Nutrient Sources


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:  the survey of pipes and ditches draining to lake is complete.  The Lumber River COG has created GIS maps with these sites and other town infrastructure.  Water quality testing has been done on a number of the outfalls, and the nutrient concentration of rainfall has also been tested.  The Town has expressed a willingness to adopt a stormwater management plan that includes ordinances and development guidelines.

Nutrient Loading from Groundwater

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

One of their recommendations is to focus on the rehabilitation of wastewater lines in groundwater recharge area, particularly along the eastern shoreline--Phase II of Town's Wastewater Collection System will rehab the 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.

Internal Phosphorus Cycling

Lake sediments serve as a natural storehouse for phosphorus.  In a lake as shallow as White Lake,  the wind can cause sediments to be re-suspended in the water, so that phosphorus becomes available for algae growth.  The same thing happens with boating use that stirs up sediments.

Nutrients in Rainfall

Rainfall samples taken in February and March 2020 averaged 0.013 mg/L of Total Phosphorus, and 0.373 mg/L of Total Nitrogen (split evenly between inorganic and organic nitrogen.

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

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.