1.  Nutrient Limitation What’s happening in the Chesapeake Bay and how does it compare to our results?

2. Past Data

3. Seasonal Trends  Winter shows little growth  Light is limiting  Spring shows elevated growth in both P and N+P treatments but not in the N treatments  P is limiting  Summer shows elevated growth in N and N+P treatments but not in P treatments  N is limiting

4. Seasonal Trends

5. Our Results How do our class results compare to the bioassays conducted by other researchers that have been done during the same season of the year? ?

6. Why?  The input of nitrogen into the Bay is closely tied to the annual flow of water into the Bay.  Freshwater inflow is generally much richer in nitrogen than phosphorus but this does not tell the whole story.

7. Oxygen Concentration (mg per liter) JFM A MJJASOND 0 2 4 6 8 10 River inputs of nitrogen and phosphorus are especially high in the late winter and early spring. Phosphorus moves into the well-oxygenated sediments. Sediments remove nitrogen from the water during late spring/early summer. Anoxic sediments release phosphorus into the water column during the late summer and early fall. MONTH

8. The Big Picture  Year-round reductions in phytoplankton will only be possible if inputs of both nitrogen and phosphorus are reduced  The primary issue now hampering the Bay’s clean-up is summoning the political and social will of citizens within the watershed to finance the implementation of these nutrient control technologies