Human Domination of the N Cycle

Ecosystems Ecology April 17, 2014

NAME______

Human domination of the N cycle 1: Examine the figure below, from the reading you were supposed to do and answer the subsequent questions.

Figure 1: Terrestrial N fixation between 1955 and 1992 (Vitousek et al. 1999)

Write a paragraph detailing what this figure is telling you. Your task here is to convert this visual expression of data to a story from the data. Feel free to discuss the figure with your group mates, but your writing should be your own (10 points).

1 According to Vitousek et al. use of N for agriculture in developed countries stabilized in the 1970’s and the rapid increases since then is from use in developing countries. Explain this statement and its implications in regard to regulation of global N pollution (10 pts).

The nitrogen Cascade The next two figures describe the relationships between nutrient inputs and nutrient concentrations. The first focuses on nitrate in rivers, the second focuses on nitrogen being delivered to the coastal zone.

Figure 2: Changes in riverine N concentrations as a function of human population density. Data from Cole et al. (1997).

2 Figure 3: Changes in riverine N flux as a function of N inputs. Data from Cole et al. (1997).

What is the difference in the x-axis between the two figures (Fig. 2 and Fig. 3) and what is the difference in the y axis (note that I do not want you to just write down what the axes say, I want you to interpret the meaning of them; 5 pts).

What is the implication of these figures (5 pts)?

3 What happens when the nutrients make it to the coastal zone? Pfiesteria piscicada is a dinoflagellate which is a common in marine environments. Dinoflagellates are single celled and are planktonic (drift in the water), although many forms have flagella and can therefore move. The are metabolically quite versatile; they can photosynthesize, absorb dissolved organic matter (like bacteria do), and also injest particles of organic matter. Dinoflagellates are brownish red in color and when they grow in large numbers (called blooms) the water can look red. Some dinoflagellates cause "red tides", which you may have heard of. The Pfiesteria story is fascinating from many points of view - ecological, political, and personal. Its life history is so bizarre that it sounds like a science fiction story. The politics center around JoAnn Burkholder, a microbial ecologist from North Carolina State University, who is either admired or chided, depending on who you ask. The politics are also those of hog industry in North Carolina. Burkholder's first paper on Pfiesteria piscicada was published in the journal Nature in 1992. Since then researchers have learned a great deal about its highly complex life cycle (more than 20 different stages), its mode of attack on fish and other animals, the action and structure of the Pfiesteria toxin, factors that stimulate the toxic forms to grow in nature, and its presence in other estuaries in the U.S. and globally. Pfiesteria piscicida was discovered by accident (science is often more serendipity than planning!) when a colleague of Burkholder noticed that the fish tilapia held in tanks suddenly died several days after being exposed to water collected in the Pamlico River, NC. The scientists observed that density of a small dinoflagellate increased before the fish death and declined rapidly in number unless live fish were introduced. The dinoflagellate produced resting cysts or non-toxic amoeboid forms in the absence of fish. When Burkholder and her colleagues looked for dinoflagellates during massive fish kills in local estuaries, Pfiesteria was abundant, but only when fish were dying. In the Nature paper they name Pfiesteria as the causative agent of the many unexplained fish kills in NC estuaries, they identify a neurotoxin from the dinoflagellate as the lethal agent, and they link fish kill events to nutrient enriched Pfiesteria blooms. In subsequent studies Burkholder reported that toxic forms of Pfiesteria were stimulated by inorganic and organic phosphate. She became embroiled in arguments with NC officials about the role of the state's hog farm effluents in stimulating Pfiesteria growth. Nitrogen entered the story in the late 1990's when the incredible nutritional versatility of the dinoflagellate became clearer. In addition to consuming dissolved organic compounds (such as in animal waste, or possibly even animal flesh), Pfiesteria retains chloroplasts from algae that it consumes when fish are not available. Pfiesteria zoospores with these inclusions, called kleptochloroplasts, are stimulated by N and P. In addition to stimulating the growth of Pfiesteria zoospores directly, N indirectly contributes to growth of the dinoflagellate because N is a limiting nutrient for phytoplankton in estuaries. Therefore N loadings stimulate phytoplankton growth, which in turn contribute to proliferation of Pfiesteria. The neurotoxin excreted by Pfiesteria deserves special mention. Until the discovery of Pfiesteria, estuarine ecologists often had a difficult time explaining to legislators and the public how too many nutrients, which sound like good things, could be bad. In addition to the vocabulary problem, nutrient loading does not directly give people diseases or make them sick. For both these reasons, explaining that nutrient loading to estuaries is a severe environmental problem has been an uphill battle. But Pfiesteria does make people sick. Both Burkholder and Howard Glascow, who works with her, suffered serious neurological effects when they unknowingly inhaled the Pfiesteria toxin. The scientists were hospitalized and affected for

4 months. Pfiesteria is the first reported dinoflagellate that produces aerosols that seriously harm human nervous systems. Symptoms include acute respiratory problems blurred vision, nausea, vomiting, extreme headaches, and severe memory dysfunction. According to Burkholder and Glasgow "For days to weeks following exposure, several laboratory personnel could recognize words individually but could not form sentences, perform simple arithmetic, or remember more than the last words of a sentence directed to them. The most seriously affected person in our laboratory, who is a highly intelligent researcher, managed only a 7-year-old's reading level for 3 months after exposure and required reading lessons at first to help regain reading ability … two others … could not remember their names or where they had lived." One of the many controversial aspects of the Pfiesteria story is the degree to which fishermen were harmed by neurotoxin aerosols during Pfiesteria blooms.

Below is a series of figures that can be pieced together to tell one part of the Pfiesteria story. Work together in groups to discuss each of the figures below and beside each figure briefly describe what the figure shows and what the implications are of the results (10 pts per figure).

Figure 4: Changes in Pfiesteria cell density in relation to differing amounts of time between when, after a fish died, a new fish was introduced and when the second fish died.

5 Figure 5: Trophic controls on stage transformations and feeding behavior of the toxic predatory dinoflagellate Pfiesteria piscicida. Several water column stages can release toxins that immobilize and kill prey. Flagellated stages attack and feed on fish excreta and tissues. After fish death these flagellated forms either encyst or transform into amoebae and continue to feed. When fish are absent, active amoebae persist in the sediments and, less commonly, in the water column, as long as alternate microbial prey are available. (From Burkholder and Glascow, 1997).

6 Figure 6: Abundance of Pfiesteria zoospores in control vs. wastewater discharge sites. From Burkholder and Glascow (1997).

Figure 7: Known geographic range of toxic Pfiesteria. All sites are associated with sudden-death fish kills and ulcerative fish disease, and where toxicity has been verified in the laboratory by bioassays using tilapia. From Burkholder and Glascow (1997).

Working individually your task is to write a newspaper article based on what is known and what is not known regarding Pfiesteria. There are new discoveries and much more complicated results that are found in the literature now but your task is to use all the data generated here (from all 7 figures) to inform the public about Pfiesteria based solely on these data. As is typical of newspaper articles, please limit your article to 300 words and include a title for the article (the article should be typed up separately and handed in with the overall assignment). You answer will be assessed based on the completeness and logical flow of the story. This includes synthesizing all the relevant data and discussing the important potential causes and consequences of Phiesteria, as well as on the structure and clarity of your writing, 30 pts).