Relationship of Chlorophyll to Phosphorus and Nitrogen in Nutrient-Rich Lakes (image) University of Minnesota Share Print E-Mail Caption Aerial view of a small lake near the city of Clear Lake, Iowa, which represents typical landscapes surrounding the lakes in this study. About 92 percent of land within Iowa is in production agriculture and crops on these lands receive large amendments of nitrogen as anhydrous ammonia and phosphorus. Excessive algae growth caused by these nutrient inputs have turned many of the lakes in this region bright green. Surprisingly, a number of lakes in this study were clearer and appeared bluer than expected, yet are far from healthy. The study authors hypothesize that very high nitrogen levels, often >10 mg/L, suppress high chlorophyll (algae) concentrations. Credit John A. Downing Usage Restrictions None Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.