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: 1967Conservation Storage: 160,100 acre-feetSurface 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/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 ReviewPendergrass & 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 Projecthttp://tiaer.tarleton.edu/pdf/PR0810.pdf

Source: Pendergrass & Hauck (2008)

Lake Somerville Historical ReviewBased 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. Hydrobiologia 513: 205-218.

Suspected CausesHigh 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 SomervilleTCEQ 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 ConditionsHigh 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 Objectives1) Identify possible contributing sources of

pollution impairments2) 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

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

Land Use

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 acresPasture – 1 cow/3 acres

Land Use Classification

Percent of Total

Pasture/Hay 35.4Forest 27.4

Rangeland 20.6Wetland 7.4

Developed 5.2Water 1.9

Cultivated Crops 1.8Barren Land 0.3

Source: Texas Pollutant Discharge Elimination System (TPDES)

PermittedDischarges

TributaryMonitoring

Source: Data Collection Initiatives to Address 5b/5c Water Bodies in the Brazos River Basin QAPP

Tributary MonitoringMonthly Monitoring (Jan 2010 – Dec 2011)• Most tributaries intermittent, except Yegua

Creek• Many events pooled or dry

Somerville DamSource: NCDC

* Indicates no pooled samples

MedianValues

* Indicates no pooled samples

MedianValues

Storm Monitoring

Median Concentrations

Location NO3-N (mg/L)

PO4-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 LoadingsNo “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

ReservoirMonitoring

Source: 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 DateAl bound P

(mg/Kg)Ca Bound P

(mg/Kg)Fe Bound P

(mg/Kg)

11881 5/25/2010 49 <2 21011881 8/24/2010 <2 8 8011881 3/23/2011 138 13 12611881 8/22/2011 105 11 158

16879 5/25/2010 45 <2 26816879 8/24/2010 <2 25 80

20532 5/25/2010 47 <2 26920532 8/24/2010 <2 13 12520532 3/23/2011 130 27 30620532 8/22/2011 98 31 156

Sediment AnalysesImportance: 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 AnalysesP Sorption – Equilibrium P Concentration (EPCo)

Station West Arm

EPCo (mg/L)

Surface PO4-P (mg/L)

Bottom PO4-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 AssaysEvaluated -• 3 Reservoir Stations & Yegua Creek• Native Algae & Test Algae (Pseudokirchneriella

subcapitata, formerly Selenastrum capricornutum)

• Maximum Growth Rate Florescence

Limiting Nutrient Algal Assays – Native Algae

Location Month

Maximum Growth RatePrimary Limiting

NutrientSecondary

Limiting Nutrient (if indicated)

2010 2011 2010 2011

Reservoir near dam

Mar P N N PMay N N P PJun P N N PJul N N P PAug N N P PSep N N P PNov N N+P P P

Limiting Nutrient Algal Assays –Native Algae

Station Month

Maximum Growth RatePrimary Limiting

NutrientSecondary

Limiting Nutrient (if indicated)

2010 2010

Yegua Creek

Mar P NMay P NJun P NJul P NAug N+P --Sep P NNov N+P P

Algal IdentificationMajor Divisions:Chlorophyta – greenCyanophyta – blue-greenDiatoms

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?