To the precision

To the precision of the  general ecological model of a river network

IVAN TUŠA

 Regional Museum in Šumperk, Hlavní 22, 787 31 Šumperk, the Czech Republic

Abstract: Two of the most  well known and often cited ecological models of streams and rivers (1 – Illies, Botosaneanu, 2 – Vannote et al.. 1980)  are evaluated critically and their  greatest imperfections are analyzed. A new model is constructed using pieces of  the above given  models. The new model that is constructed does not operate only with one stream bed but  with the entire  river network.. Three  pictures are included..   

 Keywords: Ecological model, river network, Central Europe, terminology of river-zones.

INTRODUCTION  

        Many ecological river models have been proposed. Their survey with short descriptions is given e.g.  by Hawkes (1975). His information must be, of course, supplied with
new references, especially  with paper by Vannote et al (1980), see also Allan (1995). Two of the most known ecological river models are those by Illies and Botosaneanu (1963) and  Vannote et al. (1980).
        1) Illies´model is shortly characterized e.g. by Hawkes (1975), p. 366:
        „ (i)  Rhithron is defined as that part of the stream from its source down to the lowermost point where annual range of monthly mean temperatures does not exeed 20 °C. The current velocity is high and the flow volume is small. The substratum may be composed  of fixed rock, stones or gravel and fine sand. Only in pools and sheltered area si mud deposited.
      (ii) Potamon is the remaining downstream stretch of river where  the annual  range of monthly  mean temperature exceeds 20°C, or in tropical latitudes, with a summer maximum of the month mean exceeding 25°C (Illies, Botosaneanu 1963). The current velocity  over the river bed is low and tends to be laminar. The  river bed is mainly of snad or mud, although gravel may also be present. In the deeper poos oxygen may be depleted, light penetration limited and mud deposit      
        The two reaches were further characterized faunistically. The organisms of the rhithron   were  mostly cold stenotherms and associated with running, well aerated waters. In contrast those of the potamonn were eurytherms or warm-water stenotherms, composed mostly of  organisms of lentic waters, often with a rich development of plankton in conrtast with the  spars rhithron plankton. Although species differences occured in different biogeographical  regions, it was found that the same  families tended to be  represented in the rhithron and potamon respectivelly of river in different continents.“
       Illies´ river zone  classification (Illies 1961) for world-wide application  is shown on Fig 3. Schematic meridional section from temperature north to temperature south illustrating  the effects  of geographical  conditions related  to altitude and latitude, on the zonation of rivers into rhithron and  potamon.
       Natural communities in running waters are very objectively rendered also on graphic plates by Sládečková, Sládeček (1998). They used, of course, for their river classification also the  Illies´model rhithron/potamon (see above).
       2) Description as well as the picture of the model of RCC (Vannote´s model) river continuum concept  may be  found  e.g. in the  book by  Allan  (1995), p. 276 – 277: „The river continuum concept (RCC) is a bold attemp to construct a single synthetic  framework  to describe the function of  ecosystems from source to mouth  and accomodate the variations  among sites  that  results from differences in their terrestrical setting (Vannote et al. 1980).“
        Descrition of this model is completed by a  picture with the title: „Generalized depiction of the relationship between stream size (order), energy inputs and ecosystem functions expected the river continuum  concept.“ (See  also Fig 2).    

MATERIAL AND  METHODS

       The proposed model of river network is based on the author´s  research of  conditions as well as communities in  some rivers  in the Czech Republic and Slovakia (upper Morava, and its tributaries), upper  Vltava in the Šumava Mts, Lubochňanka and Revúca in the Velká Fatra, Mts, Slovakia (Tuša 1987, 1992, 1993, 1993 and 1994, 2005 etc.).  Determinants of conditions  as well as communities found in the terrain has been simultaneously compared with items in the models  published: rhithron/potamon (Illies and Botosaneanu 1963), orders of streams (Vannote et al. 1980, Allen 1995).
    The present author has not agreed with  simplified  reality  and also  does not agree with the way the well known gives models are used in many papers, e.g. Helan et al. 1973, Krno 1982, Moon, Wimmer 1994, Helešic 1995 etc.).
   A  key point of the new model (Fig.1) is its graphical (left) part. This idea has been developing since the 1990s as  an  effort to create a graphic picture of a hypothetical and general river network.
    To describe the new model  of a  river network as it will be  discussed, it is necessary to establish some new terms:
– the main stream of a region: usually the longest river rising at the highest  altitude range of a  region and flowing down upto lowlands or empties into  the sea
– the  side streams  of a region:  tributaries of the main stream of a region
– complete streams:  streams having formed all known and possible river zones
–  incomplete streams: streams within them only some known and possible river  zones  
   may  be distinguished
      This graph is not only  a group of casual   parallel lines without a mutual relations but this graph also  illustrates  the main stream of  any  greater region (thick line in the middle) and  its left as well as right direct tributaries (thin lines to  the left and to the right of the thick line).
     The  terminology of  altitude ranges is taken from the paper by Landa, Soldán (1989).
      Pictures of  up-streams and down-streams communities are  in circles (Fig 2), taken from  Vannote  et al. (1980)  as well as plates by Sládečková, Sládeček (1998) (see  reference in Fig 1 and notes to them) were found to be suitable to  use also  here, in   the new  model (Fig 1) for short  characteristics of  communities assumed.
         Distribution of  determinants of  conditions as well as communities  are based on relatively well known fact, that in a determine region  “ nearly all is nearly everywhere“ (stony, sand, muddy bed…etc.,  occurence of some species: in the mountain streams as well as  in lowland rivers), but only  somewhere the majority of some factors  or taxa is  typical or  predominant. In the Fig 1 typical and and the most frequent condiotions values as well as taxa (communities) are given without parentheses and untypical values and taxa (communities) in parentheses. Most of the values of particular factors of environs or taxonomic structure of cummunities are given as  ranges:  „from-to“.
 

 RESULTS

a) DESCRIPTION OF RIVER NET ACCORDING TO THE NEW MODEL
          The construction of the suggested general model  of a hypothetical  river network is  based on the  fact, that within a given altitude  stretch of the main stream of a region, only  streams (its tributaries) rising in  the same or higher altitude ranges can empty into  it.
          For example, into „the higher mountain range“ (at altitude 800 – 1000 m) of  the main stream  of a  region, streams only from the range 800 – 1000 m and the streams from  the range  above 1000 m can  empty in the main stream.  Similarly, downstream into the main river of the lower mountain range  (600 – 800m)  streams  from the ranges 600 – 800 m, 800 – 1000 m as well as from the range above 1000 m can empty into the main stream.
        Short outline of the river network according to Fig1 may be given as follows (see also Fig 1,2  and study by Sládečková, Sládeček 1998):
        In  the  highest (alpine, mountain)  zones of a given region  only springs and small brooks and rivers are present. Here the main stream of the region  mostly does not differ much form side streams within  the region. All of them are stony, pure, with low value BOD5, cold, many with stretches of streams characterized by torrent riffles with very high current speed, etc…Flora/fauna as on Fig 2, Communities I,II, partly also III.
        Down river, in higher and  lower colline zones  there is a greater variety of streams and rivers to be found: spring, spring brooks, small river as well as larger river, i.e. streams of  Irst, IInd, IIIrd …order.  Also conditions as well as communities among  the main streams and side (especially smaller) streams of the region may be  very different etc…Flora/fauna as on Fig 2, Communities II (I,III) – main stream, I,II (III) – side streams.
        In the Czech Republic as well as probably in the whole Central Europe the administrative cross the boundary between salmonid and non-salmonid streams may be  usually found at  the altitude 300 – 400 m (Štefáček 1995).
       Also in the lowest (planar) zone  we may sometimes find  next to the large deep rivers with warm, slow and  turbid water and muddy bottom  smaller,  torrent streams  and rivers with colder and relatively pure water etc…Flora/fauna.: as on Fig 2:  in the main stream an in the larger side streams Communities II,III (I). in the smaller side streams Communities I,II,III.
      Examples of concrete species for different types of streams in the longitudinal zonation are
given e.g. on plates in the paper by Sládečková, Sládeček (1998), see also notes at Fig. 1.
      But it must be taken into consideration, that for any  given model of a stream we are able only to list possible taxa (species) for definite factor spectrum of environs. Only some from these taxa will occur at particular localities (e.g. Hynes 1070, Macan 1974, Allan 1995).
        Morphology of streams and rivers all over the world  (slope, bed, composition of the bottom, current, bank vegetation etc. and their longitudinal zonation) shows, in general,  similar or the same features.  It is necessary, of course, regional untypical speciality presumed. Also similar or the same morphological (ecological) types of benthic as well as pelagic communities may be expected here (compare e.g. common differences between  communities of   stony, gravel, sand, muddy bottom etc., see e.g. Hynes 1970 a.o.).
      Temperature of stream water  as well as temperature conditions of the whole regions (summer maximum, yearly mean, etc.) are one of  the most important condition determinants which are modified according to the geographical position, especially the latitude.
    It seems,  therefore, that the model of a hypothetical  catchment suggested here  shows validity  for the whole world. Only temperature conditions and items dependent on it (oxygen a.o.) must be adapted  according to the latitude.(compare also Illies 1961 and Fig.3)..
       In tropics as well as subtropics  stony bottom and riffles are combined also with relatively high water temperature (yearly max. 20 – 30 °Celsius).  In the moderate zones and also in the regions near to the Earth´s poles  stony bottom and riffles are combined largely with lower temperature (yearly max. below 20  °Celsius).
        Without streams and river having  typical water temperature (for given latitudes and altitudes) we sometimes  find  streams under a typical temperature conditions.
         The author of this paper know two cases of  thermally atypical  streams in the Czech Republic: 1) karstic streams – their water  temperature usually is  lower than it corresponds with their altitude (see e.g. paper by Sukop 1976). 2) Teplá Vltava River near Lenora, Borová Lada, etc.. This river (with relativelly small slope) is known to have maximum summer water temperature   around 20°C at 800 – 900 m above sea level (Tuša 1993, Landa et al. 1995). Any other mountain streams with such high water temperature  has not been known from the Czech Republic and Slovakia.  

b) PROPOSALS  TERMS FOR  DIFFERENT  STREAM TYPES FOR RIVER CLASSIFICATION
        The suggested general  model of a river network requires one to propose many relatively descriptive  terms (and their combination) for precisely  indicating as well as delineating different types of  streams and rivers, and their zones using some words, e.g.: 
Central European – higher mountain – mostly stony stream IInd order – unpolluted – thermally typical etc. 
       It seems that  some international rules for river classification and terminology for different types of streams and rivers should be formed.

 

DISCUSSION

      Published ecological models of stream network (the most known and used see Illies and Botosaneanu 1963 and  Vannote et al. 1980), are very common, suitable only for general description of relations and communities in streams (e.g. in textbooks and general works on streams and rivers as Hynes 1970, Pennak 1971, Hawkes 1975, Holčík 1989, Lellák, Kubíček 1991, Allen 1995). Using of these models for classsification result  in many confusions. Some of them are given below:         
       1)Only on the main stream of a region (as well as  on some large-long its left and right tributaries) all of the known river zones are (may be) formed. The longitudinal zonation only of  these large streams correspond to the description and illustrations given by Illies, Botosaneanu (1963), Vannote et al.(1980), see also Lellák, Kubíček (1991), Allen (1995) etc.
      2) Comparing description of  the Illies  model rhithron /potamon (see Introduction) and Fig 3 we may see one inaccuracy or creation of confusion. For example, equator  mountain streams and lowland streams at the North or the  South pole both  named as „rhithron“ are similar only in temperature conditions.
      3) Spring as well as spring brooks of a definite region, streams of Ist or IInd order show similar conditions  and communities also  at different altitudes. But it is confusing to organize similar streams from different altitudes into the same categories. Many authors, of course, have done it.
     4)The greatest error is, doubtless, when we  sum  e.g. several samples  from  streams Ist or IIdn  order from different altitudes  into one sample e.g. „epirhithron“ etc (see e.g. Helešic 1995).
    5) The great difficiency of the  models by Illies as well as  Vannote  as well as  the others is a fact that structure of the river network ecosystem is demonstrated on only one river bed.
    The one bed river model very limits creative thought on  river ecosystems as well as new ideas  and  approaches to new  research.

CONCLUSION

       We may conclude that  new models of streams for classification of particular rivers and river networks are necessary to form and discuss.
      It seems, that the study and comparison of differences and similarities of  conditions as well as communities in streams of the  Irst, IInd, IIIrd etc…orders (=…rhithrons“) at various altitudes  in different river network may be the first step of  resarch using this new model.

REFERENCES

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the zoobenthos. 21pp. Okresní vlastivědné muzeum v Šumperku. 
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Fig1 General ecological model of a Central Europe river catchment area. Tuša, orig.
Notes to Fig 1.
I.
Bottom: St- stones, G- gravel, Sa – sand, M –  mud. Vegetation: B – bryophytes,      HP-  higher plants, I.,II.,III.:  communities  in longitudinal profile of streams by Vannote et al.(1980) – see also Fig 2 and Allan (1995),   1,2,3,4,5: communities in  different  stream zones in the Czech Republic by  Sládečková, Sládeček (1998), re-numbered: 1- (in cited paper Plate 1 and 2) =  Crenon +   Hypocrenon, 2- ( in c.p.Plate 3   and 4) = Epirhithron and metarhithron, 3 – ( in c.p. Plate 5  and 6) = Hyporhithron, 4 – (in c.p. Plate 7 and  8) = Epipotamon, 5 – (in c.p. Plate 9 and10) = Metapotamon., —– = administrative frontier between salmonid and non-salmonid streams in Czech Republic (according to  Štefáček 1995).
II.
1) The others data given in Tab. 1 are  undertaken from the following papers: Balatka, Sládek (1962), and Tuša (1994). The most of them are verified by the  author´s own experiences
2) At communities I,II,III the size (order) of streams given by Vannote at al. (1980) are not taken into account here, aspecially in side streams at lower altitudes. In  these smaller streams we  may mostly found only small species  of fishes as well as  younger specimens of the bigger fish species.
 

 

 

 

 

Fig 2   River ecosystem. Vannote ´ s and Illies ´model are combined here. Vannote´s  model  is taken from Allan (1995), see also Illies, Botosaneanu (1963), Hynes (1970), Hawkes (1975) a.o. 

 

 

Fig 3   Generalized zonation of river into rhithron (black) and potamon (white) for worldwide application.  After Illies 1961, taken from Hawkes (1975) p. 370.