Aquat Ecol DOI 10.1007/s10452-008-9176-9
Do intermittent and ephemeral Mediterranean rivers belong to the same river type? Argyroudi Anna Æ Chatzinikolaou Yorgos Æ Poirazidis Konstantinos Æ Lazaridou Maria
Received: 22 May 2007 / Accepted: 11 March 2008 Ó Springer Science+Business Media B.V. 2008
Abstract The benthic macroinvertebrate communities and ecological quality of eleven temporary rivers (seven intermittent and four ephemeral) in Dadia National Park, north-eastern Greece, were examined with respect to the degree of flow temporality. Sampling took place during the high flow season at both ephemeral and intermittent sites and during the low flow season only at the intermittent ones, which receded to pools. Despite the remarkable seasonal variation in both the hydrology and ecology of the intermittent rivers, the various metrics and indices as well as the multivariate analyses confirmed the clear distinction between the two river types (ephemeral and intermittent). Existing European quality indices do not sufficiently differentiate between ephemeral and intermittent river types, and thus cannot reliably discriminate the degree of natural variability from human induced stressors in temporary rivers.
A. Anna (&) C. Yorgos L. Maria School of Biology, Department of Zoology, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece e-mail:
[email protected] C. Yorgos Institute of Inland Waters, Hellenic Center for Marine Research, P.O. Box 712, 19013 Anavyssos, Greece P. Konstantinos WWF Greece, Dadia project, Dadia, 68400 Soufli, Greece
Keywords Benthic macroinvertebrates Dadia National Park Ephemeral rivers Intermittent rivers
Introduction Mediterranean rivers are characterized by the irregularity of flow and harsh hydrological fluctuations (Arab et al. 2004). Extreme seasonal variation of the flow regimes often causes a marked pattern of zero or low flow and the reduction of the water surface into isolated pools along the river when the flow ceases. This results in intermittent flow in many rivers with a shifting between lotic and lentic conditions during the year (Morais et al. 2004). Depending on the degree of temporality, rivers and streams can be classified either as perennial (continuous flow) or temporary (seasonal flow). The latter are subdivided according to their dryperiod condition: intermittent rivers form chains of lotic features (isolated pools) as flow disappears but surface water is still present, and ephemeral rivers form dry stream beds as the water disappears (Bonada 2003; Uys and O’Keeffe 1997). As to their discharge regime, ephemeral streams are influent, feeding the groundwater and having channels which are above the water table in all the time of the year, whereas the intermittent Mediterranean ones are only seasonally influent (Gordon et al. 1992). Alternatively, according to the degree of predictability, temporary streams are intermittent, drying at more or less predictable times or
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episodic (ephemeral) with unpredictable discharge patterns (Williams 1996). Several studies have provided insight knowledge into the structure or traits of the benthic macroinvertebrate communities in Mediterranean temporary rivers (Bazzanti et al. 1989; Coimbra et al. 1996; Bonada 2003; Arab et al. 2004; Morais et al. 2004; Beˆche et al. 2006) or others throughout the world (Williams and Hynes 1976; Boulton and Lake 1992a, 1992b; Meyer et al. 2003). However, there is a lack of information on the ecological functioning of Mediterranean fluvial ecosystems, especially on the effects of floods, droughts, and flow variability on the structure of the communities (Bernardo and Alves 1999). Furthermore, there is a lack of references concerning benthic macroinvertebrate differences between intermittent and ephemeral rivers. The Water Framework Directive (WFD) 2000/60/ EC (European Union Council 2000) requires European countries to assess the ecological status of freshwater ecosystems using biological elements (e.g., macroinvertebrates, fish, and macrophytes), and the hydromorphological and physico-chemical elements which support them, aiming to achieve the objective of at least good ecological status in all surface waters by 2015. For purposes of classification of ecological status, results should be expressed as ecological quality ratios (EQR = Observed/Reference biological value). Thus a good ecological status implies a low level of anthropogenic alteration and only slight deviations from undisturbed conditions (reference conditions). However, water bodies (e.g., a river) at a drainage basin area scale should be differentiated by types (typology), so that reliable establishment of type-specific reference conditions are ensured, which means that observed and reference sites belong to the same type. The type of a river is characterized by general abiotic and biotic criteria and features like stream order, slope, river morphology, flow regime, altitude, and ecoregion (Muhar et al. 1993; Schmutz et al. 2000). The WFD proposes that typology should be based either on System A (using definite compulsory abiotic factors) or System B (using specific compulsory and loosely defined abiotic factors). According to System A typology, monitored rivers must have at least a 10 km2 basin area neglecting most intermittent and ephemeral rivers. According to the intercalibration exercise for the Mediterranean rivers (Van de Bund et al. 2004) based
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on a System B typology, all the sampling sites of Dadia National Park (Dadia NP) belong to the R-M5 type, small Mediterranean temporary rivers. R-M5 rivers are low order streams, their catchment is between 10 and 100 km2, the altitude is \300 m, the geology is of mixed type and the flow regime is temporary (Van de Bund et al. 2004). The purpose of this article is to examine the physico-chemical parameters, the composition of the benthic macroinvertebrate communities, and the applicability of several ecological quality indices: (1) whether intermittent and ephemeral temporary rivers belong to the same river type, and (2) to study the temporal variability of the intermittent rivers.
Study area The study was conducted in tributaries of Evros River in the Dadia-Lefkimi-Soufli National Park (hereafter Dadia NP) located in north-eastern Greece (Fig. 1). Since 1980, the area has been declared a nature reserve, and since 2003 a National Park, because of its high ornithological value for raptors and particularly for the black vulture (Aegypius monachus) (Poirazidis et al. 2004), as well as for its importance for biodiversity conservation (Helmer and Scholte 1985; Adamakopoulos et al. 1995; Grill and Cleary 2003; Kati et al. 2004; Kati and Sekercioglou 2006). It has an extent of about 430 km2, including two strictly protected core areas, which cover 73.5 km2. The altitude of the area varies from 10 to 650 m. The area’s climate is Mediterranean with short summers and mild winters (Adamakopoulos et al. 1995), whereas the bio-climate carries the characteristics of the mild meso-Mediterranean type with a dry period which varies from 40 to 75 days. All of the Dadia NP rivers are tributaries of the river Evros. The mean annual rainfall of the whole catchment is 652.9 mm and most of the rainfall is concentrated from November to June, thus this period is defined as the high flow period. These rivers are characterized by a temporary flow regime during the low (summer–autumn) flow period until November, when flow continuity recovers. In particular, some rivers within the core conservation zone dry out completely shortly after the high flow season, therefore, are characterized as ephemeral, in contrast to others within the buffer zone receding in isolated
Aquat Ecol Fig. 1 The sampling stations along the rivers of Dadia National Park (I: Intermittent rivers, E: Ephemeral rivers)
pools during the low flow season and characterized as intermittent. The intermittent rivers of the present study have a larger drainage basin area (8.27– 96.16 km2) in comparison to the ephemeral ones (0.72–1.87 km2) (Table 1). Although the area of study is not surrounded by high mountains, the ragged relief of the forested terrain produces a dense hydrographic network. Erosional procedures have created very narrow floodplains that are steeper with
increasing stream order and elevation. The ephemeral rivers plus one intermittent (all E and I1) had relatively low slope and low altitude. The ephemerals rest on recent alluvial sediments and they are surrounded by low slopes covered in soil. They do not have riparian vegetation. The intermittent studied rivers are usually surrounded by steep rocky hillslopes and riparian vegetation forms a narrow stripe next to the channel. The intermittent rivers have
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Aquat Ecol Table 1 Main environmental characteristics of the sampling sites in Dadia National Park (I: Intermittent rivers, E: Ephemeral rivers) Site
Latitude Longitude
Drainage basin area size (km2)
Altitude (m)
I1
41°060 07500 N
16.43
146
12.90
0
Slope (o)
Dominant substrate
Geology
Channel Width (m)
Width to depth ratio
8.94
Boulders
Calcareous
5.10
23.6
300
17.53
Boulders
Siliceous
2.90
8.7
74.50
155
19.33
Cobbles
Siliceous
4.30
6.9
91.90
150
22.53
Pebbles-Gravel
Calcareous
8.70
21.1
96.16
150
20.94
Cobbles
Siliceous
4.40
13.3
8.27
148
19.15
Bedrock
Siliceous
2.60
28.1
48.83
300
10.28
Boulders
Calcareous
5.00
20.8
00
26°12 24 E I2
41°090 4500 N 26°080 1600 E
I3
41°080 5000 N 26°090 3900 E
I4
41°080 0500 N 26°110 0100 E
I6
41°010 5500 N 26°060 9700 E
I7
41°020 0500 N 0
00
26°05 88 E I8
41°040 0400 N 26°030 1500 E
E2
41°060 1100 N 26°110 9700 E
0.75
154
9.29
Boulders
Calcareous
1.00
6.3
E3
41°060 1200 N
1.17
149
6.68
Sand
Calcareous
0.50
8.3
0.72
150
4.54
Bedrock
Calcareous
0.65
11.8
1.82
150
6.81
Bedrock
Calcareous
3.00
30.0
26°120 8600 E E4
41°050 0500 N 26°130 0900 E
E5
41°040 8700 N 26°150 0000 E
medium–low altitude and high gradient slope (Table 1).
settlements, pollution inputs, and of water abstraction or diversion (European Commission, 2003).
Materials and methods
Data collection
During both flow seasons (low and high), seven sites on intermittent rivers (I), belonging to the buffer conservation zone were sampled, while during the high flow season four additional sites of ephemeral rivers (E), belonging to the highly protected core zone were studied. Sampling was carried out in the low flow period October 2004 only for the intermittent and in March 2005 for the intermittent and ephemeral rivers. We assumed that in March recharge and reconnection had been established in the river, and that the biota was assumed to have recovered from the drought stress. All the studied sites were considered as reference sites because they had exclusively forest land use and absence of human
Physico-chemical parameters and habitat characteristics
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The coverage percentage of river-bank vegetation at the river channel’s edge between the water channel and the banks and the percentage coverage of the aquatic vegetation over the sampled area were estimated visually, as well as the substrate grain size using the Wentworth scale (Wentworth 1922). We calculated discharge from width, depth, and flow that were measured with a tape meter and a Swoffer 2000 flow meter. Water temperature, pH, dissolved oxygen saturation and concentration (D.O. % and mg/l), conductivity, and Total Dissolved Solids (TDS) were
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The quality of the riparian vegetation was estimated using the Spanish QBR index (Munne´ et al. 2003)
and that of the fluvial habitat by the IHF index (Pardo et al. 2002). The Hellenic Evaluation Score (HES), the Average Hellenic Evaluation Score per taxon (AHES), the Semi-HES values and its Interpretation Index (Artemiadou and Lazaridou 2005) were applied to the benthic macroinvertebrate samples to assess the ecological quality of each site. This evaluation system is a modification of the Spanish BMWP score (Alba-Tercedor and Sanchez-Ortega 1988) but it includes the relative abundance of benthic macroinvertebrates and is standardized against the habitat diversity richness of each sampling site according to GHRM (Chatzinikolaou et al. 2008). GHRM has been produced to estimate visually and rapidly whether habitat or habitats of a sampling site are rich or poor and can be regarded as an extension to the work of Extence et al. (1987) in the Lincoln Quality Index. Table 2 presents the calculated metrics of the European Intercalibration exercise for the Small Mediterranean Rivers (R-M5 type) (Van de Bund et al. 2004). All the metrics were normalized (EQR values) (being divided with their median values of the reference data set) according to the methodology proposed by the Mediterranean Intercalibration Group (Buffagni et al. 2005). Since Greece has not yet established a monitoring network for rivers, a typology and reference sites, the 11 study sites constitute the reference data set since the absence of human alteration at the area meets the criteria of WFD (European Commission 2003). The ICMiRM Indices were then calculated by summing up the multiplied EQR values of the respective metrics with their weights for the R-M5 type and were further normalized as above (Buffagni et al. 2005). We used
Table 2 Metrics and respective weights used for the calculation of the Intercalibration Multimetric Indices for Mediterranean Rivers (ICMiRM). IASPT is the Iberian average score per taxon log10(SelETD+1) is the log-transformed abundance of selected taxa of Ephemeroptera (E), Trichoptera
(T), and Diptera (D) . log10(SelEPTCD+1) is the logtransformed abundance of the above taxa plus Plecoptera (P) and Coleoptera (C). EPT is the number of families of (E), (P), (T). Pielou’s index represents the evenness of the distribution and N is the number
measured in situ using the digital poly-meter YSI 650 MDS. We analysed water samples for P-PO4 (mg/l) and total suspended solids (TSS mg/l) according to APHA (1985). Sampling of benthic macroinvertebrates We took one sample of benthic macroinvertebrates at each site with the semi-quantitative 3-min kick and sweep method (Armitage et al. 1983), using a standard pond net (surface 575 cm2 and mesh size of 0.9 mm). During the 3-min period, all existing habitats at all three sites, submerged macrophytes, bare substrate at riffles and pools, were sampled according to the Habitat Richness Matrix (GHRM) (Chatzinikolaou et al. 2006). GHRM is a modification from the US Environmental Protection Agency protocol for macroinvertebrate sampling (Cuffney et al. 1993). We placed samples in plastic bottles and preserved in 4% formaldehyde. On return to the laboratory, we sorted the animals using a 0.5 mm mesh sieve and a magnifying lens and preserved in 75% ethanol. Identification of the invertebrates was made to the lowest possible level, mainly the family level. Although we employed a semi-quantitative method, we counted abundance for every taxon, since for several biotic indices used (see Habitat and Biotic indices section) relative abundance classes are needed. Habitat and biotic indices
ICMi7RMa
Weight
ICMi10RMb
Weight
ICMi11RMb
Weight
IASPT’’-2
0.50
IASPT’’-2
0.30
IASPT’’-2
0.40
log10(SelETD + 1)
0.20
log10(SelEPTCD + 1)
0.20
EPT
0.15
EPT
0.20
EPT
0.30
Pielou’s evenness index
0.10
N-families
0.25
N-families
0.20
N-families
0.20
a
Buffagni et al. (2005)
b
Pers. communication Munne´ and Prat
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the ICMiRM Indices to estimate the quality classification of the sites using the benchmark dataset of the GUADALMED project (Table 2). The Spanish indices for the Mediterranean temporary rivers (ICMi10RM and ICMi11RM) place greater weight on the IASPT (0.4–0.5, respectively) than the ICMi7RM (0.3). Particularly, the ICMi10RM includes selected families of Coleoptera and Plecoptera (Nemouridae) [within the log10(SelEPTCD+1) metric] and are not taken in consideration within the log10(SelETD+1) metric of the ICMi7RM.
Data analysis For comparing (a) the intermittent and the ephemeral temporary rivers during the high flow season and (b) the two flow seasons of the intermittent rivers, we used the Mann–Whitney test and compared the hydromorphological and physico-chemical data and all the metrics. A clustering technique known as FUZZY (Equihua 1990), based on fuzzy sets, was also used to obtain both ordination and classification. This technique is an extension of TWINSPAN (Hill 1979), and it is particularly well suited for ecological analyses where no clear-cut transition from one class to another and many intermediate situations may occur. The grouping of sampling sites is based on the assemblages of benthic macroinvertebrates. The participation of each site to each cluster is expressed by its membership values. The sites’ membership values from the chosen fuzzy set are the ones used for their clustering. SIMPER analysis (program PRIMER, version 5.1.2.) (Clarke and Warwick 1994) was furthermore used, so as to establish which of the main families were contributing to the average Bray– Curtis dissimilarity between the clusters produced by FUZZY. The ordination multivariate analysis Canonical Correspondence Analysis (CCA) (Ter Braak and Sˇmilauer 1998) (software CANOCO) examined the relationship between the macroinvertebrate taxa [transformed to log (x+1)] or the sampling sites with the physico-chemical parameters [transformed to log (x + 1) or the % to arcsines and the pH and the water temperature values to standard scores]. This method does not require the assumption of linearity and can detect unimodal relationships between species and external variables. It is particularly suited for forward selections of environmental variables to determine
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the variables which best explain the species data (Ter Braak and Sˇmilauer 1998). For the effect of seasonality upon our data we used the season of the sampling as a covariable.
Results In the 18 sites of the study area, 8,073 individuals belonging to 63 families of benthic macroinvertebrates were collected. No statistically significant difference between the intermittent and the ephemeral streams was found regarding the number of taxa (Mann–Whitney U-test, P [ 0.05, df: 10). Multivariate analyses revealed the seasonal variability and the differences according to the degree of flow temporality (intermittent vs. ephemeral). The FUZZY clustering analysis produced three clusters (Fig. 2). Cluster A was composed of the low flow intermittent sites (IL), Cluster B included the high flow intermittent sites (IH) and Cluster C consisted of the ephemeral sites (E). According to Simper Analysis, Cluster A was characterized mostly by the Diptera family of Chironomidae and the Odonata Platycnemydidae (40.62% and 21.99% contribution, respectively), whereas Cluster B by the Diptera family of Simuliidae and the Plecoptera Taeniopterygidae (39.41% and 37.07% contribution, respectively). The
Fig. 2 Results of FUZZY clustering analysis applied to the benthic macroinvertebrate data collected from the rivers of Dadia NP in October 2004 and March 2005. The solid lines ellipses enclose samples with membership values 75–100%; dotted lines ellipses enclose samples with membership values 0.5–0.75% (I: Intermittent sites, E: Ephemeral sites, L, H: Low and High flow season respectively)
Aquat Ecol
Ephemeroptera Siphlonuridae and Plecoptera Nemouridae characterized Cluster C (48.86% and 27.04% contribution, respectively). Using seasonality as a covariable the forward selection of environmental variables (Table 3) according to the Monte Carlo permutation test (P \ 0.05), and the inflation factor criterion (\20) of CCA, only five environmental variables shown in the ordination diagram (Fig. 3) were strongly correlated with the species data. The first two axes of the ordination explained the 66.6% of the variance of the species– environmental variables relation. Covariables explained 23.15% of the total inertia (Table 4) in benthic macroinvertebrate data. Axis 1 was correlated (P \ 0.05) mainly with bank vegetation (-0.8145), drainage area (-0.7707), and slope (-0.7432), while Axis 2 with the IHF (0.7643) (Fig. 3). The ordination of the samples according to the drainage basin area size and the slope showed the differentiation of the intermittent and ephemeral samples (Fig. 3). Differences between intermittent and ephemeral rivers Intermittent sites differed significantly from the ephemeral ones (Mann–Whitney U-test, P \ 0.05, df: 10) due to their higher values of the percentage of the bank vegetation, discharge, depth, drainage basin area size, slope, dissolved oxygen (D.O.%), and pH (Tables 1, 3). The ecological quality (SemiHES) according to the Hellenic Evaluation System (HES) varied from excellent to good at the intermittent sites and from good to moderate at the ephemeral ones. Ecological quality was excellent or good at the intermittent sites and excellent, good or moderate at the ephemeral ones according to the ICMi7, ICMi10, and ICMi11 (Fig. 4). The riparian quality (QBR index) was excellent or good (54.28 ± 2.51) at the ephemeral and intermittent sites, and similarly the Fluvial Habitat Quality (IHF Index) presented good or moderate conditions (85.56 ± 2.79). Temporal variability in the intermittent rivers Water temperature (T), conductivity, concentration of Total Dissolved Solids (TDS), and P-PO4 phosphates were significantly higher during the low flow season, but concentration of Total suspended Solids (TSS) and
the percentage of oxygen saturation (D.O. %) were higher during the high flow season (Table 3) (Mann– Whitney U-test, P \ 0.05, df: 13). Of the metrics used, only the IASPT’’-2, the log10(SelEPTCD+1) and the number of EPT families were found statistically higher during the high flow season (Mann–Whitney U-test, P \ 0.05, df:13). Ecological quality was excellent or good during both seasons according to the Hellenic Evaluation System (HES). Nevertheless, in I1 it was moderate during the low flow season, according to the ICMi7, ICMi10, and ICMi11 (Fig. 4).
Discussion Hydrologic variability is widely recognized as a key ecological organizer in fluvial ecosystems (Vannote et al. 1980). The present study has examined, with the use of several abiotic and biotic metrics, whether the hydrologically different ephemeral and intermittent rivers of Dadia NP belong to the same river type. The results indicate that the above hypothesis can be rejected, primarily based on benthic macroinvertebrates, as far as this particular region of Greece is concerned. Thus, the question that arises is, whether intermittent and ephemeral rivers in a Mediterranean or European scale are to be perceived as the same in terms of ecological quality assessment, especially toward the WFD ecological assessment approach. Intermittent Mediterranean rivers have high flow predictability, while the ephemeral do not (Uys and O’Keeffe 1997). In Dadia NP, this was attributed to the larger basin area, which is related to a higher and more predictable discharge and the existing riparian vegetation of the intermittent rivers that both contribute to a subsequent complexity in benthic community composition. As far as the ecological quality is concerned, the metrics and indices of the intermittent rivers during the high flow season, presented either excellent or good quality, instead of just excellent, showing that the quality evaluation in this type of rivers was biased by their hydrologic variability. Regarding the ephemeral rivers, the HES and the Intercalibration Multimetric Indices were not capable to recognize the high degree of natural variability, which is inherently considerably increased (Uys and O’Keeffe 1997). All the sites of the present study were considered as reference due to the absence of any human disturbance. However, in some
123
123
276 347
14.8 15.8
14.5
15.3
16.5
15.1
16.5
10.8
9.5
10.3
8.4
5.7
6.0
6.8
12.6
8.4
8.9 8.7
I1L I2L
I3L
I4L
I6L
I7L
I8L
I1H
I2H
I3H
I4H
I6H
I7H
I8H
E2
E3
E4 E5
61 59
73
186
118
289
166
137
91
103
70
198
454
344
482
395
180 226
16.5 1.5
26.5
1
0
0
0
22
31.5
18
33.5
2.5
0.5
1
3
0.5
1.5 3
P-PO4 (mg l-1)
0.0127
7.33 0 7.64 0
7.8
7.64 0.007
7.86 0
8.22 0
8.07 0
8.12 0
8.19 0.0041
8.18 0.0041
7.71 0.017
7.65 0.0112
8.14 0.0198
8.09 0.007
8.37 0.0227
7.88 0.0184
7.04 0.1712 7.57 0.0212
TDS TSS pH (mg l-1) (mg l-1)
87.7 92
69
91.8
97.6
95.2
94
101.5
103.5
92
98.2
63
83.5
78
78
50.4
15.5 35.5
D.O. (% saturation)
10.2 10.68
8.11
9.79
11.72
11.71
10.89
11.83
11.48
10.47
10.72
6.2
8.52
7.7
7.6
5.03
1.54 3.6
0.19 0.16
0.22
0.01
0.55
0.11
0.74
0.11
0.09
0.12
0.05
0
0
0
0
0
0 0
D.O Flow (mg l-1) (m s-1)
0.0032 0.0054
0.0019
0.0004
0.2499
0.0334
0.9
0.5384
0.2583
0.0593
0.0484
0
0
0
0
0
0 0
Discharge (m3 s-1)
TSS—Total Suspended Solids; TDS—Total Dissolved Solids; IHF—Fluvial Habitat Index; QBR—Riparian Vegetation Index
940 90.0
112
286
182
444
255
211
400
159
108
305
698
529
742
608
Conductivity (lS cm-1)
Sample Temperature (°C)
5 10
30
5
15
5
10
0
90
70
20
0
0
0
0
0
0 0
Macrophyte cover (%)
35 5
50
40
65
90
50
45
70
70
70
80
90
80
50
50
60 80
Bank Vegetation (%)
67 53
58
66
67
53
56
54
52
52
72
49
60
42
33
51
56 36
IHF score
75 80
75
85
80
100
100
100
65
85
80
80
100
85
100
75
100 75
QBR score
Table 3 Values of the physico-chemical parameters measured at the 11 sites. E prefixed samples are for sites at ephemeral rivers whereas I at intermittent. The last letter L or H at the I stands for samples taken at the low or high flow season, respectively
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Fig. 3 Ordination of sampling sites and environmental variables along the rivers of Dadia National Park in October 2004 and March 2005 (I: Intermittent rivers, L, H: Low and High flow season, respectively, E: Ephemeral rivers)
Fig. 4 Boxplots with the mean values (±SE) of the metrics used for the calculation of the Intercalibration Multimetric Indices ICMi7 (IASPT’’-2, Pielou’ s Index, log10(SelETD + 1), EPT and number of taxa), ICMi10 (IASPT’’-2, log10(SelEPTCD+1), EPT and number of taxa) and ICMi11 (IASPT’’-2, EPT and number of taxa) for the Mediterranean rivers, as well as the metrics of the SemiHES index (number of
cases the ecological river quality was assessed as moderate. Sheldon (2005) has already stated that it is not known whether the existing approaches to river health assessment can be used to accurately assess the health of ephemeral rivers. During the low flow season only the HES could overlook the seasonal variability and assessed the ecological quality either as excellent or good, whereas the rest of the indices qualified one sample as moderate. Therefore, the ecological quality assessment at both intermittent and ephemeral rivers is not reliable yet and the applicability of the above studied indices seems to differentiate in relation to the degree of the flow temporality, with the ephemeral rivers being more vulnerable to an erroneous assessment. Both the Greek SemiHES biotic index and the Spanish ICMi10RM and ICMi11RM reveal a significant differentiation between the values of the two types of rivers, in contrast to the European ICMi7RM.
taxa, HES, AHES) for the ephemeral and intermittent rivers at Dadia NP. Marked with an asterisk (*) and (#) are the metrics and indices that presented a significant statistical difference between intermittent and ephemeral rivers and between the low and high flow season respectively, according to a Mann– Whitney test
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Aquat Ecol Table 4 CCA ordination analysis characteristics of samples and environmental variables at Dadia NP in low and high flow season of 2004 and 2005, respectively
Axes
2
3
4
Total inertia
Eigenvalues
0.237
0.204
0.096
0.075
Species-environment correlations
0.968
0.952
0.956
0.919
1.788
Cumulative percentage variance: of species data
17.3
32.1
39.1
44.6
of species-environment relation
35.7
66.6
81.0
92.3
Sum of all unconstrained eigenvalues
1.374
Sum of all canonical eigenvalues
0.663
ICMi10RM includes selected families of Coleoptera and Plecoptera (Nemouridae), which were very abundant at the ephemeral rivers and are not taken in consideration in ICMi7RM. The multivariate FUZZY analysis based on the macroinvertebrate data clustered the ephemeral and the intermittent rivers in two types, regardless of their spatial distribution (Fig. 1). Furthermore, the CCA separated the sites mainly according to slope and the drainage basin area. It is known that community composition is increasingly governed by abiotic rather than biotic factors as the physical conditions become harsh (Peckarsky 1983; Williams 1987; Uys and O’Keeffe 1997). The involvement of the biological data produced a clear distinction between the ephemeral and intermittent rivers and this reflected the overriding importance of their different flow temporality conditions. As in the small rivers of Lake Nakuru (Kenya), faunal composition and abundance are influenced by discharge-related factors (Shivoga 2001). Taxon richness has usually been found to be very low at ephemeral sites in Catalonian reference streams (Bonada 2003) but in the current study this is not the case, although the taxa found are different. EPT values did not differ statistically between the two types of rivers (P [ 0.05) although a high correlation between EPT and an increase of flow permanence has been recorded elsewhere (Feminella 1996). An average score per taxon, ASPT’, being independent of the number of taxa, seems to be influenced by decreased dissolved oxygen values plus discharge in this type of rivers (Morais et al. 2004). This is in accordance with the higher IASPT’’-2 and AHES values along with the higher percentage of dissolved oxygen and discharge found at the intermittent studied sites. Ephemeral sites are characterized by lotic/ sensitive taxa (Siphlonuridae and Nemouridae), but
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apparently they cannot support the family of Simuliidae (Diptera) found in the intermittent ones, given that Simuliidae distribution and particularly oviposition is restricted to sites which are shaded by trees and riparian vegetation (Lautenschla¨ger and Kiel 2005). Siphlonuridae and Nemouridae do not seem to be affected by the drying up of the river, probably because they undergo a long period of diapause as eggs during the dry period (Harper 1973; Voshell 1982). During the high flow season, the sensitive taxa, generally occurring in high densities are substituted by tolerant ones during the summer lentic period (Morais et al. 2004). The latter occurred in the receding summer intermittent pools, which serve as refuges during the drought period (Williams and Hynes 1976; Boulton 2003), in Dadia NP. Conclusions The present study provides evidence of the different type conditions between intermittent and ephemeral temporary reference rivers although the Mediterranean intercalibration exercise places them in the same river type (R-M5). Multivariate FUZZY and CCA analysis, based on benthic macroinvertebrate data, as well as several multimetric indices offer sound ecological evidence for a better discrimination between intermittent and ephemeral rivers. These two river types differ ecologically and need a reliable ecological quality assessment approach according to the WFD 2000/60/ EC demands. A thorough study is needed in the future to build a specific quality evaluation system adapted for these highly variable systems taking into account their degree of flow temporality. Acknowledgments This work was supported by W.W.F. Hellas funds. Field assistance was provided by V. Vasilakis, M. Katsikatsou, and L. Ilia.
Aquat Ecol
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