Impacts of hydropower dams operations on plants: A greenhouse experiment on the response of germination and performance and survival of plant seedlings to direct and indirect effects of hydrological alterations resulting from hydropower dam operations

Impacts of hydropower dams operations on plants

A greenhouse experiment on the response of

germination and performance and survival of plant seedlings to direct and indirect effects of hydrological alterations resulting from hydropower dam operations

Guillermo Guindal Estévez

Guillermo Guindal Estévez

Degree Thesis in ecology and environmental sciences 15 ECTS Bachelor’s Level

Report passed: 2 June 2015

Supervisor: María Dolores Bejarano Carrión

Impacts of hydropower dams operations on plants

A greenhouse experiment on the response of germination and

performance and survival of plant seedlings to direct and indirect effects of hydrological alterations resulting from hydropower dam operations

Guillermo Guindal Estévez

Abstract

This work helps increasing our general understanding of how plants behave under altered hydrological conditions which occur along rivers regulated by hydropower dams. Usually, natural-real environments are highly unpredictable. Consequently, research based on field data becomes challenging and results may contain uncertainty. Here, an experimental design in a greenhouse is developed. Several measured attributes of selected plant species related to germinability, performance and survival were used as indicators of the impact of watering treatments which mimic hydrological regime spilled through hydropower dams. Specifically, direct effect of water availability changes, water fluctuation and water flooding, and indirect effect through derived erosion, were tested. Results benefitted from indoors controlled conditions. They showed significant different responses depending on species and hydrological changes. In general, Helianthus annuus was slightly affected. It deal well flooding conditions, and was comparatively more affected by water fluctuation and stress.

Carex and Filipendula species showed the highest sensitivities to flow. They hardly germinated under any water treatment (few germinations under flooding for Carex and few under water fluctuation for Filipendula) and performance was very low for germinates.

Betula pubescens was in between. Contrarily to Helianthus, it was severely affected by flooding, and also for water fluctuation. It survived water stress better than Helianthus, but looked unhealthy. All species seeds but Helianthus were highly eroded. However, erosion resulting from water fluctuation was relatively higher than from prolonged flooding.

Differing responses are the result of morphological and physiological characteristics of the species which enable them to success under certain stressful conditions, such as water scarcity and anoxia. These results objectively inform about tolerance limits of selected species to key hydrological conditions and are useful for riparian areas management and environmental flows designs.

Key words: hydropower, riparian, erosion, Sweden, seed, flow alteration.

Table of contents

1. Introduction ... 1-2

2. Material and methods ... 2-4 2.1. Experiment design………2-3

2.2. Data analysis………3-4

3. Results

4. Discussion ……….10-12

5. Conclusions ... 11-12

6. Acknowledgment ……….12

7. References ... 13-14

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1.Introduction

Stream-flows have an important role in fluvial ecosystems (Walker & Thoms, 1993;

Kingsford, 2000). They affect reproduction, dispersal and distribution, adaptive capacity, performance and ultimately survival of aquatic and riparian species (Poff et al., 1997; Bunn and Arthington, 2002; Arthington et al., 2006). Not only the quality and quantity of water, but also the frequency, duration, timing and rates of flow changes interact in complex ways to regulate geomorphic and ecological processes in rivers (sensu “natural flow regime” by Poff et al., 1997). The magnitude and frequency of high flows facilitate the sediment and biological propagules longitudinal and transversal transport (Leopold et al. 1964; Nilsson et al. 2005), hence determining directly and indirectly through changes in habitats, the composition and relative abundance of species that are present in a stream. The magnitude and frequency of low flows are also key since species adapt their life cycles and develop special behavioral or physiological adaptations that suit them to these harsh conditions (Nilsen et al. 1984).

Tolerances of species to flow conditions often depend on the duration of the specific flow event. For example, prolonged flooding or water stress conditions usually displace less tolerance species (Chapman et al. 1982; Williams and Hynes 1977; Closs and Lake 1996). The timing of flow events is critical ecologically because the life cycles of many species are timed to either avoid or exploit flows of variable magnitudes (Poff et al. 1997). Finally, the rate of change in flow conditions can influence species persistence and coexistence. For example, specific floodwater recession is critical to seedling germination because seedling roots must remain connected to a receding water table as they grow downward (Rood and Mahoney 1990).

Rivers suffer from a number of human impacts which causes a rise of ecological effects that could be not appropriate for aiding various biological communities (Naiman et al. 1993;

Nilsson et al. 2005a; Helfield et al. 2007). Common river impacts are contamination and eutrophication of water, morphological alterations (i.e., fragmentation, channelization and straightening) and water abstraction and flow regime modifications (Maddock 1999; Nilsson et al. 2005b; Bakker et al. 2012). Specifically, dams are major cause of physical and hydrological changes in rivers. They interrupt sediment and water flows from upstream to downstream and also create transversal barriers which unable migration of fauna and flora.

At present, there are over 45000 large dams around the world which retain 15% of the total annual global runoff (Nilsson et al., 2005). Hydrological changes resulting from dams depend on dam and reservoir characteristics and purposes. In Sweden, hydropower represents 47’5%

of the total energy production. Hydropower is considered a renewable, clean energy source which is increasing in the north of Europe (Demirbas, 2007). However, the use of hydropower also creates different troubles to the environment (Millennium Ecosystem Assessment, 2005). Hydrological alterations resulting from hydropower plants operations affect all components (above mentioned) of the flow regime, but it is the frequency and duration of flows what change the most. Downstream and upstream river hydrology is altered due to rapid and significant sub-daily fluctuations in discharge caused either by the turning on or off of hydro-turbines to generate electricity according to variations in the market demand, namely hydropeaking (Moog, O. 1993). This unnatural flashy regime usually lacks of year seasonality. Additionally, bypassed downstream reaches suffer from very low flows or even are totally dry out.

Fortunately, the concern about restoration of deteriorated streams and rivers and their sustainable management has increased during the last decades (Stanford et al. 1995;

Bernhardt et al. 2005; Palmer et al. 2005; Arthington et al. 2006). It is crucial to develop ways to harmonize hydroelectricity production and fluvial ecosystem sustainability.

Implementation of environmental flows (Brisbane Declaration, 2007) in reaches affected by

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hydropeaking are the best tool for preventing them from ecological losses, although there still exists a lack of basic knowledge that supports correct definition of environmental flows in such areas. Specifically, in order to guarantee riparian areas conservation, it is absolutely needed to investigate the potential effects of hydropeaking on riparian communities and identify relationships between hydropeaking and the crucial steps in plants life cycles (i.e., dispersal, establishment and germination, among others) in order to quantify, correlate and predict the impacts of hydropeaking on riparian species recruitment, performance and survival. The riparian areas are key components of fluvial ecosystems as they have multiple functions within them (i.e., fluvial habitats stabilization, hyporheic water filters, flood buffering, and migration corridors, among others). The composition, abundance and distribution of plants are highly determined by the specific hydrological regime influencing the riparian zone where they grow. The broad range of riparian species behavior to stream- flows basically depends on species characteristics (i.e., traits). Assemblages of species growing in specific rivers exhibit morphological, life history and phenological traits that enable them to disperse, survive and reproduce in response to the specific flow components (Mahoney & Rood, 1998a; Karrenberg, Edwards & Kollmann, 2002; Middleton, 2002).

Consequently, the trait composition of riparian areas highly determines how (type and magnitude) stream-flow alterations impact them.

The final goal of this study was to determine thresholds of hydrological alteration which enable simultaneously sufficient hydropower production and good ecological status of riparian areas. To achieve this goal we selected several species and used them as phytometers (i.e. species utilized in a regulated way to indicate the significance of several environmental factors according to Clements and Goldsmith ( 1924) and Dietrich et al.(2013)). We then tested the behavior of the selected species, which exhibit different traits, to simulated changes of flows (water stress, water fluctuations and flooding) in a greenhouse. And finally records of germination, performance and survival of these phytometers in each of the flow condiction have been collected and analysed statistically.

2.Material and Methods

2.1 Experiment design

We selected five plant species: Betula pubescens EHRH. (European white birch), Filipendula ulmaria (L.) MAXIM. (Meadowsweet), Carex acuta L. (Acute sedge), Carex flava L. (Large yellow sedge) and Helianthus annuus L. (Sunflower). H. annuus was the only species which is not naturally found along riparian zones. It was selected due to its special features which enable easy adaptations to different habitats, such as large seeds and endosperm and foliage able to adapt to the water availability in the environment (Violle et al, 2009). Remaining species usually grow close to streams but differ in their preferred locations (i.e., distances and elevations to the water edge) according to their water requirements and resistance to prolonged flooding. All species are herbaceous except for B. pubescens, which is a tree. We carried out two different greenhouse experiments to test the effect on seeds germination, and seedlings performance and survival of: i) several most common hydrological alterations of regulated Swedish rivers, and ii) erosion derived from these hydrological alterations. We used cassettes for growing the seeds of the species. Before sowing, seeds were cold stratified inside female socks and humid sand in a fridge during 10 days. The study was carried out in the Wallenberg greenhouse facilities from the Swedish University of Agricultural Sciences (SLU) in Umeå (Sweden). Hydrological variables were tested from 30 March to 10 May, whereas erosion tests were carried from 30 March to 10 April, in 2015. The humidity of the room was between 50% and 60%. The soil of the pots was composed of a mixture of 60% organic matter, 30% silt and 10% sand, which is similar to the soil along riparian areas in northern

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Sweden. Air temperature inside the greenhouse was set between 20ºC (day temperature) and 15ºC (night temperature). And lights were on during 18 h every day.

Hydrological alterations consisted of: i) rapid and frequent water level fluctuations; iii) prolonged flooding; and iii) water stress. The formers are associated to hydropeaking downstream and upstream from hydropower plants (i.e., rising or falling discharges caused either by the turning on or off of hydro-turbines to generate electricity according to variations in the market demand (Moog, 1993), while the last characterizes bypassed river reaches downstream from hydropower plants. We sowed 24 seeds from each species in individual pots from four different cassettes, each one watered with a specific strategy in order to mimic hydrological alterations. Thus, we started with 24 replicates per species per water or erosion treatment. A cassette was used as “control” (C) and was showered twice a day to simulate natural conditions (i.e., no hydrological disturbances). Another cassette was used to test

“water stress” (WS) and was showered twice a week. The “water fluctuation” (WF) and

“flooding” (F) cassettes were placed inside plastic boxes in order to control the watering and on elevated rigid surfaces to avoid contact with the bottom of the box and soil loses. The

“water fluctuation” cassette was watered abundantly (i) four times per day during the first half of the experiment period and (ii) three times per day during the second half of the experiment, equally distributed from 7:00 h to 19:00 h, and it was left drain freely after each time watering. Drained water was removed from the plastic box every day. The “flooding”

cassette was covered with water till just below soil surface to ensure seeds or roots inundation during (i) four hours in a row from 14:00 h to 18:00 h during the first half of the experiment period and (ii) two hours from 15:00 h to 17:00 h during the second half of the experiment, and was emptied every day after this period. Every day during 49 days we checked seeds germination and seedlings survival, and every six days (a total of eight measurements) we recorded the following variables: 1) seedlings health status from 1 (i.e., unhealthy) to 3 (i.e., healthy) according to their color and smoothness; 2) shoot length; and 3) number of leaves.

Based on these measurements we calculated growth and leave production rates.

The “water fluctuation” and “flooding” cassettes were additionally subjected to erosion tests because we hypothesize that these two hydrological alterations also imply important soil losses. For this aim, we covered the outside bottom and sides of the cassettes with a permeable to water fabric to avoid that the lost soil from the pots spreads in the plastic box but still allow water drainage. The fabric was kept only during the erosion tests which was ended after 13 days. After that, all pots from the two cassettes were carefully emptied and seeds (or seedlings in some cases) which remained in the pots were visually identified and recorded (namely, seeds or seedlings which resisted erosion). From this moment onwards, we continued with hydrological variables tests on the seeds and seedlings which were able to resist erosion, but avoided erosion from “water fluctuation” and “flooding” cassettes. To avoid erosion, we removed the outside fabric from cassettes, placed a double-layer coffee- filter paper on the inside bottom of each pot from the two cassettes to retain the soil in the pot, and filled them again with new soil mixture. Remaining seeds and seedlings were sown/planted again and were followed as described above for responses to hydrology till the end of the experiment during 36 more days.

2.2 Data analysis

We analyzed whether variables related to germination, survival and performance of the species were significantly different between species and between erosion and hydrological treatments. For this aim we computed Chi-squared and Contingency Coefficients for binary categorical variables (i.e., germination and survival) and the Tau-c de Kendall for ordinal variables (i.e., health status). After erosion treatment, we considered that a seed “survived”

(or resisted) to erosion when it remained in the pot, and that a seedling survived to erosion

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when it remained alive in the pot. We considered that a seedling survived to hydrological changes when it was not dead at the end of the hydrological treatments. We carried out an ANOVA test and subsequent post-hoc tests to test significantly differences between species and treatments of quantitative variables (i.e., time required for germination, stem length, number of leaves and growth and leave production rates). P-values <0.05 indicated significant differences. Cross-tabs, frequency plots, and box and whisker plots were used for visual representation of results. We used SPSS-23 for calculations.

3.Results

3.1 Erosion

We found significant differences between the resistances of the tested species to erosion treatments (Ch² P=0.002 for species Vs. erosion-WF and P=0.002 for species Vs. erosion-W;

Figure 1 and Table 1). Erosion resulting from water fluctuation had high and similar impact on most species, remaining in the pots 34% of seeds from Bp, Ca, Cf and Fu. Ha showed a significant high erosion resistance, remaining in the pots almost 90% of the seeds. Erosion derived from flooding had different impacts on species. Again, Ha showed the highest resistances, remaining in the pots almost 90% of their seeds. Bp and Fu showed the lowest resistances, remaining in the pots 38% of their seeds. Around 60% of Carex species seeds remained in the pots after this erosion treatment. There were significant differences between the resistance of Ca seeds to the two erosion treatments, being the erosion derived from water fluctuation more impacting than the erosion derived from flooding (Ch² P=0.043;

Figure 1 and Table 1). However, the remaining species were similarly impacted by both erosion treatments (Ch² P>0.05; Table 1).

3.2 Germination

Except for Cf (Ch² P=0.217; Table 1) and somehow Fu (Ch² P=0.041; Table 1), germination of species differed significantly depending on the treatment (Ch² P<0.05 for remaining species;

Table 1). Highest germination values occurred in the control treatment where 100% of Ha, 80% of Bp and 42% of Ca germinated, although surprisingly, no germination occurred for Fu and Cf (Figures 2a). Water fluctuation severely affected Ha germination (i.e., 29% of germination), whereas water stress and flooding conditions had not important consequences on this species germination (i.e., 75% germination under both treatments; Figures 2a).

0 10 20 30 40 50 60 70 80 90 100

Bp Ca Cf Fu Ha

% Resistance to erosion

F WF

Figure 1. Percentages of the resistance to erosion resulting from the water fluctuation (Wf) and flooding (F) treatments. Betula pubescens (Bp); Carex acuta (Ca), Carex flava (Cf), Filipendula ulmaria (Fu) and Helianthus annuus (Ha).

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Contrarily, water stress and flooding were the most impacting treatments for Bp, which showed 17% of seeds germination and no germination at all, respectively. Carex species showed reduced germination values under flooding conditions, and were unable to germinate under water stress and water fluctuating conditions (Figures 2a).

3.3 Survival

Survival was not significantly different between species (Ch² P>0.05 for all species; Table 1), as it was very high for all of them regardless the hydrological treatment. All germinated individuals from Bp, Ca, Cf and Fu survived to all treatments (Figure 2b). All Ha seedlings survived to control and flooding treatments (Figure 2b) but water stress and water fluctuation was lethal for 41% and 33% of Ha germinated seedlings, respectively (Ch² P=0.000 for Ha survival in the different treatments; Table 1). Due to the less survival of some Ha to water stress and fluctuation, we found significant differences between the effect of the treatments on the survival of species (Ch² P=0.000 for survival comparisons between treatments without distinguishing species; Figure 2b and Table 1).

0 10 20 30 40 50 60 70 80 90 100

Bp Ca Cf Fu Ha

Germination

C WS F WF

0 10 20 30 40 50 60 70 80 90 100

Bp Ca Cf Fu Ha

Survival

C WS F WF

a)

b)

Figure 2. A) Germination of the species seeds in control (C), water stress (WS), flooding (F) and water fluctuation (WF) treatments. B) Survival of the species to the hydrological treatments. Betula pubescens (Bp);

Carex acuta (Ca), Carex flava (Cf), Filipendula ulmaria (Fu) and Helianthus annuus (Ha).

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3.4 Health status

The Kendall’s tau-c P<0,05 (Table 1) for comparisons of species health status in the control treatment highlighted the medium health conditions of around 30% of the germinated Bp in contrast to the healthy conditions of the remaining germinated species (Figure 3). All germinated species had similar medium or low health status under water stress, flooding and water fluctuation treatments (Kendall’s tau-c P>0,05; and Figure 5b to d) (Table 1).

Specifically, water stress and water fluctuation treatments resulted in the worst health status;

in general, Ha showed a medium health status for both treatments, Bp under water fluctuation showed better health status (50% good status) than under water stress where all the replicas showed medium or bad status, and all Fu were moderately healthy. Finally, Ha and Ca were relatively healthy under flooding conditions, as opposed to Cf.

3.5 Time required for germination

There were significant differences between species and treatments in the time species required for germination (Anova P-values <0.05; Table 1). In general, Fu and Carex species required longer period for germination than Bp and Ha. They germinated after 20 days. Bp required more than 10 days in general for germination, whereas Ha required only 5 days (Figure 4a). Seeds under water fluctuation treatments germinated significantly later than those under remaining treatments. Water stress also caused a delayed in Bp and Ha seeds germination (Figure 4a).

3.6 Stem length

There was significant differences in the stem length between species (Anova P-value=0; Table 1). Ha showed the highest stem length after the experiment. It was 66,13 cm long on average.

Bp and Ca showed similar lengths, around 3,63cm on average both. Cf and Fu showed the shortest stems (Figure 4b and 4c). The shortest stems were found for water fluctuation and

Figure 3. Health status at the end of the experiment. Betula pubescens (Bp); Carex acuta (Ca), Carex flava (Cf), Filipendula ulmaria (Fu) and Helianthus annuus (Ha).

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water stress treatments for Ha, while it was flooding which caused the shortest stems for Bp (Figure 4b and 4c).

3.7 Number of leaves

Number of leaves was significantly higher for Ha (i.e., 15 leaves on average; Anova p- value<0.05; Table 1), while Ca and Bp showed 5 leaves on average. Fu showed the lowest number of leaves (Figure 4d). Specifically, the lowest number of leaves for Ha was found under water stress, closely followed by water fluctuation, whereas the highest number was found under control and flooding treatments (Figure 4d). On the other hand, the lowest number of leaves for Bp was found under flooding conditions, while the remaining treatments did not show significant differences (Figure 4d).

3.8 Rates of stem growth and leaf production

Significantly highest rates of stem growth and leaf production were found for Ha (Anova P- values <0.05). It showed a stem growth rate of 1,38 cm/day and leaf production rate of 0,30 number of leaves/day (Figure 4e, 4f and 4g). On the contrary, the lowest rates were for Ca and Fu. Again, the rate of stem growth and leaf production was significantly low for Ha under water stress and water fluctuation conditions, while flooding and control treatments did not presented significant differences for those two variables (Figure 4e, 4f and 4g). Contrarily, Bp lowest rates were found under flooding conations, whereas these rates were similar under the remaining treatments (Figure 4e, 4f and 4g).

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Figure 4. Box ad whisker plots for the measured plant traits: a) Time of germination; b) and c) Stem length (two graphs of this variable for indicating better the Bp results); d) Number of leaves; e) and f) Rate of stem growth (two graphs of this variable for indicating better the Bp results); g) Rate of leaf production. Betula pubescens (Bp); Carex acuta (Ca), Carex flava (Cf), Filipendula ulmaria (Fu) and Helianthus annuus (Ha).

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Chi-Square Contingency Coefficient F Kendall's tau-c Value P-value Value P-value Value P-value Value P-value

Species/Resistance/ Hydrotreatment F 17,511 0,002 0,357 0,002

WF 22,357 0 0,396 0

Hydrotreatment/Resistance/S pecies

Bp 0,091 0,763 0,044 0,763 Ca 4,09 0,043 0,28 0,043 Cf 1,343 0,247 0,165 0,247 Fu 0,375 0,54 0,088 0,54

Ha 0 1 0 1

Hydrotreatment/Germinati on/Species

Bp 26,806 0 0,54 0

Ca 20,094 0 0,465 0

Cf 4,448 0,217 0,244 0,217 Fu 8,272 0,041 0,338 0,041

Ha 29,24 0 0,495 0

Species/Survival/Hy drotreatments C

WS 2,471 0,116 0,324 0,116 WF 1,667 0,435 0,378 0,435

F

Species/Resi stance/Hydr otreatment

5,861 0,21 0,233 0,21

Species/Survival/H ydrotreatments C 0,29 0,004

WS -0,218 0,17

WF 0,36 0,104

F 0,177 0,281

TimeofGerminati on/Species C 398,35 0

WS 7,465 0,013

WF 5,511 0,037

F 336,51 0

Table 1. Chi-Square, Contingency coefficient, F and Kendall’s tau-c from all the variables analysesed. Control (C), water stress (WS), flooding (F) and water fluctuation (WF) treatments. Betula pubescens (Bp); Carex acuta (Ca), Carex flava (Cf), Filipendula ulmaria (Fu) and Helianthus annuus (Ha).

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Species/StemLength

27,466 0

Species/NºofLeaves

34,211 0

LeafProduction/Species

C 274,854 0

WS 1,279 0,272

WF 2,514 0,15

F 38,187 0

StemGrowthRate/Sp ecies

C 136,912 0

WS 2,731 0,115

WF 1,773 0,238

F 17,617 0

4. Discussion

Controlled conditions in a greenhouse have allowed quantifying the potential impact on several plant species of hydropower dams which operate causing hydropeaking along rivers.

We know that magnitude, frequency and duration of flow events control many ecological processes (Poff et al. 1997), and we have proved the negative effect of unnatural flow frequencies and durations and significant decreases of flows on the germination, performance and survival of several species. Which of these parameters are the most important as well as the degree of impact of those changes depend on the species, as we see from our results. Ha showed by far the best resilience to changes on magnitudes, frequencies and durations of flows. It showed the shortest time for germination, the highest germination percentages and stem growth and leaf productions. Bp was next in the resilience scale, while Carex species and Fu showed the worst values for these variables. However, not all flow changes were similarly damaging. In general, Ha was very negatively affected by water stress and water fluctuation, although seemed to be resistant to flooding. Water stress and water fluctuation were also the most impacting treatments for Ca. On the contrary, Bp faced pretty well with water stress but was severely affected by flooding since non seeds germinated under this treatment, and by water fluctuation, which caused a delay in this species germination and resulted in negative values for health status and low values for stem growth and leaf production rates. Results from Cf and Fu must be taken with caution since germination in the control treatment was not as expected, which might indicate that seeds from these species

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would have probably benefited from longer cold stratification or higher temperatures after sowing for germination. Consequently, we cannot conclude hydrological implications on their failure.

The fact that specific species differed in their behavior to different hydrological conditions might be related to their traits (characteristics). Selected species exhibit different morphological, physiological, phenological and reproductive characteristics which make them success or fail when flow conditions change. Abilities of Ha to easily germinate despite variable flow conditions might result from the nutrient reserves of its large seeds, which make environment a no limiting factor, at least at the first stages of this species development.

Ha shows long roots which give it some abilities to survive drought condition. Bp is not tolerant to the floods since seeds were unable to germinate. Studies have shown this species lower tolerances to anoxia and waterlogging (Bejarano et al. in process) and its prefferences for the upper parts of riparian areas (Bejarano et al. 2011). Physiological traits might be beyond this behavior but further research must be carried out to prove it. However it deals very well regarding to water fluctuation and water stress. Its long tap root might be garantee water access under depleted water levels. Carex and Filipendula species are usually found along lower areas than Betula. However, results are consistent with their potential development areas, being Filipendula more successful in medium elevations and Carex more successful very close to the water edges. Flooding resistance was found for the case of Carex, whereas it was not the case for Filependula, which was slightly more succesful under water fluctuation conditions. Carex physiological characteristics, such as the presence of aerenchyma tissues, make them very tolerant to water saturation in the root zone. According to Schmid. 1984, this species might persist in riparian areas during the dry season only if the soil is able to retain enough mosture. Both Carex species and Filipendula also have seeds with high floating capacity (Nilsson et al, unpublished work). Ca can float during 275 days, Fu during 95 days and Cf during 12 days, which is an advantage for their germination in swamp areas. Whereas Fu only germinated in water fluctuation due to is specie adapted to wet environments because according with Botanical-Online. 1999, this specie is able to survive and growth in several areas such as the bank of the river, lake, swampy areas, bog.

For that we observe how all the plants of Fu have survived until the end of the experiment.

The hydrological disturbances imply stressful conditions for species. Low water availability results inimplied water stress, which means no water available in enough quantity to support basic hydrological developments. According to these requirements, we predict that Ha and Bp, the only species which geminated despite water stressful conditions, manage to grow up but we do not expect long lasting seedlings when water stress conditions persist in time.

Water flooding implies anoxia, which only really wetland species are able to face. In that case, Carex species could germinate because they are mostly aquatic species able to grow up in areas flooded temporarily and in the edge of the streams. Water fluctuation implies rises and falls of high soil moisture although not necesarily anoxia. However, soil particle size should be further analyse in combination to this hydrological variable because coarse soils such as sandy or cobble dominant soils have lower water holding capacity and hence better and faster water drainage capacity than fine sized soils such as clays.

Hydropeaking does not only imply the direct effect of flow magnitude, frequency and duration on plants, but it has also an indirect effect through the soil erosion that rapid flow changes or sustained flows caused. In Sweden, the erosion resulting from hydropeaking is magnified in winter when pieces of ice move up and down along the edges of the riparian areas following water level fluctuations (Lindt and Nilsson, 2015). Our results show that deposits of seeds on the river banks are deeply affected by these erosion processes. However, again, seeds abilities to be retained in suitable surfaces for germination vary according to

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species. Ha seeds highest resistance to erosion processes derived from hydropeaking might be related to the seeds morphological characteristics. It has large seeds between 8 and 15 mm size and 0,15 g (Flora of North America) which make them difficult to scour. On the other hand, Bp, Fu and Cf seeds worst erosion resistance values could be related to the small and light seeds they produce. Bp, Fu and Cf seeds have in this order a size and a weight of 0,2 cm and 0,6 mg (Niinemets and Valladares, 2006); 0,17 cm (Morales, 2010); 0,18 cm (Luceño et al, 2008). The grip to the soil that seeds exhibit according to their different surface roughness or texture or their shape could also influence their ability to survive erosion, because they would be easily anchored to the soil. The egg-shaped of Carex species seeds might have influenced in the realtively high resistance to erosion resulting from flooding.

Finally, we found that water fluctuation can erode significantly more seeds than water flooding. It is reasonable to think that rapid raises and falls of flow will result in higher scouring than a sustained flood situation.

5. Conclusion

Hydropower is an important sustainable resource, which is among the most used for energy production in Sweden. Nowadays it is increasing due to the drop of petroleum for energy production. For that reason our study is indispensable to set the scientific basis of a sustainable management of hydropower dams being able to balance hydropower production and environment, such as riparian areas. Understanding riparian responses from species to hydrological changes of stream flow could provide information useful in restoration projects.

The riparian species have been tested with three different conditions. The most damaging one has been the water stress followed by the water fluctuation treatment. Therefore, it can be said that flooding is the most viable method for hydropeaking. According to the results obtained, Helianthus annnuus would react on a positive way to flooding. Betula pubescens could survive in both water stress and fluctuation. Referring to carex species, they could just tolerate the flooding conditions from the dams. Finally, Filipendia ulmaria would have a positive response in flow fluctuations. These responses are very species specific dependent, because they are the result of their particular morphological and physiological characteristics as we have shown in this study. Further research on the hydrological thresholds of other species which hold any special value (key species/indicator species). Taking into account these conclusions, we could provide some recommendations for a better and more sustainable management of the riparian vegetation.

6. Acknowledgment

First, I would like to thank Maria Dolores Bejarano (my supervisor) for her every day support and availability. I also thank Anna Dietrich who helped in the stratification process and the staff from the Wallenberg greenhouse (SLU) who have colaborated in the watering duty.

Finally, I am very grateful to Daniel Carmona for his help with statistics and to Clara and my family from Spain that encourage me anytime.

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