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Cite this: Environ. Sci.: Processes Impacts, 2014, 16, 2692
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Effects of a reservoir flushing on trace metal partitioning, speciation and benthic invertebrates in the floodplain† Dorothea Hug Peter,ab Emmanuel Castellaab and Vera I. Slaveykova*ab Elimination of sediments from river reservoirs is a common management problem for hydroelectric power plants. Periodical flushing can have negative impacts downstream. This study investigated the impact of a flushing event on the physico-chemical changes in the downstream sections and on the consequences for the benthic macroinvertebrate community. A special emphasis was placed on trace metal fate, partitioning and speciation. The assessment of taxonomic diversity and the frequency of taxa with specific traits was used to estimate the impact on the macroinvertebrate community. Trace metals were measured in the dissolved and particulate fraction, in the surface sediment and in selected macroinvertebrates. Bioanalogical diffusive gradient thin films (DGT) complemented the approach. The results showed an increase of Al, Co, Mn and Ni in the dissolved fraction (Mdis). Crdis, Fedis, Pbdis, and Cudis showed strong spatial variation. In the exchangeable fraction of particulate metals, trends were contrasted, depending on the metal. The calculated free ion and DGT concentrations increased during the flush for all metals,
Received 14th July 2014 Accepted 30th September 2014
except for Cu. Accumulation in invertebrates increased only in a small number of cases. Macroinvertebrate diversity was negatively impacted as shown by lower taxonomic richness and rarefied richness after the event. Trait profiles were also affected. Overall, the study revealed that flushing
DOI: 10.1039/c4em00387j
operations have an impact on trace metal partitioning between dissolved, suspended particulate matter
rsc.li/process-impacts
and sediments, metal speciation, as well as the functional invertebrate diversity.
Environmental impact Sediment accumulated in river reservoirs is routinely ushed out to restore the storage capacity. The high SPM concentrations caused by such operations have a considerable impact downstream. This study investigated the impact on trace metal partitioning and speciation and on the consequences for the benthic macroinvertebrate community. The monitoring of total dissolved, SPM-bound, surface sediment and DGT-labile metal concentrations, of uptake by biota and the impact on the benthic macroinvertebrate community showed changes in trace metal partitioning and speciation. A short term impact on the benthic macroinvertebrate community was also detected. The increase of certain metals and the impact on the community provide valuable arguments for the discussion about best management practices concerning river reservoir sediments.
Introduction The use of rivers for electricity production is a globally growing sector. Although hydro-electricity is perceived as sustainable, there is a considerable impact of such power plants at the local
a
University of Geneva, Faculty of Sciences, Earth and Environmental Sciences, Institute F.-A. Forel, Route de Suisse 10, CH-1290 Versoix, Switzerland. E-mail: vera. [email protected]; Tel: +41 22 379 0335
b
University of Geneva, Institute for Environmental Sciences, Uni Rondeau, Battelle, Route de Drize 7, CH-1227 Carouge, Switzerland † Electronic supplementary information (ESI) available: Table S1: expected changes in relative frequencies of traits; Table S2: SPM/water partitioning of metals, log KD; Table S3: determination level of invertebrate taxa; Table S4: traits of the invertebrate taxa for which we measured uptake; Fig. S1: timeline of the ushing and sampling; Fig. S2: calculated concentrations of the free ion. See DOI: 10.1039/c4em00387j
2692 | Environ. Sci.: Processes Impacts, 2014, 16, 2692–2702
and regional scale.1,2 One current management problem is the accumulation and elimination of sediments and associated trace metals and organic contaminants in storage reservoirs.3–6 The retention of sediment in reservoirs creates a decit of sediments downstream, with possible geomorphological consequences like bed incision.7 Meanwhile, the bottom of the reservoir faces successive aggradation. Different sediment management strategies have been employed to reduce accumulation and thus loss of power productivity over time. A common practice is to lower the water level periodically and ush out the accumulated sediment with ood pulses.3,6 This re-suspension of large quantities of sediment for short periods raised concerns regarding its ecological impact upon downstream reaches.6 Several studies reported a loss in density, richness and diversity or changes in the community structure of benthic macroinvertebrates.6,8–10 The increase of ne sediment
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 30 September 2014. Downloaded by University of Massachusetts - Amherst on 14/09/2015 18:11:27.
Paper
load can result in altered substrate suitability, increasing dri, clogging of gills or lower oxygen concentrations and decreasing food availability for some groups.10 However, the impact differs among taxa according to their ecological and physiological characteristics (called traits hereaer). It is therefore important to study the inuence of disturbances on both the number and abundance of species and on their traits.11–13 Changes in trait frequencies (e.g. decrease of the relative abundance of scrapers) can be useful indicators of specic stressors. Expected changes in the relative abundance of traits under increased sediment and/or contaminants are summarized in Table S1 of the ESI.† Along with the direct impact of high concentrations of suspended solids, their re-suspension can induce changes in major water chemistry characteristics, trace metal concentrations and partitioning, as well as their availability to biota. These effects on the water chemistry of downstream reaches have received little attention,14 but increases in nitrate, ammonia, and organic matter and a decrease in oxygen were reported.15 The release of Ca2+, K+ or Mg2+ from sediments to the dissolved fraction was also described in laboratory and eld studies.16 However the
Environmental Science: Processes & Impacts
effect of ushing on the trace metal partitioning among sediment in the river bed, suspended particulate matter (SPM) and dissolved fractions remains largely unknown. Since the partitioning coefficients of a given metal among different phases vary with environmental conditions, alteration of the physicochemical parameters could alter the distribution of trace metal species within and among compartments. Metals bound to SPM matter can be released into the water or dissolved metals can be adsorbed to the solids.17 Such environmental uctuations of the trace metal distributions among phases could affect their availability to biota and consequently inuence the biota at the individual, species or community level. However such information, in particularly under eld conditions is currently missing. The major goals of the present study were two-fold: (i) to investigate the effect of reservoir ushing on the river water quality parameters, trace metal speciation and partitioning, and metal accumulation by benthic invertebrates; and (ii) to explore the impact of the reservoir ushing on the functional diversity of the benthic macroinvertebrate community. In particular the study focuses on the impact of the ushing operation in a reservoir dam on the Rhˆ one River (the Verbois dam, Fig. 1). The research approach combined physicochemical measurements in situ and in the laboratory, determination of the trace metal content in the surface sediment, SPM, dissolved fraction and biota, with an assessment of the invertebrate community diversity. Three types of endpoints in invertebrates were chosen: (i) trace metal load before and aer the event, (ii) taxonomic diversity and (iii) trait distribution. In addition, bioanalogical diffusive gradients in thin lm (DGT) devices18 allowed us to determine the labile metal fraction and to simulate exposure of biota via direct contact during the week of ushing.
Experimental
Fig. 1 Map of the four sampling points (P, S, B and C). Points P, S and B are in the main river, point C is in a secondary channel. Verbois is the storage reservoir whose flushing was studied, Genissiat is the second storage reservoir that influenced the fate of suspended particulate matter. Arve is the sediment rich glacier fed river that led to the strong accumulation of sediment in the Verbois reservoir.
This journal is © The Royal Society of Chemistry 2014
The Rhˆ one River is one of the main rivers of Europe. Despite various alterations (e.g. embankments and power production plants) throughout the last few centuries,2,19 some stretches retain a somewhat dynamic oodplain with secondary channels that provide habitats for highly diversied macroinvertebrate communities. The Rhˆ one feeds a number of power production plants. There are several diversion dams and two storage reservoirs, one in Switzerland (Verbois) and one in France (Genissiat). As the Rhˆ one receives water from a highly turbid glacier-fed river just aer it exits Lake Geneva, sedimentation is important in the Verbois reservoir (400 000 m3 per year (ref. 20)). Since the construction of the dam, sediments have needed to be evacuated periodically. Currently, these operations are coordinated between Switzerland and France and numerous measures are implemented to minimize the downstream impact of the ushing operations and avoid that the sediment is simply accumulated in the next reservoir. At the Genissiat dam, the highly turbid water is diluted by mixing the concentrated bottom water with clearer water from the top of the reservoir using the mid-level gates. Other actions to protect the oodplains include the closing off of by passed sections, the
Environ. Sci.: Processes Impacts, 2014, 16, 2692–2702 | 2693
View Article Online
Published on 30 September 2014. Downloaded by University of Massachusetts - Amherst on 14/09/2015 18:11:27.
Environmental Science: Processes & Impacts
construction of SPM-barriers and dilution with water from a nearby lake. Four sampling points were chosen to monitor SPM concentrations and their impact on trace metal speciation and partitioning. The rst point, P, is about 1 km downstream of the Verbois dam, representative of the output from Verbois. The second point, S, is downstream of Genissiat. The impact of the sediments from this reservoir and of the dilution measures described above should be measurable at this point. The two remaining points are about 35 km further downstream. One point (C) is in a secondary channel. While other secondary channels were cut from the main river during the event this one was directly connected. Moreover, this channel has been monitored for ten years in the frame of the Rhˆ one restoration project. The data on the benthic macroinvertebrates can be used to estimate the impact of ushing on this species group. The last point, B, is next to this secondary channel in the main river. It is intended to show the fate of SPM and trace metals in this sector further downstream and allows us to compare the results with the secondary channel. Samples were collected before the event and on two dates during the event. The rst date during the event was chosen to coincide with the opening of the Verbois dam. As the conditions did not turn back to normal over a long period of time, the second fauna sampling was carried out at the beginning of September (see timeline in the ESI, Fig. S1†). Field measurements and sampling The pH and conductivity were measured directly in the eld (Hach-Lange Multimeter, Rheineck, Switzerland). Temperature loggers (HOBO® Data logger, Onset) were installed in all sites during the event. Clean sampling techniques were observed for all sampling. All the glass and plastic ware were soaked for 24 h in 10% nitric acid and then rinsed at least ve times with MilliQ® water (
Published on 30 September 2014. Downloaded by University of Massachusetts - Amherst on 14/09/2015 18:11:27.
PAPER
Cite this: Environ. Sci.: Processes Impacts, 2014, 16, 2692
View Journal | View Issue
Effects of a reservoir flushing on trace metal partitioning, speciation and benthic invertebrates in the floodplain† Dorothea Hug Peter,ab Emmanuel Castellaab and Vera I. Slaveykova*ab Elimination of sediments from river reservoirs is a common management problem for hydroelectric power plants. Periodical flushing can have negative impacts downstream. This study investigated the impact of a flushing event on the physico-chemical changes in the downstream sections and on the consequences for the benthic macroinvertebrate community. A special emphasis was placed on trace metal fate, partitioning and speciation. The assessment of taxonomic diversity and the frequency of taxa with specific traits was used to estimate the impact on the macroinvertebrate community. Trace metals were measured in the dissolved and particulate fraction, in the surface sediment and in selected macroinvertebrates. Bioanalogical diffusive gradient thin films (DGT) complemented the approach. The results showed an increase of Al, Co, Mn and Ni in the dissolved fraction (Mdis). Crdis, Fedis, Pbdis, and Cudis showed strong spatial variation. In the exchangeable fraction of particulate metals, trends were contrasted, depending on the metal. The calculated free ion and DGT concentrations increased during the flush for all metals,
Received 14th July 2014 Accepted 30th September 2014
except for Cu. Accumulation in invertebrates increased only in a small number of cases. Macroinvertebrate diversity was negatively impacted as shown by lower taxonomic richness and rarefied richness after the event. Trait profiles were also affected. Overall, the study revealed that flushing
DOI: 10.1039/c4em00387j
operations have an impact on trace metal partitioning between dissolved, suspended particulate matter
rsc.li/process-impacts
and sediments, metal speciation, as well as the functional invertebrate diversity.
Environmental impact Sediment accumulated in river reservoirs is routinely ushed out to restore the storage capacity. The high SPM concentrations caused by such operations have a considerable impact downstream. This study investigated the impact on trace metal partitioning and speciation and on the consequences for the benthic macroinvertebrate community. The monitoring of total dissolved, SPM-bound, surface sediment and DGT-labile metal concentrations, of uptake by biota and the impact on the benthic macroinvertebrate community showed changes in trace metal partitioning and speciation. A short term impact on the benthic macroinvertebrate community was also detected. The increase of certain metals and the impact on the community provide valuable arguments for the discussion about best management practices concerning river reservoir sediments.
Introduction The use of rivers for electricity production is a globally growing sector. Although hydro-electricity is perceived as sustainable, there is a considerable impact of such power plants at the local
a
University of Geneva, Faculty of Sciences, Earth and Environmental Sciences, Institute F.-A. Forel, Route de Suisse 10, CH-1290 Versoix, Switzerland. E-mail: vera. [email protected]; Tel: +41 22 379 0335
b
University of Geneva, Institute for Environmental Sciences, Uni Rondeau, Battelle, Route de Drize 7, CH-1227 Carouge, Switzerland † Electronic supplementary information (ESI) available: Table S1: expected changes in relative frequencies of traits; Table S2: SPM/water partitioning of metals, log KD; Table S3: determination level of invertebrate taxa; Table S4: traits of the invertebrate taxa for which we measured uptake; Fig. S1: timeline of the ushing and sampling; Fig. S2: calculated concentrations of the free ion. See DOI: 10.1039/c4em00387j
2692 | Environ. Sci.: Processes Impacts, 2014, 16, 2692–2702
and regional scale.1,2 One current management problem is the accumulation and elimination of sediments and associated trace metals and organic contaminants in storage reservoirs.3–6 The retention of sediment in reservoirs creates a decit of sediments downstream, with possible geomorphological consequences like bed incision.7 Meanwhile, the bottom of the reservoir faces successive aggradation. Different sediment management strategies have been employed to reduce accumulation and thus loss of power productivity over time. A common practice is to lower the water level periodically and ush out the accumulated sediment with ood pulses.3,6 This re-suspension of large quantities of sediment for short periods raised concerns regarding its ecological impact upon downstream reaches.6 Several studies reported a loss in density, richness and diversity or changes in the community structure of benthic macroinvertebrates.6,8–10 The increase of ne sediment
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 30 September 2014. Downloaded by University of Massachusetts - Amherst on 14/09/2015 18:11:27.
Paper
load can result in altered substrate suitability, increasing dri, clogging of gills or lower oxygen concentrations and decreasing food availability for some groups.10 However, the impact differs among taxa according to their ecological and physiological characteristics (called traits hereaer). It is therefore important to study the inuence of disturbances on both the number and abundance of species and on their traits.11–13 Changes in trait frequencies (e.g. decrease of the relative abundance of scrapers) can be useful indicators of specic stressors. Expected changes in the relative abundance of traits under increased sediment and/or contaminants are summarized in Table S1 of the ESI.† Along with the direct impact of high concentrations of suspended solids, their re-suspension can induce changes in major water chemistry characteristics, trace metal concentrations and partitioning, as well as their availability to biota. These effects on the water chemistry of downstream reaches have received little attention,14 but increases in nitrate, ammonia, and organic matter and a decrease in oxygen were reported.15 The release of Ca2+, K+ or Mg2+ from sediments to the dissolved fraction was also described in laboratory and eld studies.16 However the
Environmental Science: Processes & Impacts
effect of ushing on the trace metal partitioning among sediment in the river bed, suspended particulate matter (SPM) and dissolved fractions remains largely unknown. Since the partitioning coefficients of a given metal among different phases vary with environmental conditions, alteration of the physicochemical parameters could alter the distribution of trace metal species within and among compartments. Metals bound to SPM matter can be released into the water or dissolved metals can be adsorbed to the solids.17 Such environmental uctuations of the trace metal distributions among phases could affect their availability to biota and consequently inuence the biota at the individual, species or community level. However such information, in particularly under eld conditions is currently missing. The major goals of the present study were two-fold: (i) to investigate the effect of reservoir ushing on the river water quality parameters, trace metal speciation and partitioning, and metal accumulation by benthic invertebrates; and (ii) to explore the impact of the reservoir ushing on the functional diversity of the benthic macroinvertebrate community. In particular the study focuses on the impact of the ushing operation in a reservoir dam on the Rhˆ one River (the Verbois dam, Fig. 1). The research approach combined physicochemical measurements in situ and in the laboratory, determination of the trace metal content in the surface sediment, SPM, dissolved fraction and biota, with an assessment of the invertebrate community diversity. Three types of endpoints in invertebrates were chosen: (i) trace metal load before and aer the event, (ii) taxonomic diversity and (iii) trait distribution. In addition, bioanalogical diffusive gradients in thin lm (DGT) devices18 allowed us to determine the labile metal fraction and to simulate exposure of biota via direct contact during the week of ushing.
Experimental
Fig. 1 Map of the four sampling points (P, S, B and C). Points P, S and B are in the main river, point C is in a secondary channel. Verbois is the storage reservoir whose flushing was studied, Genissiat is the second storage reservoir that influenced the fate of suspended particulate matter. Arve is the sediment rich glacier fed river that led to the strong accumulation of sediment in the Verbois reservoir.
This journal is © The Royal Society of Chemistry 2014
The Rhˆ one River is one of the main rivers of Europe. Despite various alterations (e.g. embankments and power production plants) throughout the last few centuries,2,19 some stretches retain a somewhat dynamic oodplain with secondary channels that provide habitats for highly diversied macroinvertebrate communities. The Rhˆ one feeds a number of power production plants. There are several diversion dams and two storage reservoirs, one in Switzerland (Verbois) and one in France (Genissiat). As the Rhˆ one receives water from a highly turbid glacier-fed river just aer it exits Lake Geneva, sedimentation is important in the Verbois reservoir (400 000 m3 per year (ref. 20)). Since the construction of the dam, sediments have needed to be evacuated periodically. Currently, these operations are coordinated between Switzerland and France and numerous measures are implemented to minimize the downstream impact of the ushing operations and avoid that the sediment is simply accumulated in the next reservoir. At the Genissiat dam, the highly turbid water is diluted by mixing the concentrated bottom water with clearer water from the top of the reservoir using the mid-level gates. Other actions to protect the oodplains include the closing off of by passed sections, the
Environ. Sci.: Processes Impacts, 2014, 16, 2692–2702 | 2693
View Article Online
Published on 30 September 2014. Downloaded by University of Massachusetts - Amherst on 14/09/2015 18:11:27.
Environmental Science: Processes & Impacts
construction of SPM-barriers and dilution with water from a nearby lake. Four sampling points were chosen to monitor SPM concentrations and their impact on trace metal speciation and partitioning. The rst point, P, is about 1 km downstream of the Verbois dam, representative of the output from Verbois. The second point, S, is downstream of Genissiat. The impact of the sediments from this reservoir and of the dilution measures described above should be measurable at this point. The two remaining points are about 35 km further downstream. One point (C) is in a secondary channel. While other secondary channels were cut from the main river during the event this one was directly connected. Moreover, this channel has been monitored for ten years in the frame of the Rhˆ one restoration project. The data on the benthic macroinvertebrates can be used to estimate the impact of ushing on this species group. The last point, B, is next to this secondary channel in the main river. It is intended to show the fate of SPM and trace metals in this sector further downstream and allows us to compare the results with the secondary channel. Samples were collected before the event and on two dates during the event. The rst date during the event was chosen to coincide with the opening of the Verbois dam. As the conditions did not turn back to normal over a long period of time, the second fauna sampling was carried out at the beginning of September (see timeline in the ESI, Fig. S1†). Field measurements and sampling The pH and conductivity were measured directly in the eld (Hach-Lange Multimeter, Rheineck, Switzerland). Temperature loggers (HOBO® Data logger, Onset) were installed in all sites during the event. Clean sampling techniques were observed for all sampling. All the glass and plastic ware were soaked for 24 h in 10% nitric acid and then rinsed at least ve times with MilliQ® water (
