Avaliação Dos Impactos Do Eucalyptus Sobre Dois Lagos Naturais No Sistema Lacustre Do Médio Rio Doce

8/11/2019 Avaliao Dos Impactos Do Eucalyptus Sobre Dois Lagos Naturais No Sistema Lacustre Do Mdio Rio Doce

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Abstract

The aim of the research was to evaluate the environmental impacts from replacing Mata Atlantic Rain

Forest by Eucalyptus spp. in the catchment of two natural lakes of the Doce River Lake System, Minas Gerais,

Brazil.

The evaluation was carried out by comparison between two lakes, the first one with the catchment

almost totally occupied by Eucalyptus spp. with another lake where Eucalyptus plantation was abandoned which

allow the growth of a secondary Atlantic Rain Forest. Each lake was sampled monthly, all along one year, fordissolved oxygen, water temperature, pH, electrical conductivity, total alkalinity, concentrations of nitrogen,

phosphorus and SiO2, STS, particulate organic matter and chlorophyll a. The phytoplankton structure and

composition were determinate. Rates of siltation and chemical composition of sediments are calculated. Also, we

Litter production and, its nutritional value for each lake were exanimate, including the rates of litter

decomposition in to the water.

Both lakes are similar in theirs dissolved oxygen concentration. The same similarities are found to

thermal behavior, which allow classifying them like hot monomitics. The water column of Eucalyptus lake show

smaller values for nitrates, ammonium, phosphates, reactive silicon, total forms of N and P, chlorophyll a, STS

and particulate organic matter. Sediments from Atlantic Forest lake were reduced in its chemical composition of

N and P, but larger concentration of organic carbon in a comparative with Eucalyptus lake.

Litter productivity of Atlantic Forest was about 8,2 t ha-1

year-1

. For Eucalyptus plamtation litter

productivity was found a value of 6,5 t ha-1

year-1

. This results in a alloctonous input of 1667 kg of litter year-1

to

the Atlantic Forest lake and, 650 kg of litter year

-1

to the Eucalyptus lake. Such differences are probably resultsof diverse structures of vegetal coverage of the lake basins.

Litter decomposition into the water in crescent order of resistence to process was: Tropical Atlantic

Forest leaves < Eucalyptus leaves< Tropical Atlantic Forest branches< Eucalyptus branches.

The phytoplanktonic community was found different among lakes: Cyanophecae dominate in to

Tropical Forest lake, while Euchlorophyceae was dominant into Eucalyptus lake. Such differences were

interpreted like a response from the ecosystem to the dissimilar alloctonous inputs.

Eucalyptus lake gets more sedimentary material (which resulted in a bigger siltation rate), with lesser

energetic value as a result of smaller quantities of organic mater. The lake surrounding by Eucalyptus needs 88

years to loss half of its volume. The lake surrounding by Atlantic rain forest needs 241 years.

Whit these results mitigation management practices are recommended, mainly expand the riparian

forest, putting Eucalyptus more distant from water.

We conclude that the replacing of original forest by Eucalyptus brought changes on quality and quantity

of alloctonous material and siltation rates, which suggest consequences to phytoplankton community.


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Documents

Avaliação Dos Impactos Do Eucalyptus Sobre Dois Lagos Naturais No Sistema Lacustre Do Médio Rio Doce