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Phosphorus, Farming, and the Environment

11/24/2014

2 Comments

 
Phosphorus is an essential nutrient for plants as no other nutrient can replace it in its roles in plant growth. It plays a key role in several plant processes but its primary purpose is to store and transfer the energy produced by photosynthesis. When phosphorus is deficient the plants will be stunted and can have a darker green colour than normal. Since it is also involved in the transformation of starches and sugars, under deficient conditions sugars can accumulate and create reddish-purple blotches.
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Figure 1: The terrestrial phosphorus cycle [Source: http://upload.wikimedia.org/wikipedia/en/9/91/Phosphorus_Cycle_copy.jpg]
Phosphorus has a permanent place on fertilizer recommendations as it is regularly found to be deficient. The most common source is mined rock phosphate which is processed to produce the fertilizer that is spread on fields. It comes either as solely phosphorus (Superphosphate) or combined with Nitrogen (MAP or DAP). After application the phosphorus has several fates, as shown in Figure 1; it can leach down, be taken up by plants and then off the field with the crop, or it can be removed through run-off or erosion.

While a useful nutrient for growing terrestrial plants, phosphorus is also the limiting nutrient in aquatic ecosystems. An increased concentration supports a larger population of algae which can cause problems for other organisms. When the algae die off, the oxygen that is used during the decomposition is no longer available for plants, fish, or animals.
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Figure 2: The aquatic phosphorus cycle [Source: http://upload.wikimedia.org/wikipedia/en/e/eb/Phoscycle-EPA.jpg]
A study completed by Winter et al. (2007) evaluated the major sources of phosphorus to Lake Simcoe from 1998 to 2004 which included septic tanks, urban runoff, sewage effluent, atmospheric, the Holland Marsh, and tributaries. Of these sources the Holland Marsh, an intensive area of agriculture, contributed the least amount, between 1 and 5%, over the studied years in comparison to the other sources (Figure 3). 
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Figure 3: The major sources of total phosphorus to Lake Simcoe for hydrologic years 1998/99-2003/04 (Winter et al., 2007)
References
  • MSU Extension Service. (2014, August 21). Why is my young corn stunted and purple?. In Corn in Mississippi. Retrieved from http://msucares.com/crops/corn/corn_stunted.html
  • Plant and Soil Sciences eLibrary. (2014). Importance of Phosphorus to Plants. In Soils - Part 6: Phosphorus and Potassium in the Soil. Retrieved from http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1130447043&topicorder=2&maxto=15&minto=1
  • Rehm, G., Schmitt, M., Lamb, J., Randall, G., & Busman, L. (2002). Understanding phosphorus fertilizers. In University of Minnesota Extension. Retrieved October 9, 2014, from http://www.extension.umn.edu/agriculture/nutrient-management/phosphorus/understanding-phosphorus-fertilizers/
  • Winter, J. G., Eimers, M. C., Dillon, P. J., Scott, L. D., Scheider, W. A., & Willox, C. C. (2007). Phosphorus inputs to Lake Simcoe from 1990 to 2003: Declines in tributary loads and observations on lake water quality. Journal of Great Lakes Research, 3(2), 381-396.
2 Comments

Lesson Learned: Bottom-up Aerator to Treat Washwater in Settling Tanks

11/11/2014

0 Comments

 
Not every solution implemented results in success. Those various mistakes and failures are discussed here as well as the lessons learned from them.

Goal: Decrease Total Suspended Solids (TSS) while increasing Dissolved Oxygen (DO) concentrations in a settling tank

Solution: Installation of a Bottom-up Aerator.
A Bottom-up Aerator works by pumping compressed air down to a diffuser (Figure 1) situated on the bottom of the tank. The air is released through the diffuser as bubbles which work their way to the surface. As the bubbles rise, the oxygen is dissolving into the water.
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Figure 1: A Bottom-up Aerator diffuser (left) and the surface disturbance caused by the system (right)
Problem: The primary goal of the settling tank is to remove suspended particles by sedimentation and removal of clear water at the surface. The bubbles surfacing from the aerator interrupted this process by keeping the particles in suspension (Figure 2). Also, water testing results showed that there was no significant positive impact on the DO (Figure 3). 
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Figure 2: Total Suspended Solids in a settling tank over time before and after Bottom-up Aerator installation, as shown by the green line
Picture
Figure 3: Dissolved Oxygen concentration in a settling tank over time before and after Bottom-up Aerator installation, as shown by the green line, with a target level of 7-10 mg/L (CCME, 1999)
Discussion: The system failed to increase the DO in the water and had a negative impact on the TSS. While a Bottom-up Aerator is suitable in other situations where particle settling is not a concern, it was not appropriate for resolving this problem. It was removed and replaced with a Surface Aerator.

References
  • Canadian Council of Ministers of the Environment (CCME). 1999. Canadian water quality guidelines for the protection of aquatic life: Dissolved oxygen (freshwater). In: Canadian environmental quality guidelines, Canadian Council of Ministers of the Environment, Winnipeg, MB.
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The Trouble with Muck: Size

11/3/2014

1 Comment

 
A common test, called the Mason jar soil test, is suggested for home gardeners to decipher their soil type.  The basic concept is to put water and a scoop of the soil into the jar, shake to thoroughly mix the soil and water, and let it stand. The sand will settle to the bottom first, followed by the silt, and finally the clay will fall out of suspension. The sand will settle in a minute, the silt will take a few hours, and clay will stay in suspension for a full day. The soil type is then determined by measuring the depth of these layers. But there’s more to soil than sand, silt, and clay. The fine organic matter particles are the last to sink and the large particles will just stay afloat.
Picture
Picture
Diagram (left) and example (right) of a Mason jar soil test
[Picture sources: (l) Pinkney (2010) and (r) Three Easy Soil Tests (2010)]
The vast majority of soil types involve varying amounts of sand, silt, and clay with a minimal amount of organic matter. Muck soils are unique in that they have anywhere between 20 and 80% organic matter.

Settling ponds or tanks, a scaled-up version of a Mason jar, is a method used to remove suspended solids from different types of wastewater. The wastewater is pumped into a large holding tank where it is held. The heavy particles will fall out of suspension and sink to the bottom leaving clear water to exit the pond. But, as the Mason jar test shows the time that wastewater needs to stay in the pond depends on the soil type.

So, settling ponds, whose entire purpose is to give particles time to sink, and muck, a soil type resistant to sinking, are a mismatched pair. They can still work together if the additional time for the muck to settle out is taken into account or as one part of a multi-step treatment process.

References
  • Pinkney, D. (2010, August 1). Starting a Garden - Understanding Your Garden Soil. In Gardening Info Zone. Retrieved October 15, 2014, from http://www.gardeninginfozone.com/starting-a-garden-understanding-your-garden-soil
  • Three Easy Soil Tests. (2010, May 21). In Cultivators Corner. Retrieved October 15, 2014, from http://cultivatorscorner.com/what-is-soil-made-of
1 Comment

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