Contents

Uncommon Blooms

Algal Growth:
  The Role of Metals

By Merrill Leffler

For almost three weeks this May, the surface of the Choptank River was running visibly red, for about 10 miles from Cambridge downstream to its mouth. "It was the largest bloom in anyone’s memory," says Pat Glibert, a professor at the University of Maryland Center for Environmental Science (UMCES) Horn Point Laboratory. And even more surprising, it consisted of a single species of dinoflagellate, Prorocentrum minimum (May’s large bloom is outlined in red in this aerial photograph of the Choptank River).

"Prorocentrum typically blooms at this time of year," says Glibert, "but it’s usually isolated in coves here and there. We just haven’t seen anything of this magnitude in the river." In the mainstem of the Bay, on the other hand, blooms covering as much as 30 miles have been observed over the years.

Nor was the Choptank the only host: the same dinoflagellate showed up in the Tred Avon and Miles rivers, and, there is some evidence says Glibert, in the Pocomoke.

The bloom seems to have gotten underway when the sun finally emerged after several days of rain that probably introduced heavy loads of nutrients from the land, according to Glibert.

But nitrogen and phosphorus loading, warming temperatures and sunlight – prime conditions for algae in general – don’t account for Prorocentrum in particular, nor can it explain why there wasn’t another species or a mixed group.

Large outbreaks of Prorocentrum are of some concern: while there are no reports of it being toxic to shellfish or humans in the Chesapeake Bay system, there have been such reports in other coastal waters. To ensure that it is not toxic, Glibert is having water samples from the Choptank evaluated.

In this experimental set-up, water samples taken from the Choptank River contain Prorocentrum minimum in cell concentrations of 100,000 per millimeter, compared to normal Bay concentrations of 100 cells per milliliter.

Whether or not this bloom serves as a warning signal for potential outbreaks of harmful algal blooms in the Bay is open to question, but "one of the situations we face in the United States," says Donald Anderson, "is that we have more toxic algae, more toxic outbreaks, more areas affected, more economic costs, and more impacts on resources."

A scientist at the Woods Hole Oceanographic Institution, Anderson has been studying harmful algal blooms for years. Everything is growing better because of nutrient pollution running into our coastal waters, he says. "It is like fertilizing your lawn, but just as you get more grass, you also get more dandelions and more crab grass."

But why more harmful algal blooms? Glibert, together with other scientists – Sybil Seitzinger at Rutgers and Deborah Bronk at the University of Georgia – has strong suspicions that explanations are to be found in the kind of nitrogen present in the water.

By way of analogy, Glibert says, "when you use fertilizers in your garden, you use different formulations of phosphorus, nitrogen and other compounds, depending on whether you’re growing grass, tomatoes or roses. While we have a good understanding of how these combinations affect gardens," she adds, "we have very limited knowledge about what we’re selecting for in coastal waters like the Chesapeake. That’s because there are different forms of nitrogen entering the Bay, and we don’t understand their dynamic relationships with algal species."

Nitrogen in the Bay

The issue is not an academic one – in the long run, understanding how different forms of nitrogen are related to the growth of particular algal species could be critical if we are to successfully restore the Bay’s degraded water quality and sustain the production of fish and shellfish.

Nutrient control, after all, has been the keystone goal of the Chesapeake Bay Program since 1987 – a 40-percent reduction is the mantra. According to Bay researchers and their increasingly sophisticated computer modeling, a 40-percent reduction from 1985 levels is the minimum necessary to keep oxygen levels in large stretches of the Bay from bottoming out at or near zero, to bring back underwater grasses, and to revive benthic habitats in the deeper waters.

Everything is growing better because of nutrient pollution running into our coastal waters.

While there has been measurable success in reducing the loading of total nitrogen and phosphorus compounds to the Bay over this last decade, from point sources such as waste treatment plants especially, there has been less success in stemming flow from diffuse sources such as agricultural and urban runoff. Glibert and her colleagues Seitzinger and Bronk have been speculating that the form of nitrogen in that runoff could have important consequences: different compounds of nitrogen – along with other available nutrients, temperature, salinity, light, oxygen concentrations and compounds such as metals – can determine which species of algae will grow.

A dominant nitrogen compound that comes off the land in fertilizer and stormwater runoff and in treated sewage discharges is nitrate, an inorganic form (inorganic because it lacks a carbon molecule). Nitrate is a natural product of microbial processes, part of the complex nitrogen cycle that first oxidizes ammonia to nitrite and then from nitrite to nitrate. Nitrate is also manufactured chemically for use in fertilizers. We know that algae readily take up nitrate, says Glibert. "We can measure it easily and we have a good deal of understanding about the dynamics."

Though researchers have been studying the uptake of dissolved organic nitrogen by algae for some years, that understanding is still limited, in part because it is more complicated to measure, says Glibert.

Organic nitrogen compounds – they include urea, amino acids and other complex molecules – can make up a large percentage of the total nitrogen arriving in coastal waters. Urea, for instance, is frequently used in lawn fertilizers, golf courses, and as a de-icer on roads and airport runways; there are also indicators that farmers are replacing nitrates with urea as fertilizer for some crops because of its slow release properties.

Seitzinger estimates that stormwater runoff may be composed of 30 to 60 percent organic nitrogen. For sewage treatment plants, the numbers range from 15 to 60 percent. In confined animal areas, organic nitrogen could comprise 60 to 90 percent of total nitrogen, and rain falling from the sky may have 30 to 70 percent of nitrogen in an organic form.

Algae and Nitrogen

Unlike their uptake of inorganic nitrate, many algae do not take up organic nitrogen directly – it first has to be recycled into inorganic forms by bacteria and other microbes. But according to Glibert, there are algae that do take up organic nitrogen compounds directly. In some instances, these algae may even compete with bacteria for the same compounds. If, for example, inorganic nitrogen such as nitrate is all used up in a particular part of the Bay, then those algal species that are better at taking up organic nitrogen (such as urea) directly could outcompete algal species that cannot, species that have to wait for microbial cycling to supply nitrogen in inorganic forms.

In a study of a golden-brown alga (the chrysophyte Aureococcus anophagefferens which has caused massive brown discolorations in coastal waters in the northeastern U.S.), Glibert found that it had a higher affinity for organic nitrogen than inorganic nitrogen. This algal species was able to absorb organic nitrogen through biochemical processes on the surface of its cell, which implies that it could outcompete algal species which lack that capability, as well as bacteria.

It is such reasoning that has led Glibert, Seitzinger and Bronk to hypothesize that an increase in the ratio of dissolved organic to inorganic nitrogen is favoring algal species that are particularly adept at using organic forms.

While organic nitrogen in the form of urea can run off the land directly, it – like inorganic nitrogen – is also the product of microbial recycling. How much urea, for instance, is coming off the land and how much is being recycled? That is an important question, says Robert Magnien of the Maryland Department of Natural Resources. Before answering it, he says, we have to find out how much organic nitrogen is in the ecosystem, what percentage Bay algae use, and how this form of nitrogen influences the development of different kinds of algal species.

Difference compounds of nitrogen can determine which species of algae will grow.

"Once you measure the dissolved organic nitrogen, can you ask where it comes from? That’s a complex question," Magnien says, "a tough one." If organic forms such as urea are found to be important in controlling the dynamics of algal or bacterial communities, then identifying specific sources becomes very important. "If there’s some direct runoff stimulating harmful algae, that might point us to a more refined management approach than just trying to reduce total nitrogen. We might be more concerned," Magnien says, "with a particular fraction of the nutrients."

First, says Magnien, we have to find out if the different forms of nitrogen make a difference, and then we have to track them.

New techniques that Glibert has had a hand in developing have made it possible to better measure the uptake of organic nitrogen. In experiments over the last couple of years, she and Bronk have found that uptake of organic nitrogen by algae was as great as and, she says, "on occasion greater than" uptake of inorganic forms (of nitrate and ammonium). One implication is that increases of organic nitrogen, relative to inorganic, correlate with the outbreak of some algal bloom species that are identified as harmful.

Aquaculture: Nitrogen in a Microcosm

While reports of harmful algal blooms in coastal waters around the world have been increasing, reports are also coming in regularly of fish kills from such blooms in aquaculture ponds. In fact, aquaculture operations – where nutrients, algae and fish are held in high concentrations – serve as microcosms of the natural world for researchers like Sea Grant Extension specialist Dan Terlizzi, who is studying algal dynamics in fish ponds.

Even algal species that do not release toxins can lead to problems if blooms are dense enough, says Terlizzi. He points to Chaetoceros, a widely distributed group of diatoms common in the Chesapeake and known for having long spines, adding that it "can injure the gills of fish at high bloom densities."

Scientists at the UMCES Horn Point Laboratory are rearing striped bass in ponds that simulate commercial aquaculture operations to study the varying effects of environmental conditions on growth.

In 1996, aquaculturist Tony Mazzacarro lost about 20,000 hybrid striped bass in his ponds at HyRock Fish Farm in Somerset County on the Eastern Shore; in 1997, he lost 8,000. The deaths were initially attributed to Pfiesteria piscicida, the dinoflagellate that has become a household word in the Chesapeake Bay region after fish kills and reports of human impacts from toxins released by Pfiesteria. But according to Terlizzi, other algal species were also found in water samples taken from the HyRock ponds, among them Gymnodinium estuariale (recently identified as Gyrodinium galatheanum), a dinoflagellate which has been implicated in fish kills in other areas, though not previously in the Chesapeake region.

Terlizzi has teamed up with Glibert to monitor the chemical composition of the ponds. One striking finding, Glibert says, is that whenever there was a bloom of harmful dinoflagellate species, the concentration of organic nitrogen compounds was elevated. "Is this cause and effect?" she asks. "Or is it a coincidence? What is leading to what?"

Could high levels of dissolved organics serve as an early warning sign for potential algal blooms? This is precisely what Terlizzi and Glibert are trying to determine.

An early warning could be critical for fish farmers. There are some actions, limited as they may be, that growers like Mazzacarro can take to mitigate the impacts of harmful algae, especially applications of the compound permanganate. (Though copper sulfate is routinely used in freshwater ponds, its use in HyRock’s saltwater ponds led to fish deaths.) Permanganate is a strong oxidizer, says Terlizzi, and has been effective in treating dinoflagellate blooms. But as Mazzacarro says, permanganate is expensive and temporary – once dinoflagellates appear in a pond, they could reappear within several weeks of a permanganate treatment.

Good water quality is a major concern to Mazzacarro – it is critical for the production of algae that in the early stages of fish growth supports the food web they need to grow; but too dense a growth can lead to the deterioration of water quality and consequent stress, if not death.

The same can be said of the Chesapeake Bay, a 200-mile-long ecosystem far too large to treat with chemicals. In the Bay, resource managers will need to control inputs of nutrients to hold down unwanted algal blooms. To do this effectively, Glibert and others suggest, they will need to understand more completely the different effects of organic and inorganic nitrogen – and to trace and control their sources accordingly.

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