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Effects of river damming on estuarine phytoplankton

Effects of river damming on estuarine phytoplankton






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    Effects of river damming on estuarine phytoplankton Effects of river damming on estuarine phytoplankton Presentation Transcript

    • Effects of river damming onestuarine phytoplankton:the Guadiana estuarycase study (SW Iberia)Rita B. Domingues1,2, Ana B. Barbosa1, Helena M. Galvão11 Centre for Marine and Environmental Research, University of Algarve, Faro, Portugal2 Centre of Oceanography, University of Lisbon, Portugal
    • THE IMPORTANCE OF RIVER FLOW river flow plays crucial role in the regulation of abiotic and biotic variablesnutrient and light availabilityprimary and secondary productioncoastal fish landings dam construction – alteration of the natural flow regime – serious effects on ecosystemsdownriver e.g., Iron Gates Dam, Danube Riversilica inputs to the Black Seatransition from a diatom-based community to dominance of non-siliceousphytoplankton rupture on diatom-zooplankton-fish food web, based on high diatom biomasses, whichbenefits fish and other organisms that rely on planktonic food during their life cycle, canultimately be expected from dam construction
    • THE PROBLEM: CONSTRUCTION OF THE ALQUEVA DAM the largest dam in Western Europe located 140 km from Guadiana River’s mouth encouraged extensive scientific research on theeffects of river damming on estuarine ecosystem,since late 1990´s Marine Microbiology Group at the University of Algarve has been studyingphytoplankton dynamics in the Guadiana estuary since 1996 previous phytoplankton studies focused on• seasonal variability of phytoplankton and environmental drivers (Domingues et al. 2005, 2007,2012; Domingues & Galvão,2007)• cyanobacteria blooms (Rocha et al. 2002; Sobrino et al. 2004; Galvão et al. 2008)• effects of nutrients and light (Domingues et al. 2011a, b, c)• tidally-induced variability of environmental drivers (Domingues et al. 2010)• influence of climate and anthropogenic stressors on phytoplankton variability (Barbosa et al.2010)• development of an ecohydrological model (Chícharo et al. 2006)
    •  however… previous studies focused only on specific periods related to the Alqueva damconstruction no integration of more than 14 years of data has been done to assess the impacts of theAlqueva dam on estuarine phytoplankton and to compare the before and after situationsfundamental knowledge for a successful management of estuaries and adjacent coastalecosystemsGOAL – understand the impacts of the Alquevadam, particularly the effects of differenthydrological regimes; compare phytoplankton andtheir environmental drivers before and after thedam started to operate
    • GUADIANA RIVER AND ESTUARY arises in Spain, flows for 810 km and drains between SE Portugal and SW Spain into theAtlantic Ocean last 70 km (tidal limit) – estuary area = 22 km2; average depth = 6.5 m; width: max = 800 m, min = a few meters mediterranean climate region (hot, drysummers; moderate winters) tides - mesotidal, semidiurnal tides vertical stratification - well mixed in middleand upper estuary; partially stratified inlower estuary
    • METHODS frequent sampling campaigns have been conducted in the Guadiana in the last decade,focusing on the freshwater tidal estuarine zone (sampling station Alcoutim) sampling – ebb flow, neap tides abiotic variables• T, S, O2•dissolved inorganic N, P and Si•PAR, Im• river flow and rainfall (http://snirh.pt) biotic variables• chlorophyll a• phytoplankton composition and abundancePortugalSpainAtlantic Ocean data analysis – data aggregated into 4 distinct periods related to the Alqueva damconstruction and operation:• 1996-1998, 2001 – pre-filling• 1999-2000 – intense land excavation period• 2002-2003 – dam filling period• 2004-2009 – post-filling period, regular dam operation
    • 020406080100Riverflow(m3s-1)Bpre-filling excavation filling post-filling01020304050Summerriverflow(m3s-1)0100200300400500600Winterriverflow(m3s-1)CRESULTS & DISCUSSION significantly different between the fourperiods river flow significantly correlated with rainfall(rS = 0.5330, n= 152, p < 0.0001)despite intense impoundment, water flowinginto the estuary is still largely controlled byrainfall river flow during summer was significantlyhigher in the post-filling period than in previousphaseselimination of the natural high and low peaksin river flow, typical of mediterranean climateregions22131 3426
    •  variability in river flow contradicts previous predictions for the Guadiana estuary:significant reduction in river flow, especially during summeralarming!Toxic cyanobacteria blooms – recurrent problem in the Guadianaestuary, during summer, associated to low freshwater flows major increase on the frequency and magnitude of cyanobacteria blooms wasexpected with dam constructionpre-filling excavation filling post-filling0102030405060Cyanobacteriaabundance(x107cellL-1)CNo dataHowever… river flow during summer increased in thepost-filling period cyanobacteria abundance decreased significantly420 x 106 12 x 106 cells L-1 97% strong negative correlation between cyanobacteriaabundance and river flow (rS = -0.48, n = 69, p < 0.0001)Cyanobacteria abundance
    •  river flow is clearly a relevant regulator of phytoplankton dynamics most problems associated with river damming are a direct consequence of changes infreshwater flownutrient inputs biological productivity050100150200250Nitrateconcentration(µM)Apre-filling excavation filling post-filling050100150200250DSiconcentration(µM)C nutrient concentrations were mostly similar (N, P) orhigher (Si) after dam filling in relation to the pre-fillingphaseNSi e.g., construction of the Aswan High dam in the Nile Rivercaused a reduction of 90% in freshwater flowdecreased nutrient inputs to the Mediterraneandisappearance of phytoplankton bloomscollapse of Eastern Mediterranean coastal fisheries
    • pre-filling excavation filling post-filling0510152025303540Chlorophylla(mgm-3) however, phytoplankton biomass and abundance decreased significantly in the post-filling period…02468101214161820Diatomabundance(x106cellL-1)ANo dataDiatom abundanceChlorophyll a020406080100120Greenalgaeabundance(x105cellL-1)BNo dataGreen algae abundanceriver flow during spring-summerlight limitation of phytoplankton growthnutrient inputs & turbiditylight availability in the water column
    • -0,100,10,20,30,40,50,60,70,8control N P Si NP SiN SiP NPSiCommunitynetgrowthrate(d-1)********Blight limitation nitrogen limitationIn: Domingues et al (2011) Est Coast Shelf Sci (doi: 10.1016/j.ecss.2010.10.033); Domingues et al (2011) Est Coast Shelf Sci (doi:10.1016/j.ecss.2010.12.008)00,10,20,30,40,5control I1 I2 I3Communitynetgrowthrate(d-1)B*****pre-filling excavation filling post-filling020406080100Im(µmolphotonsm-2s-1)B light availability was slightly lower in thepost-filling in relation to the pre-filling period
    •  alterations in river flow alterations in phytoplankton dynamics phytoplankton abundance and biomass decreased significantly in the post-filling period river flow controls abiotic variables that regulate phytoplankton dynamics (nutrient andlight availability) disappearance of cyanobacteria blooms – beneficial to the ecosystem decrease in diatom biomass is detrimental to higher trophic levelsdiatom fish alterations in phytoplankton biomass affect fish abundance and species compositionphytoplankton planktivorous fishphytoplankton carnivorous fishAdapted from Chícharo et al (2006) ECSS 70: 39-51wetdryplanktivorous fish carnivorous fish sardine (planktivorous fish) is the mosteconomically important fish in the Algarve when carnivorous fishdominate fish catches…average loss of 3 M €
    • CONCLUSIONS river flow is clearly a critical regulator of abiotic and biotic variables in the Guadianaestuary human regulation of river flow and disruption of natural flow regimesnegative impacts on the estuarine ecosystem elimination of natural peaks in river discharge and a more constant river flowthroughout the year decline in phytoplankton biomass “ecological flows” should be avoided for extended periods establishment of river flow that mimics natural river discharges, to prevent negativeimpacts on the natural patterns of biological communities
    • © Pedro MoraisThank You!Rita B. Domingues is supported by a postdoctoral fellowship awarded by the PortugueseFoundation for Science and Technology (SFRH/BPD/68688/2010).