Early in my career, I had the pleasure of spending some time working on ponds on the internationally famous W.T. Waggoner Estate Ranch. That massive amount of land covers 550,000 acres in north Texas and sits in parts of six counties, near the town of Vernon. This iconic ranch recently has been in the news. It sold, much to the chagrin of the traditionalists…not to mention those deeply in touch with its heritage and history. Just for perspective, visualize a land mass about 30 miles wide and 50 miles long, in one contiguous piece of privately owned property. I bet there are 500 ponds and lakes on that parcel. Heck, they don’t even know how many ponds they have. Most were built for watering livestock, but beginning in the 1980’s, a few of them were designated for fishing. As I traveled around the ranch with the staff game warden (yes, they have private game wardens on staff), I became convinced there are places on that property where no human foot had ever trampled…ever. I also became convinced there are too many microclimates around that ranch to count. There are arid areas with rough, rock covered cedar breaks. There are fertile soils with enough rain to support good crops of wheat. Heck, one of those wheat fields covered 20,000 acres at that point in time. It took a full day for a tractor to plow around it one time.

But, the thing that stands out to me most of all, as a passionate pond guy, was how we could go into one pasture and see a pristine, beautiful, clear pond with a few trees around it and then go less than a quarter-mile and see a pond the same color as chocolate milk with an orange tint. There were some ponds on that property that I swear looked exactly like the barren red dirt that surrounded it. The only way you could tell it was a pond was because it was flat. Even more fascinating was the fact that some of these mud holes produced some giant bass. There were not many bass, but some of them learned to play the game in those muddy waters well enough to exceed thirteen pounds.

“Checking visibility of a muddy lake to begin the process of clearing it.”

That ranch was my introduction into clearing muddy waters. We tried bales of hay that had been rained on and sometimes it helped. Often it didn’t. If not, we’d try aglime. Or, maybe some gypsum. After all, most of the clear waters on that ranch had measureable amounts of gypsum, which occurs naturally in some of the soils, especially on the western edges of that property.

Sure, we’d do the jar tests. We’d set up five or six one gallon glass pickle jars I’d grab from a football concession stand. Jar one was used as a control—just pond water. In Jars two-five, we’d add pond water and different concentrations of these various concoctions. It was fun, even if not totally helpful.

When it was all said and done, most of the time we used aluminum sulfate, alum, if you will. We’d launch a boat, have the alum in big plastic barrels sitting on a trailer backed up to the edge of the lake, and a water pump with hoses to draft pond water. On the intake side, we’d have a Venturi device we made by simply adding a smaller hose (like a one-inch hose) with a valve. The small hose was long enough to dip into a container of alum in the boat. We’d shove off with one guy driving the boat and another operating the pump. We’d mix and spray alum…and watch to see what happened to the water. At some point during that adventure, we began to see changes as little red clumps started forming in the water. It was like all those suspended clay particles became magnetic, attracting and sticking to each other. When that happened, it was our trigger to slow down. If we didn’t, we’d see a rapid pH shift in the water. A rapid pH shift would cause a fish kill. A fish kill would cause another loss…our job. It’s one of those “trickle down” economic effects. As we slowed down, the clumps would dissipate. It was fascinating to watch. We’d add a little more alum and wait. Clumps would form and then melt. Finally, when we reached the break point, the clumps would stick together, become heavy, and sink. A pond would go from chocolate milk to Caribbean blue in a matter of hours. Just as fascinating was how long a pond would stay clear after one of those treatments. We watched some of them go from muddy to clear overnight and right back to muddy the next day. We also saw some of them go clear and stay that way. It was unpredictable.

Today’s world is quite different. With our burgeoning industry, we now have resources we didn’t have back in the early 1980’s. Most pickle jars are now plastic and we have folks with microscopes in labs that can look at pond water and help us figure out why it’s so muddy… ‘er turbid. That’s the word today, turbid. There are people who have designed different products to assist with muddy, ‘er turbid, waters. Oh yes, there are still the methods of those days long ago, especially gypsum and alum, but now we can adjust the nutrients if turbidity is based around domination of a specific type of microorganism or a single cell plant or bacteria. There are also polymers available, which will specifically focus on removing certain suspended soils or solids and leave the nutrients alone.

So, nowadays, more effort is centered on diagnosing the issue and then prescribing a plan of action, rather than rolling the dice in a boat and shooting out a dose of alum. Not that those old methods won’t work, but it’s like comparing Grey Poupon mustard to French’s—it’s a refined taste. Remember one of the Laws of Nature: With every move we make, there’s a reaction in nature. Several of those Waggoner Ranch ponds we treated actually traded problems. I remember one in particular. It went from muddy to clear overnight and within a month was 90% covered in bushy pondweed. That clear water was shallow and all it needed was sunlight to grow bunches of plants all over the place.

“Collecting a sample to test with gypsum, alum or to simply see if the clay particles will settle on their own.”

More recently, we’ve done some work in central Texas, near the small burg of Hico, purportedly the final home of Billy the Kid. At least there’s a museum there about the notorious outlaw with all kinds of research proving he lived there.

Just outside Hico is John and Ellen McStay’s ranch. On that ranch resides a 14 acre lake teeming with nice bass and bluegills. The problem? The lake, which a few short years ago was a nice, healthy shade of green and you could see your feet in three feet of water, has gone turbid.

Mr. McStay became convinced the channel catfish in the lake kept it stirred up, so he and the ranch staff began harvesting catfish. Still muddy. Its color today resembles an olive-colored cupcake, sort of a deep-green batter-looking color. It doesn’t seem to be affecting the fishery, as that portion of the equation is thriving. But, it affects catching…or seems to. Team McStay can fish for hours with a minimum of luck compared to what fun they’ve had in the past and also when compared to a crystal clear lake on the ranch across the road. Launch an electrofishing boat in their lake and fish pop up all over the underwater creek channel and standing brush. But, toss out your favorite crankbait and nada, zilch, nothing.

But, there is a difference worth thinking through. Several years ago, while in the throes of one of those 100 year droughts Texas seems to be having every couple of years, the lake level dropped dramatically. The McStay’s took advantage of the drought to deepen the upper end of the lake. They added several surface acres and deepened the shoreline of other parts of the lake. They added some well water and the rains came and re-filled the parched lake. A couple years later they noticed a difference. Starting about three or four years ago, the clear water changed. Visibility dropped. Over the last 12 months, they’ve faithfully kept visibility records. They’ve collected samples of water and sent them to different labs, hoping for some analysis that will lead to a magic bullet, maybe something as simple as that alum stuff. They’ve spoken with at least five water quality experts.

It’s become almost detective-esque, like some wet water novel, hopefully with a magical ending where everyone lives happily ever after and the fish jump into the boat, begging to be caught.

Water was collected, sent to a microbiologist and found to have almost 500,000 algae cells per milliliter. 77% of those cells were bluegreen algae, cyanobacteria, if you will. That explains the olive color tint to the water. But, there’s more. Suspended non-algae particulates were even more abundant and are at least 15 times more abundant than that green stuff. Interestingly, prior water samples suggest those suspended particulates are mostly diatoms which may have been dead for eons, literally.

This more scientific approach now leads the experts to think a multi-pronged attack may be necessary, because the “problem” has several layers. First, the cyanobacteria are most likely thriving because of an imbalance of nutrients. Recent research is proving that bluegreen algaes grow when the balance of nutrients leans too heavily on phosphorus. When the proportions of usable phosphorus exceed a 20:1 ratio compared to nitrogen, cyanobacteria tend to dominate. When those ratios are closer together, more of the healthy phytoplankton can thrive, outcompeting the useless and completely non-beneficial cyanobacteria.

But, that doesn’t speak to the suspended diatoms or any microscopic clay particles (which might be one and the same).

When we dipped some of the pond water and filled an empty Dr. Pepper bottle (spontaneously harvested from the floorboard of my truck), it wasn’t long before a little cloud of dust began to settle in the tiny nooks in the bottom of that plastic vessel. At home, we added a sprinkling of powdered alum and much of the remaining solids found its way to the bottom of the bottle. But, the water was still cloudy…with that green tint. Two different samples made their way to a lab and the results began to make sense.

“Clearing Muddy Water3:  Just because water is turbid doesn’t mean fish can’t thrive.”

From our initial samples and a year’s worth of data from multiple samples, different lab evaluations, plus several brains thinking about it, the problem(s) appear to be these:

1) Bluegreen algae due to a nutrient imbalance.

2) Physical stirring of the water, due in part to the fish, but moreso because of shallow, wind-swept water in the upper reaches of the lake.

3) Suspended solids, likely due in some part to the excavation of the shallow part of the lake back in the drought. Those soils are minute, most likely the source of diatom skeletons and clay particles.

The multi-pronged attack coming together is this:

1) Minimize stirring of the water. The best thoughts, so far, are to put some windbreaks into the shallowest part of the water. Square bales of hay make the most sense, as they are easy to get. It’s windy in that part of Texas, so limiting wave action is important.

2) Analyze the ratios of nitrogen, phosphorus, and potassium to see what they are and adjust the nutrients by adding the missing elements and changing the ratios.

3) Harvesting of those fish that tend to please themselves on the bottom of a lake. Targets? Channel catfish (which aren’t overly abundant any more) and gizzard shad (which we want to quantify).

4) Consider aluminum sulfate, after the other elements are in place.

Looking back on those days at the Waggoner Ranch, back around 1981-82, our approach was shotgun-like. It worked sometimes, and sometimes it didn’t. We always seemed to get immediate results, but had we raised the hood and looked more deeply, we might have taken a different path. But, who knew? We didn’t have same tools we have today. Now we can analyze things to death if we choose. The course of action will tell the tale. For this story, on this day, we can come to some conclusions before we ask the landowner to shell out some of his hard-earned dollars to try some solution that, in years past, might work, or it might not.

Reprinted courtesy of Pond Boss magazine and author, Bob Lusk. For more information, www.pondboss.com or boblusk@outlook.com.

As we are all aware, pond management is not always as simple as we’d like it to be, but it’s the complexities and problems that make the challenge of pond management so fulfilling. There are certainly management aspects with which we could be more familiar to help us gain more answers than questions. In this segment of Pond Boss we’re going to cover basics of water quality, and in this first installment, the focus is on your pond’s pH. We’ve all heard of it, but what do we actually need to know? Turns out, pH is more than just a two letter abbreviation for anti-itch cream. It actually tells you a lot about the pond you manage.

What is it?

Well, simply put, pH is a measurement of how acidic or basic your pond water is. The scale runs from 0, being the most acidic, to 14 being the most basic, while 7 is the pH of pure water. To get a feel for what falls on either end of the spectrum, think of acidic lemons on the low end (about a 2) of the scale and baking soda on the basic side with a pH of about 12.

An important thing to remember when measuring pH, which we’ll talk about how to do later, is that each number represents a 10-fold change. So, a hot cup of black coffee on a brisk autumn morning with a pH of 5 is ten times more basic than an ice cold beer on a Friday afternoon with a pH of 4. So, that begs the question: what does that have to do with my pond?

Why is it important?

pH is one of those things that has more influence on your pond’s ecosystem than you think. In one sense, you can think of it as a measure of how ideal your pond’s water is for your fish to thrive. If your pond is too acidic or too basic, it simply doesn’t make for an environment in which your fish want to do things like eat or reproduce. In terms of our own bodies, taking a shower in water with a pH similar to vinegar (3) or anywhere near ammonia (11.5) wouldn’t be too comfortable and chances are we’d shut the water off right quick. The same goes for your crappie hole or your monster bass pond—if the pH falls outside their acceptable range, life isn’t so good for the fish or the thousands of aquatic organisms that call it home-sweet-home. pH is also influential in determining the availability of certain nutrients and heavy metals. Keep in mind though, pH can be a very temporary water quality parameter and can change constantly, so testing a water sample last week may not tell you squat about your current water pH. Now that we know what it is and why it matters, what in the world determines pH?

What determines pH in a pond?

Your pond is unique, that we know. Your soil, your rainfall, your depth and slope and the land around it—you take pride in it. All these things are instrumental in determining the pH of your pond. Your dirt or bedrock probably plays the biggest role. Georgia red clay, for example, is going to be more acidic (have a lower pH) than pond dug out of a limestone quarry and your pond’s water will show it.

Algae growth also plays a part. See, algae are big contributors to the health of your pond in that they use up carbon dioxide (CO₂) and give back oxygen- both sides of that ball benefit your fish. But, (and this is a big one), at nighttime the script gets flipped and algae are programmed to do just the opposite of what they do during the day. At night, they use up oxygen and expel carbon dioxide. Carbon dioxide dissolved in water forms a mild acid and it just so happens that as carbon dioxide goes up, pH goes down. Then, as the sun rises, plants and algae begin photosynthesis, thereby consuming CO₂ and causing the pH to rise, or become more basic, as the day goes on. *Algae blooms exaggerate pH fluctuations.* As we discussed earlier, like all things, pH is best in moderation or right in the middle of the scale. However, pH isn’t just free to swing back and forth like a kid at recess without some policing and that’s where alkalinity comes in.

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How does alkalinity factor in?

Alkalinity is the measure of how well your pond can prevent pH swings. Water that does a good job of this is termed alkaline and usually contains calcium carbonates…lime. Your pond’s alkalinity is in charge of preventing your pH from wildly changing or fluctuating—the higher your alkalinity, the lower the deviation from your pond’s normal pH can occur. In order for your pond to do this, you’ll need an alkalinity between 50 and 250 parts per million (ppm). A quick story that’ll help drive the point home goes on about a Midwestern pond manager who applied rotenone in a 10-acre lake with very low alkalinity. Its pH was never stable and the fish were so unproductive that he was able to fit the entire lake’s fishery in a 5 gallon bucket! Ever heard that the best offense is a good defense? Well, in this case, that good defense is a strong alkalinity!

Can I change my alkalinity?

You have control over your alkalinity as well. If you do get a low reading, then you’ll want to increase it. Ponds with low alkalinity are susceptible to pH swings that can and will be detrimental to your fish. Fish, crustaceans and most aquatic organisms need a certain amount of calcium in the water they swim in. In fact, it’s the only way small fish fry can grow their internal skeletons. Just like you drink milk or take Centrum silver, aquatic organisms and fish absorb it through their skin and exoskeletons. You may have heard of a fellow pondmeister ‘liming’ his pond and wondered why the heck he did it. Well, liming is the single most effective and affordable way to up the calcium in your pond. Be sure you choose calcium carbonate, not the other forms of calcium.

Where do I want my pH?

Now that we know where our alkalinity needs to be and how to get it there, what level should our pH be? Well, as mentioned earlier, pH levels which occur on either end of the scale can be dangerous, so we want to be somewhere in the middle- between 6.5 and 8.

How do I test my pH?

Now it’s time to head out to the pond (I know I won’t have to twist your arm here), but you’ll need a few things before you go. To test the pH of your pond there are two different angles to choose—electronic pH meters or pH strips.

Litmus tests, or pH strips, are the simplest, but the least accurate, way to test. It involves dropping a bit of your pond’s water on a prepared strip of paper—it changes color and you match it to the chart. That’s your pH. The more accurate, re-usable, and also more expensive, is the pH meter. It’s really just a pen you stick in the water and, bam, it reads out on a digital screen. Keep in mind these gadgets do require occasional calibration and the actual probe on the end must be kept moist.

*Alkalinity testing can be done using simple color changing strips or sophisticated water quality meters known as photometers- for the everyday pond manager the strips do the trick.

Knowing is half the battle

There’s no better way to learn about yet another aspect of pond management than to watch your own pond crash and burn with a fish kill. We’ve all heard of it, most of us have experienced it and none of us would wish it on anybody, even our worst enemies. It’s one of the hardest times for a pond manager to get through. After years of feed, TLC, and, of course, investing money, it is a devastating sight to stand by helpless as your fish roll right in front of you.

Most times the scapegoat is low oxygen, but what a lot of owners don’t often think about is how their pH might have led to the fish kill. This is especially the case after a heavy rainfall that mixes toxic gases from deep within the pond and pushes the pH back and forth. Often, low oxygen is part of the problem, but the actual problem can be a two-pronged attack on your fish from both swinging pH and low oxygen.

We, as pond managers, need as much intellectual ammo as possible to help our ponds reach their greatest potential. So, check your pH every once in a while and get a handle on your alkalinity- your fish will thank you!

Reprinted courtesy of Pond Boss magazine. For more information, www.pondboss.com or boblusk@outlook.com. featured image from greg grimes

Phosphorus is a nutrient required for life by all the organisms in and around your pond or lake. In most freshwater environments, phosphorus is the limiting nutrient, which means it’s usually the nutrient in shortest supply. But, in other parts of the country, phosphorus can be over-abundant. It’s this keystone-like characteristic that makes phosphorus so influential in your pond and so important in pond management. Fertilizer treatments in ponds with low P can triple the number of fish and one pound of phosphorus is enough to produce up to 500 pounds of algae. Whether you want a gin-clear swimming pond or a monster bass honey hole, phosphorus plays an important role in your pond.

In a clear pond with low productivity (oligotrophic), phosphorus levels would typically be under 10 parts per billion (ppb). A pond with high productivity (eutrophic) will likely have about 96 ppb (Lory). When it comes to phosphorus the old saying “a little goes a long way” holds true. Want to turn that swimming hole into a fishing hole? It only takes about one-third of a pound, or about a shot glass full, of soluble reactive phosphorus per acre-foot of water (324,522 gallons) (Aquatic Eco-Systems) to raise the levels of P in your pond to eutrophic.

To help wrap your head around parts per billion (ppb), think of it in terms of steps. On an average day you probably take about 6,000 to 7,000 steps (About.com Walking). Now, try to imagine taking a billion steps…take a moment to wipe the sweat off your brow, but don’t look down…you could be on the moon! So, whenever you hear talk about ppb, consider that just one of those steps on your trip to the moon is one part per billion…not a whole heck of a lot.

≈ .3 lbs of phosphorus

How did all this P get in the pond?

Got This One in the Bag

Next time you see your neighbor out pushing the fertilizer spreader, think about this: fertilizers come in a variety of nutrient combinations. The three major nutrients present in fertilizers are nitrogen (N), phosphorus (P), and potassium (K). So, when you’re picking out a terrestrial fertilizer and it says 10-10-10 on the bag, what does this mean? This tells you the concentrations in which the nutrients are present. A 55-pound bag of 10-10-10 fertilizer is 10% nitrogen, 10% phosphorus, and 10% potassium. This means it contains 5.5 pounds of each ingredient and enough phosphorus to raise levels in a 4-acre pond, 4 feet deep to a eutrophic status.

5 lbs of Phosphorus ≈ 55-lb bag of fertilizer

When It Rains, It Pours.

But what about runoff? As rain flows over the ground and into your pond, it brings with it nutrients from things like fertilizers and animal waste. In one urban landscape, runoff contained 0.3 pounds of phosphorus per acre per year (Graves; Neal C).

0.3 lbs of Phosphorus ≈ lots of lbs phosphorus per acre per year. I’ll let you do that math!

The Goose That Laid the Golden Egg (Sort Of)

Our ponds are home to many organisms and in some cases this includes waterfowl like ducks and geese. Did you know, the average goose dropping is 1.3% phosphorus and weighs approximately 1.2 grams (Lake Access)? Geese poop as many as 92 times a day—that’s about one-third of a cup (Lake Access)!That’s about 1.4 grams of phosphorus a day or about .85 pounds of phosphorus per year, per goose. One goose produces enough phosphorus to make one million gallons of water have eutrophic levels. Now, think about this…someone had to follow a goose and watch it poop for a whole day to find that out. Aren’t you glad you don’t have that job?

.85 lbs of phosphorus ≈ 59.86 lbs goose poop per year

Make Like a Tree… and Leaf

The average mature oak tree will shed about 60 pounds of leaves over the course of a year. That doesn’t seem like much until you realize that an average oak leaf weighs about 1.3 grams (a little less than a paperclip). Those 60 pounds of leaves can equate to about 1.5 pounds of phosphorus per year (Cowen). How many trees do you have over your pond?

1.5 lbs of phosphorus ≈ 60 lbs leaves

Feeding Frenzy

Many fish foods boast phosphorus levels less than 1.3% (Yamato Green). Average phosphorus levels in fish foods are 0.6% to 1% (Hagen…For Pets; Zeigler). At these percentiles, a 55-pound bag of fish food contains 0.3 to .6 pounds of phosphorus. How many bags of feed do you use in a year’s time. The good news? Most of that fish food becomes fish flesh, meaning the majority of phosphorus becomes fish.

0.5 lbs of phosphorus ≈ 55-lb bag of fish feed

The Many Faces of Phosphorus

Shiftier than a Tadpole in a Time Machine

We have discussed a few of the ways that phosphorus enters your lake, but where does all that phosphorus go? Phosphorus can exist in many different forms in your pond or lake. This is where it gets interesting. Even though phosphorus is in your water, it’s important to remember that it’s not all soluble reactive (ready to be used or absorbed). The phosphorus in your water can actually shift into different forms. Fish and plants in your pond actually need phosphorus (like all living things) and absorb it into their systems for growth and everyday living. So when we say that phosphorus is “shifty” or that it “shifts” in the water column, this is what we mean. Phosphorus has many faces.

A Fine Kettle of Fish

Fish are huge consumers of phosphorus. On average, fish are about 2% phosphorus or, to make it easy, there are about 2 pounds of phosphorus per 100 pounds of fish (Walker). If 1 pound of phosphorus in the form of fish food is introduced into the water .15 to .3 pounds (15%-30%) will be absorbed by the fish (Food and Agriculture Organization of The United Nations).

2 lbs of phosphorus ≈ 100 lbs of fish

Growing Like a Weed

Consider the plants that live in your pond. Two common ones you may have seen before are Eurasian water milfoil (Myriophyllum spicatum L.) and Curly leaf pond weed (Potamogeton crispus L.). Eurasian water milfoil contains .21 pounds of phosphorus per every 100 pounds of plant. By the same token, curly leaf pond weed holds about .23 pounds of phosphorus per 100 pounds of vegetation. (Madsen)

.23 lbs of phosphorus ≈ 100 lbs curly leaf pond weed

Here is an interesting fact about phosphorus and water hyacinths. A case study done at the University of Florida showed when phosphorus levels in water are increased, water hyacinth plants significantly increase the amount of phosphorus they absorb from the water. Not only that, but they increased in number as well (Haller). Isn’t it amazing how in some cases ponds and the organisms within them can adapt to maintain favorable conditions?

Pound for Pound

Now say this five times fast: For every pound of phosphorus present in your pond, 500 pounds of algae is produced!

1 lb. phosphorus ≈ 500 lbs algae

To P or not To P?

That is the real question. As you now know, phosphorus enters your pond on the sly through fish and fish food, plants and fertilizers, runoff, rain, and even geese. Whether you need a pond high in productivity or prefer a pond that’s clear, it’s important to understand that phosphorus is the key to management in most scenarios. Knowing your phosphorus levels and understanding how influential it can be is essential to effective lake management.

Reprinted courtesy of Pond Boss magazine. For more information, www.pondboss.com or boblusk@outlook.com.

Works Cited

A, Graves Gregory. “Estimation of contribution of total phosphorus from selected landuses to observe concentrations in tributaries to a coastal lagoon: Indian River Lagoon, Florida USA.” Proceedings of National Stormwater Association 2002 Conference. Naples, Florida, 2002. 1-15.

Cowen, William F. and G. Fred Lee. “Leaves as Source of Phosphorus.” Water Chemistry Program, University of Wisconsin, Madison, WI 53706 (1973): 854.

Food and Aagriculture Organization of The United Nations . n.d. http://www.fao.org/. 12 March 2012.

Hagen…For Pets . n.d. http://www.hagen.com/uk/aquatic/nutrafinmax/lowphos.cfm. 6 March 2012.

Haller, William T and D.L. Sutton. “Effect of PH and High Phosphorus Concentrations on Growth of Waterhyacinth.” Florida Agr. Exp. Sta. (n.d.): 4804: 59-61.

Kotoski, James E. “Black Earth Creek & Limnology Minifacts & Analysis.” Spring Harbor Environmental Magent Middle School, 1997.

Lory, John A. “Agricultural Phosphorus and Water Quality.” MU Guide (n.d.): G9181:1-4. http://extension.missouri.edu/explorepdf/agguides/soils/g09181.pdf. 12 March 2012.

Madsen, John D. “Predicting Invasion Success of Eurasian Watermilfoil.” Journal of Aquatic Plant Management (1998): 36:29-32.

Neal C, Reynolds B, Neal M, Hughes S, Wickham H, Hill L, Rowland P, Pugh B. “Soluable reactive phosphorus levels in rainfall, cloud water, throughfall, stemflow, soil waters, stream waters and ground waters for the Upper River Severn area, Plynlimon, mid Wales.” Sci Total Environ. (2003): Oct 1; 314-316:99-120.

Walker, David. St. Johns River Water Management District . 2002. http://www.sjrwmd.com/lakeapopka/. 6 March 2012.

Yamato Green. n.d. http://www.yamatogreen.com/phosphorus.htm. 7 March 2012.

Zeigler. n.d. http://www.zeiglerfeed.com/html/. 7 March 2012.