Tsutomu Iyobe

Effect of fog on sea salt deposition on peat soil in boreal Picea glehnii forests in Ochiishi, eastern Hokkaido, Japan

We investigated seasonal changes in the chemical properties of precipitation (bulk deposition, throughfall and stem flow) in Picea glehnii forests and neighboring Sphagnum communities in three ombrotrophic mires in Ochiishi district, northern Japan, to clarify the contribution of fog to nutrient addition to mires. Na+ and Cl– dominated the bulk deposition, followed by Mg2+, Ca2+ and SO42–, implying an oceanic influence on mire chemistry. Differences in chemical properties among bulk deposition, throughfall and stem flow increased with proximity to the coastline. There was little difference in electrical conductivity (EC) among bulk deposition, throughfall and stem flow during the period of high fog frequency, which was approximately 17 fog days per month from June to August, but there were large differences in EC during the period of low fog frequency, which was approximately 5 fog days per month from September to November. In general, throughfall and stem flow were enriched with Na+, Mg2+, Ca2+, Cl– and SO42– at the P. glehnii canopy, and seasonal trends in ionic concentration showed almost the same trend as EC. This seasonal pattern of atmospheric deposition chemistry showed that sea salt deposition on mires depends on fog occurrence. Sea salt is washed out of the atmosphere by fog when fog covers the forest canopy and, hence, throughfall and stem flow did not lead to the enrichment of chemical constituents during passage through the canopy in these mires during the season of high fog occurrence.

Acid and sea-salt accumulation in coastal peat mires of a Picea glehnii forest in Ochiishi, eastern Hokkaido, Japan

We investigated the soil chemical environment of coastal peat mires with a Picea glehnii forest and Sphagnum community in Ochiishi, north-eastern Japan. We tested the hypothesis that the soil chemical environment in an ombrotrophic peat mire is affected by the vegetation and the consequent chemical modification of precipitation by plants. We measured the chemical properties of peat pore water and precipitation both in the P. glehnii forest and the Sphagnum community and found that the forest acidifies the peat and accumulates sea salt deposited by precipitation. Picea glehnii grows in soils that have a higher salt concentration than the Sphagnum communities. We measured a stem flow salt concentration that was higher than the bulk deposition. The salt concentration in precipitation and peat pore water decreased with increasing distance from the coastline. These results imply that atmospheric sea salt deposition is effectively trapped by the P. glehnii canopy, and it then contributes to the accumulation of salt and the consequent acidification within the peat. Stem-flow water was more acidic than bulk deposition or throughfall within the P. glehnii, a forests. This means that acids are dissolved while precipitation runs through on the bark of P. glehnii, and then the acids are transferred and accumulate in the peat. The chemical modification of precipitation by P. glehnii makes the soil chemical environment more acidic than the Sphagnum community that usually makes the soil environment acidic in a peat mire ecosystem.

SITE SELECTIVITY OF PICEA GLEHNII FOREST ON SYUNKUNITAI SAND SPIT, NORTH EASTERN JAPAN

In Far East Asia, coastal dune forests dominated by the conifer Picea glehnii represent a rare plant community type A. P. glehnii forest and adjacent plant communities on the dunes of the Syunkunitai sand spit, Hokkaido, northern Japan were examined. Using the basal area of P. glehnii and Abies sachalinensis stems measured in a belt transect across a portion of the sand spit, we identified three plant community zones: SALT MARSH, PICEA, and ABIES. The three zones were distributed along a topographic gradient that was associated with differences in water table depth, salinity, and pH of soil pore water. Nearly pure stands of P. glehnii grew on a relatively level portion of the sand dune where the ground-water-table level was shallow (−10.9 to −26.3 cm, without isolated depressions). The salinity of the soil pore water was significantly lower than that in the adjacent salt marsh (Dunnett’s T3, P=0.047). The A. sachalinensis community grew on the upper slope and ridge of the dune where the ground-water-table was significantly lower (P=0.003) than in the P. glehnii forest. Our results show that the boundary between the P. glehnii forest and the salt marsh community is determined primarily by the salinity of the soil pore water, whereas the boundary between the P. glehnii and A. sachalinensis forests is determined by the ground-water-table depth and the pH of the soil pore water. Because of continual ground subsidence, the salt marsh community and P. glehnii forest will likely be submerged within 50 and 100 years, respectively.

Ion flux from precipitation to peat soil in spruce forest-Sphagnum bog communities in the Ochiishi district, eastern Hokkaido, Japan

To evaluate the contribution of proton flux from precipitation on peat acidification in mire ecosystems, we estimated ion fluxes to peat soils from bulk deposition in Sphagnum-dominated bogs and from throughfall plus stem flow in spruce forests in three cool-temperate ombrogenous mires in the Ochiishi district, northeastern Japan. We tested the hypothesis that proton fluxes from the atmosphere to peat soils are affected by vegetation types, leading to the consequent difference in soil acidity. The proton flux in bulk deposition was higher than that in throughfall plus stem flow, but the concentration of H+ in the peat surface water in Sphagnum bogs was lower than that in spruce forests. The inverse relationship between proton flux and soil water acidity means that the soil water acidity could not be explained quantitatively by proton flux from the atmosphere to the peat surface. The ion fluxes of sea-salt components were dependent on the distance from the coast to the mires. This means that the sea-salt accumulation in the peat surface soil can be directly attributed to the high flux of sea-salt from precipitation. The flux of sea-salts deposited on the mires positively correlated with the H+ concentration of the peat surface water in each community, implying that the acidity of peat surface water depends on the cation fluxes from precipitation.

SEASONAL FROST, PEAT, AND OUTFLOWING STREAM-WATER CHEMISTRY IN OMBROGENOUS MIRES IN OCHIISHI, EASTERN HOKKAIDO, JAPAN

To clarify the nutrient dynamics in peat-covered watersheds during frost, soil, chemical properties of atmospheric depostition (bulk deposition and throughfall) on mires, peat pore water, and stream-water outflows from mires were investigated at three ombrogenous mires withPicea glehnii M. forests andSphagnum spp. communities in Ochiishi, eastern Hokkaido, Japan. We investigated the depth of frozen ground as one of the factors determining chemical properties of outflowing stream water from mires. Na+ and Cl− were the dominant ion species in bulk deposition and throughfall, implying the influence of sea salts on precipitation chemistry. The electrical conductivity (EC) and Na+, Mg2+, Cl−, and SO42− concentrations in throughfall (snow) were 5–10 times higher than bulk deposition after a 25-day period without precipitation in February 2001. Throughfall was enriched with sea salts from dry deposition on the canopy, while snow was intercepted by the forest canopy. The first rain event during the seasonal soil freezing led to the enrichment of chemical components in the stream-water outflows from the mire. The frozen layer in the upper peat soil prevented the infiltration of snow melt into peat soil during the period of frost soil, and hence large amounts of salts (Na+ and Cl−) accumulated on the snow surface or within the snow cover. Rain water flowed over the frost soil layer and was enriched with chemicals from accumulated salts in the snow cover. This subsequently led to the high salt concentration in stream water just after the rain events during the season when soil was frozen.

Stem Flow Chemistry of Picea glehnii, Abies sachalinensis and Alnus Japonica and Its Effect on the Peat Pore Water Chemistry in an Ombrogenous Mire in Ochiishi, Eastern Hokkaido, Japan

We investigated the chemical properties of stemflow of Picea glehnii, Abies sachalinensis and Alnus japonica as well as peat pore water chemistry, including the distance and depth profiles of pore water chemistry, in an ombrogenous mire. The effect of stemflow on the peat pore water chemistry was clear at the stem base in the peat forest in the mire, and the peat pore water around the stem base of a tree had its own chemical properties specific to each species. P. glehnii showed the highest concentration of salts both in stemflow and peat-pore water, whereas A. japonica showed the lowest concentrations; however, the gradient of the chemical environment from the stem base to outside of the canopy is formed. The peat pore water chemistry under the canopy was mainly controlled by the chemical processes diluted by the abundant peat pore water; the stemflow movement in the high water content of the peat was more slowly because of the flat topography (< 1°). This would be due to the fact that the chemicals in stemflow would be diluted by the abundant peat pore water. The spatial heterogeneity of chemical environment between microsites within forested peatland would be also contributed indirectly through the control of microorganism activity, and nutrient regeneration mediated the surface water and the stemflow of the dominant canopy trees.