Color-coded Nutrient Pollution Maps Shine the Light! LakeO/SLE

I have been wanting to write about these water quality maps for months. Now that I am at home, social distancing, due to the coronavirus pandemic, I have no excuse. So today, we begin.

Some history: about six months ago my brother, Todd Thurlow and Dr Gary Goforth started collaborating to create nutrient pollution color coded maps. The data is compiled by Dr Gary Goforth via South Florida Water Management District’s DBHydro water quality database; and the graphics are generated by Todd. All of these computer generated images can be found on my brother’s website, eyeonlakeo. This is a site you are probably familiar with as it led the charge on Harmful Algal Bloom Lake O satellite imagery before that went public in 2018. My goal is to do the same with these maps. In time, have them “go public.” The form this data exists in the District’s reports today is very sophisticated and thus confusing for the general public. With help from Gary, Todd, and a former eighth grade teacher, (me) it doesn’t have to be!

So let’s start with overview color. Basically, any color other than green is a flashing light, especially orange-red, or dark russet! 

When looking at these maps, one must keep in mind that the map is in WATER YEARS. A water year begins on May 1 of a year and goes through the following year ending April 30th. The above map labeled “Lake Okeechobee Watershed Total Phosphorus Concentrations,” is Water Year 2019. (May1, 2018 – April30, 2019.)

Next, one must learn to think in terms of SUBWATERSHEDS and BASINS. The image above is for the entire 3.4-million acre watershed of Lake Okeechobee, and is broken into sub-watersheds and basins from large to small based on the way the water “flows” or used to. The sub watersheds are identified in bold in the table to the left and the basins are listed below.

The colors on the map are shown by scale at the bottom from green to dark red. You don’t have to be a genius to see that for instance S-154 Basin is one of the darkest color reds with a concentration of 857 “µg/L” (microgram per liter, commonly expressed as “parts per billion”, or “ppb”). In 2001, the State of Florida established a Target for the average phosphorus concentration in water entering Lake Okeechobee of about 40 ppb, so this basin’s concentration of 857 ppb is 21.4 times the Target concentration for the Lake; hence this basin has a “Target Multiple” shown in the table of 21.4.  

The color coding gives you a quick and easy way to identify which basins are close to the target (green basins) and which basins need a lot of improvement in their non-point source controls (red basins).  For a more quantitative assessment, you can check out the  “” values in the table for each basin.  It’s important to remember that while concentrations are very important to identify which basins need additional non-point source controls, such as farming or urban best management practices (BMPs), the “load” entering the lake from each basin is also important.  We’ll talk about loads in a future blog. Now let’s take a look above at map number two, the “St Lucie Estuary and Watershed Total Nitrogen Concentrations” map.   Nitrogen is the other important nutrient besides phosphorus that affects our water quality, including algae blooms.  Since we already know now how to interpret the color coding, we can easily see that the Tidal Basins – the largely urban areas around the estuary – has the lowest nitrogen concentration, i.e., the Tidal Basins has the best nitrogen water quality.  The Tidal Basin had a concentration of 824 ppb, and with a Target Multiple of 1.1 this concentration is still about 10% higher than the Target set by the State of 720 ppb.  So while this basin has the best nitrogen levels in the watershed, it still has some improvements to make in order to meet the nitrogen Target.  By contrast, Lake Okeechobee discharges, and runoff from the C-23 and C-24 basins are the darkest red and therefore have the poorest water quality, with nitrogen concentrations about 2 times the Target.    The orange to red colors for these and the C-44 and Ten Mile Creek basins indicate these basins need to implement considerably more effective source controls in order to meet the Target for the Estuary.

Todd’s website and Gary’s (http://garygoforth.net/Other%20projects.htm) show phosphorus and nitrogen maps for the Lake and St. Lucie Estuary watersheds.  They are working on maps for the Caloosahatchee River and Estuary Watershed.

In closing, these powerful visual maps give us the ability to easily “see” where the greatest problems of nutrient runoff are located; the nutrients come from many sources, including urban and agricultural activities, e.g., fertilizer application. And although the numbers and colors don’t tell us exactly where this pollution is coming from, we can determine it is problematic in the designated basins.

That’s enough for our first day. Hope it was a good one!