Lake and Watershed Issues Impacting Water Quality

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Watershed Issues: External Nutrient Loading from Stormwater--project in progress

Water Quality Planning Grant received

Total Project Cost:  $39,600

Project Start Date:  March 1, 2019

Project Completion Date:  June 30, 2020


Status:  survey of pipes and ditches draining to lake and mapping of infrastructure .  Water quality testing is dependent on rainfall.  Public workshops are underway.


Nutrient inputs from fertilization of lawns and available options for elimination of this source will also be considered.


Watershed Issues: External Nutrient Loading from Groundwater

Groundwater assessment by Shank and Zamora complete--see below.

Recommendation to focus on rehab of lines in groundwater recharge area--Phase II of Town's Wastewater Collection System will rehab main gravity line along White Lake Drive as well as other needed rehab work in this area [ $3 M loan application (to State Revolving Fund) initiated].  Phase I Loan for $2 M has been awarded and construction should begin in early 2020.

Watershed Issues: Loss of Groundwater

There is no historical data on groundwater flow rates with which to make valid comparisons to present conditions, in which the annual rate of groundwater flow varies from  0 to 6% of the volume of the lake .  Inflow and infiltration (I&I) to gravity wastewater lines is largely due to groundwater inflow (robbing the system of groundwater which would otherwise continue to flow towards the lake) and this will be significantly reduced with rehabilitation of the collection system.

Lake Issues: Algae and Changing Acidity of the Lake Water

Nuisance and harmful algae blooms are typically the result of elevated nutrient levels.  At White Lake, there are plenty of nutrients already in the system which can be rapidly recycled by growing algae and vegetation.  The availability of nutrients depends on conditions within the lake, including water temperatures, dissolved oxygen levels, and pH (acidity).  Because the pH of the lake's source water--rainfall--has changed, we can see changes in the algae and how long they stick around.


SEE LAKE MONITORING SECTION FOR THE LATEST ON ALGAE TRENDS IN THE LAKE

Lake Issues: Internal Nutrient Cycling of Phosphorus

Sediment coring study complete--see below

White Lake groundwater contributing zone

Groundwater Flows and Nutrient Inputs: Shank & Zamora Report, April 2019

A Town of White Lake-funded project

Start Date:  February 1, 2018

Completion:  April 1, 2019


Summary of Key Findings:


  1. Water balance and numerical modeling both indicate that rainfall is the dominant water source to White Lake.  Groundwater inputs are low due to the spatially limited groundwater capture zone feeding the lake.
  2. Groundwater inputs to White Lake occur mostly along the northern and eastern edges, with outward groundwater flow along the southwestern edge.  Periodic pulses of groundwater can enter the lake below the southwestern shoreline following heavy precipitation events that raise the water table above the lake level for short periods of time.
  3. Stable isotope analysis indicates no current contribution to the lake from deeper confined aquifers. [Hydrogeological assessments in the region confirm that the surficial aquifer is the source for groundwater inputs to the lake--see figure below].
  4. Although the magnitude of groundwater flowing into the lake is small compared to rainfall, the high groundwater concentrations of organic nitrogen and dissolved phosphorus along the eastern shoreline indicate that this region could be an important long-term source of nutrients to White Lake.  It is possible that short-term pulses of contaminated groundwater could enter the lake along the southern shore in the vicinity of Timberlodge Village Drive (although no elevated nutrient levels were found in the lake in that area during the study period).


Principal Investigators:

Dr. Chris Shank, BHIC

Dr. Peter Zamora, UNCW

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A Hydrogeological Map: A Cross-Sectional Slice of the Coastal Plain

The map above shows a west-east view across the region, as groundwater flow moves in an easterly direction towards the sea.  These maps are constructed from well logs for public drinking water wells and monitoring wells established by the US Geological Service and the State of North Carolina.  

The source of groundwater flow into White Lake is the surficial aquifer--it begins to increase in depth near the Robeson/Columbus County line, moving eastward.





Regional Groundwater Assessment:

This hydrogeological map (and other cross-section maps for the region) was created by Groundwater Management Associates for the Lumber River Council of Governments


Sediment Coring Project: HAB and Tetra Tech

A Town of White Lake-funded project

Start Date:  February 12, 2019

Completion:  June 1,  2019


Project Summary:

  1. Sediment cores were obtained from deeper portions of the lake with a muck/muddy bottom.  This muck comprises about half of the total area of lake bottom.  Core samples were sectioned for analysis of phosphorus fractions and levels of naturally-occurring iron, aluminum and calcium (these elements can serve as adsorbents of P, locking it up so that it is not available to algae).  In the deeper core samples a light grey clay layer was observed (shown in the photo at the left).  
  2. Total phosphorus was highest in the top few centimeters of sediment and declined with depth.  Aluminum-bound P was the most abundant form of P found in the sediments.  A similar coring project was conducted at Lake Waccamaw, and aluminum-bound P levels were quite similar in the muck samples there as well.
  3. A laboratory incubation of intact cores (under controlled conditions and no oxygen) indicated that anoxic P release from sediments is minimal.  This form of P release is common in sediments that are exposed to periods of no oxygen.  As a result, no sediment P inactivation treatment (adding a higher amount of an adsorbent such as alum or Phoslock) is needed.
  4. Sediment resuspension due to boating activity and wind is likely the primary mechanism for P release/increase in water column P in summer, while elevated pH levels can also play a role in enhancing P bioavailability.  
  5. Project scientists were in agreement that ongoing monitoring of  White Lake will provide additional information that will enable timely action when and if water column P levels reach a threshold level.
  6. Aquatic vegetation and algal mats bind up nutrients in their tissues, so removal of material that washes up along the shoreline will help to reduce the amount of nutrients being recycled within the lake.


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