Organic carbon, phosphorus and nitrogen in surface sediments of the marine-coastal region north and
south of the Paria Peninsula, Venezuela
Marly C. Martinez S. and Gregorio Martínez
1
1
Department of Oceanography, Instituto Oceanográfico de Venezuela, Universidad de Oriente, Avenida
Universidad, Cerro Colorado, Cumana 6101, Venezuela.
marly.martinez.soto @ gmail.com
goyomartinez@gmail.com
Abstract .-
The organic carbon, phosphorus and nitrogen content of silt and clay fractions of surface
sediments from the marine-coastal region north and south of the Paria Peninsula was quantified. Organic
carbon concentrations (Corg) were determined by dry combustion after decarbonation with 10% hydrochloric
acid, and total phosphorus (TP) and total nitrogen (TN) following Valderrama (1981). This information was
then used to produce maps of the iso-concentrations of the distribution of these elements in the sub-marine
continental shelf north of the Paria Peninsula (PP) and in the Gulf of Paria (GP). In the silt fraction, the Corg
concentration,TP and TN showed average values of 1.53%, 0.04% and 0.03%, respectively.The highest Corg,
PT and NT values were recorded from silts from the PP with a gradual increase towards the west and the
lowest figures were found in the GP. In the clay fraction, Corg, TN and TP had mean values of 1.64% 0.13%
and 0.04%, respectively, and showed a spatial distribution very similar to the silt fraction, indicating the
influence of ocean currents and coastal upwelling patterns.The C/N ratio had an average of 23.67 and shows
that the Corg present in the PP sediments is of marine origin, resulting from primary productivity, especially
towards the west. This zone has been identified as the most productive in this region due to coastal upwelling
and the influence of the Orinoco and Amazon rivers (Gomez 1996 and Monente 1997). In contrast, a greater
variability in the parameters measured was found in the GP sediments, probably due to the mixing of marine
and continental Corg, confirming the influence of the Orinoco and Amazon waters brought by the Guyana
Current.
Keywords: marine sediments, organic carbon, nitrogen, phosphorus, organic matter.
Introduction
Several investigations of coastal sediments have shown that these ecosystems are extremely fertile
with high organic productivity, the product of coastal dynamics such as upwelling and continental inputs from
rivers, which can provide a large supply of nutrients. On the northeastern coast of Venezuela, upwelling
phenomena occur due to the action of trade winds during the first months of the year. This affects the
hydrodynamics of the entire area and contributes to fertility as a result of increased concentrations of nutrients
in the surface layer, resulting in a short time-lag to phytoplankton growth. During the rainy season, nutrient
inputs from the Orinoco and Amazon rivers that reach this region due to sea water circulation, promote high
organic productivity.
The marine sediment is defined as an aggregate of untold numbers of insoluble particles of
unconsolidated material, which have been transported to the bottom of the oceans and seas by various
transport agents. These sediments are the ultimate repository of most of the waste generated by man, and can
thus be used as sensitive indicators for monitoring the spatial and temporal distribution of pollutants (Balls et
al.1997, Kish and Machiwa 2003). They also provide information on the geochemical changes that occur
over time in these environments and can be used to establish baseline levels in a particular area (Dassenakis et
al.1997, Rubio et al.2000, Tuncer et al.2001).
Thus, the characterization of sediments is of some importance in oceanography and geochemistry
and may help us to understand certain phenomena such as the distribution of contaminants and their
relationship to the geochemical and hydrodynamic characteristics of each marine region (Heling et al.1990).
The nature, size distribution and some physicochemical characteristics of marine sediments may help
understand the current system, the baseline redox condition, the activity of microorganisms and the nature of
the sedimentary deposits (Bonilla et al.2003)
The marine area of the Paria Peninsula (PP) represents a small portion of the southeastern Caribbean
Sea. It is bounded by Margarita Island to the west, to the east by the waters of Trinidad and Tobago, to the
south by the northeast coast of the Paria Peninsula and to the north by the Caribbean sea. The PP is located
entirely within the continental shelf, thus the waters are relatively shallow throughout the study area. A
typical phenomenon of this area is the influx of water from the Atlantic sector, which flows through the
passage between Trinidad andTobago. The Gulf of Paria (GP) is a shallow inland sea between the east coast
of Venezuela and the island of Trinidad. The GP covers an area of about 160 km from east to west and 45 km
from north to south. Average depth is around 20 m and reaches a maximum of 30 m. The waters of adjacent
rivers (Orinoco, San Juan, etc.), the Caribbean Sea and the Atlantic Ocean driven by a branch of the Guyana
Current all converge in the GP, so that it can be considered as a true mixture of watersheds. This mixture of
waters has a particular influence on the behavior of the hydrographic variables in this ecosystem.
The environmental characteristics of the PP and GP are the result of water flow and sediments
brought by the Orinoco River, the ocean currents that move along the east coast of South America that
transport a huge quantity of sediment from the Amazon River, the action of tides, waves and the current
regime of the continental shelf and the coastal upwelling regime determined by the action of the winds. All
these factors affect the physical and chemical processes of the sediments. Thus, the organic matter present has
different sources and conditions of transport, sedimentation and preservation. The study and characterization
of C, N and P in the surface sediments in the PP and GP is therefore essential.
According to Gomez (1996), the waters of the Caribbean are generally poor with a few moderately
fertile areas, such as those close to northeastern Venezuela. Regional enrichment is commonly associated
with the upwelling of subsurface waters, an annual hydrographic phenomenon that occurs during the first few
months of the year. However, the possibility of the existence of factors that promote water fertility throughout
the year has been raised. The great South American rivers (Orinoco and Amazon) and internal waves bring
nutrients, thus producing eutrophication of the waters of coastal lagoons such as La Restinga (Margarita
Island) from May to November, when upwelling becomes less intense or ceases altogether. Monente (1997)
attributes changes in the composition of the surface waters of the Caribbean to variations in the flow of the
Orinoco and Amazon rivers throughout the year, as well as efficient geochemical processes that operate
between the mouths of these rivers and the Caribbean Sea. Other processes that occur in upwelling zones near
the coast of Venezuela have already been mentioned. Regardless of the importance or likely importance of the
above mentioned phenomena, there are others that also contribute significantly to the enrichment of these
waters. East of 63 º west longitude there is an important upwelling zone close to the coast as well as
downwelling, causing rearrangement of the surface layers in the first 100 meters. This process is not
continuous and is interspersed with waters of continental origin. These two phenomena together contribute
significantly to the enrichment of surface water bodies. They are not continuous, however, but rather occurr
intermittently throughout the year in a pulse-like fashion.
With this research is to assess the size distribution of surface sediments in the region, the distribution
of C, P and total N in the silt and clay fractions of sediments in the region, linking the contents of C, P and
total N size distribution of sediments in the region, establish relationships between C, P and total N content in
the silt and clay fractions of sediments in the region and assess whether there are relationships between
content and distribution of organic compounds present in these .
With the results obtained from this project are to improve the knowledge we have on the
biogeochemical cycles of carbon species, nitrogen and phosphorus in tropical areas, which are associated with
both the minerals that form part of the sedimentary matrix and as the organic fraction present in it. On the
other hand, this study will reveal the behavior of organic matter in the north of the Paria Peninsula and the
Gulf of Paria, which is of economic importance to the country for its great fishing potential and gas potential,
thus making estimates of the wealth of the area for hydrocarbon generation.
Materials and Methods
Sediments were sampled at 44 stations set up throughout the study area, 24 in the PP and 20 in the
GP (Fig. 1), during an oceanographic campaign conducted aboard the research vessel "Guaiqueri II” in
October 2005. The position of the vessel was determined at each station using differential GPS corrections
transmitted by satellite, which guarantee a location error of less than a meter. Sampling was done using a
Petersen dredge; subsamples were then taken, which were processed and stored until analysis.
Figure 1 .- Study area in the coastal marine region north and south of the Paria Peninsula,
Venezuela.
The separation of size fractions of sediments was carried out in two stages: firstly the gravel and sand
fractions were separated from the mud fraction (silt and clay) by wet sieving after drying and weighing the
samples, and secondly, the silts were separated from the clays using a modification of the pipette method
without dispersant. This procedure is based on the rate of sedimentation of grains over different time
intervals, according to Stokes' Law (Roa & Berthois 1975). Once separated, the two fractions were subjected
to mild heating to evaporate most of the water and then left at ambient temperature. The fractions were then
quantified by weighing and classified using ternary diagrams.
Corg was determined by first applying an acid attack with HCL 10% to the samples in order to
eliminate carbonates.The samples were then dry-combusted at a temperature of 1490 °C and it was assumed
that the carbon measured was associated solely with the organic matter in the sediment that had not reacted
with the acid. Total N and P were determined using the method described by Valderrama (1981), based on the
simultaneous oxidation of nitrogen and phosphorus compounds in the samples and the resulting solution used
for both analyses. The phosphorus content was determined following the method of Murphy & Riley (1962).
Nitrogen content was ascertained by passing a 4ml aliquot through a Technicon autoanalyzer II, with a
Scientific Instruments detector AC-100, which reduced NO3 to NO2, and recording the resulting
concentrations. Total N content was calculated stoichiometrically from the nitrite concentration recorded. To
demonstrate the efficiency and accuracy of the techniques used to determine CT, Corg, NT, Pbio and PT,
were tested in quadruplicate in a sediment sample, the results are shown in Table I, showing that the methods
used for detection of these parameters are reliable and repeatable.
Table I Analysis of accuracy for certain species.
PMSL(2)11
Mean
S.D.
C.V. (%)
1
2
3
4
CT(%)
2,89
2,99
2,89
2,89
2,89
0,01
0,46
Corg (%)
1,64
1,62
1,62
1,60
1,62
0,09
0,87
NT(mg/Kg)
190,73
187,05
187,22
189,67
189,17
2,38
1,26
PT(mg/Kg)
399,99
404,58
386,12
398,89
397,39
7,91
1,99
Pbio (mg/Kg)
24,14
23,72
23,34
23,18
23,84
0,39
1,65
The parameters bathymetry, temperature, dissolved oxygen and fluorescence indicators in the bottom
waters were taken from the Environmental Baseline Mariscal Sucre Project: Abiotic Components. Final
Report, Volume II, developed by Senior et al, CAMUDOCA, Universidad de Oriente, Venezuela, which
provides data from an integrated study of the environmental characteristics of the coastal marine environment
in the northern Paria Peninsula continental shelf and the northwest sector of the Gulf of Paria.
Results and Discussion
Bathymetry, temperature, dissolved oxygen and fluorescence indicators in the bottom waters
The underwater depth of the ocean floor commonly controls the textural distribution of sediments
and the geochemistry of benthic micro- and macro-nutrients in coastal and oceanic environments. Figure 2
shows the bathymetric character of the region. Within the study area, the shallowest sediments were in the
GP, specifically in the coastal zone where they were only 4.1 m deep, while maximum sediment depths were
recorded for the PP, northeast of the coast, where they reached 144.4 m deep opposite Boca Dragon.
Bottom water temperatures in the study area (Fig. 2) are influenced by Atlantic waters flowing
through the passage between Trinidad and Tobago and those coming from within the GP. These waters show
a temperature range of between 21.38 ° C and 30.94 ° C with colder water entering from the northeast to the
PP and warmer waters located in the GP, due to its lower depth and inputs from the Orinoco River.
Figure 2 .- a) Bathymetry of the study area, b) bottom water temperature in the study area.
(Data source: Abiotic Components. Final Report, Volume II)
Dissolved oxygen in water comes from many sources, the main one being oxygen absorbed from the
atmosphere. The movement of the waves allows water to absorb more oxygen. Physical, chemical and
biological processes induce the exchange of oxygen across the air-ocean interface (Redfield 1942). Fig. 3
shows the distribution of dissolved oxygen in the bottom waters of the PP. Oxygen concentrations lower than
2.75 ml/l were found in the waters towards the central sector, which then increase to a peak of above 3.25 ml/l
in the northeastern sector. In the GP, oxygen concentrations were below 2 ml/l in areas furthest from the
shore.These low values are due to processes such as heterotrophic respiration and the bacterial oxidation of
organic matter.
Phytoplankton fluorescence is attributed to the emission of the energy absorbed by the chlorophyll a
of photosynthetic pigments (Ostrowska et al.2000). The fluorescence index (FI) is used as an indicator of
phytoplankton biomass. Many authors have shown that the FI is well correlated with chlorophyll
concentration in water bodies. The bottom waters of the northern PP continental shelf had higher FI values
towards the west (Fig. 3) and were higher than 1.5 units between the towns of Carúpano and Morro de Puerto
Santo, suggesting that there was considerable biological activity in the waters of this region at the time of
sampling. To the east, the bottom waters showed low phytoplankton activity, possibly because of a higher
proportion of suspended matter due to tidal influences at Boca del Dragón.
The waters of the Gulf of Paria are considered to be some of the least productive along the
northeastern Venezuelan coast (Benitez and Okuda 1976).The differences between values reported at
different times of the year may be attributed to seasonal variations in nutrient levels and the turbidity of the
water (Moigis and Bonilla, 1988). In the Gulf of Paria, the highest values (higher than 1.5 units) were
recorded towards the west of the study area (Fig. 6), suggesting significant phytoplankton activity compared
with the other sampling sites.The rest of the Gulf showed low biological activity, with rates below 0.5 units
although there was a slight increase in the area of Puerto de Hierro, west of Macuro, where values were
slightly above 0.5 units.
Figure 3 .- a) Dissolved oxygen in the bottom waters of the study area, b) Fluorescence indices
of the bottom waters of the study area. (Data source: Abiotic Components. Final Report, Volume II)
Texture
According to the results, the surface sediments of the PP and the GP have a mainly sandy loam
texture. However, in the central area of the PP and the central-coastal area of the GP, the sediments have a
sandy-silt texture (Fig. 4), with the GP sediments having a higher proportion of fine grains (silt and clay).
This reflects the sediment dynamics prevalent in this coastal marine region, which promote the deposition of
predominantly fine grained sediments, due to the geomorphology of the area and the flocculation of clays that
occurs when seawater is mixed with fresh water from the Orinoco River.
Figure 4 .- Spatial distribution of the texture of the surface sediments in the study area.
Organic carbon (Corg)
The Corg content of the silt fractions varied between 0.18 and 4.08%, with an average of 1.53% (SD
0.09%).We can observe from Figure 5 that the highest values were located in the westernmost part of the PP,
while the lowest figures were located mostly in the GP. The high percentages of Corg obtained in the surface
sediments are the product of the organic material (OM) contribution of continental origin (Demaison and
Moore 1980, Tissot and Welte, 1984). Marine OM inputs generated in situ also contribute to organic
productivity in the PP. Moreover, low oxygenation conditions must exist, to preserve this material in the
sediment.
High values of Corg in the PP were found in shallower areas with high dissolved oxygen and FI
values and coincide with an upwelling area, implying high primary productivity.This allows us to infer the
conditions necessary for the production and accumulation of OM. In contrast, despite the contribution of
terrestrial OM from the Orinoco Delta and that brought by the Guyana Current from the Amazon, Corg
values were low in the GP. According to Benitez and Okuda (1976), the waters of the GP should be
considered some of the least productive along the northeastern coast of Venezuela. This is because this region
is very shallow and influenced by different currents and water masses, which tend to cause mixing conditions
and therefore oxidizing conditions unfavorable for the preservation of OM in the sediments. The high
dissolved oxygen values found in the GP, and turbidity due to the suspension of fine material in the water
column prevents the passage of sunlight, thus limiting photosynthetic processes and consequently the
production of OM. The oscillation of the tides in the GP holds the fine material in suspension, which is then
exported out to sea.
In the clay fraction Corg ranged between 0.65 and 5.99%, with an average of 1.64% (SD 0.09%). As
for the silt fraction, higher percentages were found in the western sector of the area studied and the lowest
values were recorded from the GP. These distributions appear to be associated with coastal upwelling,
especially in the westernmost sector, where a high fluorescence rate and high levels of dissolved oxygen were
observed, indicating phytoplankton primary productivity. Although, in general, the silt contained the highest
percentages of OC, in rare cases, the clays accumulated a higher proportion of organic matter.This was
observed mostly for coastal samples, from both the PP and the GP. Generally, microorganism activity
increases in coastal areas, so that the carbon originating in these regions is generally associated with very fine
grain sizes. In contrast, in the open ocean other sources of carbon are present, which together with the
transport and remineralization of the OM in the water column, can produce carbon associated with slightly
larger particle sizes, or particles that are not deposited in the sediment.
Figure 5 .- a) Spatial distribution of Corg in the silt fraction of surface sediments in the study area, b)
Spatial distribution of Corg in the clay fraction of surface sediments in the study area.
Total Phosphorus and Nitrogen
The concentrations of TP in the sediments of the study area ranged between 0.02% and 0.21%,
averaging 0.04% (SD 0.001%) for the silt fraction and between 0.02 and 0.23 %, with an average of 0.04%
(SD 0.001%) for the clay fraction. The spatial distributions of TP in both fractions are shown in Fig. 6. The
lowest concentrations of TP were found in the GP and to the central and eastern sectors of the PP, but then
increased gradually towards the western sector of the PP, where the highest values were found, thus
coinciding with the Corg distribution. The spatial distribution of this element appears to be influenced by
ocean currents and coastal upwelling patterns. The production, distribution and sedimentation of OM in the
study area is affected by the discharge of the Orinoco River that impacts directly to the GP through numerous
rivers and creeks, and the contributions of the Amazon River brought by the Guyana Current.
Unlike Corg, however, TP shows a higher affinity for the clay fraction. It is known that surface water
P is depleted due to its assimilation by phytoplankton and incorporation into organic matter that aggregates
into larger particles and then settles. In general, this particulate matter is remineralized at depth. In addition,
zooplankton produce particles during feeding and excretion that settle to the deeper layers of the ocean
leading to greater proportions of TP in the finer fractions of sediments. De La Lanza and Cáceres (1994)
indicated that up to 60% of orthophosphates can be removed from the water by their adsorption in sediments,
which could explain their high concentrations in coastal areas.These same authors concluded that, in general,
the high concentrations of TP present in sediments reflect the ability or particular characteristics of the
sediments to retain phosphorus, both indigenous and allochthonous, which in turn promotes abiotic processes.
For Lai & Che Lam (2008) studied the release and retention of P in eutrophic sediments of the Mai Po
marshes, found that the enrichment of nutrients in the sediment is a potential source of P to the overlying
water and that most of TP of sediment is composed of labile inorganic phosphate.
Figure 6 .- a) Spatial distribution of phosphorus in the silt fraction of surface sediments in the
study area, b) Spatial distribution of phosphorus in the clay fraction of surface sediments in
the study area.
TN concentrations in the silt fraction of sediments in the PP and GP varied between 0.01% and
0.12%, with an average of 0.03% (SD 0.001%) and in the clay fraction between 0.02 and 0.58%, with an
average of 0.13% (SD 0.001%). The lowest TN values were recorded from the GP and in the central and
eastern part of the PP, showing a gradual increase towards the western sector of the PP, where the highest
values were found, thus coinciding with the distribution of Corg in silt and TP in both fractions (Fig. 7). There
is a small area in the center of the GP with increased concentrations of TN in the silt fraction, possibly due to
local prevailing currents, generating an accumulation effect. This effect was not observed in the clay fraction,
but a similar distribution of OC in this fraction was observed in a central coastal area of the PP. In both cases
the nitrogen and carbon probably originate from a common source from the coastal margin, such as runoff
containing these elements.The nitrogen could have both an indigenous (phytoplankton production) and an
allochthonous origin (runoff and sewage, amongst others).
As for TP, this element shows a higher affinity for fine textured sediment and is found in a greater
proportion in the clay fraction. The main source of nitrogen in marine sediments is known to be organic
matter released by the action of decomposing microorganisms (Pellerin et al, 2004). The organic matter that
accumulates in the form of particles is mineralized by the microbial flora with the liberation of ammonia.
Nitrogen may be retained by the clays present in the sediment by cation exchange, thus the affinity for the
fine grained fraction is due to the proportion of clay minerals present. However, the proportion of fixed
ammonium is dependent on the amount of this ion in solution, the type of clay present and the presence of
other ions in the pores of the sediment (Pellerin et al. 2004). In sediments, the processes of N fixation and P
availability are influenced by a variety of environmental factors including water depth, the redox state of
sediments, benthic primary production, pH and temperature (Joye and Hollibaugh 1995, An and Joye 2001).
Figure 7 .- a) Spatial distribution of nitrogen in the silt fraction of surface sediments in the
study area., B) Spatial distribution of nitrogen in the clay-silt fractions of surface sediments in
the study area.
C/N Ratio
The C/N ratio averaged 23.67 with a minimum of 10.65 and a maximum of 67.78 (SD 3.74%).
Overall, depending on the authors and their approach, these values are within acceptable ranges as reported in
the literature (Talbot and Laerdal, 2000; Tyson, 1995, Meyers, 1994, Hecky et al.1993, Hedges 1992;
Romankevich 1984, Healey and Hendzel, 1980), in the Table II summarizes the ratios of C / N given by
various authors according to various criteria and sedimentary environments. Figure 8 shows the significant
correlation between C and N in the sediments in the study area, R = 0.80. However, it can be observed that
2
the GP samples group separately from those of the PP. As mentioned previously, there are a number of factors
that make the GP sediments different from those of the PP in terms of composition, texture, and distribution.
The GP is characterized by a having a mix of waters with different properties and compositions, originating
from continental, transitional and marine sources, this makes the lack of a relationship marked by C/N in the
GP. In the PP, however, in spite of the influence of some currents, the behavior of the C/N ratio is that
expected for a marine environment, with its variations of dissolved oxygen, temperature and other
physicochemical parameters depending on depth and the influence of coastal upwelling.
Table II Ratios of C / proposed by various authors according to different criteria.
Meyers (1994)
Hecky et al.
(1993)
Talbot & Laerdal
(2000)
Hedges (1992)
C/N ratio
<10
10-20
>20
Criteria
Algae
Vascular land plants
Mix
< 8.3
Algal growth in an environment where the N is not a limiting
8.3-14.6
> 14.6
Moderate N limitation
Important limitation of N
< 13.3
Algal growth in an environment lacustrine where the N is not a limiting,
13.3-9.6
>19.6
Moderate N limitation, in a lacustrine environment
Important limitation of N, in a lacustrine environment
Highly degraded planktonic remains in marine sediments or plankton mix
fresh vascular plant debris
Nitrogen-rich organic matter associated with fine-grained
Plant organic matter transported from the continent that presents itself as
highly oxidized humic substances and low-nitrogen
Carbonate sediments, in which nitrogen-containing compounds are not
preferably preserved as particulate matter, which implies that the
degradation of these compounds is accelerated.
>10
10-13
15-85
Romankevich
(1984)
11.8-33.3
The spatial distribution of the C/N ratio (Fig. 8) in the surface sediments in the PP is fairly uniform
with values not exceeding 30 units, whereas in the GP the distribution is highly variable, with some areas
having values exceeding 50 and others where the values are as low as those of the PP. It can be argued that
even with values near 30, the OM in the PP sediments is a result of marine primary productivity, especially in
the westernmost sector where values of less than 20 coincide with the most productive zone in the area due to
coastal upwelling processes. In the GP, the higher variability may indicate different OM sources. For instance,
values exceeding 55 units are due to the presence of OM from higher plants discharged by the Orinoco River
and the waters from the Amazon brought by the Guyana Current. The mean, 23.67 (SD 3.74%) is slightly
more than twice 10, which according to Bonilla et al. (1995) indicates that the geochemical balance between
the sedimentation and decomposition of organic matter in marine sediments has been reached.
Figure 8 .- a) Relationship between Corg and TN in the surface sediments in the study area.
b) Spatial distribution of the C/N in surface sediments in the study area.
On the other hand, nitrogen is more easily degraded than carbon, thus the importance of the
accumulation of OM, reflecting intense biological activity, with organic decomposition and nitrogen release
into the water predominating. This process could be the cause of the high C/N values recorded for most of the
region, as well as mixing with continental OM. Obviously, the values of this ratio are related to sediment
texture and organic production in situ. The influence of OM of autochthonous origin predominates in the PP,
whereas in the GP there is a mix of both sources and different types of processes. Increased biological activity
and temperature increase the metabolism of organic nitrogen, NH
4
+
diffuses into the water, dissolved oxygen
penetrates into the sediment, this release being higher than that required by the phytoplankton.This
consumption of oxygen could lead to an overestimation of the depletion of organic carbon (Raine and
Patching, 1980) and indicate reduction (Bonilla, 1993, Bonilla et al, 1995).
Conclusions
High Corg, P and N values associated with shallower depths in the western area of the PP, indicate a
zone of substantial primary productivity that can be attributed to coastal upwelling processes and the
influence of the waters of the Orinoco and Amazon rivers brought by ocean currents.
The C/N ratio clearly distinguishes the OM sources between the two sectors of the study area: of
marine origin for the PP and a mixture of marine and continental origin for the GP, indicating the influence of
the Orinoco and Amazon rivers in these areas. It also indicates the presence of two types of sedimentation
environment: one slightly anoxic, thereby conserving the OM in the sediment, and the other oxic, not
permitting its conservation. In addition, the C/N ratio reveals a deficit of nitrogenous elements, limiting the
productivity of the area. Productivity in the PP, however, is not limited by TN deficiency due to a steady
supply of this nutrient to the area from the contribution of the rivers, as mentioned earlier.
The silt and clay fractions differ in their content of C and N, whereby apparently the less degraded or
more difficult to degrade N-rich organic compounds accumulate preferentially in the clay fraction, generating
a relative enrichment of nitrogen compounds in this fraction and a relative enrichment of Corg in the silt
fraction.
We found considerable differences in the distribution and content of Corg, TN and TP in the
sediments of the PP and GP, with higher concentrations in the PP, possibly due to different geomorphological
conditions as well as hydrochemical and river inputs, between the two environments. Ocean currents and the
sediment source may be the most important factors that control the composition, texture and spatial
distribution of the sediments and elements considered in this study.
According to Gomez (1996), the the fertility of the waters off northeastern Venezuela are caused by:
1) Upwelling; a hydrographic phenomenon that occurs during the first months of each year, 2) The
contributions of dissolved and particulate organic matter from the great South American rivers, particularly
the Amazon in the first few months and the Orinoco during the second half of the year, 3) Coastal lagoons
and other coastal water bodies that enrich the adjacent sea, especially from May to November and 4) The
local supply of nutrients from the erosion of the numerous islands and islets, headlands and cliffs on the
continental shelf by internal waves. According to Odriozola (2004), a surface layer of low salinity observed
during each cruise of the SIMBIOS-Orinoco indicates that both the Gulf of Paria (GOP) and the southeastern
Caribbean (SEC) are under the influence of freshwater inputs during the wet and dry seasons. According to
this author, in the GOP, this surface layer is a direct result of the discharge from the Orinoco River plume,
whilst in the SEC it could be due to the discharges from both the Orinoco and the Amazon rivers, transported
to the SEC by the Guyana Current. However, the similarity of the silicate-salt mixture found by Odriozola
(2004) to that reported by Froelich et al. (1989) for the Caribbean, suggests that water from the Orinoco River
plume, rather than the Amazon, dominates this region.This finding supports the observations made by MullerKarger et al. (1989) using satellite imagery.
Acknowledgments
To PDVSA CAMUDOCA for their financial support of the second phase of the project "Baseline
Environmental Study, Mariscal Sucre" and to the Research Council of the Universidad de Oriente for
financing the project "Geochemistry of superficial sediments of the coastal-marine region of the north and
south continental shelf of the Paria Peninsula, Sucre State, Venezuela "(CI-02-030700-1404/08). To the
Institute of Earth Sciences and the Oceanographic Institute of Venezuela for their institutional support of this
study.
Bibliography
An S, Joye S (2001) Enhancement of coupled nitrification-denitrification by benthic photosynthesis in
shallow estuarine sediment. Limnology Oceanography 46:62-74.
Balls P, S Hull, B Miller, J Pirie, Proctor W (1997) Trace metal in Scottish estuarine and coastal sediment.
Marine Pollution Bulletin 34 (1): 42-50.
Benitez J, Okuda T (1976) Distribución del nitrógeno orgánico particulado en el Golfo de Paria. Boletín del
Instituto Oceanográfico de Venezuela. 15 (1): 3 – 14.
Bonilla J (1993) Características hidrogeoquímicas: comportamiento multivariente en el bioecosistema marino
costero de Jose, Edo. Anzoátegui, Venezuela. Trab. Asc. Prof. Titular. Dpto. Oceanogr. Inst. Oceanogr.
Vzla. Universidad de Oriente, Cumaná, Venezuela, 231 pp.
Bonilla J, Fermín J, Gamboa, B, Cabrera M (1995) Aspectos geoquímicos de los sedimentos superficiales del
ecosistema marino costero de Jose. estado Anzoátegui. Venezuela. Bol. Inst. Oceanogr. de Venezuela.
Univ.de Oriente. 32 (1y2): 5-23.
Bonilla J, Aranda S, Ramírez C, Moya J, Marquez A (2003) Calidad de los sedimentos superficiales de la
Ensenada Grande del Obispo. Estado Sucre - Venezuela. Boletín del Instituto Oceanográfico de
Venezuela 42(1/2): 3 – 27.
Dassenakis M, Scoullos M, Gaitis A (1997) Trace metal transport and behaviour in the Mediterranean
estuary of Acheloos river. Marine Pollution Bulletin 34 (2): 103-111.
De La Lanza G (1994) Química de las lagunas costeras en: De La Lanza G, Cáceres C (Eds), Lagunas
costeras y el litoral mexicano. Universidad Autónoma de Baja California Sur. La Paz, México. 127198..
Demaison G, G Moore (1980) Anoxic environments and oil source bed genesis. The American Association of
Petroleum Geologists Bulletin. 64: 1179 – 1209.
Didyk B, B Simoneit, S Brassell, G Eglinton (1978) Orgainc geochemical indicators of palaeoenviromental
condition of sedimentation. Macmillan Journals. reprinted from Nature. 272(5650): 216-222.
For Lai, D. & Che Lam, K. 2008. Phosphorus retention and release by sediments in the eutrophic Mai Po
Marshes, Hong Kong. Mar. Poll. Bull. 57:349–356.
Gomez A (1996) Causas de la fertilidad marina en el nororiente de Venezuela. Interciencia 21(3): 140-146.
URL: http://www.interciencia.org.ve
Healey FP, Hendzel L (1980) Physiological indicators of nutrient deficiency in lake phytoplancton. Can. J.
Fisheries Aquatic Sci. 37; 442-453.
Hecky R., Campbell P, Hendzel L. (1993) The stoichiometry of carbon, nitrogen and phosphorus in
particulate matter of lakes and oceans. Limnol. Oceanogr. 38; 709-724.
Hedges J (1992) Global biogeochemical cycles: progress and problems. Mar. Chem. 39: 67-93.
Heling D, P Rothe, U Forstner, Stoffers P (1990) Sediment and enviromental geochemistry. Springer –
Verlag. NY. 371 pp.
Izquierdo C, J Usero, Gracia I (1997) Speciation of heavy metals in sediments from salt marshes on the
Southern Atlantic coast of Spain. Marine Pollution Bulletin., 34 (2): 123-128.
Joye S, Hollibaugh J (1995) Sulfide inhibition of nitrification influences nitrogen regeneration in sediment.
Science. 270:623-625.
Kishe M, Machiwa J (2003) Distribution of heavy metals in sediments of Mwanza Gulf of Lake Victoria,
Tanzania. Environ. International, 28: 619-625.
Meyers P A (1994) Presevation of elemental and isotopic source identification of sedimentary organic matter.
Chem. Geol. (Isotope Geoscience Section). 114; 289-302.
Moigis A, Bonilla J (1988) La productividad primaria e hidrografía del Golfo de Paria, Venezuela, durante la
estación de lluvia. Boletín del Instituto Oceanográfico de Venezuela 24 (1/2): 163 – 176.
Monente J A (1997) Phenomena contributing to the periodic enrichment of caribbean waters. Interciencia
22(1): 24-27. URL: http://www.interciencia.org.ve
Murphy J, Riley J (1962) A modified single solution method for determination of phosphate in natural
waters. Analytical Chemical Acta 27:31-36.
Odriozola A L, (2004) On the Color of the Orinoco River Plume. A thesis submitted in partial fulfillment of
the requirements for the degree of Master of Science College of Marine Science University of South
Florida
Ostrowska M, R Majchrowski, D. Matorin, Woźniak B (2000) Variability of the specific fluorescence of
chlorophyll in the ocean. Part 1. Theory of classical `in situ' chlorophyll fluorometry, Oceanologia, 42
(2)
Pellerin B, Wollheim W, Hopkinson C, Mcdowell W, Williams M, Vörösmarty C, Daley M (2004) Role of
wetlands and developed land use and dissolver organic nitrogen concentrations and DON/TDN in
northeastern U.S. river and streams. Limnol. Oceanogr.. 49:910-918.
Raine, R, Patching J W (1980) Aspects of carbon and nitrogen cycling in a shallow marine environment, J.
Exp. Mar. Biol. Ecol., 47,127-140.
Redfield A (1942) The processes determining the concentration of oxygen, phosphate and other organic
derivates within the depths of the Atlantic Ocean. Paper Phys.Oceanog. Met., Mass.Inst. Tech. and
Woods Hole Oceanog.Inst.9 (2):1-22
Roa P & Berthois L (1975) Manual de Sedimentología. 303 pp. Tip. Sorocaima, Caracas, Venezuela.
Romankevich E (1984) Geochemistry of organic matter in the ocean. Springer-Verlag. Berlin. 329 pp.
Roux L, S Roux, Appriou P (1998) Behaviour and speciation of metallic species Cu, Cd, Mn and Fe during
estuarine mixing. Marine Pollution Bulletin, 36 (1): 56-64.
Rubio B, Nombela M, , Vilas F (2000) Geochemistry of major and trace elements in sediments of the Ria de
Vigo (NW Spain): assessment of metal pollution. Marine Pollution Bulletin., 40 (11): 968-980.
Senior W, Castañeda J, Martínez G, Márquez A, Arismendi J, Lemus M, Iabichella M & Aparicio R.
Environmental Baseline Mariscal Sucre Project: Abiotic Components. Final Report, Volume II,
CAMUDOCA, Oriente´s University, Venezuela. 408pp.
Talbot M, Laerdal T (2000) The Late Pleistocene-Holocene palaeolimnology of Lake Victoria, East Africa,
based upon elemental and isotopic analyses of sedimentary organic matter. Journal of Paleolimnology
23; 141-164.
Tessier A, P Campbell, Bisson N (1979) Sequential extraction procedure for the speciation of particulate
trace metals. Anal. Chem., 51:844-851.
Tissot B, Welte D (1984) Petroleum Formation and Occurrence. Springer – Verlag. Berlin. Heidelberg.
Alemania. 699 pp.
Tuncer G, G Tuncel, TurguB t (2001) Evolution of metal pollution in the Golden Horn (Turkey) sediments
between 1912 and 1987. Marine Pollution Bulletin., 42 (5): 350-360.
Tyson R (1995) Sedimentary organic matter: organic facies and palynofacies. Chapman & Hall, London, 615
pp.
Valderrama J (1981) The simultaneous analysis of total Nitrogen and total Phosphorus in natural waters.
Marine Chemistry. 10:109-122.
Yanes C (1999) Estudio geoambiental del Delta del Orinoco: aspectos geoquímicos. Universidad Central de
Venezuela, Corpomene. 168 pp.