Intervention Options to Accelerate Ecosystem Recovery From Coastal Eutrophication

Abstract

Three decades following the onset of efforts to revert widespread eutrophication of coastal ecosystems, evidence of improvement of ecosystem status is growing. However, cumulative pressures have developed in parallel to eutrophication, including those associated with climate change, such as warming, deoxygenation, ocean acidification and increased runoff. These additional pressures risk countering efforts to mitigate eutrophication and arrest coastal ecosystems in a state of eutrophication despite the efforts and significant resources already invested to revert coastal eutrophication. Here we argue that the time has arrived for a broader, more comprehensive approach to intervening to control eutrophication. Options for interventions include multiple levers controlling major pathways of nutrient budgets of coastal ecosystems, i.e., nutrient inputs, which is the intervention most commonly deployed, nutrient export, sequestration in sediments, and emissions of nitrogen to the atmosphere as N 2 gas (denitrification). The levers involve local-scale hydrological engineering to increase flushing and nutrient export from (semi)enclosed coastal systems, ecological engineering such as sustainable aquaculture of seaweeds and mussels to enhance nutrient export and restoration of benthic habitats to increase sequestration in sediments as well as denitrification, and geo-engineering approaches including, with much precaution, aluminum injections in sediments. These proposed supplementary management levers to reduce eutrophication involve ecosystem-scale intervention and should be complemented with policy actions to protect benthic ecosystem components.

Rebuilding marine life

“…Removing pollution is a basal recovery wedge for seagrass meadows, coral reefs, and kelp forests ( Table 1). Three decades of efforts to abate coastal eutrophication have provided valuable knowledge on how actionable science can guide restoration successes 41,42,111 .…”

“…Additional interventions (e.g., restoring hydrological flows or rebuilding oyster reefs), can catalyze additional removal of nutrients while improving biodiversity 111 . Seaweed aquaculture can help to alleviate eutrophication and reduce hypoxia 111,112 . Nutrient reduction has the additional benefit of locally reducing coastal acidification and hypoxia directly and indirectly through the recovery of seagrass meadows.…”

Barriers and Bridges in Abating Coastal Eutrophication

“…Because of compounding pressures that accompanied the eutrophication of a coastal ecosystem, abatement of nutrient loading to the targeted level might not achieve the intended rehabilitation of the ecosystem. Intervention within the coastal system may be an option, including enhancing denitrification in wetlands, seagrass beds and restored oyster reefs; enhancing sediment sequestration; hydrological engineering to increase flushing and nutrient export from relatively enclosed water bodies; and seaweed or shellfish aquaculture (Duarte and Krause-Jensen, 2018). Of course, precaution should be used to avoid unintended or undesirable consequences.…”

The role of microphytobenthos in soft‐sediment ecological networks and their contribution to the delivery of multiple ecosystem services

“…As an ecosystem becomes more eutrophic, the permanent removal of nitrogen by denitrification becomes an increasingly fundamental ES provided by coastal sediments (Duarte & Krause‐Jensen, ). This step in the natural nitrogen cycle can at times remove up to 50% of reactive nitrogen in estuarine systems (Galloway et al, ).…”