Fluxes and mass balances of nutrients in a semi-intensive shrimp farm in north-western Mexico

Fluxes of suspended solids, chlorophyll a and nutrients (phosphorus, nitrate, nitrite and ammonia) were estimated in a semi-intensive shrimp farm in north-west Mexico for two consecutive cycles of production encompassing both the dry and wet seasons. A mass balance model was developed for nitrogen and phosphorus and fluxes estimated included shrimp feed, fertilization, shrimp stocked, harvest, macrofauna associated, water exchange, filling and drainage. Of the total nitrogen and phosphorus input to the ponds, 35.5% and 6.1% were recovered in 1822 kg ha−1 of shrimp harvested. Volatilization of ammonia and adsorption by sediments of phosphorus constituted 27.4% and 63.5%, respectively; the estimated environmental losses of nitrogen and phosphorus per t of shrimp produced were 28.6 kg and 4.6 kg, respectively. Assuming that all the shrimp farms in Sinaloa (Mexico), operate according to the model, the farms could represent a load corresponding to the untreated sewage generated by 56 200-192 750 and 43 500-149 170 people in terms of nitrogen and phosphorus discharged annually.