Webinar #12 - Recycled Water Quality Dynamics and Implications for Crop Health and Production (September 2014)

By: Chuan Hong

Webinar Recording

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►Hello, everyone, welcome to the webinar! I'm Chuan Hong, a professor of plant pathology at Virginia Tech. I will be leading today’s webinar on Recycled Water Quality Dynamics and Implications for Crop Health and Production.

►This is the twelfth webinar in a series, organized by the multi-institutional research team on the Specialty Crop Research Initiative Project: Integrated Management of Zoosporic Pathogens and Irrigation Water Quality for a Sustainable Green Industry. This project is sponsored by the USDA National Institute of Food and Agriculture. We greatly appreciate the AmericanHort, the Society of American Florists, the advisory panel and many farmers for their continuing support. They have played key roles in every stage of this project from proposal development to field studies and educational programs. Specifically, they have helped collecting many of the water quality data I will be presenting today.

Before we get deep into the recycled water quality, I would like you ALL to answer a few questions about your knowledge, practices and concerns in managing irrigation water quality. This will help me decide what to focus in my presentation.

Poll Question 12.1:  Do you know whether and how much water quality may differ between agricultural runoff containment ponds and natural lakes/streams (please select ONE)?
  • No, I am unaware of any difference.
  • Maybe, there are some differences.
  • Yes, they are huge differences.


Poll Question 12.2:  What are your major water quality concerns (please select ALL that apply)?
  • Dissolved oxygen
  • Electrical conductivity, salinity, total dissolved solids
  • Oxidation-reduction potential
  • pH
  • Temperature
  • Turbiditiy
  • Waterborne plant pathogens
  • Others (please specify in the CHAT box)


Poll Question 12.3:  How frequently do you take water quality measurements (please select ONE)?
  • Weekly
  • Monthly
  • Quarterly
  • Twice per year
  • Yearly


Poll Question 12.4:  What time of the day do your normally take water quality measurements (please select ONE)?
  • Early morning (before 10:00 AM)
  • Late morning (10:00 AM – 12 PM)
  • Early afternoon (Noon – 3:00 PM)
  • Late afternoon (after 3:00 PM)
  • Variable, anytime of day depending upon how much is on my plate that day

►Here is an outline of topics that will be covered in my presentation. I will begin with a few comments on the big picture of water issues, then show the water quality dynamics in recycling irrigation ponds in great details. We will also discuss what their implications for crop health and production are, and what are the major contributing factors and future research directions.

►What is in the big picture? One of the most important dimensions is water scarcity.

Without water no plant can be grown nor can any existing plants survive. That is the bottom line!

►To address this agricultural water security issue, there is a significant shift in government policy. From now on agriculture will be measured by crops per drop of water instead of per acre. This is regarded as Blue Revolution, comparable to Green Revolution.

What is Green Revolution?

The Green Revolution refers to a series of research, and development, and technology transfer initiatives, occurring between the 1940s and the late 1960s, that increased agricultural production worldwide, particularly in the developing world, beginning most markedly in the late 1960s. The initiatives, led by Norman Borlaug, the "Father of the Green Revolution" credited with saving over a billion people from starvation, involved the development of high-yielding varieties of cereal grains, expansion of irrigation infrastructure, modernization of management techniques, distribution of hybridized seeds, synthetic fertilizers, and pesticides to farmers.

The term "Green Revolution" was first used in 1968 by former United States Agency for International Development (USAID) director William Gaud, who noted the spread of the new technologies: "These and other developments in the field of agriculture contain the makings of a new revolution. It is not a violent Red Revolution like that of the Soviets, nor is it a White Revolution like that of the Shah of Iran. I call it the Green Revolution.”

Similarly, the Blue Revolution will consist of a series of research, development and technology transfer initiatives in pursuit of agricultural water security.

►There are two major strategies to pursue agricultural water security. The first strategy is to improve water use efficiency. There have been tremendous investment into this strategy and these efforts have identified two major approaches to water efficiency. One is to develop and grow drought-tolerant plant species and varieties.

This is not a choice for consumers. There was news on August 12, 2013 about a grass removal incentive program instituted in Los Angeles. LA is paying its residents $2 per square foot of grass to be removed and replaced with native, drought-tolerant plants like California lilac and species of succulents and cacti, creating a desert garden in the place of a standard, grass lawn.  

This is a great opportunity for horticulturists and growers. Some of you may have seen and begun capitalizing this opportunity.

►The second approach identified under the Water Efficiency strategy is to develop and implement waterwise culture practices. I commend Dr. John Lea-Cox of the University of Maryland and his SCRI project team on their effort. That project has produced hardware and software that will help farmers to water plants only when they need it.

►The second strategy is to capture and reuse agricultural runoff water for irrigation. This photo illustrates what was going on at an eastern VA nursery in the early 2008, after a prolonged period of severe drought in 2007. They were digging new water retention ponds and making existing ponds larger and deeper to increase their water holding capacity. They wanted to capture every drop of water on their properties.

►Have you ever seen water in irrigation ponds like “pea-soup” as shown in the photo? This is NOT uncommon for ponds receiving nutrient-rich runoff water. These green materials are algae that are nurtured by the nutrients in runoff water. They bloom periodically which presumably drives water quality fluctuation seasonally and diurnally.

►Here is an example of water quality fluctuation over time in an Eastern VA pond. We monitored water pH, dissolved oxygen (DO), oxidation-reduction potential (ORP), electrical conductivity (EC), turbidity, temperature and chlorophyll a. As you can see, there were tremendous changes over time. For example, pH fluctuated from 6.4 to 10.3. This study was published in Irrigation Science (2009).

►In the same study, we identified and reported on the four seasonal patterns:

We also identified and reported two diurnal patterns:

These patterns were observed in one pond. We were wondering whether this is happening in other ponds as well.

►That was the first question we asked in this SCRI project. Are these dramatic fluctuations typical of recycled water in retention ponds?

►To answer these questions, we expanded our survey to include nine ponds in VA, two in MD, and one in MS with three sets of instruments.

These two additional sets of data were designed to get a sense of how water quality dynamics in a pond is related to the nutrient level in in the inflow and how it is affected by weather conditions.

►Here is a list of water quality and weather parameters we have been monitoring by each set of instruments.


►Here is an example of how farmers helped set the water quality monitoring systems at each nursery. On the top left was Sean, a head grower at Nursery VA2, digging a hole for anchoring the telemetry system and solar panel.  On the top right was Thomas, my colleague known as a fixer, was installing the telemetry system. The on bottom right was Patti, my technician with Thomas setting up the cable for data communication between the unit in yellow float and the telemetry system.

►This is another photo showing the teamwork among people from different institutions and industry: John and his associate Bruk from University of Maryland, and Bill at the Nursery VA1working together to set up a Decagon system for pond VA12.

►The company technician helped us program and test run a telemetry system. Once this was done, data is transmitted from the unit to a computer in my office via this telemetry system and Verizon satellites.

►Every morning when I return to office, I can see what is going on in each pond. Here are just four computer screen shots showing the real-time data of four ponds in nurseries VA1 and VA2. In each of screen shots, there are a number of icons showing water quality parameters: pH, DO, EC, depth on the top, chlorophyll a, blue/green algae, ORP, temperature and turbidity in the bottom. For example, in the VA12 as shown in the top left, pH was 6.7; DO was 8.7 mg.L, EC was 151 uS/cm, ….

►Again, here is Patti, she is my point person running water quality monitoring stations. On the top left, she was retrieving a unit for maintenance. On the top right, an instrument with probes were completely covered with dirt. Patti has to visit each site to clean and recalibrate the instrument to make sure each working correctly as it should be.

She used to run all the stations in VA and MD, but now only the stations in VA, while John’s group is running monitoring stations in MD and Dr. Warren Copes is running one in MS.

Following I like to show some of the real readings.

►This computer screen shot shows some water temperature readings over a 6-month period from April to October 2011.  In this chart, four different colors represent four different ponds.

As expected, the general trend of temperature is seasonal.  Regardless of their dirtiness, three ponds had very similar temperature readings because they all are under the sun. However, one was quite different, lower temperatures, why, it was because this water resource is under the shade.

►This is a screen shot of turbidity. Again, as you can see turbidity readings were low for most of the time but there were spikes due to rain events.

►EC readings are interesting in the dirty ponds; they were kind of increasing first, then suddenly dropped, coinciding with thunderstorm events.

►Dissolved oxygen fluctuated from 2 to 25 mg/l. There were constant changes over time and within 24 hours. Clearly there were much more frequent and extreme fluctuations in both dirty ponds (Red and Orange) than cleaner ponds (Dark and Light Blue).

►pH fluctuated from 5.5 to 10.5. Similarly, there were much more frequent and extreme fluctuations in the dirty ponds (Red and Orange) than the cleaner ponds (Dark and Light Blue).

►Trends are similar to DO and pH but in opposite pattern, when DO was up, ORP was down.

►Chlorophyll a readings also changed dramatically over time.

►So did blue and green algae readings. You might have noticed that B/G fluctuation was quite different from that of chlorophyll a.

►What is really interesting is when pH, DO and ORP data put together, you can see how they changed simultaneously but in opposite patterns.

►All these new data show that what we reported in the 2009 paper were true.

►Confirming those findings was the beginning of a long journey. The second and much BIGGER question we asked was what these dramatic and patterned fluctuations mean to ornamental crop health, quality and productivity.

►Here is one of the latest studies showing how irrigation water salinity may affect crop productivity and quality using “Flagstaff” marigold as an example.  The plant growth decreased as the irrigation water got saltier as measured by electrical conductivity.

►On the “Yellow Climax” as well. The good news for nursery producers is that most EC readings in containment ponds are well below 1000 mS/cm. But electrical conductivity could be a problem for greenhouse producers.

►Salinity or Electrical conductivity not only affects plant growth but also impacts pathogen survival in the water according to study performed by Dr. Kong. The EC range examined were from 0 to 3.58 dS/m for periods of time from 0 to 14 days. One (1) dS/m is equivalent to 1000 mS/cm. It was very interesting that zoospores of Phytophthora species survived better in dirty water (higher EC) than clean water. Again, this is great news for farmers because most pond water has an EC range of 0.1 to 0.4 dS/m, at which zoospores do NOT do well.

►In addition to EC, she also investigated the DO impact on pathogen survival. She looked into this from two different directions: One focused on DO elevation and the other focused on reduced DO.  As expected, zoospores are aerobic. They survived the best at 5 to 6 mg/L of dissolved oxygen. Their survival decreased at both higher and lower DO levels.

►Here are an overview of what has been examined and what are being investigated from crop health and production perspectives. We have discussed EC and DO impact today, will discuss in details about water pH issues next webinar.

We have only touched the tip of the iceberg. Much more needs to be learned in terms of impacts of individual water quality parameters and their combinations on crop health and production.

►While understanding recycled water quality impacts on crop health and production is important, an equally important question we are asking now is what drives the recycled water quality in containment ponds? This is a critical step to effectively manage and manipulate water quality for better crop health and production.

Based on what we have learned so far, we have developed two hypotheses.

►The first hypothesis is that water quality dynamics in runoff containment ponds is driven by photosynthetical activities, including but not limited to, cyanobacteria, or blue and green algae, and these activities are affected by the quantity and quality of runoff water that returns to the ponds and that is being pumped out from the same ponds.

►The second hypothesis is that water in recycling irrigation ponds is thermally stratified and this stratification affects the mixing of chemistries in water columns, consequently the water quality. Here is a profiling of water temperature in one pond on May 2013 from Dr. Zhang’s latest studies: surface water temperature was above 29C while water temperature at the bottom of water column about 3.5 m deep was below 9C, so the surface water was more than 20C higher than the bottom water.

►Future research directions:

►The take-home messages:

►Before concluding the presentation, I like to thank my associates in particular of Patti, Haibo, and Ping for running most of the water quality monitoring stations, analyzing some of water quality data, investigation water quality impact on pathogen survival. I also like to thank Dr. John Lea-Cox and his team at University of Maryland, Dr. Warren Copes at USDA ARS facility in Mississippi, the Penn State Team by Dr. Gary Moorman for their contributions in water quality data collection, analysis and interpretation. I can’t thank enough all the collaborating farmers for their continuing support to this project. I also like thank you ALL for your participation and attention!

►Our next webinar will be on October 7. We will focus on water pH issue: its scope of impacts and management tools. I look forward to seeing you again next month.