River or mangrove? Tracing major organic matter sources in tropical Brazilian coastal waters
Introduction
Mangrove forests are highly productive ecosystems, and they fringe about 60–75% of the tropical coasts MacGill, 1958, Clough, 1998. Plant litter, mainly leaves, represents about one-third of production, and up to half this quantity can be exported by mangrove creeks to adjacent waters (Robertson et al., 1992). The export of these large amounts of organic material has a recognisable effect on the food webs in coastal waters (e.g. Odum and Heald, 1975, Alongi et al., 1989, Alongi, 1990).
There is also evidence for a substantial net export of dissolved organic matter (DOM), reaching the same order of magnitude as litter export in some mangrove areas (Twilley, 1985). However, no general consensus has hitherto been reached about the role mangroves play for the dissolved and microparticulate carbon budgets. There are very few mangrove areas where quantitative long-term export/import balances exist. These are Hinchinbrook Island (Australia) Boto and Bunt, 1981, Boto and Wellington, 1988, Alongi, 1996, Alongi et al., 1998, Ayukai et al., 1998, Rookery Bay (FL, USA) (Twilley, 1985) and Bragança (North Brazil) Dittmar, 1999, Dittmar and Lara, in press-a. Many inconsistencies amongst the published data may have resulted from methodological differences and from the difficulties in accurately determining material fluxes in mangroves, which is due in large and apparently random tidal-dependent oscillations (Boto and Wellington, 1988). Furthermore, differences among the studied ecosystems such as tidal-range, topography, sediment chemistry or community structure are possible reasons for inconsistencies amongst the export balances (Ayukai et al., 1998).
Chemical tracers, such as lignin-derived phenols and stable carbon isotopes, have been applied in coastal environments to identify source and fate of DOM and particulate organic matter (POM). Lignin is a unique tracer for vascular plant material, even suitable to distinguish vegetation types, e.g. between woody angiosperms, gymnosperms or non-woody vascular plants (Hedges and Mann, 1979). Therefore, it has been widely used to trace the fate and transport of terrestrial organic matter (OM) in rivers and marine environments (e.g. Hedges and Ertel, 1982, Ertel et al., 1984, Ertel et al., 1986, Hedges et al., 1986, Moran et al., 1991a, Moran and Hodson, 1994, Kattner et al., 1999). Benner et al. (1990) found that lignin-derived phenols are leached in considerable amount from mangrove leaves (Rhizophora mangle) during early diagenesis. A high percentage of lignin might therefore be present in mangrove-derived DOM. Moran et al. (1991b) traced DOM from a mangrove swamp ecosystem at the Berry Islands (Bahamas) by analysis of dissolved lignin-derived humic substances and naturally fluorescing compounds.
Stable carbon isotope measurements were applied to trace mangrove-derived detritus in coastal food webs or to study the dynamics of particulate organic carbon in mangrove environments Rodelli et al., 1984, Zieman et al., 1984, Lin et al., 1991, Hemminga et al., 1994, Honculada Primavera, 1996, Marguillier et al., 1997. Rezende et al. (1990) proposed a high contribution of marine-derived OM to total outwelling of POM from mangroves in Sepetiba Bay (Rio de Janeiro, Brazil) and suggested that outwelling may be much less significant than expected by simple mass balance studies.
In all these studies no differentiation was made between mangroves and other terrestrial plants. Therefore, a clear chemical assignment of the OM to these sources was hitherto not possible. The objective of the present investigation was to establish a chemical pattern for mangrove-derived OM, with special emphasis on the differentiation between marine, mangrove and other OM of terrestrial origin. The use of only one source indicator is not appropriate to distinguish between three sources. Therefore, a combination of several indicators, stable carbon isotopes, lignin and its parameters, was used to study origin, fate and flux of OM in a north Brazilian mangrove estuary.
Section snippets
The study area
North Brazilian mangroves are among the most extensive in the world. The research area at the Caeté River, near Bragança, is located approximately 150 km to the south-east of the Amazon Estuary (Fig. 1). These mangroves are characterised by well-developed forests with tree heights reaching 20 m and more. The dominant species are Rhizophora mangle, Avicennia germinans and Laguncularia racemosa. The catchment area of the Caeté River comprises about 3000 km2, from which about 6% (186 km2) is
Source indicators
The combined phenolic CuO oxidation products accounted for less than 1% of the DOC and POC. Highest phenol yields were found in OM at Station 1 in the Caeté Estuary. OM samples taken at the stations in the mangrove, in the middle and the mouth of the estuary exhibited generally less than half of these yields (Table 2). The HbA-fraction contained about 75% of dissolved phenols. The HbN-fraction provided more than half of syringaldehyde, less than one third of vanillyl phenols and only ca. 10% of
Conclusions
Based on lignin-derived phenols and stable carbon isotopes a chemical signature for mangrove, terrestrial and marine-derived OM was established. Outwelling of DOM and POM from the mangrove was evident from chemical tracers and generally exceeded the terrigenous input from the river's catchment area by several times. DOM and POM were exported from the mangrove to the estuary in similar proportions. A considerable amount of mangrove-POM was rapidly removed from the water column, while
Acknowledgements
We thank J. Lobbes for the introduction to the lignin analysis. We appreciate the excellent technical assistance of K.-U. Richter and M. Birkicht. We are also grateful to T. Eglinton and three anonymous reviewers for detailed and constructive comments on the manuscript. This study was carried out as part of the Brazilian–German co-operation project MADAM and was supported by the Brazilian National Research Council (CNPq) and the German Ministry for Education and Research (BMBF) under project
References (64)
- et al.
Early diagenesis of mangroves leaves in a tropical estuary: molecular-level analyses of neutral sugars and lignin-derived phenols
Geochim. Cosmochim. Acta
(1990) - et al.
Tidal export of particulate organic matter from a northern Australian mangrove system
Estuar. Coast. Shelf Sci.
(1981) - et al.
The lignin component of humic substances: distribution among soil and sedimentary humic, fulvic, and base-insoluble fractions
Geochim. Cosmochim. Acta
(1984) - et al.
Sources and reactivities of marine-derived organic matter in coastal sediments as determined by alkaline CuO oxidation
Geochim. Cosmochim. Acta
(1995) - et al.
Fungal degradation of wood lignins: geochemical perspectives from CuO-derived phenolic dimers and monomers
Geochim. Cosmochim. Acta
(1993) Carbohydrate esters of ferulic acid as components of cell-wall of Lolioum multiflorum
Phytochemistry
(1973)- et al.
The characterization of plant tissues by their lignin oxidation products
Geochim. Cosmochim. Acta
(1979) - et al.
Tracing dissolved organic substances and nutrients from the Lena River through Laptev Sea (Arctic)
Mar. Chem.
(1999) - et al.
Variation in δ 13C values for the seagrass Thalassia testudinum and its relations to mangrove carbon
Aquat. Bot.
(1991) - et al.
The composition of lignin in estuarine suspended particulates and the distribution of particulate lignin in estuaries as determined by capillary gas chromatography of cupric oxide oxidation products
Estuar. Coast. Shelf Sci.
(1989)
Nature of POC transport in a mangrove ecosystem: a carbon stable isotopic study
Estuar. Coast. Shelf Sci.
Methodological investigations on DOC determinations by the HTCO method
Mar. Chem.
Isolation and analysis of lignin-derived phenols in aquatic humic substances: improvements on the procedures
Org. Geochem.
Analysis of the products of the oxidation of lignin by CuO in biological and geological samples by reversed-phase HPLC
J. Chromatogr.
The exchange of organic carbon in basin mangrove forest in a southwestern Florida estuary
Estuar. Coast. Shelf Sci.
Abundances of benthic microfauna in relation to outwelling of mangrove detritus in a tropical coastal region
Mar. Ecol. Prog. Ser.
The dynamics of benthic nutrient pools and fluxes in tropical mangrove forests
J. Mar. Res.
Effect of exported mangrove litter on bacterial productivity and dissolved organic carbon fluxes in adjacent tropical nearshore sediments
Mar. Ecol. Prog. Ser.
Sources, sinks, and export of organic carbon through a tropical, semi-enclosed delta (Hinchinbrook Channel, Australia)
Mangroves Salt Marshes
Fluxes of nutrients and dissolved and particulate organic matter in two mangrove creeks in northeastern Australia
Mangroves Salt Marshes
Seasonal variations in concentrations and fluxes of dissolved organic and inorganic materials in a tropical, tidally-dominated, mangrove waterway
Mar. Ecol. Prog. Ser.
Estuarine Chemistry
Mangrove forest productivity and biomass accumulation in Hinchinbrook Channel, Australia
Mangroves Salt Marshes
Lignin biodegradation and transformation
Outwelling of organic matter and nutrients from a mangrove in north Brazil: evidence from organic tracers and flux measurements
ZMT-Contribution, 5. Center for Tropical Marine Ecology, Bremen
Lignin signature of aquatic humic substances
Science
Dissolved humic substances of the Amazon River system
Limnol. Oceanogr.
δ13C measurements as indicators of carbon flow in marine and freshwater ecosystems
Bull. Mar. Sci./Contrib. Mar. Sci.
Cited by (192)
Response of mangrove development to paleoclimate variation over the past 3,550 years in Phang Nga Province, Thailand
2024, Journal of Asian Earth SciencesTemporal variations of mangrove-derived organic carbon storage in two tropical estuaries in Hainan, China since 1960 CE
2023, Palaeogeography, Palaeoclimatology, PalaeoecologyTrace element, rare earth element and trace carbon compounds in Subglacial Lake Whillans, West Antarctica
2023, Science of the Total EnvironmentHigh-frequency mangrove degradation events during the Holocene climatic optimum in the Maowei Sea of tropical China
2023, Journal of Sea ResearchMultiple-biomarkers show the importance of blue carbon to commercially important fishery species
2023, Science of the Total EnvironmentSeasonal variation, contribution and dynamics of trace elements in the drainage basin and estuary of the Serinhaém river, BA
2023, Marine Pollution Bulletin