BACKGROUND

      Nutrient enrichment of coastal waters is major problem in estuaries worldwide. In the US, every urban estuary is "culturally eutrophic" and polluted with nutrients from sewage, septic systems, agriculture, and road run-off.

      Nutrient enrichment of the Florida Keys is a primary hypothesis explaining loss of corals and seagrass. Students need to understand what nutrient limitation is in order to follow the hypothesis that nutrient enrichment of the Florida Keys waters results in loss of seagrass beds and corals. The following set of questions will help you logically develop their understanding of this concept. This study done by Vince and Valiela shows that marine waters can be nitrogen limited. The researchers added N alone, P alone, N and P together, and nothing (C is the control) to seawater in containers incubated in the field (in the water). There are many studies showing that marine waters are N-limited and freshwater P-limited, although P or N limitation can occur in both marine and freshwater. Tropical waters like the Florida Keys can be limited by P because phosphate binds to calcium which is abundant in coral reefs.