Basin Ecosystem Research Program (Research Program)

Principal Investigator (Contact person)

Akio IMAI (email: aimai[at]nies.go.jp) "[at] is replaced by @"

  • Overall
  • Publications & Link

Overall

Short summary

   In order to minimize the loss of biodiversity in important ecosystems, it has been proposed to utilize the power of ecosystem functions by exploiting their effects on the soundness of the ecosystem. However, there have been few reports on quantitative methods for the evaluation of ecosystem functions in natural environments. In important ecosystems in the natural environment, the lineages and relationships between ecosystem functions and environmental factors have not been elucidated, which is why there has been no substantial progress in how best to protect, restore, and resurrect ecosystem functions.
   Our objective was to develop methodologies for the quantitative assessment of ecosystem function and we are focusing on the material and water cycles of basin ecosystems (e.g., forests, lakes and wetlands, rivers, and coastal regions). We have also performed long-term strategic monitoring of typical basin ecosystems and assessed quantitatively the relationships between ecosystem function and various environmental factors. Based on these scientific findings and associated information, we have extended our project to a large basin (the Mekong River basin) and have assessed the relationship between the losses of fishery production due to damming and the gains of production through aquaculture in the reservoirs.

Summary

   In order to minimize the loss of biodiversity in important ecosystems, it has been proposed to utilize the power of ecosystem functions by exploiting their effects on the soundness of the ecosystem. However, there have been few reports on quantitative methods for the evaluation of ecosystem functions in natural environments. Furthermore, the lineages and relationships between ecosystem functions and environmental factors have not been elucidated, which is why there has been no substantial progress on strategies to protect, restore, and resurrect ecosystem functions.
   In this program, our objective was to develop methodologies for the quantitative assessment of ecosystem function and we are focusing on the material and water cycles of basin ecosystems (e.g., forests, lakes and wetlands, rivers, and coastal regions) (Fig. 1). We have also performed long-term strategic monitoring of typical basin ecosystems and assessed quantitatively the relationships between ecosystem function and various environmental factors. Based on these assessments, we intend to develop methods and techniques for evaluating the health or soundness of basin ecosystems. One of our long-term aims is to determine the optimum conditions for the restoration and conservation of ecosystems.
   Based on these scientific findings and associated information, we have extended our project to a large basin (the Mekong River basin) and have assessed the relationship between the losses of fishery production due to damming and the gains of production through aquaculture in the reservoirs. To achieve this objective, we monitored a variety of limnological parameters in multiple reservoirs and natural lakes within the basin including the nutrients, primary productivity, concentrations of harmful algae such as Microcystis, fish production, and the carbon sources and trophic levels of major food web components. We also investigated the migration behavior of commercially important fish species and assessed the potential impacts of damming on their fishery.

Fig. 1 A Schematic framework of Basin Ecosystem Functions Research Program.

Project 1. Quantitative evaluation of links between ecosystem functions and environmental factors in natural ecosystems

   Toward the improvement of various environmental problems such as nitrogen saturation in forested areas, eutrophication and the increase of recalcitrant dissolved organic matter in lakes, and green tides in coastal seas, caused by the artificial chronic highly loaded conditions of typical natural basin ecosystems, we developed and applied methodologies and techniques to quantitatively evaluate the matter and water cycles and ecosystem functions. Based on these approaches, we assessed the relationships between ecosystem function and various environmental factors and examined methodologies for the solution and effective mitigation of such environmental problems.

Sub 1: Quantitative evaluation of links between ecosystem functions and environmental factors in a forest ecosystem

   The chronic deposition of nitrogen from the atmosphere invokes a decrease in the nitrogen retention capability of a forest ecosystem and causes the condition of “nitrogen saturation.” To evaluate quantitatively the mitigation of nitrogen saturation in an unmanaged conifer plantation brought by recovery and the improvement of ecosystem function brought by active forest management, we investigated the effects of different thinning intensities: unthinned, weakly thinned, and intensively thinned, on nitrogen leaching from the root zone. The annual amount of nitrogen leaching from the root zone in an intensively thinned plantation was estimated to be only 8% of that in an unthinned plantation based on a vertical 1D unsaturated infiltration analysis with the observed concentration of nitrate nitrogen in soil water. From the chemical analysis of herbaceous plants harvested in late summer, it was confirmed that the increase of thinning intensity clearly enhanced the growth of herbaceous plants and increased their nitrogen assimilation. The total amount of assimilation of nitrogen in the intensively thinned plantation was about six times larger than in the unthinned plantation. These results suggest that intensive thinning and well-developed herbaceous vegetation, especially the incorporation of shallow-rooted deciduous broadleaf trees, play important roles in controlling nitrogen leaching from conifer plantations via the formation of an extensive vertical root system.

Sub 2: Quantitative evaluation of links between ecosystem functions and environmental factors in a lake ecosystem

   To evaluate the links between ecosystem functions and environmental factors in Lake Kasumigaura, the second largest lake in Japan, we focused on the interactions of primary/secondary production in the water column with the pore-water quality and microbial community structure in the sediment. We developed new, rapid and non-radioactive methods such as fast repetition rate fluorometry (FRRF) and assays of bacterial productivity with bromodeoxyuridine for measuring the primary and secondary production in the water column, respectively. FRRF was proved valid as a new methodology by comparison with the estimates of primary production rates measured by a traditional method (13C method) under laboratory conditions. We also developed a large-diameter (11 cm) core-sampling system to collect sediment cores without compaction and to monitor the sediment temperature, and a desalination system for measuring the size distribution of marine DOM with high concentration of salts. These new methods developed in Sub-2 will be applied to other projects (Sub-1, Sub-3 in PJ1 and PJ2) within the Basin Ecosystem Functions Research Program.
   We also investigated the interactions of variations in algal species in the water column with the pore-water quality and microbial community structure in the sediments by analyzing water-column monitoring data and water quality profiles in the sediments. In Lake Kasumigaura, the densities of algal cells (especially diatoms) in the water column increased dramatically in 2006, and the sediments turned anaerobic because of the effect of the settled algae. Subsequently, in 2007, the concentration of ammonium ions in the sediment pore water increased sharply due to the presence of the dominant species of anaerobic microorganism, Firmicutes, which has proteolytic activity. The concentration of ammonium ions also increased in the water column because of excess release from the sediments. This release might have induced the explosive water bloom in 2010. Thus, it is likely that the dramatic increase in diatom density indirectly triggered the water bloom over several years. Based on measurements obtained using a simple self-made sediment-trap, it was found that the effect of settling rate to the sediment from the water column changed both seasonally and spatially.

Sub 3: Quantitative evaluation of links between ecosystem functions and environmental factors in a coastal sea

   We aimed to clarify the influence of the green tide formed by the Ulva species on the ecological functions of the Yatsu tidal flat in comparison with an adjacent control site, i.e., the Sanbanze tidal flat. We developed a robust method to identify three independent Ulva species based on DNA markers and found that Ulva ohnoi, which is considered an invasive species, is the dominant species in Yatsu. It was established that U. ohnoi bloomed in Yatsu throughout the year, except for late summer, whereas it was not dominant in Sanbanze.
   We investigated the impact of the green tide on the ecological functions on the tidal flat. Total species numbers and the amount of benthos in Yatsu were higher than in Sanbanze. The seasonal change found in Yatsu appeared to accompany the biomass change of Ulva. Furthermore, total phosphate and nitrogen in the interstitial water of the sediment were highly affected by the summer disappearance of Ulva in Yatsu. Therefore, these results indicate that green tides have important ecological functions such as supplying habitat for benthos and contributing to the phosphate and nitrogen cycles.
   We also investigated the effects of a green tide resulting from the invasive algal species U. ohnoi on ecological functions, via a comparison of a site where Ulva had accumulated with a bare sand site on the Yatsu tidal flat. At the site where the Ulva had accumulated, we found an increase in sediment organic matter (SOM) between winter and summer. The increase in SOM likely occurred because of on-site decomposition of large amounts of dead Ulva. Conversely, on the bare sand site, the amount of SOM was lower and there was no seasonal change observed. We also evaluated the sediment decomposition activity using a cotton-strips weight-loss assay (Harrison et al. 1988). The results indicated that the activity at the Ulva site was greater than at the bare sand site throughout the year. Although the distribution of SOM varied on the tidal flat, the stable carbon and nitrate isotopic values in a dominant macrobenthic organism (Batillaria cumingi) were the same at the two test sites. This indicates that species on bare sand sites feed on SOM derived from the sites where Ulva accumulate.

Project 2. Development of strategic environmental assessment technology and its application to watershed restoration

   We developed techniques and procedures to assess strategically the effects of dam development in the Mekong River basin, specifically regarding the balance between the losses of fishery production due to damming and the gains of production through aquaculture in the reservoirs. To achieve this objective, we monitored a variety of limnological parameters in multiple reservoirs and natural lakes in the basin including the nutrients, primary productivity, concentrations of harmful algae such as Microcystis, fish production, and the carbon sources and trophic levels of major food web components. We also investigated the migration behavior of commercially important fish species and assessed the potential impacts of damming on their fishery. Computer modeling was used to assess the effect of damming on fish species diversity, biomass, and the eco-hydrological properties of the Mekong River as an entity.
   We then implemented a strategic environmental assessment to develop effective, efficient, and science-based techniques for the restoration of mangrove and other wetland vegetation along the coasts of Vietnam and Tohoku in Japan.

Phosphorous cycling

   We investigated the patterns and processes of the sediment nutrients in reservoirs and lakes in the Mekong River basin, such as phosphorus sedimentation and cycling, and the associated reaction states. We found that sediment total phosphorus (TP) increased from littoral to pelagic areas in the water bodies. However, the organic phosphorus to TP ratio was higher in littoral areas than pelagic areas, suggesting that organic matter is supplied constantly from the hinterland to the littoral area. Such a transition from organic to inorganic phosphorus in sediment toward a deeper pelagic environment was obvious in the reservoirs, but was not the case in the natural lake (Tonle Sap), where inorganic phosphorus content was already high in the littoral area, because of its direct supply from intensive anthropogenic activities in riparian villages.

Harmful algae and cyanobacteria

   Using a real-time PCR method, we detected the harmful alga Microcystis aeruginosa in some of the water bodies. We investigated the relationships between TP and M. aeruginosa concentrations and between TP and cyanobacteria 16S rDNA concentrations among the water bodies in the Mekong basin. Log-transformed M. aeruginosa and cyanobacterial concentrations exhibited linear relationships against log-transformed TP. The slope of the regression line for the cyanobacteria was approximately 1, indicating that this group of algae increased in proportion with TP concentration. In contrast, the regression slope for M. aeruginosa against TP was >1.5, indicating that the algae increased sharply with the increase in TP concentration, as we had predicted. This implies a potential risk of harmful algal blooms that may prevail in both existing and planned dam reservoirs, given the economic growth expected in the Mekong countries and the resulting increase in nutrient levels in these water bodies.

Primary production and fish yield

   We found a positive correlation between TP and the primary productivity measured in situ using the 13C stable isotope method in the water bodies, except for the large lake Tonle Sap. Although Tonle Sap was more eutrophic than the other water bodies, its primary productivity is severely limited by a high concentration of suspended solids. Consequently, the depth-integrated primary production was no higher in Tonle Sap than in the other water bodies. We concluded that the primary productivity is constrained by low photosynthetic active radiation in Tonle Sap and by phosphorus concentration in the other water bodies. We also found a positive correlation between primary productivity and annual fish yield per unit area among the water bodies, again with the single outlier of Tonle Sap. Although the primary productivity of the lake was relatively low, its fish yield was much higher than expected given the above correlation. This implies that allochthonous inputs of organic matter from the floodplain and/or from the lake’s tributaries might play an important role in sustaining fish production in this lake, whereas the other water bodies are likely supported primarily by autochthonous production by phytoplankton and periphyton.

Food web structure

   To verify the difference in autochthonous versus allochthonous contributions between reservoirs and natural lakes, we compared the food web structure based on stable carbon and nitrogen isotope ratios. The stable isotope analysis revealed that phytoplankton and periphyton are the two most dominant carbon sources for fish in the reservoirs, whereas terrestrial plants serve as an additional carbon source for fish in natural lakes. The analysis also showed that the reliance of fish on terrestrial carbon was manifested only during the wet season, which agrees well with the flood pulse concept of Junk et al. (1989). Flood pulse is typical of a natural lake, while it is much less pronounced in a reservoir because the water level is controlled artificially, such that extreme floods are eliminated and the annual discharge pattern smoothed. Because of the limitation of carbon sources for the food web, reservoir ecosystems and ecological services (e.g., fishery production) are presumably less resilient and sustainable than in natural lakes.

Fish migration

   The most obvious consequence of damming is the blockage of fish migration. This is especially true for the Mekong River because more than half the fish species of this river have migratory life cycles. We investigated the migration of Siamese mud carp (Henicorhynchus siamensis and Henicorhynchus lobatus), two of the most economically important fish species in the Mekong River, using an otolith microchemistry technique. Otolith Sr-Ba profiles indicated extensive synchronized migrations with similar natal origins among individuals captured within the same sampling location. The profiles also revealed that the movement of H. siamensis had been severely suppressed in one of the Mekong River tributaries where a series of irrigation dams had blocked their migration path. Meanwhile, H. lobatus, collected both up- and downstream from a proposed major hydroelectric dam (the Don Sahong Dam), exhibited statistically different otolith “surface” elemental signatures but not different “core” signatures, which represent the elemental signatures of the water of a fishing ground and spawning ground, respectively. This suggests that a population of the species, dispersing from a single natal origin, migrated either up- or downstream through the proposed dam site before being captured by the fishermen. Together with other evidence, this finding raises concerns over this and other hydropower projects along this river.

Modeling the impact of damming

   To predict the distribution of fish species diversity and the impact of dam construction in the Mekong River, we developed the meta-ecosystem model, which assumed multiple (>10) riverine ecosystems characterized by unique food web structures and connected longitudinally along a river channel. We then ran a computer simulation using this model under two scenarios: dammed and undammed. The simulations showed that fish diversity decreased significantly, not only near the dam, but also in areas further upstream of the dam. Contrary to our expectations, the effect of damming on species diversity was much more severe for non-migratory fish than for migratory fish. Fish biomass increased after damming near the dam; however, this effect varied depending on the feeding types of the fish. Concurrently, we applied the National Integrated Catchment-based Eco-hydrology (NICE) model to the entire Mekong River basin to predict the impact of dam construction. NICE is a process-based model that incorporates surface-groundwater interactions, has up- and down-scaling capabilities across multiple spatial scales, and simulates feedback from hydrologic, geomorphic, and ecological processes. The model was successful in reproducing hydrological events unique to the Mekong River. The model predicted changes in hydrologic characteristics, sedimentation processes, and nutrient cycling associated with the construction of a dam and its reservoir on the main stream of the Mekong River. We plan to link these changes to a fish model to predict the responses of fish populations to dam construction.    Modeling is valuable for providing alternative plans for hydroelectric dam development in the Mekong River basin, by informing on the possible hydrologic changes and their implications for fish diversity and therefore, it allows the proposal of alternative locations for dam constructions that might have lesser impact on fish diversity, biomass, and the ecological services they provide.

Coastal ecosystem restoration

   We implemented a strategic environmental assessment on the coast of northern Vietnam to detect potential mangrove restoration sites and to monitor the recovery of biological diversity, subsequent to restoration based on periodic reconnaissance and the analysis of high-resolution remote sensing data using geographical information systems (GIS). Although mangroves are one of the ecosystems most vulnerable to sea-level rise due to global warming, mangrove wetlands have already been severely damaged in Southeast Asian countries since the 1980s because of the rapid expansion of the shrimp aquaculture industry and resulting deforestation. Ironically, most of the shrimp farms have been difficult to sustain and numerous shrimp ponds along the coast of Vietnam have become economically inefficient and abandoned. We have been successful in restoring a mangrove forest and in assessing the changes in biodiversity near the village of Ding Rui in the Quang Ninh Province of northern Vietnam.

Publications & Link

Publications

  1. Kanaya G, Nakamura Y, Koizumi T, Yamada K (2015) Seasonal changes in infaunal community structure in a hypertrophic brackish canal: effects of hypoxia, sulfide, and predator-prey interaction. Marine Environmental Research 108: 14–23

  2. Kanaya G., Suzuki T., Kikuchi E. (2015) Impacts of the 2011 tsunami on sediment characteristics and macrozoobenthic assemblages in a shallow eutrophic lagoon, Sendai Bay, Japan. PLoS ONE, 10, e0135125

  3. Kawasaki N., Kushairi M.R.M., Nagao N., Yusoff F., Imai A., Kohzu A. (2015): Release of nitrogen ande phosphorus from aquacultrue farms to Selangor River, Malaysia. JCESD 2015 2nd Journal Conference on Environmental Science and Development (in press)

  4. Tsuchiya K., Kuwahara V.S.,Hamasaki K., Tada Y., Ichikawa T., Yoshiki T., Nakajima R., Imai A., Shimode S., Toda T.. Typhoon-induced response of phytoplankton and bacteria in temperate coastal waters. Estuarine, Coastal and Shelf Science (in press)

  5. Tsuchiya K., Sano T., Kawasaki N., Fukuda H., Tomioka N., Hamasaki K., Tada Y., Shimode S., Toda T., Imai A. (2015): New radisotope-free method for measuring bacterial produciton using [15N5]-2'-deoxyadenosine and liquid chromatography mass spectrometry (LC-MS) in aquatic environments. Journal of Oceanography (on-line). DOI 10.1007/s10872-015-0310-8

  6. Zhang L., Wang S., Imai A. (2015) Spatial and temporal variations in sediment enzyme activities and their relationship with the trophic status of Erhai Lake. Ecological Engineering, 75, 365-369

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