Nutrient-Balance Modeling as a Tool for Environmental Management in Aquaculture: The Case of Trout Farming in France

Abstract

The control and prevention of nutrient pollution from fish farming plays an essential role in the French regulatory framework. Assessing nutrient emissions from fish farms is important in terms of farm authorization, taxation, and monitoring. Currently employed strategies involve both water sampling and empirical modeling. This article reports the work and outcomes of an expert panel that evaluated existing methodologies and their possible alternatives. The development and evaluation of a nutrient-balance approach was assessed as a potential alternative to currently used methodologies. A previously described nutrient-balance model was suggested and parameterized using expert choice, and its validity and applicability were assessed. The results stress that the nutrient-balance model provides more robust and relatively conservative waste estimates compared to the currently used methodologies. Sensitivity of the approach to the uneven data quality available at farm level, difficulties of on-farm measurements, as well as model requirements and limitations are discussed.

Waste loading into a regulated stream from land-based trout farms

“…Papatryphon et al (2005) also suggested that nutritional mass-balance modeling should be the preferred method of environmental impact assessments for predicting nutrient emissions in various forms. Our study showed that a nutritional mass-balance method based on very simple inputs that are easily accessible, such as average annual feed use and fish production, as well as feed specifications, is capable of providing reliable estimations for suspended solids and nutrient loads, without seasonal data.…”

“…Because of the above-mentioned temporal variations in solids transport and farm management, estimating quantitative waste outputs by hydrological or nutritional methods may lead to erroneous loading rates (Papatryphon et al 2005, Sindilariu 2007, Roque d 'Orbcastel et al 2008). However, Papatryphon et al (2005) suggested that, considering the nature of the nutrient emissions, the potential measurement error, and the variability associated with the environment and the farms, the differences between predictions and measurements may not seem important.…”

“…The nutritional method was based on data provided by feed manufacturers, farm records, and literature (Papatryphon et al 2005, Roque d'Orbcastel et al 2008 (Table 1). Although there could be seasonal variations in farm parameters such as fish stocks and feeding rates, we used the average annual feed conversion based on interviews with the farmers to estimate the average daily feeding rate.…”

“…The hydrological method is based on the measurement of selected indicators between the inlet and the outlet of fish farms by taking the flow rate into consideration (Roque d'Orbcastel et al 2008, Aubin et al 2011). However, there may be uncertainties arising from changing farm practices and sampling methodologies, which can result in temporal variations in the suspended solids and nutrient concentrations in the effluent (Cho et al 1991, Papatryphon et al 2005. This method may be required for frequent or continuous monitoring of inflow and outflow water quality to assure data precision and accuracy (Kelly et al 1996).…”

Estimating aquatic phosphorus concentrations 30 metres down-current from a rainbow trout cage array

“…There has been some success applying a similar approach to estimate nutrient concentrations in rivers that receive effluent discharges from land-based rainbow trout farms. 13 However, while nutritional mass balance models are reasonably well developed, 13,14 determining water volume flushed through fish cages can be difficult, due to the affects of cages on hydrodynamics. Drag is produced as water flows through the cage netting and around cage structures, 15,16 thereby reducing the flow velocity and increasing turbulence in adjacent waters.…”