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 ID: 761669
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Characterization of Lake Somerville Water Quality Conditions and Identification of Possible Contributing Sources of PollutionJoint Project of the Brazos River Authority and the Texas Institute for Applied Environmental Research
Lake Somerville Physical Characteristics Dam Construction: 1967Conservation Storage: 160,100 acre-feet Surface Area: 11,160 AcreAverage Depth: 4 mMax. Depth nr. Dam: 9 mConclusion: 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/LpH 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 afternoonPendergrass, D., and L. Hauck. 2008. Texas pH Evaluation Project http ://tiaer.tarleton.edu/pdf/PR0810.pdf
Source: Pendergrass & Hauck (2008)
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 biomassRoelke, D.L., Y. Buyukates, M. Williams, and J. Jean. 2004. Interannual variability in the seasonal plankton succession of a shallow, warm-water lake. Hydrobiologia 513: 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 96 th 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
Lake Somerville at the Dam
Lake Somerville at the Dam
Lake Somerville at the Dam
Lake Somerville at the Dam
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 inventoryRoutine monitoring 10 tributariesStorm monitoring 2 tributaries
Source: United States Geological Survey (USGS) 2001 National Land Coverage Dataset Land Use
Land Use & Management Major CropsCoastal – hay & grazing Rangeland – grazingSome crops – corn, oats, sorghumAnimal Production Mainly beef cows Rangeland - 1 cow/8 to 10 acres Pasture – 1 cow/3 acres Land Use Classification Percent of Total Pasture/Hay 35.4 Forest 27.4 Rangeland 20.6 Wetland 7.4 Developed 5.2 Water 1.9 Cultivated Crops 1.8 Barren Land 0.3
Source : Texas Pollutant Discharge Elimination System (TPDES) PermittedDischarges
Tributary MonitoringSource: 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
* Indicates no pooled samples MedianValues
* Indicates no pooled samples MedianValues
Storm Monitoring Median Concentrations Location NO 3 -N (mg/L) PO 4 -P (mg/L) Total P (mg/L) Birch Creek 0.05 0.02 0.22 Yegua Creek 0.03 0.02 0.10 Birch & Yegua Creeks 7 Events Most Jan-Jul 2010 due to relatively dry conditions in 2011
Objective 1 – External Loadings No “hot spots” identifiedPossible sources for further investigation: Urban development - Little Big & Brushy CreeksCropland fertilizer use – Cedar CreekWWTF discharge – Nails & Yegua Creeks
Objective 2 – Algal Growth & Internal Loadings Characterize Lake Somerville water quality conditions Reservoir Monitoring – low-level nutrientsPotential Sediment Release of P Limiting Nutrient (N, P or N+P) Algal Identification
Objective 2 – Algal Growth & Internal Loadings Monitoring Schedule 2010 & 2011March MayJuneJuly August September November
Reservoir MonitoringSource: Data Collection Initiatives to Address 5b/5c Water Bodies in the Brazos River Basin QAPP
Reservoir Conditions
Surface Surface
Top &BottomSamples
Top &BottomSamples
Are there water quality implications from Summer DO Stratification – De-stratification Events?
Sediment Analyses Potential Sediment Release of PP Fractionation – Most P bound to Fe and Al rather than Ca Fe bound P would be released under anoxic conditions
Preliminary Results P-Fractionation of Sediment Station ID Collection Date Al bound P (mg/Kg ) Ca Bound P (mg/Kg ) Fe Bound P (mg/Kg ) 11881 5/25/2010 49 <2 210 11881 8/24/2010 <2 8 80 11881 3/23/2011 138 13 126 11881 8/22/2011 105 11 158 16879 5/25/2010 45 <2 268 16879 8/24/2010 <2 25 80 20532 5/25/2010 47 <2 269 20532 8/24/2010 <2 13 125 20532 3/23/2011 130 27 306 20532 8/22/2011 98 31 156
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) Station West Arm EPCo ( mg/L) Surface PO 4 -P (mg/L) Bottom PO 4 -P (mg/L) Sediment Source or Sink May-10 0.002 0.002 No Data ? Aug-10 0.003 0.133 No Data Sink Mar-11 0.027 0.011 0.006 Source Aug-11 0.052 0.018 No Data Source
Limiting Nutrient Algal Assays Evaluated -3 Reservoir Stations & Yegua CreekNative Algae & Test Algae (Pseudokirchneriella subcapitata, formerly Selenastrum capricornutum ) Maximum Growth Rate Florescence
Limiting Nutrient Algal Assays – Native Algae Location Month Maximum Growth Rate Primary Limiting Nutrient Secondary Limiting Nutrient (if indicated) 2010 2011 2010 2011 Reservoir near dam Mar P N N P May N N P P Jun P N N P Jul N N P P Aug N N P P Sep N N P P Nov N N+P P P
Limiting Nutrient Algal Assays –Native Algae Station Month Maximum Growth Rate Primary Limiting Nutrient Secondary Limiting Nutrient (if indicated) 2010 2010 Yegua Creek Mar P N May P N Jun P N Jul P N Aug N+P -- Sep P N Nov N+P P
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 DOSediment 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 NAlgal Identification – primarily blue-green algae in summer, but steady population of greens throughout most months
Conclusions – What does this mean? Lake SomervilleWork in progress – Things still to be investigated Wind on reservoir stratificationSuspended sediment as P sourcepH , DO, and CHLA were useful response variables to indicate eutrophic conditions, even when nutrients were low
Thank YouQuestions?