Diffuse Sources of Nutrients

Research Thrust Area 2: Sustainable Management of Diffuse Sources of Nutrients

Management of non-point nutrient sources is critical in reducing coastal eutrophication. In the past, levels of nitrogen were largely coming from point sources such as wastewater treatment plants and industry. The efforts focused on point sources have largely helped reduce the levels of nitrogen in areas such as Tampa Bay and now a large fraction of the overall nutrient load is coming from diffuse sources (i.e., non-point sources) such as residential homes and transportation use.

The fundamental research question for Research Thrust Area 2 is: What innovative and sustainable non-point source nutrient management technologies and strategies can be developed, demonstrated, and evaluated for novel water management? To answer this question Thrust Area 2 is further divided into three components:

  • implementing innovative low impact development (LID) technologies for stormwater management,
  • advancing onsite wastewater systems from a management strategy more inclined for disposal/treatment, towards nutrient removal and recovery, and
  • quantifying residential fertilizer applications and loadings as they relate to socio-economic differences and presence/absence of fertilizer sales and seasonal application bans.
Nutrient Fluxes in conventional (upper) and green (lower) non-point source infrastructures.

Nutrient Fluxes in conventional (upper) and green (lower) non-point source infrastructures.

RAINmgt’s vision for Thrust 2 is illustrated in the figure on the left. Existing infrastructure (red) includes diffuse sources from (1) fertilizer application by homeowners that may be unregulated and unaware of the consequences, (2) conventional septic systems that poorly remove nutrients (particularly nitrogen) and (3) stormwater management focused on flood protection rather than nutrient management. A more sustainable diffuse source nutrient management infrastructure is shown in the lower, green, part of the figure that includes the three non-point source, diffuse technologies and strategies discussed above including: (1) low impact development (LID) systems, (2) on-site waste water treatment systems and (3) diffuse residential lawn nutrient management.

(1) Low Impact Development Technologies

LID is a structural Best Management Practice approach that works with nature to manage stormwater as close to its source as possible to promote the natural movement of water and maintain or restore a watershed’s hydrologic and ecological functions.   Among LID technologies, bioretention systems (i.e., “rain gardens” or “bioswales”) are promising for reducing nutrient loads from urban runoff.  The goal of this research component is to develop innovative and sustainable bioretention systems that can remove nutrients under the dynamic loading conditions typical of urban stormwater runoff.

(2) Innovative Onsite Wastewater Treatment Systems

Approximately one third of the wastewater in the U.S. is treated using onsite systems and the Florida Department of Health reports there are more than 2.6 million septic systems in Florida serving about one-third of the state’s 19 million residents.  These systems are designed to reduce the risks of exposure to pathogens and vectors but are not designed and optimized for nutrient removal. As attention from water quality regulators and the public in many watersheds on nitrogen loadings increases, new options are sought for onsite treatment. The goal of this research component is to optimize nitrogen and phosphorus removal in transiently loaded onsite wastewater treatment systems using innovative media materials while keeping maintenance easy for homeowners.

(3) Diffuse Residential Lawn Nutrient Management

EPA (2011) reports that approximately 50% of turfgrass (i.e., any of various grasses grown to form turf) is not fertilized.  However, the remainder is fertilized at different intensities.  In coastal areas where residential and urban land use patterns are promoted, fertilization of lawns can be an important (and even a dominant) source of nitrogen entering surface waters. Some research has been performed to quantify the release of nutrients from commercial and residential landscaping but there is not enough data on the different usage based on socio-economic factors. The goal of this research component is to quantify the release of nutrients from residential yards in a socio-economic context, with specific focus on the Tampa Bay area.