concentration & eutro

BASELINE OF Ca, Mg, Fe, Mn AND Al CONCENTRATIONS INCATATUMBO RIVER SURFICIAL SEDIMENTS

HILDA LEDO1∗, ZULAY RIVAS2, JANIO GUTIÉRREZ1,ELIZABETH GUTIÉRREZ1, JESÚS OJEDA1 and HENDRIK AVILA2

1 Laboratorio de Química Ambiental, Facultad Experimental de Ciencias, Universidad del Zulia,Módulo 2. Maracaibo, Estado Zulia, Venezuela; 2 Instituto para el Control y la Conservación de la

Cuenca del Lago de Maracaibo (ICLAM), Maracaibo, Venezuela(∗ author for correspondence, e-mail: [email protected], Fax: 58 261 7598125)

(Received 19 March 2002; accepted 11 December 2003)

Abstract. Ca, Mg, Fe, Mn and Al were determined in surficial sediment samples from CatatumboRiver (including sediments from major tributaries) a binational basin shared by both Venezuela andColombia in approximately 30% and 70%, respectively. The global mean concentration of the metalswas Al > Fe > Mg > Ca > Mn (0.376; 0.304; 0.063; 0.042; 5.9 × 10−4 mmol g−1 dry weight).The objectives of this investigation were (1) to establish metal-concentration baselines, and (2) todetermine spatial distribution of Ca, Mg, Fe, Mn and Al concentrations, in bed sediment samplesfrom Catatumbo River (including sediments from major tributaries). As Catatumbo River is themain tributary to Lake Maracaibo system (South America’s largest inland lake), its impact on theeutrophication process of Lake Maracaibo due to the formation of metal/phosphorus complexes isdiscussed.

Keywords: baseline, Catatumbo River, eutrophication, Lake Maracaibo, metals, phosphorus, sedi-ment

1. Introduction

The total load of metals in the rivers depends upon the geological and ecologicalcondition of their basin as well as the human activities being developed along theirbeds. Sediments can be considered as the result of the integration of all processesoccurring in the aquatic ecosystem (Esteves, 1988; Förstner and Wittmann, 1981)and they are indicators of the chemical history of the body of water. Furthermore,the sediment allows to know seasonal changes related to the use of oxygen and theaccumulation of organic matter which determine the form of the iron compoundsas well as their mobilization. This is similar for other metals (Margalef, 1977).Sediments act as a trap for different elements due to precipitation, exchange andabsorption reactions which occur within their structure (Bortleson, 1971). Metalscan also be found in water, particulate matter and the ecosystem organisms (Anmaret al., 1993).

There are several physical-chemical factors participating in the precipitation orimmobilization of phosphorus in aquatic environments (Bianchi et al., 1990) such

Water, Air, and Soil Pollution 155: 117–135, 2004.© 2004 Kluwer Academic Publishers. Printed in the Netherlands.

118 H. LEDO ET AL.

as concentrations of iron, aluminum, sulfate as well as organic compounds, pH,temperature and redox conditions. Moreover, the oxidation state of iron is the mostimportant factor since it controls changes in the equilibrium between sedimentsand solution. The absorption of phosphorus on iron hydroxide occurs in aerobicsoils, more than in anaerobic ones (Esteves, 1988; Bianchi et al., 1990; Teasdale etal., 2003). P is immobilized in oxygenated sediments due to retention with Fe(III).Under reducing conditions P, is released from sediments following reduction ofFe(III) to Fe(II) and the associated disruption of solid Fe(III)-PO4 forms. The ratioFe/P > 1.8 was stated by Chambers and Prepas (1994) as an important indicator ofphosphorus absorption by the sediment. When such ratio becomes lower than 1.8,desorption can occur. Manganese has a high absorption surface, therefore it re-tains phosphorus leading the precipitation of the complex manganese-phosphoruswith iron as Fe-Mn-P complex (Esteves, 1988). On the other hand, when the ratioCa/P = 3.18 phosphorus is forming complexes (Staudinger et al., 1990) such asCa3(HCO3)3PO4 and dolomite, CaMg(CO3)2, is formed when ratio Mg/Ca > 0.6(Moore et al., 1991).

This work is the first study of Catatumbo River sediments to estimate the Mn,Al, Mg, Fe and Ca content and to establish the baseline values. Additionally, therelation between phosphorus and metals mentioned above was studied, due to therelevant role of sediments acting as a trap for different elements and with the know-ledge of the formation of phosphorous complexes which limit its release to thewater column, and their relation with phosphorus content in both Colombian andVenezuelan sides along the river bed until its outlet in Lake Maracaibo (Venezuela).

The objectives of this investigation were:

– To provide baseline concentrations of Ca, Mg, Fe, Mn and Al in bed sedimentof the Catatumbo River streams;

– To describe the spatial distribution of Ca, Mg, Fe, Mn and Al concentrationsin bed sediment and correlate total phosphorus, orthophosphate and metals forall samples; and

– To discuss the ratio metal/phosphorus as an indicative of the complexes form-ation.

2. Region under Study

2.1. CATATUMBO RIVER

The hydrographic system Catatumbo River is a binational basin shared by bothVenezuela and Colombia in approximately 30 and 70%, respectively. It is locatedbetween the coordenates 72◦4′00′′ and 73◦26′19′′ of eastern length and 7◦46′30′′and 9◦31′05′′ of northern latitude. Its area is 25 563 km2 and a mean yearly flow of1147 m3 sec−1. It is one of the main tributaries to Lake Maracaibo (Venezuela) with

SURFICIAL SEDIMENT SAMPLES FROM CATATUMBO RIVER 119

load of 70% of fresh water discharged to the lake. This Lake is a central locationin Venezuela’s oil production.

Limestones mines are located in both Colombian and Venezuelan areas belong-ing to the Catatumbo River system. These limestones are used as constructionmaterial and ornament, agricultural limestone and for the production of cement.There are also phosphoric rock mines in the area flowing on the main river bed andlocated at approximately 254 and 234 km. Phosphorus also comes from severalothers sources including human disturbance of the land and its vegetation, humanwaste, sewage from septic tanks and animal waste. Soil erosion also contributeswith phosphorus and the excessive use of fertilizers for crops and lawns results ina higher amount of phosphorus going into Catatumbo River. Also, iron industry isdeveloped near the shore of the Catatumbo.

Venezuela is one of the world’s top oil producers and an OPEC member. Fre-quently, the dynamiting of the Caño Limon pipeline, in Colombia, set off alarmsin Venezuela. These events cause large spills crude oil into Catatumbo and TarraRivers which flow into Lake Maracaibo (Venezuela). This situation limits the ef-forts for sampling trips to the region.

There is not a reported project for a similar study in the zone, especially in thehigher zone of the river, and the present study is the only information available atthe moment.

2.2. LAKE MARACAIBO SYSTEM

Lake Maracaibo, the largest lake in Latin America, is a large hypereutrophic estuar-ine lake in north-western Venezuela which has suffered severe pollution problemscaused by inputs of excessive nutrients, petroleum products from a major pet-rochemical industrial park and other contaminants. The lake is considered to benaturally eutrophic, however, the current state of hypereutrophy is mainly causedby excessive inputs of nutrients from treated and untreated sewage water and in-dustrial wastes, riverine and agricultural sources as well as air pollution. Strongpetroleum activity has developed in the colombian territory of the river, which isaggravated by the sabotage of oil pipelines (guerrilla activity) which is numerousduring the year and affect mainly the river bed and therefore Lake Maracaibo basin.Catatumbo River brings approximately 70% of the fresh water to the lake, whichcould indicate a significant contribution to its eutrophication (Rivas, 2000).

Previous monitoring of the Lake showed a content of total phosphorus in thewater between 0.03 and 0.10 mg L−1 in the surface and between 0.20 and 0.30 mgL−1 in its maximum depth. Dissolved oxygen varied from 100% of saturation inthe surface to less than 10% at 15 m below, in the center of the Lake. 1% of theincident light penetrated to a maximum of 6 m. Chlorophyll values were between6–10 mg L−1 (Parra-Pardi, 1979).

In 1994, ESCAM carried out a study in Lake Maracaibo, finding dissolvedoxygen concentrations between 6–8 mg L−1 in the epilimnion and lower than

120 H. LEDO ET AL.

1 mg L−1 in the hypolimnion. Total phosphorus concentrations oscillated between0.03–0.61 mg L−1 in the surface and between 0.06–3.45 mg L−1 at the bottom.Transparency values varied between 1 and 3.5 m.

3. Materials and Methods

A total of 22 sampling stations were located close to the shore from the Colombianside until its outlet in the Lake including bed sediments from the major tributariesto the river. Figure 1 shows the sampling sites and the location of Catatumbo Riverin the Lake Maracaibo system. The dotted line is the geographic limit of bothcountries, and the dark line shows the main bed of the Catatumbo River. Fromeach location a sample of sediments of approximately 1 kg was manually collectedgiving a total of 44 samples during three periods: October–November 1993 (rainyseason); February–March 1994 (dry season) and August–September 1994 (rainyseason). All stations could not be sampled in the three periods, since during dryseason some stations were completely dry and, in rainy season, episodes of floodoccurred, which impeded to sample other stations.

Samples were frozen until experiments were performed. Total phosphorus wasanalyzed with the following method: 2.5 g of sediment were ignited for 2 hr in afurnace at 550 ◦C, allowed to cool for 1 hr before adding 10 mL of 1 N HCl andboiled for 1 hr. The sample was then filtrated, completed to 10 mL with deionizedwater and analyzed as orthophosphate using the standard ascorbic acid method(APHA, 1992). Orthophosphate was analyzed in the following way: 2.5 g of wetsediment were dissolved in 100 mL of the acid mixture H2SO4-HCl 1 N, stirred for2 hr, filtrated and analyzed by the standard ascorbic acid method (APHA, 1992).For metals determination samples were lyophilized before acid digestion in a Parrtype bomb at 105 ◦C. The final solution was analyzed by flame atomic absorptionspectroscopy using a Perkin Elmer 3100 instrument.

4. Data Analysis

For data analysis, graphics and tables were processed with all available informationto know the distribution of metals, by sampling and stations.

A simple Cluster analysis was used in order to clarify the differences betweensampling sites, sampling period and metal contents in the sediments of the area.Classification was performed using 1-Pearson coefficient as the measure of dissim-ilarity. The UPGMA (Unweighted Pair-Group Method using Arithmetic Averages)clustering method was applied.

Analysis of variance (ANOVA) was carried out to compare the levels of metalson different cluster sites.

Linear regression was performed between all elements studied with p < 0.05.


Figure 1. Location of the sampling sites in Catatumbo River. Main river bed: (4) Limones sewer,64 km; (8) Before Zulia River confluence, 120 km; (10) Before Tarra river confluence, 153 km;(11) Ecuador bridge, 194 km; (13) Las Delicias, 229 km; (14) Puerto Barco, 234 km; (15) La Gabarra,241 km; (17) Before San Miguel river confluence, 247 km; (18) Before Brandy river confluence,254 km; (20) Filogringo, 303 km; (21) Aserrio, 345 km; (22) San Pablo, 355 km. Tributaries:(5) Guasimales sewer; (6) Bravo River; (7) Zulia River; (9) Tarra River; (12) Oro River; (16) SanMiguel River; (19) Brandy River. Catatumbo River mouth in Lake Maracaibo: (1) Boca Norte;(2) Boca Sur; (3) Congo Mirador.

122 H. LEDO ET AL.

TABLE I

Phosphorus and metals in sediments in the Catatumbo River bed

Sampling Distance Station Countrya Total Mn Mg Ca Fe Al

date to Lake (See phospho-

Maracaibo Fig. 1) rus (TP)

(km) (mmol g−1 dry weight)

11/19/1993 254 18 2 0.018 0.0011 0.165 0.227 0.380 0.708

11/19/1993 241 15 2 0.008 0.0006 0.088 0.037 0.294 0.410

11/19/1993 229 13 2 0.009 0.0005 0.042 0.008 0.016 0.194

11/19/1993 194.1 11 1 0.002 0.0001 0.075 0.054 0.195 0.147

11/19/1993 153 10 1 0.012 0.0005 0.030 0.003 0.124 0.157

03/01/1994 355 22 2 0.034 0.0003 0.064 0.035 0.188 0.281

03/01/1994 345 21 2 0.032 0.0006 0.059 0.033 0.200 0.284

03/01/1994 303 20 2 0.024 0.0007 0.055 0.031 0.211 0.288

02/25/1994 247 15 2 0.007 0.0005 0.058 0.049 0.180 0.333

02/26/1994 234 14 2 0.010 0.0009 0.098 0.116 0.366 0.479

02/26/1994 229 13 2 0.001 0.0004 0.047 0.042 0.154 0.328

03/07/1994 194 11 1 0.014 0.0004 0.020 0.046 0.111 0.235

03/08/1994 120 8 1 0.007 0.0006 0.051 0.027 0.284 0.274

08/02/1994 254 18 2 0.017 0.0010 0.156 0.214 0.359 0.668

08/18/1994 247 17 2 0.011 0.0006 0.091 0.021 0.232 0.282

08/04/1994 241 15 2 0.015 0.0012 0.129 0.077 0.397 0.762

08/11/1994 234 14 2 0.005 0.0004 0.028 0.003 0.127 0.278

09/08/1994 229 13 2 0.012 0.0007 0.045 0.057 0.222 0.335

09/07/1994 153 10 1 0.005 0.0005 0.047 0.078 0.168 0.391

09/07/1994 120 8 1 0.009 0.0007 0.063 0.041 0.301 0.305

a 1 = Venezuela, 2 = Colombia.

5. Results and Discussion

Previous size particle analysis showed a homogeneous distribution in size particlecomposition in sediments from the Catatumbo River within the river basin. Aver-age results showed that 89% of the sediment has a particle size around 150 µm,which means that the sediment is classified as fine sand. No relationship wasfound between the P-concentration and metals with the particle size. Hence, sedi-ment transportation, availability, presence and distribution of P and metals are notinfluenced by particle size distribution in this sediment.


TABLE II

Phosphorus and metals in sediments from tributaries to the Catatumbo River

Sampling Tributary Station Countrya Total Mn Mg Ca Fe Al

date river (See phospho-

Fig. 1) rus (TP)

(mmol g−1 dry weight)

11/19/1993 San Miguel 16 2 0.009 0.0005 0.046 0.007 0.171 0.215

11/19/1993 Bravo 6 1 0.006 0.0009 0.110 0.018 0.458 0.363

02/25/1994 Brandy 19 2 0.025 0.0008 0.161 0.129 0.288 0.542

03/07/1994 Oro 12 1 0.011 0.0004 0.026 0.002 0.144 0.190

03/08/1994 Tarra 9 1 0.008 0.0004 0.024 0.001 0.105 0.119

03/08/1994 Zulia 7 1 0.006 0.0004 0.027 0.008 0.184 0.169

03/08/1994 Limones 4 1 0.030 0.0003 0.048 0.004 0.340 0.263

sewer

03/08/1994 Bravo 6 1 0.017 0.0005 0.021 0.014 0.152 0.203

03/09/1994 Guasimales 5 1 0.016 0.0003 0.034 0.002 0.180 0.198

sewer

08/02/1994 Brandy 19 2 0.002 0.0005 0.028 0.020 0.135 0.263

08/12/1994 San Miguel 16 2 0.007 0.0006 0.025 0.046 0.207 0.339

09/01/1994 Tarra 9 1 0.008 0.0004 0.025 0.004 0.209 0.495

09/01/1994 Oro 12 2 0.010 0.0005 0.048 0.107 0.192 0.395

09/07/1994 Zulia 7 1 0.012 0.0007 0.064 0.032 0.358 0.343

09/08/1994 Guasimales 5 1 0.006 0.0012 0.089 0.043 0.129 0.744

sewer

09/08/1994 Bravo 6 1 0.016 0.0003 0.045 0.002 0.208 0.427

a 1 = Venezuela, 2 = Colombia.

5.1. BASELINE CONCENTRATIONS OF Ca, Mg, Fe, Mn AND Al IN BED

SEDIMENT OF THE CATATUMBO RIVER STREAM

The mean concentrations found along the river bed were in the following order Al >Fe > Mg > Ca > Mn (0.357; 0.226; 0.070; 0.060; 6 × 10−4 mmol g−1 dry sediment).Phosphorus showed higher values at 254 km on the main river bed, probably dueto the presence of phosphoric rocks mines flowing into the river in the area locatedbetween 254 and 234 km approximately as can be seen in Table I. It was found thatFe and Al concentrations were higher than the other element concentrations. Thehigh values for iron and aluminum probably show the characteristics of the soils inthis region which were characterized as tertiary and quaternary (M.E.M., 1995).

Table II shows metals concentrations found in sediments of tributary rivers.The mean concentrations found in the rivers were Al > Fe > Mg > Ca> Mn (0.329;

124 H. LEDO ET AL.

0.211; 0.051; 0.028; 5.42 × 10−4 mmol g−1 dry sediment) being slightly higher inthe Colombian side.

The mean concentration for the metals in the river outlet was in the followingsequence Fe > Al > Mg > Ca > Mn (0.802; 0.563; 0.070; 0.018; 6.9 × 10−4 mmolg−1 dry sediment), as can be seen in Table III. The magnitude of these values wasexpected since the zone belongs to the type referred as accumulation of elements.Sediments are deposited in areas of quiet, slow moving water (the mouth of theriver in the opening to Lake Maracaibo) and are picked up and carried on furtherdownstream when flows increase. Much sediment transport occurs during rainyevents. Deeper parts of the lake, on the other hand, act as basins where sedimentsaccumulate.

Additionally, Figure 2 presents the log concentration (mmol g−1 dry weight) ofP, Mn, Mg, Ca, Fe and Al, along the river bed, of the surface samples taken over 3separate field sampling times in relation to the distance from Lake Maracaibo andthe evaluated Colombian and Venezuelan territories.

Values of metals found in sediments of the river show levels below minimumvalues in other ecosystems. These metals are associated with rocks, fine-grainedmineral structure, and biogenic sediments. A list of the results for another ecosys-tems is given in Table IV.

An attempt to evaluate the ‘quality’ of the sediment data, was done by com-paring it to the sediment background values in other ecosystems worldwide. Thebackground values can be used as a point of reference to establish the CatatumboRiver sediment baseline, as can be seen in Table V. No enforceable USA Federalor State Sediment Quality Standards exist for the elements under study except ironand manganese with values of 0.36 and 0.0084 mmol g−1 of dry sediment, respect-ively (Persaud et al., 1993). Venezuela has no national criteria for any elements insediments.

The natural metal/aluminum relationships shown in Table V were used to de-velop guidelines for distinguishing natural from contaminated sediments for a num-ber of metals and metalloids commonly released to the environment due to an-thropogenic activities. Aluminum was chosen as a reference element to normalizesediment metals concentrations since: it is the most abundant naturally occurringmetal; it is highly refractory; and its concentration is generally not influenced byanthropogenic sources. Additionally, aluminum is the second most abundant metalin the earth’s crust, being silicon the most abundant (Windom, 1988).

Most metals transported by rivers are tightly bound in the aluminosilicate solidphases. As a consequence, during the weathering, there is very little fractionationbetween the naturally occurring metals and aluminum. It has long been assumedthat in freshwater sediments, hydrous manganese and iron oxides provide import-ant adsorbing surfaces being probably responsible for trace metal transport in redoxsensitive environments (Morfett et al., 1988).

Since much of the natural constituents of metals in estuarine sediments arechemically bound in the aluminosilicate structure, the metals are generally non-


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126 H. LEDO ET AL.

Figure 2. Metals and phosphorus concentrations in Catatumbo River sediments. (A) Octo-ber–November 1993; (B) February–March 1994; (C) August–September 1994.


TAB

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128 H. LEDO ET AL.

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aN

R=

Not

repo

rted

.


Figure 3. Classification of variables (metals and phosphorus content) in the sediment samples.

labile. The adsorbed anthropogenic or ‘pollutant’ component is more loosely bound.Metals in the anthropogenic fraction, therefore, may be more available to estuarinebiota and may be released to the water column when sediments are disturbed (e.g.,by dredging or storms). Due to the fact that the levels of the studied metals insamples of surficial sediments in Catatumbo River and the ratios metal/aluminumare very low when compared with values established as background and crusts inother ecosystems, these results could be considered as baseline levels.

5.2. SPATIAL DISTRIBUTION OF Ca, Mg, Fe, Mn AND Al CONCENTRATIONS IN

BED SEDIMENT OF THE CATATUMBO RIVER STREAM AND CORRELATION

AMONG TOTAL PHOSPHORUS, ORTHOPHOSPHATE AND METALS

Figure 3 presents the classification of variables (metal concentrations and phos-phorus content) in the sediment, by means a simple cluster analysis, using Pearsoncorrelation coefficients (UPGMA) as a measure of similarity. According to thisdendogram, four main clusters with geochemical significance appear to exist:

(a) The Ca group: The presence of naturally occurring Ca in this group suggestsnatural origin.

(b) The Mg and phosphate group: It shows a stronger association between phos-phate and magnesium than between phosphate and other metals.

130 H. LEDO ET AL.

Figure 4. Classification of the stations using as variables the concentrations of metals and phosphorusin the sediments.

(c) The Al, Fe and Mn group. The fact that Fe and Mn appear in the same groupwith Al, suggests that weathering of natural rocks may play an important rolein the distribution of those metals in the sediments of the study area. Fe andMn oxides probably play an important role in this distribution. There are ironreserves in Colombia which could explain the high amount of iron.

(d) Total Phosphorus forms a separated group, which shows a different distributionprocess compared to the metals. Probably, ferlilizers could be the main sourceof phosphorus.

Pearson product-moment correlations between each pair of variables were used,and p-values below 0.05 indicate statistically significant non-zero correlations atthe 95% confidence level. There is a very poor correlation between total phos-phorus and the studied metals. It is also shown a positive correlation between themetals and orthophosphate which indicates that orthophosphate is the main specieinteracting with the metals. Correlations among metals are high and positive whichshow their interaction to form multiple complexes such as Fe-Mn-P, Fe-Ca-P andMn-Ca-P.


A simple Cluster analysis was used to find the differences between samplingsites, sampling period and metal contents in sediments of the area as appears inFigure 4. The concentration of metals and phosphorus were used as variables. Itwas found no clear groups in the dendrogram depicting cluster analysis. With theexception of some stations that cluster together, there is no homogeneous patternto describe the clustering and sites are not significantly different from each other.

It should be noted that this study was performed on near-shore sediments ratherthan on deeper areas of the river where sediment accumulation might occur. Thefact that no metal concentration was related to distance downstream in this rivermay be related to the low level of metal contamination.

5.3. RATIO METAL/PHOSPHORUS AS AN INDICATIVE OF THE COMPLEXES

FORMATION

In general, when dissolved metals from natural or anthropogenic sources come incontact with saline water, they are quickly absorbed to particulate matter and areremoved from the water column to bottom sediments. Thus, metals from both nat-ural and anthropogenic sources are ultimately concentrated in estuarine sediments,not the water column. When the ground water rich on trace elements contacts lessacidic surface water (the union Catatumbo River with Lake Maracaibo waters),substantial amounts of dissolved Fe and Al will precipitate as fine grained Feoxides or aluminium hydroxides. In turn, these substrates can scavenge and con-centrate other dissolved trace elements (e.g., Cu, Zn). Finally, these trace elementscould accumulate in the bed sediments of Lake Maracaibo. That is to say, thatalthough the concentrations of metals are very low, and are included as part of theground, they can influence later in the metal accumulation in sediments of the waterbody where they are transported. This can be the case of the outlet of CatatumboRiver in Lake Maracaibo, specially the formation of compounds with phosphoruswhich can influence the eutrophication process of the Lake Maracaibo.

Metal and total phosphorus concentrations were used to determine the molarratio in the Catatumbo River bed, in its tributaries and its mouth in Lake Maracaibo.The global mean ratios for these areas are shown in Table VI. Additionally, thistable shows the global mean ratios calculated from P and metal concentrations forthree sediment samples from Lake Maracaibo taken near the mouth of CatatumboRiver. These could suggest that Al, Fe, Mg, and Ca form complexes with phos-phorus, therefore, they control the phosphorus release to the water column. Themolar ratios found (Al/P; Fe/P; Ca/P and Mg/Ca) are higher than the minimum re-quired values for the formation of the mentioned complexes (Chamber and Prepas,1994; Moore et al., 1991; Dannen-Louwerse et al., 1993; Staudinger et al., 1990).Consequently, it can be stated that the metal complexes could be present in theanalyzed sediment samples, existing the Mg/Ca complex as Dolomite (Moore etal., 1991). The complex Fe-Al-P could be predominant because Fe and Al have ina higher ratio with phosphorus as compared to the other metals. Additionally, it was

132 H. LEDO ET AL.

TAB

LE

VI

Mea

nm

olar

rati

ofo

rth

est

udie

dm

etal

sin

sedi

men

t

Rat

ioC

atat

umbo

Tri

buta

ries

Cat

atum

boR

iver

Lak

eM

arac

aibo

Lit

erat

ure

Ref

eren

ce

Riv

erbe

dou

tlet

inth

e(n

ear

Cat

atum

bo

Mar

acai

boL

ake

Riv

erm

outh

)

Al/

P50

.96

41.2

618

.97

54.9

73.

13D

anen

-Lou

wer

seet

al.(

1993

)

Fe/

P31

.62

24.6

523

.47

53.0

31.

80(a

)C

ham

bers

etal

.(19

94)

6.66

(b)

Dan

en-L

ouw

erse

etal

.(19

93)

Mg/

P9.

845.

812.

7414

.22

NR

aN

Ra

Ca/

P8.

093.

090.

5020

.08

3.18

Sta

udin

ger

etal

.(19

90)

Mg/

Ca

1.22

1.88

5.48

0.71

>0.

6M

oore

etal

.(19

91)

Mn/

P0.

080.

070.

020.

06N

Ra

NR

a

aN

R=

Not

repo

rted

inth

eli

tera

ture

.


found that the mean pH value and dissolved oxygen values in sediments overlyingwater were 7.0 and 5.0 mg L−1, respectively (Gutiérrez, 1995) which indicatesthe aerobic nature of the sediments. This fact is favorable for the formation ofphosphorus and metals complexes such as Al, Fe and Ca present in the sediments.

6. Conclusions

– The present work provides baseline data for future impact assessment and in-formation on existing environmental alterations for one of the most importantriver in the binational South American region.

– The present investigation provides primary field data metals in sediments fromCatatumbo River. The global mean concentration of the metals was Al > Fe >Mg > Ca > Mn (0.376; 0.304; 0.063; 0.042; 5.9 × 10−4 mmol g−1 dry weight).

– The metal/P ratios found with the oxygen levels in the river, suggest the form-ation of metal-P complexes, especially with Fe, Al and Ca. This indicates thatonce the sediments arrive to the anoxic center of Lake Maracaibo, a phosphorussource can be developed.

Acknowledgements

The authors wish to thank the INTEVEP- Gerencia de Ecologia y Ambiente, es-pecially to Dr. Jorge Rodríguez, Ivan Galindo and Enrique Abreu, for providingfacilities to obtain samples sediment and financial partially this study.

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