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Guest post: How the Japanese earthquake may drastically impact freshwater ecosystems

April 4, 2011

Image: Dr. Toshiaki Mizuno

This week’s guest post is by Dr. Toshiaki Mizuno, a freshwater ecologist who recently worked for WWF Japan’s Freshwater Programme.  Dr Mizuno discusses the potential impacts of radioactive and chemical contaminants resulting from last month’s earthquake and tsunami on Japanese freshwater ecosystems, citing the unfortunate timing of the disaster, which coincided with the spawning season of many freshwater species.  As a result, it is likely that many of the impacts of the earthquake on freshwater ecosystems will be long-lasting and unpredictable.

Let us know your thoughts by adding your voice to the discussion in the comments box below.


Fig 1: The earthquake epicentre

The impact of one of the biggest earthquakes (Magnitude 9.0) on record suddenly occurred off the coast of north-eastern Japan on the 11th March at 14:46 local time. Over 16,000 buildings were damaged all over Tohoku and Kanto area in north-eastern Japan, including the metropolitan area of Tokyo, around 400km south-west of the epicentre (Fig.1). The earthquake triggered a huge, recurring tsunami, starting 15 minutes after initial impact. The 5-20 metre high waves destroyed buildings, roads and other infrastructure along the Pacific coastline of Japan, and triggered the spread of radioactive contaminants as a result of damage to the Fukushima nuclear power plant, near the Abukuma Highlands.

Issue 1: Radioactive contaminants impact the spawning season of freshwater species

The Abukuma Highlands. Image: wikipedia

The Abukuma Highlands area is one of the most famous examples of traditional, biodiverse Japanese landscape.  The landscape consists of three key elements: small stream and ponds, paddy fields and coppice woods. The area is rich in freshwater biodiversity, with 15 amphibian and 74 freshwater fish species documented.  Of these, 9 amphibian and 7 fish species are endemic, and 7 amphibian species and 18 freshwater fish are listed as endangered by both the local red list (compiled by the Ministry of Environment of Japan and Fukushima Prefecture), including the Forest Green Tree Frog (Rhacophorus arboreus), and the Tohoku Salamander (Hynobius lichenatus).  As such, these freshwater ecosystems are of great conservation importance.

Radioactive contaminants, spread from the Fukushima nuclear power plant impacted the most vulnerable freshwater species. Even worse, the disaster occurred when many freshwater creatures were spawning.  This spawning largely takes place in the ponds and slow streams where radioactive substances are likely to settle. As a result, we could predict that the reproductive cycle of many freshwater species will be seriously damaged by the effects of water-borne radioactive contaminants.  Conservation initiatives which monitor and manage the potential impacts of radiation on freshwater species should therefore be a high priority for the immediate future.

Issue 2: The effect of chemical contaminants and high-salinity water on freshwater ecosystems

Fig 2: The mouth of the Kitakami River

Sendai Shiogama port and Ishinomaki port are the largest ports in the Tohoku region of northern Japan, on the mouth of the Kitakami River (Fig.2), and home to many chemical industries.

The Kitakami River is the fourth largest river basin in Japan (length 249km, basin area 10150km2), containing rich freshwater biodiversity including salmonid fish (e.g. Pacific or chum salmon: Oncorhynchus keta, and Masou or Japanese salmon Oncorhynchus masou masou), Ayu (Plecoglossus altivelis altivelis) and Shijimi clam (Corbicula japonica).

The masu or Japanese salmon. Image: Kim IS,

The destructive impact of tsunami waves on port buildings released chemical materials that spread throughout the mouth of Kitakmi River. The power of the incoming waves reversed river flow direction for 50km upstream, bringing chemical contaminants and high-salinity water to inland Kitakami River. As in the Abukuma Highlands, the timing of the disaster meant that this contaminated water is likely to have severely affected the spawning cycle of many freshwater fish. The chemical contaminants will also have potentially adverse effects for the migratory lifecycles of amphidromous fish such as the salmon and Ayu.

The need for urgent research into the effects of the earthquake on Japanese freshwater ecosystems

Paddy fields liquified by the earthquake. Image: Dr. Toshiaki Mizuno

The impacts of the earthquake and tsunami have been so catastrophic and wide-ranging that there has – as yet – been little or no research into the effects on freshwater ecosystems.  This article has discussed the potential impacts of radioactive and chemical contamination of freshwater ecosystems.  However, it’s clear that these impacts are uncertain and not fully understood.  In addition to the impacts discussed in this article, the earthquake has caused the liquefaction of paddy fields , damaged canals and many other effects on freshwater systems which may take time to become fully apparent. As a result, we must urgently begin investigating the effects on Japanese freshwater biodiversity and ecosystems by the tremendous impacts of the earthquake and tsunami.

Dr. Toshiaki Mizuno


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