Understanding Shifts in Limitation of Lake Primary Productivity across Scales and Its Implications for Water Quality and Carbon Cycling

Elemental cycles on Earth are inherently coupled. The coupling of elements by primary producers has immense implications for the contributions of ecological systems to global biogeochemical cycles because the rate at which they couple elements dictates elemental fate. The rate at which coupling, or primary productivity, occurs is dictated by the degree of biological nutrient limitation. However, a wide breadth of ecological research has found that what limits primary productivity is not static in space or time, and can often work in tandem, or be co-limiters. Limitation can be influenced by catchment land use/land cover, precipitation, lake morphometry, and organismal stoichiometry. Nutrient limitation and the potential shifts to other forms of limitation have important implications for the spatiotemporal variability of biogeochemical process rates and the ultimate fates of elements.

In this body of work, we have adopted an approach that pairs a process model with data to assess shifts in limitation in several lake ecology contexts and explore the potential implications these shifts in limitation have on water quality and the global carbon cycle. In my first data chapter, I present the first experimental test of a new model describing how shifts from nutrient to light limitation control primary productivity in lake ecosystems as hydrologic inputs of nutrients and dissolved organic matter vary. In my second data chapter, I found that combinations of lake shape and hydrologic P load induce broad shifts in algal limitation status that underlie the shape and variation in the TP-chlorophyll relationship. In my final data chapter, I found that land use and climate, specifically precipitation, synergistically interact to increase organic carbon burial rates primarily because of a release of nutrient limitation that led to increases in primary productivity. My hope is that my dissertation work will foster future advances in both basic aquatic ecology research and lake ecosystem management.