Research ArticleENVIRONMENTAL STUDIES

The changing hydrology of a dammed Amazon

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Science Advances  01 Nov 2017:
Vol. 3, no. 11, e1700611
DOI: 10.1126/sciadv.1700611
  • Fig. 1 Map of the study area, which encompasses the Brazilian Legal Amazon, the Tocantins/Araguaia basin, and parts of the Paraná and North Atlantic basins, illustrating the distribution of existing small and large dams and highlighting those used in this study.

    Large dams are referred to as UHEs and have a production capacity of ≥30 MW; small dams are PCHs and have a production capacity of 1 to 30 MW. Streamflow stations used in the LOR analysis and to calculate IHA are also shown. Note that only major rivers are depicted.

  • Fig. 2

    Streamflow (A) and pre- and post-dam high pulse count (B) at the Cachoeira Morena station, located 32 km downstream of the Balbina dam, illustrating severe dam-induced HA at this station after dam construction. Note that dam construction ended in October 1987. The subsequent period without data in the figure includes reservoir filling through March 1989, during which no water was released by the dam, as well as a period of missing data from 1989 to 1991.

  • Fig. 3

    Sample LOR results for Seringal Fortaleza (A) and Aruanã (B) stations. Solid black horizontal lines represent the long-term mean annual maximum flow for each station. Dashed black and gray horizontal lines represent 5 and 10% of the long-term mean, respectively. Solid green, red, and blue curves represent the 85, 90, and 95% confidence intervals (CIs). Dashed vertical lines indicate the number of years of data required to characterize the annual maximum flow within 5 and 10% of the long-term mean with 90% confidence. LOR results illustrate that widely varying hydrologic regimes yield different LOR requirements to provide similar statistical inference (see text).

  • Fig. 4

    Number of years of flow data required to be within 10% of the long-term mean with 90% confidence across all LOR flow stations regressed against station elevation (A) and mean station discharge (B).

  • Fig. 5

    Summary of the overall magnitude (A) and type (B) of dam-induced HA observed across all dams and stations (see table S4 for dam/station naming conventions; U and D indicate upstream and downstream, respectively). Bars with the same color represent multiple stations affected by the same dam. (C) Scaling HA by electricity production capacity shows hydrologic impact (%) per megawatt, illustrating outsized impact of small dams (unfilled bars) and relative efficiency of particular dams, for example, Tucuruí (TU) versus Lajeado (LA), on the Tocantins River.

  • Fig. 6

    (A) Stations were generally more affected downstream of dams than upstream of reservoirs. (B) Cumulative impacts of multiple dams increased impacts only for parameter groups 4 and 5. P values were calculated using the Mann-Whitney U test.

  • Fig. 7 Pearson R values for linear and log regressions between station HA and predictor variables (blue and red indicate positive and negative correlations, respectively; boxed values, P < 0.1).

    The best predictors of HA were reservoir area/volume (positive correlation) and dam elevation (negative correlation). CV, coefficient of variation.

  • Table 1 Summary of hydrologic parameters used in IHA and their ecological influences.

    Adapted from IHA Manual V7 (28).

    IHA statistics groupRegime characteristicsEcosystem influences
    Group 1: Magnitude
    of monthly water
    conditions (12 indices)
    Mean or median value for
    each calendar month
    Habitat availability for aquatic organisms
    Soil moisture availability for plants
    Availability of water for terrestrial animals
    Availability of food/cover for furbearing mammals
    Reliability of water supplies for terrestrial animals
    Access by predators to nesting sites
    Water temperature, oxygen levels, and
    photosynthesis in water column
    Group 2: Magnitude and
    duration of annual
    extreme water conditions
    (12 indices)
    Annual minima, 1-day means
    Annual minima, 3-day means
    Annual minima, 7-day means
    Annual minima, 30-day means
    Annual minima, 90-day means
    Annual maxima, 1-day means
    Annual maxima, 3-day means
    Annual maxima, 7-day means
    Annual maxima, 30-day means
    Annual maxima, 90-day means
    Number of zero flow days
    Base flow index
    Balance of competitive, ruderal, and stress-tolerant organisms
    Creation of sites for plant colonization
    Structuring of aquatic ecosystems by abiotic versus biotic factors
    Structuring of river channel morphology and physical habitat conditions
    Soil moisture stress in plants
    Dehydration in animals
    Anaerobic stress in plants
    Volume of nutrient exchanges between rivers and floodplains
    Duration of stressful conditions such as low oxygen and
    concentrated chemicals in aquatic environments
    Distribution of plant communities in lakes, ponds, and floodplains
    Duration of high flows for waste disposal and aeration of
    spawning beds in channel sediments
    Group 3: Timing of
    annual extreme
    water conditions
    (2 indices)
    Julian date of each annual,
    1-day maximum
    Julian date of each annual,
    1-day minimum
    Compatibility with life cycles of organisms
    Predictability/avoidability of stress for organisms
    Access to special habitats during reproduction or to avoid predation
    Spawning cues for migratory fish
    Evolution of life history strategies and behavioral mechanisms
    Group 4: Frequency and duration
    of high and low pulses
    (4 indices)
    Number of low pulses within each water year
    Mean or median duration of low pulses (days)
    Number of high pulses within each water year
    Mean or median duration of high pulses (days)
    Frequency and magnitude of soil moisture stress for plants
    Frequency and duration of anaerobic stress for plants
    Availability of floodplain habitats for aquatic organisms
    Nutrient and organic matter exchanges between river and floodplain
    Soil mineral availability
    Access for waterbirds to feeding, resting, and reproduction sites
    Bed load transport, channel sediment textures, and
    duration of substrate disturbance (high pulses)
    Group 5: Rate and
    frequency of water
    condition changes
    (3 indices)
    Rise rates: Mean or median of all positive
    differences between consecutive
    daily values
    Fall rates: Mean or median of all negative
    differences between consecutive
    daily values
    Number of hydrologic reversals
    Drought stress on plants (falling levels)
    Entrapment of organisms on islands and floodplains
    (rising levels)
    Desiccation stress on low-mobility stream
    edge organisms

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/11/e1700611/DC1

    table S1. Hydroelectric dams analyzed with supporting information.

    table S2. Streamflow stations used for IHA analysis.

    table S3. Stations used in the LOR analysis.

    table S4. Stations used in the IHA analysis of individual dams, with supporting information.

    table S5. Stations used in the IHA analysis of multiple dams in the Amazon and Paraná basins.

    table S6. Stations used in the IHA analysis of multiple dams in the Tocantins basin.

    table S7. IHA results for streamflow stations in the individual dams analysis.

    table S8. IHA results for streamflow stations in the multiple dams analysis.

  • Supplementary Materials

    This PDF file includes:

    • table S1. Hydroelectric dams analyzed with supporting information.
    • table S2. Streamflow stations used for IHA analysis.
    • table S3. Stations used in the LOR analysis.
    • table S4. Stations used in the IHA analysis of individual dams, with supporting information.
    • table S5. Stations used in the IHA analysis of multiple dams in the Amazon and Paraná basins.
    • table S6. Stations used in the IHA analysis of multiple dams in the Tocantins basin.
    • table S7. IHA results for streamflow stations in the individual dams analysis.
    • table S8. IHA results for streamflow stations in the multiple dams analysis.

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