Impact of maintenance of Macrobrachium rosenbergii De Man, 1879 (Crustacea, Decapoda, Palaemonidae) broodstock on the water used in culture ponds

Aquaculture production generates social and economic benefits, but can also cause environmental impacts. The objectives of this study were: a) to characterise the impacts caused by the maintenance of broodstock of the giant river prawn (Macrobrachium rosenbergii) on the physical and chemical characteristics of the water used in culture ponds, and b) to evaluate the relationship between the biomass of the prawns and the impact of culture on the water used in the ponds. Between January and December 2004, we determined, monthly, the biomass of M. rosenbergii by means of biometrics, and the physical and chemical variables of the supply and effluent water from a pond used to maintain breeding stock. The results showed that the effluent water had higher contents of chlorophyll-a, suspended particulate matter (SPM), pH, dissolved oxygen, total Kjeldahl nitrogen (TKN) and dissolved Kjeldahl nitrogen (DKN), inorganic nitrogen (IN), total (TP) and dissolved phosphorus (DP), and P-orthophosphate than the supply water. The highest biomass of M. rosenbergii occurred in April (127.0 g.m-2) and the lowest in August (71.5 g.m-2), and there were positive linear correlations between the biomass of the prawns and the intensity of the increases in TKN, DKN, IN, TP, and DP of the water used in the pond. The maintenance of broodstock of M. rosenbergii increased the chlorophyll-a, SPM, nitrogen, and phosphorus contents of the water in the pond. Additionally, the increase in the biomass of the prawns intensifies the export of nitrogen and phosphorus from the pond in the effluent

Impact of maintenance of Macrobrachium rosenbergii De Man, 1879 (Crustacea, Decapoda, Palaemonidae) broodstock on the water used in culture ponds

Aquaculture production generates social and economic benefits, but can also cause environmental impacts. The objectives of this study were: a) to characterise the impacts caused by the maintenance of broodstock of the giant river prawn (Macrobrachium rosenbergii) on the physical and chemical characteristics of the water used in culture ponds, and b) to evaluate the relationship between the biomass of the prawns and the impact of culture on the water used in the ponds. Between January and December 2004, we determined, monthly, the biomass of M. rosenbergii by means of biometrics, and the physical and chemical variables of the supply and effluent water from a pond used to maintain breeding stock. The results showed that the effluent water had higher contents of chlorophyll-a, suspended particulate matter (SPM), pH, dissolved oxygen, total Kjeldahl nitrogen (TKN) and dissolved Kjeldahl nitrogen (DKN), inorganic nitrogen (IN), total (TP) and dissolved phosphorus (DP), and P-orthophosphate than the supply water. The highest biomass of M. rosenbergii occurred in April (127.0 g.m-2) and the lowest in August (71.5 g.m-2), and there were positive linear correlations between the biomass of the prawns and the intensity of the increases in TKN, DKN, IN, TP, and DP of the water used in the pond. The maintenance of broodstock of M. rosenbergii increased the chlorophyll-a, SPM, nitrogen, and phosphorus contents of the water in the pond. Additionally, the increase in the biomass of the prawns intensifies the export of nitrogen and phosphorus from the pond in the effluent

Temporal variation of biomass and nutrient status of azolla filiculoides lam: (sal viniaceae) in a small shallow dystrophic lake

This study determined the temporal variation of the biomass and the concentrations of carbon, nitrogen and phosphorus in Azolla filiculoides Lam. in a small (0.5 ha) shallow dystrophic lake located in the city of Rio Grande (Rio Grande do Sul State, Brazil). Method: Sampling was conducted monthly between November 2000 and October 2001. The macrophytes were collected randomly in three replicates with a circular collector 0.3 m in diameter and subsequently washed with tap water and oven-dried at 60 °C for determination of the dry weight and the nutrient status (i.e., carbon, nitrogen and phosphorus). Primary productivity was estimated by the variation in biomass among successive samples. Results: A. filiculoides was present in the lake throughout the year and occupied between 50 and 80% of the surface area. The biomass values ranged from 34.2 g DW.m–2, recorded in May (autumn), to 170.9 g DW.m–2 in January (summer). The highest rate of primary productivity was 3.3 g DW.m–2.d–1, observed in June. The concentrations of carbon, nitrogen and phosphorus in the plant ranged between 403 and 551 g.kg–1, 13.4 and 25.7 g.kg–1 and 0.5 and 1.9 g.kg–1, respectively. The water N:P ratio ranged between 19:1 and 368:1. Conclusion: The coverage of the surface of the lake by A. filiculoides throughout the study period and the nutritional status of the plant demonstrate the importance of the cycling of nutrients by macrophytes in this aquatic environment. The higher N:P ratio in the water column, compared with other neighboring environments without macrophytes, shows that the enrichment of the lake may result from the biological N-fixation activity produced by A. filiculoides.Este estudo determinou a variação temporal da biomassa e as concentrações de carbono, nitrogênio e fósforo de Azolla filiculoides Lam., em um pequeno lago raso distrófico situado no município do Rio Grande (Rio Grande do Sul, Brasil). Método: As amostragens foram realizadas mensalmente no período entre novembro de 2000 e outubro de 2001. As macrófitas foram coletadas aleatoriamente em três repetições, utilizando-se coletor circular de 0,3 m de diâmetro e posteriormente lavadas com água corrente e secas em estufa 60 °C para determinação do peso seco e dos nutrientes: carbono, nitrogênio e fósforo. A produção primária foi estimada pela variação de biomassa entre coletas sucessivas. Resultados: A. filiculoides esteve presente no lago durante todo o ano, ocupando sempre entre 50 e 80% da superfície do lago. Os valores de biomassa variaram entre 34,2 g PS.m–2, registrado em maio (outono) e 170,9 g PS.m–2 em janeiro (verão). A maior taxa de produtividade primária foi 3,3 g PS.m–2.d–1 foi registrada em Junho. As concentrações de carbono, nitrogênio e fósforo na planta variaram entre: 403 e 551 g. kg–1, 13,4 e 25,7 g.kg–1 e 0,5 e 1,9 g.kg–1, respectivamente. Os valores da relação N:P na coluna de água variou entre 19:1 e 368:1. Conclusão: A cobertura da superfície do lago por A. filiculoides durante todo o período do estudo e o seu estado nutricional demonstram sua importância na ciclagem dos nutrientes neste ambiente aquático. A maior relação N:P na coluna de água quando comparada a outro ambiente próximo sem a presença desta macrófita, apoia a ideia de que A. filiculoides pode ser a responsável pelo enriquecimento do lago por meio da atividade de fixação biológica de nitrogênio