Land-Based Salmon Farms Degrade Natural Waters With Dissolved Organic Materials Interview with:

Dr. Norbert Kamjunke Helmholtz-Centre for Environmental Research UFZ Department of River Ecology Magdeburg, Germany

Dr. Kamjunke

Dr. Norbert Kamjunke
Helmholtz-Centre for Environmental Research UFZ
Department of River Ecology
Magdeburg, Germany What is the background for this study?

Response: Aquacultures are of great importance worldwide but pollute pristine headwater streams, lakes, and estuaries.

Chilean salmon production is economically important, contributing ~25% of the worldwide salmon yield
(Chile ranks second of the world’s salmon-producing countries). Salmon
farming has continuously increased in recent decades; the annual
salmonid production in Chile was 820,000 tons in 2012, representing a
value of 4.9 billion USD (32% of the total worldwide value of salmonid
production). Small salmon are reared in land-based aquacultures supplied
with stream water, whereas mid-sized fish are grown in cages in lakes
and adult fish in cages along the coast. The effluents from land-based
aquaculture pollute pristine streams with nutrients, antibiotics and
organic carbon, resulting in oxygen depletion and negative consequences
for the abundance and biodiversity of stream organisms. While
aquacultures have recently started to remove suspended matter from waste
water using sedimentation basins and rotating drum filters, dissolved
components are still discharged untreated. Nutrients and dissolved
organic matter (DOM) originating from the leaching of remaining food
pellets, fish faeces and fish excretions are major components released
by aquacultures. One aquaculture in northern Patagonia was estimated to
release DOM amounting to 21% of the carbon applied as feed and 76% of
the annual fish production. What are the main findings?
Response: We performed a detailed molecular level characterization of aquaculture
dissolved organic matter quality and its bacterial degradation using four salmon aquacultures  in Chile. Fluorescence measurements, ultrahigh-resolution mass
spectrometry, and nuclear magnetic resonance spectroscopy of the DOM
revealed specific and extensive molecular alterations caused by
aquacultures. Aquacultures released large quantities of readily
bioavailable metabolites (primarily carbohydrates and peptides/proteins,
and lipids), causing the organic matter downstream of all the
investigated aquacultures to deviate strongly from the highly processed,
polydisperse and molecularly heterogeneous DOM found in pristine rivers.
The present study is the most detailed investigation of riverine DOM
quality change due to aquaculture.

The benthic algal biovolume decreased and the bacterial biovolume and
production increased downstream of the aquacultures, shifting stream
ecosystems to a more heterotrophic state and thus impairing the
ecosystem health. The bacterial dissolved  organic matter degradation rates explain the
attenuation of aquaculture DOM within the subsequent stream reaches. What should readers take away from your report?

Response: The knowledge of bacterial dissolved organic matter degradation may help to define emission thresholds for DOM to protect sensitive stream ecosystems and to design
appropriate reactors for the treatment of aquaculture effluent DOM.

The  degradation rates measured in this study might be used to calculate the
dimensions of percolated biological filters and chains of waste water
treatment ponds. What recommendations do you have for future research as a result of this study?

Response: Further studies should investigate the effect of specific pollutants on
stream ecosystems and the duration and river distance necessary for
their degradation.

We measured dissolved  organic matter degradation during base flow
conditions only. At higher discharge rates during other seasons (autumn,
winter), we would expect a lower concentration of aquaculture DOM in the
streams due to higher dilution and a longer distance downstream of the
effluent that would be necessary for degradation due to the higher flow
velocity. In addition, the lower water temperature during autumn and
winter would further decrease bacterial activity. Is there anything else you would like to add?

Response: We do not consider it advisable to install any further aquacultures on
Chilean rivers. The authorities have already imposed a moratorium on new
salmon farms in the country’s lakes. Operators are now considering the
option of moving the farming of medium-sized salmon from the lakes to
the rivers. However, these aquacultures would work with higher fish
biomasses than those rearing younger fish and would increase the pollution. Thank you for your contribution to the community.


Land-based salmon aquacultures change the quality and bacterial degradation of riverine dissolved organic matter
Norbert Kamjunke,Jorge NimptschMourad HarirPeter HerzsprungPhilippe Schmitt-KopplinThomas R. NeuDaniel GraeberSebastian OsorioJose ValenzuelaJuan Carlos ReyesStefan Woelfl & Norbert Hertkorn
Scientific Reports 7, Article number: 43739 (2017)

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