Human Impacts on Sediment in Faga'alu
- 1. “Human Impacts on Sediment in Faga’alu“ by Alex Messina, MS Watershed Science
- 2. Thank you to our collaborators in American Samoa: CRAG DMWR DOC ASEPA ASCC/DOC-Intern: Rocco Tinitali
- 3. Motivation and Research Question Land-based sources of sediment and nutrients can damage coral… Pristine Southern reef Damaged Northern reef …so where and when is the sediment generated in the watershed?
- 4. What is a watershed and why is it important for Faga’alu Reefs? *Source and transportation of sediment and pollutants that can harm coral ecosystems Storms cause muddy plume from stream to reefs
- 5. Turbid, freshwater layer during rains Polluted, degraded ecosystem Shallow, near rivermouth Deeper, near reef crest Pristine, functioning ecosystem
- 6. A history of monitoring in Faga’alu •E. Bardi, 2005: Showed that Faga’alu was highly impacted by turbidity relative to other streams •P. Houk, 2006: Related coral health to stream water quality and showed Faga’alu as highly degraded •M. Sabater, 2007: Measured high rates of sediment accumulation on reefs in Faga’alu •S. Curtis, 2011: Measured stream water quality parameters up and down stream to identify likely sources of sediment runoff
- 7. Objectives: 1) Reconnaissance of watershed to identify likely sources of sediment and nutrients 2) When, How much: Quantify streamflow, sediment, and nutrients during storm and inter-storm periods 3) Where: Where does the sediment go? 4) Watershed model and management scenarios 5) Build capacity for field monitoring and land- based pollution assessment in A.S.
- 8. Two parts: •Upper natural/undisturbed portion •Lower developed/impacted portion Tutuila, Am.Samoa
- 9. Potential Sediment Source: Natural Areas Landslides, pig disturbance? m 0 15 Can be a natural, significant source of sediment but recover quickly
- 10. Potential sources: Quarry, urban areas, agriculture 1 km 150 m Sept, 2009
- 11. Quarry: High levels of sediment runoff during rains Key factor seems to be rainfall intensity
- 12. Quarry: Flat, high traffic areas produce very turbid runoff Inadequate sediment control practices …for now…
- 13. Some quarrying activities/groundwater flow maintain high turbidity even under dry conditions
- 14. Possible source: Hospital storm drain
- 15. Conclusion from reconnaissance: Sediment is most important, sources include: 1. Quarry 2. Hospital storm drain/urban area 3. Unpaved areas/sparse grass 4. Agriculture 5. Landslides
- 16. Objectives: 1) Reconnaissance of watershed to identify likely sources of sediment and nutrients 2) When, How much: Quantify streamflow, sediment and nutrient loading during storm and inter-storm periods 3) Where: Where does the sediment go? 4) Watershed model and management scenarios 5) Build capacity for field monitoring and land- based pollution assessment in A.S.
- 17. 4 Tipping Bucket rain gauges 1 Rain gauge on Mt. Matafao: • 2,142 feet, Highest point on the island • Very difficult access trail, ~35% slope • Starting point of watershed
- 18. Objective 2: Load (tons) = Q x C Measure stream flow (Q) and sediment concentration (C) at 3 locations a) Upper watershed (“Dam”, PT#3) b) Stream below quarry (“Quarry”, PT#2) c) Outlet to the ocean (“LBJ”, PT#1) North North 0.5mi.
- 19. Measuring stream flow (Q) (L/sec) Measure depth Or “Stage” (like a ruler) Outlet site Flow measurements relate “Stage” to Stage streamflow (Q) (Height to Volume) Measuring flow at dam above quarry
- 20. Measuring sediment (C): Storm, inter-storm sampling a. Manual/Auto sampling - six storms, >300 samples b. Turbidimeter – continuous, January – May 2012, two sites Convert turbidity to sediment concentration using observed relationship Auto-sampler at Quarry site Filtering and weighing sediment at DMWR lab
- 21. Increased sediment during stormflows 1/27/12 3:15pm 3:30pm 3:45pm 4:30 pm 6:00pm
- 22. Results: Example from one sampled storm (March 7, 5.6 cm of rain) •Sediment load highest at LBJ, outlet to ocean •Responsive to rainfall – essential to monitor storms •Sediment flux higher near hospital •Responsive to rainfall Turbidimeter above quarry
- 23. Results: Storm Data % of Total Sediment(Tons) Sediment Duration Precipitation # Date (Days) (mm) Upper Lower Total Upper Lower 1 1/31/12 11 224 0.88 7.28 8.15 10 89 2 2/05/12 2.5 104 0.73 4.84 5.57 13 86 3 3/05/12 2.5 78 0.31 1.12 1.43 21 78 4 3/08/12 3 50 0.43 0.26 0.69 62 37 5 3/15/12 4 88 0.15 0.53 0.68 22 77 6 3/16/12 3 77 0.16 0.49 0.65 23 76 Total: 26 621 3 15 Average: 26 74 74% of sediment comes from the human- impacted lower watershed, most of it from the quarry 26% of sediment comes from the upper watershed from natural erosion and landsliding Over 90% of sediment is moved during storms
- 24. Objectives: 1) Reconnaissance of watershed to identify likely sources of sediment and nutrients 2) When, How much: Quantify streamflow sediment and nutrient loading during storm and inter-storm periods 3) Where: Where does the sediment go? 4) Watershed model and management scenarios 5) Build capacity for field monitoring and land- based pollution assessment in A.S.
- 25. Measuring sedimentation rates on Faga’alu reef (pilot study) 1. Differences between North and South reefs 2. Gradient away from rivermouth 3. Only 2 Monthly samples: Feb and March Hypothesized flow, and sediment accumulation Assembly N e r rg ve ater ha ri sc id h Seaw di rb Fres Tu S Installation
- 26. Improving models with new datasets MODELS: Predict sediment load based on processes but need to be calibrated to local conditions Model Objectives: 1. Scientific a. Extend existing datasets b. Quantify human impacts 2. Management a. Scenarios b. Watersed prioritization Equations developed for Map-based tools developed in mid-west agricultural management the tropics for coral conservation
- 27. Objectives: 1) Reconnaissance of watershed to identify likely sources of sediment and nutrients 2) When, How much: Quantify streamflow sediment and nutrient loading during storm and inter-storm periods 3) Where: Where does the sediment go? 4) Watershed model and management scenarios 5) Build capacity for field monitoring and land- based pollution assessment in A.S.
- 29. Next phase: CRTF Priority Watershed ->Management and Restoration • If BMPs implemented at the quarry, and Village Watershed Plan implemented, how much is sediment reduced? • How much coral will grow back naturally? With help? •Sediment control at quarry •Village Watershed Protection Plan implemented -->cleaner stream •Less sediment on reef •Coral restoration --> healthier coral