Scrubbing and Skimming

New Methods for Combating Algal Blooms

Skimming – A recent story on the Corps of Engineers use of algal skimmers in Florida to help combat toxic algal blooms reminded me of North Carolina’s own efforts to combat algal blooms. In Florida, the Lake Okeechobee skimming process uses “dissolved air flotation” to bring algae to the surface and remove it from the water column.  The process has been used effectively in wastewater treatment where the systems are contained better able to engineer but it is a relatively new approach to combating harmful algal blooms in the natural environment.

Scrubbing – A slightly different “in-line” removal process was tried in North Carolina to use scrubbing of algae. Durham partnered with HydroMentia to test the effectiveness of algae scrubbing on Falls Lake waters. In the pilot study, HydroMentia found the method had a positive effect at removing nitrogen and phosphorus, the fuel driving algal blooms (See their report  While technologies such as these may not be cheap, they may be part of the solution to the nutrient pollution challenges facing NC.

Upstream Benefits

The Falls Lake Nutrient Strategy put in place by NC DEQ in 2010 provides more than just drinking water protections for Falls Lake. Communities in the Falls watershed such as Durham benefit from the rule protections, too.  Durham’s drinking water supply comes from Lake Michie and Little River Reservoir, both located in the Falls Watershed.  This spring, local news reported that algae blooms in these waterbodies are fowling the taste and smell of water for city residents.  A cause of these algae blooms is excess nutrients in the water body combined with warming temperatures. 

The rules put in place to protect Falls Lake also benefit upstream water quality.  They address lowering nutrient pollution from sewage treatment plants, reducing polluted runoff from new development and farms while protecting streamside forests.  While implemented for Falls Lake, upstream lakes like Michie and Little River also benefit from these protections.

Due to a legislative mandate, the State Division of Water Resources is currently revising all its nutrient strategy rules.  In doing so, it’s important to realize that, while the rules target a lake or estuary, they benefit communities throughout the watershed.  


A necessary step in the environmental mitigation process is to secure long-term stewardship of the project site.  Among the responsibilities of the steward is to visit and inspect mitigation sites to make sure that the terms of the easement are being honored.  For the Neville Farms site, the stewardship responsibility of the site was arranged with Unique Places to Save (UP2S).  UP2S has a strong presence in the area near the farm, has worked on similar projects, and looks to foster relationships with landowners to develop shared goals. All these reasons made them a good fit for working with us.

UP2S signage posted to help mark the easement boundary.

Raleigh’s Welcome Change

The City of Raleigh got some good new. As reported on WRAL, the Army Corps approved the City’s request to reallocate Falls lake’s storage toward drinking water allowing the City to increase the drinking water withdrawals by 22 million gallons a day.  As we’ve covered previously, aside from drinking water, Falls Lake has several allocated uses that include flood control and sustaining ecological functions.  With this change, lake managers will look to preserve more water in the lake to supply drinking water for Raleigh.

Why is this good news for the City?  Raleigh has struggled to identify long-term water sources to provide for its growing population and even explored creating a new reservoir.  With this move, Raleigh’s water supply is more secure for the foreseeable future.  It also raises the importance of upstream watershed protection.  If Raleigh is going to be counting more on Falls Lake, the City, State and region should be stepping up efforts to prevent its pollution and protect its long-term health.

Falls Lake (Source: Army Corps of Engineers.)


25-Year Jordan Water Quality Trends

A US Geological Survey Report released late in 2018 provides a needed review of water quality trends for select NC rivers and streams over the last 25-years (1989-2013). Importantly, the report focuses on the quality of water flowing to drinking water reservoirs in North Carolina.  Here, I’ll briefly cover the results affecting Jordan Lake where data both in streams and the Lake were analyzed to gauge what’s happening and what’s needed to protect our drinking waters.

What’s happening? 

Over the 25-year study period, population in counties surrounding the Lake grew by 85%. Not surprisingly, during that period developed land use nearly doubled in watersheds draining to Jordan Lake, typically coming from less polluting forested land use.  Also, during that time, improvements have been made to waste water treatment plants that have reduced the discharge of pollutants even though the plants were serving more users.  Overall, there are a mixture of factors that have influenced water quality flowing to Jordan Lake.

What are the trends?

In a word, mixed.  Generally, monitoring of nutrients in streams near Jordan Lake showed improvement TP concentrations more than TN (See Figure 1). Conditions in Jordan Lake, however, were less promising with stations showing increased concentrations for both TN and TP.  Much like our estuaries, organic nitrogen was the primary form of N that increased during the period of study.


Increases in triangle-area population continue to put a strain on Jordan Lake both for adequate quantity and quality for its users.  Even though management efforts over the study period resulted in some in-stream water quality improvement, conditions continue to be poor at the lake demonstrating the continued need for policies protective of the Lake.

Monitoring Stations near and in Jordan Lake used in the 25-year study. Source: USGS 2018.

Extreme Storms, Harmful Blooms

Interesting insight from UNC Research Hans Paerl on what impacts we may be seeing from the extreme storms like hurricanes Matthew and Florence in the coming years.


Chesapeake Check-In

The Chesapeake Bay has experienced problems similar to those in NC’s estuaries as it relates to nutrient pollution. Low-oxygen “dead zones’ have resulted in persistent fish kills and stressed or diminished aquatic ecosystems.

Area draining to the Bay stretches from from New York to Virginia and has had federally coordinated efforts to curb nutrient pollution since the 1980’s.  These efforts combined with funding to improve wastewater treatment and improved development and agricultural practices have all played a role in improving water quality in the Chesapeake though not as much as bay managers would like.

The news this year is mixed.

Good News: In spite of a predicted larger than average dead zone “due to higher spring flows and nitrogen loading from the Susquehanna and Potomac rivers”,  hypoxia (i.e. low oxygen) in the Bay for the month of July was historically good.

Bad News: Overall, summer hypoxia was average with late summer conditions worse than average.

What’s this mean?  The challenge of reducing nutrient pollution and its associated water quality problems is formidable. As covered previously, sustained effort, political will, and funding are needed to make a positive impact.  Even then, increased population, loss of wetlands and forest, and the misuse of nutrients can overwhelm these efforts, neutralizing progress.  NC is in the process of re-adopting its nutrient rules. In doing so, it should look for opportunities to eliminate pollution loopholes and find ways to strengthen the overall effectiveness of its nutrient reduction strategies.

Chesapeake Hypoxia Trends. Source: Maryland Department of Natural Resources.

Plan For the Worst

Hurricane Florence had numerous effects on North Carolina: Flooded neighborhoods, ruined crops, damaged infrastructure, and submerged businesses to name a few.  All that water created what state officials were calling a 500 to 1000 year flood.

Indeed, floods put portions of the Lumber, Cape Fear, and Neuse at record or near-record flood levels.  One of the negative effects of the storm was inundation of poultry houses, swine farms  and hog waste lagoons located in the floodplain.  The State estimated that waste from 50 lagoons washed out into the floodwaters and that 5,500 pigs and 3.4 million chickens drowned. While awful, many of these same facilities were flooded 2 years ago by Hurricane Matthew and/or 20 years ago by Hurricane Floyd.

How can the state better prepare for future storms?  Twenty years ago, the state began a program to move hog facilities out of the floodplain.  Reportedly, 43 high risk hog farms either moved or were closed in the years following Floyd. While a positive step, increased funding is needed to relocate the many remaining hog farms from the 500-year floodplain which seems to be the new norm for planning purposes.

After three 500 year storms in 20 years, planning for extreme events is something the state should undertake to minimize environmental impacts from future extreme weather events.

Organic matter in Florence’s floodwaters flowing from rivers to the ocean.

Source: NASA Earth Observatory

Open the Flood Gates

Following up on the previous post, managers of Falls and Jordan lakes are nearing the end of their lake draw down.  For two weeks after Hurricane Florence made landfall, the flood storage usage of these lakes was in full effect as manages nearly eliminated water release from these dams.  While that helped downstream communities from having additional upstream floodwaters piled onto already devastating floods, it also led to extremely high water levels at the lakes.

With the downstream floods abated, lake managers began drawing down the lakes’ levels September 25th.  As demonstrated by Hurricane Florence, uses of these lakes goes well beyond drinking water and their conservation remains a high priority.

Falls Lake draw down after Florence. The Lake nearing its managed target level of 252 ft.

Downstream Falls Water Releases – A hydrograph that could only be created under a man-made conditions.

Florence Flood Mitigation

We touched on the uses of Jordan and Falls Lake in a previous post.  One of those uses is currently evident in the aftermath of the recently passed Hurricane Florence.  The storm dumped between 6 and 12 inches of rain over the Falls Lake Watershed. With those rainfall totals, discharge from the lake should be higher than normal or raging.

The flood storage use of the Lake’, however, requires that the Army Corps hold back water to help mitigate downstream flooding.  With that objective you get the following hydrograph for Falls Lake where 62% of its storage is intended for flood control:

Lake managers will keep discharges from the Lake low to try to mitigate downstream flooding.  They’ll hold the water behind the dam until the downstream flooding ebbs. Until that happens, however, you can walk across the Neuse below Falls Lake.

No flow below the Falls Lake Dam. Lake managers are trying to mitigate flooding from Florence.