Full Terms & Conditions of access and use can be found at
https://www.tandfonline.com/action/journalInformation?journalCode=tjfe20
Journal of Freshwater Ecology
ISSN: 0270-5060 (Print) 2156-6941 (Online) Journal homepage: https://www.tandfonline.com/loi/tjfe20
Macroinvertebrate Communities and Habitat
Structure in Least-Impacted Hill Streams of Central
Portugal
Kieran A. Monaghan & Amadeu M.V.M. Soares
To cite this article: Kieran A. Monaghan & Amadeu M.V.M. Soares (2008) Macroinvertebrate Communities and Habitat Structure�in�Least-Impacted�Hill�Streams�of�Central�Portugal , Journal of Freshwater Ecology, 23:2, 315-325, DOI: 10.1080/02705060.2008.9664204
To link to this article: https://doi.org/10.1080/02705060.2008.9664204
Published online: 06 Jan 2011.
Submit your article to this journal
Article views: 126
View related articles
Macroinvertebrate Communities and Habitat Structure
in Least-Impacted
Hill Streams of Central Portugal
Kieran A. Monaghan and Amadeu M.V.M. Soares
CESAM and Departmento de Biologia
Universidade de Aveiro, Campus Universitario de Santiago 38 10- 193 A veiro, Portugal
E-Mail: kamonaghan @ua.pt ABSTRACT
We surveyed macroinvertebrate communities in 3 1 hill streams in the Vouga River and Mondego River catchments in central Portugal. Despite applying a "least- impacted" criterion, channel and bank management was common, with 38% of streams demonstrating channel modification (damming) and 80% with evidence of bank
modification. Principal component analysis (PCA) at the family and species level related the macroinvertebrates to habitat variables derived at three spatial scales
--
site (20 m), reach (200 m), and catchment. Variation in community structure between sites was similar at the species and family level and was statistically related to pH, conductivity, temperature, flow, shade, and substrate size at the site scale; channel and bank habitat and riparian vegetation and land-use at the reach scale; and altitude and slope at thecatchment scale. While the effects of river management were apparent in various ecologically important habitat features at the site and reach scale, a direct relationship with macroinvertebrate assemblages was only apparent between the extent of walled banks and the secondary PCA axis described by species data. The strong relationship between catchment scale variables and descriptors of physical structure at the reach and site scale suggests that catchment-scale parameters are valuable predicators of
macroinvertebrate community structure in these streams despite the anthropogenic modifications of the natural habitat.
INTRODUCTION
Monitoring and managing water resources require knowledge of ecological communities as defined by hydromorphological and physicochemical criteria. While the a priori assignment of key environmental parameters provides an appropriate practice for reference designation (Davis and Simon 1995, Karr and Chu 1999), comparative evaluation indicates that the broad generalizations of ecoregion, size, geology, and altitude only provide relatively crude discrimination in comparison to posteriori
assignment based on multivariate analysis of biological data (Davy-Bowker et al. 2006). Given the pragmatic objectives of bioassessment, Logan and Furse (2002) pointed out that a failure to distinguish an appropriate level of biological resolution risks a
monitoring program that is excessive and therefore expensive on one hand or inadequate and failing to provide adequate protection on the other. Understanding the relationship between biological communities and the river habitat is therefore critical to successful river management and biological assessment (Chaves et al. 2006). Where detailed ecological and environmental databases have been available, exploratory analytical techniques have played an important role in developing and testing assessment techniques (Wright et al. 2000, Bailey et al. 2003).
Regardless of their a priori or posteriori derivation, the description of ecological reference conditions from catchment scale variables represents a major objective for river managers because it reduces the susceptibility of type I1 errors associated with insidious human activities. However, despite the apparent hierarchical organization of the physical habitat (Frissell et al. 1986), the potential influence of other factors precludes the simple assumption of a direct link between large-scale catchment features and parameters of the
ecological community (Gergel et al. 2002). Furthermore, given the broad extent of human
interference in river systems, the definition of quasi-pristine or "high status" river systems typically permits minor modifications (e.g., Raven et al. 1998, Oliveira et al. 2005, Chaves et al. 2006). Channelhank modifications alter the natural dynamics of discharge and thus may have important ecological effects (Aheam et al. 2005, Armitage et al. 2001, Stanley et al. 2002) and alter the expected sequential changes associated with the hierarchically organized river habitat (Stanford et al. 2001). Consequently, descriptive studies detailing the relationships between river organisms and the river habitat are fundamental to developing an understanding of ecological organization and provide an important opportunity to test some of the basic assumptions that underpin assessment design.
Previous studies of Portuguese river systems have highlighted the importance of the pronounced seasonal variation in discharge (Coimbra et al. 1996, Graga and Coimbra 1998, Pinto et al. 2006). Where flow is intermittent, macroinvertebrate assemblages become dominated by lentic taxa with nutrients, substrate character, and riparian and catchment land-use providing important discriminators of community structure (e.g., Aguiar et al. 2002, G r a ~ a et al. 2001). Surveys at the catchment scale in the central region have highlighted the primary importance of physical and hydrological variables (Chaves et al. 2005, Feio et al. 2006), indicating the potential to define ecological quality on the basis of the physical habitat (e.g., Oliveira and Cortes 2005). While catchment scale variables have been identified as important discriminators of community organization (Chaves et al. 2005, Feio et al. 2006), the extent to which they are systematically linked to species assemblages through a hierarchically structured habitat has not been explicitly evaluated. However, the need to investigate their relationship is particular important in Portuguese river systems, given the paucity of non-impacted reference conditions and the broad extent to which channel and bank habitats have been modified (Chaves et al. 2006).
This study examined the macroinvertebrate communities of "least-impacted" hill streams in central Portugal. Describing macroinvertebrates at two levels of taxonomic resolution, we used exploratory statistical analysis to investigate the relationship between ecological organization and habitat parameters derived at three respective scales
--
the sample-site (20 m), the reach (200 m), and the catchment; to determine keyenvironmental variables associated with ecological variation at the family and species level; to investigate the relationship between the spatial hierarchy of measured habitat parameters and macroinvertebrate communities; and, to assess the effects of channel and bank management on stream habitat and macroinvertebrate assemblages.
METHODS AND MATERIALS
Study area
The Vouga River and Mondego River basins drain areas of 3,635 krn2 and 6,645
krn2, respectively. Eucalyptus and pine plantations dominate land use in upland areas and
give way to moor and scrub at higher altitudes. Commercial agriculture is mainly located in the lower alluvial plains and is limited to small-scale subsistence production in upland areas; urban development is overwhelmingly concentrated in coastal areas (Abelho and Graqa 1996, Ferreira et al. 2006). Average annual precipitation varies from 2,800 mrn in mountainous areas to 1,200 mm or less in coastal areas; almost three-quarters of the annual precipitation falls between October and March. Site selection targeted relatively small, discrete catchments to provide statistically independent streams and improve the relevance of catchment land-use classifications. "Least-impacted" criterion specified an absence of industry, commercial agriculture, and extensive urban development. Selection of sites was based on the inspection of 1:50,000 topographical maps, followed by a visual survey of a selected catchment and, when possible, consultation with local inhabitants to confirm the absence of any major impacts.
Sampling surveys
Surveys were conducted in August 2004 during the summer low-flow period when macroinvertebrate biodiversity in the rivers of central Portugal is at a maximum (Chaves et al. 2005). The 3 1 sites ranged from second to fourth ~ r d e r and represented 16 tributaries of the Vouga River and 15 tributaries of the Mondego River. Despite the criterion of least-impacted, channel and bank management associated with subsistence management (irrigation, abandoned mills, flood protection) was common, with 38% of streams demonstrating channel modification (damming) and 80% with evidence of bank modification. Such alterations were typically effected with alluvial material, represented by a wall of large boulders either across the channel or reinforcing the bank.
Environmental details were derived at three spatial scales
--
the site (the location of macroinvertebrate sampling, with a longitudinal distance of 20 m), the reach (a longitudinal distance of 200 m immediately upstream of the biological sampling station), and the catchment (derived from 1 :50,000 topographical maps). Site parameters included an estimate of mean substrate size (based on proportionate distribution of respective size classes), mean channel width and depth, flow, the percentage of riparian shading, and water quality. Parameters of water quality were described with in situ measurements (temperature, pH, and conductivity) and with samples maintained frozen until laboratory analysis (nitrate, nitrite, and orthophosphate). At the reach scale, habitat surveys were based on a modified version of the UK Environment Agency's River Habitat Survey(Environment Agency 1997), recording details of the channel, banks, and riparian and catchment land-use according to alternative descriptive categories at 10 spot checks 20 m apart, combined with an overall description designed to capture additional habitat features and those missed in spot checks. At the catchment scale, map-derived variables were slope (over 1 km), altitude, distance from source, and stream link magnitude
(Shreve 1966).
Macroinvertebrate samples were collected with a pond net (500 pn mesh-size) using a standard two-minute kick-sampling in typical riffle habitats; other habitat types (margins, pools, vegetation, woody debris, etc.) were sampled in proportion to their occurrence using a combination of kick sampling and kick and sweep techniques as appropriate for conditions. Samples were elutriated on site and preserved in 70% ethanol. Macroinvertebrates were separated from organic and mineral matter in the laboratory and identified to the lowest practical level (genuslspecies) except for Chironomidae (tribe), Simuliidae (family), and Oligochaeta (order). Where specific identification was not possible but particular features permitted definitive distinction, taxa were assigned to species types. At the family level, functional feeding guilds were assigned based on established taxonomic-functional generalizations. For analytical purposes "family" refers to family level identification except Oligochaeta (order); "species" refers to the lowest practical level as described above.
Data analysis
Structural characteristics recorded by the reach-scale habitat surveys were reduced to key variates to describe major habitat trends among sites. Characteristics were generalized by calculating mean values for spot check features. Categorical variables were coded as dummy variables with fuzzy coding used to describe variation in classifications (LepB et al. 2003). Major changes in habitat characteristics across sites were described in terms of principal components (PC's) following ordination by principal component analysis (PCA). By excluding slope, altitude, and the extent of management intervention from ordination analysis, the resultant PC's were limited to an expression of habitat characteristics that could be could be subsequently investigated in relation to these potentially deterministic criteria. Habitat characteristics were separated into features describing the channel, banks, and riparian-catchment land-use to evaluate their
respective importance. The relationship between habitat features described at the site, reach, and catchment scale were investigated by Pearson's product-moment correlation (P-MC). The extent of bank management was described according to a "wall-index" determined by totaling the number of spot check records that included a walled bank adjacent to wetted channel (scoring 1) and the number of walled banks set back h m the wetted channel (scoring 0.5). Channel dams were included as either presentlabsent.
Preliminary analysis of macroinvertebrate data by detrended correspondence analysis based on segments described a primary axis tumover of 1.7 for family data and 1.9 for species data, indicating that the distribution of individuals would be best
approximated by a linear ordination model (LepT; et al. 2003). The relationships between environmental variables and community organization macroinvertebrates were ordinated by PCA based on log transformed abundance data, centering the data matrix by species. The relationships between PCA site scores and environmental variables were assessed by P-MC. The effects of management intervention were investigated by one-way ANOVA for the presencelabsence of dams and by P-MC of the wall-index.
RESULTS
Sites ranged in altitude from 90 to 1,040 m above sea level, with slope ranging from 1.9 to 32'. In general ionic content of stream waters was low; conductivit ranged
-Y
from 36.6 to 230.0 @.m-', with only four streams registering above 100 pS.m
.
Nutrients were low; nitrate ranged from 0.120 to 1.94 m g ~ " , nitrite from 0.02 to 0.03 1 m g ~ ' , and orthophosphate from 0.0 to 0.25 m g c t .Physical habitat
The first two ordination axes of channel features explained 50.9% of the total variation. The primary axis, Channel- 1 (27.8%), described a transition from relatively deep rivers with bedrock and boulder substrate to rivers with cobble and pebble substrate and an increased incidence of course woody debris, while the secondary axis, Channel-2 (22.1%), captured variation in in-stream vegetation and flow (Table 1). Primary variation in bank features, Banks-1 (28.9%), ranged from sites with banks of a non-eroding vertical profile with vegetated or non-vegetated sidebars to banks with an eroding or composite
Table I. Sumnary of principal component axes based on principal component analysis (PCA) of habitat features recorded from reach scale habital surveys. Percentage variance explained by each PCA axis is given in parentheses. Within the hbl+ variables are shown in order with axis loadings in paratheses (+ve and -ve values).
Channel-l Channel-2 Bsnlrs- l Ranks-2 Land-1
- (27.8%) (22.1%) (28.9%) (21.4%) (59.4%)
Boulder Sand Venical banks Vegetated sideban Moorland heatb
(+0.73) (+0.81) (+0.79) (+0.74) (t0.65) Bulrock (+0.69) Sedges, m d s , mshes (+0.63) Emergenl boulders/ Rocks (+0.57) Depth (+0.36) Tree roots (-0.52) Gravel (-0.62) Cobble (-0.68) Channel embeddedness (-0.76) Branches (-0.79) Free floating (44.67)
Emergent broad leaves (44.57) Floating leaved (44.44) Filamenlous algae (+0.41) No vegetation (-0.20) Moss (-0.27) Pebble (0.3 I) Flow diversity (-0.4 1) Cllrrent velocity (-0.47) Stable cliff (t0.75) Bwldw (+0.69) Vegetated sidebars (+0.36) Non-vegetated sidebars (4.30) Undercut (-0.14) Complex vegetation (-0.32) Eroding banks (-0.54) Earth banks (-0.76) Composite banks (-0.79) Material (+0.58) Bank lop height (+O 54) Complex vegetation (+0.35) No Features (+0.29) Composite (-0.1 1) Stable (-0.15) Steeply sloping (-0.28) \Jndcrcut (-0.44)
Non-vegetated side bar
(-0.66) Improved grassland (+0.53) Rough pasture (+0.42) Tilled Land (4.26) InlexmiUent trees (+O. 17) Eucalyptus plantation (-0.3 1 ) Broad-leaved woodland (0.37) High structural complexity (-0.56) Overhanging bows (-0.77) Deciduous shade (-0.99)
profile. Primary variation in land uselriparian vegetation (Land-1) captured 59.4% of the recorded variation and described a general trend from moorland heath to improved grassland and rough pasture to broadleaf woodland and eucalyptus/pine plantations.
Habitat parameters measured at the site, reach, and catchment scales were statistically related (Table 2). At the site scale, mean substrate index was strongly related to ordination scores for Channel- I, Banks-2, and Land- 1, and at the catchment scale, altitude. The reach scale parameters Channel-1 and Banks-2 were related to the
catchment scale parameters altitude and slope, while Land-1 was significantly correlated with altitude.
The extent of river management was related to various habitat variables, with the wall-index significantly related to flow (P-MC coefficient = -0.504, P<0.01), ordination scores for Banks-1 (0.650; P<O.001), and Channel 2 (0.416; Pc0.05). Sites with channel dams (20.5 m) registered significantly higher scores for Channel-2 compared to sites without dams (F1,29=3.97r Pc0.05).
Biological data
In total, 207 different taxa were distinguished at the lowest level of identification, representative of 74 families and 14 orders. Assemblages were dominated by Insecta, with Plecoptera the most numerically abundant (representing 25% of all individuals identified) followed by Diptera (24%) > Trichoptera (17%) > Ephemeroptera (15%) >
Coleoptera (13%) > Ondonata (5%) > non-insect taxa (1%). Taxonomic richness between the two river systems was similar, with mean taxon richness of 34.9 at the family level and 55.2 at the species level in the Vouga River drainage basin compared to 35.1 and 55.5 in the Mondego River basin.
Ordination based on family level data explained 30.7% of the variation in the first two axes. The classification of feeding guilds indicated that these trends in taxonomic structure were underpinned by trends in functional organization, with shredders and predators negatively correlated with axis 1 (P-MC coefficients of 0.557, P<0.001; 0.432, Pc0.01, respectively), while collector-gatherers were positively correlated with axis 1 (P- MC = 0.447; P<0.01). The additional ecological information represented by the species data reduced the extent of variation explained by the first two ordination axes to 23.6%.
Trends in ecological data were related to habitat parameters at various spatial scales. At the site scale, principal variations in species (13.4%) and family (19.0%) data were significantly correlated with conductivity and pH; also, family data were related to flow, and species data were related to channel width (Table 3). Secondary variation at both taxonomic levels was strongly related to temperature and overhead shade, with species data also related to flow and mean substrate size. At the reach scale, primary ecological variation among species was related to Channel-2 and Land- 1, with secondary
Table 2. Product m m t cornlation coefficients between habitat parameters measures st the site, reach, and catchment scale. Significance levels: *P<O.OS; **P<0.01;"*P4.001.
Habitat parameters
Parameters Channel-1 Channel-2 Banks-I Banks-2 Land-I Link mag. Distance- Slope Altitude s w m Substrate size 0.729*** -0.96 -0.270 0.482'* 0.456'. -0.070 0.101 0.337 0.362' Flow 0.288 -0.346' -0.504'' 0.137 -0.083 -0.222 -0.272 0.394' 0.314 Width 0.156 0.193 -0.006 0.162 0.161 0.602*** 0.372 -0.089 0.063 Deplh 0.331 0.179 -0.253 0.295 0.273 0.351' -0.010 0.262 0.215 Channel- 1 -0.193 0.565'** 0.782". -0.039 -0.104 0.504** 0.669"* Chnnncl-2 0.2% 0.24) 0.427' 0.084 -0.009 -0.240 0.108 Banks-l 0.026 0.026 0.OSO -0.187 -0.335 Banks-2 0.427' 0.001 0.01 1 0.484'' 0.486" Land- l 0.041 -0.057 0.199 0.656*** Link mag. 0.717*** 0.467** 0.184 Dift~dx- 0.429' -0.128 source Slope I k 0.460.' 319
variation related to Channel-2, Banks- 1, and Land- 1. Primary variation among macroinvertebrate families was related to Land-1, with secondary variation related to Channel-2. At the catchment scale, principal variation was significantly related to altitude and slope for species data and altitude only for family level data, while secondary variation was significantly correlated to distance fiom source for species level data.
While the influence of river management was apparent in various habitat features at the site and reach scale (Table 2), a direct relationship with ecological organization
was only apparent between the wall-index and the secondary ordination axis describing species-level variation, Species-2 (P-MC coefficient = -0.334; P<0.05).
Table 3. Product-moment correlation coefficients between macroinvertebrate community structure described at the family and species level (PCA axes 1 and 2) and environmental variables measured at the site, reach and catchment (map) scale. Significance levels: *P<0.05; **P<O.Ol;***P<O.OOl.
Parameters Species- 1 Species-2 Family- 1 Famil y-2 (13.4%) (i0.2%) (19.0%) (1 1.7%) Site scale Substrate size 0.147 0.374* 0.242 -0.186 Width -0.368* 0.159 -0.288 -0.076 Depth -0.070 -0.196 -0.036 0.124 Flow -0.3 18 -0.497** -0.365* 0.111 Shade -0.303 -0.538** -0.325 -0.350* Nitrite -0.172 -0.039 -0.144 0.158 Nitrate 0.252 0.292 0.242 0.078 Phosphate 0.159 0.1 11 0.157 0.190 Conduct 0.371* -0.169 0.390* 0.224 Temp 0.122 0.686*** 0.214 -0.384* PH -0.643*** 0.143 -0.565*** 0.197 Reach scale Channel- 1 0.255 0.270 0.323 0.037 Channel-2 0.401* 0.383* 0.319 0.370* Banks- 1 -0.05 1 -0.393* -0.105 -0.141 Banks-2 0.265 0.147 0.205 0.284 Land- 1 0.424* 0.500** 0.463** 0.151 Catchment scale Link magnitude 0.243 -0.310 0.228 -0.126 Distance-source 0.342 -0.358* -0.073 -0.268 Slope -0.369* 0.135 0.227 0.184 Altitude 0.348* -0.033 0.580*** 0.270 DISCUSSION
The relatively high taxonomic richness observed in this study conforms to the general geographic pattern described by Graqa et al. (2004) of macroinvertebrate richness increasing towards the north of the Iberian Peninsula and is comparable with findings from other broad scale surveys in the central region employing similar sampling strategies. The total of 74 taxa at the family level corresponds closely with the survey of Feio et al. (2006) who recorded 88 families fiom 54 stream sites in the Mondego River catchment and that of Chaves et al. (2005) who documented 99 families from 18
Mondego River streams. At the species/genus level, the distinction of 207 taxa is relatively high compared to the 208 taxa recorded from a greater number and wider range
of stream types studied by Feio et al. (2006); however, direct comparison is complicated by potential differences in the resolution of identification achieved by the "lowest practical level." In a more detailed, taxonomically restricted study of the Trichoptera from the same streams, Feio et al. (2005) distinguished 70 specieslgenera from 18 families. The 63 species and 18 tricopteran families encountered in our study indicate that despite the restrictive survey criteria, these stream types incorporated a large and representative portion of the regional species pool.
Although the relationship between environmental parameters and community structure differed according to the alternative ecological descriptions at the family and species level, pH, conductivity, and temperature were consistently related to community change across sites. These general descriptors of water quality have been repeatedly identified as key determinants of community organization in various wide-scale surveys in Portugal and elsewhere (Graqa et al. 2004, Pinto et al. 2004, Wright et al. 1984), with elevated levels of conductivity and pH associated with a variety of factors including bedrock geology, land use, and polluting effluents (Monaghan et al. 2000, Ortiz et al. 2005, Townsend et al. 1983). In this survey, these trends in water quality were associated with changes in land-use and riparian vegetation at the reach scale and altitude at the catchment scale.
For the streams in this region with pronounced seasonality and associated variation in discharge, the dynamics of water temperature, coupled with a tendency towards lentic conditions, may be particularly important determinants of community organization (Bogan et al. 2007, Graqa et al. 2004). This dynamic perspective of temperature and hydrology is further supported in this study by the contrasting statistical relationship between flow and temperature on respective ordination axes. However, in terms of explaining ecological variation, the intrinsic importance of flow and shear stress in benthic habitats (Doledec et al. 2007, Statzner et al. 1986) cannot be separated from the potential influence of discharge on water quality.
Previous studies of Portuguese river systems have indicated the overwhelming importance of benthic substrate as a determinant of community structure (Chaves et al. 2005, Feio et al. 2006, Pinto et al. 2004). However, the substrate index calculated in this study was only significantly related to community structure described by the species data, while at the reach scale, ecologically important features of the benthic channel were described by the secondary ordination axis rather than the primary one. Its apparent reduced importance in this study may be associated with various factors of study design. At the site scale, the substrate index was based on the proportionate occurrence of substrate within a 20 m transect of the stream, inclusive of all wetted channel areas, while macroinvertebrate samples were predominately derived from riffle habitat (67%). Furthermore, despite their inclusion in the substrate index, some benthic habitats, such as bedrock, were under represented in terms of additional sampled area (constituting 33% of macroinvertebrate samples) due to the difficulties of sampling such habitats with a pond net. At the reach scale, the lack of a significant relationship in the primary axes of channel habitat suggests that the major variation in habitat features were of relatively minor ecological importance under the contemporary environmental conditions. In this context, the large scale of habitat features described by Channel-1, (bedrock, boulder, course woody debris) are notable, given that biological sampling coincided with a reduction in the volume of water that may have diminished their (submerged) architectural importance to benthic macroinvertebrates during this period.
The classification of functional feeding guilds indicated that the trends in
taxonomic structure across sites were underpinned by differences in ecological processes. The negative correlation of shredders along the primary ordination axes, corresponding with statistically significant relationships for shading at the site scale and Land-1 at the reach scale (describing an increase in complex vegetation structure, overhanging bows,
and deciduous shade), was likely associated with an increased input of leaf litter. In contrast, the proportional increase in collector-gatherers in sites with positive axis 1 scores was associated with an increase in simple vegetation structure and tilled land that may have been associated with increased inputs of organic sediments (e.g., Benstead et al. 2004). Although the lack of autecological information for macroinvertebrate taxa at the species level precluded a more detailed interpretation of the trends described by the species ordination, some general patterns are similarly suggestive of a link between ecological hnction and habitat. For example, a significant portion of the increased ecological information at the species level resulted from the comparatively high diversity in beetle taxa, in particular among the Elmidae (12 species) and Hydraenidae (1 1 species), that was positively associated with the secondary ordination axis. The
importance of soft earth banks in the life-cycle requirements of these taxa (Brown 1987, Elliott 2006, Ribera 2000) may explain why an association with Banks-1 was apparent at the species but at the not family level.
In terms of the general objectives of this study, the small-scale management alterations in these streams were of relatively little importance in determining the major trends in macroinvertebrate community structure across sites. Nonetheless, the
association between management and numerous habitat parameters at the site and reach scale indicates its well documented potential to influence ecologically important features, with walled banks changing the flow and the storage and transport of organic and inorganic material (Armitage et al. 2001, Tiemann et al. 2004, Cortes et al. 1998) and channel damming altering the longitudinal continuity (Chaves et al. 2006, Lake 2003, Marks et al. 2000). However, in general the insect taxa that predominated the "dry- season" communities of these streams were more directly explained by other structural and physicochemical parameters, which were related to the natural spatial hierarchy of habitat features, indicating that our sampling strategy provided an appropriate and potentially sensitive means of interpreting ecological conditions across several spatial scales. While the family-level trends in this study suggest the potential of
macroinvertebrates to interpret land-use and riparian conditions, the species data provided the only significant relationship with management intervention (Species-2 vs. wall-index, explained by the abundance and diversity of beetle taxa), which emphasizes the importance of species identification for the development of more sophisticated bioassessment tools in this region (cf., Feio et al. 2006).
In recent a review of classification systems for European streams, Sandin and Vendonshot (2006) recommended that temperature, slope, and stream size be used as key factors in the initial distinction of river types. In our study, the catchment scale variables of altitude and slope were strongly associated with community structure, which confirms their relevance as large-scale integrators of habitat features important to
macroinvertebrate communities (Herlihy et al. 2005, Monaghan et al. 2000, Richards et al. 1993, Verdonschot 2006). The correlation between these catchment-scale variables and the various descriptors of physical structure at the reach and site scale suggests that these rivers conform to the hierarchical model descried by Frissell et al. (1986), which indicates the potential to use these gross-scale parameters as predicators of ecological communities. Our data corroborate previous studies involving detailed habitat surveys in highlighting the importance of developing appropriate methods of habitat assessment in Portuguese rivers and indicate the value of the macroinvertebrate community as a useful indicator of physical habitat quality (Oliveira and Cortes 2005, Feio et al. 2006, Chaves et al. 2006).
ACKNOWLEDGEMENTS
We thank Miguel Fonseca for help with the field work, Abel Ferreira for technical help with field and laboratory equipment, and Antonio Nogueira Jose for assistance with
software packages. Much of the macroinvertebrate identification was completed during a placement with the River Communities Team, CEH Dorset, for which we thank John Blackburn for help with macroinvertebrate taxonomy, Rick Gunn for help with equipment and logistics of laboratory work, and Iwan Jones for facilitating the placement. This research was supported by the FundaqZo para a Cikncia e Tecnologia, Ministkrio da Ciencia e do Ensino Superior.
LITERATURE CITED
Abelho, M. and M. A. S. Graqa. 1996. Effects of eucalyptus afforestation on leaf litter dynamics and macroinvertebrate community structure of streams in central Portugal. Hydrobiologia 324: 195-204.
Aguiar, F. C., M. T. Ferreira, and P. Pinto. 2002. Relative influence of environmental variables on macroinvertebrate assemblages from an Iberian basin. Journal of the North American Benthological Society 21 : 43-53.
Ahearn, D. S. and R. A. Dahlgren. 2005. Sediment and nutrient dynamics following a low-head dam removal at Murphy Creek, California. Limnology and
Oceanography 50: 1752-1 762.
Armitage, P. D., K. Lattrnann, N. Kneebone, and I. Hams. 2001. Bank profile and structure as determinants of macroinvertebrate assemblages-seasonal changes and management. Regulated Rivers-Research and Management 17: 543-556.
Bailey, R. C., R.H. Noms, and T. B. Reynoldson. 2003. Bioassessment of freshwater ecosystems: using the reference condition approach. Kluwer Academic Publishers, Springer, New York.
Benstead, J. P. and C. M. Pringle. 2004. Deforestation alters the resource base and biomass of endemic stream insects in eastern Madagascar. Freshwater Biology 49: 490-50 1.
Bogan, M. T. and D. A. Lytle. 2007. Seasonal flow variation allows 'time-sharing' by disparate aquatic insect communities in montane desert streams. Freshwater Biology 52: 290-304.
Brown, H. P. 1987. Biology of riffle beetles. Annual Review of Entomology 32: 253-273. Chaves, M. L., P. M. Chainho, J. L. Costa, N. Prat, and M. J. Costa. 2005. Regional and
local environmental factors structuring undisturbed benthic macroinvertebrate communities in the Mondego River basin, Portugal. Archiv Fur Hydrobiologie
163: 497-523.
Chaves, M. L., J. L. Costa, P. Chainho, M. J. Costa, and N. Prat. 2006. Selection and validation of reference sites in small river basins. Hydrobiologia 573: 133-154. Coimbra, C. N., M. A. S. Graqa, and R. M. Cortes. 1996. The effects of a basic effluent
on macroinvertebrate community structure in a temporary Mediterranean river. Environmental Pollution 94: 30 1-307.
Cortes, R. M. V., M. T. Ferreira, S. V. Oliveira, and F. Godinho. 1998. Contrasting impact of small dams on the macroinvertebrates of two Iberian mountain rivers. Hydrobiologia 389: 51-61.
Davis, W. S. and T. P. Simon. 1995. Biological assessment and criteria, tools for water resource planning and decision making. CRC Press, Florida.
Davy-Bowker, J., R. T. Clarke, R. K. Johnson, J. Kokes, J. F. Murphy, and S. Zahradkova. 2006. A comparison of the European Water Framework Directive physical typology and RIVPACS-type models as alternative methods of establishing reference conditions for benthic macroinvertebrates. Hydrobiologia 566: 91-105.
Doledec, S., N. Lamouroux, U. Fuchs, and S. Merigoux. 2007. Modelling the hydraulic preferences of benthic macroinvertebrates in small European streams. Freshwater Biology 52: 145-164.
Elliott, J. M. 2006. Critical periods in the life cycle and the effects of a severe spate vary markedly between four species of elmid beetles in a small stream. Freshwater Biology 5 1: 1527-1 542.
Environment Agency. 1997. River habitat survey, 1997 field survey guidance manual. Environment Agency, Bristol.
Feio, M. J., T. B. Reynoldson, and M. A. S. Graca. 2006. The influence of taxonomic level on the performance of a predictive model for water quality assessment. Canadian Journal of Fisheries and Aquatic Sciences 63: 367-376.
Feio, M. J., R. Vieira-Lanero, V. Ferreira, and M. A. S. Gram. 2005. The role of the environment in the distribution and composition of Trichoptera assemblages in streams. Archiv Fur Hydrobiologie 164: 493-5 12.
Ferreira, V., A. Elosegi, V. Gulis, J. Pozo, and M. A. S. Graca. 2006. Eucalyptus plantations affect fungal communities associated with leaf-litter decomposition in Iberian streams. Archiv Fur Hydrobiologie 166: 467-490.
Frissell, C. A., W. J. Liss, C. E. Warren, and M. D. Hurley. 1986. A hierarchical framework for stream habitat classification
-
viewing streams in a watershed context. Environmental Management 10: 199-2 14.Gergel, S. E., M. G. Turner, J. R. Miller, J. M. Melack, and E. H. Stanley. 2002. Landscape indicators of human impacts to riverine systems. Aquatic Sciences 64:
1 18-128.
Graqa, M. A. S., P. Pinto, R. Cortes, N. Coimbra, S. Oliveira, M. Morais, M. J. Carvalho, and J. Malo. 2004. Factors affecting macroinvertebrate richness and diversity in Portuguese streams: a two-scale analysis. International Review of Hydrobiology 89: 151-164.
Graqa, M. A. S. and C . N. Coimbra. 1998. The elaboration of indices to assess biological water quality. A case study. Water Research 32: 380-392.
Grap, M. A. S., R. C. F. Ferreira, and C. N. Coimbra. 2001. Litter processing along a stream gradient: the role of invertebrates and decomposers. Journal of the North American Benthological Society 20: 408-420.
Graqa, M. A. S., P. Pinto, R. Cortes, N. Coimbra, S. Oliveira, M. Morais, M. J. Carvalho, and J. Malo. 2004. Factors affecting macroinvertebrate richness and diversity in Portuguese streams: a two-scale analysis. International Review of Hydrobiology 89: 151-164.
Herlihy, A. T., W. J. Gerth, J. Li, and J. L. Banks. 2005. Macroinvertebrate community response to natural and forest harvest gradients in western Oregon headwater streams. Freshwater Biology 50: 905-919.
Karr, J. R. and E. W. Chu. 1999, Restoring life in running waters: better biological monitoring. Island Press, Washington, DC.
Lake, P. S. 2003. Ecological effects of perturbation by drought in flowing waters. Freshwater Biology 48: 1161-1 172.
LepS,
J. and P. Smilauer. 2003, Multivariate analysis of ecological data using CANOCO. Cambridge University Press, Cambridge.Logan, P. and M. Furse. 2002. Preparing for the European Water Framework Directive
-
making the links between habitat and aquatic biota. Aquatic Conservation-Marine and Freshwater Ecosystems 12: 425-437.
Marks, J. C., M. E. Power, and M. S. Parker. 2000. Flood disturbance, algal productivity, and interannual variation in food chain length. Oikos 90: 20-27.
Monaghan, K. A,, M. R. Peck, P. A. Brewin, M. Masiero, E. Zarate, P. Turcotte, and S. J. Ormerod. 2000. Macroinvertebrate distribution in Ecuadorian hill streams: the effects of altitude and land use. Archiv Fur Hydrobiologie 149: 421-440.
for streams in northern Portugal. Aquatic Conservation-Marine and Freshwater Ecosystems 15: 189-210.
Ortiz, J. D., E. Marti, and M. A. Puig. 2005. Recovery of the macroinvertebrate community below a wastewater treatment plant input in a Mediterranean stream. Hydrobiologia 545: 289-302.
Pinto, P., J. Rosado, M. Morais, and I. Antunes. 2004. Assessment methodology for southern siliceous basins in Portugal. Hydrobiologia 5 16: 19 1-2 14.
Pinto, P., M. Morais, M. Ilheu, and L. Sandin. 2006. Relationships among biological elements (macrophytes, macroinvertebrates and ichthyofauna) for d i f f m t core river types across Europe at two different spatial scales. Hydrobiologia 566: 75-
90.
Raven, P. J., P. J. Boon, F. H. Dawson, and A. J. D. Ferguson. 1998. Towards an integrated approach to classifying and evaluating rivers in the UK. Aquatic Conservation-Marine and Freshwater Ecosystems 8: 383-393.
Ribera, I. 2000. Biogeography and conservation of Iberian water beetles. Biological
Conservation 92: 13 1-1 50.
Richards, C., G. E. Host, and J. W. Arthur. 1993. Identification of predominant
environmental factors structuring stream macroinvertebrate communities within a large agricultural catchment. Freshwater Biology 29: 285-294.
Sandin, L. and P. F. M. Verdonschot. 2006. Stream and river typologies
-
major results and conclusions from the STAR project. Hydrobiologia 566: 33-37.Shreve, R.L. 1996. Statistical law of stream numbers. Journal of Geology 1 : 17-37
Stanford, J. A. and J. V. Ward. 2001. Revisiting the serial discontinuity concept.
Regulated Rivers-Research and Management 17: 303-31 0.
Stanley, E. H., M. A. Luebke, M. W. Doyle, and D. W. Marshall. 2002. Short-term changes in channel form and macro invertebrate communities following low-head
dam removal. Journal of the North American Benthological Society 2 1 : 172- 187.
Statzner, B. and B. Higler. 1986. Stream hydraulics as a major determinant of benthic invertebrate zonation patterns. Freshwater Biology 16: 127- 139.
Tiemann, J. S., D. P. Gillette, M. L. Wildhaber, and D. R. Edds. 2004. Effects of lowhead dams on riffle-dwelling fishes and macroinvertebrates in a midwestern river. Transactions of the American Fisheries Society 133: 705-7 17.
Townsend, C. R., A. G. Hildrew, and J. Francis. 1983. Community structure in some southern English streams
-
the influence of physicochemical factors. Freshwater Biology 13: 521-544.Verdonschot, P. F. M. 2006. Evaluation of the use of Water Framework Directive- typology descriptors, reference sites and spatial scale in macroinvertebrate stream typology. Hydrobiologia 566: 39-58.
Wright, J. F., D. Moss, P. D. Armitage and M. T. Furse. 1984. A preliminary
classification of running-water sites in Great Britain based on macroinvertebrate species and the prediction of community type using environmental data. Freshwater Biology 14: 221-256.
Wright, J. F., D. W. Sutcliffe, and M. T. Furse. 2000. Assessing the biological quality of freshwaters: RIWACS and other techniques. Freshwater Biological Association, Ambleside, Cumbria.
