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Characterization of Lake Somerville Water Quality

Characterization of Lake Somerville Water Quality

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Characterization of Lake Somerville Water Quality

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  1. Characterization of Lake Somerville Water Quality Conditions and Identification of Possible Contributing Sources of Pollution Joint Project of the Brazos River Authority and the Texas Institute for Applied Environmental Research

  2. Lake Somerville Physical Characteristics Dam Construction: 1967 Conservation Storage: 160,100 acre-feet Surface Area: 11,160 Acre Average Depth: 4 m Max. Depth nr. Dam: 9 m Conclusion: Shallow lake (not prone to persistent summer thermal stratification)

  3. Lake Somerville Watershed

  4. Lake Somerville (Segment 1212) Relevant Criteria: • 24-hr. Average DO: 5 mg/L • 24-hr. Minimum DO: 3 mg/L • pH Range: 6.5 – 9.0 S.U.

  5. Lake Somerville (Segment 1212) Texas 303(d) List Impaired for: • Depressed DO as of 2008 • High pH levels as of 2002 Concerns for: • Increased chlorophyll-a concentrations • Harmful algal blooms (Cyanobacteria)

  6. Lake Somerville Historical Review Pendergrass & Hauck (2008) pH Evaluation: • All pH exceedances occurred in summer months (June – August) • All but one pH exceedance occurred in the afternoon Pendergrass, D., and L. Hauck. 2008. Texas pH Evaluation Project http://tiaer.tarleton.edu/pdf/PR0810.pdf

  7. Source: Pendergrass & Hauck (2008)

  8. Lake Somerville Historical Review Based on algal data from Roelke et al. (2004): • Spikes in pH above 9.0 and dips below 8.5 correspond with spikes and dips in algal biomass Roelke, D.L., Y. Buyukates, M. Williams, and J. Jean. 2004. Interannual variability in the seasonal plankton succession of a shallow, warm-water lake. Hydrobiologia513: 205-218.

  9. Suspected Causes High pH – • Removal of inorganic carbon (i.e., dissolved CO2) through photosynthesis when algal productivity is high Depressed DO – • Respiration from large populations of algae

  10. Lake Somerville TCEQ Trophic Classification (2010): • Classified as hypereutrophic based on TSI for CHLA, Secchi and TP • Mean CHLA Ranked 96th out 100 Reservoirs • CHLA values trending upward Trophic Classification of Texas Reservoirs 2010 Texas Water Quality Integrated Report for Clean Water Sections 305(b) and 303(d) (Nov. 18, 2011) http://http://www.tceq.texas.gov/assets/public/compliance/monops/water/10twqi/2010_reservoir_narrative.pdf

  11. Water Quality Conditions High algal productivity and historically low dissolved inorganic nutrient levels in Lake Somerville & Yegua Creek

  12. Lake Somerville at the Dam

  13. Lake Somerville at the Dam

  14. Lake Somerville at the Dam

  15. Lake Somerville at the Dam

  16. Project Objectives • Identify possible contributing sources of pollution impairments • Characterize Lake Somerville water quality conditions

  17. Objective 1 – External Loadings • Identify possible contributing sources of pollution impairments • Land use and management inventory • Routine monitoring 10 tributaries • Storm monitoring 2 tributaries

  18. Land Use Source: United States Geological Survey (USGS) 2001 National Land Coverage Dataset

  19. Land Use & Management Major Crops • Coastal – hay & grazing • Rangeland – grazing • Some crops – corn, oats, sorghum Animal Production • Mainly beef cows Rangeland - 1 cow/8 to 10 acres Pasture – 1 cow/3 acres

  20. Permitted Discharges Source: Texas Pollutant Discharge Elimination System (TPDES)

  21. Tributary Monitoring • Source: Data Collection Initiatives to Address 5b/5c Water Bodies in the Brazos River Basin QAPP

  22. Tributary Monitoring Monthly Monitoring (Jan 2010 – Dec 2011) • Most tributaries intermittent, except Yegua Creek • Many events pooled or dry Somerville Dam Source: NCDC

  23. Median Values * Indicates no pooled samples

  24. Median Values * Indicates no pooled samples

  25. Storm Monitoring • Birch & Yegua Creeks • 7 Events • Most Jan-Jul 2010 due to relatively dry conditions in 2011

  26. Objective 1 – External Loadings No “hot spots” identified Possible sources for further investigation: • Urban development - Little Big & Brushy Creeks • Cropland fertilizer use – Cedar Creek • WWTF discharge – Nails & Yegua Creeks

  27. Objective 2 – Algal Growth & Internal Loadings • Characterize Lake Somerville water quality conditions • Reservoir Monitoring – low-level nutrients • Potential Sediment Release of P • Limiting Nutrient (N, P or N+P) • Algal Identification

  28. Objective 2 – Algal Growth & Internal Loadings • Monitoring Schedule 2010 & 2011 • March • May • June • July • August • September • November

  29. Reservoir Monitoring • Source: Data Collection Initiatives to Address 5b/5c Water Bodies in the Brazos River Basin QAPP

  30. Reservoir Conditions

  31. Surface Surface

  32. Top & Bottom Samples

  33. Top & Bottom Samples

  34. Are there water quality implications from Summer DO Stratification – De-stratification Events?

  35. Sediment Analyses Potential Sediment Release of P P Fractionation – • Most P bound to Fe and Al rather than Ca • Fe bound P would be released under anoxic conditions

  36. Preliminary Results P-Fractionation of Sediment

  37. Sediment Analyses Importance: Wind-Driven Suspension P Sorption – Equilibrium P Concentration (EPCo) Sediment EPCo > Water Column P (Sediment P may move into the water column) Sediment EPCo < Water Column P (Water column P may move into the sediment)

  38. Sediment Analyses P Sorption – Equilibrium P Concentration (EPCo)

  39. Limiting Nutrient Algal Assays Evaluated - • 3 Reservoir Stations & Yegua Creek • Native Algae & Test Algae (Pseudokirchneriellasubcapitata, formerly Selenastrumcapricornutum) • Maximum • Growth Rate • Florescence

  40. Limiting Nutrient Algal Assays – Native Algae

  41. Limiting Nutrient Algal Assays –Native Algae

  42. Algal Identification Major Divisions: Chlorophyta – green Cyanophyta – blue-green Diatoms

  43. Objective 2 – Algal Growth & Internal Loadings • Reservoir monitoring supported conclusion that pH peaks and depressed DO related to algal abundance • Monitoring top and bottom depths was inconclusive on release of nutrients from bottom sediments with low DO • Sediment fractionation indicated primarily Al and Fe bound P

  44. Objective 2 – Algal Growth & Internal Loadings • EPCo indicate sediments at times may be a source of P • Limiting Nutrient for in-lake algal growth mainly N • Algal Identification – primarily blue-green algae in summer, but steady population of greens throughout most months

  45. Conclusions – What does this mean? Lake Somerville • Work in progress – Things still to be investigated • Wind on reservoir stratification • Suspended sediment as P source • pH , DO, and CHLA were useful response variables to indicate eutrophic conditions, even when nutrients were low

  46. Thank You Questions?