Reconstructing Water Quality Histories in Western Reservoirs

Paul Gremillion, Ph.D., P.E.Associate ProfessorCivil & Environmental Engineering DepartmentNorthern Arizona University

Content

• Sedimentation in Reservoirs• Direct Indicators of Reservoir History• Proxy Indicators of Environmental Conditions• Case Studies

Sedimentation in Reservoirs

Source: Reservoir Limnology, Thornton et al.

http://www.gly.uga.edu/railsback/1121DeltaProgradation.jpeg

Direct Indicators of Reservoir History

Roosevelt Lake, Arizona

Roosevelt Lake, Arizona

Roosevelt Lake, Arizona

Direct Analysis of Sediments Can Reveal:1. Rate of loss in storage capacity.

Direct Analysis of Sediments Can Reveal:1. Rate of loss in storage capacity.2. How the rate of capacity loss may change

with climate change.

Direct Analysis of Sediments Can Reveal:1. Rate of loss in storage capacity.2. How the rate of capacity loss may change

with climate change.3. Erosion patterns associated with wildfire.

Proxy Indicators

Objective Analyte / Proxy

Chronology • 137Cs or 239Pu ~ 50 yrs• 210Pb ~150 yrs• 14C ~100 – 15k yrs• Event-based chronology

Primary Productivity • Diatoms• Biogenic silica• 13C (in some systems)

Anoxia • Ratios of redox-sensitive metals• Molybdenum stable isotopes• Benthic invertebrates

Fire • Charcoal• Magnetic susceptibility

Proxy Indicators

Objective Analyte / Proxy

Hydrology • Magnetic susceptibility• Inorganic ion ratios• Particle size distributions• Compound-specific isotopes

Sediment Redistribution • Acoustic surveys• 137Cs or 239Pu inventories• Particle size distributions

Ecosystem Assemblages • Pollen• Diatoms

Atmospheric Pollutants • Chemical extraction + elemental / isotopic analysis

Case Study: Mercury Deposition

Case Study: Mercury Deposition

Case Study: Watson Lake, Arizona

Objective:Collect and analyze sediment cores from Watson Lake to detect historical changes in• Nutrient loading• Primary productivity / trophic

state• Sources of nutrients

Case Study: Watson Lake, ArizonaAnalytical Approach:• Changes in nutrient loading:

TN, TKN, TP• Changes in source of nitrogen:

Nitrogen-15• Changes in source of organic

matter: N/P, C/N, Carbon-13• Changes in primary

productivity / trophic state: Carbon-13, TP

Conclusions

Sediment records in western reservoirs tend to be high in information content:• Magnitude and effects of erosion events.• Changes in water quality.• Changes in watershed characteristics.• Patterns of atmospheric deposition to

watersheds.