Eutrophication model

Trophic state

Rel

ativ

e Im

port

ance

Thalassia testudinumSyringodium filiformeHalodule wrightiiRuppia maritimaMacroalgae Microalgae

Oligotrophic Eutrophic

Explicit model of ecosystem behavior #1

Eutrophication will lead to changes in relative abundances of primary producers in a predictable way.

Progressive eutrophication or light reduction

Seag

rass

Lea

f N:P

20

30

40

50

60

0 .05 0 .1 0 0 .1 5 0 .2 0 0 .2 5

0 .5

1 .0

1 .5

2 .0

2 .5

3 .0

N utr ien t-rep le te

O ligotro p h icP -lim ited

O ligo tro p h icN -lim ited

Eu troph ica tion

E u troph ica t ion

N :P = 30 :1

L eaf tissu e P co n ten t (% of d ry w eig h t)

Lea

f tis

sue

N c

onte

nt (%

of d

ry w

eigh

t)

Explicit model of ecosystem behavior #2

Eutrophication will shift N:P ratios of primary producers towards a taxon-specific “Redfield ratio”

Progressive eutrophication or light reduction

Seag

rass

Lea

f 13

C

-16

-14

-12

-10

-8

-6

Explicit model of ecosystem behavior #3

Eutrophication will shift seagrass 13C towards more negative values because of increased discrimination against 13C in low light conditions

Progressive eutrophication or light reduction

Seag

rass

Lea

f 15

N

-4-202468

1012

Anthropogenic processed NAnthropogenic processed N

Anthropogenic fertilizer N

Anthropogenic processed N

Anthropogenic fertilizer N

Decreased N uptake relative to supply-greater fractionation

Not-so-Explicit model of ecosystem behavior #4

Eutrophication will cause some kind of change in 15N of primary producers

Control Treatment

25cm x 25cm randomly placed for benthic coverage

25cm x 25cm set sites for benthic coverage

10cm x 10cm randomly placed for canal wall coverage

Elemental ratio, stable isotope sampling

We will also specifically identify and count the conspicuous fish and invertebrates along each transect