Frequently Asked Questions about water quality, treatment, and conservation

Ponds & reservoirs

What steps do I need to take to install a constructed wetland?

Planning

  • Step 1: Information gathering
  • Step 2: Talk to an expert
  • Step 3: Site selection
  • Step 4: Time for an Engineer

Construction and Establishment

  • Step 5: Construction
  • Step 6: Establishment
  • Step 7: Filling the wetland

Operation

  • Step 8: Monitoring
  • Step 9: Maintenance

These nine steps are discussed in detail in the Constructed Wetlands: A How to Guide for Nurseries.

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Who can I go to for advice on installing a constructed wetland to clean up our runoff water.

First, please download the free resource “Constructed Wetlands: A How to Guide for Nurseries”, this comprehensive resource can help answer many of your questions.  An Extension specialist in your state is also a good place to start.

If you want additional details/ technical advice are needed, please contact Dr. Sarah White (swhite4@clemson.edu).

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Have other nurseries installed constructed wetlands to treat runoff water?

Yes. Download this case study for further details.

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How much maintenance is required to keep constructed wetlands working?

Wetland maintenance is relatively simple. A few tasks must be completed periodically to keep the wetland in good working order.

  • Maintain pumps and outfall pipes moving water into the wetlands
  • Remove animal pests. Beavers and/or nutria from wetlands if they invade, because they will disrupt hydrology and short-circuiting treatment efficiency
  • Remove plant pests. Willows (Salix sp.) and other deep-rooted species should be removed from the wetland at regularly timed intervals
  • Clear vegetation from outlet pipes at end of wetland cells
  • Remove sediment from forebays or stilling ponds

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What's the difference between surface-flow and subsurface- flow constructed wetlands, and which should I use?

Surface-flow wetlands – water flows above the surface of the sediment or media substrate, typically a clay or native soil that is impervious to water penetration and through the stems of aquatic plant vegetation.  Water is visible on the surface of the wetland treatment system.

Subsurface-flow wetlands – water flows through the media substrate, on which are planted aquatic plants.  Water is typically not visible in this type of treatment system.  This could have benefits for applications in more arid regions where evaporation is of concern.

The type of wetland most suited for installation at your operation depends upon a variety of factors: land availability, concentrations (load) of contaminants to be removed, volume of water to be treated, climate.  These site specific characteristics should be discussed with extension specialists, consultants, and/or engineers helping you design your treatment system.

Download this article for further details.

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What type of plants should I use to establish constructed wetlands?

A list of recommended sepcies is in the table below. Plant choice depends on a variety of factors:

  • the contaminants that needs to be removed
  • if specific cultivars are better adapted / have shown greater capacity for contaminant removal
  • relative invasive-potential of the aquatic (wetland) plant.
Wetland Plants

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How large does my constructed wetland need to be?

Constructed wetland

Sizing of constructed wetlands depends upon the contaminants you are interested in removing.  The amount of time it takes for water to travel through a wetland (from inflow to outflow) is called the Hydraulic Retention Time (HRT), which should range from 3 to 10+ days, depending upon the volumes of water treated and the concentration/load of contaminants within the water.

A 3 to 5 day retention time should be adequate to manage most contaminants in warmer (temperate / tropical) climates, whereas in cooler climates (Zone 6 and below) longer retention times may be needed.

If your average daily runoff volume ranges from 20,000 to 30,000 gal, and you estimated you needed a 4 day HRT, that would mean you want to size your wetland to hold 4 times the volume of your average daily runoff. It would need to be sized to hold 80,000 to 120,000 gallons of water.  You would use that volume for calculating the required surface area and depth.

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Do constructed wetlands remove pesticides?

Pesticide removal in constructed wetlands is controlled by a variety of factors:

  • the physico-chemical characteristics of the compound itself – basically predictors of how the chemical will move in the environment.  Will it stay in water? Will it bind with sediments?
  • processes within constructed wetlands themselves that remove pesticides – sedimentation, microbial degradation, other chemical-reaction based degradation processes (e.g. breakdown by light), and plant uptake
  • site specific factors – organic matter, pH, clay content, hydraulic retention time, plant presence (yes/no), flow conditions (intermittent vs. permanently flooded)

Some trends exist with regard to removal efficacy in constructed wetlands:

  • High removal (84-97% removal efficacy): Organochlorines (e.g. endosulfan and pentachlorophenol), strobilurin/strobin (e.g. azoxystrobin, trifloxystrobin), organophosphates (e.g. chlorpyrifos, dimethoate, glufosinate, and parathion), and pyrethroids (e.g. bifenthrin, cyhalothrin, cypermethrin, esfenvalerate, and permethrin).  These groups have low water solubility.
  • Low removal (24 – 50% removal efficacy): triazinone (e.g. metribuzin), aryloxyalkanoic acid groups (e.g. dichlorprop, MCPA, mecoprop), and urea-based pesticides (e.g. diuron, linuron).  Water solubility is variable and does not help to predict remediation efficacy.

Predicting whether constructed wetlands will effectively remediate the pesticides of concern to you is a challenging process – and highly technical.  Please consult with Dr. Sarah White (swhite4@clemson.edu) if you want additional information about this topic.

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Do constructed wetlands remove nutrients from nursery runoff?

Constructed wetland

A constructed wetland

Yes. Research with constructed wetlands in various geographic regions shows removal rates of range from 50 to 99% for nitrogen and from 25 to 98% for phosphorus.  These results are based on specific experimental conditions and large-scale field trials.

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Control pH & salts

Do you have any suggestion on what acid to use to lower pH so that we can use ethephon?

Ethephon is a plant growth regulator used widely to improve branching and control flowering in horticultural crops.  The pH of the spray tank is definitely important for ethephon effectiveness, as well as other pesticides. See http://edis.ifas.ufl.edu/pi193 and https://ag.umass.edu/fact-sheets/effects-of-ph-on-pesticides-growth-regulators.

In the US there is a number of commercially available adjuvants that are marketed as buffering agents, and can be used to adjust spray tank pH. Many of these products include a pH indicator dye.

Some growers adjust pH using a mineral acid such as 35% sulfuric acid (battery acid). However, these acids are very caustic and require appropriate gloves, safety glasses, and other protective clothing. Always add acid to the pesticide mix, not vice versa.  Depending on the alkalinity of your spray tank, you may only need a very small amount of acid to drop tank pH. Add a little acid, mix, and then measure pH. You can measure pH with a pH meter (ideally around pH 4.0 to 4.5 for ethephon, but this varies for different pesticides).

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How can I reduce salts in a flood floor watering system?

If the issue is dissolved salts coming from the irrigation water source (i.e., not primarily from the fertilizer) there are not a lot of options in flood floor systems because no leaching occurs with subirrigation. If the irrigation water electrical conductivity (EC) without fertilizer added is much above 0.7 mS/cm, using flood irrigation alone is difficult on long-term crops because ions accumulate in the root substrate.

 

The first priority with irrigation water that has a high EC is to try to purify the water (for example, reverse osmosis or blend with rain water). A periodic top watering with booms or hose can help to leach out salts and rebalance the nutrients in the root substrate. However, do not recycle the resulting runoff to the same crop because it is likely to have high levels of ions, such as sodium or chloride.

 

If the high EC is coming from over-application of fertilizer, and the EC of the irrigation water itself is low (0.7 mS/cm or below), there are more options. There is plenty of good research and grower experience that plants grown with flood irrigation can thrive with lower fertilizer rates compared with top watering because there is no leaching with subirrigation. For example, http://journal.ashspublications.org/content/118/6/771.full.pdf

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Will reclaimed water hurt my plants?

It depends. Sometimes reclaimed water can contain relatively high levels of salts. If irrigation is managed properly, for example with adequate leaching during irrigation, moderate levels of salts (salinity) will not reduce crop growth. If you are considering use of reclaimed water - contact your extension specialist or local agent for help.

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What is reclaimed water?

Reclaimed wastewater is treated wastewater from a wastewater treatment plant - it's safe to release into the environment, but not safe to drink.

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How much acid needs to be added to control alkalinity of my irrigation water?

First have your water tested – irrigation water with over 150 ppm CaCO3 alkalinity often requires injection of an acid to avoid high substrate-pH problems in your crop. Select the acid used (for example, sulfuric, nitric, phosphoric, or citric acid), being aware the acids differ in the nutrients added and safety issues in handling concentrated acid. To select the appropriate acid concentration for your water quality use the AlkCalc online tool from the University of New Hampshire.

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Is the pH of my water too high?

Nutrient availability (micro- and macro-nutrients) to plants is best when the pH of your water source is between 5.5 and 6.5.  Though higher pH values generally don’t harm plant growth (exception – acid-loving crops), availability of micronutrients may decline, along with increased potential for problems related to salinity.

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Why is pH control important?

Most plants grow best at a pH of 5.4 to 6.4 in container substrates. The irrigation water quality (especially pH and alkalinity) is one of the factors that drive substrate-pH up or down. You can find out more at the University of Guelph website

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Should I add acid and chlorine into my pond?

Pond

The pH in my pond water is very high (often around 10 when I measure at midday). The pond is a mix of rainwater and the leached nutrient solution from my hydroponic greenhouse vegetables, which I reapply to other crops in containers.

Don't add acid into the pond. Instead, add acid into the irrigation water with an injector at the time when the solution is pumped out of the pond onto crops.  This approach is more likely to control pH than adding acid into the pond when pH will naturally fluctuate.

Don't add chlorine into the pond. Chlorinating the pond is also unlikely to reduce algae in the presence of high nutrient levels, sunlight, and high pH. Injecting chlorine after the water is pumped from the pond and irrigation water is also acidified is most likely to be effective.

Don't be too concerned about the high pH. The pond's pH will increase during the day because algae remove carbon dioxide from the water during photosynthesis in the presence of sunlight. Carbon dioxide (CO2) is acidic in water. Algae and microbes tend to drop pH in ponds during the night as they respire and add CO2 back into the water.

Send a pond water sample to a lab for nutrient testing. High pH in the pond can cause micronutrients to precipitate out (become insoluble). As algae and microbes grow in the nutrient solution, the nutrient balance may change - so it will be useful to know what nutrients are actually dissolved in the water. That can help you decide if any extra nutrients should be injected back into the solution when reusing this water.

A diagnostic test of the pond water can also measure alkalinity (think of this as dissolved limestone). High water alkalinity causes more issues than high water pH if the pond water is used for irrigation. Highly alkaline water has the greatest effect on increasing substrate-pH of irrigated crops over time.

If practical, you could cover the pond to reduce algae growth and pH fluctuations.

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Why is the pH of my pond so much higher in the afternoon?

The pH of a pond containing algae will increase during the day because algae remove carbon dioxide from the water during photosynthesis in the presence of sunlight. Carbon dioxide (CO2) is acidic in water. Algae and microbes tend to drop pH in the pond during the night as they algae respire and add CO2 back into the water.

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What salinity level is harmful to plants?

It depends on a variety of factors: how you irrigate your crops, the crop mix grown (as some crops are more sensitive than others), and the relative ratios of positively charged minerals (cations) like calcium, magnesium,and sodium in solution.

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Monitor quality

Where can I get my irrigation water checked for Pythium or Phytophthora spores?

Petri dish

Eucalyptus leaf discs for baiting Phytophthora are placed onto a selective agar culture medium to test for the presence of the pathogen (the thread-like rings around the leaf discs). Photo by Dr. Robert Wick, University of Massachusetts.

Check whether your state university extension plant diagnostic lab can run the sample. For example, the University of Massachusetts Plant Diagnostic Clinic plates out water samples to test for Pythium and Phytophthora to the genus level.

You can also send a sample to the University of Guelph, which does a DNA fingerprint-type analysis for a range of pathogens down to the species level.

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Why is the pH of my pond so much higher in the afternoon?

The pH of a pond containing algae will increase during the day because algae remove carbon dioxide from the water during photosynthesis in the presence of sunlight. Carbon dioxide (CO2) is acidic in water. Algae and microbes tend to drop pH in the pond during the night as they algae respire and add CO2 back into the water.

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How do I collect a water sample to submit it for analysis?

Sample Bottles: Bottles should be clean. Use a 16 oz. plastic water bottle.

Sampling Technique: Before filling, rinse the sample bottle out three times with the water being collected. Fill the bottles completely and cap tightly (Don’t leave air space at the top if possible).

Sampling Timing & Location: Water should be collected at the same depth (if pond, river, stream, etc.) or location (e.g. pump). Collect sample at the same time of day water is used to irrigate crops. If collected from the end of irrigation lines – let the line flush sufficiently before collecting the sample (wait 2 minutes or so after irrigation system turns on to collect from the bypass or at a sprinkler head).

Sample Handling and Storage: Avoid sample agitation and prolonged exposure to air. Identify each bottle by attaching an appropriate label (Date & time collected, location, your name/operation). Store the sample in cool/dark location (i.e. refrigerator (best) or in a cooler on ice) until submitting to lab for analysis. IF sending sample to a lab – ship overnight with samples kept cold in an insulated shipping container with ice-packs. Sample doesn’t need to be frozen – but needs to be kept cold in the dark to reduce changes in sample composition between sampling time and analysis by the lab.

Submit the sample(s) for analysis as soon after sampling as possible. Ideally the samples should be analyzed within 24 hours of sampling.  

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Conserve water

What resources are available to help me in planning and funding irrigation improvements at my nursery?

Assistance is available from experts at your state's land grant university and/or local cooperative extension office. Many of these experts are collaborators in the Clean WateR3 project. You should also check with your regional USDA Natural Resources Conservation Service for both technical expertise as well as funding opportunities, such as the Environmental Quality Incentive Program.

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Do plant consumers care about the water I use in plant production?

Yes, some do. An online survey conducted by Michigan State University researchers in May 2015, with 1555 consumers throughout the U.S., showed that using recycled water was less important than the plant species and price, as important as using insect management strategies to protect pollinators, but more important than reusing recycled containers.

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How do I determine my annual irrigation costs?

Annual irrigation cost can be divided into two categories: annual cost of ownership and annual cost of operation.

The annual cost of ownership procedure is represented by the DIRTI (Depreciation, Interest, Repairs, Taxes, and Insurance) formula that spreads the actual cost of ownership of an equipment investment over its usable lifespan or investment period. This formula will provide you with the annual cost of the original investment in equipment and improvements.

Annual operating cost will include an estimate of energy cost and labor attributable to the average operation of the equipment. A greater number of small applications will favor systems that have low labor costs, where a smaller number of large applications would favor system with high labor and low investment attributes. Systems with low energy cost primarily for pumping are favored by higher total annual use where low initial cost often compensate for higher energy cost if a low total volume of water is applied annually.

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Are soil moisture sensors reliable enough to control irrigation in container nurseries?

YES. After several years of research at the University of Maryland and other research sites, we have found that soil moisture sensor technology is a reliable grower management tool. We have been able to demonstrate that sensors can reduce water use and runoff compared with subjective grower decisions.

Soil moisture sensors are already being used to control irrigation in multiple nurseries and greenhouses.  The moisture sensors can be linked wirelessly to a central controller and data can be accessed over the internet.

Our past research collaborating with multiple researchers can be found at http://www.smart-farms.net. This research is continuing as part of the Clean WateR3 project.

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What is a good source of information about best management practices to conserve water?

Check with your state university nursery production specialist on BMP resources and grants that apply to your location. There may be benefits including grants to reduce cost of installing water-saving technologies, and a certification process that can reduce environmental impacts of your nursery. Many free training resources are available online here

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Contaminants: nutrients and agrichemicals

What properties need to be considered when choosing an ultracarb filter?

Should we choose a coconut shell or coal-based filter? Should it be pre-wetted and acid washed?

In the most recent study at the University of Florida, Clean WateR3 researcher and MS student George Grant found there was no significant difference in in paclobutrazol removal between 8x30 mesh coconut or 8x30 mesh coal-based granular activated carbons. This study occurred over a short period of time with a slower flow rate than in a commercial-scale system. It is possible that activated carbon types vary in their shelf-life, but we do not know at this point.

 

The acid and pre-wetted treatments both reduce the percent ash content and make for a 'cleaner' carbon. The ash content on activated carbon is basically fine dust that will wash away when you first start running the system. The ash will turn water black, and an initial back flow is recommended when new carbon has been installed until this ash is washed out. It’s unknown if there are additional costs associated with these treatments, but in theory, they produce a high quality activated carbon that is easier to handle or install. 

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What are the options for removing nutrients from my irrigation water?

You can find an overview at the University of Guelph website.

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Do constructed wetlands remove nutrients from nursery runoff?

Constructed wetland

A constructed wetland

Yes. Research with constructed wetlands in various geographic regions shows removal rates of range from 50 to 99% for nitrogen and from 25 to 98% for phosphorus.  These results are based on specific experimental conditions and large-scale field trials.

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Do constructed wetlands remove pesticides?

Pesticide removal in constructed wetlands is controlled by a variety of factors:

  • the physico-chemical characteristics of the compound itself – basically predictors of how the chemical will move in the environment.  Will it stay in water? Will it bind with sediments?
  • processes within constructed wetlands themselves that remove pesticides – sedimentation, microbial degradation, other chemical-reaction based degradation processes (e.g. breakdown by light), and plant uptake
  • site specific factors – organic matter, pH, clay content, hydraulic retention time, plant presence (yes/no), flow conditions (intermittent vs. permanently flooded)

Some trends exist with regard to removal efficacy in constructed wetlands:

  • High removal (84-97% removal efficacy): Organochlorines (e.g. endosulfan and pentachlorophenol), strobilurin/strobin (e.g. azoxystrobin, trifloxystrobin), organophosphates (e.g. chlorpyrifos, dimethoate, glufosinate, and parathion), and pyrethroids (e.g. bifenthrin, cyhalothrin, cypermethrin, esfenvalerate, and permethrin).  These groups have low water solubility.
  • Low removal (24 – 50% removal efficacy): triazinone (e.g. metribuzin), aryloxyalkanoic acid groups (e.g. dichlorprop, MCPA, mecoprop), and urea-based pesticides (e.g. diuron, linuron).  Water solubility is variable and does not help to predict remediation efficacy.

Predicting whether constructed wetlands will effectively remediate the pesticides of concern to you is a challenging process – and highly technical.  Please consult with Dr. Sarah White (swhite4@clemson.edu) if you want additional information about this topic.

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What are slow sand filters?

Slow sand filters (SSF) are a water treatment method that use sand on which microorganisms grow. These microorganisms are capable of degrading biological and chemical pollutants in runoff water, including Phytophthora and tobacco mosaic virus (TMV).

The disadvantage of SSFs is that slow flow rate of water through the sand is needed to attain treatment. A rule of thumb is one square foot of sand bed can treat about 0.06 gallons (0.2 liters) per minute. A large sand filter is needed to treat large volumes of water.

More information is available in this video.

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Contaminants: particles and debris

Why should I care about particle filtration?

Filtration of irrigation water involves removing organic and inorganic particulate matter (debris, sediment, soil particles, algae, etc.) from the water prior to treatment for pathogens. Pre-filtration is important for two reasons. Firstly, larger particulate matter has the potential to clog the irrigation system (e.g. emitters). Secondly, the effectiveness of many pathogen treatments (e.g. all chemical treatments using oxidizers, UV) is decreased significantly in the presence of particulate organic matter. You can learn more at the University of Guelph website.

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What is clogging my irrigation drippers?

Clogged emitter

A bad case of biological clogging

Clogging of your irrigation drippers could be caused by biological, chemical, or sediment issues

Biological: The clogging material is usually slimy organic material. Soaking the drippers in a dilute bleach solution should clean up biological material (test the drippers can handle the corrosive material first).

If the material is biological, determine where the contamination is occurring (water source, or within the irrigation tanks or pipes). Send in water samples from different locations within the irrigation system to a lab for analysis of total aerobic bacteria counts. Counts higher than 10,000 colony forming units per milliliter indicate a high clogging risk from biofilm.

You will probably need to shock the system with a high rate of an oxidizer (such as chlorine, chlorine dioxide, or a peroxyacetic acid product) to clean the lines. Do not let shock solutions contact your crop. To keep the irrigation lines clean, you could then add a low concentration of a water treatment chemical such as chlorine. With any product, follow EPA label instructions and extension recommendations.

Emitter with iron deposits

Emitter with iron deposits

Chemical: The material may look like powder or be gritty and crystalline. Soak drippers in vinegar (low pH) – if this cleans up the emitters then a chemical problem is likely. Send samples of this soak solution, your irrigation water, and the applied nutrient solution (if you use water-soluble fertilizer) to a testing lab to analyze what specific ions are reacting from your water and/or fertilizer. Knowing the specific ions is needed to take action. For example, you may need to inject acid to reduce precipitation of calcium deposits, or oxidize and filter to remove iron and manganese. A shock with a line cleaner is likely to be needed to unclog lines. Do not let shock solutions contact your crop.

Drippers soaking in a solution of bleach or vinegar

Soaking drippers overnight in different solutions (bleach or vinegar) can help diagnose the problem

Sediment: The material may look and feel gritty. When you soak in warm water, solid particles may drop out. Sediment  indicates the need for more filtration,  with a finer filter pore size than the emitter size. You may need to blast out lines with high pressure, and use a line cleaner to unclog lines. Do not let shock solutions contact your crop.

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Is duckweed bad for my pond? Do I need to control it?

It depends. If duckweed is clogging your pump of filter, then yes - some treatment or pre-filter is needed to keep the floating plants away from your pump intakes. But wholesale treatment of your pond with a herbicide labeled for use over water is not the best solution. As this will not control the duckweed population long term (only changing fertility practices will) - and has potential to introduce herbicide residues to your crops when pond water is used for irrigation later. 

If control is not based on actual pump related problems - but rather to the appearance of your pond (i.e. it looks bad) - think about these plants as free labor - helping to limit algal growth (shading), cool the water, and cycle nitrogen and phosphorus - keeping your pond healthy.

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Contaminants: pathogens and biofilms

Which water treatment technology should I use to control pathogens?

Many technologies are available. An effective system generally requires prefiltration, followed by a sanitizing treatment technology. Options include chemical (e.g., chlorine or ozone), physical (e.g., heat or UV), or biological (e.g., constructed wetlands or slow sand filtration) approaches. Published research on efficacy of different treatment technologies is summarized in our Waterborne Solutions tool. You can compare technologies at the University of Guelph website

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How do I know if I am adding enough chlorine into my irrigation water to control plant pathogens?

Measuring chlorine

Select a meter that will measure free and total chlorine.

Decide on the target chlorine dose. To check for research on dose response of chlorine or other sanitizers for a range of pathogens, use our Waterborne Solutions tool under Grower Tools on this website. For example, 2 ppm of free chlorine is a commonly applied dose which can control Pythium and Phytophthora zoospores.

You need a reliable meter with reagents to test for both total and free chlorine - check common brands for water quality monitoring such as Hach, Hanna, or Pulse Instruments. Although free chlorine is the most effective sanitizing form of chlorine, it is also important to measure total chlorine to avoid phytotoxicity (beware of ever applying more than 5 ppm total chlorine or 2 ppm of free chlorine).

Invest in a reliable inline dosage measurement and control system. You should have inline sensors to measure pH and oxidation-reduction potential (ORP), and possibly ppm of chlorine. Most phytotoxicity problems result from faulty equipment or calculations - don't fix one problem (pathogens) while creating another (phytotoxicity).

Check that the dilutor or injector is working correctly. Calculate how much chemical is being applied for a given volume of water. You can also use our ppm to Recipe tool in backpocketgrower.org, under Tools, to help calculate the dose.

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Do constructed wetlands remove pathogens?

Pathogens and Wetlands

We know constructed wetlands remove human pathogens. But there is little definitive information regarding their remediation efficacy for plant pathogens (for example Phytophtora and Pythium). A goal of the Clean WateR3 project is to provide answers to this question.

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