Preliminary draft.
LARGE RIVERS OF SOUTH AMERICA: toward the new approach
J.J. Neiff
INTRODUCTION
It is likely that water consumption for life maintenance is the most important of the multiple uses of
water. In great part of the biosphere, water is very scanty, or it is even unattainable, and, what is even more
serious, a progressively less amount of water can be devoted to direct consumption because of the increasing
of pollution. Therefore, an increasing number of people counts on a less amount of water.
It is just as worrying that the loss of the water quality also affects all these forms of life in the
biosphere, being it now expected a decrease in the biodiversity at the continents level, with impact on human
populations, an even more difficult fact to measure.
Superficial waters are the most reachable for men, but only continental fresh waters allow its direct
use for human, plant and pets consumption.
Diagrammatically, availability of superficial water at continental level depends on the positive water
balance of rains and the landscape physiography to retain it, accumulate it, or allow its runoff towards the sea.
For an equal amount of superficial available water, continents have different proportion of cumulated
water (bodies of lentic water) and running water (lotic environment).
South America is in a privilege situation since it has a greater volume of flow of superficial running
waters, that result from the constant flow starting with some rain drops and reaching the sea. This fact ensures
countries possibilities to dispose of "new" and clean water in the future, under the condition that the adequate
use of the basins ecosystems can prevent the erosion processes, pollution caused by the pour of toxic
substances, or by the effect of acid rains.
The design and adequate monitoring of the different programs of flood control in urban
conglomerates, hydric exploitation for the energetic production, navigation and other possible alterations of
the pulsatile regime is just as important.
South American's geographic singularity: large rivers
As Morello (1984) describes in his "South American ecological profile", the surfaces of the South
American continent double those of Europe and reach the southern latitudes of the biosphere. However, owing
to its triangular shape with it vertice looking south, its climate has a great oceanic influence, and as a
consequence, it is warmer than the one of the same latitude in the northern hemisphere.
Orographically, South America is an asymmetric continent, with a continuous mountain chain (the
Andes Mountain Range) the height of which reaches the troposphere and two shields or high cores: the
Guayana and the Brazilian one. The remaining surface corresponds to big pieces of flatland with little concave
surfaces, except in the austral Andes region and in a part of the Patagonia, where there is a great number of
lakes of glacial origin formed in the pleistocene that are, currently, under a tempered climate.
Most runoffs in South America have sense and general W-E direction (Orinoco, Amazonas rivers)
and most of the water and sediments moving along the continent are originated in the Andes mountains (of
alkaline tendency, with a great amount of sediments of fine silt-sand and loam texture and a less amount of
clay).
A minor amount of water runs-off with a predominant North-South direction (Paraguay, Paraná and
Uruguay rivers) with neutral to slightly acid waters and unselected sediments (clay to coarse sand), coming
from the geological erosion of the shield of Brazil.
According to the orographic origin of waters, and to biotic transformations that take place in vast
flatlands, waters running along the rivers may be: "white water" (with a great amount of fine slit-sand and
loam of the Andes Mountains); "black waters" (with few suspended sediments and a high content of dissolved
and particulate organic matter); and "clear" (with intermediate characteristics). This simple classification
developed by Sioli (1975) for the basin of the Amazonas river more than 30 years ago is currently applicable
today to most large rivers in the continent.
Based on Troll's criteria to the north of Buenos Aires, the warm and wet maritime climates prevail
(OAS, 1973). They receive their humidity and rains from the atmospheric circulation in the Atlantic ocean.
Resulting from this physiographic and climatic characteristics, South America is the continent where
large rivers collect the greatest amount of superficial water to spill it into the Atlantic ocean. The three largest
basins of the continent (Orinoco, Amazonas and Paraná), contribute with 13% of the total suspended solids
delivered by all rivers to the oceans (Tundisi, 1994).
In the table 1 made with data provided by Welcomme (1985) and Neiff et al., (1994), is possible to
see the importance of large rivers in South America compared to other continents.
Discharge (table 1, column 1), in relation to the surface of each basin, is always greater in South
America than in other continents (see: rate 2/1 in the table).
When comparing the surface of continents, and the discharge of large rivers, it results that the amount
of running water in relation to the continental surface is much greater in South America (Fig. 1).
Brief comparison of lakes and large rivers functioning in South America
In most South American lakes, superficial waters are of Pleistocene origin and have accumulated
disturbances from geologic times, and the impact of antropic activities (control of water in tributary rivers,
contaminants, sediments). In large South American river waters, only stays for some months flowing along the
continent, thus carrying and transferring minerals and organisms through the basin.
Let's us exemplify, in lakes the percentage of the volume of water annually renewed is very low
compared to the volume comprised in the basins. Water circulation is produced in one or more seasonal
periods, and the mixture efficacy essentially depends on the physical attributes, specially in temperature. The
periodic circulation of water depends greatly on the amount of solar energy that the mass of water receives
locally.
Lakes, therefore, can be considered as systems with great potential energy and low kinetic energy.
From the energetic point of view, they can be considered as "cummulators" with a slow active volume: the
hypolimnion.
In South America, large rivers can comprise small and large lakes in their basin, as well as wetlands,
other lentic environments, but the greatest volume of water is temporarily or permanently in horizontal
movement. The water renewal rate, in a determined section, is high compared to cumulated water. The
concentration of elements (nutrients, organisms, sediments) must be expressed in relation to the discharge
values and not in volume units.
The greatest amount of power that goes through the system is kinetic and this is of great importance
when analyzing the nutrients flow, temporal distribution patterns of organisms, the use and handling of rivers.
Physiographic differences and, particularly the land slope, can determine the presence of tributaries
and quick runoffs and slow runoffs sectors. These latter do not have the typical characteristic of vectorial flow
(typical of rivers) since they can run-off in one or other direction during the different periods of the year,
depending on the volume of flow of the collector stream.
The table 2 shows some characteristics that enable to compare rivers with mountain vectorial
landscapes to rivers with flatland landscape (equipotential) from the concept submitted by Gonzalez Bernaldez
(1981).
Consequences of the movement of water in large rivers
The main difference as regards lakes is the horizontal movement of water and, besides, between small
and large rivers is that in the former case, water moves only temporarily while in large rivers, flow is
permanent and organizes the distribution patterns and the organisms abundance. They are, therefore, systems
or macrosystems where water, nutrients, sediments and organisms pass through a certain runoff section at a
certain speed.
For a better understanding of the functioning of the fluvial macrosystem variability, a "typical" lake
(for example the Mascardi lake, Rio Negro, Argentina) can be compared to a dam lake (for example, Yaciretá
dam on Paraná River at Argentina).
A very simple example made up with a glass (with the lake volume, relatively constant) and two
tubes: one is the income of water and the other is the outlet of superficial water, can be applied.
2
Volume (v) comprised in the glass is the cumulated information (generally speaking) in a certain time
(t). If water were not renewed (utopia) the internal organization would depend on the amount and quality of
elements comprised in the glass (nutrient species, etc.), on the energy fluctuations that our "glass" (or water
body) seasonally receives and on interactions of elements within the system.
In lakes:
Q1
S
Q2
Total internal change: TTRi   P  E  S  Q1  Q2
where:
P = Energy inflow (precipitation, solar energy)
E = Energy outflow (runoff, termal advenction, etc.)
S = Surface area
Q1 = Inflow of information (water, sediments, spp.)
Q2 = Outflow of information (water, sediments, spp.)
t = time
But in rivers:
Q1
V
Then:
Total turnover rate 
Q2


TTR  1  Qt12 / V  TTRi
Total turnover time
TTt = 1/TTR
We would now place the income of water tube (nutrients, sediments, organisms) Q 1 in the graphic,
and the outlet tube that will bear the Q2 symbol. In this second example there is, besides the internal
metabolism of the system, an inflow of information (nutrients, sediments, organisms) unit of time.
Normally, in lakes and rivers, the volume is relatively constant and the income and outlet volume of
flow vary in an analogous way.
The turnover rate (TTR) is the percentage of the total water comprised in the glass that comes in or
out in a certain period of time. The turnover time is reciprocal to the turnover rate and states the necessary
time for a complete renewal of water in the glass.
If the glass has a 1 litre capacity and 100 ml income per day, the turnover rate will be 100/1000, or
0,1 or 10 per cent per day.
Both rates are of significant use in order to value the exchange of information of the system under
analysis. In practice, the turnover time rate is generally used. The TTR would be different along the river
sections. Values of nutrient concentration in rivers offer a small amount of information if not discussed with
the volume of flow data crossing this point or section.
Turnover time for the Yacyretá dam (placed in the watercourse of the Alto Paraná) is about 3 weeks.
This same assessment, made for the Mascardi lake, has an approximate value of five years.
Water renewal in large rivers (and of other elements of the system) is quite high as regards the
information volume comprised in the system. For such reason, the indices application described in the system
status cannot be the same to those used in the study of systems of low turnover (as it happens in most lakes).
The biocenosis analysis with the use of indices of dominance, abundance, equitability, diversity and
other, of known use in low turnover time ecosystems (Hulbert, 1971), have a low use to indicate the
organization complexity and the functioning of communities that live in large rivers. Most known indices
3
express the organisms distribution in a number of species. The disadvantage that they have is that they do not
incorporate the turnover-time and turnover-rate magnitude.
Going back to our example of the glass: an increase of 10 individuals (or species or information
units, generally speaking) can give the same result even when the flow rate in the system varied in great
manner. If the outlet rate (death, emigration) were 0, the change rate would be 10. But it would also be 10 if
200 individuals were incorporated, with a 190 exit, or if 1000 were incorporated and 990 got out.
These indices are not very sensitive to explain the changes in systems with a high populational
turnover due to the horizontal movement of the water during floods in the river valleys. They can also end up
in misleading conclusions since in several occasions the diversity is kept with small change even when there is
a 60% renewal of the species forming the community between high waters and low waters phase (Frutos,
1993; Zalocar de Domitrovic, 1993). Still when comparing extreme situations of low waters and others with
extraordinary flood, the specific diversity does not reflect significant contrasts. The use of the simplest
similarity index (as the one of Sörensen) to different situations of extreme high and low waters state that
similarity is less to 30% for phytoplankton (Fig. 2).
In biotic systems of rivers, mainly in those of high change rate as planktonic groups or those of
invertebrates that live in plants the complexity analysis requires to know the change rate, the response time
and the possibility for a population or community to repeat its structure throughout time (Poi de Neiff and
Bruquetas, 1989; Huszar, 1994).
In order to graphically represent this idea: perception is completely different when we observe the
blades of a fan which is not working (that is to say, without performing its essential function) and the one we
obtain when the blades move at different revolutions per minute.
In our example of the fan, we should now think that each blade is a species (or population or
bioform) and that our "fan" could have "X" number of blades (as many as different elements that form our
community) each of them represented in a different color. Therefore, our perception "would have a different
color" by the number of colors (species, elements) forming the blade, and the speed we give to the fan.
Yet, the problem gets more complex since in the case of rivers, changes are not produced in the form
of cycles (bio-geo-chemical cycles are not cyclic within the system) and because flows are produced as energy
pulses and matter pulses presenting flood phases and dry phases.
Both phases form the "hydro-sedimentologic pulse" (or simply "pulse"). And the way of these pulses
is variable throughout the century, and even in a decade. Variability throughout the long series of time shows
regularities that may be profitably studied by the use of the rescaled range analysis since it allows to find
hydrologic variability tendencies (Armengol et al., 1991).
In rivers, the amount of water that goes through a certain section and in a certain unit of time varies
generally in a sinusoidal way, as a consequence of the rain distribution, physiography and basin soils.
Frequency, scale and duration of dry and flood phases depend on the topographic position of the river
islands and on the ecosystems occupying the floodplain, and they will also receive -with a greater or less
frequency- the hydrologic events that take place during summer or in winter. Each river, or section of the river
receives with a greater or less regularity a flood phase or a dry phase of certain magnitude.
This group of hydrologic attributes defines the characteristics of the pulsatile system or "FITRAS"
function (Frequency, Intensity, Tension, Regularity, Amplitude and Seasonality) as they were defined in
previous contributions (Neiff, 1990b, Neiff et al. 1994). In the figures 3 and 4 and the FITRAS function is
graphically described, thus being different according to the different topographic levels of the floodplain.
Ecologic consequences of the pulse system
It is generally known that the floodplain landscape of large South American rivers is very different
from the high land ecosystems limiting the river. It is also known that there are biotic differences among the
different sectors of the watercourse and of the floodplain.
In large rivers with floodplain laterally located (fringe-floodplains, in sensu Wellcomme, 1985), it is
possible to find a growing complexity as regards organization in a transversal sense of that of the watercourse
of the river.
Marchese & Ezcurra de Drago (1992) describe a typical zonation with complexity increase (amount
of species, specific diversity, trophic niches) from the main watercourse to the minor tributaries (Fig. 5). This
increase in the richness of species in a section transversal to the Low Paraná was related with modifications in
4
the physical and chemical properties of the environment (discharge, sediments texture, organic substance,
dissolved oxygen).
For phytoplankton and zooplankton (Zalocar 1990, 1992, 1993) the trends are similar (table 3).
Junk et al. (1989) explained that a significant part of the biotic organization of rivers with floodplain
is ruled by "flood pulses" and that periodic flood events produce stress situations for biota, reflected in a
system "resetting". Bonetto (1975, 1976) explained that floods produce "rejuvenation" processes in
ecosystems forming part of the river.
Biocenosis of large rivers are regulated by the hydrodynamic of pulses. But low water phases are as
important as flood periods (Neiff, 1990b; Neiff et al. 1994). And this is not only a semantic problem regarding
the "flood pulse" concept given by Junk et al. (op. cit.).
During this dry phase, plants suffer from an acute stress, as it has been documented (Neiff and Poi de
Neiff 1990) due to the leaves abscision and growth arrest.
Vertebrates fauna find a less amount and quality of environments during this dry phase, therefore a
concentration (overload of individuals) is produced in a surface up to 5 to 10 times less than the one of the
flood period, and animals are more vulnerable.
I desire to emphasize that the dry phase is a powerful selection factor on the distribution and
abundance of the animals and plants. Most of the fish populations can not survive, or suffer important losses
during very extended droughts. (Merron et al., 1993).
Floods represent a change macrofactor in the biotic structure. However, there are trees with
morphologic, anatomic and physiologic adaptations to perform their photosynthesis even under immersion
conditions (Joly and Crawford, 1982; Fernandes Correa and Furch, 1992; Neiff and Reboratti, 1989; Tundisi,
1994). Some trees stay up to nine months with the soil covered by water without noticeable modifications in
their growth, even in cases of long-term floods that cause the death of a great amount of trees of the gallery
forest in one year (Neiff et al. 1985). The phenology of some species of the Amazon varzeas would not be
affected by the floods (Oliveira, 1995).
Rooted vegetation of floating leaves growing in the floodplain lakes has ecophenes of its own, of the
flood phase and the dry phase (Junk 1970; Neiff, 1979). When covered by flood water, they speed up their
growth and modify their anatomy and morphology (Neiff, 1979), thus attaining -during this stress phaseproductivity values up to five times greater than the average annual productivity value (Neiff 1990a) as it is
shown in table 4. This productivity response has not been noticed during the flood phase in the Amazonas
floodplain (Junk, 1986).
Some tools to get to know the biotic variability of large rivers
The water temperature regime of the South America large rivers is little known and requires highpriority as a tool within the Global Change Program. Interactions among physical, chemical and biological
factors at regional and local level need be incorporated in the thermal study of these rivers (Budiko et al.,
1994).
Species richness in a determined environment or section of a river, the use of productivity or the
amount of individuals can help as indicators of the system's complexity (Fig. 5).
It is quite useful to analyze the biotic variability in pulsatile systems, employing rates that combine
populations abundance according to ranges, with respect to frequency values in the community (McNaughton
& Wolf, 1984). The shape of these curves provides information as regards stress situations that take place
during long floods (Fig. 6) in different biotic groups (Poi de Neiff and Bruquetas 1989).
During the critical periods the diversity decrease and the distribution of the relative abundance shows
a geometric curve.
We could be use an index that combine three biotic parameters: abundance, as mean density (or
individual numbers in each hydrologic phase, or better: moment within the phase); frequency, i.e. the number
of phases (or moments within the phase) occupied, as expression of the niche amplitude; and the mean
weighted or barycentre, i.e. the mean weighted by the density of population in each hydrologic phase, to
evaluate the position of a population or populations for a given hidrologic curve.
Finally:
5
h
Nh X h 
PPh 
h
 Nh
where:
PPh = Population position in a hydrosedimentologic pulse.
X h = Mean coordinate weighted by density of population in each pulse h.
Nh = Population density in the hydrologic phase (or date) h.
The "ABC method" (abundance/biomass comparison) were proposed by Warwick (1986) for
detecting pollution effects on macrobenthic communities. Thereinafter, Meire and Deren (1990) proposed the
ABC index:
ABC 
Bi  A i
N
where:
Bi = % dominance of species i (ranked from the highest to the lowest biomass)
Bi = % dominance of species i (ranked from the most to the least abundant
species)
N = total number of species.
The index is negative in heavily stressed conditions and positive in unstressed conditions. The
number of times the cumulative percentage dominance as the percentage of the total number of species minus
one (cumulative biomass dominance).
Coeck et al. (1993) concluded that the method gives information about both pollution and physical
disturbance. I think that ABC index can be tested to analyze the fluctuations of the communities induced by
the river regime (pulses).
For certain studies, it is necessary to know which population/s is/are the one/s which constantly
occupies/y an important space or volume within the system throughout a series of time, in relation to other
biotic components of the system.
For such purpose, I suggest the use of the prevalence index:

Prevalence index: P 
2
  Ui / N  t o ... t1  n
spp
0
where:
Ui = Unit of importance (Productivity, Density, Other)
N = Importance value magnitude
This index can be used in an attempt to explain the dynamics of groups in ecosystems regulated by
pulses, and specially, in those with a high change rate, due to marginal flows (in Lewis et al. concept 1990)
such as plankton of floodplain lakes that exchange the water with the one of the river course. Such as other
indices, it can be of use to analyze the biotic variability in long series of time, since it gives place to an idea of
prevalence and persistence of populations in environments with a great variability.
One of the generally accepted ideas is that the biotic complexity, mainly the species richness,
increases towards the lower sector, towards the mouth. This does not occur in rivers such as Paraguay-Parana
(Neiff, 1990b) where the greater biotic complexity is found in the Gran Pantanal of Matto Grosso, in the high
basin of Paraguay. This complexity is related to the extension and spatial variability of wetlands comprised in
the basins of these large rivers, and with the FITRAS hydrologic function along the river (Neiff, op.cit.). But,
also the temperature fluctuations are one of the most important causes of the biotic complexity in tropical
rivers.
Production of organic matter
6
In Patagonian lakes of South America, greater productivity is generally concentrated in the top of the
water column, with low values in the hypolimnion. The greatest part of the trophic nets are based on the
phytoplankton. Magnitudes can vary in different lakes, but the productivity gradients are vertical.
In large rivers of the South America, productivity is generally greater when considering the basin as
an analysis unit. The greatest amount of energy is captured by macrophytes and by floodplain forests (Neiff,
1990a).
Efficiency in the accumulation of energy has differences in transversal transections to the
watercourse, with higher values towards the floodplain. Assessments for the potamophytoplankton are 3-6
tn.ha.year-1 (García de Emiliani y Anselmi de Manavela, 1983; Perotti de Jorda, 1980; Rai and Hill, 1984),
while vegetated lakes with Eichhornia crassipes attain values from 12 to 16 tn.ha.year-1 (Perez del Viso et al.,
1968; Lallana, 1980; Neiff and Poi de Neiff, 1984; Junk, 1986), and the gallery forest of the islands of some
rivers have frequent values of 20-36 tn.ha.year-1 (Neiff, op.cit.; Neiff and Reboratti, 1989).
Utilization of phytomass and necromass
Currently, the percentage of this primary production transferred to consummers is not known and,
what is even less known is the efficiency throughout trophic nets. The direct consumption of plants is low, on
the one part due to the low amount of herbivorous and to a great amount of plants with hard tissues that turn
out to be almost trophically unattainable.
A great part of the incoming power through productivity of the plants is captured by consummers
from the organic detritus in different processing grade. This is not exclusive of large South American rivers
(Vannote et al., 1980; Cummins et al., 1983).
The main difference is that in these South American rivers with large flood plains, the organic debris
do not come from the same earthly ecosystems, but from the vegetation growing in the same river, and
therefore, it is autochthonous, as in the detritus originated therein.
The organic matter produced is always high, mainly owing to the vegetation contribution of wetlands
comprised in the floodplain. Respiration is low since the oxygen in the water is quickly exhausted, giving
place to the formation of intermediate organic components that characterize "clear waters" and "black waters",
and to an organic stock that remains in the system as necromass.
There is a lot of bibliography stating that rivers behave as "heterotrophic" systems since respiration is
higher than production.
In large South American rivers, great rate variations take place: P/R when considering different subbasins. However, rivers with large flood plains have values higher to 1, considering the river as it is: the
watercourse + its floodable plain.
It will be convenient to avoid the use of terms originated in the Limnology of lakes to define the
trophic condition of rivers, since the P/R balance is conditioned by the horizontal movement and the
permanence time of the water in the sector under analysis. For such reason, the capacity of the system is not
expressive to capture the energy from nutrients and transmit it through the trophic nets.
The P/R rate in these large rivers is also very difficult to estimate, since the income of nutrients
depends greatly on the high basin and the lateral flows in the floodable plain (from and to the watercourse).
To get a quick idea of the basin metabolism (or a sector of it), it would be of great use to know the
quantity and quality of the organic substance transmitted, and the saturation level of oxygen in the water. Both
represent the "fuel" and the "combustive agent" from the capture and accumulation of power to the
disintegration of organic substance (Neiff, 1990b). Both magnitudes attain characteristic values for each
hydrologic phase of such basin.
The organic stock magnitude for two flood phases with the same magnitude, also depends on the
amplitude duration of the previous dry phase and the moment of the year when flood takes place.
The concentration of organic carbon and its fractions, permit a sintetic idea of the metabolism of the
river basin. A comparison between Uruguay and Paraná suggest a more significant role of the latter as a
biodegrading water body: carbon in particulate aminoacids and sugars seems twice is abundant in the Uruguay
(Mañosa and Depetris, 1993). According to Richey et al. (1991) DOC represents 50% of the total carbon
transported by Amazonas and the dissolved humic compounds represents 60% of the DOC.
The size of particles of the organic substance present in large South American rivers is of significant
importance as a synthetic indicator of processes that occur in the basin (Mulholland, 1981; Degens and
Ittekkot, 1985). When the slope and the water volume of flow are similar, the percentage differences among
7
the thick organic substance content, fine particulated and dissolved, depends on the oxygen availability in the
water; and this latter depends greatly on the flow conditions (volume of flow, residence time of the water).
The amount of total organic carbon and the proportions of POC and DOC in the waters depend of the
hydrologic phase of the pulse with a higher values during the extraordinary floods (Kempe and Depetris,
1990; Depetris and Kempe, 1993).
A selection process favouring the use of the organic debris has been produced, since it is a trophic
resource always present. According to Bonetto (1976) 60% of fish productivity of the Parana river is
concentrated in detritivourous fish. Works by Bowen et. al. (1988) have stated important morphologic,
physiologic and selective food behavior adaptations of detritivorous fish.
Decomposition of organic substance
The decomposition rate of the organic matter expressed by the "k" coefficient (Olson, 1963) allows
the exploitation of the P/R rate for different ecosystems of the basin of these large rivers; investigating the
efficiency of the decomposition process during the flood-phase (potamophase) and the dry-phase
(limnophase). It also allows the comparison of the kinetic disintegration of the organic matter for species
growing from semi-lotic waters to the external border of the floodplain.
The available information for the Paraná basin (Poi de Neiff and Neiff, 1988,1989; Hammerly et al.
1989; Poi de Neiff y Bruquetas, 1991; Bruquetas and Neiff, 1991; Neiff and Poi de Neiff, 1990; Poi de Neiff ,
1991; Bruquetas de Zozaya and Poi de Neiff, 1993) allows to summarize some tendencies.
The decomposition rate mainly depends on two principal factors: quality of organic substance (lignin:
nitrogen ratio or better C:N ratio), and the oxygen availability in the water. The duration and the dry-phase
magnitude have consequences over the process, and the moment of the year in which it takes place is just as
important.
The time required for a 95% loss of Tessaria integrifolia, Salix humboldtiana, Polygonum
accuminatum, Panicum grumosum and Eichhornia crassipes leaves are 88, 158, 176, 353 and 50 days
respectively, under aerobic conditions.
The decomposition rate of E. crassipes leaves is 3 times quicker in well oxygenated waters of
connected lakes during the greatest part of the year to the watercourse of the river that in anaerobic conditions
of lakes sporadically coupled to the river. For a 95% decomposition of P. repens, Thalia multiflora and Typha
latifolia leaves the estimate time were 325, 545 and 1000 days respectively, under anaerobic conditions.
When the water level lowers abruptly and the soil remains dry, the decomposition time of the
necromass of the same plant doubles (Bruquetas and Neiff, 1991).
During winter, the necromass that breaks up in the water finds a 15-18ºC temperature while during
summer, the process occurs between 22 and 32ºC.
Finally, the production of organic matter (Neiff, 1990a) is equal to, or higher than, the one broken up
(Poi de Neiff, 1991 and 1993) in a river with floodplain as the Low Paraná. The P/R rate is closely related to
the pulse function (FITRAS).
The hydrosedimentologic regulation of the river, and specially the additive effects of dams can alter
the FITRAS function in some or all the ecosystems of flood plains. From this alteration, changes in the P/R
quotient, and in the quality and quantity of organic debris available for consummers can be expected. The
chain effects deserve special investigations.
8
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12
River
Table 1: LARGE RIVERS OF THE WORLD
Annual mean discharge near the mouth
(after Welcomme, 1985; Neiff et al., 1994)
1 = mean discharge (1000 m3.sec-1); 2 = drainage area (1000 km2); 3 = length (km)
South America
Africa
River
1
2
3
1
2
Amazon
Orinoco
Paraná
Tocantins
Magdalena
Uruguay
Sao Francisco
Total
rate 2/1=40.3
212.5
17
16
10.2
7.5
3.9
2.8
269.9
5711
870
2278
896
238
230
665
10888
6437
2151
3998
2700
1600
1612
2900
21398
Congo
Zambezi
Niger
Nile
Senegal
Total
rate 2/1=169.8
39.7
7.1
6.1
2.8
0.9
56.7
North America
Missouri
St. Lawrence
Mackenzie
Columbia
Yukon
Frazer
Nelson
Móbile/Tombigbee
Susquehanna
Total
rate 2/1=155.1
17.3
14.1
7.9
7.3
5.1
3.2
2.3
1.6
1.1
59.9
3184
1274
1784
660
921
235
1059
107
71
9295
Total
rate 2/1=112.5
6.2
4.1
3.5
2.6
2.2
1.7
1.7
1.4
1.1
24.5
806
322
355
279
143
496
94
69
194
2758
3968
1280
1100
2944
338
9630
4700
3500
4200
6650
1633
20683
Asia
6020
4000
4241
1954
2654
1360
2570
598
710
24107
Europe
Danube
Pechora
Dvina
Neva
Rhine
Dneper
Rhone
Po
Vístula
3
2850
1809
726
1312
2200
816
648
1084
11445
Yangtze
Brahmaputra
Ganges
Yenisei
Lena
Irrawaddy
Ob
Mekong
Amur
Indus
Kolyma
Sankai
21.8
19.8
18.7
17.4
15.5
13.5
12.5
11
11
5.6
3.8
3.6
1920
924
1047
2560
2396
424
2455
793
1822
916
637
117
5980
2900
2506
5540
4400
2100
5410
4000
4444
2900
2513
1957
Godavari
3.6
294
1440
3.3
2.5
2.0
1.8
1.5
1.4
1
171.3
665
189
304
355
276
535
243
18872
4845
1056
1120
1725
2400
1900
1067
60203
Hwang-Ho
Pyasina
Krishna
Indigirka
Salween
Tigris-Euphrates
Yana
Total
rate 2/1=110.1
Table 2:Breaf comparison of flatland and mountain rivers of South America
Characteristic
Vectoriality
Subtropical flatland rivers
Minimum (equipotentials)
Mountain rivers with temperate
climate
Vectorials
Physiography
Complete basin is reception-discharge
Zone of head-waters - transport - delta
Time of water concentration
High
Low
Kinetic energy
Low
High
Hydrometric regime
Bimodal:
autumn
Suspendid load
Low
Variable
Bedload
Low and fine
Commonly high, coarse
Water flow
Meanly vertical
Meanly horizontal
Hydraulic
vegetation
effects
maximums
in
summer
and Commonly unimodal spring-summer
of High
Moderate-low
Organic matter
High Production
Moderate-low
CPOM (a)
Low
High
FPOM (b)
High
Moderate-low
DOM (c)
High
Low
Biotic structure
Continuum
Communities or continuum
(a) Coarse particulate organic matter
(b) Fine particulate organic matter
(c) Dissolved organic matter
Table 3: Paraná river cross section. Species reachness in lotic and lentic environments near of the
Confluence of the Paraná and Paraguay rivers.
Channel (1)
Island water bodies (2)
(3)
Ox-bow lake, fringe
floodplain (4)
CYANOPHYTA
19
13
12
CHLOROPHYTA
91
83
68
BACILLARIOPHYCEAE
57
48
43
CHRYSOPHYCEAE
8
7
4
XANTHOPHYCEAE
2
6
16
EUGLENOPHYTA
24
70
85
CRYPTOPHYCEAE
4
7
8
DINOPHYCEAE
2
4
6
Total de especies
207
238
242
(1) Zalocar de Domitrovic, Y. y E.R. Vallejos, 1982. Ecosur, 9(17): 1-28.
(2) Zalocar de Domitrovic, Y., 1990. Ecosur, 16(27): 13-29.
(3) Zalocar de Domitrovic, Y., 1992. Rev. Hydrobiol. Trop., 25(3): 177-188.
(4) Zalocar de Domitrovic, Y., 1993. Ambiente Subtropical, 3: 39-67.
Table 4: NET PRIMARY PRODUCTIVITY (ON DRY WEIGHT BASE) IN PARANA RIVER FLOODPLAIN, DOWNSTREAM OF PARANA-PARAGUAY
CONFLUENCE. (After Neiff, 1990 b)
Stress Period
Long. (days)
N.P.P. Stress
Period (Tn.Ha-1)
N.P.P. Annual
Period (Tn.Ha-1)
Production Rate
(g.m-2.d-1)
N.P.P. Effective
Annual(Tn.Ha.-1.yr1)
Production Rate
(g.m-2.d-1)
Polygonum
ferrugineum
14
2.50
65.18
17.85
18.30
5.10
Ludwigia
peploides
11
1.96
65.04
17.81
6.7
1.84
Victoria
cruziana
10
0.29
10.58
2.90
0.89
0.24
Nymphoides
indica
10
0.85
31.02
8.50
2.20
0.60
Echinochloa
polystachya
12
1.72
52.31
14.33
14.10
3.86
Species
FLOOD
PERIOD
Potamophase
References: (*)
P = Pond
BW = Backswamp
IS = Island
LOW-WATER
PERIOD
Limnophase
Site (*)
Year
El Gato (IS)
1987
La Guardia (Sta.Fe) (BW)
1971
Baupé (Chaco) (P)
1976
Don Felipe (Sta.Fe) (P)
1971
La Cacerola (Sta.Fe) (P)
1971
Fig. 2 (adapted from Zalocar, 1993): Comparison of phytoplankton diversity and similarity index before and after the flood in a
pond of Paraná river floodplain.
Fig. 5 (adapted from Marchese and Ezcurra de Drago, 1992): Alluvial valley of the Lower
Paraná River: transverse zonation of the benthos in lotic environment.
Fig. 6 (adapted from Poi de Neiff, 1989): Distribution of the
relative abundance of invertebrate species associa- ted with
aquatic vegetation. The mean monthly water level of
Paraná River are given for Puerto Corrientes. No more
Paraná water enters the floodplain below the level indicated
by the horizontal dotted line.