Aquaculture has a sustainability problem

The increasing importance of aquaculture in fish production contributes to the shortage of the critical resource phosphorus and thereby endangers food security in the long term if no counter measures are taken. This is shown by a study just published in Nature Communications of a group of Imbalance-P researchers.

Phosphorus is an essential element for all forms of life on Earth. The rapid rise of human demand for food has quadrupled phosphorus inputs in form of fertilizers into the biosphere since the pre-industrial time. Due to the rapid exploitation of the finite phosphorus sources and inefficient use of P,  future food security is at risk. As a consequence, the European Union has included phosphorus into the list of 20 critical raw materials which for which supply security is at risk and economic importance is high in 2014. Regulations for phosphorus fertilizer use in agricultural production has lead to improvements in the use of phosphorus, but it’s use in fishery and aquaculture has not been considered yet. This should change, as a new study shows that fish production consumes substantial amounts of phosphorus at a very low efficiency: Globally, only roughly a quarter of the phosphorus that is used to raise fish is being harvest, while the remaining is being lost potentially causing harm in nearby ecosystems (e.g. biodiversity losses). “The phosphorus that enters rivers and ocean is lost as it is difficult to be recovered. Therefore, these losses must be minimized to ensure phosphorus is available for future generations.” says co-author Prof. Josep Penuelas, from CSIC-CREAF.

Finfish, crustaceans and mollusks (hereafter generalized as fish) are becoming more and more important as a protein source in the human diet: in 2013, 17% of all animal protein consumed by mankind originated from fishery and aquaculture. Whereas captured fish satisfy their phosphorus need from naturally occurring food source (e.g. other fish, plankton), aquaculture relies on phosphorus addition in form of fish food or fertilizer to enhance plant growth (for herbivory fish) to grow fish. As the share of fish originating from aquaculture is increasing, from less than 5% in the 1950s to roughly 50% in the 2010s, the originally landwards flow of phosphorus by fishery has reversed to loss of phosphorus from land in the form of fertilizer and feed additives. On average, about 80% of the added phosphorus in aquacultures is not being harvested, which poses a sustainability issue if no measures are taken to reduce this fraction.  “We estimated that harvested fraction of added phosphorus in aquaculture has to more than double by the year 2050 to allow a phosphorus sustainable fish production”, says Dr. Jordi Sardans, from CSIC-CREAF.

“Phosphorus is a non-renewable yet limited and vital nutrient for crops. We should start to think about how to recycle and reuse phosphorus in fish consumption to grow more crops, while minimise phosphorus we put into water especially for aquaculture” says Dr. Yuanyuan Huang, the leader of the study.

Huang, Y., Ciais, P., Goll, D.S. et al. The shift of phosphorus transfers in global fisheries and aquaculture. Nat Commun11, 355 (2020) doi:10.1038/s41467-019-14242-7

Link to the paper:

Greener springs are causing hotter, drier summers

For the first time, two phenomena that occur in different seasons are connected: the high temperatures advance and extend springs, so that the vegetation grows more intensely and absorbs more moisture from the soil. The consequence is much drier and warmer summers.

With climate change-induced warming bringing spring forward and extending the season’s duration, plants’ growth period is beginning earlier and lasting longer too. Green foliage is therefore taking more and more water from the ground, and the evaporation of that water intensifies moisture loss. The main consequences are longer, hotter, dryer summers and more frequent heatwaves in much of the Northern Hemisphere. Despite the two phenomena taking place in different seasons of the year, a study entitled Summer soil drying exacerbated by earlier spring greening of northern vegetation, published in the journal Science Advances, has shown that they are connected.

The study was led by Xu Lian from Peking University (China), and involved Josep Peñuelas, a CSIC researcher based at CREAF (Spain), as well as researchers from AustraliaBelgiumFranceGermany, the UK and the USA.

Primaveres més verdes provoquen estius més secs i calorosos

Analysing satellite and climate simulation data on the entire Northern Hemisphere between 1982 and 2011 enabled the scientists to link increased greening in spring with reduced soil moisture in summer, a finding that climate simulation computer models support. “The influence of early greening on soil dryness is more complex than we thought”, says Xu Lian. “This phenomenon causes water to be lost very rapidly by transmitting it into the atmosphere in large quantities”, he continues. “The water lost is then returned in the form of precipitation over the Earth though. We’ve shown that this mechanism mitigates water losses caused by greening; if it didn’t, the drying of the planet’s surface would be much more severe.”

According to Josep Peñuelas, the study highlights “a positive reaction that often goes unnoticed: an increase in greenhouse gas concentrations and the warming it entails are causing a shift in plant phenology towards earlier leafing, which is reducing soil moisture in summer and compounding the extreme summer temperatures for which global warming is directly responsible”.

A change in climate pattern

The effect of the situation in question is not uniform throughout the Northern Hemisphere. For example, central Siberia and certain European croplands are benefiting from a higher-than-usual rate of precipitation thanks to the evaporation of water to their west. The conclusion is that the evaporated water is taken over the Urals by air masses blown from west to east and then falls as rain on the aforementioned locations.

Greener springs are causing hotter, drier summers

Image: Lluís Comas

One of climate research’s main challenges is to explain what is behind the extreme situations we are experiencing nowadays, such as the recent droughts in northern latitudes. The interseasonal processes the study deals with “could be a factor in current extremes and can be expected to place additional pressure on soil moisture in the summer and terrestrial ecosystems as the climate changes”, remarks Chris Huntingford from the UK Centre for Ecology and Hydrology.

Among its numerous consequences, soil drying can raise local near-surface air temperatures and trigger and worsen heatwaves. On the basis of climate simulations, the study calculates that soil drying due to spring starting earlier could increase the number of extremely hot summer days by one per decade and push the maximum temperature up by 0.07°C per decade. Although these changes may seem relatively minor, the severity of the heatwaves likely to occur in four or five decades will underline just how significant they are.

Reference: Lian, X., Piao, S., Li, L.Z.X., Li, Y., Huntingford, C., Ciais, P., Cescatti, A., Janssens, I.A., Peñuelas, J., Buermann, W., Chen, A., Li, X., Myneni, R.B., Wang, X., Wang, Y., Yang, Y., Zeng, Z., Zhang, Y., McVicar, T.R. 2020. Summer soil drying exacerbated by earlier spring greening of northern vegetation. Science Advances 6 : eaax0255


Les primaveres més verdes estan provocant estius més secs i calorosos

Per primera vegada es connecten dos fenòmens que passen en estacions de l’any diferents: les altes temperatures avancen i allarguen la primavera, per tant la vegetació creix més intensament i absorbeix més humitat del sòl. La conseqüència és estius més secs i calorosos.

L’augment de temperatures que comporta el canvi climàtic fa avançar i allargar la primavera i, per tant, la vegetació comença a créixer abans i durant un període més llarg. Això provoca que les fulles verdes dels arbres extrauen cada vegada més aigua del sòl, que en evaporar-se accentua la pèrdua d’humitat. La principal conseqüència són estius més secs, llargs i calorosos, així com onades de calor més freqüents a gran part de l’hemisferi Nord. Si bé els dos fenòmens tenen lloc en estacions de l’any diferents, l’estudi Summer soil drying exacerbated by earlier spring greening of northern vegetation publicat a la revista científica Science Advances ha posat de manifest que estan connectats.

La recent investigació està dirigida pel professor Xu Lian de la Universitat de Pequín (Xina) i hi ha intervingut el professor Josep Peñuelas, investigador del CSIC al CREAF, juntament amb investigadors d’AlemanyaAustràliaBèlgica, els Estats UnitsFrança i el Regne Unit.

Primaveres més verdes provoquen estius més secs i calorosos

L’anàlisi de dades obtingudes per satèl·lit i amb simulacions climàtiques a tot l’hemisferi Nord des de 1982 fins a 2011 han permès vincular l’augment de la verdor de la primavera amb la disminució de la humitat del sòl a l’estiu. A més, es confirma que aquesta connexió pot ser replicada mitjançant models informàtics dissenyats per simular el sistema climàtic. En paraules del professor Xu Lian, autor principal de la recerca, “la influència de la verdor primerenca en la sequedat del sòl és més complexa del que es pensava. Aquest fenomen causa pèrdues d’aigua molt ràpides al transmetre’n una gran quantitat a l’atmosfera. Ara bé, l’aigua perduda es recupera com a precipitació posterior sobre la Terra. Hem demostrat que aquest mecanisme alleuja les pèrdues d’aigua que es produeixen amb el reverdiment, en cas contrari l’assecament de la superfície terrestre seria molt pitjor”.

Per al professor Josep Peñuelas, l’estudi “revela una reacció positiva que sovint passa inadvertida: un augment de les concentracions de gasos d’efecte hivernacle i l’escalfament associat causen una fenologia de la vegetació més primerenca que redueix la humitat del sòl a l’estiu i que, alhora, s’afegeix als extrems de calor estiuencs causats directament per l’escalfament global”.

Un canvi de patró climàtic

Ara bé, aquest efecte no es manté homogeni en tot l’hemisferi Nord. Per exemple, la Sibèria central i alguns terrenys de conreu d’Europa es beneficien d’un índex de precipitacions major de l’habitual, justament gràcies a l’evaporació en d’altres punts ubicats al seu Oest. La conclusió és que les masses d’aire que circulen d’Oest a Est passen els Monts Urals i precipiten l’aigua evaporada en aquestes zones.

Primaveres més verdes provoquen estius més secs i calorosos

Foto: Lluís Comas

Un dels principals reptes de la investigació climàtica és explicar què impulsa les situacions extremes actuals, com ara les recents sequeres de la latitud nord. Els processos interestacionals que apunta l’estudi “poden explicar en part els extrems actuals i es pot esperar que exerceixin una pressió addicional sobre la humitat del sòl a l’estiu i els ecosistemes terrestres a mesura que el clima canvia “, apunta el professor Chris Huntingford, del UK Centre for Ecology & Hidrology.

L’assecament del sòl pot tenir nombroses conseqüències, com ara elevar la temperatura de l’aire local prop de la superfície terrestre i desencadenar onades de calor o fer-les més severes. A partir de simulacions climàtiques, la investigació estima que la sequedat de la Terra a causa de l’avançament de la primavera pot allargar els estius extremadament calorosos de l’ordre d’un dia per dècada i augmentar la temperatura 0,07 °C també cada 10 anys. Si bé d’entrada semblen magnituds petites, en 4 o 5 dècades les onades de calor previstes poden ser tan fortes, que aquests petits increments passarien a ser molt rellevants.

Reference: Lian, X., Piao, S., Li, L.Z.X., Li, Y., Huntingford, C., Ciais, P., Cescatti, A., Janssens, I.A., Peñuelas, J., Buermann, W., Chen, A., Li, X., Myneni, R.B., Wang, X., Wang, Y., Yang, Y., Zeng, Z., Zhang, Y., McVicar, T.R. 2020. Summer soil drying exacerbated by earlier spring greening of northern vegetation. Science Advances 6 : eaax0255