in water, while the adults die shortly after their wedding dance above surface. You can also see caddisflies, \u201cwater builders\u201d or \u201cliving wood\u201d, who build houses from small stones and bits of wood. Others, however, do not care a bit for building and prefer hunting using nets, waiting for what comes in the flow. Larvae living in the water flow are sometimes taken downstream \u2013 and the winged adults have to fly up river, so that the new generation can again drift downstream. And some have \u201ctaxi cabs\u201d for that \u2013 for example, larvae of freshwater pearl mussels, tiny glochidia, cling to the gills of trout, who feed them as well as give them a ride. Adult mussels then only sit in the gravel, waiting for what the river will bring. In the current billow water plants: crowfoot (Batrachium<\/em>), watermilfoil (Myriophyllum<\/em>), and starwort (Callitriche<\/em>).<\/p>\n

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Marsh-marigold (Caltha palustris<\/em>)<\/p><\/div>\n

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Larger rivers host larger species. With more water \u2013 unless the turbines of hydroelectric power plants have flogged them to bits \u2013 come grayling, as well as migrating eel and salmon. The river bottom is home to barbel, carp, catfish, white pike, asps, and pikeperch hunt above them. Tubifex<\/em> worms dig into the bottom, mosquito larvae float on the surface \u2013 oxygen is scarce in these waters, so they breathe atmospheric oxygen. You can encounter various mussels here, but also diving bell spiders, predatory great diving beetles, and on the surface, there are pond skaters (insects!) and backswimmers. Afloat, there are water-lilies, delicate green duckweed, while Canadian waterweed often surprises swimmers underwater. The water has turned from clear to brown-green, there is enough heat, there is no fear of drying up.<\/p>\n\n\t\t\t