Nursery growers have implemented a variety of solutions, with varying degrees of success, to reduce the excessive biological growth usually found in recycled water irrigation ponds. This growth is responsible for the clogging of intake filters and subsequently, expensive maintenance costs. With little in the way of research or scientific data to support alternative methodologies and no clear standards of practice for effective pond management, there is a critical need in the sector for reliable information on affordable and sustainable solutions to improve water quality.
Several projects focusing on water quality are currently being funded through the COHA research cluster. Minimizing horticultural impacts on surface water quality to encourage re-use through enhanced pond management is one of these projects being led by Dr. Jeanine West of PhytoServ. With an end goal of helping growers to manage their irrigation costs through environmentally appropriate and sustainable improved pond management strategies, this project is part of the Cluster Project and is funded by the Canadian Ornamental Horticulture Alliance (COHA-ACHO) and by the Government of Canada under the Canadian Agricultural Partnership’s AgriScience Program
According to Dr. West, “Almost all nursery growers use recycled water and it is inevitable that they experience issues related to excessive growth of aquatic weeds, algae and cyanobacteria, also known as blue green algae, especially in the warmer summer months. This research project will focus on investigating new methods of controlling the flow of nutrients and especially phosphorous into ponds, and to study various in-pond treatments to improve overall water quality.”
The research project has been designed to take into consideration the requirements of three very diverse audiences. The general public’s increasing concern for the environment is further reinforced by the aesthetics and risks of algae and cyanobacteria in our ponds and lakes. Various ministries across Canada, at both the provincial and federal levels now have in place application and discharge regulations to control the excessive use of nutrients, especially phosphorous and nitrates. And farmers have a need for effective and sustainable pond management strategies that will help them to meet environmental regulations while at the same time mitigating the costly impacts from clogged irrigation systems.
The first phase of the project, completed in 2019 with considerable input from a Technical Advisory Committee, was to design, construct and test a reliable experimental design which would allow for effective comparisons of various water quality treatments. “Arriving at a suitable project design was no easy task,” explains Dr. West, “as it needed to be bigger than a bench scale design, but we had physical and budgetary constraints to consider as well.”
A total of five nursery locations across Ontario were selected as research sites and each one brings unique site challenges and therefore opportunities to the project. “As we’ve come to expect, each of the participating nurseries have been very cooperative in helping us to install the various on-land or in-pond structures necessary for this project,” notes Dr. West adding that several nursery sites have assisted in the installation of media beds to study the impacts of pre-pond treatments.
With a stated objective of employing a systematic evaluation and comparison of various pond management tools, the project devised by Dr. West and her research team consists of up to five mesocosms (in-pond enclosures, or test cells) at each test location. Each mesocosm has a volume of 1-2 m3 (depending on the pond depth), is framed with PVC tubing to allow for flotation, as it was important that water be able to flow around the sides and bottom of each cell. The wall material eventually chosen by the advisory team is a plastic material commonly used as a wind barrier. “Our technical advisory team struggled with the concept of permeability and its ultimate impact on project results. We ultimately determined that the most accurate data would be realized by a limited exchange of water between the mesocosm and the pond water.”
At each site, the project is designed to test up to five mesocosms including a control, and up to four of the following treatments: submerged aquatic macrophytes, aeration through mechanical bubblers, a phosphorus-binding media, vegetative shade through the use of duckweed, and mechanical shading through the use of shade cloth.
At one farm, the research team has also installed a series of PhytoLinks™, or floating planted islands which, similar to constructed wetlands, are specifically engineered to improve water quality. The PhytoLinks™ were installed in channels within a narrow pond, with one channel empty (control), one with two PhytoLinks™, and one with two PhytoLinks™ and a suspended material that serves as a surface for growth of periphyton, a complex microorganism population known to assist in nutrient uptake.
Any research project conducted in outdoor environments is subject to many unpredictable variables and Dr. West and her team have encountered the usual challenges. With several of the research sites being located far from reliable electrical sources, Dr. West found herself becoming an expert in the design and installation of small solar systems to power an aerator.
An exceptionally hot summer in 2020 resulted in excessive water use, impacting the water depth in some ponds. And of course, this year the team found themselves dealing with the ultimate disruptor – the unforeseen impacts of a global pandemic.
As most of the work planned for 2020 has been outdoors and in low-contact environments, Dr. West and her team have been able to successfully mitigate potential impacts of the impacts of Covid19. Working with collaborator Dr. Ann Huber, the team was fortunate to be able employ qualified family members as technicians, making it possible to comply with Covid19 workplace guidelines.
The limited water testing conducted in 2019 was mostly to validate the research design and system installations. Actual water sampling to record and analyze the effectiveness of each treatment, is being conducted throughout 2020 and 2021. A YSI meter or sonde-type multi probe is used to test and record various parameters such as temperature, pH levels, dissolved oxygen levels, chlorophyll a and phycocyanin levels, turbidity and conductivity. Further water and sediment samples are sent to A&L Canada Laboratories to test for nutrient and chemical levels. Grab samples of algae, aquatic plants, and cyanobacteria are collected regularly and diagnosed by Dr. Ann Huber of the Soil Resource Group to look for other trends and indicators of pond health. Some of the most revealing results to date are the inadequacy of water quality indicators in some of the traditional measurements, and the need to explore a range of parameters and testing approaches to truly get a picture of overall pond health.
Confirms Dr. West, “We will share our results with the industry at the end of the season, but with the caveat that there are too many variables at play in any single year, in particular seasonal weather conditions and changes in production practices, to make those results conclusive. Even the two full years of testing we will be able to conduct as part of this project will not be sufficient to provide definitive results but will hopefully point us in the right direction. Ideally, we should be looking at an analysis after five years of testing; hopefully we will be able to extend our experiment past the time restrictions of this research project.”