Nutrient and microbial dynamics in high-intensity, zero-exchange shrimp ponds in Belize

Abstract

Microbial and phytoplankton processes, and their effect on water quality were examined over a 3 week period in 5 high-intensity (120 animals m -2 ) shrimp (Litopenaeus vannamei) ponds of varying crop ages at Belize Aquaculture Ltd. (BAL) in central America. These ponds were characterized by zero water exchange throughout the crop, plastic lining and high aeration rates. Nitrogen (N) and organic carbon (C) inputs, in the form of fishmeal-based feed, grain-based feed and molasses, resulted in high concentrations of dissolved organic and inorganic N (2.29-5.56 and 0.17-10.66 mg l -1 respectively) and dissolved organic C (14.20-48.10 mg l -1 ).Phosphate levels were also high, ranging from 0.07 to 1.17 mg l -1 . The high nutrient concentrations promoted the growth of bacteria, phytoplankton (mostly autotrophic flagellates) and protozoa. Up to 40% of the bacteria were associated with flocculated matter. However, bacterial numbers and oxygen (O 2 ) consumption in the water column did not appear to increase with crop age. This may be due to a reduction in the C:N ratio below the optimum for bacterial growth. Up to 22% of the O 2 consumption was due to nitrification and there was some indication of lowering of total ammoniacal N (TAN) concentrations and an increase in nitrite and nitrate levels in older crops. Both phytoplankton and bacteria were responsible for high rates of ammonium uptake. In ponds with high nitrate concentrations, nitrate uptake rates were also high. Phytoplankton productivity remained high irrespective of crop age and ponds fluctuated between net O 2 production (autotrophy) and net O 2 consumption (heterotrophy) irrespective of crop age. This reflected the highly dynamic nature of the bacterial and phytoplankton populations with frequent blooms and crashes of individual phytoplankton species. The high mixing rates resulted in phytoplankton and other detritus remaining suspended in the water column. However, a small area of sludge (<2% of pond area) did accumulate containing a high N and C content, and high porewater TAN. This study showed that despite what is generally considered as poor water quality in the ponds, i.e. high nutrient concentrations, high and unstable phytoplankton numbers, and high bacterial numbers, shrimp production was high relative to conventional ponds. There appeared to be scope for increasing bacterial production in these systems by increasing the C:N ratio, and hence C availability for bacterial growth. However, it remains to be established which microbial processes are likely to be promoted, and if the benefits of this outweigh the costs.

An integrated fish–plankton aquaculture system in brackish water

“…Only sediment has to be removed from the zooplankton pond. This system is partly similar to those developed by Shnel et al (2002) for tilapia and Burford et al (2003) for shrimp.…”

Fertilização Orgânica Com Carbono No Cultivo Intensivo Em Viveiros Com Sistema De Bioflocos Do Camarão Branco Litopenaeus Vannamei

“…Entretanto, um dos maiores problemas destes sistemas é a deterioração da qualidade da água, devido ao acúmulo de compostos nitrogenados tais como a amônia (NH3+-NH4+), nitrito (NO2-) e nitrato (NO3-) (Colt & Armstrong 1981). Este problema gera preocupação quanto a sustentabilidade ecológica devido a descarga de efluentes ricos em nutrientes nas águas costeiras (Naylor et al 2000;Burford et al 2003), obrigando um maior controle sobre a biossegurança e tratamento dos efluentes gerados nestes sistemas de cultivo (Tacon et al 2002). Diante deste contexto, tornam-se necessárias mudanças nas estratégias de manejo para que a qualidade da água dos cultivos possa ser mantida em boas condições e redução de possíveis impactos ambientais.…”

“…Portanto, os benefícios ao meio ambiente são consideráveis quando comparados aos do sistema de produção de camarões tradicional (semi-intensivo), com aproveitamento mais eficiente no uso da água e da terra (Boyd & Clay 2002). Projetos pilotos realizados em uma fazenda comercial em Belize (Burford et al 2003;Boyd & Clay 2002), nos Estados Unidos pelo Waddell Mariculture Center (Wasielesky et al 2006a;Browdy et al 2001) e na Estação Marinha de Aquicultura da Universidade Federal do Rio Grande (Wasielesky et al 2006b, Emerenciano et al 2007, Ballester et al 2009Krumennauer 2011) (1987) No tratamento com fertilização de carbono não foi feita a renovação de água, apenas a reposição da água perdida por evaporação, aproximadamente 10% do volume total.…”

Remoção de compostos nitrogenados e fosfatados de efluentes por meio de reator anaeróbico com fluxo ascendente

“…Com o aumento da população bacteriana, ocorre a formação de macroagregados ou flocos, constituídos principalmente por bactérias, microalgas, partículas orgânicas e inorgânicas, protozoários e outros microrganismos (Burford et al, 2003;Balcázar et al, 2006). As trocas limitadas de água proporcionam aos sistemas de cultivo a redução ou a eliminação de infecções microbianas na água de cultivo, reduzem Em cultivos do tipo heterotrófico, depois de seguidos ciclos de cultivo, a água reaproveitada não tem mais condições de uso.…”