The spatial and temporal variability of water levels was investigated across a section of floodplain in the Pantanal that represents typical geomorphic and ecological complexity of these environments. A series of 11 staff gauges were installed along a 12-km transect running perpendicularly from the Cuiabá River into the floodplain. The staff gauges were monitored fortnightly during the flood seasons from 2004 to 2007. Contrary to what is often assumed, the water surface profile was never level, and it was particularly variable when there was less water on the floodplain. Water surface slope varied from 1.4 9 10 -4 (unitless) to 1.3 9 10 -3 indicating substantial water movement that was verified by flow observations. The spatial patterns of water level variation were repeated across years, even though there was considerable interannual variation in magnitude and duration of floodplain inundation. In 2004 and 2005, the duration of inundation was 121 and 120 days, respectively, but in 2006 and 2007, inundation lasted 166 and 157 days, respectively. These observations reveal considerable small-scale spatial variability in the water surface profile, but with persistent patterns over space and time that are related to the river hydrograph and the channels that convey flood waters across the area. This study contributes to our understanding of inundation hydrology and its linkages to ecosystem processes, and additionally provides a valuable data set for calibration and validation of remote sensing approaches to measurement of inundation area and water movement across floodplains.
To identify factors affecting the spatial distribution of soil seed banks of herbaceous species in the Pantanal floodplain, Brazil, the aims of this study were: to characterize the seed bank in terms of the abundance, richness and composition of germinated seeds; to relate these characteristics to flood duration, elevation, chemical and physical properties of the soil and to examine the seed bank's spatial pattern. Soil samples were collected at 14 points and were then placed in a greenhouse to allow germination to occur. Each sample point had the flood level monitored, the elevation measured and the soil properties identified. A total of 1710 seedlings from 26 species were recorded, of which Echinodorus tenelus was the most abundant (24.9%). Cyperaceae and Poaceae were the richest floristic families (5 species each), with Alismataceae the most represented in terms of number of individuals (36% of the total). Duration of flooding plays an important role in determining Pantanal soil seed banks. The flood pulse influences the abundance (r = 0.79; P = 0.006; partial), richness (r = 0.61; P = 0.02; partial) and composition of the soil seed bank (Pillai trace = 0.552; P = 0.027), carrying the seeds to areas where the duration of flood is longer. Except for aluminium, the soil characteristics expressed by the first principal component of PCA exert indirect positive effects on the seed bank. This is because this component was correlated with the duration of inundation (r = 0.76). Elevation and the toxic effect of aluminium do not vary sufficiently to be able to influence seed bank characteristics. The correlograms show that soil seed banks have no discernible spatial pattern, even though most species are dispersed hydrochorically. This suggests that, at the scale of the study, the tendency for flooding to cause homogeneous dispersion has no influence on seed-bank spatial structure, because of the complexity of flood-plain geomorphology.
There are 104 hydroelectric facilities proposed to be installed in the watersheds that feed the Pantanal, a vast floodplain wetland located mostly in Brazil. The Pantanal is host to 23 long‐distance migratory fish species that ascend upland tributaries to spawn. A Geographic Information System was used to predict the impact of hydroelectric dams on potential migration routes for these species. Both anthropogenic (hydroelectric dams) and natural barriers were included in the analysis. Natural barriers were identified by river slope. Critical river slopes of 10 and 25%, above which fish were predicted to be incapable of ascending, were modeled as natural barriers. Based on this model, we show that between 2 and 14% of rivers in the Pantanal watershed are naturally blocked to fish migration. An additional 5 to 9% of rivers are currently blocked due to 35 existing hydroelectric facilities. If all proposed dams are built, the area flooded by new reservoirs will triple and the river kilometers blocked will double, blocking 25 to 32% of the river system to fish migration. The Taquari and Cuiabá River sub‐basins will be the most impacted, each having more than 70% of their rivers blocked. The impact of individual proposed facilities on the loss of migration routes is related to their proximity to existing barriers. Fourteen of the proposed dams are upstream from existing barriers and will therefore not further restrict long‐distance fish migration routes while proposed dams are predicted to close an additional 11,000 to 12,000 km of river channels.
Tropical river basins have experienced dramatically increased hydropower development over the last 20 years. These alterations have the potential to cause changes in hydrologic and ecologic systems. One heavily impacted system is the Upper Paraguay River Basin, which feeds the Pantanal wetland. The Pantanal is a Ramsar Heritage site and is one of the world's largest freshwater wetlands. Over the past 20 years, the number of hydropower facilities in the Upper Paraguay River Basin has more than doubled. This paper uses the Indicators of Hydrologic Alteration (IHA) method to assess the impact of 24 of these dams on the hydrologic regime over 20 years (10 years before and 10 years after dam installation) and proposes a method to disentangle the effects of dams from other drivers of hydrologic change using undammed “control” rivers. While most of these dams are small, run-of-the-river systems, each dam significantly altered at least one of the 33 hydrologic indicators assessed. Across all studied dams, 88 of the 256 calculated indicators changed significantly, causing changes of 5–40%, compared to undammed reaches. These changes were most common in indicators that quantify the frequency and duration of high and low pulses, along with those for the rate and frequency of hydrologic changes. Importantly, the flow regime in several undammed reaches also showed significant alterations, likely due to climate and land-use changes, supporting the need for measurements in representative control systems when attributing causes to observed change. Basin-wide hydrologic changes (in both dammed and undammed rivers) have the potential to fundamentally alter the hydrology, sediment patterns, and ecosystem of the Pantanal wetland. The proposed refinement of the IHA methods reveals crucial differences between dam-induced alteration and those assigned to other drivers of change; these need to be better understood for more efficient management of current hydropower plants or the implementation of future dams.
Abstract:The purpose of this work was to characterize and quantify phytophysiognomic units at mesoscale and evaluate their relationships with flood intensity, flood duration and topography. The study was conducted at a 25 km 2 Long-Term Sampling Site (LTSS), located within the floodplain of the Cuiabá River in the Pantanal of Mato Grosso. The phytophysiognomic units were determined from the supervised classification of CBERS 2B sensor CCD satellite images. The maps of flood intensity, flood duration and of topography were generated from the spatial interpolation of planialtimetric field surveys. Four phytophysiognomic units were identified; Campo inundável (flooded grassland) was the unit with the largest area of occurrence, followed by Cordilheiras (dense arboreal savanna), Landizal (seasonally flooded evergreen forest), and Cambarazal (monodominant Vochysia divergens Pohl. forest), respectively. Campo inundável is distributed mainly in areas of high flood intensity and duration and low topographic positions. Cambarazal predominates in areas of medium flood intensity and duration and intermediate elevation, Landizal in areas of high flood intensity and duration and low topographic position, whereas Cordilheiras are characterized by low flood intensity and duration and location in higher elevations. Statistical tests indicated that flood intensity is the main factor responsible for the mesoscale distribution of phytophysiognomic units in the northern Pantanal. Keywords: flood intensity and duration, topography, floodplain vegetation, remote sensing, Cuiabá River, ecohydrology.FANTIN-CRUZ, I., GIRARD, P., ZEILHOFER, P., COLLISCHONN, W. & CUNHA, C.N. Unidades fitofisionômicas em mesoescala no Pantanal Norte e suas relações com a geomorfologia. Biota Neotrop. 10(2): http://www.biotaneotropica.org.br/v10n2/pt/abstract?article+bn00410022010.Resumo: Este trabalho teve por objetivo caracterizar e quantificar as unidades fitofisionômicas em mesoescala e estabelecer suas relações com a intensidade e duração da inundação e com a topografia. O estudo foi realizado no Sítio de Amostragem de Longa Duração (SALD), implantado em uma área de 25 km 2 localizado na planície de inundação do rio Cuiabá, Pantanal de Mato Grosso. As unidades fitofisionômicas foram determinadas a partir da classificação supervisionada de imagens CBERS 2B sensor CCD. Os mapas de intensidade e duração da inundação e topografia foram gerados a partir da interpolação espacial de levantamentos planialtimétricos de campos. Foi evidenciada a existência de quatro unidades, sendo o Campo (pastagem inundável) a unidade com maior área de ocorrência, seguido pelas Cordilheiras (savana arbórea densa), Landizal (floresta inundável sempre verde) e Cambarazal (floresta inundável monodominante de Vochysia divergens Pohl.) respectivamente. O Campo apresentou sua maior distribuição em áreas de alta intensidade e duração de inundação e topografia baixa. O Cambarazal predomina em áreas de intensidade média e duração e topografia alta, o Landizal em áreas com intensidade e...
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