CHAPTER 15
The Use of Carbon Stable Isotopes to Investigate the Origin and
Distribution of Suspended and Sedimentary Organic Matter in a
Semi-enclosed Mediterranean Marine System
A. Mazzola!, G. Sara l , and R.H. Michenerl
ABSTRACT
The natural stable isotope values of different primary sources have been used to trace the fate
of organic carbon that enters in the marine food webs of Stag none di Marsala (Italy). Water and
sediment samples were collected monthly (March 1996 - February 1997) at 3 stations, characterized by different amounts of vegetal cover and analysed to determine total organic matter
(OM), phytopigments, biopolymeric organic carbon (BPC) and stable carbon isotopic composition (013C), the latter measured also in main primary producers. Sedimentary OM accumulated
in summer, while total suspended organic matter reached highest concentrations in May and
December. The concentration of chlorophyll-a carbon in the sediments and suspended material (on average 227 ± 165}lg C g-1 and 14 ± 8.7}lg C 1- 1 respectively) were highest in spring and
autumn. Sedimentary BPC concentrations showed several peaks throughout the year, suspended BPe concentrations peaked in May and in summer.The CS 13 C from suspended particulate matter and sediments (on average -19.5 ± 2.7%0 and -13.0 ± 3.1 %0 respectively) followed a gradient of enrichment moving towards the inner part of the Stag none. The CS 13 C of primary sources
ranged from -21.4%0 (phytoplankton) to -4.5%0 (seagrass detritus). The Dauby's model (1989)
was used in order to estimate the contribution of each primary carbon source to sedimentary
and particulate reservoirs. In the northern basin, OM in sediments was mainly influenced by
macroalgae carbon (46%), while that in the water column was influenced by phytoplankton
(60%) and microphytobenthic (30%) carbon. In the southern basin, main sedimentary carbon
sources were seagrasses and their detritus (61 %, mainly Posidonia), while in the water column
were phytoplankton and microphytobenthos (50% and 24% respectively). The role of some
physical constraints (wind and tidal energy) in influencing isotopic composition of organic matter is discussed.
Introduction
In recent years. several authors investigated
organic matter flows and food web structures
using stable isotope ratios as natural tracers
(Lajtha and Michener 1994; Griffiths 1998). The
bulk of organic matter (Le. particulate and sedimentary) in shallow environments originates
from different primary (such as phanerogames,
macroalgae, phytoplankton and microphytobenthos) and secondary sources (such as plankton, benthos and fish). These sources provide
organic matter with varying degrees of availability to consumers and with different extent as
a function of environmental gradients (Valiela
1984).
In shallow coastal systems, resuspension.
sedimentation and lateral drifting are the primary processes controlling the quality and quantity
of organic matter (MacIntyre et aL 1996; Sara et
al. 1999). Sediment resuspension events, which
are mainly driven by wind energy (Smaal and
Haas 1997; Sara et al. 1999), may contribute to
sediment-water exchange. Hopkinson (1985)
suggested that resuspension may control the relative amounts of organic carbon as well as the
sites and rates of organic matter degradation in
the water column and benthos. As a conse1 Laboratorio di Biologia Marina e Ricerche, Dipartimento di Biologia Animale, Universita di Palermo, Via Archirafi 18,90123
Palermo, Italy
2 Department of Biology, Boston University, Boston, Massachusetts, USA
F.M. Faranda. L. Guglielmo, G. Spezie (eds)
Mediterranean Ecosystems: Structures and Processes
© Springer-Verlag Italia 2001
The Use of Carbon Stable Isotopes to Investigate the Origin and
Distribution of Suspended and Sedimentary Organic Matter in a
Semi-enclosed Mediterranean Marine System
A. Mazzola!, G. Sara l , and R.H. Michenerl
ABSTRACT
The natural stable isotope values of different primary sources have been used to trace the fate
of organic carbon that enters in the marine food webs of Stag none di Marsala (Italy). Water and
sediment samples were collected monthly (March 1996 - February 1997) at 3 stations, characterized by different amounts of vegetal cover and analysed to determine total organic matter
(OM), phytopigments, biopolymeric organic carbon (BPC) and stable carbon isotopic composition (013C), the latter measured also in main primary producers. Sedimentary OM accumulated
in summer, while total suspended organic matter reached highest concentrations in May and
December. The concentration of chlorophyll-a carbon in the sediments and suspended material (on average 227 ± 165}lg C g-1 and 14 ± 8.7}lg C 1- 1 respectively) were highest in spring and
autumn. Sedimentary BPC concentrations showed several peaks throughout the year, suspended BPe concentrations peaked in May and in summer.The CS 13 C from suspended particulate matter and sediments (on average -19.5 ± 2.7%0 and -13.0 ± 3.1 %0 respectively) followed a gradient of enrichment moving towards the inner part of the Stag none. The CS 13 C of primary sources
ranged from -21.4%0 (phytoplankton) to -4.5%0 (seagrass detritus). The Dauby's model (1989)
was used in order to estimate the contribution of each primary carbon source to sedimentary
and particulate reservoirs. In the northern basin, OM in sediments was mainly influenced by
macroalgae carbon (46%), while that in the water column was influenced by phytoplankton
(60%) and microphytobenthic (30%) carbon. In the southern basin, main sedimentary carbon
sources were seagrasses and their detritus (61 %, mainly Posidonia), while in the water column
were phytoplankton and microphytobenthos (50% and 24% respectively). The role of some
physical constraints (wind and tidal energy) in influencing isotopic composition of organic matter is discussed.
Introduction
In recent years. several authors investigated
organic matter flows and food web structures
using stable isotope ratios as natural tracers
(Lajtha and Michener 1994; Griffiths 1998). The
bulk of organic matter (Le. particulate and sedimentary) in shallow environments originates
from different primary (such as phanerogames,
macroalgae, phytoplankton and microphytobenthos) and secondary sources (such as plankton, benthos and fish). These sources provide
organic matter with varying degrees of availability to consumers and with different extent as
a function of environmental gradients (Valiela
1984).
In shallow coastal systems, resuspension.
sedimentation and lateral drifting are the primary processes controlling the quality and quantity
of organic matter (MacIntyre et aL 1996; Sara et
al. 1999). Sediment resuspension events, which
are mainly driven by wind energy (Smaal and
Haas 1997; Sara et al. 1999), may contribute to
sediment-water exchange. Hopkinson (1985)
suggested that resuspension may control the relative amounts of organic carbon as well as the
sites and rates of organic matter degradation in
the water column and benthos. As a conse1 Laboratorio di Biologia Marina e Ricerche, Dipartimento di Biologia Animale, Universita di Palermo, Via Archirafi 18,90123
Palermo, Italy
2 Department of Biology, Boston University, Boston, Massachusetts, USA
F.M. Faranda. L. Guglielmo, G. Spezie (eds)
Mediterranean Ecosystems: Structures and Processes
© Springer-Verlag Italia 2001