27 October 2016 – What happens on land affects our oceans. For example, when rainfall washes fertilizers from agricultural land into rivers, they end up in the sea, where they can cause harm to fish and other marine organisms.
Fertilizers contain nutrients such as nitrogen and phosphorus. Concentrations of such nutrients cause environmental damage on land and at sea.
Excess nutrients in the marine environment can lead to a process called eutrophication, where the nutrients nourish the growth of algae; when the algal growth becomes excessive and dies it robs the water column of oxygen, affecting the health of the marine environment.
New research, http://bit.ly/2eUP4jh, by the University of Adelaide, in a study of kelp forests and seagrass beds in South Australia's St Vincent's Gulf, suggests that nutrient pollution from adjacent cities, towns and agricultural land, is changing sounds made by marine life, and potentially upsetting navigational cues for fish and other sea creatures.
Published online in the journal Landscape Ecology, the research found that marine ecosystems ̶ degraded by eutrophication caused by run-off from adjacent land ̶ are “more silent” than healthier comparable ecosystems.
The marine soundscape comes largely from the snapping of shrimps, but also the rasping of sea urchins and fish vocalizations.
“We know that sound is very important for some species of fish and invertebrates to find sheltering habitats in reefs and seagrass beds. The demise of biological sounds is likely to have negative impacts on the replenishment of fish populations,” says study leader Associate Professor Ivan Nagelkerken, in the University of Adelaide's Environment Institute.
Climate change is compounding the problem. As oceans warm due to climate change, it renders them more conducive to growth of algae associated with excess nutrient loading. Coastal ecosystems, and the livelihoods of those that depend on them, will be most affected. Ocean acidification, another consequence of climate change where excess carbon dioxide is being absorbed by oceans, further weakens marine ecosystems.
The link to agriculture
In many areas across the globe, a large proportion of nutrient pollution originates from agricultural crop and livestock production. The potential for pollution is exacerbated where fertilizers are not used efficiently, and excess “unused” fertilizers are washed away to the environment. Other poor practices, such as disposal of untreated effluent from livestock operations into waterways, are a big problem. Nutrient pollution also originates from urban wastewater that is discharged into waterways and the marine environment.
“Our crop and livestock farmers need to be aware that what they do, or do not do, can have dire impacts on downstream ecosystems,” says Christopher Cox, a programme officer with UN Environment’s Ecosystems Division.
For further information on the Global Programme of Action for the Protection of the Marine, see UN Environment Publication website.
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