Effects of rainfall on water quality in six sequentially disposed fishponds with continuous water flow

Abstract

An investigation was carried out during the rainy period in six semi-intensive production fish ponds in which water flowed from one pond to another without undergoing any treatment. Eight sampling sites were assigned at pond outlets during the rainy period (December-February). Lowest and highest physical and chemical parameters of water occurred in pond P 1 (a site near the springs) and in pond P 4 (a critical site that received allochthonous material from the other ponds and also from frog culture ponds), respectively. Pond sequential layout caused concentration of nutrients, chlorophyll-a and conductivity. Seasonal rains increased the water flow in the ponds and, consequently, silted more particles and other dissolved material from one fish pond to another. Silting increased limnological variables from P 3 to P 6 . Although results suggest that during the period under analysis, rainfall affected positively the ponds' water quality and since the analyzed systems have been aligned in a sequential layout with constant water flow from fish ponds and parallel tanks without any previous treatment, care has to be taken so that an increase in rain-induced water flow does not have a contrary effect in the fish ponds investigated.Keywords: water exchange, fishpond, limnology, water quality, rainfall.Efeito da chuva na qualidade da água em seis viveiros de piscicultura com fluxo contínuo de água em disposição seqüencial ResumoO estudo foi efetuado durante o período de chuva (dezembro-fevereiro) em seis viveiros de produção semi-intensiva de peixes, a fim de avaliar o efeito da chuva na qualidade da água de viveiros que apresentam fluxo contínuo de água, a qual é passada de um viveiro para outro sem tratamento prévio. Foram amostrados oito pontos de coleta nas saídas dos viveiros. O viveiro P 1 (próximo à nascente) apresentou as menores concentrações físicas e químicas da água e as maiores no viveiro P 4 (considerado um ponto crítico recebendo material alóctone proveniente de outros viveiros e do escoamento do setor de criação de rãs). A disposição seqüencial dos viveiros estudados promoveu aumento nas concentrações dos nutrientes, clorofila-a e condutividade. As chuvas características desta época do ano aumentaram o fluxo de água nos viveiros e conseqüentemente, carreando material particulado e dissolvido de um viveiro para outro e, promovendo um aumento das variáveis limnológicas em direção do P 3 ao P 6 . Os resultados sugerem que a chuva no período de estudo afetou positivamente a qualidade da água dos viveiros estudados, porém, como os sistemas analisados estão dispostos em distribuição seqüencial e escoamento constante da água de viveiros e tanques paralelos sem tratamento prévio, cuidados devem ser averiguados para que o aumento do fluxo de água provocado pelas chuvas não tenha efeito adverso nos viveiros estudados.Palavras-chave: viveiros, limnologia, qualidade da água, fluxo contínuo, chuva.

Water quality in six sequentially disposed fishponds with continuous water flow

“…Two-way nested ANOVA was applied to physical and chemical parameters in order to compare sites (P 1 -P 6 and W) and periods (May, October and January) (SOKAL; ROHLF, 1981). Significance level was p < 0.05.…”

“…Total phosphorus is removed primarily by cation exchange reactions with the substrate and algae community, even though climate factors such as heavy rainfall (January) may affect the availability of this nutrient in the water (SIPAÚBA-TAVARES et al, 2007). Although no significant differences were observed (p > 0.05) between periods with regard to chlorophyll-a, it tended to increase as from pond P 3 (p < 0.05).…”

“…As a rule, shallow artificial systems with a continuous water flow may occasionally cause small variations in pH and alkalinity rates (SIPAÚBA-TAVARES et al, 1998). In fishponds, CO 2 and H + from nitrifying bacteria and other acids produced by the organism decrease pH rate (SIPAÚBA-TAVARES et al, 2003).…”

“…The fishponds are environments with great management requirements. In fact, such conductivity is associated with accumulative effect of the current caused by the water's continuous flow and consequently to the short residence time (SIPAÚBA-TAVARES et al, 2007). Currently higher rates of conductivity were reported in fishponds (P 4 -P 5 ) which are directly affected by organic and inorganic, as occurred in the case of P 4 which receives water originating from ponds P 1 , P 2 , and P 3 and from the frog culture, whose daily wash causes a great amount of organic matter being introduced into the pond.…”

“…However, depending on flow rate and pond depth, continuous water flow may present a concentrating or diluting effect on the materials contained in the water (SIPAÚBA-TAVARES et al, 2003).…”