ABSTRACT: Over 12 million fish have been killed in Texas since 1985 due to toxic golden algae (prymnesium parvum) outbreaks, resulting in huge losses to local economies. Although various investigations have been conducted on the conditions promoting blooms, the mechanism by which algal growth occurs is unclear. Most outbreaks occur in agricultural watersheds and coincide with the application of pre-emergent herbicides. We hypothesize that atrazine and Roundup inhibit the growth of obligate photosynthesizing organisms and cause a shift in the planktonic community to facultative aerobic organisms. This should correspond to a statistically significant difference in population diversity and relative abundance of all species. The population of p. parvum in the aerobic state should increase and produce toxic metabolites.
Procedure: We will randomly collect water samples from nearby Lake Tanglewood, which has experienced fish kills due to golden algae outbreaks. Aquaria with a half gallon of water will be inoculated with water samples and aerated constantly using an air pump. Aquaria will be subjected to 12 hour photoperiods. Population diversity and relative abundance will be measured frequently over 3 days or more under atrazine concentrations of 0 (control), 0.1, 1, and 10 ppb while populations will be assessed under Roundup levels of 0.1, 1, 10, and 100 ppb.
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I know that scientific writing is oftentimes a bit too succinct and technical, so the idea for this project comes from a problem occurring in Texas: golden algae blooms. During January-March, the water in some places turns golden brown and thousands of dead fish rise to the surface. The state of Texas will then come in and clean everything up, but it will take a couple of months for an area to recover from a bloom like that and for fish to come back and repopulate. This is caused by golden algae (latin name prymnesium parvum) which multiplies for unknown reasons. When it does this it gives off a toxin to fish which are very sensitive because they have gills. Molluscs and shellfish tend to die off too, and no one knows why this is happening.
We believe this is occurring because atrazine, an herbicide, is running off into the surface water and causing this algal bloom. Golden algae is a "mixotroph", which means it survives normally by getting light energy and conducting photosynthesis, where it produces oxygen as a byproduct. When it is in this state it causes no harm. However, the alga can revert to a "heterotrophic state", in which it consumes other organic nutrients (lipids or fats, amino acids, bacteria) for food. When it does this, it gives off toxic metabolites to catch and digest its food, and that is when the poisons are given off.
Atrazine causes this reaction by inhibiting photosystem II, which is the first step in photosynthesis. When the alga cannot photosynthesize, it goes into its heterotrophic state, where it consumes other nutrients and bacteria for food, and gives off these toxins. There is a lot of atrazine runoff from agricultural lands, and most fish kills happen in the watersheds of these farms. If we find that atrazine does cause the golden alga to give off toxins and kill other plankton, farmers may need to establish corridors between their farms and watersheds which will reduce atrazine runoff (introduce native plants to narrow strip of land which will uptake the pesticide and reduce pollution).
So for my experiment, I'm going to a lake which has experienced a bloom to sample water and collect plankton. I'll combine all the water, mix it up with a plankton, and then put it all into a bunch of different aquaria. In half of the aquaria I'll have different concentrations of atrazine, and in half I'll have different concentrations of Roundup. Then I'll have a few aquariums which have no herbicides, this is my "control", and I'll compare the effects of the varying concentrations of atrazine and Roundup to that of the aquariums with no herbicides.
From this information I should be able to establish a "dose-response curve", this is a graph which shows the dose of the herbicide on the x-axis and the response on the y-axis. My response variables (what I'm testing for) will be the relative abundance of the algae (how much golden algae is there compared to the other types of algae) and population diversity (low population diversity = just a few species of algae, high population diversity = many different species). We predict that the relative abundance of golden algae will increase with increasing levels of either herbicide, while population diversity will decrease.
With the dose response curve, regulatory agencies such as the EPA or Texas Department of Parks and Wildlife/Texas Council on Environmental Quality should be able to establish acceptable levels of atrazine and Roundup in waters which are sensitive to golden algae outbreaks. We may reccomend a NOAEL, or "no observable effects level", the level of herbicide in the water (i.e. 10 parts per billion) at which we see no effect whatsoever on the planktonic community. This information should help these agencies to monitor outbreaks and areas which are particularly vulnerable to fish kills. In addition, this will make regulatory agencies increasingly aware of the ecological nature of risk assessment and toxicology.
In toxicology, we frequently test the effects of a certain chemical or pesticide on a target species, such as fathead minnows or rats (in the case of carcinogens). However we don't really take ecology into account. For example in this study, atrazine is not normally toxic to fish. However, atrazine kills off phytoplankton and causes golden algae to give off poisons which are toxic to fish. So, atrazine turns out to be indirectly toxic to fish. When atrazine was being tested for the public market, no one thought to test it in an ecosystem or on algae of any kind, because what does it matter if an herbicide kills off algae? That's just less scum on the surface of most ponds and lakes, right?
In certain cases, that logic may be true. But increasingly, we're finding out that it's important to study the effects on the entire ecosystem. If an herbicide runs off into surface water and kills off all phytoplankton, well, what are the zooplankton going to eat? And then if the zooplankton die, what will smaller fish eat? And larger fish, once those fish die? So what happens is we have "trophic-level effects" on a large scale, which, if we don't test for, will happen in the real world. Algal blooms, fish kills, problems with invasive species, all can be the products of our limited ability or desire to study the effects of toxins on a species without realizing the relationships that species has with its food web and surrounding environment.
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