Nutrient Limitation
What’s happening in the
Chesapeake Bay and how does
it compare to our results?
S
Past Data
Seasonal Trends
S Winter shows little growth
S Light is limiting
S Spring shows elevated growth in both P and
N+P treatments but not in the N treatments
S P is limiting
S Summer shows elevated growth in N and N+P
treatments but not in P treatments
S N is limiting
Seasonal Trends
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?
?
Why?
S
The input of nitrogen into the Bay is closely tied to the annual flow of
water into the Bay.
S
Freshwater inflow is generally much richer in nitrogen than phosphorus
but this does not tell the whole story.
Sediments remove
nitrogen from the
water during late
spring/early
summer.
8
(mg per liter)
Oxygen Concentration
10
6
4
2
0
J F M A M J J A S O N D
MONTH
River inputs of nitrogen and phosphorus are especially
high in the late winter and early spring. Phosphorus
moves into the well-oxygenated sediments.
Anoxic sediments
release phosphorus
into the water
column during the
late summer and
early fall.
The Big Picture
S Year-round reductions in phytoplankton
will only be possible if inputs of both
nitrogen and phosphorus are reduced
S 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