The nature of fertility and its consequences in aquatic ecosystems has long been the subject of intensive research, with two motivations:

• The study of nutrients is basic to the understanding of natural ecosystem processes. Plant nutrients control production of plant biomass, which in turn energizes all other parts of the foodweb, including grazers, predators and microbes.
• Global degradation of aquatic ecosystems is occurring due to human mobilization of plant nutrients. Nutrient enrichment (eutrophication) causes large increases in the abundance of aquatic plants. Lakes are especially sensitive to enrichment, which causes algal populations to expand many times beyond their natural abundances.

Enrichment favors nuisance algal species that form scums, secrete toxins and cause deep waters of lakes to become anoxic dead zones. Much of the use and beauty of lakes is lost when lakes are fertilized by humans. Water quality protection in many nations, including the United States, emphasizes reduction of the vast human mobilization of both nitrogen (N) and phosphorus (P) that has enriched surface waters.

William M. Lewis Jr, professor of ecology and evolutionary biology at CU Boulder and director of the CIRES Center for Liminology, will present a lecture focusing on the projected outcome of withdrawal from enrichment: Can anthropogenically-enriched aquatic ecosystems be restored to a natural state?