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MONITORING OF FLOODPLAINS:
LIMNOLOGICAL INDICATORS
Fritz Schiemer
Abstract
Monitoring programmes are required in order to define the extent of natural variability, identify trends as a result
of man-made perturbations and clarify the effects of restoration and management programmes.
A key factor for understanding the properties of floodplains is the hydrological connectivity between the river and
alluvial zone via groundwater exchange and flood events. The nature of floodplain ecosystems is strongly de-
pendent on the dynamic intersection and areal extent of flood pulses, which imply local and large-scale distur-
bances. This creates the mosaic of successional stages - aquatic to terrestrial - with its characteristic functional
properties and high biodiversity.
On a larger spatial and temporal scale, monitoring the environmental status of floodplains can be done through
wide-range mapping of habitat types using remote sensing or other large-scale monitoring procedures.
On a more detailed scale, which is required to define precise management procedures, a complex array of both
physiographic and biological indicators will be necessary. Physiographic and biological data must be intercali-
brated and analyzed in order to understand the causal relationships between the main functional properties of
floodplain ecosystems (nutrient cycling, production and decomposition, import and export processes between
river and floodplain, erosion and sedimentation, e.g. clogging of aquifer, terrestrification processes etc.) as well
as the habitat conditions for a characteristic biota.
Schiemer, F.: Monitoring von Flußauen: Limnologische Indikatoren
Eine regelmäßige Erfassung des ökologischen Zustandes ist erforderlich, um die Auswirkungen anthropogener
Störungen oder - im positiven Sinn - von Revitalisierungs- und Managementmaßnahmen auf Flußauen, vor dem
Hintergrund der natürlichen Variabilität, beurteilen zu können.
Der Schlüsselfaktor für das Verständnis der Ökologie von Flußauen sind die hydrologische Vernetzung von Fluß
und Au. Die ökologischen Gegebenheiten hängen stark von der zeitlichen und flächenmäßigen Ausdehnung von
Hochwässern ab, die klein- und großräumige Störungen bewirken. Diese schaffen ein Mosaik von Sukzessions-
stadien und eine hohe Biodiversität.
Für die Entwicklung von Revitalisierungs- und Managementkonzepten, ist ein komplexes Indikatorsystem erfor-
derlich. Es soll die wesentlichen funktioneilen Prozesse (Nährstoff-Kreisläufe, Produktion und Dekomposition,
Austauschprozesse, Erosion und Sedimentation), und die Lebensraumerfordemisse für charakteristische Lebens-
gemeinschaften beschreiben. Über Erfahrungen mit physiographischen und biologischen Indikatoren an der
Donau wird berichtet.
Schiemer, F.: Monitoroväni ncnich niv: biologicke indikatory sladkych vod
Monitorovacf programy jsou vyznamne zhlediska definovänf rozsahu prirozene variability, stanovenf trendu
vyvoje v düsledku zasahu cloveka, a vyhodnocenf vysledkü revitalizacf a planü hospodarenf. Klicovym bodem k
porozumenf zakladnfch vlastnostf rfcnfch niv je znalost hydrologickeho rezimu, zävisleho na propojenf mezi
rekou a aluviälnf zonou cestou vymeny spodnf vody a povrchovych zäplav. Charakter ffcnfch niv je vyrazne
zavisly na dynamickem prüsecfku a plosnem rozsahu zaplavovych pulsü, ktere v sobe zahmujf mistnf i velk-
oplosne rusive zasahy. Toto vytvärf mozaiku sukcesnfch s tad if - od vodnfch k suchozemskym - se svymi charak-
teristickymi funkcnfmi vlastnostmi a vysokou biodiversitou.
Pri rozsählejsfm plosnem a casovem mefftku jsou k monitoroväni pffrodnfho charakteru rfcnfch niv vhodne druzi-
cove snfmky jednotlivych typü lokalit. Pfi detailnejsfm meh'tku je tfeba pouzft medody fyzikälne-zemepisne
spolu s biologickymi indikatory. Fyziografickä a biologickä data musejf byt vzäjemne porovnäna a analyzoväna
spolecne, jestlize chceme pochopit pffcinne vztahy mezi hlavnfmf funkcnfmi vlastnostmi rfcnfch niv (jako je
kolobeh zivin, produkce a dekompozice, procesy importu a exportu mezi fekou a nivou, eroze a sedimentace,
napr. zazemnovänf atd.) a poznat zivotnf podmfnky organismü charakteristickych pro danou lokalitu.
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1. INTRODUCTION c) smaller river sections (e.g. WWF area
downstream of Vienna: interest to de-
Monitoring with appropriate indicators is velop a floodplain restoration method-
required to recognize ecological change. ology); this requires more detailed as-
This is particularly relevant prior to major sessment and monitoring procedures
management decisions. We need to know d) reaches (e.g. in order to define habitat or
how - in which direction - and how fast microhabitat value for particular species
ecological conditions are changing. or detailed functional processes).
In setting up a monitoring programme, the
aims must be clearly defined, otherwise
irrelevant data sets will be collected. 2. KEY FACTORS OF FLOOD-
The general objectives of a monitoring PLAIN ECOSYSTEMS
programme will determine to some extent
its structure and the indicators chosen.
The selection of efficient indicators re-
quires an understanding of the functioning
Objectives can be an assessment of: of floodplain systems. One key factor is
a) the status quo of a wetland system and floods.
the extent of natural variability, or It is widely recognised that lateral ex-
b) ecological trends following man-made change processes between the river and its
perturbations, or riparian zone dominate the longitudinal
c) effects of engineering, management and processes in the sense of the river contin-
restoration programmes. uum concept (CHAUVET & DECAMPS,
1989, NAIMAN et al., 1988, NAIMAN &
Monitoring can be orientated towards:
DECAMPS, 1990, SCHIEMER & ZALEWSKI,
- conservation (conservation potential,
1992, SEDELL et al., 1989, WELCOMME,
extent of human alterations, 1979). These lateral effects depend on the
"Hemerobie": distance from original extent of the riparian zone, its geomor-
conditions, habitat requirements for tar- phology, and on river hydrology. With the
get species), or duration and areal extent of flood waves,
- resource use (e.g. drinking water quality, production and carbon dynamics are gen-
self-purification). erally enhanced. This long-recognised re-
lationship has recently been re-emphasized
The type of programme and the parameters by JUNK et al. (1989) as the FLOOD
selected will, on the other hand, largely PULSE CONCEPT.
depend on the spatial scale under consid- Flood waves are not only significant for
eration. Fig. 1. illustrates different scales of nutrient and carbon dynamics, but also
focus in the example of the Danube. determine the geomorphology and patch
dynamics of the floodplain system. Floods
The programme can focus on the: are responsible for resetting early succes-
a) whole drainage basin (e.g. assessment of sional stages and - by controlling the
general levels of human impact in the population size of strong competitors -
drainage basin, remaining areas of allu- create a high, disturbance-mediated diver-
vial forests and their status); sity level. A further significant aspect of
b) larger river sections (e.g. downstream of floodplain ecology can be described as the
Vienna: controversy between hydro- CONNECTIVITY CONCEPT:
power and conservation options; this re- The hydrological connectivity of the river
quires large-scale monitoring of conser- and its backwaters via surface and
vation value and ecological functions); groundwater at the various water level
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100m
embankment
Fig. 1. Spatial scale of flood plain monitoring programmes in the example of the Danube. For
explanations, see text.
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stages is decisive for nutrient recycling, The construction of a series of hydropower
production, decomposition, sediment for- impoundments (as of 1954 in Austria), had
mation and clogging of the groundwater even more serious ecological consequences
aquifer (e.g. AMOROS & Roux, 1988, and resulted in an almost complete discon-
HEILER et al. 1994). nection between the river and its flood-
The hydrological integration between river plains.
and backwaters is a significant habitat pa-
rameter for species which require different We have identified different types of dis-
aquatic microhabitats in the course of their connection between the river and its back-
life cycle, e.g. certain species of fish waters in the Austrian Danube (Fig.2):
(SCHIEMER & SPINDLER, 1989).
The significance of the hydrological con- a) In the free-flowing sections of the Da-
nectivity can be illustrated using the Da- nube the lateral connectivity and hy-
nube as an example. draulic exchange between river and
When we recall the original conditions of former side-arms via groundwater is
the Austrian Danube prior to the Danube still high. In certain backwaters the hy-
regulation starting in 1875, the braided drography exhibits strong fluctuations
river system in the alluvial plains was and sediments are temporally exported
characterized by a rich structure with re- by through-flowing floods. In such dy-
gard to velocity pattern and substrate namic backwater types the growth of
conditions. Temporary lentic conditions aquatic macrophytes is generally low.
occurred in the elevated side arms. Floods
resulted in an erosion and export of sedi- b) Exchange conditions are reduced in
ments. Water level fluctuations caused more highly elevated zones and behind
good aeration and flushing of the ground- flood levees (e.g. in the Lobau at Vi-
water aquifer over a large lateral extent. enna). The erosive forces of floods are
This original high degree of connectivity missing or strongly reduced, although a
changed drastically in many European river reduced hydraulic connection via the
systems at the turn of the century due to groundwater exists. The amplitude of
major regulation schemes designed to con- the hydrography is lower, and sediments
trol floods and improve shipping condi- are accumulated and further inhibit ex-
tions. change with the groundwater. Macro-
The straightening and enforcement of a phyte growth plays a major role in nu-
main channel and abandonment of side trient exchange, sediment formation and
channels had major effects on: accumulation. Higher water retention
a) the ecological conditions of the river results in significantly increased internal
itself (increase in flow velocity, bedload loading processes.
erosion, and deepening of the river bed);
b) the exchange conditions between river c) In the former floodplains lateral to hy-
and riparian zone; and dropower dams, the hydrological ex-
c) the relative proportion of alluvial habitat change can be almost completely ab-
types (SCHIEMER & WAIDBACHER, sent; this fosters the above-mentioned
1992). sedimentation and clogging processes.
The characteristic properties of flood-
The ecological trends initiated by these plain systems are lost.
large regulation schemes over a hundred
years ago still continue today (e.g. ter-
restrification processes with concomitant
vegetational changes).
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Fig. 2. Types of hydrological connections of the river and its backwaters in the Austrian Da-
nube. Left side figures: black arrows = water exchange. Right side figures (limnological
characteristics): vertical columns = amplitude of seasonal water level fluctuations. White
arrows = nutrient exchange processes. Fine dots = fine sediment accumulation. Note the
infiltration of the sediments in the groundwater aquifer under conditions of disconnection.
3. RELEVANT PARAMETERS Depending on the specific objectives of the
IN THE ASSESSMENT OF monitoring programme some parameters
may be more significant than others (Table
FLOODPLAIN ECOSYSTEMS
2).
Keeping in mind that flood pulses and hy-
4. EXAMPLES OF INDICATORS
drological connectivity function as key
factors, we can define the relevant charac-
The indicative value of hydrochemical and
teristics in the assessment and monitoring
faunistic data for monitoring floodplain
of floodplain ecosystems:
ecosystems is illustrated using selected
a) with regard to their functions (e.g. eu-
examples from the Austrian Danube.
trophication and terrestrification proc-
esses, nutrient dynamics, etc.), and
Hydrochemical parameters
b) with regard to the habitat requirements
of characteristic species and communi-
Geochemical values (e.g. conductivity,
ties of aquatic and semi-aquatic habitats
silicate) - in combination with hydro-
(Table 1).
graphic data - are good indicators of hydro-
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logical connectivity or disconnection of the accumulation and sediment quality can be
river and its backwaters. used as long-term indicators.
Nutrient chemistry (e.g. P , N0 ) consists Figs 3 and 4 show chemical characteristics
tot 3
of process-oriented parameters. of various water bodies in the disconnected
alluvial plains of the Danube upstream of
Table 1. Relevant characteristics in the the hydropower station at Althenwörth.
The mean values (and variability) deter-
assessment of floodplain ecosystems:
mined in a seasonal study in 1985 show the
good discrimination between the different
* structural properties
habitat types.
patch structure (e.g. habitat
distribution), ecotone pattern and
Biotic indicators
packing
* patch dynamics
Biotic indicators can be specifically useful
extent and time scale of distur-
due to the species-specific, integrated re-
bances,
sponse to many environmental variables.
successions
When autecological requirements of char-
* hydrological connectivity
acteristic species associations are well es-
* limnological processes
tablished, they provide useful evaluation
nutrient dynamics, production and
criteria for the structural and functional
decomposition, sediment formation
quality of rivers with reference to original
& erosion, clogging of the aquifer
conditions.
* pollution levels
accumulation of toxic substances,
For assessing the habitat quality of back-
e.g. heavy metals
waters we currently employ a system of
fauna groups which integrate different
qualities, for example (see Fig. 5)
Table 2. Significance (! = weak; !!! = high)
of monitoring of various characteristics
- aquatic molluscs and water beetles with
for conservation and resource use:
small-scale aquatic habitat linkages (1)
(e.g. FOECKLER, 1990)
conservation resource use
- fish which require littoral spawning sites
structural !!!
and which species-specifically change
properties
their habitat requirements in the course
patch dynam- !!! ;
of their life cycle (2) (e.g. SCHIEMER et
ics
al. 1991),
hydrological • • • !!!
- heterotopic aquatic insects (3), amphibi-
connectivity
ans (4) (e.g. BLAB, 1978, WARINGER &
limnological • • •
WARINGER-LÖSCHENKOHL, 1990) and
processes aquatic birds (5) (e.g. DOBROWOLSKI,
pollution j !!! 1973) which require different combina-
levels tions of aquatic and terrestrial habitats.
In combination with trophic indicators like The combination of faunistic data therefore
Chi a and macrophytic cover, they provide reflects, in an integrative way, ecological
important information on the trophic state, qualities of the aquatic/terrestrial transition
production and decomposition processes. zone (SCHIEMER, 1992; IMHOF et al. 1992).
Chemical data allow short-term and small- Fish communities are clearly good indica-
scale resolution of processes. Sediment tors of habitat structure as well as of the
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-h
rH
20
300-1
•+
200-
100-
5 10 1415 8 4 3 11 12 30 6
-1
lig Si.l
2000-
[-4-1 1 i
-+•
1000-
Si
5 101415 8 4 3 11 12 30 6
Fig. 3. Conductivity and silicates (mean values and seasonal variability in 1985) of various
water bodies in the dammed alluvial plain upstream of the hydropower dam at
"Althenworth". Waterbodies are marked by numbers. The first group (5, 10, 14, 15) repre-
sents the Kamp river and backwaters connected to it. The second group (8, 4, 3, 11, 12)
represents isolated backwaters and artificial gravel pits. The third group represents the Da-
nube (30) and a small brooklet, Krems (6).
ecological integrity of large river systems Fig. 6 shows in. a simplified scheme the
because many species have complex habi- links of the fish fauna to the different zones
tat requirements in the course of their life of the alluvial plain of the Danube:
cycle.
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/*g PI
300- 4i
l+H-i
-h
200- -h
-
100'
5 10 14 15 8 4 3 11 12 30 6
/wg N'l
3000 n
2000-
N-NO
3
5 10 14 15 8 4 3 11 12 30 6
Fig. 4. Total phosphorus and nitrate of various waterbodies in the dammed alluvial plain up-
stream of the hydropower station "Althenwörth" (see Fig. 3).
riverine species which are strictly bound - species bound to disconnected branches
to the river itself, of the river (with a high development of
riverine species which require zones of vegetation),
low flow, e.g. backwaters with open - eurytopic species found in different
connections to the river, during certain habitat types.
periods of their lifecycle,
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Fig. 5. Spatial dimensions and habitat complexity of selected indicator groups in the land-
water ecotones of floodplains. Points = reproductive zone, arrows = habitats of older
stages. 1: aquatic molluscs, 2: fish, 3. heterotopic aquatic insects e.g. odonates, 4. amphibi-
ans, 5. water birds. From SCHIEMER (1992)
The riverine guild was found to be most dam was completed clearly demonstrated
diverse and most endangered. The majority that the riverine species have already
of these species are on the "Red lists" of strongly declined and that the relative pro-
endangered taxa. portion of eurytopic forms (e.g. bream,
Regulation and especially the construction Abramis brama, roach, Rutilus rutilus, and
of hydropower dams has resulted in severe silver bream, Blicca bjoerknd) has in-
degradation of their habitats. The changes creased.
induced by damming can be elucidated by Our studies revealed that important habitat
a comparison of the fish stock in free- links are due to the requirements during the
flowing sections and in impounded areas early life history. In backwaters without
(Fig. 7). The fauna in the free-flowing river connection to the river, the fish fry is com-
is characterized by a clear dominance of posed of eurytopic and limnophilic species.
nose, Chondrostoma nasus (L.), followed Open backwaters are dominated by eury-
by barb, Barbus barbus (L.). The percent- topic forms. The 0+ stages of rheophilic
age of eurytopic species is low. A compari- species are found exclusively in the natu-
son with the catch statistics in an im- rally structured littoral zone of the river
poundment ( at Melk) 5 years after the itself. A high diversity and a large number
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Rheophilous Limnophilous
R. p. virgo S. erythrophthalmus
L. idus L. delineatus
B. barbus T. tinea
V. vimba R. s. amarus
P. cultratus M. fossilis
G. schraetser
Z. zingel
Z. streber
Eurytopic
L.cephalus E. lucius
A. aspius <c R.rutilus
C.nasus A. alburnus
G.gobio B. bjoerkna
A.ballerus A.brama
A. sapa C. a.gibelio
C.carpio
L.lota
S. lucioperca
P. fluviatilis
G.cernuus
P. marmoratus
Fig. 6. Ecological guilds of fish species to be found in the different habitat types of the allu-
vial system (river, connected and disconnected backwaters). See text. (From SCHIEMER,
1988).
of endangered species were encountered only in the naturally structured littoral
among the 0+ population in small bays and zone of the river itself, and
shallow-sloped gravel banks of the river 2. the very lowest population density of
shore. The lowest population density and fish fry and the lowest species diversity
species diversity of the 0+ age class were are found along the linear, artificial
found along the linear, artificial shorelines. shorelines.
Several structural elements of the shore
Two important results are immediately appear to be essential for fish recruitment.
obvious from this comparison: This is schematically illustrated in Fig. 8.
(1) The necessary stream bed structures for
1. the fry of rheophilic species are absent reproduction have to be in close prox-
in both backwater types and are found imity to the larval microhabitats.
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