Impact of dams on biogeochemical processes in Iberian rivers

Transcription

1 SCARCE 5 th Annual meeting, Tarragona, October 213 Impact of dams on biogeochemical processes in Iberian rivers D. von Schiller, L. Ponsatí, I. Aristi, M. Arroita, V. Acuña, A. Elosegi, S. Sabater

2 Background >8, reservoirs and associated dams operate worlwide, 45, of which are large (>15m tall) (Marks 27 Sci. Am.) Benefits: Hydroelectric power generation, supply of water for irrigation, drinking and recreation, flood control, stabilization of flow for navigation. Costs: Displacement of people, sediment trapping, alteration of river ecosystems El Grado reservoir (Spain) Margalef reservoir (Spain) Siurana reservoir (Spain)

3 Background In Spain: >12 reservoirs, >6, hm 3 water stored, >1 reservoirs larger than 5hm 3 Source: There are still important knowledge gaps regarding the impact of dams on river ecosystem structure and especially on river ecosystem function

4 Objective & Hypothesis We aimed to determine the impact of hydrologic regulation by dams on in-stream processes (biofilm activities, ecosystem metabolism and nutrient uptake) We hypothesized: UPSTREAM (Control) RESERVOIR DOWNSTREAM (Impact) Lower hydromorphological stability Lower biomass/detritus accumulation Lower biofilm activity rates Lower metabolic fluxes Lower net nutrient uptake Higher hydromorphological stability Higher biomass/detritus accumulation Higher biofilm activity rates Higher metabolic fluxes Higher net nutrient uptake

5 Study sites.3-2 km river reaches located upstream (Control) and downsteam (Impact) from 3 reservoirs Cinca river Mediano-El Grado reservoirs (835 hm 3 ) Montsant river Margalef reservoir (3 hm 3 ) Siurana river Siurana reservoir (12 hm 3 )

6 Methods Structural parameters - Continuously: Discharge, Cond., Temp. -3 times (Summer, Aurtumn, Winter): Hydrogeomorphology, physicochemistry, algal and detritus biomass Functional parameters 3 times (Summer, Aurtumn, Winter): - Biofilm activitiies - Whole-reach metabolism - Whole-reach nutrient uptake

7 Methods: Epilithic biofilm functioning - Enzymatic activities: β-d-glucosidase (BG) (LAP) Leucine-amino-peptidase - Respiratory capacity (ETS) Alkaline phosphatase (APA) - Effective quantum yield (Y eff ) - Maximum phosynthetic capacity (Y max ) C UP C DW RESERVOIR Control I UP Impact I DW

8 Methods: Ecosystem metabolism Open system two-station method (Odum, 1956; Reichert et al. 29) Dissolved O 2 (mg L 1 ) C UP C DW RESERVOIR Control YSI DO sonde (at 1 min intervals for 24h) Gross primary production (GPP) Ecosystem respiration (ER) I UP I DW Impact

9 Methods: Ecosystem net nutrient uptake Dynamic mass-balance approach (based on Roberts & Mulholland 27) C UP Net uptake flux (U net ) : Control U net = (Conc UP *Q UP ) - (Conc DW *Q DW ) + (Conc GW *Q GW ) C DW RESERVOIR Sigma Autosampler (at 2 h intervals for 24h) + Levellogger I UP Impact net release source steady state net uptake sink I DW

10 1/1/12 Results: Hydromorphological stability Cinca Siurana High flow events = 15 Siurana Control High flow events = 11 Cinca Control Discharge (m 3 s -1 ) Discharge (m 3 s -1 ) Control Siurana Impact High flow events = Cinca Impact High flow events =6 Discharge (m 3 s -1 ) RESERVOIR Discharge (m 3 s -1 ) Impact 1/1/9 7/1/9 1/1/1 7/1/1 1/1/11 7/1/11 1/1/8 7/1/8 1/1/9 7/1/9 1/1/1 7/1/1 1/1/11 7/1/11 1/1/12 1/1/8 7/1/8

11 Results: Hydromorphological stability Sediment motion and riverbed disruption were 29-55% higher in impact than in control reaches. Stability times were longer in impact than in control reaches, but minor differences between reaches in Montsant and Siurana during some periods.

12 Results: Water physicochemistry Discharge Temperature Alkalinity TDN TDP DOC Site Season Reach (L/s) ( C) (mg CaCO 3 /L) (mgn/l) (mgp/l) (mgc/l) Cinca Summer C I Autumn C I Winter C I Siurana Summer C I Autumn C I Winter C I Montsant Summer C I Autumn C I Winter C I

13 Results: Algal and detrital biomass Cinca Siurana Montsant Algal biomass (µgchl-a cm -2 ) C I Control Impact Cinca C I Siurana C I Montsant 1 Benthic organic matter (gafdm m -2 ) gafdm/m S A W S A W S A W Summer Autumn Winter Summer Autumn Winter GLM Main effects: Control < Impact (p<.1) S A W S A W S A W Summer Autumn Winter GLM Main effects: Control < Impact; (p=.17) Montsant>Cinca&Siurana (p=.2)

14 Results: Biofilm activity Cinca Siurana Montsant Control Impact BG (mmol MUF cm -2 h -1 ) GLM Main effects: Cont < Imp p<.1 LAP (mmol AMC cm -2 h -1 ) APA (mmol MUF cm -2 h -1 ) S A W S A W S A W GLM Main effects: Cont < Imp p<.5 GLM Main effects: Cont = Imp

15 Results: Ecosystem metabolism GPP or ER (go 2 m -2 day -1 ) GPP * ER * Control Impact SS DF MS F p River Season Reach SS DF MS F p River Season Reach

16 Results: Net nutrient uptake 2 U net -TDN Control Impact U net (µg m -2 min -1 ) 1 * -1-2 SS DF MS F p Stream Season Reach

17 Results: Net nutrient uptake 2 U net -TDN U net -TDP Control Impact U net (µg m -2 min -1 ) 1 * -1-2 SS DF MS F p Stream Season Reach

18 Results: Net nutrient uptake 2 U net -TDN U net -TDP U net -DOC Control Impact U net (µg m -2 min -1 ) 1 * -1-2 SS DF MS F p Stream Season Reach

19 Summary & Conclusions Damming causes profound changes in the biophysical template of downstream-located river reaches Higher hydromorphological stability Higher biomass/detritus accumulation In-stream functional response to damming is moderate At biofilm scale: generally higher activity rates At ecosystem scale: higher metabolic rates and nitrogen uptake Reservoirs and their associated dams cause discontinuities along river networks in terms of in-stream biogeochemical processes that should be added to the effect of the reservoirs themselves

20 Summary & Conclusions To learn more check out: Aristi I, Arroita M, Larrañaga A, Ponsatí L, Sabater S, von Schiller D, Elosegi A, Acuña V (in press) Flow regulation affects ecosystem metabolism in Mediterranean rivers. Freshwater Biology. Ponsatí L, Acuña V, Aristi I, Arroita M, García-Berthou E, von Schiller D, Elosegi A, Sabater S (in press) Biofilm responses to flow regulation by dams in Mediterranean rivers. River Research and Applications. von Schiller D, Ponsatí L, Aristi I, Arroita M, Acuña V, Elosegi A, Sabater S (in prep.) Nutrient cycling discontuinities in regulated Mediterranean rivers.

21 Acknowledgements L. Flores, L. Nakis, L. Boithias, L. Vergoñós SCTs ICRA Predoctoral Grant UPV/EHU (I. Aristi) Predoctoral Grant Basque Country (M. Arroita) Juan de la Cierva Grant (jci ; D. von Schiller) SCARCE project (Consolider-Ingenio 21 CSD29-65) My