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Highlights • We examined impacts of a hydroelectric dam on igapó forests in the Brazilian Amazon. • Tree species composition changed in distinct ways depending on the topography. • Dominance of a few flood-adapted species increased in lower topographies. • Higher topographies showed higher floristic similarity with upland forest. • Assessment of future hydroelectric dams should incorporate downstream impacts. Abstract The monomodal flood pulse of major Amazonian rivers is a seasonal phenomenon that determines ecological and biogeochemical processes in adjacent floodplain forests. River damming transforms the pattern of downstream flood pulses and provides a natural disturbance to which the native biota might be poorly adapted. Severe modifications of the flood pulse were recorded in the Uatumã River after the installation of the Balbina dam, Central Amazonia. Flood pulse regulation increased mortality of flood-adapted species in the black-water floodplain (igapó) forest. No previous studies have investigated impacts of flood pulse regulation on the species composition and forest structure of igapó forests. Therefore, we examined species composition and forest structure of igapó forests along a regulated river in comparison to a pristine tributary, the Abacate River, evaluating soil texture characteristics and flood duration. In order to assess potential encroachment of species less sensitive to flood alteration, we also inventoried adjacent non-flooded upland forest in each river section. A quantitative inventory of all trees with diameter at breast height (DBH) ≥5 cm was carried out in low-igapó , high-igapó and adjacent upland forests, totaling one half-hectare in each river. In both rivers investigated, the clay fraction of the soil was significantly related to tree height. Flood duration was correlated to DBH and basal area, with the largest trees found in low-igapó forests which are exposed to long-term flooding. Species composition, richness and diversity significantly responded to flood duration. Species richness was highest in upland forests and lowest in low-igapó forest. In the pristine river, tree species composition exhibited a turnover of species along the flooding gradient. In the regulated river, flood intensification in the low-igapó forest increased dominance of a few flood-adapted species, which produced floristic dissimilarity to all forest types investigated. On the other hand, high-igapó forest showed higher floristic similarity with upland forest due to flood suppression that contributed to encroachment of species commonly described in secondary upland forests. Our results emphasize the urgent need for Brazilian environmental regulatory agencies to incorporate downstream impacts in the environmental assessments of dam projects in the Amazon Basin. [ABSTRACT FROM AUTHOR]

The annual and regular flood pulse is the main hydrologic feature found in the large floodplains along Amazonian rivers triggering nutrient cycles, growth rhythms and life cycles of the biota as well as primary and secondary productivity. The construction of hydroelectric dams in the Amazon basin substantially alters the hydrologic regime resulting in severe social, ecological and environmental impacts. While the majority of studies evaluate these impacts in the area of the reservoir and the surroundings of the dam, we focus on disturbances in floodplain forests downstream of the hydroelectric power plant, in this case the Balbina dam, constructed in the 1980s damming the Uatumã River (Central Amazonia). The lowest topographies in the floodplain forests downstream of the dam are dominated by dead trees of Macrolobium acaciifolium (Benth.) Benth. (Fabaceae), a flood-tolerant species forming annual tree rings in consequence of the flood pulse. In this study we evidence alterations in the magnitude and frequency of the hydrologic conditions of the Uatumã River downstream of the hydroelectric power plant comparing the pre-dam (1973–1982) and post-dam (1991–2012) period analyzing a set of biologically relevant hydrologic indicators. To investigate the relationship between the hydrologic changes caused by the dam and the year of death of individuals of M. acaciifolium we use cross-dating techniques (dendrochronology) and radiocarbon dating ( 14 C) as two independent methods. Cross sections of 17 dead individuals were analyzed and individual tree-ring series cross-dated with a well-replicated living trees’ chronology of the same species and region (1804–2012). The outermost tree ring was isolated to perform radiocarbon dating. The dendrochronological and 14 C proxies matched in 88% of the cases, while in the 12% mismatched maximum deviation at least one year. Trees died during periods of consecutive years of inundation, up to two decades after the implementation of the hydroelectric dam. Considering the planning of construction of several dozen dams in the Amazon region there is a critical need to include the downstream impacts in all discussions of hydroelectric implementation. [ABSTRACT FROM AUTHOR]

The riparian forest reduces the amount of light entering streams, which limits autochthonous primary production. The aim of this study was to evaluate temporal variation of autochthonous primary production in pristine and altered streams, with the goal of identifying indicators of change in environmental integrity in the southern Brazilian Amazon. We evaluated free algal biomass in the water column, the presence of periphyton, and the richness and cover of aquatic herbaceous plants in 20 streams (10 pristine and 10 altered, i.e., with riparian deforestation) during the dry period, at the beginning of the rainy period, and at the end of the rainy period. In altered streams, we recorded the presence of macroscopic periphyton and the amount of algal biomass varied between the dry and flood seasons. Variations in hydrological periods did not contribute to changes in algal biomass in pristine streams; we did not observe the presence of macroscopic periphyton these streams. In altered streams, 23 aquatic herbaceous species were identified, versus only four in the pristine streams. Results showed that riparian deforestation contributes to increased autochthonous primary production, which is also influenced by different hydrological periods, with algae and aquatic herbaceous plants responding differently to dry and rainy periods. The responses of these primary producers confirm their role as important bioindicators of change in the environmental integrity of southern Amazonian streams. [ABSTRACT FROM AUTHOR]

Abstract: Himatanthus sucuuba is a tree species that occurs in Central Amazonian white water floodplains and in non-flooded uplands. The objective of this paper was to verify whether flooding causes differences in germination percentages, seedling mortality as well as alterations of leaf number and biomass increments, related to the habitat of origin of the seeds (várzea floodplain versus terra firme upland, in the following V and TF, respectively). To test this effect, seeds from populations of both habitats were collected, and germination percentages were calculated under different experimental conditions. One hundred seeds collected in three sites of the floodplain and one hundred seeds from three sites of the upland were placed in trays for germination in a greenhouse in the Amazon Research Institute (INPA) in Manaus, Brazil. Seedlings with a height of 7cm were then subjected to a period of 120 days of flooding in tanks with three treatments: control, waterlogging (root system and the base of the stem), and complete submersion. Ground water from the INPA was used in the tanks and was changed at weekly intervals. Germination percentages were high in most treatments. Seedling mortality was significantly higher in seedlings originating from upland, reaching 100% in submerged seedlings. On the other hand, várzea-originated seedlings showed no mortality under waterlogging or submergence. Height growth of waterlogged seedlings from floodplains exceeded that of the control. Submerged seedlings did not grow, independently of the origin, and those originating from uplands died after about 100 days. Number of leaves and leaf area were significantly lower under partial submersion than in the control, independently of the origin of the seeds. Under total submersion abscission of all leaves was verified 30 days after inundation for seedlings of both origins. In the V population, all seedlings survived the waterlogged period, whereas in the TF population, 30% of the seedlings died when subjected to waterlogging. With complete submergence, in the V population 30% of the seedlings had died after 120 days, in the TF population after 90 days mortality was 100%. The results show that germination, seedling growth and seedling survival in H. sucuuba differ among populations of floodplain and upland sites: V plants performed better than TF plants under waterlogging and under submersion. The results strongly indicate that ecotypic differentiation exists between these two populations of H. sucuuba individuals in the two habitat types, which may be enforced by a strong selective pressure due to the regular occurring flood pulse. [Copyright &y& Elsevier]

Abstract Large dams built for hydroelectric power generation alter the hydrology of rivers, attenuating the flood pulse downstream of the dam and impacting riparian and floodplain ecosystems. The present work mapped black-water floodplain forests (igapó) downstream of the Balbina Reservoir, which was created between 1983 and 1987 by damming the Uatumã River in the Central Amazon basin. We apply remote sensing methods to detect tree mortality resulting from hydrological changes, based on analysis of 56 ALOS/PALSAR synthetic aperture radar images acquired at different flood levels between 2006 and 2011. Our application of object-based image analysis (OBIA) methods and the random forests supervised classification algorithm yielded an overall accuracy of 87.2%. A total of 9800 km2 of igapó forests were mapped along the entire river downstream of the dam, but forest mortality was only observed below the first 49 km downstream, after the Morena rapids, along an 80-km river stretch. In total, 12% of the floodplain forest died within this stretch. We also detected that 29% of the remaining living igapó forest may be presently undergoing mortality. Furthermore, this large loss does not include the entirety of lost igapó forests downstream of the dam; areas which are now above current maximum flooding heights are no longer floodable and do not show on our mapping but will likely transition over time to upland forest species composition and dynamics, also characteristic of igapó loss. Our results show that floodplain forests are extremely sensitive to long-term downstream hydrological changes and disturbances resulting from the disruption of the natural flood pulse. Brazilian hydropower regulations should require that Amazon dam operations ensure the simulation of the natural flood-pulse, despite losses in energy production, to preserve the integrity of floodplain forest ecosystems and to mitigate impacts for the riverine populations. Graphical abstract Unlabelled Image Highlights • Considerable floodplain forest loss occurred downstream of the Balbina dam from flood pulse changes; • Several tree species are still suffering mortality, which may increase dead stand areas; • Remote sensing methods used here may be applied to other floodplains with massive tree mortality by damming; • Downstream igapó forests are highly sensitive to the loss of low water periods resulting from flow alteration by dam operations; [ABSTRACT FROM AUTHOR]

To understand the ecological relevance of fish-forest interactions, we sampled fish for a period of 8 months in a lowland forest of the Brazilian Amazon and evaluated the germination of intact seeds recovered from the intestine of three species of congeneric and sympatric freshwater sardines, Triportheus albus , T. angulatus and T. auritus. The number of seeds consumed by the three fish species and the possible effect of individual fish size on seed germination were investigated. We captured 150 individual sardines, of which N = 59, contained 982 intact seeds from seven flooded forest tree species. All the seeds were already pulped due to the digestive process and were sown to check its germination rates. We selected two pioneer tree species, Cecropia latiloba and Laetia corymbulosa , which were the two most consumed seeds to analyze the effects of its passage through the fishes' digestory tracts on seed germination rates and speed, compared to intact seeds directly collected from trees (control). Seeds harvested from the wild were not scarified or scrapep to remove the pulp because of the large amount of diminutive seeds of the two pioneer tree species. Fish body size did not affect the probability of germination of the consumed seeds of C. latiloba or L. corymbulosa. For both plant species, there was a reduction in the probability of germination of seeds taken from the intestine of fish in relation to control seeds collected in nature. Control seeds also germinated faster than those consumed by fish. Despite the seemingly negative effects on germination rates and speed after passing through the digestory tracts of the freshwater sardines, the fishes' ability to transport seeds away from the parent plants can compensate for the loss of viability of some of the ingested seeds, especially when the proportion of viable seeds remains high. • Sardines of three species consumed 982 intact seeds of seven tree species from the flooded forest. • Cecropia latiloba and Laetia corymbulosa were the species with the highest number of seeds consumed by sardines. • Seeds of Cecropia latiloba and Laetia corymbulosa consumed by fish have a low probability of germination. • Fish body size did not affect the probability of germination of C. latiloba or L. corymbulosa. • Controls germinated faster than those consumed by fish. [ABSTRACT FROM AUTHOR]