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CRES: Component: Terrestrial Sediment Budget

• Objectives
• Description
• Relation to Other Research Components
• Milestones
• Contact Information

Project Components:

• Sediment Loading and Associated Impacts
• Water Column Transports Processes
• Physical Oceanography
• Transport of Watershed-based materials: Sediment Studies
• Coral Diseases
• Demographic Studies: Coral Reef Communities
• Coupling Species and Habitat
• Socioeconomic Studies
• Ecological and Socioeconomic Coupling
• MPA and Marine Reserve Studies
• Database Management

You are here: Home › Biogeography › Products › CRES › Component: Terrestrial Sediment Budget

CRES: Component: Terrestrial Sediment Budget

OBJECTIVES

Marine ecologists have long recognized that coral reef communities can be adversely affected by disturbances associated with land development. The effects of increased sediment delivery on reef communities is one of the most important environmental problems in the Caribbean (Gardner et al., 2003) because of coral sensitivity to this type of disturbance, their importance to local economies, and the magnitude of the increase in sedimentation after disturbance. While this issue has been widely recognized by scientists, there have been few efforts to quantify and model sediment production and delivery in the Caribbean with the purpose of protecting coral reefs. The two-year “Terrestrial Sediment Budget” component of this project is intended to address this issue by achieving the following two main objectives:

1. To quantify the rate of sediment production from individual sources of sediment within the study area and to identify the factors controlling those rates.
2. To measure and model the rate at which land-based sediments originating from the Parguera area are being delivered into the wetland and marine environments.

DESCRIPTION

Although previous soil erosion research has been conducted in Puerto Rico, most of it has focused on agricultural lands and is not widely representative of coastal zone land use. The type of land development that occurs in La Parguera creates an array of highly-erodible surfaces such as cutslopes, fillslopes, and highly-compacted and unvegetated surfaces (i.e., dirt roads and homesites). This project follows a sediment budget approach (Reid & Dunne, 1996) to measure and model surface erosion rates from all natural and anthropogenic sources of sediment found on the study area. The study area (shown in Figure A) encompasses the small catchments draining towards the coastline between Punta Guayacán and Punta Papayo.

The field-component of the study will quantify surface erosion and runoff development rates from specific types of landscape units under natural rainfall conditions. Silt fences (Robichaud and Brown, 2002), will be used to measure sediment production from individual sources of sediment ranging in source areas from tens to several thousand squared meters. A total of 40 to 50 silt fences will be installed in 2003 and monitored as part of this study. Rainfall intensities will be measured by two tipping-bucket type raingauges.

This project will also document runoff and suspended sediment yield at the road segment and watershed scales. While road runoff rates will be measured by use of eight-inch portable cutthroat flumes, watershed-scale measurements will be made at two natural channel cross-sections. Each runoff measuring station will be equipped with a pressure transducer attached to a datalogger. Suspended sediment samples will be collected with USGS DH-48 and SS-59 type samplers. Road runoff data will be used to calibrate parameters for a coupled Green-Ampt and kinematic wave infiltration-runoff routing model. Watershed-scale runoff and suspended sediment data will be used to estimate sediment yield rates into the wetland and marine environments in La Parguera.

Pending the availability of additional funding it is the intention of this component of the project to develop a GIS-based sediment budget system that incorporates our empirical sediment production data. This system will estimate watershed-scale increases in sediment delivery rates that arise from land development, while also providing a means to evaluate the relative importance of specific sediment sources within the study area. Watershed-scale sediment yield estimates derived from model runs are intended to be compared to the empirical data collected as part of this study.

RELATION TO OTHER RESEARCH COMPONENTS

The results produced by the land-based sediment budget study are strongly linked to other components of the CRES Parguera project. A connection between measured watershed-scale runoff/sediment yields can be made with changes in salinity and turbidity being measured by the "Water column transport processes" component of the study. A strong correlation between terrestrial inputs of sediment from the La Parguera area and turbidity in the bay might signal the importance of local sediment sources in controlling marine water column conditions. The lack of any correlation between these measurements might imply that marine water column conditions are controlled by other factors such as resuspension of sediment already deposited on the bottom of the bay or sediment sources outside of the La Parguera area. The “Transport of watershed-based materials” study will allow us to compare current watershed-scale sediment yields to bay sedimentation rates over the past several thousand years.

MILESTONES

CONTACT INFORMATION