Akira Haraguchi

The carbon content characteristics of tropical peats in Central Kalimantan, Indonesia: Estimating their spatial variability in density

Clarification of carbon content characteristics, on their spatial variability in density, of tropical peatlands is needed for more accurate estimates of the C pools and more detailed C cycle understandings. In this study, the C density characteristics of different peatland types and at various depths within tropical peats in Central Kalimantan were analyzed. The peatland types and the land cover types were classified by land system map and remotely sensed data of multi-temporal AVHRR composites (1-km pixel size), respectively. Differences in the mean values of volumetric C density (CDV) were found among peatland types owing to the variability in physical consolidation from peat decomposition or nutrient inputs, although no vertical trends of CDV were found. Using a step-wise regression technique, geographic variables and the categories of peatland type and land cover type were found to explain 54% of the variability of CDV within tropical peatlands in some conditions.

Measuring organic carbon, nutrients and heavy metals in rivers receiving leachate from controlled and uncontrolled municipal solid waste (MSW) landfills.

Since landfilling is the common method of waste disposal in Malaysia, river water is greatly exposed to the risk of contamination from leachate unless proper leachate management is carried out. In this study, leachates from three different types of landfills, namely active uncontrolled, active controlled and closed controlled, were characterized, and their relationships with river water chemistry were examined monthly for a year. The influence of leachate on river water chemistry from each type of landfill depended on many factors, including the presence of a leachate control mechanism, leachate characteristics, precipitation, surface runoff and the applied treatment. The impact of leachate from an active uncontrolled landfill was the highest, as the organic content, NH(4)(+)-N, Cd and Mn levels appeared high in the river. At the same time, influences of leachate were also observed from both types of controlled landfills in the form of inorganic nitrogen (NH(4)(+)-N, NO(3)(-)-N and NO(2)(-)-N) and heavy metals (Fe, Cr, Ni and Mn). Improper treatment practice led to high levels of some contaminants in the stream near the closed controlled landfill. Meanwhile, the active controlled landfill, which was located near the coastline, was exposed to the risk of contamination resulting from the pyrite oxidation of the surrounding area.

Effects of water-table oscillation on redox property of peat in a floating mat.

Seasonal changes in redox potential (Eh) of peat were investigated in a floating mat which experiences a periodical inundation. In the inundated season (late December-June), Eh of the peat within 3 cm of the surface was 150-200 mV vs. NHE (standard hydrogen electrode) and it fluctuated little. It became <50 mV in July, although the mat surface emerged from water and the peat surface was in direct contact with the air. Redox potential began to increase in late July and reached its maximum in early November (...)

A chronosequence approach for detecting revegetation patterns after Sphagnum -peat mining, northern Japan

The aim of this study is to detect how vegetation development proceeds after Sphagnum-peat mining and how physical and chemical factors in groundwater are related to the revegetation patterns in Sarobetsu mire, Hokkaido, Japan. A total of 189 plots on peat-mining sites were set in a chronosequence and 18 plots were set on unmined control sites. A vegetation survey was conducted, and seasonal changes in groundwater levels and chemistry (pH, electrical conductance, total nitrogen, total phosphorus, anions, and cations) were monitored. Species richness and plot cover tended to increase with increasing age, but were significantly lower in mined sites than in unmined sites dominated by Sphagnum spp. The trends in vegetation change were (1) bare ground, (2) grasslands dominated by grasses and sedges, e.g., Rhyncohospora alba, Phragmites communis, and Moliniopsis japonica and (3) Sphagnum-dominated vegetation. The characteristics of groundwater level during the plant-growth period mostly determined vegetation recovery, i.e., Sphagnum establishment was promoted when groundwater declined greatly in early summer. The patterns of temporal vegetation changes affected by groundwater characteristics were detected by chronological sequence, and hydrological factors in groundwater were more important for revegetation than chemical factors. The original vegetation has not returned after three decades.

Nutrient dynamics in a floating mat and pond system with special reference to its vegetation

Chemical properties of waters and their seasonal changes were studied in Mizorogaike Pond, a system of pond and floating mat. The following six sites including contrasting habitats and water conditions were monitored to assess nutrient dynamics in the system: 1) a pool on the mat, 2) margin of aSphagnum cuspidatum community, 3) an artificial ‘well’ (water layer beneath the floating mat), 4) aMenyanthes trifoliata community in a hollow, and 5) & 6) two sites in the open water. On the floating mat, the water around theSphagnum community had lower pH values, while that in theM. trifoliata community had higher pH values. This difference was related to the influence of flood water, the extent of which was determined by the microtopography. Seasonal changes in water chemistry on the mat suggested that pond water flooding the mat in late autumn and winter is important for the nutrient supply to the mat surface vegetation in this system. Water chemistry of the ‘well’ suggested that the diffusion of inorganic nitrogen occurs from beneath the peat layer. Two types of cluster analysis based on the mean values for chemical variables and the patterns of fluctuation in these variables were performed. The six sites were classified into similar groups which were identified by water type (pool, hollow, well and open water) by both types of analysis. The results showed that a common kind of perturbation should operate in determining the status of nutrient dynamics in the various water types.

Effects of scale-dependent factors on herbaceous vegetation patterns in a wetland, northern Japan

Herbaceous vegetation was examined in an Otanoshike wetland in northern Japan to clarify the relationships between vegetation patterns and environmental factors with different scales. Alders (Alnus japonica) have recently invaded and might modify the herbaceous vegetation. In total, 150 50 × 50 cm plots were established on the transitional areas between alder thickets and grassy marshland. Cover was measured for the vascular plant taxa, and canopy area, number of stumps, number of mounds, water depth, elevation difference, litter thickness, soil organic matter, and soil pH were measured in each plot. TWINSPAN cluster analysis classified four vegetation groups: (i), grasslands represented by Phragmites australis, Trientalis europaea, Lythrum salicaria, and Hosta rectifolia; (ii), Calamagrostis langsdorfii, and Polygonum thunbergii grasslands with Spiraea salicifolia; (iii), reed swamp dominated by Phragmites australis, and (iv), marshland dominated by Carex lyngbyei. Canonical correspondence analysis indicated that water depth primarily divided vegetation groups 1–2 and 3–4. Alder established in drier sites mostly by re-sprouting, and the canopy affected light and soil conditions on the ground surface. The second axis of canonical correspondence analysis was related to the canopy area and soil pH, and explained the vegetation differentiation between groups 1 and 2, and groups 3 and 4. In conclusion therefore, scale-dependent or hierarchical variables affected the vegetation patterns in different ways, that is, the herbaceous vegetation was first differentiated by water depth that was corresponding to alder establishment on a large scale, and subsequent light and soil conditions were second determinants on a small scale.

Effect of flooding-drawdown cycle on vegetation in a system of floating peat mat and pond

The relationship between vegetation and seasonal changes in water level was examined in a system of terrestrializing floating peat mat and pond in a warm temperate zone. The duration of flooding, or drawdown period, is related to vegetation in the mat. The first process of terrestrialization would be the attenuation of floating-sinking movement of the mat and the consequent stabilization of water level. Water level at the time when the movement of the mat was attenuated determined the subsequent vegetation change at the site. Two series of succession according to terrestrialization were recognized, and started from initial conditions of low and high water levels respectively. Habitats in low initial water levels experienced short flooding and long drawdown periods. Species changes in the successional series were:Menyanthes trifoliata-Rhynchospora fauriei-Eriocaulon sikokianum-Sphagnum cuspidatum. Submerged peat was experimentally emerged, and the crowded community ofRhynchospora fauriei andEriocaulon sikokianum established within one or two years. Appearance of these species was controlled by the water level of the habitats in winter. Another series of species changes in terrestrialization process was:Menyanthes trifoliata-Phragmites australis-Carex thunbergii orIsachne globosa. Habitats of these types of vegetation were in the area with relatively high initial water level (long flooding and short drawdown) when the floating-sinking movement of the mat attenuated. After the temporal paludification, the water level was lowered by the accumulation of peat in the process of terrestrialization.

Effect of pH on photosynthesis of fiveSphagnum species in mires in Ochiishi, northern Japan

In a laboratory experiment, the pH dependence of photosynthesis was investigated for fiveSphagnum species:S. fuscum, S. magellanicum, S. girgensohnii, S squarrosum andS. fallax, that are common in mires in Ochiishi, northern Japan. The maximum photosynthetic rate ofS. fuscum occured at the lowest pH among the species. The photosynthetic rate ofS. girgensohnii, S. squarrosum andS. fallax varied little between pH 5.2 and pH 7.5, whereas the photosynthetic rate ofS. fuscum andS. magellanicum tended to decline as pH increased. The results indicate thatS. fuscum is most adapted to acidic conditions, whileS. girgensohnii, S. squarrosum andS. fallax are adapted to a wide pH range of ambient waters.

Rhizome growth of Menyanthes trifoliata L. in a population on a floating peat mat in Mizorogaike Pond, central Japan

Abstract The growth of rhizomes of Menyanthes trifoliata L. was investigated in a floating mat in central Japan in order to examine the phenotypic properties of the rhizomes and hence to clarify the role of these organs. The part of the rhizome which elongated in autumn had high specific dry weight during autumn and winter, and the specific dry weight decreased in early spring when generative buds and leaves started to develop. This part of the rhizome has a function for dry matter storage. The part of the rhizome which elongated in summer had a low specific dry weight. Rhizomes with low specific dry weight are thin and long and are useful for occupation of the peat surface, hence playing a role in vegetative expansion. The percentage of generative buds and lateral buds formed was related to the size of rhizomes formed in the preceding year. The percentage of generative bud formation increased with increasing rhizome size. In contrast to generative buds, lateral bud formation was restricted to rhizomes 2–32 cm in length: rhizomes longer than 32 cm never formed lateral buds.

Seasonal changes in oxygen consumption rate and redox property of floating peat in a pond in central Japan

Seasonal changes and temperature dependence of the oxygen consumption rate were measured in the surface peat of a floating mat. A simple model succeeded in reproducing the seasonal pattern in Eh changes at the peat surface. This included two terms: oxygen supply rate as a function of water-table depth and oxygen consumption rate as a function of temperature and microbial activity. The model explained well the minimum and maximum Eh in July and October, respectively. The activity of aerobic microbes in the peat was important in determining redox properties in the floating mat.