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The Invisible River _ Extraordinary Biodiversity
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00:00There are places where what normally remains hidden becomes visible.
00:13Magical underwater realms in which fish and birds have developed very special hunting techniques.
00:20The creatures live here in an element that has become rare.
00:37Clean groundwater.
00:40But what is this treasure that so few of us know about?
00:50Where can we find this precious resource that supports and links together the most diverse habitats?
01:20.
01:27Hidden in the Upper Rhine Valley between the Black Forest and the Vosges is a place you wouldn't expect on this plateau.
01:38Hidden in the upper Rhine Valley, between the Black Forest and the Vosges, is a place
01:47you wouldn't expect on this plateau.
01:51A spring in the middle of the valley.
01:56It feeds a small pond.
01:58Its water is a constant 11 degrees Celsius.
02:02On cool days it steams, just like a heated jacuzzi.
02:10Thunder holes is what local people call these rare springs, because they look as though
02:15thunderbolts have punched holes in the ground.
02:20Here, what we normally never see gushes towards the light, ground water.
02:28It positively bubbles out of the earth.
02:35In late winter, the warm water attracts bathers.
02:38A northern pike luxuriates in the cozy spring water, like a guest in a wellness spa.
02:52The ground water has only limited oxygen, so the trout is a little short of breath.
03:00It's especially in spring that the male pike gather in the warm pool.
03:06They bear scars, signs of battles fought.
03:14Gradually, more and more pike arrive.
03:22She is the object of their desire, a large female pike.
03:26Her abdomen is bulging with eggs.
03:38During time turns the predators into tender cavaliers.
03:57For weeks, the suitors don't let the female out of their sight.
04:01They don't want to miss the decisive moment.
04:14More and more pike pursue the female.
04:18They perform a unique underwater dance.
04:21Every gigolo tries to get closest to her.
04:31With a whip of her tail, the female releases hundreds of tiny eggs, to which the males add
04:36their sperm.
04:39It's a love dance which leaves the question of paternity open.
04:53The most persistent admirers follow the female until the very last eggs have been expelled,
05:05thereby begetting more progeny than the other suitors.
05:17This pike paradise doesn't lie in untouched countryside, but in the upper Rhine valley.
05:24Why is it here, in the middle of the plateau, that the ground water comes to the surface?
05:29The upper Rhine valley is like a huge basin surrounded by mountains, which were pushed up 50 million years
05:44ago.
05:45The Black Forest to the east, and the Vosges in the west.
05:54It's in the mountains that the water bubbling out in the plain begins its journey.
06:11Up here it's colder than in the valley.
06:20The clouds form and get caught in the hills.
06:25Rainwater collects in many small streams.
06:33The water is crystal clear and still free of pollutants.
06:49It's so clear that, with a bit of luck, a very rare creature may be spotted.
07:01The stone crayfish survives only in remote streams, far away from roads or pollution.
07:13This feathered swimmer also needs clear, fast flowing rivulets.
07:20The white-throated dipper raises its ravenous young by the mountain stream.
07:26It's the only songbird in the world that can dive.
07:41It catches insect larvae underwater for its young.
07:54It dives scores of times.
07:56The fledglings keep her busy around the clock.
07:59This dipper has perfected its hunting technique.
08:03It's caught a caddisfly larva, not to eat, but to use as bait.
08:08A fish has fallen for the ruse.
08:20It has the larva in its mouth.
08:23But it and the larva end up as bird food.
08:33This hunting technique has never before been observed in a white-throated dipper.
08:48Also in pursuit of insect larvae are small fish like the common minnow.
08:57They, in turn, are pursued by young trout.
09:03Minnows are on their menu.
09:07But as long as the trout aren't hungry, the small fish are safe.
09:22The mountain stream flows on down towards the valley.
09:28The streams join together into rivulets, which finally empty into the Rhine.
09:36But some of the water takes a completely different route.
09:48One which remains hidden from animals and humans alike.
09:55The rainwater seeps into cracks and crevices.
10:05It meets with impermeable rock and flows underground into the upper Rhine valley.
10:11There it joins up with still more groundwater, which comes from the Alps, to form Europe's largest groundwater reservoir.
10:19It extends across the whole valley like an invisible river.
10:26At some places in the valley, the groundwater appears again.
10:31Where the soil is loose, it takes the path of least resistance to the surface.
10:36Creating ponds like this thunder hole.
10:46Like this thunder hole.
10:53It's not just the pike who appreciate the constantly warm groundwater.
10:58Sticklebacks breed directly next to the underwater springs.
11:10It's the male that takes care of the brood.
11:12It fans fresh water and therefore oxygen over the eggs.
11:21And keeps uninvited guests away from the breeding ground.
11:28What looks like a twig is a caddisfly larva in its armor plating made of plant remains.
11:44A genuine specialist thrives in the thunder hole.
11:48The fen pondweed.
11:51It feels at home here because the spring contains very few nutrients, like nitrates and phosphates.
12:04Where the water is not so pure, the pondweed is displaced by algae and other plants.
12:13Sometimes a koipu will visit the waters.
12:17These large rodents originally came from South America.
12:21Until some of them escaped from fur farms in Europe.
12:25Since then, they have been proliferating rapidly along the Rhine.
12:34The koipus are herbivores and they feed mainly in the fields bordering the rivers.
12:51The threat for the groundwater comes not from the koipus, but from further up.
13:04The problem comes when the rain turns into a cloudburst.
13:15Some days the rainfall is as much as otherwise in a whole month.
13:19This causes flooding in the meadows.
13:36At the same time the groundwater rises, so more and more water flows in.
13:41That's fine for white storks and other birds.
13:49As the meadows flood, mice and worms provide easy prey.
13:57But the flood water spreads further and further.
14:00And finally reaches the river, full of groundwater.
14:21From the surrounding fields, the flood water brings something that threatens the groundwater habitat.
14:26Nutrients that can cause algae to spread rapidly and cloud the river.
14:36But sometimes there's a blessing in disguise.
14:39In spring, the flood water is warmer than the groundwater.
14:43So the two don't mix.
14:45They form two layers, as in a latte macchiato.
14:49Good news for the pike.
14:50Where the two layers meet, they can find insects and fish.
14:57The murky flood water does not spread down to the river bed.
15:02So this time the creatures that live here are spared.
15:05The cloudy water makes everything dark below, which wakes up a nocturnal eel.
15:19Soon the flood water recedes and the spell is broken.
15:36But the flood has left something behind in the spring river.
15:41A European chub.
15:50The fish was washed into the thunder hole.
15:54Not a good place for a chub.
15:57The pike are just waiting for a meal.
16:02The small fish keeps very still, otherwise its fate would be sealed.
16:12The highly sensitive sensory cells on the head and flanks of the predator detect even the smallest movement in the water.
16:21Can the chub remain undiscovered?
16:28The danger seems to have passed.
16:45But the chub does not know the pike's hunting technique.
16:52He's lurking, concealed, until the prey swims right under his nose.
17:05A narrow escape.
17:06But in the end, the perseverance and the huge mouth of the hunter win out.
17:26If a fish swims in front of a pike's mouth, a reflex reaction snaps it shut.
17:32The predator prefers to swallow its scaly prey head first.
17:52Without the constant flow of ground water, there'd be no thunder hole here.
17:57And no pike.
17:58The ground water has created a wild habitat that's species rich.
18:09In the immediate neighborhood though, it's man that determines what grows and what doesn't.
18:15The spring is surrounded by fields.
18:19The more intensely they're farmed, the greater the threat to the ground water.
18:23The farmers spray their fields with weed killers and insecticides.
18:34These seep down into the ground water and pollute the underground current.
18:40This is not only harmful for wild plants and animals, it's also a threat to the drinking water that's pumped into tall water towers.
18:52Excessive fertilizing, whether with mineral fertilizers or manure, is also harmful to the ground water.
19:02Whatever gets into the ground water, reappears somewhere else.
19:13The nutrients contained in fertilizers pollute the delicate wetlands.
19:17The result is that algae overrun everything else.
19:27Fertilizer residues are becoming an ever greater problem for nature and drinking water worldwide.
19:33This also applies to the upper Rhine Valley, where hardly any land remains unused.
19:48A few wetland areas survive simply because of the ground water.
19:53It forces its way out of the ground in hollows, making the land too soggy for cultivation.
20:06Lakes and reed beds are formed.
20:14Wetlands like these marshy areas are a paradise for waterfowl.
20:19Great cormorants have chosen one of the few trees in the marsh as their common roost.
20:32Here they're safe from enemies.
20:36The marsh provides ample food for all.
20:39For the spotted redshank chasing sticklebacks.
20:43And for the great egret.
20:49The cormorant has set itself quite a task.
20:52The cormorant has set itself quite a task.
21:04Has it overreached itself?
21:12It's all just a question of technique.
21:13A wild boar sow is rearing her young on a small island in the marsh.
21:27A safe home for the offspring.
21:28But to find food, the family must also leave its haven sometimes.
21:39Wild boars are amazingly good swimmers.
21:43Otherwise, they couldn't be island residents.
21:44Wild boars are amazingly good swimmers.
21:45Otherwise, they couldn't be island residents.
21:46Wild boars are amazingly good swimmers.
21:48Otherwise, they couldn't be island residents.
21:52Wild boars are amazingly good swimmers.
21:53Wild boars are amazingly good swimmers.
21:54Wild boars are amazingly good swimmers.
21:57Otherwise, they couldn't be island residents.
22:00The marsh also acts as a nursery for white storks.
22:20In the surrounding fields they find frogs, worms and mice for their brood.
22:27The marshy meadows are also an El Dorado for flowers and insects.
22:44Now though, wetlands like these have become extremely rare.
22:50In the upper Rhine Valley too. Butterflies, grasshoppers.
22:55And spiders only breed in meadows that are not intensively cultivated and only mown in the season.
23:05Then even very rare flowers can flourish, like wild gladioli.
23:10In the protection of the plants, the Eurasian curu nests in the wet meadows.
23:25In 2017, the year of the last count, there were only a handful of breeding pairs left in the upper Rhine Valley.
23:37From year to year, there are fewer and fewer fledglings looking for food.
23:53These may be the last shots of young curlews in this region.
24:03When night falls on the marsh, other animals make themselves heard.
24:08Dusk is the starting signal for countless thousands of eager voices.
24:16Together they launch into a many-voiced concert of chirping and croaking.
24:21Amphibians are particularly active on rainy nights.
24:36Common frogs and European tree frogs go looking for partners.
24:55Yellow-bellied toads or edible frogs.
25:00Frogs, all of them try to attract a partner with their croaking.
25:05But sometimes, a deadly enemy comes along instead.
25:19For grass snakes, frogs are at the top of the menu.
25:22They scent their prey with their tongues.
25:35It's tough on the frog that the snake can dislocate its jaw.
25:40So it can eat prey that's quite a bit bigger than it is itself.
25:44The frogs, lucky enough to escape, will live to croak another day.
26:03The marshland is a small oasis in the upper Rhine Valley.
26:07Created by the groundwater, which links perfect habitats like wet meadows, pools and rivulets.
26:17And keeps them alive.
26:18If the earth were transparent, a vast groundwater reservoir would be visible.
26:35Far mighty than the Rhine, the underground river flows slowly to the north.
26:40It's a treasure that humans help themselves to.
26:55Farmers grow maize in huge monocultures.
26:59The maize flourishes splendidly in the sun-drenched upper Rhine Valley,
27:04especially when it's watered.
27:06Some of the sprinklers are kept running even during the hottest hours of the midday sun.
27:12What the plants don't take up evaporates in the summer sun,
27:16which takes its toll.
27:18The groundwater can sink by up to two centimeters a day in July.
27:27Streams fed by the groundwater dry out.
27:30This spells doom for plants, fish and invertebrates.
27:44This summertime wave of death can only be avoided if the farmers of the upper Rhine Valley
28:00use the groundwater more sparingly.
28:02People have left their mark on the plateau between the Vosges and the Black Forest.
28:22Even right next to the Rhine, they have radically altered the landscape.
28:41When heavy machines are used to tear up the land, they strike right into the underground river.
28:46Every new hole immediately fills up with groundwater.
28:55Sand and gravel are sought after building materials.
29:04They're extracted on a large scale in the upper Rhine Valley.
29:09But what starts out as an act of destruction can become a second chance for nature.
29:29Along the Rhine, new artificial wetlands are being created.
29:40Flooded gravel pits.
29:44After years of extraction, the pits are exhausted.
29:47Nature quickly gains a foothold again in the shallow shore areas.
30:07The groundwater river also flows through the gravel pit, breathing life into it.
30:14Plants and animals grow and swim literally in the middle of the groundwater.
30:25A dead leaf on its way down into the deeps, into a shady, bizarre world.
30:36The artificial light illuminates places to which sunlight hardly penetrates.
30:41Thirty metres below the surface, there are hardly any plants anymore.
30:52Freshwater sponges, which look like coloured stones, filter suspended particles out of the water.
30:59Sometimes they serve as cosy places to sleep.
31:10Bryozoa, tiny moss animals, cover a sunken bush.
31:16With their cilia fronds, they swirl miniscule particles into their mouths.
31:21Snails graze algae from the stones, and in turn, wet the appetite of the crayfish.
31:32Which always carries its cutlery with it.
31:35That's practical if you have to extract your meal from a hard shell.
31:43At a depth of 50 metres, creatures wait for everything that sinks down here.
31:49The decomposers.
31:51They include lake fly larvae.
31:52And flat worms.
31:53They feed on dead plants and animals.
31:54The decomposers.
31:59They include lake fly larvae.
32:01And flat worms.
32:02They feed on dead plants and animals.
32:03The Sludge worms form strange circles.
32:05During digestion, the decomposers exhaust the oxygen dissolved in the water.
32:06The decomposers.
32:08They include lake fly larvae.
32:12They feed on dead plants and animals.
32:24Sludge worms form strange circles.
32:25During digestion the decomposers exhaust the oxygen dissolved in the water.
32:31dissolved in the water.
32:35Freshwater sponges then die and are eaten by amphipods.
32:45If the oxygen is completely used up, the water releases iron compounds which stain the ground
32:52orange.
32:56White bacterial lawns also grow here.
33:00Natural spectacles which can only be seen for a few weeks in the year.
33:09If oxygen rich water arrives in the depths again, crustaceans and fish return.
33:19The dark underwater world is open to them once more, and they are off hunting for food.
33:29Like pioneers on an alien planet.
33:36In the shallower areas of the gravel pit, hunger drives a feathered underwater hunter.
33:50A young great-crested grebe is off on one of its first hunting ventures.
34:02The lake is teeming with fish.
34:10But the fish are too agile for him.
34:22But the fish are too agile for him.
34:32So the grebe dives even deeper, driven by hunger, into the plants.
34:44And then there's the question of breathing.
34:57And then there's the question of breathing.
34:58The predator has to surface again after a minute at the latest, with no prey for his efforts.
35:12Then he notices that one of his relatives is more successful.
35:30The predator is soon driven off, and the hunt resumes.
35:46Finally, the tactic pays off.
35:48A fish hiding among the plants is caught in a lethal trap.
36:00This has never been observed before.
36:03Great-crested grebes swallowing their prey under water, and carrying on with the hunt as long
36:10as their breath lasts.
36:20Up to three fish per dive disappear in the grebes peak.
36:34Abandoned gravel pits filled with water can replace to some extent
36:39what people have destroyed.
36:50The river that gave the Upper Rhine Valley its name is no longer a wild natural river.
36:57It's been converted into a shipping canal.
37:00Its course has been straightened, and its banks fortified.
37:23Below the surface, the Rhine is a bit of an underwater wasteland.
37:31Hardly any plants and only a few species of fish.
37:35Long, tactile organs and a huge mouth make the Wells catfish a perfect predator in murky waters.
37:44What remains a mystery is why these giant fish, up to two and a half meters in length,
37:57regularly collect in large groups, and always in the same place.
38:03The catfish don't gather for mating or for hunting together.
38:09Could it be that they are just looking for contact with each other?
38:15The barren underwater landscape offers hardly any hiding places, with a few exceptions.
38:27Gobies make their home among the bottles and stones.
38:33Since the turn of the millennium, these ground fish have been migrating via canals from the Black Sea to the Rhine.
38:40They have hardly any natural enemies in their new home, but they do have a huge appetite.
38:58The immigrant gobies are reproducing at an explosive rate.
39:03They are already on the menu of the catfish, but whether that will be enough to limit their proliferation remains to be seen.
39:10The straightening of the Rhine began in 1817.
39:22Towns and agricultural land developed where the river once formed meanders.
39:28Since the beginning of the 20th century, the Rhine has been navigable for large ships.
39:34Many of its lateral branches were drained.
39:38Others were cut off from the Rhine by embankments.
39:42Only in the few remaining branches of the Rhine can we detect what it must have been like at one time in the whole of the Upper Rhine Valley.
39:57An intertwined labyrinth of water and land.
40:04An underwater jungle, hunting grounds for waterfowl and fish.
40:12Here too we find groundwater springs which ensure that the cut-off branches of the Rhine don't dry out.
40:19These river branches provide underwater patterns for waterfowl and waterfowl and fish.
40:26These river branches provide underwater paradises full of hiding places and spawning grounds.
40:33More than 50 different species of fish live here.
40:40More than 50 different species of fish live here.
40:47More than 50 different species of fish live here.
40:54More than 50 different species of fish live here.
41:21As the water flows through the river branches, strange creatures gather to breed.
41:28At first sight, brook lampreys look like small eels.
41:34But instead of jaws, they have circular suction mouths.
41:39The females use them to clear spawning pits.
41:45Mating is the climax of lampreys lives and also their culmination.
41:50Shortly afterwards, they die.
41:59Very few of the Rhine's former branches are in such good condition as these idyllic lamprey spawning grounds.
42:07Despite their groundwater springs, many branches of the Rhine are slowly dying.
42:20Over the years, ever new generations of algae develop and decay.
42:26The leaves fall into the groundwater and decompose, leaving behind a thick sludge which builds up on the bottom and blocks the vital freshwater springs.
42:41Contact with the groundwater flow is broken.
42:53In the stagnant water, the oxygen content falls.
43:00The survivors are undemanding tench, common carp, and common bream.
43:24In some places, there are still a lot of larger fish to be found.
43:29But the former biodiversity is lost.
43:35For years now, conservationists have been trying to halt the slow decline of the former Rhine branches.
43:50They bring in heavy equipment to clear new paths for nature.
43:58Excavators create openings in the embankments of the Rhine.
44:06At the next high-water mark, the river can flow through again.
44:11Channels conduct the river water deep into the forests, which have long been cut off from the river.
44:26The river water flushes the sludge away from the bottom, which opens up the groundwater springs again.
44:37This restores a habitat that's dependent on the ebb and flow of the water, the alluvial forest.
44:50Sponges establish themselves on roots projecting into the water, and fish find cover again.
45:00Upstairs, the tree trunk attracts sunbathers.
45:09The water and the forest revive each other.
45:19The many plants in the alluvial forest filter and purify the water.
45:24For some inhabitants, this idyll is not without its dangers.
45:35Kingfishers use branches hanging over the water as hunting hides.
45:44A fat catch like this is bound to impress his mate.
45:47Some, especially sunny spots, attract animals that used to be very common along the Rhine.
46:02Well into the 19th century, European pond turtles were caught in their thousands and ended up as turtle soup.
46:18The straightening of the Rhine did the rest.
46:21The species died out along the Rhine.
46:23Biologists have been breeding the creatures for the last 25 years, in order to re-establish them here.
46:40When they are five years old, they are released into the former Rhine branches.
46:44They are then big enough and safe from herons and storks.
46:51Whether or not their efforts will bear fruit, and the pond turtles will reproduce on their own, remains to be seen.
46:58The water and wealth of plant life attract winged beauties.
47:23Dragonflies need healthy water to reproduce.
47:31Dragonflies need healthy water to reproduce.
47:46Most varieties mate near the water itself.
47:49Some females simply shed their eggs in flight.
48:03Others attach them to water plants, which just means getting their abdomen a little bit wet.
48:09A pair of common blue damselflies, in tandem flight, go looking for a place to lay their eggs.
48:19Then something remarkable happens.
48:24The female crawls down a stalk under water, and threatens to take the male down with her.
48:31At the very last second, the male lets go.
48:41The female steadfastly continues under water, up to two meters deep.
48:45Here it drills its eggs into the stem of the plant.
48:52It has a thin film of air around its body, which acts like gills, enabling the damselfly to extract oxygen from the water.
49:03The egg-laying process can last up to an hour and a half.
49:14This far beneath the surface, the eggs won't dry out, even when the water level in the Rhine branch drops.
49:20Finally, the female simply lets go.
49:27But the surface tension prevents the female from flying away.
49:44Making her easy prey for the predatory pond skaters.
49:51But now, male damselflies come to the female's defense.
50:01But that's not the end of the airborne rescue operation.
50:05A male damselfly tries to pull the female out of the water, not totally selflessly.
50:16He wants to mate with the damsel.
50:18But he's not alone in that.
50:20He has to fight off a whole swarm of competitors.
50:35The display of strength succeeds, and the female is rescued.
50:50Without the all-important groundwater, none of the stories of the dragonflies, the great-crested grebes, or the pike in the upper Rhine Valley would take place.
51:01It's not enough just to protect this vital natural treasure when it comes to the surface.
51:11The Rhine branches, gravel pits, and thunder holes are, after all, only the visible parts of the ground water that flows beneath our feet.
51:22SPIKE
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