, 2012) (Fig. 2). On the other hand, reductions in sediment fluxes to coastal areas are primarily due to retention within impoundments (Syvitski et al., 2005). Reservoirs now retain 26% of the global sediment flux, resulting in an overall 10% decrease compared to the prehuman sediment load (Syvitski et al., 2005). Overall, these changes in terrestrial sediment fluxes to coastal ecosystems directly affect habitat formation of benthic environments through enhanced sedimentation or coastal erosion. Global fluxes of nitrogen (N) and phosphorus (P) to coastal areas have increased due
to human activities (Cloern, 2001 and Galloway et al., 2008), with a doubling of riverine, reactive N and P fluxes in the preceding 150 years (Galloway et al., 2004 and Mackenzie et al., 2002), and a rise in atmospheric
deposition of N from land to coastal areas (Galloway Selisistat in vivo et al., 2004). Increases in these fluxes to the coastal zone are due to agricultural crop and livestock production, fertilizer application, discharge of urban and industrial sewage, and fossil fuel burning (Galloway et al., 2008), as well as removal of the ecosystems’ filtering and buffering capacity (e.g. riparian zones and floodplain wetlands, (Verhoeven et al., 2006). Further substantial increases in riverine fluxes of N and P to coastal areas are projected (Galloway Selleck CHIR-99021 et al., 2004), particularly in tropical regions (Mackenzie et al., 2002). Nutrient loadings to the Great Barrier Reef lagoon, for example, have increased 6-fold for N and 9-fold for P since European settlement in the 19th century (Kroon et al., 2012) (Fig. 2). Excess nutrient inputs to coastal areas increase net primary production and lead to eutrophication either (Cloern, 2001), which in extreme cases causes widespread hypoxia (Diaz and Rosenberg, 2008), and contribute to loss of ecosystem diversity, structure and functioning (Lotze et al.,
2006). Modification of terrestrial pollutant fluxes, and consequent declines in reef water quality have resulted in detrimental impacts on physical, ecological and physiological processes of reef-building corals (Coles and Jokiel, 1992 and Fabricius, 2011). Compared to other terrestrial pollutants, the effects of changes in freshwater fluxes on coral reefs have received relatively little attention. Proxy records from coral cores indicate both enhanced (Hendy et al., 2002) and reduced (Prouty et al., 2009) freshwater fluxes into tropical waters since the late 19th century. Cases of coral mortality, bleaching and disease, associated with reduced salinity due to extreme rainfall, land runoff, and groundwater discharge, have been documented on coral reefs around the world (Coles and Jokiel, 1992). Conversely, reduced freshwater fluxes may result in increased salinity in coastal embayments, detrimentally affecting downstream coral communities (Porter et al., 1999).