RIVER ECOLOGY Authors: Stoyan Mihov, Ivan Hristov Translation: Katya Ancheva Design Concept © Twist Advertising Printed at Geosoft EOOD

Home , Iskar (river), Osam, River ecosystem, Vacha (river)

BOOKLET EN 2011

Conservation Biodiversity Sustainability RIVER ECOLOGY Authors: Stoyan Mihov, Ivan Hristov Translation: Katya Ancheva Design Concept © Twist Advertising Printed at Geosoft EOOD

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WWF-Bulgaria WWF-România 38 Ivan Vazov Str., floor 2, apt. 3-4, Str. Ioan Caragea Vodă nr. 26A, 010537, 1000 Sofia sector 1, Bucureşti Phone: +359/2 950 50 40, +359/2 950 50 41 Tel: +40 21 317 49 96 Phone /fax: +359/2 981 66 40 Fax: +40 21 317 49 97 [email protected], www.wwf.bg [email protected], www.wwf.ro CONTENT

INTRODUCTION ...... 05

THE RIVER AT LENGTH ...... 05 Sinuosity ...... 06 Riffles and pools ...... 06

THE RIVER AT WIDTH ...... 07 Horizontal structure of the river corridor ...... 07 Riverbed (bottom) ...... 07 Floodplain ...... 08

RIVERS IN DEPTH ...... 11 Vertical structure of the river corridor ...... 11

THE RIVER IN TIME ...... 12 Processes occurring in river corridors ...... 12 River runoff and flooding ...... 12 Sediment transport ...... 13 Riverbed processes ...... 14

RIPARIAN VEGETATION ...... 16

RIVER BIOCORRIDORS ...... 18

WATER QUALITY ...... 19 Suspended solids ...... 19 Dissolved oxygen ...... 19 Water temperature ...... 20 pH ...... 20 Nutrients ...... 20 Toxic (poisonous) substances ...... 21

ANTHROPOGENIC CHANGES IN RIVER CORRIDORS AND THEIR IMPACTS ...... 21 River straightening ...... 21 Gravel extraction ...... 23 Interruption of the river continuum by dams, hydropower stations, artificial lakes, trout thresholds ...... 25 Stream management – water intake ...... 26 Cutting down riparian vegetation, “clearing” river beds ...... 26 Water pollution ...... 27 Decreased retention capacity of watersheds ...... 27

RIVER RESTORATION IN BULGARIA ...... 28 Restoration of the link between the Danube River and the wetlands of Persina Island near Belene ...... 28 Restoration of Veselina River Meander near the Mindya Village ...... 29 Straightening of the Rusenski Lom River near Ivanovo Rock Monasteries . . . . 33 INTRODUCTION

The origin and development of component of the living body called human civilization are closely related “river”. to rivers. Over 90 percent of the human settlements in Bulgaria are We frequently overlook the fact that located in the vicinity of a river. This rivers have four spatial dimensions may be why the word “river” evokes – length, width, height (depth) and positive emotions and associations time (Fig. 1). Actually, even if it seems of things pure, clean, and calm. At that the river height is the water level the same time, being so close to and the width is the distance between human activities, rivers are subject its two banks, this is not a completely to various and quite often negative accurate perception considering the impacts. For most people, a river contemporary concepts of the river, means water flowing from the its ecosystems and the river corridor, mountains to the sea. However, which are much broader. flowing water is only one (essential)

Fig.1. The river corridor in time and space Time

(10/1998) © FISRWG

Width

Length

Vertical

WWF 2011 – River Ecology page 4 THE RIVER AT LENGTH Longitudinal structure of the river corridor

All rivers, regardless of their type, have cones. Other sediments are carried the same stages of structural changes further downstream. Erosion from source to delta. and deposition processes are in equilibrium in the transfer zone. The profile of every river can be Most of the lowland water courses divided into three zones (Fig. 2). in Bulgaria belong to this zone, including the Bulgarian section of • Source zone (headwaters) – the Danube River. mountain streams that slope rapidly downhill and form V-shaped river • Deposition zone – of rather low valleys, often forming waterfalls. slope; flow velocities are slow, These rapids shape and carry large- forming wide meanders. Most of size sediments downstream. the sediments, including the finest ones, settle in this area. The river • Transfer zone – characterized by mouth often opens into a wide a lower altitude. The flow velocity delta bottomed by fine sediments, is slower, the river bed becomes and the river splits into many wider, and meanders form. Some arms. In Bulgaria such zones are of the larger sediments settle at the formed only in the lower course interim area between the source of rivers that flow directly into the zone and the transfer zone, thus Black Sea. forming the so-called sediment

According to Miller, Jr., G. Tyler, 1990. Living in the Environment: An Introduction to Environmental Science, 6th Edition, în FISRWG (10/1998). Stream Corridor Restoration revised and added by Stoyan Nikolov, Stoyan Mihov and Ivan Hristov

Lower altitude, slower velocity, Very low slope, and wider riverbed. Erosion slow velocity, large and deposition processes are bends (meanders) in equilibrium in the sediment are formed and transfer zone. the river splits into arms. Most of the sediment Source zone deposits, including (headwaters) the finest drifts, are deposited in this zone.

Steep slope and Transfer zone fast velocity. Large size sediments are Deposition zone formed and carried downstream.

Fig. 2 Length-wise zoning of a river

WWF 2011 – River Ecology page 5 Sinuosity

Natural rivers are never straight. Such successive sequencing is also a We can calculate the sinuosity index precondition for quick and complete by dividing the mid-river length by dissolution of pollutants. It is not by the length of the river valley. When chance that straightened (regulated) the sinuosity index is more than 1.3, rivers with altered sequencing of pools the river is defined as meandering and riffles lose not only a significant (Fig.4). part of their fish population and other aquatic life, but also most of their self- This index is invariable for the purification capacity. relevant river section. This means that if the river course becomes straight as a consequence of human interference or natural “shortcutting” of a meander, disbalance will occur and the river will try to restore its previous sinuosity (Fig. 10). Riffles and pools Fig. 3. Regular sequencing of pools and riffles. Regardless of the form of their beds, all rivers have equidistant sequencing of shoals and deeper sections, called riffles and pools. They are linked to Midstream the river midstream – a line which benchmarks the deepest section of the river and where the water flows fastest. Pools are formed in the (10/1998) © FISRWG midstream, next to the outside bank Pool of a watercourse bend. Riffles are formed between two bends where the midstream goes from one river bank Riffle to the other (Fig. 3). The distance between two pools or two riffles – a common feature for all rivers – is 5 to 7 times the width of the river, Pool measured at its highest water level.

The sequencing of pools and Riffle riffles within a river section, and the existence of various habitats illustrates the variety of life adapted Stream Corridor Restoration: Principles, Processes, and Practices - The Federal Interagency Stream to both fast and slow currents and Restoration Working Group serves as a precondition for a well (FISRWG) (15 Federal agencies of the US gov‘t). GPO Item No. 0120-A; SuDocs No. A 57.6/2: EN 3/ functioning river ecosystem. PT.653. ISBN-0-934213-59-3

WWF 2011 – River Ecology page 6 Fig. 4. The Osam River at Obnova village before and after its straightening.

Longitudinal axis of the river valley Osam River before straightening Osam River after straightening © Stoyan Nikolov, Stoyan Mihov and Ivan Hristov © Stoyan Nikolov,

Before the straightening of the Osam River, the sinuosity index in the illustrated section was 3.55, which defined it as strongly meandering. After the straightening, the index became 1.02 which defines the river as “straight”. The shortcut of the river course reduced its length more than 3 times its natural length. THE RIVER AT WIDTH Horizontal structure of the river corridor

The basic component of river corridor between the river corridor and the is the riverbed. This is a naturally adjacent landscape. lowered landform usually used as a passageway for flowing water. The Riverbed (bottom) next component is the floodplain – this is the neighbouring part of the The shape and size of the riverbed riverbed, flooded by high water at are defined by the equilibrium of different intervals varying from very four basic factors – the energy often to seldom. The floodplain may of the water stream (slope and be situated on either one or both water velocity) and the resistance river banks, depending on relief. The of substratum (particle size of the next component is the transition sediment and its runoff). If we upland fringe, which begins above illustrate this on a scale where we the floodplain and forms the frontier have the sediments on one side and

WWF 2011 – River Ecology page 7 the water energy on the other, every floodplain up to the altitude reached decrease in the water energy will by a flood peak of given frequency result in smaller sediment particles (every 100 or 500 years). The and in the widening of the riverbed. topographic floodplain is used in The river equilibrium is reached spatial planning and development, when all four variables are balanced and all the activities therein must (Fig. 5). consider the risk of flooding. For instance, no human Floodplain settlements or important infrastructure facilities should The floodplain is theoretically be developed in the floodplains. divided into two parts: hydrologic floodplain and topographic The floodplains, especially those floodplain (Fig. 6). downstream, are dynamic systems with many various components that The hydrologic floodplain is an undergo a continuous process of area inundated about two out of formation or disappearance every three years. The topographic (Fig. 6 and Fig. 7). floodplain includes the hydrologic

Fig. 5 Riverbed equilibrium

Width of the river

Size of sediments River slope

Fine Coarse Steep Slant

Sedimentation Erosion

According to Hagerty, D.J., Piping/Sapping Erosion 1: Basic Considerations. Journal of Hydraulic Engineering, 117(8) in FISRWG (10/1998). Stream Corridor Restoration revised and added by Stoyan Nikolov, Stoyan Mihov and Ivan Hristov

WWF 2011 – River Ecology page 8 • Meander scrolls – old alluvial • Natural levees or sand-bars – these deposits that mark the former are formed during flooding when passageway of the riverbed. large amounts of sediments are carried out by waters that disperse, • Oxbow lakes or abandoned river losing most of their energy and bends – former river meanders depositing the coarser sediments that were gradually cut off the on one of the river banks, thus riverbed. They can be in different forming an embankment. stages of development – from those still linked to the river to those which are rather far away and almost dried up.

Fig. 6 Transverse structure of the river corridor

  Topographic floodplain   Transition zone Transition  Hydrologic floodplain  zone

Riparian vegetation

Level of flood peak

Level of regular flooding

Wet meadow Island Natural embankment According to Bayley, Peter, 1995. Understanding Large Riparian wetland River-Floodplain Ecosystems. Bioscience, March, 1995, Oxbow River bed Vol. 45, No. 3, page 154, fig. 1. in FISRWG (10/1998). Stream Corridor Restoration, revised and added by Stoyan Nikolov, Stoyan Mihov and Ivan Hristov

• Splay – structures that form at high Wildlife in rivers depends on all water when streams under pressure these floodplain components. For break through natural levees and instance, many of the carp species spread deposits into a fan-shaped need backswamps and oxbow lakes structure. to spawn. These are also the places where fish fry find food and shelter • Backswamp – wetlands that are amongst the water vegetation. formed after high water as a result of Draining of riparian wetlands natural levee formation which or cutting off their link with the prevents water going back to the river is one of the main reasons riverbed, thus prolonging the that downstream fish population flooding period. decreases.

WWF 2011 – River Ecology page 9 © FISRWG (10/1998) FISRWG © Lateral arm Chute Island Clay plug Meander scrolls Oxbow lake Splay Natural levee Riparian wetlands Fig. 7 River components in floodplains Stream Corridor Restoration: Principles, Processes, and Practices - The Federal Interagency Stream Restoration Working Group Group The Federal Interagency Stream Restoration Working Stream Corridor Restoration: Principles, Processes, and Practices - ISBN-0-934213-59-3 57.6/2: EN 3/PT.653. A (15 Federal agencies of the US gov‘t). GPO Item No. 0120-A; SuDocs (FISRWG)

WWF 2011 – River Ecology page 10 RIVERS IN DEPTH Vertical structure of the river corridor

The water level of most rivers varies an equatorial jungle. In the past, greatly depending on the season. The floodplain forests were widespread in seasonal level of rivers usually varies Bulgaria. Today such forests are only between 10-20 cm and 6-7 m (such as partly preserved along Danube islands, the Danube). The seasonal increase of the rivers of Kamchiya, Ropotamo, water level has an important role in Tundja, and the islands of the supporting river ecosystems. Rivers Maritsa River; on the other hand such often link to adjacent wetlands only floodplain forests have been completely at high water level, which is often the destroyed along the Iskar, Vit, Osam, only possibility for fish populations to Yantra and Sturma rivers. migrate. River depth does not end where its Unique vegetal systems develop bottom lies. The riverbed usually lies on on the banks of rivers with higher water-saturated, old river sediments. variations of water levels, especially This groundwater runs to or from the in the lower course; they are very river down the river valley. The stream well adapted to such conditions. in the riverbed is usually just a small These are the floodplain forests. part of the water flow running through One characteristic feature of their the valley. The level of groundwater vegetation is the impenetrable lianas. depends on the level of water in the riverbed. In dry seasons, surrounding Due to their appearance and areas drain into the river bed and extremely rich variety of animals groundwater runs towards it. During and plants, the floodplain forests flooding, the groundwater direction in Bulgaria are reminiscent of may reverse (Fig. 8).

Fig. 8 Relation between river and groundwater

The river saturates the land The river drains up the land (usually in springtime) (usually in summertime) © FISRWG (10/1998) © FISRWG

    Groundwater level Groundwater level

WWF 2011 – River Ecology page 11 Until the mid-20th century the wild species in our section of the Danube. carp made up 60% of the fish capture Nowadays the river hosts different in the Danube. After that dams were “wild” varieties of the cultured carp, built and much of the marshes dried which only morphologically imitate up. As a result, by the end of the 20th the appearance of their ancestors; they century wild carp was included into make up about 6% of the fish capture the Red Data Book of Bulgaria and (noting that the total fish capture is researchers consider it an extinct nearly ten-fold lower). THE RIVER IN TIME

Processes occurring in river corridors

“You cannot step twice into the same can vary within very wide limits for river” – next time the river will not the same river. For instance, in some be the same. This maxim of the torrential catchment basins (almost ancient Greek philosopher Heraclitus half of the basins in Bulgaria), the probably describes most precisely runoff may increase 100 times after a the dynamic nature of rivers. downpour.

River runoff and flooding The seasonal increase of water runoff and associated flooding are natural and Water transfer from precipitation unavoidable processes. into rivers and oceans and vice versa, including its vaporization, is known With regard to people, flooding may as the “water cycle”. This is the main cause serious consequences – from driving force of the river ecosystem. positive (the ancient Egypt civilization River runoff is the quantity of water developed on the banks of the Nile that moves through a spot of the River) to disastrous ones. river over certain time. This indicator

Fig 9. Forms of sediment movement

Underwater dunes Rolling Hopping Sliding with the flow

According to Dunne, Thomas; Leopold, Luna B., 1978. Water in Environmental Planning, W. H. Freeman and Company in FISRWG (10/1998). Stream Corridor Restoration, revised and added by Stoyan Nikolov, Stoyan Mihov and Ivan Hristov

WWF 2011 – River Ecology page 12 Flooding does not “damage” nature. the normal functioning of the river On the contrary, this is a cyclic process corridor. Spring high water is a that serves an important role for prerequisite for fish migration. The “fight” against flooding has This is the main concept in the been particularly evident in the 20th new European Directive 2007/60/ century. Numerous massive structures EC on flood risk assessment and have been erected to combat or limit management. The occurrence or the effects of flooding. Now we can non-occurrence of flooding is not in see that many of these technical our hands, but it is up to us whether solutions are effective against small flooding will significantly damage and medium floods, but not against human settlements and important the big ones. Sometimes they even infrastructure, or will impact forests increase the damage. Reconsideration and grasslands with minimum or no of this concept started in the middle of damage. It is a question of choice the 20th century. Nowadays in Europe and management – should we decide and globally we do not speak about to build within the river floodplain a “fight” (or even about “defense”) or let it be used for other purposes against flooding, but about flood considering the risk? control and reduction of damage. The regular water flow through flooding. If this process and the link riparian wetlands is also important with the river is broken, these areas because it carries away dead organic will silt up, the succession or “natural material and cleans the area. Many aging” will accelerate and they will backswamps exist due to periodical finally disappear. Sediment transport

The movement of eroded soil and bottom. They roll, hop or slide in the rock particles in water flow is called water depending on their size and transport of sediments. Sediment density (Fig 9). transport is measured by the number of undissolved particles that pass The sediment load of a river consists through a river spot over a certain of suspended and bedload sediment. time. The energy required to carry the particles and move them downstream • Suspended sediments are fine relates to the difference between the particles which are easy to move by velocities of water in different strata. turbulence in the bottom layer. These particles can be taken Water in bottom layers moves more up high in the water column and slowly due to higher friction, while transported a long distance with water in upper layers flows faster due no further contact with the riverbed to lack of friction. Thus a whirlpool, as long as the water has enough or vortex, is formed between the turbulence. The main part of the two water layers – this spiralling river solid load (50-90%) consists movement carries particles off the river of suspended sediments. The

WWF 2011 – River Ecology page 13 source of suspended sediments is mainly by rolling or hopping. The the entire river basin and the fine size of bedload sediment is the particles brought by rainwater same as that in the river bed in the and as a result of the soil erosion given river section. The source of on the river banks. bedload sediments is the riverbed • Bedload sediments are the bottom itself and, to a much lesser extent, particles, which are dense and the erosion of the banks and other big enough to move downstream sources.

One of the most popular examples for the importance of the link between river and riparian wetland is the lake of Srebarna. High spring water in the past used to carry away tons of nutrients, organic material, and even floating reed islands. With the building of a dam in 1948 between the lake and the Danube River, the conditions in the lake suffered an abrupt change. The lake started filling up with mud and organic waste, the open water surface began to shrink, and many fish and birds disappeared. The first attempt to partly restore the junction with the Danube was made in 1963. A sluice-gate was built into the retaining dam wall, but was abolished soon after that. In 1979 a section of the highest west zone of the dam was demolished. This made it possible for the high waters of the Danube River to enter the lake reserve.

This was an important step, but far from being enough, because it only enables water movement in one-way (from the Danube River to Srebarna) once in several years. The problems continue to intensify. In 1993 the reserve was about to be taken off the UNESCO World Heritage List.

In 1994 a canal with a sluice-gate was built to let Srebarna “breathe”. Thanks to this, Danube water can enter into the lake every year. It slows down succession process, but it does not solve the problem. As long as both the natural inflow of Danube waters to the lake and the equally important water runoff from the lake into the Danube are not provided, the Srebarna reserve will still be in danger.

Riverbed processes

The processes of erosion, sediment Sand dunes in the lower part of the transport, and deposition interacting river course also shift from their with vegetation make river corridors initial location. Sometimes they very dynamic ecosystems. Rivers surface over the water and form small constantly change shape and islands that may be carried away and location. New meanders and arms destroyed by the next high floods. are formed, old ones are abandoned; Riparian vegetation takes possession the riverbed itself shifts (Fig. 10). of some of these islands which can This phenomenon is called migration exist for several decades, continuously of the river corridor. relocating and changing their shape

WWF 2011 – River Ecology page 14 (Fig. 11). We can find most of the of key importance when planning riparian islands in Bulgaria along the human activities in river valleys – Danube and Maritsa Rivers (there especially in floodplains. Sometimes are about 120 to 140 islands in the it is not difficult to forecast the Romanian-Bulgarian section of the shifting of a river, and thus spare Danube River). Being aware of and considerable funds for reinforcement monitoring riverbed processes are of bridges, roads etc.

Fig. 10. River corridor migration - the same river section is shown in four different successive periods

New meander forming Meander cutting off the mainstream New meanders forming

Oxbow lake © Stoyan Nikolov, Stoyan Mihov and Ivan Hristov © Stoyan Nikolov,

Direction of riverbed relocation Direction of stream

Fig 11. Riparian island relocation

Previous locations of the island

The island nowadays © Stoyan Nikolov, Stoyan Mihov and Ivan Hristov © Stoyan Nikolov,

WWF 2011 – River Ecology page 15 RIPARIAN VEGETATION

Riparian vegetation is a very Wood canopy along smaller important component of the rivers may completely cover and river corridor, and its ecosystem overshadow the riverbed, while significance is even higher. Specific this effect is only partial along wood species adapted to the river larger rivers. The overshadowing conditions develop along all rivers. or “doming” of the water course With regard to natural rivers, this by riparian vegetation has an vegetation forms a continuous belt extremely strong influence on water temperature and sunlight Fig. 12 Roots of the Black alder © Stoyan Nikolov, Stoyan Mihov and Ivan Hristov © Stoyan Nikolov,

from the river spring to the mouth. penetration, which favours the The most typical species in Bulgaria development of phyto-plankton. to be found along the streams are willows and alders. River banks Riparian vegetation plays an important in the mountains are covered by role in river bank consolidation and green alder. Downstream its place prevention of coastal erosion. is consecutively replaced by white The roots of the black alder are and black alders. Different species entangled under the water into specific of willow, white and black poplar flat netting which retains even the and elm gradually become present. finest particles of the bank layers. The sycamore is another riparian tree species typical only for the Other riparian species such as willows lower courses of our southern rivers have similarly entangled roots but less (Struma, Mesta, tributaries of Arda, potential to protect against erosion etc.). (Fig. 12).

WWF 2011 – River Ecology page 16

Ivan Hristov Ivan and Mihov Stoyan Nikolov, Stoyan © Nutrients catching in roots

River with riparian vegetation in place Nutrients (nitrogen, phosphorus, etc.) phosphorus, (nitrogen, Nutrients Shadowing Stabilized bank Development of water vegetation River bank erosion River with removed bank vegetation

Nutrients (nitrogen, phosphorus, etc.) Fig. 13. The role of riparian vegetation

WWF 2011 – River Ecology page 17 The roots of riparian vegetation can “clean” some 80% of the nutrient also serve as a filter that “swallows” pollutants that would otherwise flow most of the nutrients dissolved in into the river. groundwater before reaching the river (Fig. 13). Once again, the black Vegetation in catchment basins alder appears to be a remarkable considerably slows down rainwater tree. It is a species that has one of runoff to the river, thus decreasing the highest capacities to extract the risk of a high tide. The abundant nutrients from groundwater. vegetation controls evaporation from Therefore sometimes even a thin earth surface and keeps groundwater (10-15 m) riparian belt of alder forest near the surface. Fig. 14. Rivers are migration corridors for organisms which depend on the water and the forest habitats © FISRWG (10/1998) FISRWG ©

Stream Corridor Restoration: Principles, Processes, and Practices - The Federal Interagency Stream Restoration Working Group (FISRWG) (15 Federal agencies of the US gov‘t). GPO Item No. 0120-A; SuDocs No. A 57.6/2: EN 3/PT.653. ISBN-0-934213-59-3 RIVER BIOCORRIDORS Rivers are important migration temporarily polluted places, gravel corridors. We know that water pits etc. It is even more important wildlife migrates with the purpose of for water life to be able to go back feeding, breeding and to compensate and re-colonize an area when for the river flow both upstream and conditions are restored. For instance, downstream the river. The possibility fish may leave a river section to migrate enables water life to avoid which suffered a severe pollution unfavourable river sections, such as discharge impact and then restore

WWF 2011 – River Ecology page 18 its population in neighbouring river In the past, vast forests covered the sections. If there are functional barriers lowlands. Nowadays forests in the in the biocorridor such as dams, lowlands are fragmented and small. strongly polluted sections, or concrete They are dotted amongst vast areas riverbeds, migration is hindered and of farmland, urban developments, the relevant river section may remain and highways, which are an with no fish for long time even if the overwhelming barrier for forest conditions improve. wildlife.

Another key component of the river River corridors are often the only biocorridor is the continuous belt of natural link between isolated forest riparian vegetation. This is a basic areas and the survival of a large interlink for many animals in the course number of plants and animals that of their regular migrations. depends on them (Fig. 14). WATER QUALITY The quality of water is of paramount also serve as a “carrier” of pollutants, importance for the functioning of such as micro-organisms and toxic river corridors. Even if the river is substances, which adhere to the in a good hydro-morphological and bottom particles and can thus be hydrological condition and is not carried a long distance. The source of subject to straightening, even if it dissolved substances, as mentioned preserves its riparian vegetation, and above, is mainly erosion, both even if there are no dams or artificial natural and induced by man. Gravel lakes built along it, any disturbance of extraction from rivers is one of the the physical and chemical features can main causes for continuous turbidity make the river corridor non-functional. of water. Some of the more important water parameters are as follows: Dissolved oxygen

Suspended solids The most important feature of any water course is its oxygen content. Suspended solids or suspended Most of the aquatic organisms sediments are a natural component “breathe” dissolved oxygen. Its of the physical and chemical concentration in water depends characteristics of the river. If they mostly on water temperature and exceed the normal quantities, this may salinity. Sources of oxygen are the generate serious problems in the river atmosphere and the photo-synthesis corridor. Their high concentration of river plants and algae. When the and continuous impact may lead oxygen concentration is under 3-4 to asphyxiation of wildlife that use mg/l, a few fish can survive, while gills for respiration such as fish, under 2 mg/l the environment invertebrates, larvae of amphibians, is considered anaerobic; if such and fish eggs. Suspended solids can concentration persists longer, it can

WWF 2011 – River Ecology page 19 result in completely “dead” water station and the dramatic decrease body. Extinction caused by low in temperature in Vacha and Arda oxygen concentration often occurs Rivers downstream the dams of in the smaller, channelled and Krichim and Studen Kladenets. “cleaned” rivers in the plains. This is often induced by high temperatures pH combined with water pollution from different oxidizable organic or other The acidity or alkalinity of water is substances (deoxydation from re- also of key importance to aquatic suspended organic sediments in the organisms. Most aquatic organisms Iskar River is illustrated below). are adapted to live in water with a pH between 5 and 9 (distilled water Water temperature is pH 7), and many organisms are adapted to specific pH limits where This is also a basic water any deviations lead to problems characteristic for it determines the in reproduction processes, ion oxygen concentration in water, and exchange and viability. Water pH furthermore, many aquatic organisms depends on both the substratum in have very narrow limits of tolerance the river course and rainwater. For to changes in water temperature. instance, if sulphate or chloride ion Thus, every single temperature concentration in air is high, rainwater change results in changes of their will be acid and the acidity of river metabolism, breeding capacity and water will increase. Abrupt changes even viability. Moreover, many in pH also occur when wastewaters chemical processes in water depend are discharged into the river. on temperature, such as sorption of organic toxicants, which has Nutrients an indirect impact on the living organisms. Water temperature Besides oxygen, CO2 and water, depends mainly on three factors – air all plants, including algae, need temperature, earth temperature and nitrogen, phosphorus and other sunlight. For instance, if riparian chemical elements in the form of vegetation is cut away and the various soluble compounds. These stream is exposed to sunlight, the chemical substances are called temperature would go up and the nutrients. The deficiency of some of oxygen contents in water would these elements limits the growth of decrease. As a consequence, the plants. On the other hand, the excess flora and fauna will change. Water of nutrients results in eutrophication, temperature is also influenced by the usually characterized by an excessive inflow of higher or lower temperature development of algae or an “algal streams – this is the so-called bloom”. The “algal bloom” or temperature pollution. The most “sliming” of water, as often referred typical examples are the increased to, is actually extensive development temperature of a Danube River of single-celled algae. Eutrophication section resulting from the cooling leads to oxygen depletion in water plant of the Kozloduy nuclear power during the night, when plants breathe

WWF 2011 – River Ecology page 20 but there is no photosynthesis and it Toxic (poisonous) substances often results in the death of fish and other aquatic organisms that breathe Under natural conditions water may dissolved oxygen. Apart from changes contain small quantities of different in fauna and flora, such rivers suffer chemical compounds that are toxic deterioration of water quality. The to water life. As a result of human water becomes unsuitable for many activities, the concentration of many industrial and farming purposes. In of these substances exceeds the ecosystems affected by human impacts, safety limits. Man has created many the main sources of nutrients are toxic substances that do not occur in agriculture (fertilizer leaching into nature such as biocides – pesticides, groundwater) and sewage systems. herbicides etc. Heavy metals are also Nowadays nutrients are identified extremely toxic and can accumulate as one of the main pollutants of in living organisms. Sources of toxic freshwater ecosystems. elements are again agriculture and wastewater. ANTHROPOGENIC CHANGES IN RIVER CORRIDORS AND THEIR IMPACTS River Straightening erosion of both the river banks and bottom, i.e. the river starts “eating” One of the most negative anthropogenic its own bed and digs into the ground impacts is the so-called straightening until it reaches harder bedrock. and the construction of embankments The increased erosion results in in the mid and lower streams of almost higher water turbidity, which is a big all large rivers of Bulgaria during the problem for all aquatic organisms mid-20th century. The main purpose because it reduces the penetration of of these actions was to provide sunlight into the water. Fine particles more farmlands for developing the clog to the gills of the animals that economy and to combat flooding. The breathe dissolved oxygen. consequences of these activities are very serious and in many cases do not solve, Another, even more serious problem but intensify the problems. The main related to riverbed incision is the consequence of river “straightening” by lowering of groundwater levels. The building dikes and cutting off meanders problem is particularly exacerbated from the rivers is that the river becomes where these processes are combined shorter and steeper (Fig. 4). The new with the gravel extraction. The river river is narrower due to the dikes built and neighbouring groundwater on its banks (Fig. 15). All of this result are interconnected bodies, and in faster water flow and higher water the drop of water levels in the levels during floods (Fig. 16). The river (in some cases down 5 or 6 faster flow itself results in intensified m) leads to a parallel decrease in

WWF 2011 – River Ecology page 21 the groundwater level because the These changes affect all the components river acts as a draining channel. of riparian ecosystems – riparian The lowering of groundwater levels wetlands, wet meadows and floodplain results in withering of riparian trees forests dry up (Fig. 17). The loss of and a general drainage of adjacent meanders and pools leads to the farmland; wells run dry and boreholes extinction of many species of plants dry up. This problem affects virtually and animals associated with slower and all the main rivers in our country. deeper waters.

The Maritsa, Dzherman, Struma and River straightening reduces the river’s Iskar are amongst the most severely self-purification capacity because impacted rivers. Even the Danube of shortened contact of the water River bed has lowered. According with the bed layer (this is where self- to WWF research during the last purification processes mainly occur). 40 years, the average sinking of the Changing the bottom substrate also Danube in the Bulgarian section is results in a thorough change of benthic over 1 m. communities and dominance of rheophile species that are adapted to fast streams.

Fig. 15. Straightening of the Lesnovksa River in Ravno Pole © Stoyan Nikolov, Stoyan Mihov and Ivan Hristov © Stoyan Nikolov,

WWF 2011 – River Ecology page 22 Gravel extraction

Gravel extraction is also a serious damage, may take years to restore problem for river systems. On one the equilibrium. The first inhabitants hand, it speeds up the erosion process will be inferior organisms followed of both the banks and the river by more superior ones and so on, bottom, and on the other hand it up to the highest level of food chain, has a huge impact on the biological namely fish, birds and mammals. system. This impact includes direct The river bottom is the main eradication of organisms – with the biological filter “responsible” for extraction of bottom sediments all the the self-purification of streams. immobile or slow moving life forms Recovering of the self-purification are removed from their habitat. ability can take several decades. The new bottom is sterile; it has no bacteria or other organic substances. Re-colonization of such a sterile bottom is a slow and gradual process which, depending on the extent of

Fig. 16. Straightened rivers are shorter, narrower and steeper than the natural ones.

Level of straightened river or river with impaired river catchment area Rainfall

Level of natural river ) 2 ) 2 Rainfall (l/m River level (l/m © Stoyan Nikolov, Stoyan Mihov and Ivan Hristov © Stoyan Nikolov, 0 1 2 3 4 Timeline (days)

Quite often the pits left after which kill any remaining life forms gravel extraction become traps for not only in the pit, but also further organic matter due to accelerated downstream. This impact is of sedimentation. They quickly fill particular concern regarding rivers up with branches, leaves, dead that run through densely afforested plants, fine organic particles and areas. It is extremely severe when other decaying organic matter, thus high waters run through such a place taking up the oxygen and releasing and transport all the decaying matter. toxic gases like hydrogen sulphide, This uses all the oxygen kilometres

WWF 2011 – River Ecology page 23

Ivan Hristov Ivan and Mihov Stoyan Nikolov, Stoyan © Wetlands dry up Wetlands Old riverbed Riparian vegetation dries up

Dike

Groundwater level Groundwater

Groundwater level Groundwater Former groundwater level groundwater Former Former land profile Dike undermining Dike Wells dry up Wells 10-20 years after river straightening Fig. 17. Riverbed lowering as a result of erosion and gravel extraction Soon after river straightening

WWF 2011 – River Ecology page 24 downstream and leads to extinction of Dams also modify the hydrological life forms. regime of the river. Depending on the height of the dam wall, an Water turbidity caused by the presence artificial lake of a different size of suspended solids prevents sunlight takes shape behind it. Water therein from penetrating into the water and is much slower and conditions hinders photosynthesis. The suspended are created for accumulation of solids also asphyxiate gilled aquatic fine sediments. This completely organisms – mainly mussels, fish, changes the flora and fauna of the snails, and crustaceans. Turbid waters environment. The accumulation of hinder fish breeding because the fine organic matter and sediments behind suspended particles clog the mucous the dam wall may lead to mass membrane of fish eggs and asphyxiate extinction of water life. In the case the fry. of larger dam walls, e.g. dozens of meters high, water is usually released Interruption of the river continuum by dams, from the bottom layers of the lake hydropower stations, artificial lakes, trout where it is not only short of oxygen, but also very cold. This kind of thresholds temperature pollution is quite often neglected, but it is very serious and Interrupting river courses by dams, impacts large sections of the rivers. hydropower stations, artificial lakes, In some cases aquatic communities and so on, has a serious impact on change completely. migrating aquatic life. This impact is most severe to fish because many of the Another problem is the dramatic fish species perform seasonal breeding, daily change of river levels after the feeding and other migrations up and hydropower station (hydropeaking). down the stream. This impact is also This unnatural process can kill of particular concern regarding species riparian communities, putting a lot that migrate for breeding, such as the of stress on the remaining ones. Common Nase (Chondrostoma nasus) When a dam is built, sediment and the Zarte (Vimba vimba), for their transport downstream is suspended, survival depends on their access to which results in incision of the the breeding sites usually located in river bed after the dam, increased the upper sections of the river. The erosion and all the other negative presence of migration barriers may consequences described above completely destroy the population (Fig. 19). of these species in the short term (Fig. 18).

On September 10, 2008, the Lakatnik hydropower station situated on the Iskar River released more water than anticipated for several hours. As a result, the sediments in the artificial lake behind the dam came up to the surface, dissolved into the water and killed tens of thousand of fish downstream. There is no statistical data about other small aquatic life forms. It should be noted that this happened only four months after the hydropower station was put into operation, and the amount of sediments was much less than it would be after years of operation.

WWF 2011 – River Ecology page 25 Stream management – water intake • Increase of water temperature, especially in small mountain For our everyday needs, industry tributaries where riparian trees and farmland irrigation we use fully overshadow the river course huge amounts of fresh water. Most and prevent water overheating. of it comes from rivers or from The removal of this vegetation leads underground sources which feed the to increased water temperature and rivers. This naturally leads to water changes in river ecosystems. This is of decrease in rivers, resulting in serious particular concern regarding the trout consequences: many rivers dry up area, where the removal of riparian in their upper sections, where most vegetation results in the extinction of of the catchments areas for potable trout population. water are located. In other places the water volumes drop under their • Increase of nutrient pollution. The critical minimum and the riparian absence of riparian belt of vegetation vegetation dies. leads to unhindered passage of nutrients via groundwater from the Cutting down riparian vegetation, “clearing” farmland. Where there is a vegetation river beds belt, up to 90% of the nutrients are captured and absorbed before reaching the river. Cutting down riparian vegetation – whether to clear the riverbed, to • Intensified erosion of river banks. combat flooding or to reclaim land for The roots of plants and especially farming – leads to: those of trees have an important structural role on the reinforcement Fig. 18 Interruptions in the river corridor and habitat changes caused by dams (hydropower station, artificial lakes and other man-made structures) © Stoyan Nikolov, Stoyan Mihov and Ivan Hristov © Stoyan Nikolov,

WWF 2011 – River Ecology page 26 of river banks because they retain rivers. As a consequence, the runoff the soil particles and prevent the is considerably changed. Floods are water from carrying them away. more frequent with higher waters, and dry seasons become longer. Water pollution It is well known that deforested areas This is one of the best known and easily erode, which favours torrents. most commented negative impacts Different forests have different of human activity on water. Until retention capacities depending recently it was considered the most on the root systems and forest significant problem of river health. As floor. Research has shown that old a consequence of wide discussion and deciduous forests have the highest measures taken, there is a decrease water retention capacity. in pollution of rivers in Bulgaria and ahhava worldwide. In urbanized areas, where the Decreased retention capacity of watersheds possibility for rainwater infiltration is virtually zero because of impervious Deforestation, transformation of areas covered by asphalt and areas into arable land for farming, concrete, it takes less time for urban development and cutting off rainwater to reach the rivers than floodplain areas result in a decreased in natural environs. This eventually water retention capacity of watersheds, leads to serious flooding because at which take in, retain and gradually downpour huge amounts of water release precipitation water into the reach the river at the same time, and the river does not have the capacity to Fig. 19. Changes in sediment transport resulting from dams

Organic sediments

Accumulation of river sediments River level prior to dam building

WWF 2011 – River Ecology page 27 take it in. other hydrotechnical structures cut Riparian floodplains act as buffers off almost 80% of the floodplains that where the overflow spreads out and provided retention areas along the subdues the flood peak. Later, part Danube River. The situation is similar of the water goes gradually back into for the floodplains along the other the river reducing the period of low rivers of Bulgaria. water. In the 20th century dams and

Bulgarian forest engineers have a long and rich experience in mastering erosion and torrents in over 2,000 water courses of Bulgaria. Since 1905, when the first Flood Control Office was established, a number of erosion control activities were implemented, including reforestation of 0.82 million ha. These measures are effective in reducing soil erosion, retaining water in forests, reducing the erosion of riverbeds, strengthening the rivers banks and decreasing the transfer of sediments.

A typical example of successful erosion control measures was set with the Iskar Dam Lake. After its construction in 1954, erosion control measures were taken to decrease the sediment amount in the lake, which was about 930,000 m3 per year. Over 20 years, 19.7 thousand ha within the dam watershed were afforested and a series of other erosion control activities were carried out. These measures successfully reduced the annual transfer of sediments to 447,000 m3 per year. RIVER RESTORATION IN BULGARIA

In the recent years of changing triggered the first attempts to restore environmental perceptions, the the natural state of rivers. Below are understanding of natural river three examples of the activities carried services mentioned above together out in Bulgaria by WWF for integrated with the awareness that most of restoration of pilot sections of the the so-called natural disasters are Danube, Yantra and Rusenski Lom actually induced by human activity, rivers. Restoration of the link between the Danube River and the wetlands of Persina Island near Belene

The wetlands of Persina Island began to gradually dry up, losing to a (Belene) in Persina Nature Park are large extent their important ecosystem among the most important breeding role. In 2007 the wetlands of Persina sites in the lower Danube for various Island were re-linked to the Danube water birds and most of the Danube River under the “Project for Wetlands fish species. After protection dikes Restoration and Pollution Reduction” were built around the entire island in as part of the “Lower Danube Green the mid-20th century, the wetlands Corridor” initiative. The project was

WWF 2011 – River Ecology page 28 carried out by the Ministry of the Already in the first year after the lock Environment and Water in Bulgaria was opened, tons of fish came into and the main donor was the Global the marshes to spawn their eggs; Environment Facility (GEF). birds came back as well. Nowadays, hundreds of rare bird couples The restoration of the wetland on nest in the marshes, consisting of Persina Island was achieved by ferruginous duck, pygmy cormorant, opening the protection dike at three greylag goose, great crested and red- points; in addition two-way gateway neck grebes, terns, herons and others. locks and connecting channels to the A group of Dalmatian pelicans comes marshes were built. The farmlands in regularly to the island and in the near the western part of the island, where future they will probably start nesting the prison inmates of Belene used to there again for the first time after half work, are protected by an intermediate a century of absence. dike and a new draining canal with an automatic drainage pump station The Danube marsh of Kalimok – not (Fig 20). far from the town of Tutrakan – was restored in the same way and under The restored wetland is a human- the same project. It had also dried controlled floodplain of about 2,200 up in the mid-20th century and ha. The depth of flooding varies up to turned into hatcheries, which proved 2.5 m. At this water level, four relatively unsuccessful. Thus, almost 2,000 large marshes shape in the eastern part ha have been re-flooded by Danube of the island – Murtvo Blato, Peschina, waters and large colonies of birds Staroto Blato and Dyulova Bara, as well went back to hatch there as they did as several smaller ones. in the past. Restoration of Veselina River Meander near the Mindya Village

The Yantra River runs through a threshold had to be built to raise terrain of a small displacement its level enough for enabling it to and is characterized by a very high run back to its old bed (Fig. 21). coefficient of sinuosity, which means Nowadays the Veselina River flows that it has many meanders. Most of again down its old meander, where these meanders have been cut off slower and warmer waters provide and the riverbed straightened. The breeding conditions for many fish consequences of this “straightening” species like chub, pike, carp, as well were described above. WWF together as amphibians and birds; it also with local people from Mindya village provides additional protection at high in the region of Veliko Turnovo, water. restored the connection of the Veselina River, a tributary of the Yantra, with its former meander near the village. When the river meander was cut off in previous times, the river dug nearly 150 cm deeper into its bed, so now a

WWF 2011 – River Ecology page 29 © Stoyan Nikolov, Stoyan Mihov and Ivan Hristov Ivan and Mihov Stoyan Nikolov, Stoyan ©   Gardata lock Martvoto Blato

Staroto Blato 

South lock  Northern lock gate

Peschina Marsh

  Floodplain land Outer protection dyke Draining canal Inner protection dike Pump station Belene prison area BELENE bridge Pontoon Fig. 20. Restored wetlands on Persina Island (Belene) in Pers ina Nature Park

WWF 2011 – River Ecology page 30 Fig. 21. Restored river meander of the Veselina River near Mindya village

Outlet



Artificial riverbed dug for river straightening

  Inlet

Dike



WWF 2011 – River Ecology page 31 Fig. 22. Master plan of the restoration of the Rusenski Lom River near Ivanovo

 Rusenski Lom River

Dike

Dike cutting  

Asphalt road 

Rock church “Mother of God” in Ivanovo

WWF 2011 – River Ecology page 32 Straightening of the Rusenski Lom River near Ivanovo Rock Monasteries

In the mid-20th century most of the Thanks to this approach, now during lower flow of the Rusenski Lom River high water the river may spread out, was fully diverted. This measure settle down and go back into its bed was unsuccessful at some sections without flooding the surrounding because of frequent flooding and high land (Fig. 22 and Fig. 23). groundwater. Therefore, most of the land “reclaimed” from the river has At the same time, overflows in the been converted into fishponds, which floodplain terrace provide feeding proved to be economically inefficient places for the black stork, habitats for and quite often destroyed during rare water plants and breeding places times of high water. That is why many for a number of fish and amphibian of these fishponds today are out of species. The project was implemented operation and abandoned. in 2009 by the Rusenski Lom Nature Park Directorate, “Friends of Such is the case of the Rusenski Lom Rusenski Lom” Club and WWF with river section near the Ivanovo rock the support of the Bulgarian Ministry monasteries. The asphalt road to the of Culture, and was funded by WWF rock monasteries is situated atop of the and the German Federal Ecological river protection dike. Part of the visitor Foundation DBU. infrastructure to the archaeological reserve is also established at the same ground level. On the right bank of the river behind the protection dike, there are several fishponds that no longer serve their initial purpose. High water floods the road, preventing access to the rock monasteries and damaging the infrastructure. When water overflows the dike, it can no longer go back into the river. The flood in 2006 washed away the bridge and the alcoves on the island once again. The dike partly broke in three places. The flooded land remained under water over one year. WWF started restoring the river and measures were completed in 2009. In this case, the water itself suggested the solution to the problem. The dike was further opened in three places. It is the first example in Bulgaria for application of the principle “more space for the river – more safety for people”, proven yet in mid-20th century.

WWF 2011 – River Ecology page 33 Fig. 23. Rusenski Lom River at flooding

Protection dike

River level at high water

Regular river level

Flooding before restoration

Temporary overflow Flooding after restoration Dike cutting

WWF 2011 – River Ecology page 34 WWF is one of the world’s leading independent environmental organizations with 5 million supporters and a global network, which operates in more than 100 countries. In the Danube-Carpathian region WWF is implementing projects focused on the conservation of protected areas and wetlands restoration along the Danube and its tributaries.

On June 5th 2000, at the WWF initiative, the Ministries of Environment of Bulgaria, Romania, Moldova and Ukraine signed the Lower Danube Green Corridor Agreement, recognizing the importance of creating a network of sustainably managed protected areas and the need to reconnect and restore Danube’s floodplain to the natural dynamics of the river. The Lower Danube Green Corridor, is the most ambitious wetlands restoration initiative in Europe.

WWF promotes the concept “more space for rivers, more safety for humans” through the restoration of the floodplain/wetlands along the rivers, which will help reduce floodrisk. 80% of Danube’s floodplain was lost and converted into agricultural land, losing thereby one of its most important functions: storing water during floods and releasing it back into the Danube during the periods between the floods. The restoration of at least 300.000 ha along the Danube would contribute significantly to reducing flood risk and would generate valuable environmental benefits and services to the local communities. WWF is implementing a few pilot wetlands restoration projects along Danube and in the Danube Delta.

WWF is lobbying for sustainable solutions for transport development on the Danube, which will not jeopardize the biodiversity and its natural processes specific to the Lower Danube – the last free-flowing sector of the river. Plans and projects in different phases of implementation, such as the one which concerns the common sector Romania-Bulgaria, the Călărași-Brăila sector, Bâstroe canal, are thretening the natural balance of the river, adding yet to other pressures (pollution, dredging etc.). The Lower Danube, downstream Iron Gates, is also the last segment of the migration route of the sturgeons fom the Black Sea upstream in the Danube for spawning. The implementation of such projects without taking into account the environmental issues will contribute to the extinction of already endangered species. WWF’s slogan ,,Fit the ships to the river, not the river to the ships,, is promoting the use of inovative technologies for building new types of ships, interventions that will not alter the free-flowing conditions and use of River Information Systems.

WWF is also working for an adequate management of the protected areas along the Danube. Thus, optimal conditions will be created in order to protect endangered species such as the Pygmy Cormorant and Ferruginous Duck as part of a Life (EU) Nature Project - ,,Green Borders,, - implemented in Romania and Bulgaria. Approximately 18.000 pairs of Ferruginous Duck and 39.000 pairs of Pygmy Cormorant are found in Europe at the moment. The Lower Danube hosts a significant part of these two species: 7% of the Ferruginous Duck population and 17% of the Pygmy Cormorant population are living in this area.

WWF 2011 – River Ecology page 35 River Ecology 100% RECYCLED • RIVER ECOLOGY RIVER

80% More than 80% of the length of the Danube has been regulated 177 Today only a third of the world’s 177 large rivers remain free-flowing, unimpeded by dams or other barriers

€20 BILLION For the period 2010-2027 the measures necessary 20 MILLLION EN toWh improvey we are water here quality in the Danube were If there is no URL The Danube provides estimatedTo stop the at 20degrad billionation Euro of the planet’s natural environment and

to build a future in which humans live in harmony and nature. drinking water for 20 WWW.PANDA.ORG/DCPO million people

Why we are here To stop the degradation of the planet’s natural environment and This edition is developed under the Lower Danube Riverside With URL - Regular to build a future in which humans live in harmony with nature. Nature Conservation Project carried out by WWF Danube- Carpathian Programme and co-funded by WWF Germany www.www.panda.org/dcpo and the German Federal Environmental Foundation (DBU).