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The same parameters as in figure 1, for Lake 303, fertilized with nitrogen and phosphorus at a ratio of 15 : 1 (weight), as designated by the shaded area. Note the rapid increase in chlorophyll a, followed by a decrease in proportion to the decline in phosphorus, while excess nitrogen accumulates as nitrate. The arrow designates a forest fire in the catchment, which burned most of the vegetation and organic soil.
