Bryophyte Fontinalis Antipyretica Research Articles

Interest of a multispecies approach in active biomonitoring: Application in the Meuse watershed

A biomonitoring approach based on a single model species cannot be representative of the contaminations impacts on the ecosystem overall. As part of the Interreg DIADeM program (“Development of an integrated approach for the diagnosis of the water quality of the River Meuse”), a study was conducted to establish the proof of concept that the use of a multispecies active biomonitoring approach improves diagnostic of aquatic systems. The complementarity of the biomarker responses was tested in four model species belonging to various ecological compartments: the bryophyte Fontinalis antipyretica, the bivalve Dreissena polymorpha, the amphipod Gammarus fossarum and the fish Gasterosteus aculeatus. The species have been caged upstream and downstream from five wastewater treatment plants (WWTPs) in the Meuse watershed. After the exposure, a battery of biomarkers was measured and results were compiled in an Integrated Biomarker Response (IBR) for each species. A multispecies IBR value was then proposed to assess the quality of the receiving environment upstream the WWTPs.The effluent toxicity was variable according to the caged species and the WWTP. However, the calculated IBR were high for all species and upstream sites, suggesting that the water quality was already downgraded upstream the WWTP. This contamination of the receiving environment was confirmed by the multispecies IBR which has allowed to rank the rivers from the less to the most contaminated. This study has demonstrated the interest of the IBR in the assessment of biological impacts of a point-source contamination (WWTP effluent) but also of the receiving environment, thanks to the use of independent references. Moreover, this study has highlighted the complementarity between the different species and has emphasized the interest of this multispecies approach to consider the variability of the species exposition pathway and sensibility as well as the mechanism of contaminants toxicity in the final diagnosis.

All for One: The Role of Colony Morphology in Bryophyte Desiccation Tolerance.

In the last decade, several works showed that even bryophytes from aquatic environments, if slowly dehydrated, can cope with desiccation in a response like the one from desert bryophytes. This led to the hypothesis that, if bryophytes from contrasting habitats can have similar responses, desiccation tolerance (DT) is partially inductive and not only constitutive as previously proposed and, therefore, colony morphology might be the key trait responsible for controlling dehydration rate essential for DT induction. Morphology and life form may be determinant traits in the adaptation of bryophytes to habitats with different water availabilities and corresponding predicted levels in the DT inducibility spectrum. Bryophytes from habitats with different water availabilities were dried as individual shoots and as a colony. The bryophyte Fontinalis antipyretica is fully aquatic presenting a streamer life form, while the three terrestrial species present turf life form with different sizes and degrees of space between individuals in the colony. Two species were collected under trees with moist soil presenting short turf (Tortella tortuosa) and long turf (Campylopus pyriformis) life forms. Another species was completely exposed to sun light with no surrounding trees and a tall turf life form (Pleurochaete squarrosa). We used chlorophyll a fluorescence parameter Fv/Fm (maximum potential quantum efficiency of Photosystem II) as a proxy to photosynthetic fitness throughout the contrasting dehydration rates (fast and slow). These bryophytes with different life forms were submitted to an X-ray computed microtomography (µ-XCT) to assess the three-dimensional inner structure and visualize locations for water storage. Shoots dried slow or fast according to the dehydration they were exposed to, as expected, but they presented similar dehydration rates across different species. However, the aquatic moss F. antipyretica, was unable to recover from fast drying, and after 24 h the recovery following slow drying was lower than the other species. The other three species presented full recovery after 24 h, either at the individual or colony level, and either from slow or fast drying. The only exception was the colonies of Campylopus pyriformis following fast drying that presented a slightly lower recovery, probably due to a looser colony structure.

Influence of dehydration rate on cell sucrose and water relations parameters in an inducible desiccation tolerant aquatic bryophyte

During desiccation, plant cells are subjected to very low water potentials. Osmoregulation through increase of soluble materials (e.g. soluble sugars, compatible inorganic ions) is a response to the decreasing turgor pressure in the cells. In bryophytes, sucrose acts as an osmolyte and also stabilizing membranes and proteins through vitrification. We used psychrometric measurements in the aquatic bryophyte Fontinalis antipyretica Hedw. to construct pressure–volume isotherms and determine the water relations parameters under fast and slow dehydration rates. Sucrose was also quantified. The starting hypothesis was that a slow dehydration rate would increase sucrose concentration, thereby decreasing the osmotic potential at turgor loss point, and would also increase cell wall elasticity, postponing turgor loss and allowing time for induction of molecular and structural acclimation mechanisms. In fact, we found that slowly dehydrated samples presented more elastic cell walls, allowing cells to shrink and maintain turgor, helping to better preserve their metabolic functions and therefore to induce desiccation tolerance (DT). On the other hand, in fast dehydrated samples the osmotic potential at turgor loss point decreased, indicating the activity of osmoregulation processes, possibly connected to the increase observed in sucrose content. Upon rehydration, fast dried samples lost 50% of the sucrose through leakage due to cell membrane rupture, while slow dehydrated leaves maintained their sucrose content constant. DT appears to be achieved through slow dehydration, meaning that a high sucrose content alone does not contribute to DT establishment. Moreover, in natural conditions external water can be maintained at very high values due to the life form of F. antipyretica, which grows in long and compact floating stems in streams, allowing a slow dehydration rate required for induction of other DT mechanisms.

Differential proteomics of dehydration and rehydration in bryophytes: evidence towards a common desiccation tolerance mechanism

All bryophytes evolved desiccation tolerance (DT) mechanisms during the invasion of terrestrial habitats by early land plants. Are these DT mechanisms still present in bryophytes that colonize aquatic habitats? The aquatic bryophyte Fontinalis antipyretica Hedw. was subjected to two drying regimes and alterations in protein profiles and sucrose accumulation during dehydration and rehydration were investigated. Results show that during fast dehydration, there is very little variation in protein profiles, and upon rehydration proteins are leaked. On the other hand, slow dehydration induces changes in both dehydration and rehydration protein profiles, being similar to the protein profiles displayed by the terrestrial bryophytes Physcomitrella patens (Hedw.) Bruch and Schimp. and, to what is comparable with Syntrichia ruralis (Hedw.) F. Weber and D. Mohr. During dehydration there was a reduction in proteins associated with photosynthesis and the cytoskeleton, and an associated accumulation of proteins involved in sugar metabolism and plant defence mechanisms. Upon rehydration, protein accumulation patterns return to control values for both photosynthesis and cytoskeleton whereas proteins associated with sugar metabolism and defence proteins remain high. The current results suggest that bryophytes from different ecological adaptations may share common DT mechanisms.

Accumulation of uranium by aquatic plants in field conditions: Prospects for phytoremediation

A study was undertaken to determine Uranium concentrations in water and aquatic plants in the uraniferous region of Beiras, Central Portugal. Samples were collected from running water (n=200) at places where aquatic species were observed. Plant samples were collected from 28 species of submerged, free-floating and rooted emergent plants including 2 bryophytes and 1 pteridophyte. Uranium concentrations in surface waters ranged from 0.23 to 1217μgL−1. The aquatic plant species studied, including several previously untested species, exhibited the ability to accumulate U in concentrations many times that of the ambient water. In general submerged plants exhibited higher U content followed by rooted emergent and free floating species. The highest U concentrations were observed in the bryophyte Fontinalis antipyretica (up to 4979mgkg−1) followed by Callitriche stagnalis (1963mgkg−1), Callitriche hamulata (379mgkg−1), Ranunculus peltatus subsp. saniculifolius (243mgkg−1), Callitriche lusitanica (218mgkg−1), and Ranunculus trichophyllus (65.8mgkg−1). In two out of three rooted emergent species U seemed to be preferentially partitioned in rhizome/roots with highest rhizome U content recorded in Typha latifolia (380mgkg−1). Among the free-floating species, the highest U content (42.5mgkg−1) was seen in Lemna minor. The bryophyte F. antipyretica and Callitrichaceae members seem to be promising candidates for the development of phytofiltration methodologies based on U accumulation, abundance and biomass production.

Physiological Effects of Exposure to Arsenic, Mercury, Antimony and Selenium in the Aquatic Moss Fontinalis antipyretica Hedw.

Laboratory experiments were carried out to determine the effects of exposure to different concentrations of As, Hg, Sb and Se on photosynthetic and respiratory rates and on photosynthetic efficiency in the aquatic bryophyte Fontinalis antipyretica Hedw. Specimens of the moss, collected from a clean site, were incubated in solutions of As, Hg, Sb and Se (at concentrations ranging from 0.1 μg l−1 to 10,000 μg l−1) for up to 22 days. The photosynthetic and respiratory rates were then determined by the light/dark bottle technique, and the photosynthetic efficiency was measured by the saturation pulse method. Although different responses were observed in relation to the concentration of the elements, clear responses in net photosynthesis and photosynthetic efficiency were generally only observed in the moss exposed to the highest concentrations of these elements in solution. Mercury was apparently the most toxic of the elements studied. Net photosynthesis and photosynthetic efficiency were also related to tissue concentrations of these elements in the moss. Despite the higher toxicity of Hg, this element can be accumulated at high concentrations in moss, probably at extracellular sites. For Sb, the same tissue concentration had very different physiological effects depending on the initial concentration to which the moss was exposed in solution. Temporal trends in chlorophyll fluorescence were more stable than trends in net photosynthesis. The respiratory rate was very variable and was not clearly related to the concentration of elements in solution or in moss tissues.

β-N-Methylamino-L-alanine exposure alters defense against oxidative stress in aquatic plants Lomariopsis lineata, Fontinalis antipyretica, Riccia fluitans and Taxiphyllum barbieri

Four different aquatic plants, the Pteridophyte Lomariopsis lineata and the Bryophytes Fontinalis antipyretica, Riccia fluitans and Taxiphyllum barbieri, were tested for their capacity to absorb the neurotoxin β-N-Methylamino-l-alanine (BMAA) from water and thus their possible applicability in a “Green Liver System”. After exposure to 10 and 100μgL−1 BMAA for 1, 3, 7 and 14 days exposure concentration of medium and tissue were analyzed by LC-MS/MS. The amount removed by the plants within only 1 day was equal to the biological degradation of 14 days. Comparing the “BMAA-removal” capacity of the 4 tested aquatic plants R. fluitans, L. lineata and T. barbieri turned out to be most effective in cleaning the water from this cyanobacterial toxin by up to 97% within 14 days.Activity of the antioxidant enzymes peroxidase (POD) and catalase (CAT), as well as biotransformation enzyme glutathione S-transferase (GST) was compared between exposed and control plants to determine possible harmful effects induced by BMAA. Whereas the Bryophytes displayed increased POD activity and subsequent adaptation when exposed to the lower concentration, as well as partly inhibited antioxidant response at the higher applied BMAA concentration, the Pteridophyte L. lineata reacted with increased POD activity during the whole experiment and increased GST activity after longer exposure for 14 days.To give a recommendation of the suitability of an aquatic plant to be used for sustainable phytoremediation of contaminated water, testing of removal capacity of specific contaminants as well as studying general physiological parameters giving hint on survivability in such environments has to be combined.

Modelling of lead removal by an aquatic moss

Aquatic bryophytes are frequently used as biomonitors for trace metals in aquatic ecosystems. Nevertheless, their special characteristics also allow using them as biosorbents to clean industrial wastewaters. As biosorption is a low cost and effective method for treating metal-bearing wastewaters, understanding the process kinetics is relevant for design purposes. In this study, the ability of the aquatic bryophyte Fontinalis antipyretica to remove lead from simulated wastewaters was evaluated. Three kinetic models (pseudo-first order, pseudo-second order and Elovich) were fitted to the experimental data and compared by the F-test. Previously, the effect on biosorption of parameters such as the initial solution pH, contact time and initial metal ion concentration was investigated. The initial pH of the solution was found to have an optimum value is in the range 4.0-6.0. The equilibrium sorption capacity of lead by Fontinalis antipyretica increased with the initial metal concentration. For an initial metal concentration of 10 mg L⁻¹, the uptake capacity at equilibrium was 4.8 mg g⁻¹. Nevertheless, when the initial concentration increased up to 100 mg L⁻¹, the uptake of lead was 10 times higher. The pseudo-second order biosorption kinetic model provided the better correlation with the experimental data (R²=1.00). The applicability of the Langmuir and Freundlich adsorption isotherms to the present system was also assessed. The maximum lead sorption capacity by Fontinalis antipyretica was 68 mg g⁻¹.

Removal of Pb(II) from wastewaters by Fontinalis antipyretica biomass: Experimental study and modelling

Aquatic bryophytes are frequently used as biomonitors for trace metals in aquatic ecosystems. Nevertheless, their special characteristics also allow using them as biosorbents to clean industrial wastewaters. As biosorption is a low-cost and effective method for treating metal-bearing wastewaters, understanding the process kinetics is relevant for design purposes. In this study, the ability of the aquatic bryophyte Fontinalis antipyretica to remove lead from simulated wastewaters was evaluated. Previously, the effect on biosorption of parameters such as the initial solution pH, contact time and initial metal ion concentration was investigated. The biosorption process is highly pH-dependent, and the favorable pH for maximum Pb2+ adsorption on the aquatic moss was found to have an optimum value in the range 4.0–6.0. The equilibrium sorption capacity of lead by Fontinalis antipyretica increased with the initial metal concentration. For an initial metal concentration of 10 mg L−1, the uptake capacity at equilibrium was 4.8 mg g−1. Nevertheless, when the initial concentration increased up to 100 mg L−1, the uptake of lead was 10 times higher. Maximum adsorption rates were achieved almost in the first 10–20 min of contact, and a further increase in the contact time had a negligible effect on the Pb2+ sorption. Three kinetic models (pseudo-first order, pseudo-second order and Elovich) were fitted to the experimental data and compared by the F-test. The pseudo-second order biosorption kinetic model provided the better correlation with the experimental data (R 2 = 1.00). Probably the chemisorption is the rate-limiting step and the biosorption mechanism follows a pseudo-second order reaction model. The applicability of the Langmuir and Freundlich adsorption isotherms to the present system was also assessed. The equilibrium experimental data of lead sorption was very well described by the Langmuir model with R 2 values exceeding 0.993. The maximum lead sorption capacity by Fontinalis antipyretica attained a value of 68 mg of lead ions per gram of aquatic moss.

Induction of oxidative stress biomarkers associated with heavy metal stress in Fontinalis antipyretica Hedw.

The aquatic bryophyte Fontinalis antipyretica Hedw. was exposed to different heavy metals (Cd, Cu, Pb, Zn) at 0, 0.1, 1, 10, 100 and 1000 μM concentrations. Lipid peroxidation and anti-oxidative responses in apices were evaluated after 2 and 7 days of exposure. Most treated plants showed increased levels of lipid peroxidation and enzyme activities (superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GRD), ascorbate (APX) and guaiacol (GPX) peroxidases, compared to control (untreated) plants. Most of our results suggest that plants possess antioxidant enzymes which operates either unspecifically (SOD and APX) or depending on the nature of the contamination (CAT, GPX, GRD). However, for the highest metal concentration tested, these cellular defence systems seemed overwhelmed since MDA levels increased significantly. These results confirm the important role of antioxidant defences in the mechanisms of plant-resistance to heavy metal stress. Moreover, two types of concentration–response trends were identified: clear monotonous relationships were often found for SOD and MDA while bell-shaped trends were usually observed for APX, GPX and GRD. These tendencies are discussed with emphasis on possible use of these responses as plant biomarkers for freshwater biomonitoring surveys.

Self-organizing feature map (neural networks) as a tool in classification of the relations between chemical composition of aquatic bryophytes and types of streambeds in the Tatra national park in Poland

Concentrations of the elements Al, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Ni, Pb and Zn were measured in the aquatic bryophytes Fontinalis antipyretica, Platyhypnidium riparioides and Scapania undulata. These bryophytes were sampled from streams flowing through granites/gneisses, limestones/dolomites and sandstones in the Tatra national park in Poland. The Self-organizing feature map (SOFM) or Kohonen network was used to classify the bryophytes according to the concentrations of the elements. This method was verified using principal component analysis (PCA) to check whether this well-known technique would give similar results. Both the self-organizing map and ordination by PCA yielded distinct groups of aquatic bryophytes growing in streams flowing through different types of rock, groups which differed significantly in the concentrations of certain elements. Bryophytes from granites/gneisses were distinguished by higher concentrations of Cd and Pb, while those from sandstones had a higher concentration of Cr and those from limestones/dolomites had higher concentrations of Ca and Mg. The SOFM and PCA ordinations thus yield identical classifications of bryophytes from the Tatra mountains streams.

Determination of Florfenicol in Freshwater, Sediments and Bryophyte Fontinalis antipyretica by HPLC with Fluorescence Detection

Novel procedures for the determination of florfenicol in freshwater, sediments and bryophyte Fontinalis antipyretica, using reversed-phase high-performance liquid chromatography are described. Liquid chromatography was performed on a 5 µm PuroSpher RP-18E® column using methanol and 0.05 M phosphate buffer (18/82 v/v, pH 7.3) as mobile phase (0.8 ml min−1) and fluorescence detection (excitation wavelength 265 nm and emission wavelength 295 nm). Florfenicol was determined in centrifuged freshwater samples. Florfenicol was extracted from sediments and bryophytes samples by using a solid-liquid extraction step followed by a solid phase extraction step. Linearity was confirmed over the concentration range 25–1000 ng mL−1 water and 50-1000 ng g−1 sediment or bryophyte. Limits of detection and quantitation were 8 and 25 ng mL−1 water and 17 and 50 ng g−1 sediment or bryophyte respectively. Mean extraction recoveries of florfenicol from sediments and bryophyte were from 85.9 to 109.1%.

Modelling the extra and intracellular uptake and discharge of heavy metals in Fontinalis antipyretica transplanted along a heavy metal and pH contamination gradient

Samples of the aquatic bryophyte Fontinalis antipyretica Hedw. were transplanted to different sites with the aim of characterizing the kinetics of the uptake and discharge of heavy metals in the extra and intracellular compartments. The accumulation of metals in extracellular compartments, characterized by an initial rapid accumulation, then a gradual slowing down over time, fitted perfectly to a Michaelis–Menten model. The discharge of metals from the same compartment followed an inverse linear model or an inverse Michaelis–Menten model, depending on the metal. In intracellular sites both uptake and discharge occurred more slowly and progressively, following a linear model. We also observed that the acidity of the environment greatly affected metal accumulation in extracellular sites, even when the metals were present at relatively high concentrations, whereas the uptake of metals within cells was much less affected by pH.

Ion-paired solid phase extraction as a sample preparation strategy for the high-performance liquid chromatographic determination of oxytetracycline in the bryophyte Fontinalis antipyretica

Oxytetracycline (OTC) is one of the major antibacterial agent used in freshwater fish farming. Because of its rapid decomposition rate in sediments, it is difficult to monitor OTC in the freshwater environment. Fontinalis antipyretica is known for its bioaccumulation properties. Determining OTC concentration in F. antipyretica by HPLC was a real challenge because pigments coextracted with OTC. Ion-pairing was used in the clean-up procedure to improve the selectivity of the C 18 solid phase extraction. Octanesulfonic acid was used as counter-ion. Tetracycline was used as internal standard. The linearity ranged between 100 and 1000 ng/g and limits of detection and quantitation were 30 and 100 ng/g, respectively. Mean recovery for OTC was 48.2% and the validation procedure demonstrated that the method was selective, reliable and precise enough to allow environmental monitoring. This method was applied to a 25 days experimental study showing the bioaccumulation of OTC by the bryophyte F. antipyretica.

Determination of oxolinic acid in the bryophyte Fontinalis antipyretica by liquid chromatography with fluorescence detection

A large amount of oxolinic acid administered in freshwater fish farms reaches the environment. In order to allow environmental monitoring, an HPLC method to determine oxolinic acid in the bryophyte Fontinalis antipyretica was developed. Nalidixic acid was used as an internal standard. Oxolinic and nalidixic acids were extracted by cracking the bryophytes in liquid nitrogen with 0.1 M acid oxalic solution in ethyl acetate and a liquid–liquid clean up procedure was then performed. Mobile phase was a 0.02 M orthophosphoric acid aqueous solution–acetonitrile mixture (70:30, v/v). The stationary phase was 5 μm PuroSpher RP18e and quinolones were detected by fluorescence. The linearity, accuracy and precision of this method were demonstrated by a validation assay. The limits of detection and quantitation were 1 and 10 ng/g respectively. The linearity range was 10 to 500 ng/g. This method was applied to a 25 days experimental study performed with the bryophyte Fontinalis antipyretica.

Biomonitoring of sporadic acidification of rivers on the basis of release of preloaded cadmium from the aquatic bryophyte Fontinalis antipyretica Hedw.

A technique is proposed for biomonitoring of sporadic acidification events in rivers. Individuals of the bioindicator species are pre-incubated with a chemical marker, then transplanted to the test location for the period of interest, then analysed for marker content; acidification events are inferred on the basis of the degree of reduction in marker concentration. To assess the validity of the proposed technique, we performed laboratory trials with the aquatic bryophyte Fontinalis antipyretica Hedw. as bioindicator species, and cadmium (Cd) as marker. The bryophytes were pre-incubated with a Cd solution, obtaining saturation concentrations in the extracellular compartment and near-saturation concentrations in the intracellular compartment. In a first series of experiments, Cd-preloaded bryophyte apices were maintained for 1–30 h in water of different pH; the results clearly indicated that the amount of Cd released is dependent on pH. In a second series of experiments, Cd-preloaded bryophyte apices were maintained for 1–24 h in water with various combinations of pH and aluminium (Al) concentration (Al being a highly toxic element that is typically mobilized in acid waters). In these experiments, pH again had a marked effect on the amount of Cd released, while Al concentration had no consistent effects. To facilitate data analysis, Davidson-type equations were fitted to the results of the second series of experiments, allowing prediction of medium acidity on the basis of Cd concentration remaining in the extracellular and intracellular compartments.

The effect of pH on the kinetics of intra- and extracellular uptake of Al in Fontinalis antipyretica: changes in the cellular contents of K, Mg, and Ca.

The effect of acidity on the accumulation of Al in the aquatic bryophyte Fontinalis antipyretica was studied. The main interest of this study was in characterizing the relationship between the two parameters, as Al is typically mobilized in acidic environments, where it becomes extremely toxic. With this aim, a series of laboratory experiments were carried out where samples of F. antipyretica were held in tanks of water with different concentrations of Al (0.1-3 mg L(-1)) and levels of acidity (pH 3-5. 8). The incubation time varied between 1 and 24 h. In general, the greatest accumulations of both intra- and extracellular Al were found at a pH of 4.4. With the results obtained, the kinetics of both intra- and extracellular Al uptake was characterized, and models constructed for different combinations of Al and acidity. The study was completed by examining the relationship between the pH of the holding water and bioaccumulation of Al and the variation in concentration of cations essential to plant life, which are also indicators of changes in cellular physiology (K, Mg, Ca). In general, losses of these elements were found at intra- and extracellular locations, especially at high pH.

Background concentrations of heavy metals in aquatic bryophytes used for biomonitoring in basaltic areas (a case study from central France)

Studies were made of the aquatic bryophytes Fontinalis antipyretica Hedw., Platyhypnidium rusciforme (Neck.)Fleisch and Chiloscyphus sp. (Hoffm.)Dum. from streams embedded in basaltic rocks (Le Puy, central France). Water from these streams possessed elevated levels of Cu, Zn, Sr, V, Ba, Ni and Co, reflecting the geochemistry of the basalts, a basic type of igneous rocks containing elevated levels of these elements. The concentration of elements in bryophytes is correlated to the chemical composition of water of their sampling sites. Contents of trace elements in plants were higher than background values. The elevated levels of these elements possibly caused disturbances in the ionic equilibrium within the bryophytes. The molar ratio between contents of Ca and Mg in water (from 0.44 to 1) was different from that typical for natural water.

Inertia and Resilience in the Responses of the Aquatic Bryophyte Fontinalis antipyretica Hedw. to Thermal Stress

The physiological responses of the aquatic bryophyte Fontinalis antipyretica Hedw. to high temperatures, ranging from 16 degreesC (control) to 34 degreesC, were investigated experimentally. Plant samples were maintained at the temperature under study for up to 25 days with regular determination of physiological variables (pigment ratio and photosynthetic and respiratory rates). Physiological responses to temperature did not differ significantly between mosses collected from a normal river site and from a river site with abnormally high temperature due to input from a hot spring. Simple curve-fitting procedures and summary statistics analogous to those used in toxicological research were employed to compare responses as revealed by the different physiological variables. In a second series of experiments, the capacity of F. antipyretica to recover from high-temperature stress was investigated by maintaining samples at 30 degreesC for 2, 4, or 10 days, then transferring the samples to normal conditions (16 degreesC) for 40 days. Physiological variables were again monitored at regular intervals throughout both phases of the experiment. In general, good recovery was observed even after exposure to high temperatures for 10 days. The results of these assays allow quantification of the relationship between a pigment ratio and net photosynthesis rate.

The exchange process between river and groundwater on the Central Alsace floodplain (Eastern France)

The recent canalisation (in the nineteen sixties) of the upper Rhine has modified the exchange processes between the river and its groundwater in the floodplain of Alsace. The Rhine seeps through its gravelly bed and in this way feeds the nearby groundwater table by means of the so-called ‘Rhine filtrates’. Using a few groundwater stream examples, this paper presents the characterization and localisation of these infiltrations. The Rhine filtrates are characterized by a high level of chloride and a low level of nitrate, these compounds being hydrological tracers, specific for the Alsatian floodplain (chloride resulting from contamination by the potash mines in the south of Alsace). They are also defined by high levels of phosphate and mercury (very localized injection). Phosphate is responsible for eutrophication which is observable in the appearance of specific aquatic macrophyte communities. Groundwater contamination by mercury is reflected by its accumulation in the bryophyte Fontinalis antipyretica sampled in ground-water streams. Thus aquatic vegetation, and more particularly the distribution of macrophyte communities, is used as an ecological descriptor of the exchange between the Rhine and its groundwater. The maximum injection of Rhine filtrates occurs between two areas of stillwater (hydroelectric dams), where the Rhine dominates its plain and where the substrate is constituted of coarse gravels.