6.Research on Conservation and Restoration of Coastal Ecosystems

Background and Objectives

The legal regulation system related to the coastal environment has recently shifted in line with the change in public concern. Bay Renaissance Projects have been established successively for Tokyo, Osaka, Ise, and Hiroshima Bays. The restoration goal of each bay seems to have shifted from that of a clean sea to that of a sea with high productivity and biodiversity. The idea is also introduced
in the “Act for the Promotion of Nature Restoration” enacted in FY 2002, and the draft report on “6th Total Load Pollution Control” submitted in 2005. Among several restoration options, construction of tidal flats and seaweed/seagrass beds as well as restoration of borrow pits, are appointed as the main target of restoration technologies to realize a coastal water environment with high productivity and biodiversity.
In light of this background, research on technology for conservation and restoration of coastal ecosystems as well as basic scientific studies on the structures and functions of ecosystems should be promoted as a restoration goal. To evaluate the effectiveness of each technology and to
select appropriate measures suitable for the purposes, development of an innovative ecological model for coastal waters is also needed.
The report published by UN Environment Program (UNEP) in 2009 demonstrates that coastal ecosystems vigorously absorb CO₂ and that conservation of coastal ecosystems such as seaweed/seagrass beds is extremely important to mitigate climate changes. The concept is focused with the term of “blue carbon”. However, the quantification of CO₂ absorption by coastal ecosystems remains unclear and developing methodology to promote CO₂ absorption is indispensable.

Research topics

We have conducted preliminary research in a variety of ecosystems to understand the structures and functions. By examining coastal ecosystems of tidal flats and seaweed beds, we are promoting research to pursue technology developments, which will achieve a healthy coastal environment through the construction and restoration of tidal flats as well as seaweed/seagrass beds. We are evaluating the effects of filling borrow pits with dredged sediments, which is a new promising method of beneficial use of dredged materials for coastal water restoration. We are incorporating bio-geophysical approaches, which are a novel idea for tidal flat ecosystem studies. The feeding behavior and food source of higher trophic level organisms such as migrating birds have been studied, because such animals are good indices of biodiversity. Including all these results, a next generation model for coastal ecosystem is to be formulated. In addition, we will suggest measures to promote CO₂ absorption by coastal ecosystems through field observation to understand the effectiveness.

Activities in FY 2010

In FY 2010, we promoted research on the relation between several bio-geophysical parameters such as suction and benthos activity in tidal flats as a part of studies on design and construction technologies of tidal flats with geotechnical approaches. We also performed a lab experiment on various benthos as well as conducted a field survey on the relation between geophysical dynamics and biological activities/distributions in natural tidal flats. We examined selection behavior and habitat distribution of multiple benthos in sediment environment as well.
Observations on the feeding behavior and food sources of sandpipers and plovers, which are the major migrating birds to tidal flats in Japan, were performed in FY 2010. Biofilms on the surface of sediments were identified as a major diet for various small shorebirds, providing us with novel evolutionary insight. In addition, fish gathering in tidal flats was also revealed to feed on biofilms.
We initiated a special research program to evaluate the performance of CO₂ absorption in coastal ecosystems in FY 2009. We selected Lake Furen in Hokkaido as a field site and conducted a large-scale field observation during summer and winter to quantify absorption by organisms and abiotic environments in FY 2010. We detected that inorganic carbon was sequestrated in the benthic system of the Lake Furen all year round.
Focused on improving effective water environment by supplying high-oxygen water that had been experimented in Nakaumi as one of the research projects on restoration of borrow pits other than filling, the relation between the continuous period of aeration and effective restraint of phosphorus release rate was analyzed in FY 2010.
Further, the technology of filling borrow pits with dredged sediments to be planned in Hakata Bay was compared with the aeration method.
A new ecosystem model including a bacteria loop in semienclosed coastal seas was developed and completed in FY 2010. The model was linked with a simple benthic one and was applied to Ise Bay to reproduce long-term water quality variations. The formation process of density stratification
and hypoxia were simulated in Ise Bay, and the bacterial activities contributing to the organic production and the oxygen consumption in the water column were quantified.

Sea grasses accumulated on a beach, forming a “blue carbon” sequestration and a CO₂ absorption survey on a tidal flat