Samia Aquino

Coral reefs chronically exposed to river sediment plumes in the southwestern Caribbean: Rosario Islands, Colombia

Politicians do not acknowledge the devastating impacts riverine sediments can have on healthy coral reef ecosystems during environmental debates in Caribbean countries. Therefore, regional and/or local decision makers do not implement the necessary measures to reduce fluvial sediment fluxes on coral reefs. The Magdalena River, the main contributor of continental fluxes into the Caribbean Sea, delivers water and sediment fluxes into the Rosario Islands National Park, an important marine protected area in the southwestern Caribbean. Until now, there is no scientific consensus on the presence of sediment fluxes from the Magdalena River in the coral reefs of the Rosario Islands. Our hypothesis is that high sediment and freshwater inputs from the Magdalena have been present at higher acute levels during the last decade than previously thought, and that these runoff pulses are not flashy. We use in-situ calibrated MODIS satellite images to capture the spatiotemporal variability of the distribution of suspended sediment over the coral reefs. Furthermore, geochemical data are analyzed to detect associated sedimentation rates and pollutant dispersion into the coastal zone. Results confirm that turbidity levels have been much higher than previous values presented by national environmental authorities on coral reefs off Colombia over the last decade. During the 2003-2013-period most of the Total Suspended Sediments (TSS) values witnessed in the sampled regions were above 10mg/l, a threshold value of turbidity for healthy coral reef waters. TSS concentrations throughout the analyzed time were up to 62.3mg/l. Plume pulses were more pronounced during wet seasons of La Niña events in 2002-2003, 2007-2008, and 2009-2010. Reconstructed time series of MODIS TSS indicates that coral reef waters were exposed to river plumes between 19.6 and 47.8% of the entire period of analysis (2000-2013). Further analyses of time series of water discharge and sediment load into the coastal zone during the last two decades show temporal increases in water discharge and sediment load of 28% and 48%, respectively. (210)Pb dating results from two cores indicate sedimentation rates of ~0.75 cm/y of continentally exported clastic muddy sediments that are being deposited on the carbonatic shelf. The cores contain sediments with heavy metals and their concentrations are frequently above the ecologically accepted standards. Overall, the last decade has witnessed stronger magnitudes in fluvial fluxes to the coastal region, which probably coincide with associated declines in healthy coral cover and water quality. Our results emphasize the importance of local stressors, such as runoff and dispersion of turbid plumes, as opposed to ocean warming, disease and hurricanes, which have played a larger role on other coral reefs in the Caribbean. Coral reef management across the southwestern Caribbean, a coastal region influenced by continental fluxes of numerous rivers flowing from the Andes, may only be effective when land and marine-based stressors are simultaneously mitigated.

Floods in Urban Areas of Brazil

Abstract Floods in three very different urban areas of Brazil are presented in this chapter: Sao Paulo, the largest city of South America; the mountain basins of Santa Catarina State, southeastern Brazil; and the city of Rio Branco (Acre State), a typical medium-sized city of the southwestern Brazilian Amazonia. Sao Paulo represents a case of uncontrolled and disorganized urban growth, typical of many cities of southeastern Brazil where the infrastructure and production systems (railroads, roads, and industries) have been settled on the alluvial plains. Santa Catarina disasters are produced because of a combination of tropical storms in a region of mountain fluvial basins that are characterized by flash floods, slope instability (landslides), and urban occupation of the valleys. The Amazonian city of Rio Branco suffered similar fast population growth and because of the cultural Amazonian tradition of “living near the river” suffered many consequences from flooding. The intensive urbanization in both Sao Paulo and Rio Branco around and within the floodplains has introduced many problems involving rain-water drainage. Urban interference in the drainage system is strong in Sao Paulo. The city’s flat topography, associated with channel rectification and the pluvial drainage system, improves surface runoff and consequently water concentration in the lowest areas. On the other hand, obstructed and underfitted sweepers are responsible for many of the small but frequent localized floods. In both cities, floods are more a planning than a natural problem, and the number of deaths and affected people related directly to floods is very small when compared with countries like Bangladesh, India, or China. Nonetheless, the number of persons affected is high, and the diseases and urban problems brought by floods are significant.