Horska-Schwarz S., Spałek K., 2010. The evolution of the Oder valley in terms of fluvial processes and anthropogenic changes.
The Problems of Landscape Ecology, Vol. XXVIII. 229–240.
The evolution of the Oder valley in terms of fluvial processes and anthropogenic changes
Sylwia Horska-Schwarz
1, Krzysztof Spałek
21 Institute of Geography and Regional Development, University of Wrocław, pl. Uniwersytecki 1, 50-136 Wrocław
e-mail: Sylwia@horska-schwarz.pl
2 Laboratory of Geobotany and Plant Conservation, Department of Biosystematics University of Opole, Oleska 22, 45-052 Opole
e-mail: kspalek@uni.opole.pl
Abstract: The rapid development of the natural environment of the Oder valley was initially associated with natural processes (circulation of matter, energy and information in an undisturbed system). With time, however, it transpired that the essential factor generating structural and functional changes was stress linked with human activity (circulation of matter, energy and information in a disturbed system). Drainage basin deforestation and increased slope soil erosion caused a rise in supply of mineral matter to running waters. Change in the nature of water transport (a rise in the amount of suspension in water) and increased deposition of sediments rich in organic substances within flood plains led to formation of a level of so-called ‘agricultural silt’. Further environmental changes were a result of devel- opment of industry. Pollution of fluvial waters led to deposition of harmful substances in the near-channel zone and formation of a further level of so-called ‘industrial silt’. Human activity was accompanied by a change in environmental quality (pollution), as well as fragmentation of habitats, a rise in invasive species and a fall in biodiversity.
Key words: Oder valley, environmental structure, alluvia, agricultural silt, industrial silt, heavy metals, fragmentation of habitats, biodiversity, invasive species, flood, river regulation
Outline of the development of the Oder valley
It is generally accepted that deposition of alluvia in the river valleys of Central Europe began around 10,000 years ago (Becker, 1982). In the case of Polish rivers, including the Oder, issues in assessment of age and conditions for sedimentation of deposits remain moot (Lindner, 1977; Aleksandrowicz et al., 1981; Kalicki, Krapiec, 1995). Gaps in the chronology of alluvial deposits are due to the absence of suffi- cient quantities of the materials necessary for dating, as well as to the great dynamism of the environment and the fact that sedimentation conditions are difficult to reconstruct. Analysis of individual stages in the development of river valleys, now greatly transformed by man, is a challenging task, since structural con- ditioning and environmental processes determined by such factors as climate change are subject to the stress created by these centuries of human activity.
Climate change is undoubtedly of vital importance in the development of a river valley environment:
periods exhibiting increased fluvial processes are often correlated with phases of warming (e.g. 9000–
8000 BC). Transformation of the spatial and functional structure of the environment were determined from the beginning by changes in plant communities. Species of broadleaf tree appeared in river valleys under the conditions of a milder climate. In moist periods trees were felled owing to increased erosion of river- banks, then transported or deposited (in situ) in alluvia (Krąpiec, 1996). Fossil oak trunks, of Quercus robur and Quercus petraea, have long been excellent material for dendrochronological study (in Norway, Great Britain, Germany and Poland; Eckstein et al., 1975; Fletcher, 1977; Delorme, Leuschner, 1983;
Kalicki, Starkel, 1987). On the basis of dates obtained (by radiocarbon dating) periods of increased river activity linked with an increasingly moist climate have been determined, these being: 6800–6450 BC, 3300–3000 BC and 1500–1300 BC (Starkel, 1983; Rutkowski, 1987; Kalicki, 1991); 7222–6780 BC;
6678–6450 BC; 3385–3250 BC; 3168–2980 BC; 1779–1214 BC; 1300–1158 BC. It should be added that a significant role has been played in transformation of river valley environmental structure by single, catas- trophic occurrences, that is, by floods. The distinct cooling of the climate of 1400–1320 BC (probably due to volcanic eruption on Santorini) led to a rise in the number of ice jam river floods, with levels of alluvia from this period containing trees with mechanical damage, presumably caused by ice floes (Kalicki, 1991).
In the case of the Oder valley, the lower levels of the flood terraces, formed of sands and fluvial gravels, are covered by agricultural silt, the age of which has been established (by radiocarbon dating) as around 2,700 years, a period of intensive agriculture linked with the development of the Lusatian culture (Szcze- pankiewicz, 1956). The level of agricultural silt (soil with high cereal grain particle content) is the first evidence of these great changes occurring throughout the drainage basin as a result of human activity.
Owing to superficial run-off from the catchment areas closest to the river, considerably more organic and mineral matter was collected. This material was deposited over flood plains during successive swellings, while the meandering of the Oder favoured a comparatively small drop in the terrain. The years AD 225–
325 were a crucial period in the development of Polish river valleys, registered in the alluvia as increased accumulation of trunks. It is generally accepted that at the end of this period a gradual revival in forest took place. Together with a rise in temperature (AD 425–5751) and intensive economic development increased river erosion again occurred, which led to the felling of young trees and their accumulation in alluvia (Baillie, 1994). Distinct traces of settlement in the Oder valley come from the period AD 600–900, these linked with an intensive development in trade and agriculture (running along the Oder in antiquity was a route connecting the Roman Empire with the Baltic Sea). A further stage is closely associated with a change in climate (‘the Little Ice Age’) in Europe and North America. It is possible to distinguish periods of cooling, the Oort Minimum (AD 1010–50), Wolf Minimum (AD 1280–1340) and Spoerer Minimum (AD 1420–1530), and periods of warming in which heavy floods occurred and, as a result of bank erosion, meanders were cut off, trees felled, trunks accumulated in alluvia and sediments rede- posited.
The economic development of the years 1720–1892 (probably dependent on a rise in temperature) marked the beginning of the so-called industrial age, which may be divided into three stages (Cronin, Dwyer, Kamiya, Schwede, Willard, 2003).
• 1736–85 – following the flood in 1736, regulatory works were begun on the Oder, an effect of which was a shortening of the river by around 60 km; many meanders were artificially severed from the ac- tive channel. In 1785 regulatory works were begun on the largest tributaries of the Oder, e.g. the Warta. The end of the period saw an intensification of extreme phenomena in the form of floods.
• 1800–54 – further regulation of the river occurred: according to the Bohumín Protocol1 of 1819, over 10,000 spur dykes and around 262 km of dam were built on the Oder; in 1822 the Kłodnica Canal was opened, one of the oldest canals on the continent of Europe with locks (modernised in 1934 as the Gliwice Canal); in 1840 construction of locks and weirs began. Floods were recorded in 1804, 1813, 1831 and 1854, the latter named ‘the flood of the century’.
• 1871–92 – further locks were constructed and water and hydrotechnical infrastructure expanded, the Oder becoming a waterway of European significance; a rapid rise occurred in ecological barriers in- troduced to the valley in the form of further embankments, canals, locks and weirs. Agriculture saw a period of intensive development, with reclamation of boggy land and a rise in acreage of farmland and green arable land at the cost of forest complexes and marshlands, while exploitation of aggregate and soils occurring in the valley commenced. A reduction in floodland and change in water conditions led to depletion of biocoenosis, the beginning of oxbow lake degradation. Fragmentation of the land- scape, a rise in the number of anthropogenic boundaries and barriers, exploitation of mineral raw ma- terials, isolation and defragmentation of ecosystems and a rise in the share of invasive species all oc- curred.
The 20th century brought about further environmental changes triggered by development of agriculture and construction of impoundment lakes and polders. However, along with growth in expenditure on flood defence came a consistent rise in losses caused by successive floods (Bobiński, Żelaziński, 1996). Initial plans for modernisation of the Oder provided for the building of around 256 artificial reservoirs in its catchment area, of a total capacity of 19,906,500 m3 of water. In the years 1903, 1924, 1934 (the ‘Year of Noah’), 1940 and 1947 several large floods were recorded on the Oder. Following the Second World War, a part of the polders, e.g. those between Opole and Wrocław, were developed and received housing estates and arable fields. Subsequent years – 1960, 1965, 1970, 1972, 1977, 1979, 1980, 1981 and 1985 – brought an increase in extreme phenomena. The end of the 1980s was a period of ‘relative’ stabilisation.
At this time the significance of inland navigation fell owing to a transformation in the economic policy of the state, while at the same time a fall in arable land in the flood zone and a rise in wasteland were registered.
With the abandonment of drainage system maintenance and cleaning, drainage ditches silted up and fragments of the valley previously drained reverted to bogland. Residential development encroached boldly on floodland. The 1990s abounded in floods – experienced in 1991, 1994, 1996 and 1997 – the last being named ‘the millennium flood’.
The 21st century ushered in with it a rise in the strength of extreme phenomena, with the material losses following the flood in 1997 and 2006 forming the basis for modernisation plans for the Oder water- way. The past decade has seen an attempt to adapt the river for flood defence, yet also the need to pre- serve the ‘relics’ of nature. The influences associated with the planned redevelopment and adaptation of the Oder for the passage of floodwaters may be in nature linear (changes in the transverse and longitudi- nal profile of the channel, changes in the shape and length of the bank line and changes linked with tech- nological infrastructure, whether roads, boulevards, bank reinforcement or embankments), superficial (construction of the Racibórz reservoir, levelling of the bed, i.e. desludging, levelling of land in the inter- bank area, i.e. lowering of the flood terrace, and change in the structure of vegetation) and punctual (ex- pansion of infrastructure, i.e. weirs, locks, waste storage sites, storage sites for sediments from desludg- ing, often polluted, spur dykes etc.). The need to dismantle old elements such as floodbanks (high cultural
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1 Protokoll über die beim Ausbaue des Oderstroms zu befolgenden Grundsätze, 1819.
value) and adapt polders anew to the passage of floodwaters brings with it numerous conflicts: housing estates located within constitute a problem, the social aspect thus requiring consideration alongside the natural.
Phases in oxbow lake development
The formation of the oldest system of meanders in the Oder valley should be connected with the fact of the climate growing moist in the Atlantic period. However, the formation of the youngest generation of oxbow lakes and the evolution of their structure is a result of regulatory works conducted on the Oder at the turn of the 18th century and at the present time. Owing to the artificial severance of meanders from the active chan- nel a system of oxbow lakes was created partially or permanently deprived of contact with the river. The contemporary pace of their degradation is very great. It transpires that the effects of floodbank construction and restriction of floodwaters to the region of the interbank area have been disastrous (disturbance of the natural circulation of matter and energy throughout the valley). In the interbank area (the inundation range) the processes of bank and bed erosion have undergone an intensification and a system of flood channels and side bars has formed, while in the area of the plain cut off from floodwaters, accumulation of silts has been artificially arrested. Development of agriculture and reclamation of boggy land has led to the lowering of the groundwater table, further accelerating the process of bog and silty soil degradation. Absence of river- and floodwater flow, and thus the ‘refreshing’ of an oxbow lake through flooding, the delivery of organic sub- stances from soils used agriculturally and the eutrophication of waters have all become a cause of their
‘disappearance’. Compact hollows of stagnating water in which dead plant remains accumulate are often the sole evidence for the course of past channels. Water rich in biogenic substances rapidly undergoes eutrophi- cation and an oxbow lake becomes overgrown. This process gained in strength in the 1970s (with the
‘chemicalisation’ of agriculture), while at present a great threat to water condition is posed by the reappear- ance of pollutants (phosphates and nitrates) accumulated in drainage ditches (e.g. during flooding).
On the basis of field and laboratory work and cartographic materials several generations of oxbow lake have been identified corresponding to individual stages in the development of the Oder valley. Their trans- formation was a result of fluvial processes, but also human activity. Based on component structure, four chief phases in oxbow lake development have been distinguished (Horska-Schwarz, 2006):
Phase 1 – youth – is the initial stage, a change in river channel course and formation of a system of me- anders in constant contact with the active channel, high water exchange dynamics, a low bank vegetation share and a raising of side bars and undercutting of banks during flooding – active erosional undercutting.
Phase 2 – development – is the stage at which slow transformation of environmental structure occurs, associated with change in sedimentation conditions in the valley and regulation of the channel; severed fragments of meander function as oxbow lakes filled with water, periodically refreshed by floodwaters, with the seasonality of the erosional and accumulative processes conditional on the size of the flow of water in the river. In the final period a gradual stabilisation in structure occurs: the succession of vegetation leads to the consolidation of bank form – of natural levees, point bars etc. – and erosional undercutting, re- newed during flooding, with the material included in new water transport and redeposited within the flood plain in such forms as sand shadows or mega-ripple marks.
Phase 3 – maturity – sees permanent separation of the oxbow lake from the active channel, the absence of water exchange between the oxbow lake and active channel leading to a rise in the pace at which silting up occurs, with the trough of the oxbow lake filling with a mineral and organic sediment. The inflow of dietary miner-
als from fields brings about increased eutrophication of the waters and there is an increase in the share of aquatic vegetation and rushes, with succession of vegetation leading to a consolidation of channel forms; fa- vourable conditions arise for the formation of silty and bog soils. A typical community is the bog forest.
Phase 4 – senectitude – is the ‘disappearance’ of the oxbow lake owing to a permanent loss of contact with river waters, a change in environmental structure occurring; bank and channel forms are barely per- ceptible in the morphology and often degraded. In the initial period vegetation indicates groundwater lying near the surface, while the final period sees the transformation of bog soils into post-bog soils. Change in water conditions is accompanied by transformation of habitats and succession of vegetation.
Invasive species in the Oder valley: expansion of plants foreign in origin
It has transpired that the spread of organisms and species beyond the limits of their natural range is of significance for nature. Survival of species introduced intentionally by humans or brought accidentally into new areas varies greatly. A part are incapable of competition with local species and appear ephemerally, whereas others demonstrate a competitive potential allowing for their lasting settlement or even displace- ment of indigenous taxa. At the close of the 20th century the process comprising proliferation and settle- ment of alien species of fungus, plant and animal had become so serious that it is named among the several most important causes of the threat to biological diversity in the 21st century (Abbot, 1992; Carl- ton, Geller, 1993; Vitousek et al., 1996; Mooney, Hobbs, 2000; Kolar, Lodge, 2001; Tokarska-Guzik, 2005). From the point of view of the protection of nature particular attention should be turned to invasive species, which are characterised by high predispositions to competition and potential for penetration of a natural community. It is estimated that to be found permanently settled within Europe are several hundred species of plant foreign in origin, their number dependent on region. In the Czech Republic 397 species have been noted (Pyšek et al., 2002), in Germany to date 417 (Kowarik, 1999); in Poland the number is similar, amounting to over 400 (Zając et al., 1998; Mirek et al., 2002; Tokarska-Guzik, 2003, 2005).
Permanently settled non-indigenous plant species occur rather frequently in the Oder valley, most often on its banks, more rarely in oxbow lakes. Centuries of human economic activity in the valley, extremely intensive in many periods, was and continues to be conducive to the proliferation and settlement of such species. Many among them, such as, say, Acorus calamus and Elodea canadensis, have become com- mon elements of the flora of Poland (Tomaszewicz, 1979; Zając, Zając 2001). Characterised below, there- fore, are only selected examples of foreign species confirmed in the Oder valley, chosen from among those most invasive or potentially capable of endangering the native flora.
Echinocystis lobata (Michx.) Torr. & A. Gray
This is a species North American in origin, brought to Europe at the end of the 19th century and begin- ning of the 20th as an ornamental plant (Balogh, 2001; Tokarska-Guzik, 2005). It appeared in Poland in the first half of the 20th century (Zając et al., 1998) and occurs at present throughout the country, particu- larly frequently, however, in south-eastern and central parts (Zając, Zając, 2001; Tokarska-Guzik, 2005), where it spreads on the banks of rivers, streams, lakes and ponds as well as on ruderal land (Dajdok, Kącki, 2003; Tokarska-Guzik, Dajdok, 2004; Tokarska-Guzik, 2005). In the Oder valley the spe- cies occurs at numerous sites in a variety of habitat types.
Eragrostis minor Host
This species originates in south-eastern Europe and western Asia and appeared in central Europe, in- cluding in Poland, at the beginning of the 19th century (Kornaś, 1968; Landolt, 2000; Tokarska-Guzik, 2005). It was first recorded on the territory of Poland within its present borders in 1838, specifically in the vicinity of Nowa Wieś Wrocławska and Gajowice, near Wrocław (Grabowski, 1843; Wimmer, 1868; Fiek, 1881), and Prószków, in the Opole region of Silesia (Fiek, 1881). It occurs at present throughout the coun- try (Zając, Zając, 2001; Tokarska-Guzik, 2005), where it spreads on wasteland, road verges, sports fields and railway land, and between paving slabs (Tokarska-Guzik, 2005). Eragrostis minor occurs quite rarely on the sandy banks of the Oder and its oxbow lakes.
Erechtites hieraciifolia (L.) Raf. ex DC.
This species originates in North and South America and was first confirmed as present in Europe in 1876, in the vicinity of Zagreb. (Meusel, Jäger, 1992; Górski et al., 2003). It was first recorded on the territory of Poland within its present borders at Prószków, in the Opole region of Silesia (Schube, 1903), and is currently associated with 100 sites in the country, these concentrated above all in the south-west (Zając, Zając, 2001; Górski et al., 2003; Tokarska-Guzik, Dajdok, 2004). The species spreads in moist coniferous forests, mixed and acidic oak forests and clearings, and on forest tracks and ruderal sites (Górski et al., 2003), as well as in reed communities, riparian forests and beech woods (Tokarska-Guzik, Dajdok, 2004). It occurs very rarely on the banks of oxbow lakes, most often in Phragmition reed communities.
Impatiens glandulifera Royle
This species originates in the Himalayas and eastern part of India (Lhotská, Kopecký, 1966) and was brought to Europe as an ornamental plant in the first half of the 19th century. The earliest record of its cultivation comes from 1839 and the botanic garden at Kew in Great Britain (Lhotská, Kopecký, 1966;
Pyšek, Prach, 1995). In Silesia, however, the species appeared at the end of the 19th century (Schube, 1903), these instances being the first recorded in Poland (Tokarska-Guzik, 2005). It is currently associ- ated with scattered sites throughout the country, although it is more common in southern Poland, where it occurs in places in large numbers, particularly in valleys with rivers and streams (Dajdok et al., 1998, 2003; Tokarska-Guzik, Dajdok, 2004; Tokarska-Guzik, 2005). In the Oder valley the species occurs rather frequently in a variety of habitat types.
Reynoutria japonica Houtt.
This species originates in eastern Asia (Conolly, 1977; Bailey, 1999) and arrived in Europe in the first half of the 19th century, where it was cultivated from 1825 (Mandák et al., 2004); half a century later it appeared in Poland. At present it is settled in many European countries, as well as in North America
(Jalas, Suominen, 1988; Alberternst et al., 1995; Seiger, 1997; Child, Wade, 2000; Zając, Zając, 2001;
Mandák et al., 2004; Tokarska-Guzik, 2005). It is distributed throughout Poland, particularly in the south- western and southern parts of the country (Zając, Zając, 2001; Tokarska-Guzik, 2005), where, beyond anthropogenic habitats, it encroaches on the habitats of the riverside (Dajdok, Kącki, 2003; Tokarska- -Guzik, Dajdok, 2004; Tokarska-Guzik, 2005). The species is a very common element of the flora on the banks of the Oder, where it usually forms a single-species thicket. It is among the most invasive of the foreign species in the Oder valley.
Reynoutria sachalinensis (F. Schmidt) Nakai
This species originates in eastern Asia (Conolly, 1977; Bailey, 1999) and was brought to Europe in 1863, soon escaping the sites of its cultivation (Sukopp, Starfinger, 1995; Mandák et al., 2004).
At present it is settled in many European countries (Jalas, Suominen, 1988; Alberternst et al., 1995;
Child, Wade, 2000; Zając, Zając, 2001; Mandák et al., 2004). It is distributed throughout Poland, par- ticularly in the south-western part of the country (Zając, Zając, 2001), where, beyond anthropogenic habitats, it encroaches on the habitats of the riverside (Tokarska-Guzik, Dajdok, 2004). The species is a rather common element of the flora on the banks of the Oder, where it usually forms a single-species thicket. Along with Reynoutria japonica it is among the most invasive of the foreign species in the Oder valley.
Reynoutria xbohemica Chrtek & Chrtková
A hybrid of Reynoutria japonica and Reynoutria sachalinensis, this species was described for the first time in the Czech Republic in 1983 (Chrtek, Chrtková 1983), the presumed manner of its creation being presented by Bailey et al. (1995). At present it is settled in Europe (Alberternst et al., 1995; Fojcik, Tokar- ska, 2000; Balogh, 2003), being in Poland associated with scattered sites in the southern part of the coun- try (Fojcik, Tokarska, 2000; Tokarska-Guzik, Dajdok, 2004). The species is currently rather a rare element of the flora on the banks of the Oder. The possibility of its occurring considerably more frequently in the future cannot be excluded.
Rudbeckia laciniata L.
This is a species American in origin, brought to Europe at the beginning of the 17th century or earlier as an ornamental plant (Kornaś, 1968; Jalas, 1993; Tokarska-Guzik, 2005). Its first site in a natural habitat within the present borders of Poland was given as the Sudetes (Fiek, 1881). At present it occurs particu- larly often in the south of the country (Zając, Zając, 2001; Tokarska-Guzik, 2005), where it spreads on the fringes of river and stream channels as well as on unused meadowland, weirs around fish ponds, hard shoulders of roads, parkland of country houses and old graveyards (Tokarska-Guzik, Dajdok, 2004;
Tokarska-Guzik, 2005). The species occurs in ever greater numbers in the Oder valley, appearing in a variety of waterside community types, including Phragmitetea reed communities.
Solidago gigantea Aiton
This is a species American in origin, brought to Europe at the beginning of the 18th century or earlier as an ornamental plant (Kornaś, 1968; Weber, 1998; Zając et al., 1998; Tokarska-Guzik, Dajdok 2004). At present it occurs commonly throughout Poland (Zając, Zając, 2001), where it usually spreads in habitats more moist than the previous species, on the fringes of river and stream channels and weirs around fish ponds, as well as in riparian forests (e.g. Guzikowa, Maycock, 1986; Dajdok, Kącki, 2003; Machnik, 2003;
Tokarska-Guzik, Dajdok, 2004; Szymura, Wolski, 2006).
Solidago gigantea is a very common element of the flora on the banks of the Oder, where it usually forms a single-species thicket. It occurs in a variety of habitat types and is among those foreign species in the Oder valley which are highly invasive.
Summary
Research on the environmental structure of the Oder valley confirms that the development of natural units linked with natural processes often taking the character of catastrophic events is at present deter- mined anthropogenically. Circulation of matter, energy and information in the valley was artificially dis- turbed as a result of human activity, that is, agriculture, industry and regulation of the river. Interference in the natural system led to transformation or degradation of natural units of varying rank, with this accom- panied by a fall in biodiversity and a rise in invasive species.
Environmental changes determined by growing anthropopressure are reflected in the environmental structure of the Oder valley. They encompass a number of processes and relate to such factors as sedi- mentation conditions in the valley, manner of land use, physical and chemical properties of deposits, geochemical processes (geochemical denudation and geoaccumulation of heavy metals), water condi- tions, soil degradation and composition as regards species in plant communities.
The processes generated by external stimuli cause (depending on the intensity of the stimulus) short- term or lasting changes in environmental structure, leading as a consequence to:
– restoration of structure – reversion to the equilibrium preceding the change;
– degradation of structure due to impairment of the self-regulation mechanism (further development may run in varying directions and lead to formation of disparate structures depending on local condi- tions);
– formation of new structures anthropogenic in origin.
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