Biology Reference
In-Depth Information
4.5 Use of Isotope Discrimination
The stable nitrogen isotope
15
N discrimination (
15
N) has been frequently used to
determine nitrogen sources in ecosystem studies (Peterson and Fry
1987
;
McKinney et al.
2001
; Cole et al.
2004
; Lapointe
2004
). The underlying
assumptions are that the
∂
15
N of sources are known and that primary producers
take up
15
N in proportion to availability in a predictable manner (Cifuentes et al.
1988
). The natural abundance of
15
N in many sources has been measured, including
fertilizer (0
∂
;
Heaton
1986
). Groundwater, depending on the amount of microbial processing
that selects for
), sewage (10
-20
), soil (5
), and rainfall (
3
to
5
‰
‰
‰
‰
‰
‰
14
N and leaves the remaining N in
15
N, can exceed 30
(Page
1995
). Cohen and Fong (
2005
) showed that
Ulva intestinalis
did not differentially
select
14
N over
15
N in a range of N concentrations and isotopes proportions. Rather,
the species took up
14
N and
15
N in direct proportion to the amount in the source,
suggesting that this alga may be useful for determining N sources in estuaries.
However, uptake preference for
15
N-ammonium rather than
15
N-nitrate can result in
differences in tissue
‰
15
N that may confound its use as an indicator. For example, if
ammonium from sewage with a low
∂
15
N and nitrate from groundwater with a high
∂
15
N co-occur in an estuary and the algae take up more ammonium, then it will
appear that the sewage is a more important source relative to groundwater even
though it may not be. Teichberg et al. (
2010
) showed that
∂
15
N of macroalgae is
generally heavier where DIN concentrations are higher due to increased N loads
associated with wastewater rather than other N sources in many coastal waters.
Fast-growing algae, such as
Ulva
spp. and
Gracilaria
spp., are better at reflecting
the
∂
15
N values of the N source in a shorter period of time (Aguiar et al.
2003
;
Teichberg et al.
2008
), but this might not be the case when examining slower
growing algae such as
Fucus vesiculosus
(Deutsch and Voss
2006
).
∂
4.6 Aquaculture
Seaweeds have an essential role for maintenance and expansion of sustainable
marine aquaculture (Chopin et al.
2001
; Neori
2008
; see also Chap.
22
by Buchholz
et al.). The integration of seaweeds to marine animal cultures has long been
recognized as the most promising approach to reduce the excess nutrients released
by aquaculture activity, due to the high nutrient uptake efficiency of macroalgae,
their fast growth rates, and economical and practical aspects of their cultivation
(Vandermeulen and Gordin
1990
; Shpigel et al.
1993
; Chopin et al.
2001
;
Hern´ndez et al.
2006
;L
uning and Pang
2003
; Neori et al.
2004
). Research and
development of integrated mariculture, recently known as integrated multi-trophic
aquaculture (IMTA), has advanced over the last 20 years (Neori et al.
2004
),
although it still needs to be implemented at a larger scale by the modern global
industry (Hern
´
ndez et al.
2002
). Some of the state-of-art seaweed-based integrated
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