A macrophyte communities sequence as an indicator ... - Springer Link

Hydrobiologia 410: 17–24, 1999. J. Garnier & J.-M. Mouchel (eds), Man and River Systems. © 1999 Kluwer Academic Publishers. Printed in the Netherlands.

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A macrophyte communities sequence as an indicator of eutrophication and acidification levels in weakly mineralised streams in north-eastern France Gabrielle Thi´ebaut & Serge Muller Universit´e de Metz, UPRES ‘Ecotoxicit´e, Biodiversit´e et Sant´e Environmentale’, Laboratoire de Phyto´ecologie, Ile du Saulcy, 57045 Metz Cedex, France Key words: eutrophication, acidification, macrophyte communities, weakly mineralized streams, France

Abstract The Northern Vosges streams are subjected to acidification upstream and to eutrophication downstream. A bioindicator scale of the degree of eutrophication and of the level of acidification, based on four aquatic macrophyte communities, was established in these weakly mineralized streams. Aquatic plant communities therefore begin as Group A, develop into Group B and become Group C or D downstream. The A community was characterized by bryophytes (Scapania undulata, Sphagnum sp.) and Potamogeton polygonifolius in oligotrophic, acidified to weakly acidified, and poorly buffered streams. The B community, defined by P. polygonifolius and the appearance of Ranunculus peltatus and Callitriche species (C. platycarpa, C. hamulata) was found in oligotrophic waters with a higher buffer capacity than the A community. The C community was determined by the disappearance of P. polygonifolius and the appearance of Elodea species (E. canadensis, E. nuttallii) and rare species in mesotrophic and neutral streams. The D community, with very high nutrient loading, was characterized by the abundance of Callitriche obtusangula, by the presence of Amblystegium riparium, Fissidens crassipes and the development of filamentous algae. This macrophyte sequence corresponded to an upstream to downstream zonation, which was characterized by an increase in buffer capacity and in nutrient levels and a decrease in protons and aluminium load.

Introduction Freshwaters are highly sensitive to any input of nutrients or acidifying substances. Increasing human activities, particularly urbanisation, agricultural and industrial activities, lead to an increase in nutrients. Large nutrient inputs have accelerated eutrophication. In many lakes and rivers world-wide, the input of large quantities of phosphorus from agricultural runoff and sewage, and also of nitrogen (mainly as runoff from agricultural land), produces ideal conditions for high algal growth (Lee, 1973) and macrophyte decline (Phillips et al., 1978). Thus, the main channels of the Rhine and the Meuse rivers are characterized by a dense plankton which develops rapidly in the nutrient rich river waters (Admiraal et al., 1993). In the Alsacian plain, aquatic macrophyte communities can be used as bioindicators of eutrophication in calcareous

streams (Carbiener et al., 1990; Trémolières et al., 1994; Robach et al., 1996). In the Netherlands, acidification is always accompanied by nitrogen enrichment (Arts et al., 1990). Research on the effects of acid deposition and acidification on aquatic biota has been ongoing in Europe and North America for the last 20 years, and many comprehensive studies have been published (Grahn, 1977; Roberts et al., 1985; Farmer, 1990). In the Vosges mountains, investigations of acidification started in 1985 with the aim of characterizing the degree of water acidification (Massabuau et al., 1987; Probst et al., 1995; Guérold et al., 1995). These studies have shown a drastic decrease in fish and aquatic animal biodiversity in acidified headwater streams. Even though research has been conducted in several areas and concerned many different organisms, it has not been exhaustive and there are gaps in our un-

18 derstanding of the response of organisms to acidic or eutrophic conditions. These gaps have often occurred because funding has focused on chemical mechanisms and modelling the response of systems rather than on making resource inventories or resolving uncertainties in biological responses to acidification and eutrophication. In the Northern Vosges, Muller (1990) has established a preliminary sequence of increasing eutrophication based on macrophyte communities in weakly mineralized waters. Later, Thiébaut & Muller (1996) described more precisely this eutrophication sequence by using multivariate analyses and by increasing the network. A comparison was done with the Alsacian plain sequence (Robach et al., 1996). In parallel, an other preliminary study has consisted in assessing the acidification degree and in researching the impact of acidification on macrophyte communities (Thiébaut et al., 1996). In this present study, the first objective was to research the relationships between aquatic plants and water quality in a widespread assessment. The purpose was to define an aquatic macrophyte communities sequence as an indicator of the degree of eutrophication and of acidification in the weakly mineralized streams of the Northern Vosges streams (N-E, France) by using a multivariate approach and by spatial and temporal comparisons between streams located in the same catchment.

Study site The study area is situated in north-eastern France. The landscape pattern of the Northern Vosges consists of sandstone mountains of 200–580 m in altitude topped by rocky conglomerate, surrounded by steep cliffs. The regional climate is subcontinental. Winters are cold, with more than 100 days of frost and an annual temperature of 8.6 ◦ C. Summers are relatively hot. The mean rain fall is 900 mm. The Northern Vosges represent an acid-sensitive area in France, receiving high levels of acid deposition (Dambrine et al., 1994). The streams are subject to eutrophication (Muller, 1990; Thiébaut & Muller, 1996; Thiébaut & Muller, 1998) and to acidification (Thiébaut et al., 1996). The 23 chosen streams are located in the Moder catchment. They drain a forested area covered by acidic soils ranging from brown acidic soils to podzolic soils. This hydrological network flows in alluvial deposits characterized by low calcium carbonate concentration.

Forty two sites were selected in order to represent a wide range of physico-chemical parameters in sections of streams that were more or less homogenous in terms of their morphometric parameters (length, depth, width, slope, flow velocity...).

Material and methods Two methods were used, a biological one consisting of a periodic survey of the macrophyte communities and a physico-chemical monitoring of the water. Floristic data At each sampling site, a river section of 50 m was chosen. A semi-quantitative inventory using cover percentage of abundance-dominance (Braun-Blanquet, 1964) was carried out. The botanical survey was conducted during the growing season in 1993, 1994 and 1995. The nomenclature has followed the literature for the bryophytes (Smith, 1992) and for vascular plants (Lambinon et al., 1992). To avoid identification errors, Sphagnum and filamentous algae were not designated to species. Physico-chemical data Water samples were collected every three months from January 1993 to December 1995. Seven physicochemical variables were analyzed: pH, conductivity, nutrients (PO4 3− , NH4 + by spectrophotometry), NO3 − (ion chromatography), ANC ‘Acid Neutralising Capacity’ (Gran’s titration) and total aluminium (ICP after acidification with HNO3 ). Statistical procedures The floristic data were analyzed by a Factorial Correspondence Analysis (FCA). Species and sites were distributed according to their position along the two principal axes. An agglomerative hierarchical cluster analysis (Ward’s method, Pearson squared distance measure) was used to identify physico-chemical groups and to arrange them in a hierarchical system. The results of this cluster analysis were combined with an ordination by a Principal Component Analysis (PCA). PCA was used to derive an ordination of the 7 selected physicochemical variables. The data matrix X represents the mean value of physico-chemical parameters on 42

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Figure 1. FCA ordination diagram of the Northern Vosges streams data. Species points on the edge of the diagram are rare species, whereas species at the centre may either be unimodal with optima at the centre or bimodal.

sites. The individual principal axes provide separate ordination of the sampling sites. The assessment of the relationship between the macrophyte species and the physico-chemical variables was undertaken by calculating correlation coefficients (Student tests).

Results Floristic composition The FCA, carried out from the data matrix species × sites, showed an increasing gradient of acidification and a decreasing gradient of eutrophication. The first axis, having an eigenvalue of 0.19, was characterized by species typical of acidified and oligotrophic waters such as Sphagnum sp. and Potamogeton polygonifolius on the left, and species typical of neutral and eutrophic waters such as Callitriche obtusangula, Amblystegium riparium or Fissidens crassipes and Vaucheria sp. on the right. The composition of each aquatic macrophyte unit confirmed the floristic communities, previously defined by Muller (1990) and Thiébaut & Muller (1996). Four plant communities, named A–D, were determined (Figure 1).

Community A was characterized by a vascular plant Potamogeton polygonifolius, often associated with Glyceria fluitans and Scapania undulata in spring sites. This floristic group was very heterogenous. Bryophyte species such as Chiloscyphus polyanthos, Sphagnum sp., Dicranella palustris and the algae Batrachospermum sp. had a narrow distribution in this group, whereas Scapania undulata was a wide distributed species. Community B was defined by the appearance of new vascular plants such as Callitriche species (C. platycarpa, C. stagnalis and C. hamulata) and Ranunculus peltatus in upstream sites. Bryophyte species such as Scapania undulata, Chiloscyphus polyanthos were also found, when the habitat conditions (presence of rocks, no turbidity...) allowed their establishment. Community C was mainly determined by the disappearance of Potamogeton polygonifolius and by the appearance of Elodea species (Elodea canadensis, E. nuttallii). Rare and protected species in this area, Oenanthe fluviatilis, Potamogeton alpinus and Myriophyllum alterniflorum, were found in this group. Ranunculus peltatus and Callitriche species were well developed in these downstream sites. Community D was characterized by the appearance of Callitriche obtusangula. Filamentous algae

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Figure 2. PCA- ordination diagram on the two principal components. Table 1. Characteristics of chemical groups identified by Hierarchical Cluster Analysis Group I

Group II

Group III

Group IV

Group V

Number of sites

1

9

17

11

4

pH Conductivity µS/cm ANC µeq/l Al µg/l P-PO4 3− µg/l N-NH4 + µg/l

4.4 55 −41 510 16 37

5.7 52 69 165 13 35

6.5 53 175 63 34 54

7.0 72 350 79 63 95

7.0 94 509 56 179 218

such as Vaucheria sp., bryophyte species such as Fissidens crassipes and Amblystegium riparium were often associated with Callitriche species, with Ranunculus peltatus and with Elodea nuttallii. Aquatic weeds such as Vaucheria sp. or Callitriche obtusangula were abundant in these downstream sites. Physico-chemical composition of streams The PCA was carried out on the physico-chemical data × sampling sites (Figure 2). The first axis of the PCA, defined principally by pH (r = −0.80), ANC (r = −0.92), conductivity (r = −0.88), ammonianitrogen (r = −0.82), phosphorus (r = −0.82) and to a lesser extent nitrate (r = −0.69), explains 60.4% of the physico-chemical variability. The second axis of the PCA is correlated with aluminium (r = −0.83) and explains 19.8% of the physico-chemical variance.

Five groups were identified by Hierarchical Cluster Analysis (Table 1). The group I represents an acidified, un-buffered, oligotrophic stream with high aluminium levels, whereas the group II was less acidified. In the group III, waters were more buffered than in the first two groups. The nutrient levels slightly increased whereas the aluminium load decreased in the group III. The first three weakly mineralized groups were characterized by an oligo-mesotrophic level, whereas the degree of acidification decreased. The group IV and V represent neutral sites, well buffered and more mineralized than other groups. The main difference between the group IV and the group V was the high nutrient levels in the last group. This cluster method separated upstream sites (group I) and downstream sites (group V). The streams were subjected upstream to acidification (low ANC, high aluminium load, acidic pH) in the groups I and

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Figure 3. Relationships between PCA and FCA axes.

II and downstream to eutrophication (high nutrient levels) in groups IV and V. The group III sites were generally not sensitive to acidification or to eutrophication. They were buffered, weakly acidified and had moderate nutrient concentrations. Relationships between macrophyte species and physico-chemical composition of the water The FCA confirmed the ecological gradient suggested by the PCA. Aquatic macrophytes were distributed along an upstream to downstream zonation, which was characterized by an increase in eutrophication and a decrease in acidification of the water in the streams. Relationships between the chemical data and the flora were tested (Figure 3). A significant negative correlation between axis 1 of the PCA and of the FCA (Student test R 2 = −0.49, p < 0.01) and between axis 2 of the PCA and of the FCA (Student test R 2 = −0.36, p < 0.02) was established.

Discussion The A plant community corresponded to chemical group I, II and to a lesser extent to group III and IV. This heterogeneity reflected the variability of the physico-chemical conditions in which Potamogeton polygonifolius can be developed and the variability of the morphometric conditions (Table 2). Chemical group I (site 1), which is strongly acidified (pH = 4.4) and has a high aluminium load ([Al]= 510 µg/l), was mapped as A for vegetation composition (no plants apart from Scapania undulata). Scapania undulata, the only species present in the most acidified upstream

sites (sites 1, 2, 5, 6, 7) has an exceptionally high tolerance to acidity and toxic metal levels in North America (Stephenson et al., 1995), in Europe (Tremp & Kohler, 1995) and Japan (Satake et al., 1989). The natural acidified sites near peat bogs (group II: sites 3, 4, 8, 9) were colonized by Potamogeton polygonifolius and to a lesser extent by Sphagnum sp. The upstream sites belonging to group III (10, 13, 16, 17, 18) and to group IV (site 23) were mapped as A because of the presence of Potamogeton polygonifolius and the absence of Callitriche species and Ranunculus peltatus. These non acidified upstream sites could be considered as the reference A aquatic plant community. The relative rarity of bryophyte species could be explained by the presence of sand in the stream bed in the upper catchment area and the lack of rocks (Stephenson et al., 1995). The B plant community corresponded generally to group III. Bryophytes were found, when the habitat conditions allowed their establishment. Site 11, classified in group II and not in group III, was mapped as B because of the presence of Ranunculus peltatus and Callitriche species. Located downstream of a peat bog, it was a site sensitive to acidification, in which Ranunculus peltatus was present but not abundant. Tremp & Kohler (1991) have experimentally shown that Ranunculus peltatus is sensitive to acid pH. The absence of Callitriche species (C. platycarpa, C. stagnalis, C. hamulata) and Ranunculus peltatus from spring sites could be explained by a proton sensitivity or by a too low bicarbonate concentration (low ANC). ANC can be a limiting factor in a poorly buffered water for aquatic vegetation (Roelofs et al., 1984; Arts et al., 1990).

22 Table 2. Synoptic table of communities A to D based on frequency of species and physical-chemical characteristic Plant community number of sites

A 15

B 10

C 10

D 7

Potamogeton polygonifolius Batrachospermum sp. Scapania undulata Glyceria fluitans Sparganium emersum Chiloscyphus polyanthos Rhynchostegium riparioides Fontinalis antipyretica Callitriche hamulata Callitriche platycarpa Callitriche stagnalis Lemna minor Ranunculus peltatus Berula erecta Potamogeton crispus Myriophyllum alterniflorum Potamogeton alpinus Potamogeton variifolius Elodea canadensis Oenanthe fluviatilis Potamogeton berchtoldii Elodea nuttallii Vaucheria sp. Amblystegium riparium Callitriche obtusangula Fissidens crassipes pH conductivity (µS/cm) ANC (µeq/l) [N-NH+ 4 ] µg/l [P-PO3− 4 ] µg/l [N-NO− 3 ] mg/l Total aluminium (µg/l)

IV(2) I (+) III (+) IV(2) I(+) I(+)

V(1) I(+) IV (+) V(1) III(1) III (+) I (+) II (+) III(1) III(2) IV(+) II(+) II(1) II(1) . . . . . . . . . . . . 6.4 (0.2) 50 (6) 150 (44) 49(14) 22 (11) 0.3 (0.1) 66 (33)

. . II (+) V(+) IV(1) II +) II(+) III (1) V(1) III(2) IV(+) III (+) II(2) I(1) I(1) II(+) I(+) I(+) III(3) I(2) I(2) I(2) I(+) I(+) . . 6.9 (0.2) 69 (10) 323(90) 86 (35) 53 (19) 0.4 (0.1) 49 (12)

. . I (+) V(+) III(1) III (+) III (+) III (1) V(2) II(1) III(+) IV(+) II(3) I(2) . . . . I(1) I(+) I(+) III(3) I (1) IV(+) V(3) IV (+) 7.0 (0.2) 85 (16) 412 (139) 170 (109) 139 (46) 0.8 (0.3) 95 (35)

. . . . . . . . . . . . . . . . . . 5.8 (0,5) 56 (6) 82 (68) 43 (13) 20 (26) 0.4 (0.2) 154 (109)

(V: 80–100%; IV: 60–80%; III: 40–60%; II: 20–40%; I: 0–20%). In brackets, the mean coefficient of abundance -dominance and standard deviation of chemical variables.

The C plant community was usually associated with group IV. The site 20 classified in group III, was mapped as C (absence of Potamogeton polygonifolius). The large development of Callitriche species could be attributed to the high phosphorus level ([PPO4 3− ] = 100 µg/l). Phosphorus is the main limiting factor for aquatic plants (Lee, 1973). This increase in the phosphorus level was due to the domestic sewage of a village. This upstream site was weakly mineralized (conductivity = 64 µS/cm). This weak

mineralisation explains the classification in chemical group III rather than in group IV. Rare and threatened species were essentially found in this C community, in which there are no limiting chemical factors (high phosphorus and bicarbonate). The D plant community corresponded to group V. Sites 30 and 31, mapped as D, were classified in group IV although they were as rich in nutrients as the sites of group V. The regrouping of these sites in group IV can be explained in the same way as above. They con-

23 tained high aluminium and nutrient loads. The high aluminium load in disturbed sites (sites 30, 31) was responsible for the increase in the mean aluminium value of the D community (Table 2). The high level of nutrients can be explained by the installation of a fish farm and domestic effluents upstream of these sites. The role of fish farms and domestic sewage in the enrichment of water nutrient content is clearly established in the literature (Trémolières et al., 1994). The bryophytes Fissidens crassipes and Amblystegium riparium, found in nutrient rich waters, express the deterioration of the water quality (Haury & Muller, 1991). Species such as Callitriche obtusangula and Amblystegium riparium are found in eutrophic waters in weakly mineralized waters, whereas they appear in mesotrophic waters in mineralized waters (Carbiener et al., 1990; Robach et al., 1996). Two hypotheses could be proposed to explain the difference of ecological niche for Amblystegium riparium and Callitriche obtusangula in these two types of environment: a more efficient absorption of phosphorus by plants in alkaline waters, or the requirement of a higher phosphorus concentration in calcium poor waters (Robach et al., 1996). The diversity and the abundance of aquatic macrophytes rose along an increasing gradient of nutrient and mineral loading and a decreasing sequence of proton and aluminium load. A scale based on the succession of macrophyte communities, A–D, along an upstream to downstream zonation, reflects the degree of increasing eutrophication and of decreasing acidification in streams. The upstream A and B plant communities were developed in acidified waters, whereas the downstream C and D plant communities were found in non acidified waters. The main difference between the A and B communities was the degree of acidification (acidified for A, weakly acidified for B), whereas between the C and D communities it was the nutrient level (mesotrophic for C, eutrophic for D). For 65% of the sites, the classification according to the type of plant community corresponded to the chemical composition of the water. The relationships between the chemical data and the flora were significant but weak (Figure 3). The few floristic sites misclassified in their chemical group corresponded to highly disturbed sites. Acidification and eutrophication were responsible for a disruption in the functioning of the ecosystem. Chemical analyses only represent one point in time and space. Aquatic macrophyte surveys, on the other hand, reflect the inherent temporal variability. Macrophytes also have

the advantage that they exist throughout the season and respond to disturbances. The spatial integration of eutrophication and acidification processes at the basin scale as well as the links between these two types of human disturbances is reflected by the composition and the structure of aquatic macrophyte communities. One example was given by the analysis of the sites 30 and 31. These upstream weakly acidified and weakly buffered sites with high aluminium load contained high nutrient levels (sites 30, 31: [P-PO4 3− ]: 130 µg/l; [N-NH4+ ]: 115 µg/l). They were subjected to acidification (relatively high aluminium load) and to eutrophication. The impacts of these perturbations were superimposed. This situation lead to a decrease in the aquatic vascular plant richness: the absence of oligo-acidophilous species such as Potamogeton polygonifolius and of meso-neutrophilous species such as Elodea sp., Myriophyllum alterniflorum, Ranunculus peltatus. Tolerant pollutant species such as Callitriche obtusangula, C. platycarpa and Amblystegium riparium were abundant in these eutrophicated sites. The composition of the aquatic communities became impoverished. However, the biomass was important.

Conclusions The Northern Vosges streams are subjected to acidification upstream and to eutrophication downstream. A scale of bio-indication of eutrophication and acidification by aquatic macrophyte communities was established. Upstream, bryophytes (Scapania undulata, or Sphagnum sp.) and Potamogeton polygonifolius were found in oligotrophic, acidified streams, whereas downstream, Callitriche obtusangula, filamentous algae such as Vaucheria sp. and bryophyte species such as Amblystegium riparium and Fissidens crassipes were found in the most eutrophic sites. Uncertainties remain, particularly in our understanding of the responses of aquatic plants to eutrophication and acidification. The biological impact of interactions between acidification and eutrophication on aquatic plants should also be researched. The reconstruction of changes in communities should identify the initial floristic communities present in these weakly mineralized streams. A comparison with others weakly mineralized areas such as Limousin or such as Brittany should be done to discuss the relative effects of acidification and eutrophication. Only by examining a complex problem, such as acidification and eutrophication, using many different approaches

24 and perspectives can we develop a comprehensive view of the responses of aquatic macrophyte communities to stress.

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