[00:00:00] Bridget Scanlon: Welcome to the Water Resources Podcast. I am Bridget Scanlon. In this podcast, we discuss water challenges with leading experts, including topics on extreme climate events, overexploitation, and potential solutions towards more sustainable management.
So we'd like to welcome Thomas Harter to the Water Resources Podcast.
Thomas is a professor at the Department of Land, Air and Water at UC, University of California, Davis. Welcome and also a professor of Cooperative Extension. His research covers many areas at the water agriculture nexus. focusing primarily on groundwater, but also including water resources, water quality, and using field studies and modeling analysis.
So today we're going to talk about his global conference on groundwater that he conducted last June, his work with the Sustainable Groundwater Management Act in California. And his groundwater quality work on nitrate and salinity in the Central Valley. Thank you so much, Thomas, for joining me today.
[00:01:10] Thomas Harter: Thank you for having me, Bridget. This is great. Really honored.
[00:01:13] Bridget Scanlon: So Thomas, you organized an incredible conference last year. I think it was the third conference entitled Toward Sustainable Groundwater in Agriculture and was held in San Francisco in June. And maybe it meant some of the listeners may not realize how important the linkages between groundwater and agriculture are and water in general with agriculture.
What we often hear is that irrigation accounts for 70 percent of global water withdrawal and 90 percent of water consumption. So it's the elephant in the room. So maybe you can give us a feel for what the different topics were that we're discussing the conference and, what were the surprises or what you learned from it?
[00:01:57] Thomas Harter: Yeah. So as you mentioned, this is the third time we have organized this and put this together, but our first time was in 2010 and the second time in 2016. The conference really comes out of the fact that there rarely is an opportunity for us in the applied research realm to come together across the agriculture water spectrum, let alone the specifically the groundwater agriculture spectrum, I go to conferences where I'm either being a researcher in that realm, groundwater and agriculture. I go to conferences where I talk to soil people in agronomy, people and farmers, and then I go to conferences where I talk to groundwater people, but there's no soil scientists or agronomists or agricultural folks.
And, but there are quite a few of us that worked at this nexus between groundwater and agriculture. And in this conference came out of a really big need for bringing people together that work both in the groundwater arena, either as groundwater and hydrologists, engineers, hydrogeologists. In an agricultural setting or that work in the agricultural setting from an agricultural perspective or a regulatory perspective or an NGO perspective and are concerned about groundwater and bringing people across this nexus together, also bringing people together that work in various disciplines, economics, Engineering, hydrogeology, monitoring, but then also management and dealing with the social aspects of actually managing water in an agricultural region.
And then the other piece that is often disconnected and that this conference has tried to bring together is the integration of quantity and quality. Usually there's people that work on the quantity side and then there's the people that work on the quality side. They're largely disconnected partly also because our regulatory systems, at least in the United States are, have these two aspects disconnected to a large degree with few exceptions.
And so the purpose of this conference was again, to bring people together that work from these different disciplines. And it also, not just in academia, but actually bring people that are working on the ground regulators. Growers, people that represent growers and work with growers to this conference to talk about all of these various issues that are happening.
And so at the conference, we had a wide range of issues. We had almost an entire track, focused on nitrate and salinity. and that goes from how do we know how much nitrate is there? How do we monitor nitrate? How do we then engage with the growers and regulate growers? What are regulatory measures that can be used?
What are ways to then get growers to actually implement best management practices? What is our understanding of the issue? How much does nitrate actually impact groundwater? What is the legacy of nitrate in groundwater and how it also then impact surface water. Nandita Basu was one of our keynote speakers and gave a very beautiful presentation on how the legacy of nitrogen losses into groundwater ultimately affect the Mississippi river and then lead to this large dead zone in the Gulf of Mexico every year. And then similarly here in, in these larger aquifer systems, we have a lot of legacy of nitrogen loading that leads to significant issues with drinking water, where communities in California largely depend on groundwater for drinking water and even more so domestic well owners, hundreds of thousands of domestic well owners, many of them being impacted by high nitrate.
So looking at what the causes are, what we know about, where we are between where the loading happens and where people then see a nitrate problem, whether it's in the rivers or in wells, how we can assess that, but then also ask the question, what can these communities do? What can the farmers do look also at some of the economic aspects?
So that was on the nitrate side, on the salinity side as well, we had people, we had tracks on interaction between groundwater and surface water and looking at groundwater dependent ecosystems at the interface of agriculture, looking at how agricultural pumping affects base flow, that then impacts stream ecosystems and riparian ecosystems, other groundwater dependent ecosystems.
We had sessions on the supply side. We looked at managed aquifer recharge and specifically managed aquifer recharge in agricultural regions. Their agriculture is a lot of land in California. The idea of agricultural managed aquifer recharge is. In the semi-arid regions where there is a lot of water demand for agriculture and urban areas, often as is good case in California, water rights are allocated or over allocated already.
And the only water that's not being used and going to the ocean are these, or during these really large rainfall events or snowmelt events where we have flooding, happening. And so being. looking at how can we manage getting some of these floodwaters somewhere where it can be recharging groundwater.
And that's a key question in the agricultural landscape. Fundamentally is a key player there because we do have some recharge sites that can supercharge groundwater where we can get a lot of water into the ground. In a short period of time over a relatively small acreage, a few hundred acres, few thousand acres perhaps, of making a current water bank.
Did a lot of work in 2023 siphoning off water that would've otherwise been lost and banking it in groundwater. But over the course of 12 or 18 months, the current water bank being the largest water bank we have in the state. The agricultural landscape might not be super high supercharger, so to speak, when it comes to groundwater research, but there's a lot of agricultural land available that we could think about using during these short periods of time, and we have a lot of water.
And using the existing infrastructure that we have for irrigation to then actually take some of this water off and send it on these agricultural lands. So there's a lot of research done on that. There's questions about water rights. There's questions about, infrastructure that needs to be built to do something like this.
There's questions about legacy loading in the agricultural landscape that would be mobilized by such managed agri for recharge and how to manage that. There's questions around agronomic side. Can we actually flood an almond orchard? Can we flood an alfalfa field? Can we flood a wheat field? I just came back yesterday, from a, research experiment that my colleague, Dr.
Dahlke is doing with her students. Or we're looking at, can we do this on dairies where there's a lot of manure applications, or is this going to just cause havoc in groundwater when we do Manage Act for Recharge on a field that's been seeing manure applications last four months ago, only four months ago, and has been manure applied for years on it.
So there's a lot of these kinds of questions and, or how do we do Manage Act for Recharge to get around some of these water quality issues that, that may be cropping up because of like a sea loading.
[00:09:07] Bridget Scanlon: you covered a lot of different topics in the conference and with the title of the conference being toward sustainable groundwater and agriculture, I think, trying to manage these extremes, which in California all the time, you're either in a flood or a drought.
So manage that for recharge. And then so much of the land being agricultural makes sense to have recharged to try to apply manage that for recharge in those areas. And then, as you say, you've got the infrastructure to bring the flood flows and then flood the fields in the winter and even the perennial tree crops, the almonds and others, maybe they're not negatively impacted by that flooding, which, and you've got this huge reservoir of depleted aquifers underneath that could take that water and then it could move towards more sustainable management.
I, what I thought was interesting looking at the agenda and reading some of the abstracts and stuff was that you had people from all over the world.
[00:10:01] Thomas Harter: Yes. I was just going to say, and this was not a California focused conference although we always take advantage of it.
[00:10:06] Bridget Scanlon: But you had people from Europe and China.
[00:10:09] Thomas Harter: People from Europe, from Asia, from Africa, from Latin America. We really tried to bring people together that might be working very locally in Asia or in Africa or in Latin America somewhere to this conference. And one of the things that I have found fascinating at this conference as well as past conferences is.
While the politics or the situational background framework might be very different depending on which country you're from or which state you're from in North America, the core issues are very similar in the conflicts that exist between different water users, including the environment are very similar.
And so that's people connect on that and that allows the this is where I think that where the feedback that we've received on this conference, where this conference really thrives is. This opportunity to actually talk about what you're doing and realizing, Oh, somebody else can actually is interested in this because they're having very similar issues.
You might have had a different approach to might've had a different solution. So to add to maybe my previous answer on the topics, there's also a very large part of this conference that's about governance. And if economics and how to connect with the local stakeholders, groundwater is currently something we manage locally, even if we have an EU wide law as in the European Union, governing groundwater, it ultimately is often managed at the state and more often even at, at the local district or county or water agency level.
And people therefore tend to be working at that scale and being focused on that scale and being able to connect people across the world, working on similar problems. It turns out to be hugely productive and very inspiring for people. And what I've seen in the past too is people take ideas and bring them to their regulators and actually change how they do things.
[00:12:06] Bridget Scanlon: Right. So one of the things that I found interesting was when the people from Europe, Denmark and the Netherlands, we've seen that in the news and farmers having their tractors across the roads to provide barriers or to make a statement about some of the issues and concerns that they have.
But nitrate, is a huge issue in those small countries where it's intensively cultivated and agriculture is huge. Reading the abstract about the Denmark presentation, entirely dependent on groundwater, the whole country, and, then high nitrate and sandy soils and health concerns and stuff like that.
And then the Netherlands, half of it being agriculture and nitrate leaching, linked to agriculture. So it was really nice to get a perspective from other regions. I think that's the really fun thing about some of these conferences.
[00:12:57] Thomas Harter: And to see, we tried to bring speakers to the table, especially on our plenary sessions that could also highlight some of the real success stories.
Denmark's really been able. And so has the Netherlands been able. Maybe not to get exactly where they want to be, but to turn around on the long-term trend. in terms of Denmark, throughout the middle, latter part of the 20th century, they've seen increasing nitrate concentrations as we do in many other regions, And with engaging with farmers, also with regulations, some of them top down and very unpopular, some of them unsuccessful in the long run, they were put into place in the short run, but were so unpopular that they eventually got toppled.
But they have been able to put these diversity of efforts to at least begin to turn around nitrate concentration trends in groundwater, not at a small cost. And so talking about how do we incentivize something like this, how do we change the economic incentives to do this and how do we work with the messaging?
Again, always mostly focused on the farmer, on the grower is really important. And I think part of what we're seeing, what is interesting to me is the role that people play that are in an advising role to farmers. I, there, there are. Larger farmers that are very progressive and are really interested in sustainable management of their farms that have the capacity and initiative to actually work on this and get engaged in this.
But there are many farmers, they do their job. They are mostly focused on their crops. And they rely on farm advisors to, they rely on consultants to help them with doing their job. In the U. S. we're blessed with this cooperative extension system and that we have through our land grant universities where you have farm advisors in most every county that can engage in these issues and help growers improve their management practices.
We have in the U. S., under the U. S. Department of Agriculture, the Natural Resource Conservation Service has resource conservation districts, across the country. And so there's significant amount of support from people to help farmers do the best job in terms of management practices. And Europe started to emulate that now under the nitrate directive.
And it's interesting to see how there's this building of this capacity, which I think ultimately is really important, both in terms of managing for water quality, as well as in managing for water supply in the agricultural landscape.
[00:15:39] Bridget Scanlon: Right. Well, that's great. And you've been working with Cooperative Extension for most of your career. Some of the presentations during the conference were on the Sustainable Groundwater Management Act in California. We heard from Claudia Faunt and others about that, which was passed in 2014. And you are quite involved with different basins and working in that area. Maybe you can give us some background. It's incredible. These high and medium priority basins, all the, plans that are being developed, the agencies that are being developed to manage this. And maybe you can describe what status, what is the current status of the work and how you see it evolving.
[00:16:21] Thomas Harter: Yeah. So I'm really happy to see so many people on your podcast actually talk about this, the Sustainable Groundwater Management Act.
It's now 10 years old. It brought Californians from a place where we had a legal system to deal with groundwater rights, groundwater use, but we didn't have, we didn't have a law in place that would proactively actually manage groundwater. SGMA did that. And the Sustainable Groundwater Management Act, as we refer to it as SGMA, put in place maybe one of the most progressive.
agendas for managing groundwater in that it is not only looking at groundwater supply and making sure that water levels aren't falling, it actually defines sustainability much more broadly as the absence of undesirable results, not only with respect to water levels in groundwater storage, but also with respect to land subsidence, with respect to water quality, and with respect to groundwater dependent ecosystem and surface water.
And so it fundamentally integrates the supply side with the quality side and it integrates. The supply, the groundwater supply side with a surface water supply side, the initial focus of the implementation of SGMA was on getting agencies on the ground, huge administrative experiment with 200 plus 250 plus agencies being formed to be locally responsible to then by 2020 and what we call high priority basins, it actually, I take that in what we call critically overdrafted basins.
Thanks. They had to complete their plans by 2020, everybody else by early 2022. And these agencies all had to write their groundwater sustainability plans. We've seen many have cooperated with a neighboring agency. So we have out of these 250 agencies, we have somewhere or over a hundred groundwater sustainability plans.
Now they are reviewed by the Department of Water Resources, which is one of our two state agencies dealing with water.
[00:18:24] Bridget Scanlon: And the Water Groundwater Resources Control Board, is the other agency that's involved in this, process. I guess there are 42 high priority basins and 21 medium priority basins, so that's 63 altogether, and you have 114 groundwater sustainability agencies.
And then they each develop plans. And as you mentioned, the critically overdrafted basins have already submitted their plans. And in 2025, there are already approved groundwater sustainability plans. So, during the conference in June, some of the presentations focused on SGMA, and one was on the McMullen Area Groundwater Sustainability Agency that is entirely dependent on groundwater.
And reading the abstract, I thought it was very interesting. They were very positive about their progress. I guess they had recharged 19,000 acre feet of water during the 2023 floods. And it plans to recharge 4,000 acres. And as you mentioned, cultural areas are ideal for managed aquifer recharge because you've already got the infrastructure to bring the flood water to these fields and then recharge the aquifers and then.
You've got suitable soils, you've got coarse grained soils in the Central Valley, eroded from the mountains, and so it's ideal for managed aquifer recharge. So, I thought that was a very interesting presentation during the conference.
[00:19:53] Thomas Harter: It was, it's a very interesting situation too. And it's a very clever approach.
This is a basin that has overdraft. They call it a white area. We call it white areas here in California areas that do not have surface water supplies and now have water management agencies that are exclusively dealing with groundwater and the sort of hiding behind that overdraft number is the fact that it's a hundred thousand plus acre district with mostly perennial crops.
Their water use is close to 300,000 acre feet, so not having surface water supply and using 300, 000 acre feet of water and then only having something like 100, 000 acre feet of overdraft, where's all the rest of the water coming from, right? Well, it's coming in and underneath, they're actually at the bottom of the groundwater system.
They're at the center of the valley. they're getting all this underflow, but because of the overdraft, they have created space in the last 50 years to store more water. And he happened to sit next to the California aqueduct. And at the end of the, at the end of the federal project, and so they have access to water that somebody else would want to bank.
So the offer is out there to basically buy themselves a savings account. And buy into this groundwater bank, which would be operated by doing recharge either in recharge basins or through directly through farmland in that district. And one of the things that I thought was most brilliant about what this district is doing is engaging with growers to do Managed Aquifer Recharge is very different from buying a bunch of land as a district, hiring engineers and consultants to design the recharge basins or whatever you do to do Managed Aquifer Recharge, and then have an engineered, managed, predictable system. When you deal with growers, we're supposed to take water from you at some random times, but possibly and put it on their crops.
You're not dealing with engineers anymore. And so what the district did is it created what they call the Managed Agri Food Recharge University, which is a brilliant idea to get growers engaged in Managed Agri Food Recharge because, I don't see Agricultural Managed Agri Food Recharge being successful without continuously engaging with the grower and being sure that A, the grower knows that this is on their radar, that they know what to do about it, that they are aware of best management practices, And this district is actually doing that.
And I, and that's the part that I, we're still lacking in other areas of California is that direct engagement with growers through training and where people are starting to think about.
[00:22:35] Bridget Scanlon: Well, I think that's fantastic, Thomas, because the spreading basins in the engineered systems, like you mentioned, the Kern Water Bank or Arvin Edison Water Bank, they are limited in the area.
And then you are using that land only for that purpose. But if you can recharge cropland or in, for you've got perennial trees and stuff in the winter, then that doesn't have to be taken out of production to facilitate this recharge. And when we did analysis in Arizona looking at the spreading basins managed aquifer recharge, we found that the areas that were just being recharged, that were irrigated by surface water, recharge much more water than the spreading basins themselves because it's a much larger area.
And you have got so much more potential. So I think that's fantastic. That's really cool. And I guess he used a number of different terms, flood managed aquifer recharge, ag managed aquifer recharge.
[00:23:30] Thomas Harter: Yeah. So we all have our terms. The Department of Water Resources prefers the term flood managed aquifer recharge or flood MAR because it's somewhat independent from whatever we're doing this on in a flood plain.
That's just a natural landscape or that's a, that is perhaps a preserve. Or whatever, doing it on agricultural land or whatever, doing it on urban lands that have recharge basins. So, but MAR is a more general term, but it captures in California, that term captures the fact that we're doing MAR to tug away water that would otherwise flood lands potentially and go out to the ocean.
And basically captured that one part of our surface water supply that's not yet captured by existing water rights and existing infrastructure.
[00:24:18] Bridget Scanlon: I can recall talking to some people at the Department of Water Resources, maybe 10, 15 years ago about saying, talking about trying to capture some of the water that went to the ocean.
But a lot of people felt well, we need that water to go to the ocean, but not anymore. We want to capture as much as possible. And I think we've heard some of that recently with the LA fires and stuff. Some people talking about that, but so optimizing this process, then taking advantage of the irrigation infrastructure and all the land area, the cropland and stuff, it's fantastic.
And, we really help move towards more sustainable management, which SGMA is all about. So now I'd like to switch gears a little bit. I know you've talked a little bit already about the conference and water quality, but you've done so much work on nitrates during your career. And I think you had a huge report come out, or a couple of reports in 2012 with Jay Lund that was supported by a legislative mandate, I think, addressing nitrate in California's drinking water, focusing on the Tulare Basin and the Salinas Valley.
So maybe you can describe that a little bit, that work, Thomas, and what the drivers were and how you did the work and what some of the findings were and how that has evolved over time.
[00:25:39] Thomas Harter: So the drivers for that report go back almost another decade into the late 1990s. And in fact, it would actually go back to the creation of the Clean Water Act in the U.
S. and here in California. California was a couple of years ahead of the federal government in creating in the late 1960s legislation that would address water quality in general, both surface water and groundwater, and essentially create a permitting program so that potential polluters would be required to actually go through a permit process before they are discharging potential pollution into surface water and to groundwater.
The groundwater portion of the California legislation was not taken up in the federal legislation, the federal clean water act, the federal clean water act, almost exclusively focuses on dischargers of pollution into surface waters. It is very focused on point source discharges through the permitting process, but also since the 1990s on non point source diffuse discharges into stream systems through what we call the total maximum daily load process or TMDL process.
That, in California, similarly the focus was on point source discharges, especially to surface water. And there was an exemption from the permitting program for agriculture and urban stormwater runoffs, agricultural runoff and urban stormwater runoff. And in the late 1990s, partly to address the more rehearsal engagement with TMDL and implementation of the TMDL section of the Clean Water Act, the California legislature took away the exemption from agriculture and urban stormwater and said, no, you also need to enroll into a permitting program.
You need, we need a permitting program to, so we can proactively manage your discharges, your diffuse discharges into surface water, but under California law, also into groundwater. And so in 2002, we created what we call the Irrigated Lands Regulatory Program to control surface water discharges to groundwater 2007, we saw the very first permitting program for a diffuse source of discharge to control their nitrate leaching into groundwater. And that was the dairy industry. So we had what we call the dairy water in 2007. And then following up on that in 2012, the Irrigated Alliance program began to engage on groundwater nitrate control programs.
At parallel to that effort, the legislature asked the state water board to essentially inform them and create a report on who's doing nitrate pollution, what's happening to it in groundwater and specifically nitrate pollution of groundwater, what's happening to it in groundwater and who's impacted by it.
And this, and then when you plan that out, tell us. What everybody can do, but we can do about these three things.
How can we reduce loading?
How can we remediate what's already in groundwater
What are the alternative supplies for the people that are impacted by high nitrate in groundwater?
And then tell us how much that costs.
How much does the pollution reduction cost? How much does the remediation cost and how much does it cost to provide alternative supplies? And what are the policies we already have and what policies should be put in place was super clever. It was one paragraph in a piece of legislation in 2008, we were asked to lead that report.
I worked with 10 colleagues of mine, Jay Lund, and I led the effort here at University of California, Davis, very diverse group on these questions. As you can easily imagine, we had to deal with urban water supplies and water treatment systems. We had to deal with economics of nitrogen management. We wanted to understand the nitrate leaching into groundwater, the amount of nitrate leaching, and who was doing what, literally who was doing what, map that out across the focus was at the time on the southern part of the Central Valley and the Salinas Valley, two very intensively managed, agriculturally managed regions with high nitrate pollution levels.
But we also worked with agronomists and economists to look at how this could be approved and what it would cost. What kind of policies we have and what kind of policies could be put in place. The mandate that the Lead Legislature had on this report was that whatever the State Water Board would ultimately recommend as an outcome of our work would need to be implemented within two or three years.
So there was an implementation phase to this, which put a lot of, put a lot of weight on this report. And so as a result of that, we've now seen programs that actually provide safe drinking water to communities that are impacted and domestic well users that are impacted by nitrate. It's also informed this area land circuitry program and a dairy program and a third program that works in that space, which is what we call the nitrate and salt pollution management program or Central Valley salts program.
And under that program, we now have nitrogen nitrate management cells whose primary and responsibility for now is to actually be the local agency to provide safe drinking water to communities that are impacted by nitrate. And, or, and this is the other efforts that are happening is to either see that smaller community systems, often economically disadvantaged communities, that they either get treatment operations up and running.
The issue there being often the maintenance of those and the cost of that maintenance. So where possible, there are efforts to hook them up to a larger system that already has that capacity and that maintenance capacity in place. There have been efforts and continue to be efforts to address the fact that there have been hundreds of thousands of people in the state of California exposed to high nitrate levels in their drinking water. And that's an effort that's ongoing. Right. Yeah. on, on our end, we continue to ask questions around how can we then, and this is where the area that Alliance program and the dairy program are heading is, they are really programs to control the discharges into groundwater in the first place.
And so initially it was about taking stock, who is doing what, who's growing which crop, how much fertilizer do they apply on a dairy? How much manure gets applied? How much are they harvesting? Doing some basic nitrogen mass balances to see where do we see, where do we see large surplus of nitrogen? Where do, where would you have a more reasonable surplus of nitrogen?
And how would management practices potentially then be able to reduce the nitrogen surplus, which is really what's ultimately impacting groundwater, because in the Central Valley, which is so flat that we have actually relatively little runoff, all that nitrate that's extra, if it's not.
[00:32:31] Bridget Scanlon: If it is not used by the crops, then it's going to recharge the groundwater.
[00:32:34] Thomas Harter: It's not used, but the surplus that's not used by the crop would mostly be leaching to groundwater. So there's been a lot of documentation of that. There's a lot of monitoring. Growers are now actually reporting on an annual basis, their nitrogen use on a field by field level not just farm, but actually down to the field scale, there's been a lot of opposition to that from the agricultural industry, mostly because farmers look at that and say it as their private industry information. and they compromise That was reached between a regulator and industry was that the industry would essentially, organize itself, into about 13 coalitions. That act on behalf of their individual growers. We have tens of 30, 40, 000 growers here in the central valley, managing about 7 million acres of irrigated lands.
They would collect this information on behalf of the regulator, isn't directly available to the public. But the critical information, which is the larger scale information, is available and is transparent. And so that reporting has been happening. And where the next step then was in this program, which we after about 5 to 10 years of data collection, where we, the next step in that was, Let's define more specifically how we actually measure nitrate leaching to groundwater, and then let's set targets of what that leaching, what would be an allowable amount of nitrate leaching under the agricultural landscape to not impair groundwater moving forward.
We already have a lot of impairment of groundwater. The goal is to get groundwater back to where it's. Meeting drinking water standards, because that is one of the major beneficial uses of groundwater in California. And the question was, how do we then dial these targets? So to get that, we get eventually, even if it takes.
Decades to get there, but that we eventually get to cleaner groundwater.
[00:34:34] Bridget Scanlon: It's really nice that the program was divided into those three parts, looking at the sources and the loading, and then looking at groundwater and then looking at the impacts on the consumers, whether the domestic and community water systems and the nitrate maximum contaminant level for drinking water in groundwater is 10 milligrams per liter nitrate as nitrogen.
And so trying to bring the groundwater back. And so you have a number of potential sources of nitrate in the central valley. So how did those rank relative to each other? how did the dairies rank relative to the fertilizers on crops and other potential sources?
[00:35:16] Thomas Harter: So the biggest source of nitrate in groundwater is agriculture, and that's the nature of the beast.
Agricultural doesn't operate in a container, they operate in the open landscape. I like to say, we all love protein rich foods, we love healthy foods and so protein is associated with healthy foods. Protein is mostly nitrogen, so anything that grows in the landscape, of course, contains a lot of nitrogen.
And the challenge to the grower is to bring that nitrogen into the field in ways that then are taken up by the plant. as opposed to leaching to groundwater. There's always some inefficiencies in that system, but given that we produce at a relatively intensive level, almonds are using up 250 pounds of nitrogen per acre about the same number in kilograms per hectare on a dairy which grows forage crops.
They might on under best of circumstances, they grow corn in the summer. Cut it in late August for silage, green for silage. They might seed in some Sudan grass, grow it for 60 days, cut it green for silage. And then they'll have winter grains, oats, barley, triticale, wheat that they will seed in November and harvest in mid April green for silage.
30 tons of corn in the summer, 14 tons of sudangrass in the fall, 18 tons of winter grain in April. So, really large crop, 400 pounds of nitrogen per acre. If we look at typical recharge rates in the agricultural landscape with irrigation, it might be under less efficient systems, it'll change in the future and is changing, but we typically assume about 300 millimeters of recharge, one acre foot per acre of recharge.
In that one acre foot, if you have 27 pounds of nitrogen, that's 10 milligrams per liter of nitrate N, right? That's the same. It's a different unit, same amount. So as a yardstick in that report, we said, well, there's going to be some atmospheric losses in the subsurface. So. If things, if the value is over 35 to 40 pounds of nitrogen per acre, that surplus, then it becomes high risk when you grow a 250 pound per acre of nitrogen, where nitrogen 250 pounds get removed or on a dairy for 400 pounds of nitrogen are removed. Managing your inputs to that field so that losing more than 30 or 40 pounds, that's like trying to drive. I say that's like trying to drive a giant tank where you don't have a steering wheel. You just can slow down either the left chain or the right chain on the tank through a bar door with an inch of space on each side at 60 miles an hour.
So it's, it's a precision task that's really difficult. And so that's where knowledge on and improvements in practices is going to be really important that we have in California is you produce 20 percent of the milk in the United States. We have 1. 7 million dairy cows that produce large amounts of milk. but that's also protein, right? And then to put the cow to produce that protein in the milk, it'll all take, if the protein that goes through the mouth of the cow, that a cow, 25 percent may be going into the milk, 28 percent may be going to milk, the rest comes out the back end, the cow, and then we need to deal with it.
And historically cows would graze on pastures. They eat from the pasture, 25 percent of the nitrogen that they eat goes into the milk, and the rest goes back on the pasture to grow more pasture, and typically those pastures had some legumes in there, clover, other legumes that would make up that 25 percent that actually gets removed from the pasture, right?
But it was a recycled system. When we moved to these larger dairy farms where now it becomes highly inefficient to walk the cows back and forth from the pasture into the milking barn twice a day or three times a day, we separated that manure management from the food growing. And in the process, farmers were able to say, Oh, I can have a bigger barn without necessarily having a bigger field because they could import feed.
But they still have the same amount of manure. And so we end up with about 450, 000 acres of land that's being managed by dairy farmers that manage these 1. 7 million milking cows. They produce somewhere on the order of 300, 000 tons of nitrogen. That's half of the nitrogen needs of the entire state of California's agriculture on about 5 percent of the land, right now, not all of it goes on that land. There's a lot of losses. There's a lot of exports to lands immediately surrounding these dairies,
these animal farms with respect to manure. And that's our, in terms of nitrate risk to groundwater, that's our biggest issue is we need to figure out ways.as we said in our report 10 years ago, we need to figure out ways how to make this manure look, smell, sell, ship like normal commercial fertilizer.
Then we can sell it back to Nebraska where we get our corn from to make ethanol in our ethanol plants here in California. Which then gets, by the way, the distillers digest it, gets fed to the cows. So all that ore nitrogen comes back to our cows in California from the core nitrogen from Nebraska.
[00:40:59] Bridget Scanlon: We're running out of time a little bit, but I would like to just talk a little bit about salinity and the Central Valley becoming a closed system so that you are accumulating salts.
And that is also another challenge. And this. ABSCAL, Anthropogenic Basin Closure and Groundwater Salinization work that you did with Graham Fogg and others. Maybe you could just briefly describe that and how you might be able to deal with this buildup of salinity over time that's inevitable.
[00:41:29] Thomas Harter: It's a very important phenomenon that I think it.
When Richard and Graham and I started working on this is something that, as Graham has pointed out, is hugely underappreciated, the potential for it. When we talk about salinity related to groundwater or related to agriculture, typically we talk about salt buildups in soils because bare soil evaporation somewhere you start irrigating and water table builds up and comes close to the land surface and the land surface picks up water from the water table and the salt are left behind as a crust on the surface.
Or you may have internally closed basins as you have in some parts of Western Texas, New Mexico, or in the, in Nevada, where you have a closed basin where surface water collects in a lake, like Mono Lake, and evaporates, or in the Dead Sea for that matter in Israel. At the border with Jordan and the water evaporates and leaves behind large amounts of salt.
That's typically where we think about saline that when we think about salinization, that's what we think about, but what happens in these in semi arid irrigated regions as well, not just here in California is. Where normally these groundwater basins would be often recharged at the mountain front by rivers that percolate into groundwater by precipitation surplus that percolates into groundwater and then recharge balances with a discharge somewhere downstream into a river.
And salt gets moved through that groundwater system, partly also generated in the groundwater system. We now are in a place where we no longer have that discharge to the stream because we're actually pumping most of that water out of the ground, put it back on the surface, and they'll leave behind the salt.
And those salts are being very effectively leached by the farmers out of the root zone because it would hurt the plants. And so then they travel back down to groundwater. And with them, you have continued input of outside sources of surface water. In California, they come from the mountains surrounding the Central Valley.
They come down from the Central Valley Project or from the State Water Project. From Northern California being shipped to California. The Southern part of the Central Valley. It carries maybe not a lot of salinity, but it carries sufficient salinity to add to that salt. That's already in this groundwater basin and that addition to the salt is never going to go away where we partially or fully close our groundwater basins to discharge into surface water and that closure over many generations time in these larger groundwater basins.
So we're talking hundreds to hundreds of years will build up large amounts of salinity and essentially cause an irreversible, largely irreversible amount of salt buildup. And that's the part that Rich looked at and Rich Pauloo looked at in, in his paper, in his ABSCAL paper on a mass balance basis in the basic vertical one dimensional system for the southern part of the Central Valley to show just what the order of magnitude in time and in salinity built up would be under these close conditions.
And we're following that currently up with a. More three dimensional model for the entire Central Valley. Where we're looking at these salt sources and how that salt buildup actually then works out in a more spatially distributed way than Rich did in his very important conceptual paper. And modeling paper.
[00:45:06] Bridget Scanlon: Right. And I think that is fascinating. And I think, another one last point is that with the managed aquifer recharge, that you can mobilize the salts or nitrates as in the unsaturated zone. But your analysis suggests that would flush through the system fairly quickly and so that managed aquifer recharge might actually be beneficial and could ultimately lead to improved water quality.
[00:45:31] Thomas Harter: I like to use the analogy of a moat around a castle, if, and this goes for both salts and for nitrate, to the degree that we have many disadvantaged communities that are smaller, it's the smaller communities that are also often the economically disadvantaged communities in the Central Valley that are most impacted by it.
Nitrate, potentially salt, although on the salt side, it'll be also agriculture. But the, if you recharge a lot of clean water, like in a moat around these towns, through managed aquifer recharge, if you basically put managed aquifer recharge into the source zone of their public water supply, you can dilute both salts and nitrate.
this is not one of these industrial contaminants where six orders of magnitude of nitrate The concentration is six orders of magnitude above a regulatory limit. We're talking about having concentrations that are two, three, four times above regulatory limits. And so dilution goes a long way to rid ourselves of the pollution and the same could be said for some of that salinity, but fundamentally the important part is that we reconnect groundwater back to surface water as a way to export salts in the long run.
and that's a big challenge to think about and what that would potentially mean for areas where water levels now are a hundred feet or more below ground surface.
[00:46:52] Bridget Scanlon: That's a lot of recharge. So maybe we can just finish up, Thomas. Do you feel like you're, are you optimistic about the future of agriculture in the Central Valley and with Sigma going on and all of these other regulatory?
[00:47:05] Thomas Harter: let me put it this way. I'm not pessimistic. I think.as has been pointed out by other speakers on your podcast, when the Public Policy Institute of California published, and I was part of their team in 2019 future of the San Joaquin water futures at the San Joaquin Valley. They pointed out the fact that even with the, with the restrictions that Sigma opposes on water use.
With the cutbacks in water use that are absolutely necessary for us to come into balance with what nature provides us, if we are clever about it, if we are clever in terms of the decisions on what crops we grow and where we grow them and how we grow them, the impact to agriculture will be a reduction that's going to be on the order of 5 to 10 to 15, maybe even 20%, but that's not 100%, right?
We're talking about a significant locally, very painful cutback in agriculture. But in the long term, I don't see agriculture, I don't see the need for agriculture in California to go away neither or to necessarily be cut in half or down to three quarters, but we have to be, we have to be cautious and we have to engage on how to most, how to convert that agricultural economy.
that not only growers depend on, but many employees depend on, and downstream economic sectors depend on, how to manage that transition in ways that's least economically painful for those regions, especially in the central and southern part of the Central Valley.
[00:48:40] Bridget Scanlon: Well, thank you so much, Thomas. Thomas Harter is professor at the Department of Land, Air, and Water Resources, and also in Cooperative Extension.
And really appreciate that you did a super job of explaining all of this. A lot of complex issues related to groundwater and agriculture. Thanks a lot.
[00:48:56] Thomas Harter: Bridget, thank you for having me. Honored to be here.
