Potential Effects of Runoff, Fluvial Sediment, and Nutrient Discharges on the Coral Reefs of Puerto Rico

Abstract

Coral reefs, the foundation and primary structure of many highly productive and diverse tropical marine ecosystems, have been degraded by human activity in much of the earth's tropical oceans. To contribute to improved understanding of this problem, the potential relation between river sediment and nutrient discharges and degradation of coral reefs surrounding Puerto Rico was studied using streamflow, suspended-sediment, and water-quality data. Mean annual runoff for the 8711 km 2 island is 911 mm, about 57% of mean annual precipitation (1600 mm). Mean annual suspended-sediment discharge from Puerto Rico to coastal waters is estimated at 2.7-9.0 million metric tonnes. Storm runoff transports a substantial part of sediment: the highest recorded daily sediment discharge is 1-3.6 times the mean annual sediment discharge. Hurricane Georges (1998) distributed an average of 300 mm of rain across the island, equivalent to a volume of about 2.6 billion m 3 . Runoff of more than 1.0 billion m 3 of water and as much as 5 to 10 million metric tonnes of sediment were discharged to the coast and shelf.Nitrogen and phosphorous concentrations in river waters are as much as 10 times the estimated presettlement levels. Fecal coliform and fecal streptococcus concentrations in many Puerto Rico rivers are near or above regulatory limits. Unlike sediment discharges, which are predominantly episodic and intense, river-borne nutrient and fecal discharge is a less-intense but chronic stressor to coral reefs found near the mouths of rivers. Negative effects of riverderived sediment and nutrient discharge on coral reefs are especially pronounced on the north, southwest, and west coasts.

Long-Term Impacts of Non-Sustainable Tourism and Urban Development in Small Tropical Islands Coastal Habitats in a Changing Climate: Lessons Learned from Puerto Rico

“…Therefore, the combination of a very high road density network that increases the incidence of landslides accompanied by a fast pace of land transformation to urban spaces suggests that current sediment yield rates may be among the highest ever experienced on the island. The manifestation of peak sediment yield rates during a period of fast urban expansion has been documented elsewhere (Wolman, 1967), and it appears to be supported locally by the relatively high suspended sediment yields documented for the island (570-1,900 mg/km 2/ yr) (Larsen & Webb, 2009) and the marine sedimentation record obtained at specific locations (Ryan et al, 2008). Therefore, the combined impacts of increased construction activities, not only along coastal areas, but also across the entire island, with the lack of implementation of the existing land use plans, and the poor implementation of mandatory erosion-sedimentation control regulations have resulted in long-term water quality degradation by sediments and on declining conditions of coastal ecosystems.…”

“…Assisted by a deliberately deficient enforcement of environmental safeguards, socioeconomic and political development in PR following World War II explicitly encouraged a move towards industrialization at the expense of agricultural production (Dietz, 1986) and environmental deterioration (Berman-Santana, 1996;Concepción, 1988). Even though implementation of this new economic model allowed for the recuperation of an island-wide forest cover (Grau et al, 2003;Rudel et al, 2000), it also introduced its own new set of water quality issues (Hunter & Arbona, 1995) that have established a legacy of documented stress and detrimental effects on marine ecosystems in various parts of the PR archipelago, largely as a result of eutrophication and sedimentation impacts (e.g., Goenaga & Cintrón, 1979;Goenaga, 1991;Hernández-Delgado, 2005;Hernández-Delgado et al, 2010, Hernández-Delgado & Sandoz-Vera, 2011Larsen & Webb, 2009;Loya, 1976).…”

“…Among the various affected marine ecosystems, coral reefs stand out as they are particularly susceptible to increased sediment delivery rates (Fabricius, 2005;Rogers, 1990). Terrestrial sediments are considered as a major threat to PR's coral reef systems (Hernández-Delgado, 2005;Larsen & Webb, 2009). Land disturbance in PR associated to the deforestation that began in the 1820's and the extensive use of land for agriculture that lasted until the middle of the 20 th century was responsible for significantly increasing the rate of soil erosion on the island through the combination of increased landslide activity and surface erosion (Larsen, 1997).…”

Spatial linkages between coral proxies of terrestrial runoff across a large embayment in Madagascar

“…1 and 3 in Kremen et al, 1999;Green and Sussman, 1990). The difference in slope influences the flow speed and thus the amount and type of dissolved and particulate transports (Milliman and Syvtski, 1992;Larsen and Webb, 2009). The continuous vegetation cover at ANDRA binds and protects sediment from erosion but allows leaching of HA, while the plain at IFAHO is much less densely vegetated, most likely facilitating sediment erosion (Douglas, 1967).…”

An Interdisciplinary Erosion Mitigation Approach for Coral Reef Protection – A Case Study from the Eastern Caribbean

“…for the recuperation of an island-wide forest cover (Rudel et al, 2000;Grau et al, 2003;Valdés-Pizzini et al, 2011), it also introduced its own new set of water quality issues (Hunter and Arbona, 1995) that have established a legacy of documented stress and detrimental effects on coral reef communities in various parts of the Puerto Rican archipelago (e.g., Loya, 1976;Goenaga and Cintrón, 1979;Goenaga, 1991;Hernández-Delgado, 2000Morelock et al, 2001;Larsen and Webb, 2009;Hernández-Delgado et al, 2010, Hernández-Delgado andSandoz-Vera, 2011). …”