EFFECT OF THE SANDBAR OPENING ON BIOMASS AND METALLIC COMPOSITION IN TYPHA DOMINGENSIS PERS IN THE IQUIPARI LAGOON,

SÃO JOÃO DA BARRA, RJ, BRAZIL

Carlos Eduardo Rezende, Jorge Assumpção & Marcelo Trindade Nascimento Universidade Estadual do Norte Fluminense – Centro de Biociências & Biotecnologia, Laboratório de Ciências Ambientais – Av. Alberto Lamego 2000, Campos dos Goytacazes, 28015-620, RJ, Brazil.

ABSTRACT

Typha domingensis is a common freshwater macrophyte occurring in the coastal lagoons, of the Rio de Janeiro State. In this paper, we focussed on the metallic composition (Al, Cd, Cu, Cr, Fe, Mn, Ni, Pb and Zn). and biomass variation after an anthropogenic impact (sandbar opening). The study was carried out in the Iquipari lagoon, located in the São João da Barra district, Rio de Janeiro State, Brazil. Samples were taken in September and November before and after, respectively, the artificial linkage of the lagoon with the ocean. The biomass was sampled twice along the lagoon and divided into three fractions: leaves; shoots; and rhizome + root. Most of the elements had higher concentrations in the roots, only Mn showed the high concentrations in the leaves. These results showed that metallic composition was affected by the sandbar opening, with an increase in the concentration of most elements, suggesting the need of further studies on the dynamics of nutrients and metals, before and after sandbar openings to develop management politics.

INTRODUCTION

Over the last decades, the tropical and subtropical coastal areas have been subjected to fast human development, resulting in problems of sanitary order and ecological unbalance, particularly along the protected areas such as coastal lagoons, bays and estuaries. Two of the most serious of environmental problems caused by the disordered form of space occupation are the eutrophication of water bodies, as well as the reduction of the natural equilibrium between biotic and abiotic processes. Coastal lagoons have been studied by several authors due to their important role in the land – sea interface (Knoppers, 1994).

There are almost 50 coastal lagoons in the Northern region of Rio de Janeiro state. Some of them, experience the opening of artificial sandbars as part of the social-cultural behavior stimulated namely by the fishermen’s perception of potential reduction in fish population and water quality. This social-cultural behavior is transmitted over different generations in the local population and is directly dependent on perceptions that are not supported by scientific knowledge.

Iquipari Lagoon has been used mainly for agricultural and fishing activities. However, after 1990 a significant increase in tourism has been noticed in this area. These activities interact with each other through time and space, creating in all cases, conflicts and related environmental modifications in soil use, water quality and ecological balance.

In this ecosystem, T. domingensis Pers. beds are important contributors to the primary productivity of the coastal lagoons, and is one of the most widely distributed species along the Brazilian coastal lagoons. The present study aims to measure the above-ground and bellow-ground biomass and metallic composition of T. domingensis Pers. during the two water levels stages to verify the biological response provocated by human induced stress, as well as, its importance on the biogeochemical cycles to several elements in the coastal lagoon.

MATERIAL AND METHODS

Iquipari Lagoon is a small coastal lagoon (1,4 km²) with an extension of 10 km, located in the North of Rio de Janeiro State, São João da Barra Municipality, Brazil at 21^o 44’ 20” and 21^o 48’ 12” S, and, 41^o 01’ 34” and 41^o 02’ 04”W (Figure 1 A and B).

Figure 1: Iquipari Lagoon and its Location in Brazil and Rio de Janeiro State (1 A). Sampling Zones (1 and 4) are delimitated by dashed lines (1 B).

Plant material was collected before (August/1996) and 75 days after the sandbar opening (November/1996). Samples of T. domingensis Pers. were randomly collected in each zone by using quadrats of 1 m2 (n=3 per Zone). Each sample was weighted, separated into three fractions (leaves, shoots and rhizome+roots), oven-dried (60^o C/~48h), ashed in a mufle furnace (450^o C/24h) and the ashes dissolved and evaporated in a hot plate (100^o C) with a concentrate acid mixture (HNO₃:HCl, 3:1). The final solution was maintained in HNO₃ 0,5N and all elements were performed by ICP– AES (Al, Cd, Cu, Cr, Fe, Mn, Ni, Pb and Zn). All samples were analyzed in duplicates, whenever difference between analytical duplicates were higher than 10%, the samples were discarded and analyzed again.

RESULTS AND DISCUSSION

The water volume for the lagoon was estimated in 1.1x10⁶ m³ before the sandbar opening, with a drastic reduction, circa 70%, 28 h after the opening. However, using the water volume value estimated after the opening and mean rainfall we can predict that the lagoon returns to initial level in about 1 month, considering the mean rainfall data for this period. Suzuki (pers. comm.) studied the hydrological and hydrochemical changes at the same stations and observed that salinity showed the following pattern: 1) Zone I not showed a significant change and determined values were maintained around <0.5 p.s.u.; and 2) Zone 4 change from ~0,5 to 12 p.s.u..

Total biomass of T. domingensis in Zone I was similar between prior and after the sandbar opening (4,00 and 3,83 kg.m^-2). However, in Zone 4 a significant reduction in biomass was found after the sandbar opening (from 8.52 to 6.07 kg.m^-2), as a result of its relative sensitivity to salinity (Glenn et al, 1995). The perceptual distribution was similar during the both sandbar stages (Rr > L ³ S; 41%, 32% and 27%, respectively). Belowground biomass for this vegetation type is poorly documented in the literature; our results showed that T. domingensis Pers. translocated a large fraction of their net primary production to rhizome+roots growth.

Table 1: Metallic Composition in Plant Parts (Leaves “L”; Shoots “S” and Rhizome + Roots “Rr”) of T. domingensis Pers. at Before and After Sandbar Opening

Zone I Before	Al (mg.g^-1)	Fe (µg.g^-1)	Mn (µg.g^-1)	Zn (µg.g^-1)	Cu (µg.g^-1)	Cr (µg.g^-1)	Ni (µg.g^-1)	Pb (µg.g^-1)
L	67.5±8.2	149±10	40.0±2.3	3.73±0.35	0.32±0.03	0.32±0.02	0.19±0.06	0.41±0.01
S	155±11	474±37	24.0±2.1	2.97±0.21	0.34±0.04	0.63±0.03	0.15±0.01	0.32±0.04
Rr Mean	432±16 218	1,976±121 866	11.0±0.2 25.0	6.40±0.11 4.37	0.46±0.01 0.37	0.91±0.06 0.62	0.34±0.03 0.23	0.55±0.02 0.43
Zone 4 Before	Al (mg.g^-1)	Fe (µg.g^-1)	Mn (µg.g^-1)	Zn (µg.g^-1)	Cu (µg.g^-1)	Cr (µg.g^-1)	Ni (µg.g^-1)	Pb (µg.g^-1)
L	221±17	204±14	70.0±1.1	3.51±0.14	0.46±0.01	0.58±0.05	0.25±0.01	0.40±0.04
S	432±16	152±12	22.0±1.0	3.48±0.16	0.55±0.04	1.07±0.14	0.55±0.01	0.34±0.03
Rr Mean	2,374±64 1,009	1,696±10 684	15.0±2.0 35.7	8.53±0.22 5.17	1.10±0.03 0.70	1.89±0.06 1.18	0.69±0.08 0.50	1.35±0.04 0.70
Zone I After	Al (mg.g^-1)	Fe (µg.g^-1)	Mn (µg.g^-1)	Zn (µg.g^-1)	Cu (µg.g^-1)	Cr (µg.g^-1)	Ni (µg.g^-1)	Pb (µg.g^-1)
L	265±26	157±7.5	29.0±2.0	3.44±0.16	0.66±0.04	0.74±0.06	0.43±0.04	0.41±0.07
S	136±7.4	178±6.7	64.0±1.1	5.64±0.23	1.04±0.03	3.35±0.15	1.55±0.01	0.31±0.03
Rr Mean	835±141 412	1,115±82 483	76.0±1.6 56.3	41.0±4.12 16.7	1.34±0.17 1.01	0.82±0.01 1.64	0.52±0.07 0.83	1.36±0.08 0.69
Zone 4 After	Al (mg.g^-1)	Fe (µg.g^-1)	Mn (µg.g^-1)	Zn (µg.g^-1)	Cu (µg.g^-1)	Cr (µg.g^-1)	Ni (µg.g^-1)	Pb (µg.g^-1)
L	106±4.1	355±22	68.0±2.1	6.37±0.33	0.43±0.03	0.96±0.13	0.72±0.21	0.23±0.05
S	56.4±6.9	210±24	15.0±0.4	7.69±0.12	0.34±0.02	0.46±0.05	0.26±0.04	0.06±0.07
Rr Mean	252±8.9 138	2,788±194 1,118	9.0±0.4 30.7	11.4±0.66 8.49	0.65±0.05 0.47	0.87±0.08 0.76	1.48±0.08 0.82	0.46±0.08 0.25

The metallic composition in leaves, shoots and rhizome+roots (Rr) of T. domingensis Pers. are presented in Table 1, except for Cd what was not detectable in any fraction of the plant. All values are in the range reported for non – contaminated areas (Lacerda & Rezende, 1986). The results also showed the same distribution patterns for most elements (Rr>S>L) except Mn, for which leaves had the major concentrations (L > S > Rr). Macrophytes are known to supply their roots with oxygen translocated from leaves changing the sediment phycico-chemical characteristics. One results of this process is the oxidation of reduced compounds, and therefore coprecipitation several elements with iron-hydroxide and manganese-oxide around the roots. Another important process is the increase of elements bioavailability under vegetated sediments. However, the processes described above do not explain the results of Mn, where leaves showed the highest concentrations. Manganese is an essential element, has great internal mobility and several studies have shown that this element can also be absorbed by living parts of leaf cells (Lacerda & Rezende, 1986).

The mean concentration of all elements in the plant tissues (Mean of L, S and Rr values) did not show a clear trend between zones. However, there was a tendency for the highest concentration values to be found in samples collected after the closure of the sandbar excepted to Al, Pb and Cu (Z₄); Fe (Z₁); and Cr (Z₁ and Z₄). In both zones, the element concentrations in the plant fractions analysed were ranked Al>Fe>Mn>Zn>Cr>Cu>Pb«Ni (before) and Al>Fe>Mn>Zn>Cr>Ni«Cu>Pb (after opening). Rezende et al (1991) using an identical approach to Ruppia maritima L., found similar ranking element concentrations only for the leaf fraction. Differences in the distribution patterns can be related to the essenciability and mobility of these elements within the plant and their uptake mechanisms. However, the scale of observation described above, can also change the interactions between physical (e.g. salinity, dissolved oxygen and temperature) and biological (e.g. evapotranspiration and growth rate) properties.

From the element abundance, two groups were easily recognized: 1) Al, Fe, Mn and Zn and 2) Pb, Cu, Cr, Ni. Aluminum is a structural component of plant parts and Fe, Mn and Zn plays an important roles as enzymatic activators involved in glycolisis and the Krebs Cycle. The second group is less available and has low internal mobility. Correlation between elements and plant fractions were found for Al with Pb, Cu, Cr and Ni (rs > 0,600), suggesting that these elements are in structural parts. In both zones, the local sediments are rich in organic matter content and fine particles, and have low ionic strength, semi-anoxic and anoxic conditions, specially when the sandbar is closed. However, the sandbar opening changes drastically the environmental characteristics, affecting the plant growth rate, element uptakes and their bioavailability.

In conclusion, our results suggest that the effects of environmental changes caused by sandbar openings affects plant performance, but more studies on the relationship of mineral nutrition of plants and the environmental metabolism are need to elucidate this question.

ACKNOWLEDGEMENTS: CER & MTN received a grant from Conselho Nacional de Desenvolviemento Científico e Tecnológico (CNPq) and UENF/FENORTE. The authors would like to thank the support in the field and laboratory activities of technician of the Laboratório de Ciências Ambientais Arizolli A.R. Gobo.

REFERENCES:

Gleen, E; Thompson, TL; Frye, R; Riley, J & Baumgartner, D (1995) Aquatic Botany, 52: 75–91.

Knoppers, B (1994) In: Coastal Lagoons Processes. Elsevier Science Publishers, pp. 243–286.

Lacerda, LD & Rezende CE (1986) Revista Brasileira de Botânica, 9: 87–90.

Rezende, CE; Pfeiffer, WC; Lira, CA; Torres, JPM & Lacerda, LD (1991). In: International Conference on Heavy Metals in the Environment (Ed. JG Farmer, Edinburg), Vol.1: 543–546.