Braganca Peninsula Research Articles

Distribution of mangrove vegetation along inundation, phosphorus, and salinity gradients on the Bragança Peninsula in Northern Brazil

The Braganca Peninsula, in northern Brazil is characterized by macrotides (4 m) and specific edaphic conditions, which determine the local mangrove forest’s development. This study, conducted during the dry season evaluated the spatial patterns of Rhizophora mangle and Avicennia germinans species across an inundation gradient. Along a transect of 700 m, measurements of structure forest, soil moisture, porewater salinity, extractable phosphorus (extr.-P) in sediments, and phosphorus in the leaves (leaf-P) were conducted. The A. germinans (100 %) occurred in high intertidal (HI) zone. A. germinans (59 %) and R. mangle (41 %) co-occurred in mid intertidal (MI) zone, while R. mangle (58 %) predominated in low intertidal (LI) zone, followed by A. germinans (37 %) and Laguncularia racemosa (5 %). Covariance analysis (ANCOVA) indicated that salinity and soil moisture means are significantly different between the mangrove forests, but do not correlate with inundation frequency (IF). The means of extr.-P were significantly different in mangrove forests and correlated with IF and leaf-P. The inundation frequency, the availability of P in the sediments, phosphorus in the leaves and interstitial salinity are all important factors contributing to the distribution of the mangrove tree species A. germinans and R. mangle on the Braganca Peninsula.

Flooding effects on phosphorus dynamics in an Amazonian mangrove forest, Northern Brazil

We examined porewater salinity, soil redox potential (Eh), soil extractable phosphate (extr.-P), leaf phosphorus (leaf-P) and plant growth in relation to inundation frequency (IF) and mangrove species distributions along a 600 m transect in the Braganca Peninsula, North Brazil. The forest species composition changed across the tidal zone with Avicennia germinans dominating (99.1%) the high intertidal (HI) zone where the IF was 41–67 d.y−1, Rhizophora mangle, Laguncularia racemosa and A. germinans co-occured in the mid intertidal (MI), and a mixed R. mangle (47.1%) - A, germinans (41.2%) stand occupied the low intertidal (LI) zone with an IF of 124–162 d.y−1. Low IF resulted in high Eh levels (200 mV) in the HI zone relative to the LI where Eh ranged from 0–100 mV. The IF showed a significant positive correlation with extr.-P (r = 0,89; p = 0.05) and a negative association with Eh (r = −0,75; p = 0.05). An ANCOVA confirmed that Eh and extr.P were influenced by flooding. Variations in these factors were reflected in patterns of P leaf tissue concentrations across the gradient; however, a MANCOVA showed that leaf-P was not related to tree height, tree volume or basal area. Water-logging conditions, porewater salinity, and P dynamics in the sediment appear to influence the forest structure. We suggest that P availability plays an important role in controling mangrove species distributions but not their growth.

Sediment porewater salinity, inundation frequency and mangrove vegetation height in Bragança, North Brazil: an ecohydrology-based empirical model

An empirical model based on an ecohydrological approach was developed, which allows the integration of hydrographical, topographical and physicochemical information with vegetation characteristics of mangroves and marshes of the Braganca Peninsula, North Brazil. A synoptic distribution of sediment porewater salinity was produced with isolines derived from predicted porewater salinity values from a GIS-based, multiple regression model. It includes a non-linear function of calculated inundation frequencies, the measured salinity distribution in the adjacent estuaries and sediment porewater salinities determined in the dry season. An excellent fit between measured and predicted porewater salinities was obtained. Highly significant correlations were found between vegetation height, inundation frequency and predicted porewater salinities. The relationship between vegetation height and predicted porewater salinities indicated the existence of at least three data ‘clusters’, which probably respond to different height to diameter-in-breast-height proportions according to age and environmental stress conditions. The porewater salinities produced by the model proved to be a solid proxy for the average stress situation of mangrove vegetation. The model offers good potential as a tool for analysing wetland dynamics, particularly at a synoptic, basin level.

A Model of Holocene Mangrove Development and Relative Sea-level Changes on the Bragança Peninsula (Northern Brazil)

Based on the integration of geological information, the pollen record, radiocarbon data, and modern mangrove distribution, this paper proposes a model of evolutionary development for mangroves on the Brazilian Braganca Peninsula driven by relative sea-level changes from the middle to late Holocene. After a postglacial relative sea-level rise (RSL), the mangrove habitats on the Braganca Peninsula began to develop at about 5100 years BP close to the current RSL, originating in the middle of the peninsula. Between 1800 and 1400 years BP, this littoral area underwent a maximum RSL fall of 1 m below the current one, followed by a gradual RSL rise until 1000 years BP, when the modern RSL was reached. Between 5100 and 1000 years BP, the RSL of the Braganca coastline was probably never higher than 0.6 m above the present level. The first Holocene mangrove forest (5100 years BP) in this region disappeared from the plains due to RSL fall and was replaced by herbaceous vegetation (Cyperaceae and Poaceae).

Temporal changes of mangrove vegetation boundaries in Amazonia: Application of GIS and remote sensing techniques

The present work analyses a 25-year timeseries of radar and satellite images, andidentifies areas with losses and gains ofvegetation coverage along ∼166 km of Para'scoastline (North Brazil) and in the innerparts of the Braganca peninsula. Thegeomorphology of this region hassignificantly changed in recent years. Aresult of these changes has been a retreatof the mangrove vegetation along thecoastline, mainly due to landward sandmigration, which covers the mudflat andasphyxiates the vegetation. Image analysissuggests that the loss of vegetationcoverage has been the dominating process inthe last 25 years, occurring on ∼ 42% ofthe Braganca coastline and adjacentareas. Vegetation has remained stable along∼ 39% of the coastline, while mudsedimentation has allowed mangrovedevelopment along ∼ 19% of it. On the otherhand, during this period of time, mangroveshave invaded 3.4 km2 (∼ 38%) of theelevated herbaceous flats in the highestsectors of the Braganca peninsula.Despite other possible causes for mangrovedeath along the coastline, such as littoraldrift currents or cyclical changes incoastal sediment dynamics, the invasion ofmangrove into herbaceous elevated flats inthe central peninsula cannot be attributedto these factors. The current dynamics ofvegetation coverage change seem to becompatible with a long-term trend relatedto the predicted rates of sea-level rise.

Evaluation of triterpenols and sterols as organic matter biomarkers in a mangrove ecosystem in northern Brazil

Mangrove leaves, sediment, and excrement from the mangrove crab Ucides cordatus from the coastal areas of the Braganca peninsula in North Brazil were analysed to determine suitable biomarkers for mangrove-derived organic matter. Leaves of Rhizophora mangle (red mangrove), the dominant species in the area, were characterised by high amounts of β-amyrin, germanicol, taraxerol, and lupeol. Avicennia germinans (black mangrove) mainly contained betulin, lupeol, and β-sitosterol, whereas significant quantities of β-sitosterol and lupeol were typical of Laguncularia racemosa (white mangrove), the locally least abundant species. Except for betulin, the excrement of U. cordatus contained all of the above substances, but most strongly reflected the triterpenol signature of R. mangle leaves, the predominant diet of this crab. Surface sediments from various mangrove locations had relatively uniform compositions that possibly reflect tidal mixing. Sediment extracts were dominated by taraxerol and contained smaller amounts of β-amyrin, germanicol, and lupeol. Only sediments in a marsh area, dominated by Sporobolus virginicus (seashore dropseed) and Eleocharis sp. (spikerush), revealed a different biomarker distribution. Core samples of subrecent sediment (up to 4000 14 C yr BP), for which previous pollen analysis indicated vegetation dominated by mangroves, had compositions similar to that of the surface sediment. Taraxerol was the main component in the examined mangrove sediments and may be a marker for mangrove matter in this region, although analysis of plant material did not unequivocally support this. Germanicol is suggested to be a biomarker for organic matter from R. mangle in North Brazil. It was detected in older sediments, and was not significantly affected by ingestion by land crabs.

Implications of mangrove dynamics for private land use in Bragança, North Brazil: a case study

This work analyses effects of recent variations in the tidal inundation frequency in a mangrove ecosystem in the Braganca peninsula, North Brazil, and its implications for land occupation and use. Field data, time series of remote sensing images and local legislation were analysed focusing on the potential socio-economic impact of a changing environmental setting due to a rise in relative sea level. In the investigated period (1972-1997), vegetation changes along the coastline indicate net losses of mangrove coverage. In the central part of the peninsula, a topographically higher herbaceous plain con- stituting part of a farm presents an active progression of mangrove forest into an area previously dominated by grasses and herbs. This area measured 8.8 km 2 in 1972 but was gradually reduced to 5.6 km 2 in 1997, while progressively replaced by a monospecific stand of the black mangrove, Avicennia germinans. A linear extrapolation indicates that the elevated plain may be completely covered by mangrove by 2035. Current Brazilian legislation prohibits the extraction of mangrove trees without an officially approved management plan. Thus, the usable area of the farm has suffered a reduction by ca. 36% over 25 yr and we predict that it could be entirely replaced by mangroves in the next 35 yr. In this case study, legislation and ecosystem characteristics are analysed and a management plan discussed which could represent income alternatives for affected resource users at the local and re- gional level.