Inspection Services Blog

2020 Nutrient Management Conference Q&As – Session 5: Managed Aquifer Recharge on the Central Coast

The California Department of Food and Agriculture (CDFA) Fertilizer Research and Education Program (FREP) and Western Plant Health Association (WPHA) presented their annual Nutrient Management Conference as a webinar October 28-29. This series of five blog posts links to each conference session and highlights the most common questions asked by the conference audience and presenters’ responses during the Q&A sessions.

Presentation: Water Resource Management in the Pajaro Valley

Presenter: Brian Lockwood, General Manager /Hydrogeologist, Pajaro Valley Water District Management Agency (Presentation link)

This talk highlighted the state of water management in the Pajaro River Basin. The basin is unique in the diversity of water use requirements and coastal challenges to managing groundwater resources. Over the years the basin had experienced groundwater overdraft leading to seawater intrusion, which threatens many stakeholders’ access to freshwater resources. Mr. Lockwood described the various projects and programs that the Pajaro Valley Water Management Agency (PVWMA) has designed and implemented to stop groundwater overdraft and seawater intrusion that is ongoing in the region. This talk emphasized stakeholder involvement and the programs that have been implemented with the grower community to improve water management in the region and preserve and recharge freshwater resources.

Q&As

Q: What advice/suggestions might you have for Sustainable Groundwater Management Act (SGMA) recharge projects in the Central Valley?

A: There is a lot of great work being done especially in Tulare irrigation district. It is very important to collect data and understand the characteristics and hydrogeology below the soil surface and identifying sand, clay, and silt layers with regard to installation of monitoring wells. Core samples can help for that purpose. In contrast to Central Coast, where we are space-limited, Central Valley has a lot of land that can be used in recharge projects.

Q: What is the actual goal in fighting saltwater intrusion? Will a strip of intrusion close to the coast be continued to be tolerated in the long-term?

A: The goal is to protect groundwater quality within the aquifer. Higher concentration of salt behind the coastal area and how it will be tolerated is one of the conservations to be discussed. SGMA says that what is “significant and unreasonable” must be addressed. Maybe there is some salt intrusion but is not significant and unreasonable and maybe we can provide enough supplemental water supply without having a significant negative effect on crop production and potable water supplies. Other strategies can be used. For example, desalinization facilities like the one in Orange County or pumping out the salt water and replacing it with high quality freshwater.

Presentation: Enhancing Groundwater Recharge in the Pajaro Valley

Presenter: Dr. Andrew Fisher, Hydrogeology Professor, University of California, Santa Cruz (Presentation link)

California’s recent drought has exacerbated water management challenges, but also provides once-in-a-lifetime opportunities, especially through development and implementation of the Sustainable Groundwater Management Act. Fisher, students, and colleagues are collaborating with landowners, agencies, and regional stakeholders to implement a vertically integrated research program. Goals are to identify locations where stormwater could contribute to enhanced groundwater recharge, conduct site investigations to assess local conditions, create implementation projects and quantify their performance, improve water quality, and develop incentives that can encourage broad participation and engagement. This presentation highlighted recent accomplishments, opportunities, and challenges in managing groundwater resources to enhance resilience and sustainability.

Q&As

Q: Do you think use of deep-rooted cover crops could be incentivized to help with recharge and denitrification?

A: There are several beneficial practices that can be incentivized; however, the challenge is quantifying the benefits and how the benefits of each practice is calculated compared to the whole farm. What is the net benefit of a recharge project for a grower? Growers need to know this information to make decisions. Basins are given the opportunity to employ management practices that best fit their needs and the characteristics of their basin. However, the benefits of any practice should be quantified to ensure successful adoption of that practice. 

Q: What is the source of recharge water other than precipitation and how does water quality impact beneficial uses of that water?

A: We are currently using the runoff that is generated after precipitation in our projects and the key is the intensity of the storm events and whether it can be used for recharge depending on the soil nutrient legacy of a site. However, there are other sources that can be used for recharge projects such as imported water, water released from upstream dams, and periodic flows from major rivers. It is important to consider the variability of water quality in any of these sources.

Q: How can soil carbon amendments impact water quality? What are the risks of generating greenhouse gases?

A: The basic concept comes out of permeable reactive barriers to treat ground water in place and are installed in vertical walls. At a large scale, it should be cheap enough to justify the effort. In our area, redwood is cheap and does not prevent microbial activity, so the denitrification process will not be stopped. We have tested almond shells and they work well too. The key to make it work for many people is finding local sources. Biochar might be a good source too, but the challenge is it being expensive and hard to handle. We’re seeing evidence of complete denitrification in our trials which means that the final product is di-N and not nitrous oxide, so there will be no concern about creating greenhouse gasses. If you provide the right conditions, you can get complete denitrification, which is complete removal of that N from the system. However, if the system is not fully efficient, it can also result in losses of nitrous oxide, but this system has shown to be very efficient based on the design and management.

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For more than 25 years, FREP has presented its pioneering fertilizer research at annual conferences. Since 2007, FREP has collaborated with the Western Plant Health Association (WPHA) to create a conference that balances technical research with discussion on practical application. Presenters from academia, industry, and agricultural consulting provide general and technical information, current research and data, and practical applications addressing statewide and regional nutrient management issues. Visit the Annual FREP/WPHA Conference webpage for links to all the 2020 conference sessions and the 2020 Conference Proceedings booklet.


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