Chapter 9 Nutrients and Seagrasses
237
Table 2. Tentative values for the fluxes represented in Fig. 2. For each flux, whenever possible, a range of values found in the
literature is given, as well as a reasonable average, which has been computed excluding outliers. Data are in g N m
−2 yr
−1 ,
except where indicated as percent of annual N demands for growth (%). In those cases (%), the average has been estimated
applying the percentage to the seagrass annual demand, which can eventually be somewhat unrealistic. This table does not
present an exhaustive literature review, and it is only aimed at providing a very rough estimate of the order of magnitude of the
main exchanges between compartments from the point of view of N dynamics. In a few cases, no reliable estimates are
available.
Flux
number Flux description
Average
Range
Source
Primary producers demand a
Epiphytes
11
2–23
From data in Koch and Madden (2001),
Cambridge and Hocking (1997), Nelson and
Waaland (1997), and Alcoverro et al. (1997)
Seagrass
30
3–90
Estimated combining data in Duarte (1990)
and Duarte and Chiscano (1999)
1
Nutrient import though advection
(dissolved and particulate)
–
–
2
Nutrient uptake by seagrass leaves
12 b
26–47
T. testudinum (Lee and Dunton, 1999b)
2.5
P. oceanica (Lepoint et al., 2002b)
3
Nutrient uptake by epiphytes
–
–
4
Epiphytes leaching
–
–
5
Leaf leaching
<1
1–4%
These data refer to P (see text)
<10%
Borum et al. (1989)
6
Internal recycling
5
10–50% Includes resorption, storage, re-use, etc. See
text for references
7
Sedimentation
15
0.3–60
See text for references
8
Ammonification
114
18–176
Z. capricorni (Boon et al., 1986a)
7–1069
P. oceanica (L´ opez et al., 1995)
26–38
T. testudinum–E. acoroides (Williams, 1990)
123–
136
Z. marina (Caffrey and Kemp, 1990)
9
N uptake by seagrass roots
12 b
28–51
T. testudinum (Lee and Dunton, 1999b)
3.3
P. oceanica (Lepoint et al., 2002b)
10
Inorganic N release by sediment
1
0.53–
1.56
Mixed tropical beds (Erftemeijer and
Middleburg, 1995)
5–20
E. acoroides (Holmer and Olsen, 2002)
1.2
Z. capricorni (Eyre and Ferguson, 2002)
0.3–0.5
T. hemprichii (Miyajima et al., 2001)
1.9
T. testudinum (Ziegler and Benner, 1999)
11
Denitrification
<1
0.05–
0.7
(up to
3.6–
18)
Average for the lowest, most frequent range;
see text for references
12
Nitrogen fixation
1–10
0.1–2.5
Temperate seagrasses (see text for references)
2.7–15
Tropical seagrasses (see text for references)
13
Leaf fall
20 c
14
Leaf consumption by herbivores
4 d
<1–
90%
15
Feces production
3
Estimated from the assimilation efficiency for
N given by Thayer et al. (1982)
16
Regeneration by herbivores
4
1.9–6
T. hemprichii (Koike et al., 1987)
17
Regeneration during leaf litter decay
8
10–46% See text for references
a Plant and epiphyte demands have been estimated as the product of annual primary production and their respective average N
content.
b Average uptake by leaves and rhizomes has been estimated assuming that external demand is met equally by uptake of leaves
and roots (see justification in the text). External demand is the annual demand minus the internal recycling.
c This flux has been estimated as the total N demand minus the part ingested by herbivores (flux 14), and this is multiplied by
0.74, which is the average fraction of N remaining in falling leaves, relative to living ones (estimated from data in Duarte, 1990
and Hemminga et al., 1999).
d Consumption was assumed to be, on average, 15% of primary production; to estimate N flux, the fact that some herbivores
prefer old, nutrient-poor leaves has not been considered.
237
Table 2. Tentative values for the fluxes represented in Fig. 2. For each flux, whenever possible, a range of values found in the
literature is given, as well as a reasonable average, which has been computed excluding outliers. Data are in g N m
−2 yr
−1 ,
except where indicated as percent of annual N demands for growth (%). In those cases (%), the average has been estimated
applying the percentage to the seagrass annual demand, which can eventually be somewhat unrealistic. This table does not
present an exhaustive literature review, and it is only aimed at providing a very rough estimate of the order of magnitude of the
main exchanges between compartments from the point of view of N dynamics. In a few cases, no reliable estimates are
available.
Flux
number Flux description
Average
Range
Source
Primary producers demand a
Epiphytes
11
2–23
From data in Koch and Madden (2001),
Cambridge and Hocking (1997), Nelson and
Waaland (1997), and Alcoverro et al. (1997)
Seagrass
30
3–90
Estimated combining data in Duarte (1990)
and Duarte and Chiscano (1999)
1
Nutrient import though advection
(dissolved and particulate)
–
–
2
Nutrient uptake by seagrass leaves
12 b
26–47
T. testudinum (Lee and Dunton, 1999b)
2.5
P. oceanica (Lepoint et al., 2002b)
3
Nutrient uptake by epiphytes
–
–
4
Epiphytes leaching
–
–
5
Leaf leaching
<1
1–4%
These data refer to P (see text)
<10%
Borum et al. (1989)
6
Internal recycling
5
10–50% Includes resorption, storage, re-use, etc. See
text for references
7
Sedimentation
15
0.3–60
See text for references
8
Ammonification
114
18–176
Z. capricorni (Boon et al., 1986a)
7–1069
P. oceanica (L´ opez et al., 1995)
26–38
T. testudinum–E. acoroides (Williams, 1990)
123–
136
Z. marina (Caffrey and Kemp, 1990)
9
N uptake by seagrass roots
12 b
28–51
T. testudinum (Lee and Dunton, 1999b)
3.3
P. oceanica (Lepoint et al., 2002b)
10
Inorganic N release by sediment
1
0.53–
1.56
Mixed tropical beds (Erftemeijer and
Middleburg, 1995)
5–20
E. acoroides (Holmer and Olsen, 2002)
1.2
Z. capricorni (Eyre and Ferguson, 2002)
0.3–0.5
T. hemprichii (Miyajima et al., 2001)
1.9
T. testudinum (Ziegler and Benner, 1999)
11
Denitrification
<1
0.05–
0.7
(up to
3.6–
18)
Average for the lowest, most frequent range;
see text for references
12
Nitrogen fixation
1–10
0.1–2.5
Temperate seagrasses (see text for references)
2.7–15
Tropical seagrasses (see text for references)
13
Leaf fall
20 c
14
Leaf consumption by herbivores
4 d
<1–
90%
15
Feces production
3
Estimated from the assimilation efficiency for
N given by Thayer et al. (1982)
16
Regeneration by herbivores
4
1.9–6
T. hemprichii (Koike et al., 1987)
17
Regeneration during leaf litter decay
8
10–46% See text for references
a Plant and epiphyte demands have been estimated as the product of annual primary production and their respective average N
content.
b Average uptake by leaves and rhizomes has been estimated assuming that external demand is met equally by uptake of leaves
and roots (see justification in the text). External demand is the annual demand minus the internal recycling.
c This flux has been estimated as the total N demand minus the part ingested by herbivores (flux 14), and this is multiplied by
0.74, which is the average fraction of N remaining in falling leaves, relative to living ones (estimated from data in Duarte, 1990
and Hemminga et al., 1999).
d Consumption was assumed to be, on average, 15% of primary production; to estimate N flux, the fact that some herbivores
prefer old, nutrient-poor leaves has not been considered.