RESUMOOs ecossistemas aquáticos continentais brasileiros, em sua maioria com extensas regiões litorâneas, são propícios à ocorrência de macrófi tas aquáticas. Neste trabalho são utilizados resultados de pesquisas desenvolvidas no Brasil para discutir os principais fatores limitantes à produção primária de macrófi tas aquáticas, bem como os impactos antrópicos sobre estes fatores limitantes. Os fatores limitantes abordados são temperatura, radiação fotossinteticamente ativa, velocidade de corrente, variação do nível de água, concentrações de nutrientes (nitrogênio e fósforo) e carbono inorgânico. Utilizamos estudos realizados em campo, mas também resultados de experimentos em laboratório, pois estes permitem que se isolem variáveis que controlam a produção e o crescimento de macrófi tas aquáticas. As alterações antrópicas nos ecossistemas aquáticos interferem no crescimento e na produção primária de macrófi tas aquáticas. A eutrofi zação artifi cial promove o crescimento de macrófi tas fl utuantes, emersas e mesmo submersas. A construção de represas em rios também interfere no crescimento de macrófi tas alterando a velocidade de corrente e o padrão de variação de nível de água. Estes dois fatores são importantes controladores da produção destes vegetais. O conhecimento sobre os fatores limitantes ao crescimento de macrófi tas aquáticas no Brasil é ainda muito escasso. Poucos ambientes e poucas espécies têm sido estudados, difi cultando a comparação de resultados. A formação de pesquisadores, a ampliação das áreas geográfi cas em estudos de campo, o desenvolvimento de experimentos em laboratório em condições controladas e a realização de eventos científi cos específi cos sobre macrófi tas aquáticas podem contribuir para reduzir a lacuna de conhecimento técnico e científi co sobre esta comunidade aquática. Palavras-chave: Produção primária, nutrientes, radiação fotossinteticamente ativa, temperatura, carbono inorgânico. ABSTRACT STUDYING THE LIMITANT FACTORS TO PRIMARY PRODUCTION OF AQUATIC MACROPHYTES IN BRAZIL.The littoranean ecosystems of Brazil generally present vast areas colonized by aquatic macrophyte plants. In this work we present and discuss a number of studies about the main limitant factors to primary production of aquatic macrophyte plants in Brazil, and the underlying effects of human activities. The limitant factors here discussed would include temperature, photosynthetic active radiation, current speed, and available amounts of nitrogen, phosphorus and inorganic carbon. Studies in the fi eld as well as in the laboratory are discussed. Laboratory studies enable assessing the effects of isolated variations in the rearing conditions over the growth of aquatic macrophytes. Such studies are scant in Brazil. Anthropogenic alterations on aquatic ecosystems affect the growth and primary production of aquatic macrophytes. Humaninduced eutrophication promotes the growth of free-fl oating, emerged, and submerged algae. The construction of dams also interferes on macrophytes growth, because it causes changes in...
We compared the values of the biomass, chemical composition and nutritive value of the emergent aquatic macrophyte S. alterniflora in a river affected by the discharge of domestic sewage (Guaú River) and in an unpolluted river (Itanhaém River). S. alterniflora, water and sediment samples were obtained in the two rivers in November, 2001. The Guaú River presented the highest levels of Total-N and Total-P in the water (415 and 674 µg.L-1, respectively) and in the sediment (0.25 e 0.20% of the Dry Mass, respectively), when compared to the water (TN = 105 µg.L-1; TP = 20 µg.L-1) and the sediment (NT = 0.12% DM; PT = 0.05% DM) of the Itanhaém River. Aerial (316 g DM.m-2) and subterraneous (425 g DM.m-2) biomass of S. alterniflora were significantly higher in the Guaú River than in the Itanhaém River (146 and 115 g DM.m-2, respectively). In addition, the values of TN, protein, TP, lipids and soluble carbohydrates were significantly higher in S. alterniflora biomass from the Guaú River. On the other hand, the values of the polyphenols and the cell wall fraction were significantly higher in the biomass of S. alterniflora from the Itanhaém River. We concluded that domestic sewage discharge in water bodies may increase the biomass and change the chemical composition of S. alterniflora. The high N and P availability in the water of the Guaú River is probably the cause of the higher biomass, TN, TP, protein, lipids and soluble carbohydrates measured in S. alterniflora in this river.
Effect of Urucu oil (Brazilian Amazon) on the biomass of the aquatic macrophyte Eichhornia crassipes (Mart.) Solms (Pontederiaceae)Efeito do petróleo de Urucu (Amazônia/Brasil) sobre a biomassa da macrófita aquática Eichhornia crassipes (Mart.) Solms (Pontederiaceae) caused total mortality (100%) in E. crassipes after 84 days of exposure. The decomposition of the oil and the dead biomass of E. crassipes reduced the dissolved oxygen and pH, and increased electrical conductivity and concentrations of total phosphorus in the water; Conclusions: We conclude that an oil spill can cause total mortality in the local population of one macrophyte species, but not of another. This may alter the macrophyte species diversity in the impacted region. In the case of E. crassipes and Pistia stratiotes, an Urucu crude oil spill could favor E. crassipes, the species less sensitive to oil.
Objective: Aquaculture generates social and economic benefits, but also causes impacts on the environment. One of the major impacts is the release of untreated effluents into rivers, reservoirs, and lakes, which can affect aquatic populations and communities. In this study, we tested the hypothesis that effluent from aquaculture favors the growth of the floating aquatic macrophyte Salvinia molesta; Methods: The study was carried out in a non-impacted reservoir (NIR) and in another reservoir (IR) that is impacted by discharges of aquaculture effluents, and lasted for nine months. In each of the reservoirs, we installed four experimental units containing 10 ramets of S. molesta. Monthly, we measured limnological variables of the water and the biomass of S. molesta in both reservoirs; Results: The temperature, turbidity, electrical conductivity, alkalinity, chlorophyll-a, total Kjeldahl nitrogen, and total phosphorus were higher in the IR in all the collection months. At the end of the experiment, the concentrations of total nitrogen and phosphorus in the biomass of S. molesta from the IR were higher than those in plants from the NIR. The estimated support capacity (K) for S. molesta in the NIR was 3.0 ± 0.7 g DM.m-2 and in the IR was 37.4 ± 2.4 g DM.m-2 ; Conclusions: It was concluded that the discharge of aquaculture effluent modifies the limnological characteristics of the water of the receiving reservoir, and that the growth of Salvinia molesta is favored by the aquaculture effluent, because of the increases in the concentrations of nitrogen and phosphorus in the water.
Objective: Aquaculture generates social and economic benefits, but also causes impacts on the environment. One of the major impacts is the release of untreated effluents into rivers, reservoirs, and lakes, which can affect aquatic populations and communities. In this study, we tested the hypothesis that effluent from aquaculture favors the growth of the floating aquatic macrophyte Salvinia molesta; Methods: The study was carried out in a non-impacted reservoir (NIR) and in another reservoir (IR) that is impacted by discharges of aquaculture effluents, and lasted for nine months. In each of the reservoirs, we installed four experimental units containing 10 ramets of S. molesta. Monthly, we measured limnological variables of the water and the biomass of S. molesta in both reservoirs; Results: The temperature, turbidity, electrical conductivity, alkalinity, chlorophyll-a, total Kjeldahl nitrogen, and total phosphorus were higher in the IR in all the collection months. At the end of the experiment, the concentrations of total nitrogen and phosphorus in the biomass of S. molesta from the IR were higher than those in plants from the NIR. The estimated support capacity (K) for S. molesta in the NIR was 3.0 ± 0.7 g DM.m-2 and in the IR was 37.4 ± 2.4 g DM.m-2 ; Conclusions: It was concluded that the discharge of aquaculture effluent modifies the limnological characteristics of the water of the receiving reservoir, and that the growth of Salvinia molesta is favored by the aquaculture effluent, because of the increases in the concentrations of nitrogen and phosphorus in the water.
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