Reference Conditions of Alpine Streams: Physical Habitat and Ecology

REFERENCE CONDITIONS OF ALPINE STREAMS:PHYSICAL HABITAT AND ECOLOGY

L. FÜREDER1∗, C. VACHA1, K. AMPROSI1, S. BÜHLER1, C. M. E. HANSEN1 andC. MORITZ2

1 University of Innsbruck, Institute of Zoology and Limnology, Innsbruck, Austria; 2 ARGELimnologie, Innsbruck, Austria

(∗ author for correspondence, e-mail: [email protected])

(Accepted 25 January 2001)

Abstract. Natural and near-natural streams are rare in the densely populated areas of the Alps.A variety of anthropogenic impacts have resulted in the alteration and sometimes even completedestruction of these systems. Nowadays it is difficult to find un-impacted streams that are stronglyneeded to define the natural variability and ecosystem processes. The results from freshwater invent-ories and habitat assessments conducted in protected areas in Austria (Nationalpark Hohe Tauern)and Italy (Naturpark Rieserferner-Ahrn) were used to develop a comprehensive typology of Alpinestreams. Three different levels were used to discriminate between the distinct stream/river types:source (glacial vs. non-glacial), hierarchy (i.e. location within the stream system) and topography/channel morphology. Important characters defining the structure and function of these stream typesare gradient, substrate composition, flow pattern and riparian vegetation. Benthic fauna assemblagesfrom 99 near-natural stream segments in glacial and non-glacial systems demonstrated the effect ofglaciation on abundance levels of the total macroinvertebrate fauna, EPT taxa (Ephemeroptera, Ple-coptera and Trichoptera) and the chironomid subfamily Diamesinae in different altitudes. A generaldecrease of abundances with increasing altitude was found. While stream segments with a degree ofglaciation >10% primarily showed reduced abundances at all altitudes, lower (<10%) or no glaciationdid not influence invertebrate abundances at lower reaches. Due to the near-natural conditions of theselected stream segments, a valuable definition of reference conditions of Alpine streams based onhabitat characteristics is available. As a basis it offers excellent opportunities to conduct holisticinterdisciplinary studies in protected areas in the future.

Keywords: alpine streams, glaciation, habitat assessment, natural parks, reference conditions, streamtypology

1. Introduction

Natural or near-natural stream ecosystems, a precious resource, are rare in thedensely populated areas of the Alps. A wide spectrum of anthropogenic impactshas resulted in an alteration of catchments and their river channels, sometimes evenin a complete disruption of stream and river systems. Besides the various anthro-pogenic impacts for water use (water abstraction for power generation, irrigation,snow generation, etc.), channel alterations (for flood protection) have been shownto generate severe effects on stream ecology (Petts, 1984; Boon, 1992; Petts et al.,

Water, Air, and Soil Pollution: Focus 2: 275–294, 2002.© 2002 Kluwer Academic Publishers. Printed in the Netherlands.

276 L. FÜREDER ET AL.

1994). In many regions it appears difficult to find suitable, non-impacted, nature-like stream sections which are necessary for the understanding and definition of thestructure and function of stream ecosystems.

In national and international programs, e.g., Austrian Clean Water Act (Moogand Chovanec, 2000), EU-Water Framework Directive (Rat der Europäischen Union,1999), reference states of streams and rivers (non-impacted, near-nature) are neededto assess the ecological status of European water bodies. Stalzer and Blöch (2000)in their preface to the international symposium ‘Assessing the Ecological Integrityof Running Waters’ (Jungwirth et al., 2000) pointed out that today, river manage-ment has to be orientated at the natural and river-type-specific characteristics. TheAustrian water management strategies are currently focusing on nature-like riverengineering and ecological integrity assessments. The definition of reference sys-tems for their orientation and standards is strongly needed to build an essential steptowards a comprehensive understanding of ecosystem functioning and its deviationfrom natural conditions.

The economic development together with a variety of anthropogenic impacts(land use, agriculture, flood protection and hydroelectric power generation) haveresulted in a severe modification of water courses. Impaired rivers dominate inmany regions in the Northern hemisphere (Dynesius and Nilsson, 1994). In a gen-eral overview of alpine rivers, Martinet and Dubost (1992) reported that only 10%of the river reaches were ‘near-natural’. A recent study of 52 Austrian rivers witha catchment >500 km2 (Muhar et al., 2000) resulted in the alarming fact that only6% (284 of 4915 km river sectors assessed) have maintained a natural/nature-likecharacter, and 15% (762 km) showed good habitat quality. 79% (3869 km) weremoderately to heavily impacted. Also rivers at higher elevation are impacted byman and impairment, together with water diversion, are commonly found. In aninventory of Austrian glacial streams, Hasslacher and Lanegger (1988) reported38.4% of glacial streams impacted by hydropower generation; when also plannedprojects were considered, this value increased to 63.8%.

These various impacts often have very complex and synergistic effects on theaquatic community and ecosystem functioning, but such effects are often difficultto estimate and quantify. For example, catchment land use may have multiple in-fluences on aquatic communities and ecosystem processes, ranging from decreasedshading and resulting higher temperatures; increased turbidity, nutrient, pollutantand organic matter concentrations; and considerable changes in sediment budget,flow pattern and channel form (Townsend and Riley, 1999). To fully understandthe ecological ramifications of anthropogenic impacts, a fundamental knowledgeof the complexity and dynamics of morphologically intact stream or river systemsis needed.

Several methods to characterize reference conditions have been used and dis-cussed (Friedrich and Lacombe, 1992 provide an overview of methods executedin several European countries), either in the study of historical conditions of riversfrom maps or descriptions and in the search of comparable non-impacted stream

REFERENCE CONDITIONS OF ALPINE STREAMS 277

or river sections. In lowlands and Alpine valleys where land-use and settlementhave considerably altered the landscape, it might be difficult to find reference riversystems. At higher elevations non-impacted stream and river segments still exist.

Clear definitions of the reference state are pre-requisite for a better understand-ing of natural spatio-temporal heterogeneities and for effective ecosystem man-agement (Stanford and Ward, 1992; Ward, 1997, 1998; Ward et al., 1999a). Thereference condition should be applicable to an individual waterbody, such as astream segment, but also to similar waterbodies on a regional scale (Gibson et al.,1996). Nationalparks in general offer these prerequisites due to the pristine condi-tion of wide areas, both in a historical and future perspective. Usually, these areaswere in fact chosen for protection because of their natural state and the presentprotection status ensures sustaining near-nature conditions.

A full understanding of changes to ecosystem structure and function along thecontinuum from pristine to profoundly impacted requires knowledge of physical,chemical and ecological properties at many temporal and spatial scales (Townsendand Riley, 1999). Few investigations have considered streams at higher elevationsand especially a lack of biological data from a variety of alpine stream types (Ward,1994; Milner and Petts, 1994). For multiple purposes in ecological river manage-ment a holistic knowledge of stream types is a prerequisite. Biological assessmentstoo require holistic approaches (abiotic and biotic criteria) to evaluate regionalstream types. On a regional scale for the Alps, from the montane to the alpinelife zone we are not aware of studies covering the whole set of stream types andcomprehensive biological data from pristine, near-nature conditions.

The goals of the study reported herein were to (1) present an inventory of fresh-waters in the protected areas of Nationalpark Hohe Tauern, Austria and NaturparkRieserferner-Ahrn, Italy, (2) provide comprehensive information on the ecologicalstatus of a selection of these streams, (3) present a typology of alpine streams basedon habitat assessment criteria, and (4) discuss some important aspects shapingAlpine stream insect assemblages (e.g. the role of glacial influence and altitudeon abundance and richness).

2. Methods

2.1. STUDY AREAS

The study areas comprise two large protected regions in the Austrian and ItalianCentral Alps, the Nationalpark Hohe Tauern (NPHT), founded in 1971 with an areaof 1787 km2, and the bordering Naturpark Rieserferner-Ahrn (NPRA), founded in1988 with an area of 315 km2 (Figure 1). An inventory of existing freshwaterswas established in both national parks as a base for a future freshwater monitoring.A total of 279 streams (981 km stream/river length, catchment area >1 km2) and136 lakes and alpine ponds in the Hohe Tauern Nationalpark as well as 65 streams


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TABLE I

Freshwater inventory, habitat assessments and Alpinestream typology in Nationalpark Hohe Tauern (NPHT)and Naturpark Rieserferner-Ahrn (NPRA): number of se-lected streams, lakes and parameters used for inventoryand habitat assessment

NPHT NPRA

Area [km2] 1787 315

Freshwater inventory

Number of streams/rivers 279 65

Number of lakes 136 29

Number of parameters 22 22

Habitat assessment

Number of streams/rivers 15 18

Number of stream reaches 200 154

Number of parameters 61 61

Alpine stream typology

Number of stream reaches 161 –

(178 km) and 29 lentic waters in the Naturpark Rieserferner-Ahrn were included(Table I).

2.2. DATA SETS

The applied methods for the freshwater inventory, habitat assessment and streamtypology followed a hierarchal structure. Each method block was dependent on thepreceding level, but also defined specific adaptations in general aspects. An intenseliterature research (about 600 records) regarding freshwater specific investigationsand data in the protected areas as well as available reports and inventories fromgovernmental and Nationalpark administration offices resulted in 22 criteria to beincluded in the freshwater inventory. The inventory was established as an ACCESSdatabase and is available in the governmental and national park administrationoffices.

Specific streams and rivers were randomly selected for habitat assessmentswhich followed basically regional and/or nationwide accepted methods (Werth,1992; Hütte et al., 1994; Amt der Tiroler Landesregierung, 1996a), as adapted dueto the special situation in high alpine areas. Field mapping and analysis produced adatabase for 354 stream reaches (in both national parks) from 33 streams and rivers,


which were selected randomly according to their relative presentation in the na-tional parks, and comprised 61 habitat assessment categories for each stream reach.For a clear demonstration, the results were summarized and assessed within fourassessment classes (high, good, moderate and bad habitat quality). The results ofthe habitat assessments are available as ACCESS and also GIS-based (ARC-View)databases.

A combination of selected methods (as summarized and suggested by Moog andWimmer, 1990) and the results of preceding assessments (38 out of 61 categories)enabled a comprehensive characterization of alpine stream and river systems. Forthe definition of stream/river types in the alpine region, 161 stream reaches that hadhigh habitat quality were selected and classified according to three main criteria:origin (glacial vs. non-glacial), location within the stream network [headwater,middle and lower reaches; following principally the biocoenotic concept by Illiesand Botosaneanu (1963)] and channel morphology (meandering, braided, sinuous,constrained). According to these criteria, specific combinations of letters define aparticular stream type.

Catchment gradient for specific stream reaches was averaged from maps. Thepercentage of glaciation was retrieved either from unpublished reports or if notavailable, calculated from maps (catchment area–glaciated area). Several indiceswere calculated after estimation of the relative abundance of specific classes. Sub-strate classes were defined according ÖNORM M 6132 (Austrian Standards, 1995);current velocity as ‘stagnant’, ‘low’, ‘fast’, and ‘turbulent’; and riparian vegetationas ‘no’, ‘herbaceous’, ‘bushes’ and ‘trees’.

Personal and other data sets, exclusively from non-impacted, near-natural streamsections (located also outside the national parks), were used for the characterizationof alpine stream invertebrate assemblages (Figure 1B). Sampling methods corres-ponded to procedures described in ÖNORM M 6232 (Austrian Standards, 1995).For this publication, a major focus was put on the importance of glacial influenceand altitude on stream invertebrate assemblages, richness and abundance.

3. Results

3.1. INVENTORY OF ALPINE STREAMS

The inventory of alpine streams comprises 344 streams and rivers in the wholeprotected area of 2102 km2 (Hohe Tauern and Rieserferner-Ahrn together) rangingacross several life zones. The average length of the streams is 3.5 km in NPHT(total length 980.7 km) and 2.7 km in NPRA (total length 178 km), although NPHTholds longer rivers (up to 20 km). In both national parks the percentage is highestfor <4 km river length (76% in NPHT and 81.5 in NPRA). Many of the selectedstreams drain glaciated catchments, i.e. about 50% in NPHT but less (<20%) inNPRA; the degree of glaciation varies depending on location within the national


Figure 2. The status of stream habitat quality of selected rivers in the two protected areas NPHT andNPRA.

park and also within the catchment. Streams without glacial influence are morenumerous in NPRA (81.5%) compared to NPHT (49.5%). Most of the inventorystreams have small catchment areas (>80% are less than 10 km2) and low streamorders (relative proportion is highest for second and third order streams, becausemost first order tributaries were not included in the inventory), and many drainseveral vegetation zones, the highest percentages comprise rivers draining twozones: alpine/subalpine (32.3% in NPHT and 33.8% in NPRA), subalpine/montane(31.9% in NPHT and 21.5% in NPRA). Again, because most tributaries were notconsidered in the inventory, the percentage of streams draining the alpine life-zoneis low in both national parks.


TABLE II

Alpine stream types: definitions according to glacial influence, hierarchy ( = location within theriver network), and topography/channel morphology (abbreviations indicated by bold letters in thedescription or originating from german terms which are then listed in prackets)

Code Description Characteristics

1. Level: Origin

AG Alpine stream draining Glaciatedcatchments

Alpine streams with glacial influence (for a detailedcharacterisation see reviews by e.g. Ward, 1994;Milner and Petts, 1994; Füreder, 1999)

A Alpine stream without glacialinfluence

Alpine streams without glacial influence (for a de-tailed characterisation see reviews by Ward, 1994;Füreder, 1999)

2. Level: Hierarchy

KY KrYal (sensu Steffan, 1971),glacial headwater, close to theglacial snout

Stream segments adjacent to the glacier; continu-ously cold temperatures, very little diel and sea-sonal fluctuations (1–2 ◦C); usually high diel andannual variations in discharge and turbidity; lowprimary production

GR Glacio-Rhithral (sensu Füreder,1999), alpine stream reach withconsiderable glacial influence,some distance to the glacier

Below kryal reaches, streams experience flow pat-tern, temperature fluctuation, turbidity, substrate in-stability which are different from rhithral streamsand highly influenced by glacial runoff

KR KRenal/Hypokrenal (sensu Illiesand Botosaneanu, 1963),non-glacial, spring-fed/groundwater-dominatedheadwater stream

Stream reaches adjacent to springs and ground-water sources experience ± stable conditions intemperature and flow

RH RHithral (sensu Illies, 1961),non-glacial, spring-fedgroundwater-dominated streamor streams dominated bysnowmelt in some distance fromthe source

With increasing distance to the spring, the influenceof seasonal differences in environmental conditions(rainfall, snow melt, solar radiation, air temperat-ure) become more distinct

3. Level: Topography/channel morphology

ST Lentic conditions prevail(‘STillwasser dominiert’)

Low gradient stream reach; lentic conditions due tonatural damming (e.g. rocks)

MA MeAndering system Meandering reach in very low gradients, at higherelevations predominately in non-glacial systems,otherwise in lowlands

AL ALluvium Multiple braided river reach with dynamic channelalterations, low gradient; predominately in glacier-fed rivers at higher elevations

BV Sinuous reach with bifurcations(‘Bogig Verzweigt’)

Moderate to low gradient, wider valley or channel


TABLE II

(continued)

Code Description Characteristics

3. Level: Topography/channel morphology (continued)

BU Sinuous reach withoutbifurcations (‘BogigUnverzweigt’)

Moderate to low gradient, smaller valley or channel

GU Constrained reach withoutbifurcations (‘Gerade,Unverzweigt’)

Topography provides low channel development;canyons; usually steep to moderate gradient

MU ‘Megalithal’ dominated reach(‘Megalithal dominierteUmlagerungsstrecke’)

Steep gradient, boulders and large rocks dominate,very dynamic conditions in discharge and substratemovement; predominately in glacier-fed rivers

WA WAterfall Steep to vertical gradient

Special class

SA Lake/pond outlet (‘SeeAusrinn’) Lake/pond outlets are specific running waterreaches to some degree depending on the abiotic,biotic and trophic conditions of the lake

RK Spring (‘RheoKrene’) The actual spring (‘eukrenal’ sensu Illies 1961)characterized by a very stable abiotic setting (tem-perature, discharge)

IN INterstitial reach Stream reach where flow is underground (intersti-tial)

HA Small tributaries ‘HAngbach) The multitude of small and short tributaries, that –depending on the topography – predominately drainsteep slopes

3.2. HABITAT ASSESSMENTS

Stream reaches of similar habitat structure, assessed as coherent sectors, had vari-able lengths and were distributed across the whole altitudinal spectrum. The habitatassessments resulted in high percentages of pristine habitat conditions. In NPHT87.5% and in NPRA even 96.5% of the 187 km stream and river reaches indicated ahigh or good habitat quality (Figure 2). Moderate to severe anthropogenic impactswere recorded only for a minor percentage.

3.3. TYPOLOGY OF ALPINE STREAMS

Subsequent analysis for the type-specific characterization of Alpine streams andrivers resulted in quite a number of running water types. Glacial or non-glacialorigin, the location within the stream network and topography of the catchment


were chosen to define specific stream and river characteristics. The demonstra-tion of stream (channel form, substrate) and catchment (vegetation) characterist-ics provided a definition of reference conditions based on habitat and channel-morphology criteria. The results illustrate the approach at three different levels(Table II). The first level distinguishes between glacier-fed streams and streamswithout a glacier in their catchment. The second level takes into account the bio-coenotic concept and recent literature (Illies and Botosaneanu, 1963; Ward, 1994;Füreder, 1999), implying that with increasing distance from the source, abioticfactors (like temperature, channel stability, discharge fluctuations, etc.) change. Ata third level, channel morphology and channel development, gained from field ob-servations, are considered. Special types are stream/river reaches that are differentand independent from the previous levels: lake outlets, actual springs, interstitialflow and the numerous small and turbulent tributaries draining steep valley slopes(regardless of their origin).

In the possible combination of these levels, each Alpine stream type was clearlydefinable, e.g. AG-KY-ST as a glacier-fed alpine stream (AG), headwater (kryalsegment, KY), and lentic conditions predominating (ST), A-RH-MA as a highalpine stream draining a non-glaciated catchment with very low gradient and ameandering channel.

3.4. GRADIENT, SUBSTRATE, RIPARIAN VEGETATION

The comprehensive set of near-natural stream types resulted in a clear descriptionof the altitudinal distribution of stream types, provided valuable characters likegradient and substrate composition, and gave estimates of gradient and altitud-inal effects on channel morphology, vegetation and flow patterns (Figures 3A–F).Substrate was shown to be dependent to a high degree on the catchment gradient(Figure 3A). The individual stream types reflected these differences of gradientand substrate composition Figures 3B–C). The relative composition of riparianvegetation followed an altitudinal gradient (Figure 3D). A higher vegetation index(i.e. higher proportion of trees and shrubs) was found at lower altitudes, but thendecreased (alpine grassland, herbaceous plants, no vegetation) with increasing alti-tude. Some reaches with no riparian vegetation (vegetation index = 1) were foundat all elevations (e.g. due to rocks in canyon and steep stream segments). Likesubstrate composition, flow patterns reflected their dependence of gradient and thedevelopment of channel types (Figure 3E). Individual stream types principally candevelop at all altitudes, but some showed a tendency to occur at higher elevations(e.g. alluvium, lake outlets, streams with lentic conditions).

3.5. STREAM FAUNA AND GLACIAL INFLUENCE

The fauna dataset from 99 non-impacted, near-nature alpine stream sites (rangingfrom 1000 to 2500 m a.s.l.) produced 287 seasonal means of abundances and 487


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Figure 4. Abundance and number of aquatic macroinvertebrate taxa along altitudinal gradients.

individual taxa (most at species or species-group level). Abundances differed con-siderably between sites, ranging from a few thousand to almost 100 000 Ind. m−2.While total invertebrate abundance seemed to decrease with increasing altitude(Figure 4A), no distinct pattern was observable when richness was considered(Figure 4B). While altitude did not show a clear effect, the degree of glaciation in-fluenced abundance and number of taxa. Mean abundances of the total benthos and


Figure 5. Distribution of mean abundance and mean taxa numbers [total invertebrates, EPT (Ephem-eroptera, Plecoptera, Trichoptera) and Diamesinae] in streams within catchments exhibiting variousdegrees of glaciation.

of Ephemeroptera, Plecoptera and Trichoptera (EPT) decreased with increasingglaciated area in the catchment (Figure 5A), and in contrast, the mean Diamesinaeabundance increased. Number of taxa of total invertebrates, EPT and Diamesinaewere highest at <10 and 11–30% glaciation (Figure 5B), intermediate at no, moder-ate and high glaciation, but lowest at a degree of glaciation between 51–70%. Theproportions between total, EPT and Diamesinae taxa numbers appeared to remainthe same in all classes.


Figure 6. Altitudinal distribution of aquatic invertebrate abundance in (A) kryal–glacio-rhithralstreams (n = 116; y = 31736 – 12.12x; r = –0.30); (B) streams with <10% glaciation (n = 29; y =110100 – 54.79x; r = –0.73) and (C) no glaciation (n = 91; y = 66902–25.40x; r = –0.40). Confidenceintervals 95%.


When three different degrees of glaciation (no, <10, >10%) were considered,total abundance followed a very clear pattern. Running waters with a glaciation>10% (Figure 6A) showed a general low abundance, which decreased with eleva-tion (Pearson Product-Moment Correlation, r = –0.30), streams with a low degreeof glaciation (<10%) showed a more evident decrease of abundance with increasingaltitude (r = –0.73; Figure 6B). Streams with no glaciation generally had higherabundances than others, especially at lower sites (r = –0.40; Figure 6C).

4. Discussion

Freshwaters comprise a prominent feature in alpine areas. With the inventory of344 streams and rivers (1159 km) and the habitat assessments of 354 reaches (from33 streams and rivers comprising 187 km) in randomly selected running watersin protected areas in Austria and Italy, a comprehensive characterization of alpinestreams and a database is available which resulted in the present typology.

The great proportion of non-impacted streams is not, however, a feature ofalpine systems at higher elevations but has primarily to do with the protected natureof the studied areas. In a demonstration of the ecological integrity in rivers with acatchment area >500 km2, Muhar et al. (2000) found only 6% of the assessedrivers remaining with high habitat quality, 15% had good habitat conditions, buta very high percentage (79%) was moderately to heavily impacted. A comparableinventory of streams and rivers in Tyrol, including selected streams and rivers fromheadwaters to lowlands, resulted in a similar picture (Amt der Tiroler Landesregier-ung, 1996a, b): In the provinces Kufstein and Kitzbühel, 71 and 88%, respectively,of the assessed running waters showed various anthropogenic impacts and madeoptimizing ecological management necessary. In a similar study in the BavarianAlps (Nationalpark Berchtesgaden, Germany), Franz (1992) reported almost halfof 230 km of stream length showing still natural/near-nature conditions, only alow percentage resulted in the class with bad habitat quality. These and our ownresults demonstrate the high ecological and socio-economic value of protectedareas–regions where almost undisturbed areas are still present on a large scale.

Stream-type-specific characters are strongly needed in a variety of aspects inecological managements (Moog and Wimmer, 1990; Muhar et al., 2000) and arean essential basis for developing assessment systems as demanded in the EU WaterFramework Directive (WFD; Rat der Europäischen Union, 1999), which is cur-rently in the state of implementation. The stream types here presented, based onthe origin, hierarchy and channel/watershed morphology, together with the de-tailed characterization from habitat measures, provide important information forthe definition of reference conditions for impact measures and for the evaluation ofthe ecological status of alpine streams. The principal components of the abiotic mi-lieu of river ecosystems–hydrology, temperature and channel morphology–reflectregional-scale climate and geology. Mangelsdorf and Scheurmann (1980) demon-


strated the importance of regional topographic conditions, climate and transportmechanisms for the longitudinal, vertical and lateral dimensions of channel devel-opment. In our study, stream type specific characters (e.g. channel form, substratecomposition, flow pattern) corresponded well to the gradient. Riparian vegetationalso followed to some degree the natural altitudinal pattern, although in strictly an-thropogenic unaltered conditions the woody aspect of the vegetation cover shouldprevail up to 1800–2000 m (treeline in the Central Alps). In these areas, landuse(pastures) becomes evident; however, the low riparian vegetation index may alsobe associated with little vegetation cover in steeper areas (e.g. canyons).

Faunal characteristics of alpine streams are still poorly known, but are alsohighly needed in the holistic approach suggested by the WFD (Rat der Europäis-chen Union, 1999). On the basis of Illies’ Ecoregions (Illies, 1978), a regionalscale stream typology has to be implemented into the WFD. Some attempts are inprogress (e.g. European Commission funded project ‘AQEM’), to develop methodsand standards for a future European stream typology. The rivers considered how-ever have principally a large catchment area, hence most of Alpine streams treatedin our study would not be included. Therefore, the present stream typology for theAlpine region is of great value and provides additional information for the WFDand future standards.

Although detailed information on reference insect assemblages are now avail-able for specific alpine stream types, e.g. glacier-fed and spring-fed headwaters(e.g. Schütz, 1999; Füreder et al., 2000, 2001; Lencioni et al., 2000; Schütz et al.,2000, 2001) and various springs (Bonetti and Cantonatti, 1996), only a few public-ations deal with the effect of glacial influence on lower reaches (‘glacio-rhithral’rivers). Glacial influence is recorded to have a pronounced effect on abundancesand taxa numbers in alpine streams, especially at higher altitudes (for a review seeWard, 1994; and Füreder, 1999). Milner and Petts (1994) presented a model linkingtaxa occurrence downstream of the glacial snout to distance from the glacier andtime since deglaciation. Recent studies in glacier-fed headwaters (e.g. Brittain etal., 2000) principally supported the model, others however demonstrated also aclear dependence on seasonal aspects (varying groundwater and glacial influence)for river sections or networks (Tockner et al., 1997; Ward et al. 1999b; Fürederet al., 2001). Quantitative results, especially for areas distant from glaciers arehowever still lacking.

In our study, the benthic fauna exhibited general low abundances at altitudesabove 2000 m. The decreasing pattern with increasing elevation appears to be inde-pendent from the degree of glaciation, although kryal/glacio-rhithral segments havegenerally lower abundances than spring-fed systems. Glacier-fed systems above2000 m however, can have higher abundances too. High abundances and speciesnumbers from these areas are reported for the benthic fauna (Klein and Tockner,2000; Schütz et al., 2001), Chironomidae (Füreder et al., 2001) and homotopic taxa(Klein and Tockner, 2000); densities, species numbers, diversity and the occurrenceof specific taxa are often tied to specific seasonal conditions, i.e. increased ground-


water influence in specific channels (Ward et al., 1999b) or winter cover (Schütz etal., 2001).

Below 2000 m a.s.l., the degree of glaciation around 10% seems to be a thres-hold. Stream segments with a higher degree of glaciation have a tendency towardslow invertebrate densities despite a few exceptions. Running waters with no glacierin their catchment were not evidently reduced in their fauna densities.

Due to a variety of factors influencing species occurrence and abundance inrunning waters (Braukmann, 1987), a clear context between physiographic settingsand biocoenosis is in many cases not evident. Comparable stream segments (samestream types), although similar in their stream type may differ considerably inrespect of their biota. That may in part explain the variation between the streams.

The two major approaches to biological monitoring that have emerged in thepast 20 yr (Karr and Chu, 2000), the river invertebrate prediction and classificationsystem (RIVPACS) and the index of biological integrity (IBI), use the biota as anultimate integrator of human actions. Both use a concept of reference condition,organize sites into classes with a select set of environmental characteristics, assesschange and degradation caused by human effects, require standardized sampling,laboratory, and analytical methods, score sites numerically to reflect site condi-tion, define ‘bands’ or condition classes representing degrees of degradation andproduce analyses needed to select high-quality areas as acquisition and conser-vation priorities (Karr and Chu, 2000). The present stream typology of Alpinestreams based on habitat assessment criteria as well as on information gainedfrom the freshwater inventory and a preliminary discussion of fauna characteristicsand their dependence on glaciation and altitude, characterizes the heterogeneouspatterns of alpine running waters. With the three levels of criteria for the presentedtype-specific characterization, i.e. origin, hierarchy and topography/channel mor-phology, essential features affecting stream ecosystem functioning in alpine areasare described. Together with the assessed criteria a comprehensive characterizationof alpine streams and an estimate of the ecological potential of running watersystems in the Alps between 1000 and 2500 m a.s.l. is available. As a basis itoffers excellent opportunities to conduct holistic interdisciplinary studies to es-timate the role of abiotic conditions and channel morphology and the interactionbetween riparian vegetation, nutrient availability and in-stream heterogeneities andthe various aquatic organisms in running water ecosystems.

Our results regarding reference conditions portrait the ecological integrity ofvery important headwaters, whose ecological status may have severe effects on avariety of lower landscapes, and provide new perspectives for river ecologists andpeople involved in running water restoration and conservation measures. However,they also emphasize the need for more investigations, regarding the role of riverinedynamics and landscape characteristics on the structure and function of alpinestream ecosystems. Especially, the available database from the two protected in-vestigation areas provide a wide spectrum for future experimental and deterministicapproaches.


Acknowledgements

We thank several people who provided funding and assistance in data supply. Mostof the data presented are results from investigations funded by Nationalparkrat desNationalparks Hohe Tauern in Austria and Autonome Provinz Bozen in Italy (Amtfür Naturparke). Aquatic invertebrate data from a variety of running waters weregratefully received from Universität für Bodenkultur, Hydrobiologie, Vienna, andARGE Limnology, Innsbruck.

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Reference Conditions of Alpine Streams: Physical Habitat and Ecology

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