500 likes | 777 Views
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. Lake Somerville Physical Characteristics .
E N D
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
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)
Lake Somerville Watershed
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.
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)
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
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.
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
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
Water Quality Conditions High algal productivity and historically low dissolved inorganic nutrient levels in Lake Somerville & Yegua Creek
Project Objectives • Identify possible contributing sources of pollution impairments • Characterize Lake Somerville water quality conditions
Objective 1 – External Loadings • Identify possible contributing sources of pollution impairments • Land use and management inventory • Routine monitoring 10 tributaries • Storm monitoring 2 tributaries
Land Use Source: United States Geological Survey (USGS) 2001 National Land Coverage Dataset
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
Permitted Discharges Source: Texas Pollutant Discharge Elimination System (TPDES)
Tributary Monitoring • Source: Data Collection Initiatives to Address 5b/5c Water Bodies in the Brazos River Basin QAPP
Tributary Monitoring Monthly Monitoring (Jan 2010 – Dec 2011) • Most tributaries intermittent, except Yegua Creek • Many events pooled or dry Somerville Dam Source: NCDC
Median Values * Indicates no pooled samples
Median Values * Indicates no pooled samples
Storm Monitoring • Birch & Yegua Creeks • 7 Events • Most Jan-Jul 2010 due to relatively dry conditions in 2011
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
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
Objective 2 – Algal Growth & Internal Loadings • Monitoring Schedule 2010 & 2011 • March • May • June • July • August • September • November
Reservoir Monitoring • Source: Data Collection Initiatives to Address 5b/5c Water Bodies in the Brazos River Basin QAPP
Surface Surface
Top & Bottom Samples
Top & Bottom Samples
Are there water quality implications from Summer DO Stratification – De-stratification Events?
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
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)
Sediment Analyses P Sorption – Equilibrium P Concentration (EPCo)
Limiting Nutrient Algal Assays Evaluated - • 3 Reservoir Stations & Yegua Creek • Native Algae & Test Algae (Pseudokirchneriellasubcapitata, formerly Selenastrumcapricornutum) • Maximum • Growth Rate • Florescence
Algal Identification Major Divisions: Chlorophyta – green Cyanophyta – blue-green Diatoms
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
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
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
Thank You Questions?