Using seaweeds as bioindicators to map nutrient zones of influence from fish farms and other sources

by Dr Thierry Chopin, University of New Brunswick, Canada

Fish farms release nutrients into the environment in either particulate organic or dissolved inorganic forms. Particulate nutrients generally settle onto the seafloor quickly and rarely disperse more than a few hundred meters.
 

Dissolved nutrients are excreted by fish directly in the water column and can represent significant proportions of these nutrients (for example, between 68 and 87% of nitrogen). However, much less is known about dissolved nutrients, their dispersion, assimilation and persistence within the marine environment.

Dissolved nutrients can be difficult to measure; their chemistry can be complex. In the case of dissolved inorganic nitrogen (DIN), it can be in the form of ammonium (NH4+), ammonia (NH3), nitrate (NO3-) or nitrite (NO2-).

Measuring dissolved nutrients through the analysis of water samples from highly dynamic waters, created by tides and currents and generally sought as dispersing sites by the aquaculture sector, can be a logistic nightmare, time consuming and expensive, due to the need for continual and repeated sampling. Moreover, some fractions, such as NH3 and NH4+, which can represent up to 90 percent of DIN, can be rapidly lost to the atmosphere through volatilisation and assimilation by other surrounding organisms. Consequently, nutrient enrichment, especially as short-lived pulses, can be difficult to detect. However, dilution and dispersion should not be considered the solution to nutrification of the environment.

Read more, HERE.

The Aquaculturists

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