Harmful algal blooms (or HABs) occur when colonies of algae, under the right conditions, grow out of control and produce toxic or harmful effects on people, fish, shellfish, marine mammals, and birds.
Every U.S. coastal and Great Lakes state experiences harmful algal blooms. In California, reports of harmful algal blooms have increased from 91 in 2016 to 241 in 2019. In 2020, Stockton experienced a severe harmful algal bloom; it marked the first year that algal blooms spread into the San Joaquin and Calaveras Rivers so early in the summer and fall months. Drought and heat are factors that increase harmful algal blooms, so all indications are that harmful algal blooms will again make headlines this year.
Dr. Hans W. Paerl is the Kenan Professor of Marine and Environmental Sciences at the UNC-Chapel Hill Institute of Marine Sciences, Morehead City. His research includes microbially-mediated nutrient cycling and primary production dynamics of aquatic ecosystems, environmental controls of harmful algal blooms, and assessing the causes and consequences of storms and floods on nutrient enrichment and hydrologic alterations of inland, estuarine and coastal waters.
Dr. Peggy Lehman is a Senior Scientist at the Department of Water Resources specializing in estuarine studies of the food web, harmful algal blooms, wetland, and water quality.
Delta Independent Science Board member Dianne McKnight introduced the agenda item by acknowledging that there are numerous potential drivers for the growth of these hazardous algal blooms. There are also questions about what controls the extent of toxin content in the algae for themselves, as this can vary several orders of magnitude per gram of algal biomass.
From a drinking water treatment perspective, the control of algal blooms has been an operating concern for 80-90 years. Adding low concentrations of copper sulfate is a common approach that prevents the development of large amounts of algae in a water supply, but it is usually avoided because it can cause taste and odor complaints.
Dr. McKnight pointed out that in the context of water treatment, the approach was to anticipate the bloom before it happened and then treat the water to avoid those conditions.However, it’s a much larger problem now, where the challenge is to understand the drivers for these blooms to have any chance of anticipation and address those problems.
HANS PAERL: The drivers of harmful algal blooms
Dr. Hans Paerl’s presentation focused on global issues of cyanobacteria blooms and their drivers, and how by understanding the drivers, we can develop a long-term control strategy for algal blooms that deals with the issue of nutrient over-enrichment as well as climatic changes, which are playing a synergistic role in the development and proliferation these blooms.
Humans have a lot to do with harmful algal blooms, he said. With more development and more people on earth, more nutrients are being released, and it’s the increased nutrient inputs of both nitrogen and phosphorus that are responsible for these blooms. Also, water use and hydrologic modifications play huge roles. Those hydrologic modifications can be human-induced such as reservoirs or damming rivers, but there are also the climatic changes taking place – more extreme rainfall events and more extreme droughts.
Climate change plays an interactive role, he noted, and they are increasing as the long history of these blooms has been documented.
Harmful algal blooms are not just a freshwater issue. It was thought of as a lake or a freshwater problem until a decade or two ago, but in recent years, the blooms have been expanding into estuaries, such as the Bay-Delta. It’s also a global issue: algal blooms have occurred in a Brazilian lagoon, the St. Johns River in Florida, which is a tidal river, and Lake Pontchartrain of New Orleans – all of which had microcystis blooms. Blooms occur in the Baltic Sea, which has a long history of blooms as well as eutrophication.
Factors driving algal blooms
The graphic on the slide is a pictorial of an ecosystem that shows how algal blooms are formed. Nutrients are an issue, with much of it coming from agricultural, industrial, residential, and urban sources. When those nutrients get into a water body, they can be used by the phytoplankton. And they are utilized differentially, depending on the physics of that system.
Dr. Paerl explained that cyanobacteria in a poorly mixed system tend to dominate in terms of utilizing nutrients because they can control their buoyancy and form surface blooms; that takes up the light and shades the plants underneath, causing hypoxia or low oxygen problems.
“So they run the show in stratified systems,” he said. “They come up during the day, do their photosynthesis, and then at night, they can go down and get nutrients. And so they have figured it all out. Stratification is a big issue.”
The other big thing is residence time. The flux of water through a system plays a critical role. “It turns out that cyanobacteria are pretty slow growing compared to other phytoplankton taxa,” he said. “So in systems where you have high flow, cyanobacteria often don’t win out; you get other phytoplankton running the show, which are faster-growing, like diatoms, for example.”
Dr. Paerl said the worst-case scenario is if there is a wet spring or wet period, which brings nutrients into the system, that is then followed by a drought. “The nutrients are in the system, and then the physics take over, and you get stratification. And unless the system gets flushed more often or for longer periods, the cyanobacteria win out for the reasons that I’ve already mentioned.”
He noted that there could be food web issues with cyanobacteria blooms. Many of them are not grazed effectively, certainly not by zooplankton, so they could end up in the microbial loop. “There can often be sort of choke points in terms of them being able to be grazed readily by crustaceans, zooplankton, and then go up to food web. So that’s an issue too, because if the blooms are accumulating, and then it crashes, then you just get a lot of carbon that’s going down to the sediments and not really being utilized in a food web context.”
China’s Lake Taihu
A worst-case scenario is China’s Lake Taihu, where Dr. Paerl has been working for about 13 years. In the last three decades, the lake has changed from a desirable diatom-dominated oligotrophic lake to a mesotrophic lake to a eutrophic lake impacted by nutrient enrichment from the growth and development surrounding it. This includes two large cities with more than 7 million people and an expansion of agriculture, which has resulted in more nutrient loads coming into the lake.
Lake Taihu is a microcystis-dominated system. Dr. Paerl emphasized that microcystis is one of the cyanobacterial bloom formers that cannot fix nitrogen.
“That’s important because it depends on either external loads of nitrogen or regenerated nitrogen coming back into the system, which brings into play the nitrogen question,” he said.
He presented a slide showing the dimensions of the problem. The graph in the upper left-hand part of the slide is the TN (Total Nitrogen) /TP (Total Phosphorus) ratio in the lake over three years. Early in the year, there’s a lot of nitrogen coming in with fertilization of the fields and the spring rains. The TN/TP ratio is huge – 60, or even higher, he pointed out. The red line shows the Redfield ratio, which is the ratio of nitrogen and phosphorus required for balanced growth; when nitrogen and phosphorus exceed this ratio, the result is runaway eutrophication and toxic algal blooms.
“Early in the spring, it exceeds the Redfield ratio by a lot; but then later in the summer, you can see it actually dips down below the ratio,” said Dr. Paerl. “So from that, we formed a hypothesis pretty early on that maybe the problem in Lake Taihu is not just one nutrient, but both nutrients. In the spring, you have excess nitrogen, so it’s likely that phosphorus is limiting; But in the summer, you have what looks like dropping below Redfield. So nitrogen could be limiting in the summertime.”
To test this hypothesis, they used bioassays, which is a method to identify the nutrients that are potentially most limiting and establish the nutrient input cutbacks required for nutrient-limited control. (More info here.) The bioassays were suspended in the lake, so they were experiencing natural light and temperature; the researchers used mesocosms as well.
The experiments were performed starting in spring, summer, fall, winter, and then the following year. The sample for chlorophyll at the beginning of the bioassay is the initial bar, shown in black; the control is the white bar. Nitrogen is the gray bar, phosphorus the striped bar, and the hatched bar is phosphorus and nitrogen together.
“What you can see is that in the spring, phosphorus is the nutrient that stimulates production that was during that high nitrogen load,” said Dr. Paerl. “But then in the summer, it shifts into a system where nitrogen additions become more stimulatory. If you look at the two years, they’re kind of different, although they showed the same pattern.”
“This can change from year to year due to hydrology and how much loads the system is receiving, which varies from year to year,” he continued. “That’s a variable that needs to be looked at in terms of ultimately establishing thresholds of nutrient limitation. But the bottom line is that if you add N and P together, you get more than N alone or P alone. So yes, the lake is dual nutrient-limited. But if but it looks like both nutrients really make a difference in the end in terms of enrichment, and ultimately sustaining the bloom.”
The slide shows a 48-hour incubation of the bioassay. The upper ones are the triplicate controls, then nitrate addition, then phosphate addition, and N and P. together.
“I think it’s pretty clear evidence that both nitrogen and phosphorus are important in this particular system,” he said.
So the question is, is Taihu just an extreme situation of these cyanobacteria blooms? Or is it a looking glass to other systems?
Lake Erie has had two waves of harmful algal blooms. Back in the 1960s, there was an establishment of blooms mostly dominated by nitrogen-fixing cyanobacteria. Strong phosphorus reduction strategies were imposed, and sure enough, the bloom was knocked back. Dr. Paerl noted that most of those strategies were point source reductions like wastewater treatment plants. The algal blooms have returned in the last decade or so, and they have shifted from nitrogen fixers to microcystis, which is not nitrogen fixer.
“We’re looking now beyond just P as a control because microcystis requires nitrogen, and if it’s coming up like gangbusters, there must be a connection to nitrogen as well,” he said. “And what we’re finding in more contemporary bioassays is that sure enough, nitrogen is a key stimulatory nutrient for these blooms to develop in Lake Erie. But N and P together give you more than alone, which hints at dual nutrient controls.”
Dr. Paerl acknowledged that their bioassay results have been criticized by the folks that do whole lake fertilizations, so he presented a slide with data from papers that have been published on those experiments. Mostly these experiments have been done in the northern temperature regions of the world, both in Europe and North America and in the Experimental Lake Area.
“The bottom line is that if you add N, you usually can get more stimulation just by adding N as opposed to P,” said Dr. Paerl. “But if you add N and P together, you get more than N and P alone. So these experiments are showing very similar results to what we see in short-term bioassays that are executed in other places.”
He presented a slide showing globally all the studies that he could gather that have summarized the experiments that have been done.
“These are global examples of lakes, estuaries, and riverine environments that all have cyanobacteria blooms on them and where bioassays or whole lake experiments have been run,” he said. “And they showed us dual nutrient limitation issue as well.”
What can be done to address harmful algal blooms?
Dr. Paerl noted there are a lot of ways of knocking back these blooms – increase flushing rates to reduce residence time, use mixing devices, food web manipulations, ultrasonic treatment, upstream wetland development to try to reduce the inputs of nutrients, chemical treatments , encouraging competition by having more desirable plants in the system, and taking the nutrients out of the lake by dredging or even capping the sediments. These are all strategies that have been used.
“But the bottom line is that you’re not going to get anywhere unless there’s some comprehensive nutrient input reduction at the same time,” said Dr. Paerl. “All of these other strategies can work in the short term, but often you have to repeat them. For example, in the case of copper additions, you often have to repeat the treatment of copper sulfate, for example, to knock back the bloom. So you’re really chemically modifying the system that you’re trying to treat. And you’re not removing the nutrients.”
“You can remove them by dredging, but that’s a pretty radical step in most instances because you’re destroying the benthos,” he continued. “And depending on the size of the system, it’s often very impractical to do that. I only know of a few examples where dredging has been successful. Only in a few cases in Sweden, for example, in very small lakes, but they had to be accompanied by also reducing inputs of nutrients at the same time.”
What can we do in California? “You can do all these things, probably, except maybe increasing the flushing rate; that would be an environmentally friendly way of dealing with it, but given the competition for water, that’s simply out of the question in California,” advised Dr. Paerl. “So my suggestion is to develop nutrient input thresholds that reduce nutrients to a point where you actually can do something about reducing the bloom, even when all these other conditions are favorable, such as warming, long drought periods, etc.”
“Without really facing the nutrient reduction strategy, we’re going to get recurring blooms, particularly under climatic change conditions where we have more extreme inputs of nutrients due to high rainfall, high input, and then followed by droughts without reducing nutrients,” he said. “I think we’re just going to be faced with this problem more severely.”
Regarding nitrogen and phosphorus, Dr. Paerl noted that it used to be back in the 50s and 60s that by reducing phosphorus, the bloom would be knocked back, and water quality would improve.
“One thing you have to remember is that we’ve now gone through in many instances, even 100 years of accelerated phosphorus input to these systems,” he said. “The issue with phosphorus is that once it gets into a system, it doesn’t go away. It’s just cycling between the sediments and the water column. And unless you physically remove the phosphorus or cap it, you’re faced with a phosphorus legacy in these systems. That’s one reason why nitrogen has become an equally important nutrient to deal with, because at least if you reduce the inputs of nitrogen, and nitrogen fixation doesn’t make up for it, denitrification will allow nitrogen to be left from the system.”
“So the additional strategy then is to hold the line on phosphorus inputs but have a pretty aggressive way of reducing nitrogen,” he said. “ And by that, I mean total nitrogen and to really have a long-term strategy. There are ways of trying to establish these thresholds; there are nutrient dilution bioassays, for example, where we actually dilute out the nutrients instead of adding them. And we get to a point where we see that we are, in fact, controlling the growth of the bloom organisms. I can provide information on the nutrient dilution bioassays, which we’ve used in Taihu to now establish what the threshold should be and how much the nutrients need to be reduced to get to some sort of a controllable point.”
Dr. Paerl warned those numbers often are not small. In Lake Taihu, for example, 30 years of aggregated nutrient inputs have led to very excess nutrients in the lake.
“Our nutrient solution bioassays are showing that the inputs of nitrogen have to be reduced by about 50%; for phosphorus, maybe 30% or so. So, these are not small numbers. But that’s the reality we’re facing with 100 years or more of just allowing nutrients to get into these systems.”
He then closed with some recommendations.
“You have to reduce both N and P in most cases because of the P legacy issue. The nutrient bloom thresholds are likely to be specific for systems. But in many instances in which we’ve tested them, it looks like at least a 30% reduction should be targeted.
“We may need to reduce these inputs even more in a warmer stormier world because blooms like it hot; the cyanobacteria like really warm conditions and episodic events like big storms followed by droughts favor these blooms.
“The input reductions need to be year-round. That question gets asked to me all the time, can we just reduce nitrogen in the spring and phosphorus in the summer? Many of these systems have pretty long residence times. So reducing a nutrient for only a few months isn’t going to buy you much.”
“And lastly, warmer, longer growing seasons, and this doesn’t really apply to the Bay-Delta, but ice goes off earlier and comes on later. So the window of opportunities for these blooms is expanding globally, particularly in high latitude places.”
Dr. Paerl then concluded with a thank you to his collagues in the US, China, Europe, and elsewhere.
PEGGY LEHMAN: Harmful algal blooms in the Delta
Dr. Peggy Lehman, a Senior Scientist at the Department of Water Resources, then discussed harmful algal blooms in the Bay-Delta.
In 1999, the first blooms were spotted in the estuary. At the time, the colonies looked like shredded lettuce and spaced far apart, so it didn’t seem to be too big of a problem. However, in recent years, there have been massive harmful algal blooms, particularly in harbor areas. Last year in 2020, it was the worst, with the toxin concentrations soaring up to 1000 micrograms per liter of microcystis at Stockton, which was far beyond what was expected.
When the blooms first started, there was only microcystis aeruginosa; then up to 10 strains of that; after that, different microcystis species appeared, and now there are mixed cyanobacteria blooms. The three main species now are microcystis, dolichospermum, and aphanizomenon, among other cyanobacteria that could also bloom. The toxins began with just microcystin exclusively, and beginning in 2016, microcystis, anatoxin, and saxitoxin.
“It has been quite an expansion,” said Dr. Lehman. “Our bloom season was three months or so; now it’s seven months, and it is because the temperatures have increased in the spring. It’s seven months, and we’re still counting as there’s no telling how long these blooms can go. Usually, the blooms start when the water temperature comes about 19°C (66°F). Then the colonies go down to the bottom and stay on the sediments once the temperature reaches about 15°C (59°F).”
The blooms started initially in the San Joaquin River and occasionally in Suisun Bay, but now there are blooms in the northern estuary and floodplains, as well as some of the freshwater habitats. Toxin concentrations used to be less than one micrograms per liter; last year, it’s up to 1000 micrograms. The drinking water reservoirs usually had less than one microgram per liter, but lately, they have been at the caution level reaching at times to two to eight micrograms per liter.
“Throughout the system, we see these shifts in microcystis, and it has been huge,” said Dr. Lehman.
Dr. Lehman presented a slide showing total microcystis concentration measured last year. The red circles indicate where microcystis concentration was at dangerous levels – up to 1000 micrograms per liter in several places throughout the estuary, mostly around Stockton and Discovery Bay. The potential for expansion throughout the system is considerable because there are so many places with high levels.
What are the causes?
High nutrient concentrations: There are many nutrient inputs throughout the estuary – a lot of nitrate, ammonium, and phosphate. There’s no limitation there. Ammonium is important, and there’s a focus on that in the estuary. Microcystis grows very well in ammonium, very fast relative to other species on the ammonium, but it also grows in nitrate. Based on studies, we know it’ll use whatever nitrogen is available, so total loads are an issue, she said.
Water temperature: Water temperature has increased with summertime water temperatures reaching 28°C (82°F). The cyanobacteria grow very well at those temperatures; it’s just fostering the blooms.
Long residence time in dry conditions: The X2 index relates to the distance upstream from the Golden Gate where there is two parts per 1000 salinity at the bottom; it is an index of residence time. When X2 is 85 kilometers or more, there are a lot of blooms in the system. Between water temperature and residence time, we can describe about 80% of the variation in the blooms, she said.
The figure on the slide shows the interplay of the factors: the X2 index is on the left and the water temperature on the right. When X2 is above 85 kilometers, and the water temperature is 25°C (77°F), there is peak microcystis growth in the system. This is something that can be predicted well with just a simple regression, she said.
Herbicides: Laboratory work looking at how microcystis, some phytoplankton, diatoms, and others respond to various herbicides found that microcystis is less responsive to herbicides than other species such as diatoms. So the chemicals we put in the environment are really important, said Dr. Lehman.
There is also now evidence that microcystis and other cyanobacteria are dominant in the system covary with Phenylobacterium. Phenylobacterium only occurs when there is a high decomposition of these herbicides. So herbicides could potentially be contributing to the problem.
In terms of exposure, Dr. Lehman said they have found microcystis in all the beasts of the estuary. “There is a way that this moves up the system,” she said. “One that has been demonstrated is threadfin shad, which are common prey in the system. And they gobble microcystis; they love it. And their bellies can be distended with microcystis. And you can actually see green on the side because they have so much stuffed in their tummy. And so a fish coming along and eating a threadfin shad will get a large dose of microcystis. So there is a lot of movement from the lower food web up through predation.”
Zooplankton are affected by microcystis; studies have shown that increased mortality occurs in response to microcystis in the water column; it varies among species. Fish species, such as the splittail and Delta smelt, all show responses to the presence of microcystis in their diet or the water; they do not do well. There haven’t been any direct studies on phytoplankton in this system; however, fieldwork has shown that when there are cyanobacteria, there’s a huge shift in the phytoplankton community. Microcystis blooms decrease bacterial diversity; they also covary with Phenylobacterium, which is directly associated with the inorganic byproducts of herbicides.
So what do we do now?
“Right now, given what we had last year, in 2020, we need to focus on safety,” said Dr. Lehman. “People in this estuary could not even go out on the water with their boats. And we now know that there’s even an aerosol component to microcystis. It is dangerous for people to be in the Delta. And this is a huge recreational area and huge fishing area, so it’s a problem.”
Nationwide, there are those working along the coast on early warning systems, focusing on in situ real-time monitoring for toxins and species composition that’s pretty sophisticated; these systems can be out in the water and relay data through satellite. These are becoming common tools for the perennial blooms out along the coasts, and they might be able to be deployed in the Delta. Dr. Lehman said there are some great modelers in IEP, and forecast modeling is not out of the realm of possibility. These types of systems could warn people so they could protect themselves.
“The key here is information transfer,” said Dr. Lehman. “The public should be able to find out what’s going on immediately in the location that they’re at. And there’s a lot of information and tools out there from our colleagues looking at HABs on the coast. For instance, there’s an app you can get on your cell phone that will download information straight from satellite monitoring systems, so you can know if, at your location, there’s a HAB present.”
She acknowledged the very active community in the Delta that could be engaged to help monitor for the blooms, and there is good work being done at the State Water Board. There are many simple tools to use – sticks and small vial systems so people can know if it’s safe or not and help feed information into the system on a local basis.
“There’s a lot we may need to do right now to help people be safe,” she said.
What do we do over the long term? “We have to reduce the nutrients in the system if we really want to control it,” said Dr. Lehman. “We have to do our due diligence to try and minimize climate change impacts; the water temperature and the drought are hurting us. That’s hard for us to change locally. And I know that nutrients are hard for us to change locally because of all the farming we have; it’s really hard for most farmers to control their nutrients to the level we need because of the economics of the situation. So we have a tough road there. I have talked to a lot of farmers about this. This is hard for them.”
We could look at some of the treatments, but the problem is that the Delta is so big, she pointed out. These treatments only work in small locations, but there may be areas such as marinas where treatments might help get the concentrations down.
“We have a long way to go,” said Dr. Lehman. “But I think we need to start focusing on this because of the danger to the public, the lack of our ability to use the system, and the danger posed to the food web.”
Reducing nutrient inputs to the Delta
Dr. Lehman was asked where the state of California is right now in terms of discussing the need to reduce nutrient inputs to the Delta.
“I don’t know,” she said. “The State Water Resources Control Board is talking about ammonium reductions. And we have a program established right now to try and get the ammonium down. But total nutrient reduction – that’s really not on the table right now. It’s more ammonium reduction through controlling what’s happening with the treatment plants. I’m not sure that the level of nutrients they’re going to affect in their treatments will be sufficient to take out the microcystis blooms. The focus is a lot on ammonium, but there still will be a lot of nitrogen left. They’re talking about it, but there’s no fixed ratios and no fixed concentrations that have been decided, as far as I know.”
The role of mussels
Dr. Steve Brandt noted, “In Lake Erie when the resurgence of microcystis came in the second wave, there was discussion about the impact of the zebra mussel and that it had somehow altered the nutrient phosphorus ratios and also had some selective predation against microcystis. Is there any indication that corbicula played a role? Or is it playing a role at all in microcystis? And if not, are there any other foodweb implications we ought to be thinking about?”
“Locally, we don’t have any studies that have looked at it,” said Dr. Lehman. “We do see microcystis in the clam, so we know they’re taking it in. I don’t know that they’re having an effect in one way, and another, they might. The one thing that they do influence is they increase the water transparency. Microcystis does sit on the bottom of the water column. As more light gets into the water column, it enhances the microcystis’ ability to grow, but also it increases the temperature of the water column. I think that that could be enhancing microcystis. But any other way, we haven’t done any studies to verify any effect.”
“The blooms in Lake Erie, many of them are surface-dwelling blooms, or at least during most of the day, they’re at the surface,” said Dr. Paerl. “So they’re kind of away from the benthic grazers to begin with. Knowing how good microcystis is at utilizing reduced nitrogen and recycled nitrogen, I think if anything, the clams may have actually enhanced the internal recycling rates of both phosphorus and nitrogen in Erie.”
“This happens in other lakes, too,” he continued. “For example, in Taihu, there’s a lot of clams, and in fact, the Chinese fish them and eat them. Of course, I would never eat one of those, but they’re supposed to be delicious; maybe it’s the microcystis that makes them taste good. The bottom of the lake is covered by these giant freshwater clams, and basically, it seems like the impacts, if anything, might be positive as opposed to being negative.”
“That’s what I was thinking,” said Dr. Brandt. “In Lake Erie, it was the zebra mussels that promoted microcystis.”
“Maybe,” said Dr. Paerl. “I think the bigger issue is that for a long time, nobody paid any attention to nitrogen. It was so phosphorous-focused. The watersheds around Erie are heavily fertilized with chemical fertilizers, a lot of it for biofuel production, which is a whole other story, but a lot of nitrogen is leaking through the system now. And the fact that we see more non-nitrogen fixers is telling us that the community structure has changed, probably in response to the fact that there’s more nitrogen available. My inclination is, let’s start worrying about what’s coming in from the watershed. We can argue about the zebra mussels for a long time, but I think they’re kind of a secondary modifier, maybe of the community.”
Expansion of wetlands
Of these different approaches, given the importance of nitrogen and the scale of the Delta, do you think expansion of wetlands is one of the more pragmatic approaches that might work?
“There are a lot of projects in the pipeline to expand the wetlands in the Delta, so those may be helpful,” said Dr. Lehman. “We’ll see. Time will tell on that. There are problems expanding these wetlands; we need to find the land, and that not so easy. With the change in climate, we’re seeing a reduction in wetland habitats that are available. So it’s kind of tough. The plan is to do some expansion, and more expansion couldn’t hurt as far as I’m concerned. Some of the work I’ve done with wetlands does demonstrate this quite a bit of processing of nutrients, so that’s good. Certainly, ammonium is immediately transferred to nitrate, and there’s quite a bit of uptake. But I think we have to do more in-depth studies in the very few wetlands we have to work with to kind of understand what’s needed and where it’s needed.”
“I’m all in favor of wetlands,” said Dr. Paerl. “I think they’re great in terms of removing nutrients, particularly nitrogen. The big question is land availability. One thing that I wonder about is whether or not some agricultural lands could be converted to wetlands. We pay farmers not to grow crops for other reasons. Can we pay them to have wetlands in their operation? That has been going on in North Carolina. The largest corporate farm east of the Mississippi is located in the county I live in. It’s an open grounds farm; they grow corn, cotton, soybeans – the usual stuff they grow here. But they actually have dedicated some of their lands to treating nutrients through wetlands. This has been a real success story. They have been able to reduce nitrogen throughput from their operation by 50%. So I think we got to start thinking creatively about this. If we pay farmers not to grow crops, we can certainly pay them to do some innovative things with the land.”
“One question I have about wetlands in California is that the rain all comes in once, right? And the rest of the time, there’s no rain,” said Dr. Paerl. “That’s a consideration in terms of the operation of wetlands.”
If we’re trying to convince policymakers to invest a lot in nutrient reductions, do we have any stories of how successfully reversing algal blooms through nutrient reductions? Do we have the evidence we need to build a quantitative model?
“There’s been a phosphorous story for a long time,” said Dr. Paerl. “But with nitrogen, we are starting to get some stories now that are success stories. For example, in some of the tributaries along the Chesapeake Bay, even here in North Carolina, the Neuse River estuary where a TMDL is in place for reducing nitrogen and reducing chlorophyll content. Then there are some good examples in Europe. The Himer Fjord, which is a fjord that comes down from Stockholm into the Baltic Sea. … In China, they are starting to have some improvements in places including around Taihu; they have converted farmland to treat nitrogen in particular and have shown localized success stories – not in the open Lake, but around some of the bays around the lake by encouraging the growth of macrophytes and again, enhancing denitrification. I think wetlands are really good for nitrogen, and phosphorus, too. But you have to harvest the stuff out of there to get rid of the phosphorus. So, that could be an issue. So yes, there are success stories that are evolving. Limnologists have only recently really started worrying about nitrogen. Paradigms are hard to break, I’ve discovered, and, but it’s happening.”
During public comment, Barbara Barrigan-Parilla, Executive Director of Restore the Delta, noted that she has secured a grant to begin working on a youth science training and communication plan for tracking HABs in the Delta. They will be working with the State Water Board on the effort. The intent is to train high school and college students to begin tracking and testing waters and reporting to the Water Board on what is happening within the Delta with HABs starting in San Joaquin County. The ultimate goal is to become a certified citizen science program and then replicate it in other parts of the Delta.
“There really has to be a strengthening in the connection between your research and engaging public health and safety agencies at the county level in the Delta. It’s not only to understand the science but also to really develop a timely and proper public response. The last two years have been problematic because we cannot get county health departments to get signage up quickly. We know that we have homeless people using these polluted waters with HABs for sanitation; we know that people’s pets are dying. … We are not anywhere near where we should be with a public response. I understand that our health departments and our emergency and environmental service departments have been under great stress with COVID. But we really need to put a long-term response in place as we work to track and mitigate this.”
Ms. Barrigan-Parilla also noted the comment about wetlands replacing farmland to mitigate this. However, in the Delta, addressing a problem in one area can cause a problem in another. “It’s also my understanding, though, that wetlands may actually increase the methylation of mercury, which is an entirely different problem. So all I’m asking is that there’s a total picture put together to make sure that if we’re working to solve one problem, another problem isn’t going to worsen.”