**Abstract**

Mangroves are areas of permanent preservation, but anthropogenic interference in this ecosystem (for example the launching of pollutants from industrial, mining, fertilizer by farmers, sewage) is increasing startlingly. Preserve and look for ways to bioremediate mangroves is fundamental, since these maintain the productivity of coastal ecosystems and is thus regarded as a natural nursery. The need to study the mangroves has been growing in recent years, particularly in respect to the environmental characteristics of this ecosystem. This chapter aimed to draw a parallel between the damage that can be caused by the trace elements nickel and iron on the mangrove ecosystem, more specifically affecting the nutrition of mangrove plants, in addition to showing possible effects of the interaction of these metals with humic substances of organic matter acting on the mitigation of stresses caused to the ecosystem under study. Through surveys of the information covered in this chapter, it can be observed that the presence of trace elements such as Iron and Nickel at high levels can cause eminent stress to the plant structure within the scope of its sedimentary physiology and biochemistry. It is necessary to subsidize further studies so that it is explicit and approved by the scientific community that, this environment, which is sensitive and important, the basis for various trophic levels, needs greater attention from government officials for its preservation, as well as the restoration of those many mangroves that are polluted by being close to urban places, receiving an exacerbated supply of pollutants.

**Keywords:** mineral stress, biostimulant, mangrove, plant mineral nutrition

### **1. Introduction**

The Mangrove is a coastal ecosystem, in transition between terrestrial and marine environments, characteristic of tropical and subtropical regions [1]. Despite being considered an ecosystem associated with the Atlantic Forest, the Mangrove is made up of areas of little biological diversity, but of great functional diversity [2].

It is composed of highly specialized halophyte vegetation, adapted to fluctuations in salinity, subject to the tidal regime and characterized by colonizing muddy sediments with low oxygen levels, on poorly consolidated substrates [3].

It suffers from water input from both the continent and the marine environment, the Mangrove ecosystem is of recognized importance, having primary primary productivity, filtering, storing and making available organic matter and nutrients, with a fertilizing influence on the adjacent coastal waters [4]. The "tangle" of Mangrove roots captures, traps and stabilizes interstitial sediments, forming a natural physical barrier against the erosion mechanisms generated by waves, tides and currents, promoting stabilization of the coastline [5]. In addition, canopies of vegetation protect adjacent terrestrial environments from strong ocean storms and winds [6].

Underestimated in the past, the Mangrove was considered an inhospitable environment for a long time [7]. Until the mid-1970s, the progress of the coast was equivalent to clean beaches, sanitary landfills, ports and cultivation to take advantage of the land of the old mangroves, which would have future consequences [8]. Regarding the economic and social importance of this ecosystem, this approach was partly responsible for the construction of ports, spas, coastal highways, urban expansion and the release of raw sewage into its channels, considerably reducing its extent [9].

In more recent times, the mangroves were cut and grounded for the expansion of cities and the implementation of various enterprises [10]. Most of the vegetation of the Mangroves in the city of Vitória has been destroyed in the last decades due to several factors, among which the occurrence of landfills, real estate speculation, urban projects, slums, sewage disposal and deforestation stand out [11]. In different parts of the world and in an increasingly present way, in parallel with the degradation process, ways are developed to recover the impacted environments and even provide conditions necessary for the creation of new areas [12].

Due to this phase of expansion of recovery, there are now several techniques that may or may not include planting and the recovery of an ecosystem can be defined as the act of returning it, as far as possible, to a condition close to the original [13]. This management method is based on knowledge of the processes essential to the development and sustainability of the productivity of the system as a whole and not of its parts, therefore, it is necessary to acquire specialized knowledge about plants and animals, that is, it is necessary to know, first of all, the structure and functioning of the ecosystem [14].

Several Brazilian municipalities are already working with replanting, recovery and restoration of mangroves, however, there is still a need to investigate which factors interfere in the growth and development of these plants. One of these factors is probably the accumulation of heavy metals in the substrate, which combined with the massive presence of organic matter and its main component, humic substances, which is recognized as a potential plant biostimulant [15, 16], may be causing a greater accumulation of these elements, which in high concentrations become harmful to plants, leading to death [17]. Therefore, according to the above, studies on the interaction of the mangrove with other biotic and abiotic components of this ecosystem are necessary. Data of this nature will be essential when adapting restoration and recovery methods. In addition, municipal, state and federal public authorities will be able to more safely base possible interventions in this ecosystem, since the law states that it is their obligation to recover degraded areas.

The purpose of this chapter is to carry out a consistent approach to mangroves and the intrinsic effects of trace elements on the specie *Rhizophora mangle* L. in order to subsidize the understanding in the treated area for the scientific community.

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*Effect of Trace Elements Accumulation on Mangrove Ecosystem and Their Interaction…*

Mangroves are present on about 60–75% of the planet's tropical coast. These ecosystems play an important role in the carbon balance of coastal systems, with an export of terrestrial carbon [C] to the oceans (11%) about 15% of the total carbon that is deposited in current marine sediments [18]. Mangroves contribute about 10% of the terrestrial dissolved organic carbon when compared to other habitats and this large export of organic matter directly interferes with the food webs of coastal systems [19–22]. Recently, coastal ecosystems are being strongly impacted by natural climate change and human activities that affect their structure and food web, resulting in broad economic consequences. In addition, adjacent oceans provide considerable amounts of nutrients to coastal ecosystems and regulate nutrient

The mangrove can reach high levels of primary production. Mangrove litter provides trophic subsidy in adjacent coastal waters (the "outwelling hypothesis"), through a food web the debris is converted into a more palatable microbial biomass, which in turn acts as a dominant food source for the higher trophic levels [24]. In view of the economic importance of fishing in mangrove systems and adjacent waters, trophic dependence is a widely publicized function on mangroves and an

The mangrove is an ecosystem that occurs in tropical coastal areas related to low, flat and estuarine regions, bordering lagoons, rivers or channels, waterlogged, brackish areas, being influenced by the tidal regime, but absent from direct wave actions [26]. All of these aspects influence the large deposition of sediments and organic matter. It is considered a link, as it is a transition area between marine, terrestrial and freshwater environments and is characterized by the high variation that occurs between these areas due to the regimes of both aquatic and terrestrial environments. The substrate has a pasty consistency, little compacted, swampy, rich in organic matter, little oxygen and subject to tidal regime [27]. These systems are generally young, as their dynamics produce constant changes in these lands, the

Regarding their origin, the characteristic species of mangroves have records from the Eocene (period when angiosperm species began to occupy the land-sea transition areas) about 60 million years ago [31]. In order to have all this adaptation on the part of the plants in the system as currently, there was at that time an adaptive evolution of angiosperms from the end of the Cretaceous and beginning of the Eocene in such a way that the plant species started to adapt and tolerate high concentrations of salts in the sediment, whose first species were the genus Rhizophora and Avicennia resulting from continental drift. These species occur in practically all

From the mangroves that have disappeared, it is possible to point out the formation of terraces of marine construction where beach sandstone and raised sandbank occur, dehydrated and consolidated by clay and humid cement. Mangroves are systems in constant dynamics, with some of them still in full expansion, with a constant movement of the horizon or superficial layer of the mangrove due to the

The penetration of mangrove roots in deep regions allows the reduction of tidal currents leading to the accumulation of clay and sludge, components of the nutrient cycling process that sustains the high productivity in the mangrove system [36]. Sediments are characterized by being native or alien, accumulating fine fractions due to their low energy in the environment, justifying fluid retention [37].

**2.1 Characterization, location and importance of mangroves**

*DOI: http://dx.doi.org/10.5772/intechopen.96778*

important argument for their conservation [25].

result of constant advances and retreats of the tides [28–30].

latitudes where there are mangroves [30, 32].

withdrawal and sedimentary deposition [33–35].

**2. Mangroves**

dynamics [22, 23].
