Interannual Variability of Nitrogen Limitation in a Desert Lake: Influence of Regional Climate

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Abstract
A systematic evaluation of limnological and experimental indicators of nutrient limitation in Pyramid Lake during 1989–92 clearly show that N is the nutrient most limiting to phytoplankton. This conclusion is supported by dissolved inorganic nutrient ratios, seston elemental composition, nutrient enrichment bioassay experiments, and blooms of N2-fixing algae. However, the degree of N limitation expressed during the three years varied considerably. A comparison of interannual patterns of N limitation with weather data collected at the lake suggests that differences among years can be attributed to climatic variations. Our study indicates that climatic variations affect N availability by altering the timing of winter deep mixing, varying the potential for upwelling during spring, and varying the rate of spring warming of surface waters. Summer wind patterns also appear to be an integral factor controlling initiation, development, and collapse of the annual bloom of Nodularia spumigena, a N2-fixing blue-green alga. The results of this study emphasize the need to consider climatic variations in assessing the general nutrient status of lakes.