Reducing marine eutrophication may require a paradigmatic change

Abstract

Marine eutrophication in the North-East Atlantic (NEA) strongly relies on nutrient enrichment at the river outlets, which is linked to human activities and land use in the watersheds. The question is whether human society can reduce its nutrient emissions by changing land use without compromising food security. A new version of Riverstrahler model (pyNuts-Riverstrahler) was designed to estimate the point and diffuse nutrient emissions (N, P, Si) to the rivers depending on land use in the watersheds across a large domain (Western Europe agro-food systems, waste water treatment). The loads from the river model have been used as inputs to three marine ecological models (PCOMS, ECO-MARS3D, MIRO&CO) covering together a large part of the NEA from the Iberian shelf to the Southern North Sea. The modelling of the land-ocean continuum allowed quantifying the impact of changes in land use on marine eutrophication. Pristine conditions were tested to scale the current eutrophication with respect to a "natural background" (sensu WFD), i.e. forested watersheds without any anthropogenic impact. Three scenarios representing potential management options were also tested to propose future perspectives in mitigating eutrophication. This study shows that a significant decrease in nitrogen fluxes from land to sea is possible by adapting human activities in the watersheds, preventing part of the eutrophication symptoms in the NEA rivers and adjacent coastal zones. It is also shown that any significant achievement in that direction would very likely require paradigmatic changes at social, economic and agricultural levels. This requires reshaping the connections between crop production and livestock farming, and between agriculture and local human food consumption. It also involves cultural changes such as less waste production and a shift towards lower-impact and healthier diets where half of the animal products consumption is replaced by vegetal proteins consumption, known as a demitarian diet (http://www.nine-esf.org/node/281/index.html).

Barriers and Bridges in Abating Coastal Eutrophication

“…The ineffectiveness or inertia of present measures for reducing agricultural nutrient losses has also prompted use of these models to explore whether the eutrophication abatement goals of the EU's North-East Atlantic Ocean goals are achievable. Linking marine ecosystem models with outputs from a watershed model, Desmit et al (2018) concluded that decreases in nitrogen fluxes from land sufficient to prevent eutrophication symptoms could not be achieved by implementing wastewater treatment and conventional good agricultural practices, alone. Achieving effective nutrient load reductions would likely entail substantial social, economic and agricultural changes that reshape connections between crop production and livestock farming, and between agricultural and local human food consumption.…”

Long-Term Dynamic in Nutrients, Chlorophyll a, and Water Quality Parameters in a Coastal Lagoon During a Process of Eutrophication for Decades, a Sudden Break and a Relatively Rapid Recovery

“…It is a process that, beyond causing contamination by nutrients or an increase of organic matter supply which enhance primary production of the ecosystem (European Environment Agency [EEA], 2001), represents a fundamental change in the energetic base of the same (Nixon, 2009). This may propagate through the system in various ways and produce a great variety of changes in the structure and dynamic of the ecosystem (Likens, 1972;Nixon, 1995Nixon, , 2009Gamito et al, 2005;Ferreira et al, 2011;Desmit et al, 2018).…”

Changes in chlorophyll concentration and phenology in the North Sea in relation to de‐eutrophication and sea surface warming

“…The North Sea is subject to relatively high anthropogenic riverine loads of nitrogen (N) and phosphorus (P) (Lancelot et al ; Jickells ; Brion et al ) with an additional significant atmospheric input of nitrogen (Troost et al ): 10% to 30% of the nitrogen in the Southern North Sea originates from the atmosphere (Dulière et al ). This drives intense phytoplankton blooms with large phytoplankton biomass accumulation (usually expressed as chlorophyll [Chl]) in most coastal zones between March and October (Cadée and Hegeman ; Rousseau et al ; Desmit et al , ; OSPAR_Commission ). Depending on the morphology and hydrology of the receiving basin and on phytoplankton community structure, eutrophication may lead to different symptoms such as foam events (caused by blooms of the colonial haptophyte Phaeocystis), hypoxia or even dead zones, nutrient imbalances allowing toxic species occurrence, inhibition of zooplankton egg production, and/or changes in community structure (Jickells ; Rousseau et al ; Colijn et al ; Daro et al ; Philippart et al ), and these phenomena can be further complicated by climate change (Painting et al ).…”