In order to understand the determining factors of the geographical variation of buffering in the ... more In order to understand the determining factors of the geographical variation of buffering in the world's vegetated catchments, this study examined the HCO3-leaching of 107 experimental watersheds selected from regions ranging from tropical rain forests to humid continental or subpolar forests including several temperate grassland. With consideration of the soil development and the factors controlling it, the influences of geological, climatological, and topographical conditions on discharge HCO3-concentrations and fluxes are examined. The HCO3-discharge fluxes from catchments were correlated with climatological indexes. The increase of annual mean temperature reflected the increase in fluxes, although this tendency was not that significant in the precipitation-flux relationships. Notable differences in these correlations were not found among three major groups of bedrock types; igneous, metamorphic, and sedimentary groups, with exceptions being noted at the sites having materially HCO3-rich calcite, dolomite and volcanic ash. There were, however, exceptionally high flux sites whose fluxes could not be predicted by the empirical model when considering only temperature and precipitation controls. These sites belong to the mountainous part of the Japanese archipelago that is orogenically active and have in common steep hillslopes. Positive correlations were found between relief ratio, which was calculated by dividing elevation difference between highest and lowest points in the catchment by the distance between those two points, and fluxes in igneous and sedimentary groups including these high-HCO3-flux sites. These facts suggest that it is a fundamental requirement to consider the status of the soil forming when discussing the global variations in the buffering of watersheds. The differences in geomorphologic conditions controlling soil development are also just as important as the climatological effects. 1. Introduction Acid rain in northern Europe and northeastern America has caused stream and lake acidification in forested catchments but has not had indisputable direct effects on forest vegetation. The research activities on fresh water acidification as an effect of atmospheric acid deposition have brought about the rapid progress in biogeochemistry studies in the cold humid forest ecosystem in these regions [e.g., Likens et al., 1979; Reuss et al., 1987]. In the second half of the 1980s, several catchmentscale hydrochemical models were proposed by the American and European researchers investigating acid rain effects, especially for long term prediction. During that time, the modeling of the buffering mechanisms at the catchment scale. was improved [Cosby et al., 1985; Gherini et al., 1985; Bergstrom et al., 1985; Wolford et al., 1995]. The principle concept of freshwater acidification in northern Europe and northeast America was described by Reuss et al. [1987]. According to their review, the widespread acidification of Copyright 1999 by the American Geophysical Union. Paper number 1999GB900029 0886-6236/99/1999GB900029512.00 surface water in these regions is due to the "superposition" of acid deposition on the natural acidifying processes in soil. They show that the naturally acidified soil profile is sensitive to excess acid deposition. However, it does not necessarily indicate that the anthropogenic acid deposition itself caused the acidification of the soil profiles. Strong mobile acid anions such as SO42' and NO3' with atmospheric deposition have accelerated the mobilization of H* and inorganic A13* which has naturally existed in reservoirs at exchange sites for thousands of years. At that time, Galloway and Cowling [1978] and Reuss et al. [1987] paid attention to the weathering potential as an origin of the buffering capacity. They made maps of sensitivity to freshwater acidification based on bedrock geology. The maps show the geographical distribution of the buffering capacity of soils within North America and northern Europe. Recently, acid rain issues are attracting the attention of not only European and North American communities, but also eastern Asian societies including a number of developing countries [Carmichael, 1997; Satsangi et al., 1997; Shaoxing et al., 1997; Somboon, 1997]. The people of these countries seriously worry about the freshwater acidification and damage to forest resources by soil acidification. The environmental science community in Japan continues to pay attention to the 969 64 Dunn Mill Creek
Recent studies have demonstrated the importance of water movement through the bedrock in the rain... more Recent studies have demonstrated the importance of water movement through the bedrock in the rainfall‐runoff process on steep hillslopes. However, quantitative information on this process is still limited. The objective of this study was to address the following questions: (1) How large is the area where bedrock groundwater seeps into the soil layer, and (2) what is the rate of water flow out of the bedrock? To address these questions, detailed hydrological, hydrochemical, and thermal measurements were conducted at a forested steep unchanneled granitic concave slope in the Tanakami Mountains, central Japan. The relationship between the amplitude of annual soil temperature variation and the measurement depth showed that in a normal low‐flow period, the seepage area ranged between 14 and 21 m2 and the ratio of this area to that of the whole catchment was about 2.0%. In a drought period the seepage area ranged between 3.5 and 5.5 m2, and the ratio to the whole catchment was around 0.5%...
Methane (CH 4) uptake by soil can possibly be suppressed more in regions with heavy summer precip... more Methane (CH 4) uptake by soil can possibly be suppressed more in regions with heavy summer precipitation, such as those under the East Asian monsoon climate, as compared to that in regions with a dry summer. In order to determine how precipitation patterns affect seasonal and spatial variations in CH 4 fluxes in temperate forest soils, such fluxes and selected environmental variables were measured on different parts of a hill slope in a cypress forest in central Japan. On the upper and middle parts of the slope, CH 4 uptake was observed throughout the year, and the uptake rates increased slightly with soil temperature and decreased with soil water content. The CH 4 flux predicted using data for the middle and upper parts of the slope ranged from À1.12 to À0.83 kg-CH 4 ha À1 y À1 (i.e. CH 4 uptake by soil) and from À2.30 to À2.04 kg-CH 4 ha À1 y À1 , respectively. In contrast, in the relatively wet lower part of the slope near an in-stream wetland, large CH 4 emissions (>2 mg-CH 4 m À1 d À1) were observed during the rainy summer. In this wetter plot, the soil functioned as a net annual CH 4 source in a rainy year. Hence the variation in CH 4 flux with a change in soil water conditions and soil temperature on the lower part of the slope contrasted to that on the upper and middle parts of the slope. The predicted CH 4 flux for this lower plot ranged from À0.45 kg-CH 4 ha À1 y À1 in a dry year to 1.80 kg-CH 4 ha À1 y À1 in a rainy year. Our results suggest that consideration of the soil water conditions across a watershed is important for estimating the CH 4 budgets for entire forest watershed, particularly in regions subject to a wet summer.
Japanese Journal of Limnology (Rikusuigaku Zasshi), 2006
In order to model the stream water chemistry in a forest catchment, the model should include func... more In order to model the stream water chemistry in a forest catchment, the model should include functions describing both the biogeochemical cycle and the hydrological pathways as the transportation system for solutes and suspended substances. Although several catchment-scale models have been developed based mainly on the data collected under non-monsoon climate corditions in the northeastern United States and northern Europe, it is questionable whether these models are able to simulate the seasonal changes in streamwater chemistry in a forest catchment under monsoon climate conditions. This is because the monsoon-driven precipitation seasonality affects subsurface-groundwater mixing, and this in turn strongly influences the seasonal variation in streamwater chemistry. To simulate this effect in a catchment-scale response, it is important to combine biogeochemical and hydrological models that will be able to express the effects by soil and groundwater storage and their mixing.
Agricultural Implications of the Fukushima Nuclear Accident, 2013
A massive amount of radioactive substances, including cesium-137 (137 Cs), emitted from the disab... more A massive amount of radioactive substances, including cesium-137 (137 Cs), emitted from the disabled nuclear power plant has deposited on the forested areas in the northeastern region of Honshu Island, Japan after the Fukushima Daiichi nuclear power plant accident. Forests in these regions are particularly important not only for the forest products industry but also for source areas of drinking water and for residential environments. To clarify the mechanisms of diffusion and export of 137 Cs deposited on the forested ecosystem, we initiated intensive fi eld observations in a small catchment, including forest and farmlands, in the Kami-Oguni River catchment in the northern part of Fukushima Prefecture. The following expected major pathways of 137 Cs diffusion and export were investigated: (1) transportation by water movement of dissolved and particulate or colloidal forms through hydrological processes and (2) diffusion through the food web in terrestrial and aquatic ecosystems of forests. Preliminary fi ndings indicated the following: (1) most of the 137 Cs was discharged as suspended matter, and particulate organic matter appeared to be the most important carrier of 137 Cs. High water fl ow generated by storm accelerated the transportation of 137 Cs from the forested catchments. Estimation of 137 Cs export thus requires precise evaluation of the high fl ow acceleration during storm events. (2) Because litter and its detritus may form the biggest pool of 137 Cs in the forested ecosystem, 137 Cs diffusion occurs more rapidly through the detritus food chain than the grazing food chain. Most predators have already ingested 137 Cs, particularly in aquatic environments. An urgent question is when and how 137 Cs diffuses through grazing food chains and how rapidly Chapter 16
Page 1. Chapter 12 Hydrology and Biogeochemistry of Temperate Forests Nobuhito Ohte and Naoko Tok... more Page 1. Chapter 12 Hydrology and Biogeochemistry of Temperate Forests Nobuhito Ohte and Naoko Tokuchi 12.1 Introduction Temperate forests are distributed extensively in middle latitude regions, where the mean annual ...
Cryoconites are microbial aggregates commonly found on glacier surfaces where they tend to take s... more Cryoconites are microbial aggregates commonly found on glacier surfaces where they tend to take spherical, granular forms. While it has been postulated that the microbes in cryoconite granules play an important role in glacier ecosystems, information on their community structure is still limited, and their functions remain unclear. Here, we present evidence for the occurrence of nitrogen cycling in cryoconite granules on a glacier in Central Asia. We detected marker genes for nitrogen fixation, nitrification and denitrification in cryoconite granules by digital polymerase chain reaction (PCR), while digital reverse transcription PCR analysis revealed that only marker genes for nitrification and denitrification were abundantly transcribed. Analysis of isotope ratios also indicated the occurrence of nitrification; nitrate in the meltwater on the glacier surface was of biological origin, while nitrate in the snow was of atmospheric origin. The predominant nitrifiers on this glacier bel...
Even within homogeneous geological and climatological settings, the spatial variability of specif... more Even within homogeneous geological and climatological settings, the spatial variability of specific discharge and some solute concentrations in headwater catchments often increases with decreasing stream order and sub-catchment area, and there is a certain catchment size where the variability is minimized. A simulation model based on the subsurface-bedrock groundwater mixing concept was proposed to determine mechanisms of this scale-variability relationship. Generally, it is difficult for the headwater small catchment to be determined its catchment area of the bedrock groundwater discharge while that of the subsurface groundwater can be measured based on topographical information, and the actual catchment area for the bedrock groundwater is often different from that for the subsurface runoff. The model presented in this paper focuses on this _gdiscrepancy_h in the actual catchment area between the subsurface and bedrock groundwater runoff as an origin of the variability among the lo...
To clarify how hydrological processes affect biogenic methane (CH 4) production and emission from... more To clarify how hydrological processes affect biogenic methane (CH 4) production and emission from soil surfaces, we analyzed the d 13 C of CH 4 and CO 2 and chemical constituents dissolved in groundwater at a wetland in the headwater catchment of a temperate forest in Japan. We estimated the contribution of acetate fermentation using the d 13 C isotope mass balance of dissolved CH 4 and CO 2. CH 4 production pathways (e.g., acetate fermentation and carbonate reduction) changed temporally and spatially with hydrologically controlled redox conditions. The proportion of methanogenesis attributable to acetate fermentation usually decreased with temperature, suggesting that carbonate reduction dominated under conditions of high CO 2 concentration. In particular, the groundwater table and summer temperatures were key controlling factors in the interannual and intra-annual changes in CH 4 production pathways, controlling oxygen supply and consumption and, therefore, redox conditions in the soil. Under high temperature and high water table conditions during summer, the soil was strongly reduced and the proportion of carbonate reduction increased. Acetate fermentation also increased episodically, resulting in sporadic increases in d 13 C-CH 4. The calculated acetate contribution obviously decreased in periods of low water table and high temperature when the soil surface was relatively oxic, implying deactivation of acetoclastic methanogenesis under oxic conditions. Thus, hydrological processes control the supply of these electron donors and acceptors and therefore play an important role in determining the relative proportions of CH 4-producing pathways. Our results also indicate that an increase in acetate contribution under highly reducing conditions stimulates CH 4 production and emission from the soil surface.
The stable isotopic composition of dissolved inorganic carbon (υ 13 C-DIC) was investigated as a ... more The stable isotopic composition of dissolved inorganic carbon (υ 13 C-DIC) was investigated as a potential tracer of streamflow generation processes at the Sleepers River Research Watershed, Vermont, USA. Downstream sampling showed υ 13 C-DIC increased between 3-5‰ from the stream source to the outlet weir approximately 0Ð5 km downstream, concomitant with increasing pH and decreasing PCO 2. An increase in υ 13 C-DIC of 2Ð4 š 0Ð1‰ per log unit decrease of excess PCO 2 (stream PCO 2 normalized to atmospheric PCO 2) was observed from downstream transect data collected during snowmelt. Isotopic fractionation of DIC due to CO 2 outgassing rather than exchange with atmospheric CO 2 may be the primary cause of increased υ 13 C-DIC values downstream when PCO 2 of surface freshwater exceeds twice the atmospheric CO 2 concentration. Although CO 2 outgassing caused a general increase in stream υ 13 C-DIC values, points of localized groundwater seepage into the stream were identified by decreases in υ 13 C-DIC and increases in DIC concentration of the stream water superimposed upon the general downstream trend. In addition, comparison between snowmelt, early spring and summer seasons showed that DIC is flushed from shallow groundwater flowpaths during snowmelt and is replaced by a greater proportion of DIC derived from soil CO 2 during the early spring growing season. Thus, in spite of effects from CO 2 outgassing, υ 13 C of DIC can be a useful indicator of groundwater additions to headwater streams and a tracer of carbon dynamics in catchments.
Hydrology and biogeochemistry of forested catchments A Joint US-Japan Seminar on Forest Hydrology... more Hydrology and biogeochemistry of forested catchments A Joint US-Japan Seminar on Forest Hydrology and Biogeochemistry was held on 1-4 February 2000 at the East-West Center in Honolulu, Hawaii. The purpose of the seminar was to examine the similarities and differences in catchment hydrology research between Japan and the US and to highlight some of the recent and ongoing studies from both countries. A workshop component of the meeting facilitated informal exchange of ideas and approaches to educate the participants on activities in both regions. McDonnell and Tanaka (HPToday Commentary, this issue) synthesize the questions and discussions that emerged from the meeting, that provides the framework for a robust quantitative description of hydrological flowpaths that control biogeochemistry at the catchment scale in forested systems. Studies of catchment hydrology have evolved differently in the US and Japan. Much catchment research in the US has been motivated by interest in explaining stream water chemistry. In contrast, investigations on catchment hydrology in Japan have been more process oriented, initiated by geotechnical questions (Tsukamoto, 1963). As a result, the strengths of the two countries differ. Interdisciplinary approaches are common in the US but rarer in Japan. On the other hand, Japanese hydrologists have developed very sophisticated and novel hillslope and catchment monitoring approaches that aid in the interpretation of processes. Until recently, interactions between hydrological scientists in Japan and the US have not been extensive. The last formal exchange was the US-Japan Joint Seminar on Integration of Physical Insight Into New Approaches in Hydrology held in Hawaii in January 1987. Bras et al. (1988) synthesized these discussions and papers into a special issue of the Journal of Hydrology (Vol. 102). Since this 1987 seminar, the field of hydrology has grown rapidly and the scope of research within the two countries has also changed. Understanding the linkages between hydrology and biogeochemistry of small forested catchments has been highlighted in the US by recent National Research Council (NRC) reports as one of the most pressing needs in watershed research (Eagleson, 1991; Hornberger, 1997). Understanding the interactions between hydrology and biogeochemistry as a critical and under-recognized component of watershed research has also been emphasized (e.g. Cirmo and McDonnell, 1997). Several programmes at the US National Science Foundation (NSF) now promote research on these interactions. Japan has many instrumented headwater catchments (operated by various university researchers and the Japan Forestry and Forest Products Research Institute), several of which were highlighted during the 1987 meeting. Reports of research at these sites have appeared recently in international journals such as Water Resources Research (e.g.
Nematomorph parasites manipulate crickets to enter streams where the parasites reproduce. These m... more Nematomorph parasites manipulate crickets to enter streams where the parasites reproduce. These manipulated crickets become a substantial food subsidy for stream fishes. We used a field experiment to investigate how this subsidy affects the stream community and ecosystem function. When crickets were available, predatory fish ate fewer benthic invertebrates. The resulting release of the benthic invertebrate community from fish predation indirectly decreased the biomass of benthic algae and slightly increased leaf breakdown rate. This is the first experimental demonstration that host manipulation by a parasite can reorganise a community and alter ecosystem function. Nematomorphs are common, and many other parasites have dramatic effects on host phenotypes, suggesting that similar effects of parasites on ecosystems might be widespread.
To quantify the contributions of atmospheric nitrogen deposition and mechanisms of nitrate discha... more To quantify the contributions of atmospheric nitrogen deposition and mechanisms of nitrate discharge to stream, nitrogen chemistry and isotopes (delta 15N and delta 18O of NO3-) of streamwater were studied as part of an ongoing study of nutrient dynamics at the Sleepers River Research Watershed in Vermont, USA. We employed novel analytical procedures for high throughput of NO3- isotopic measurements. The denitrifier method for measurement of delta 15N and delta 18O of NO3- requires a smaller volume of water samples than previously applied methods, thus it enables fine resolution analysis of isotopes for stream, well, and soil water samples. Samples were collected throughout the spring 2003 snowmelt. Snowmelt runoff was initiated in the middle of March and peaked at the end of the month. Then, the runoff rate decreased gradually through April and May, and responded to several storm events. The highest concentration of NO3- in the stream was observed at the beginning of snowmelt (the end of March), and thereafter it declined continuously. The temporal course of NO3- discharge process during snowmelt period was divided into four phases based on changes in the relationship between runoff rate and NO3- concentration. During the earliest phase (very low runoff rate and highest NO3- concentration) isotope signatures, especially delta 18O of NO3-, indicated higher contribution of the atmospherically derived NO3-, meaning that the direct discharge from snow pack was the dominant source of NO3- to the stream. This also suggested that streamwater consisted only of a small volume of groundwater discharge and melt water of the in-stream snow pack and/or stream-covering snow pack. The delta 15N and delta 18O isotope compositions of NO3- during the middle phase of snowmelt indicated that the contribution of the NO3- generated by nitrifiers in soil increased gradually accompanied with increase of groundwater level. These detailed descriptions in the changes of NO3- discharge during snowmelt events were enabled by the dual-isotope analysis of NO3-. The fine resolution isotope analysis of NO3- in our experiment can provide advantages for elucidating the discharge mechanisms of nitrogen in forested watersheds with high atmospheric nitrogen depositions.
The denitrifier method to determine the dual isotopic composition (d 15 N and d 18 O) of nitrate ... more The denitrifier method to determine the dual isotopic composition (d 15 N and d 18 O) of nitrate is well suited for studies of nitrogen contributions to streams during runoff events. This method requires only 70 nmol of NO 3 À and enables high throughput of samples. We studied nitrate sources to a headwater stream during snowmelt by generating a high-temporal resolution dataset at the Sleepers River Research Watershed in Vermont, USA. In the earliest phase of runoff, stream NO 3 À concentrations were highest and stream discharge, NO 3 À concentrations, and d 18 O of NO 3 À generally tracked one another during diurnal melting. The isotopic composition of stream NO 3 À varied in-between atmospheric and groundwater NO 3 À end members indicating a direct contribution of atmospherically-derived NO 3 À from the snow pack to the stream. During the middle to late phases of snowmelt, the source shifted toward soil NO 3 À entering the stream via shallow subsurface flow paths.
To investigate the effects of bedrock permeability on the linkage between hillslope and riparian ... more To investigate the effects of bedrock permeability on the linkage between hillslope and riparian groundwater in a weathered granite headwater catchment, the groundwater dynamics were studied using intensive hydrometric and tracer observations. Water flow from the hillslope, through the hillslope/riparian interface, and into the riparian zone consists of two components: saturated through flow on the soil-bedrock interface during storms and groundwater flow within the permeable bedrock occurring year-round, except during the driest season. Most of the water, which will contribute to the stream, infiltrates the largest part of the catchment and the hillslope area and recharges the deeper groundwater body. Therefore bedrock permeability is an important factor in determining the hillslope-riparian linkage.
In order to understand the determining factors of the geographical variation of buffering in the ... more In order to understand the determining factors of the geographical variation of buffering in the world's vegetated catchments, this study examined the HCO3-leaching of 107 experimental watersheds selected from regions ranging from tropical rain forests to humid continental or subpolar forests including several temperate grassland. With consideration of the soil development and the factors controlling it, the influences of geological, climatological, and topographical conditions on discharge HCO3-concentrations and fluxes are examined. The HCO3-discharge fluxes from catchments were correlated with climatological indexes. The increase of annual mean temperature reflected the increase in fluxes, although this tendency was not that significant in the precipitation-flux relationships. Notable differences in these correlations were not found among three major groups of bedrock types; igneous, metamorphic, and sedimentary groups, with exceptions being noted at the sites having materially HCO3-rich calcite, dolomite and volcanic ash. There were, however, exceptionally high flux sites whose fluxes could not be predicted by the empirical model when considering only temperature and precipitation controls. These sites belong to the mountainous part of the Japanese archipelago that is orogenically active and have in common steep hillslopes. Positive correlations were found between relief ratio, which was calculated by dividing elevation difference between highest and lowest points in the catchment by the distance between those two points, and fluxes in igneous and sedimentary groups including these high-HCO3-flux sites. These facts suggest that it is a fundamental requirement to consider the status of the soil forming when discussing the global variations in the buffering of watersheds. The differences in geomorphologic conditions controlling soil development are also just as important as the climatological effects. 1. Introduction Acid rain in northern Europe and northeastern America has caused stream and lake acidification in forested catchments but has not had indisputable direct effects on forest vegetation. The research activities on fresh water acidification as an effect of atmospheric acid deposition have brought about the rapid progress in biogeochemistry studies in the cold humid forest ecosystem in these regions [e.g., Likens et al., 1979; Reuss et al., 1987]. In the second half of the 1980s, several catchmentscale hydrochemical models were proposed by the American and European researchers investigating acid rain effects, especially for long term prediction. During that time, the modeling of the buffering mechanisms at the catchment scale. was improved [Cosby et al., 1985; Gherini et al., 1985; Bergstrom et al., 1985; Wolford et al., 1995]. The principle concept of freshwater acidification in northern Europe and northeast America was described by Reuss et al. [1987]. According to their review, the widespread acidification of Copyright 1999 by the American Geophysical Union. Paper number 1999GB900029 0886-6236/99/1999GB900029512.00 surface water in these regions is due to the "superposition" of acid deposition on the natural acidifying processes in soil. They show that the naturally acidified soil profile is sensitive to excess acid deposition. However, it does not necessarily indicate that the anthropogenic acid deposition itself caused the acidification of the soil profiles. Strong mobile acid anions such as SO42' and NO3' with atmospheric deposition have accelerated the mobilization of H* and inorganic A13* which has naturally existed in reservoirs at exchange sites for thousands of years. At that time, Galloway and Cowling [1978] and Reuss et al. [1987] paid attention to the weathering potential as an origin of the buffering capacity. They made maps of sensitivity to freshwater acidification based on bedrock geology. The maps show the geographical distribution of the buffering capacity of soils within North America and northern Europe. Recently, acid rain issues are attracting the attention of not only European and North American communities, but also eastern Asian societies including a number of developing countries [Carmichael, 1997; Satsangi et al., 1997; Shaoxing et al., 1997; Somboon, 1997]. The people of these countries seriously worry about the freshwater acidification and damage to forest resources by soil acidification. The environmental science community in Japan continues to pay attention to the 969 64 Dunn Mill Creek
Recent studies have demonstrated the importance of water movement through the bedrock in the rain... more Recent studies have demonstrated the importance of water movement through the bedrock in the rainfall‐runoff process on steep hillslopes. However, quantitative information on this process is still limited. The objective of this study was to address the following questions: (1) How large is the area where bedrock groundwater seeps into the soil layer, and (2) what is the rate of water flow out of the bedrock? To address these questions, detailed hydrological, hydrochemical, and thermal measurements were conducted at a forested steep unchanneled granitic concave slope in the Tanakami Mountains, central Japan. The relationship between the amplitude of annual soil temperature variation and the measurement depth showed that in a normal low‐flow period, the seepage area ranged between 14 and 21 m2 and the ratio of this area to that of the whole catchment was about 2.0%. In a drought period the seepage area ranged between 3.5 and 5.5 m2, and the ratio to the whole catchment was around 0.5%...
Methane (CH 4) uptake by soil can possibly be suppressed more in regions with heavy summer precip... more Methane (CH 4) uptake by soil can possibly be suppressed more in regions with heavy summer precipitation, such as those under the East Asian monsoon climate, as compared to that in regions with a dry summer. In order to determine how precipitation patterns affect seasonal and spatial variations in CH 4 fluxes in temperate forest soils, such fluxes and selected environmental variables were measured on different parts of a hill slope in a cypress forest in central Japan. On the upper and middle parts of the slope, CH 4 uptake was observed throughout the year, and the uptake rates increased slightly with soil temperature and decreased with soil water content. The CH 4 flux predicted using data for the middle and upper parts of the slope ranged from À1.12 to À0.83 kg-CH 4 ha À1 y À1 (i.e. CH 4 uptake by soil) and from À2.30 to À2.04 kg-CH 4 ha À1 y À1 , respectively. In contrast, in the relatively wet lower part of the slope near an in-stream wetland, large CH 4 emissions (>2 mg-CH 4 m À1 d À1) were observed during the rainy summer. In this wetter plot, the soil functioned as a net annual CH 4 source in a rainy year. Hence the variation in CH 4 flux with a change in soil water conditions and soil temperature on the lower part of the slope contrasted to that on the upper and middle parts of the slope. The predicted CH 4 flux for this lower plot ranged from À0.45 kg-CH 4 ha À1 y À1 in a dry year to 1.80 kg-CH 4 ha À1 y À1 in a rainy year. Our results suggest that consideration of the soil water conditions across a watershed is important for estimating the CH 4 budgets for entire forest watershed, particularly in regions subject to a wet summer.
Japanese Journal of Limnology (Rikusuigaku Zasshi), 2006
In order to model the stream water chemistry in a forest catchment, the model should include func... more In order to model the stream water chemistry in a forest catchment, the model should include functions describing both the biogeochemical cycle and the hydrological pathways as the transportation system for solutes and suspended substances. Although several catchment-scale models have been developed based mainly on the data collected under non-monsoon climate corditions in the northeastern United States and northern Europe, it is questionable whether these models are able to simulate the seasonal changes in streamwater chemistry in a forest catchment under monsoon climate conditions. This is because the monsoon-driven precipitation seasonality affects subsurface-groundwater mixing, and this in turn strongly influences the seasonal variation in streamwater chemistry. To simulate this effect in a catchment-scale response, it is important to combine biogeochemical and hydrological models that will be able to express the effects by soil and groundwater storage and their mixing.
Agricultural Implications of the Fukushima Nuclear Accident, 2013
A massive amount of radioactive substances, including cesium-137 (137 Cs), emitted from the disab... more A massive amount of radioactive substances, including cesium-137 (137 Cs), emitted from the disabled nuclear power plant has deposited on the forested areas in the northeastern region of Honshu Island, Japan after the Fukushima Daiichi nuclear power plant accident. Forests in these regions are particularly important not only for the forest products industry but also for source areas of drinking water and for residential environments. To clarify the mechanisms of diffusion and export of 137 Cs deposited on the forested ecosystem, we initiated intensive fi eld observations in a small catchment, including forest and farmlands, in the Kami-Oguni River catchment in the northern part of Fukushima Prefecture. The following expected major pathways of 137 Cs diffusion and export were investigated: (1) transportation by water movement of dissolved and particulate or colloidal forms through hydrological processes and (2) diffusion through the food web in terrestrial and aquatic ecosystems of forests. Preliminary fi ndings indicated the following: (1) most of the 137 Cs was discharged as suspended matter, and particulate organic matter appeared to be the most important carrier of 137 Cs. High water fl ow generated by storm accelerated the transportation of 137 Cs from the forested catchments. Estimation of 137 Cs export thus requires precise evaluation of the high fl ow acceleration during storm events. (2) Because litter and its detritus may form the biggest pool of 137 Cs in the forested ecosystem, 137 Cs diffusion occurs more rapidly through the detritus food chain than the grazing food chain. Most predators have already ingested 137 Cs, particularly in aquatic environments. An urgent question is when and how 137 Cs diffuses through grazing food chains and how rapidly Chapter 16
Page 1. Chapter 12 Hydrology and Biogeochemistry of Temperate Forests Nobuhito Ohte and Naoko Tok... more Page 1. Chapter 12 Hydrology and Biogeochemistry of Temperate Forests Nobuhito Ohte and Naoko Tokuchi 12.1 Introduction Temperate forests are distributed extensively in middle latitude regions, where the mean annual ...
Cryoconites are microbial aggregates commonly found on glacier surfaces where they tend to take s... more Cryoconites are microbial aggregates commonly found on glacier surfaces where they tend to take spherical, granular forms. While it has been postulated that the microbes in cryoconite granules play an important role in glacier ecosystems, information on their community structure is still limited, and their functions remain unclear. Here, we present evidence for the occurrence of nitrogen cycling in cryoconite granules on a glacier in Central Asia. We detected marker genes for nitrogen fixation, nitrification and denitrification in cryoconite granules by digital polymerase chain reaction (PCR), while digital reverse transcription PCR analysis revealed that only marker genes for nitrification and denitrification were abundantly transcribed. Analysis of isotope ratios also indicated the occurrence of nitrification; nitrate in the meltwater on the glacier surface was of biological origin, while nitrate in the snow was of atmospheric origin. The predominant nitrifiers on this glacier bel...
Even within homogeneous geological and climatological settings, the spatial variability of specif... more Even within homogeneous geological and climatological settings, the spatial variability of specific discharge and some solute concentrations in headwater catchments often increases with decreasing stream order and sub-catchment area, and there is a certain catchment size where the variability is minimized. A simulation model based on the subsurface-bedrock groundwater mixing concept was proposed to determine mechanisms of this scale-variability relationship. Generally, it is difficult for the headwater small catchment to be determined its catchment area of the bedrock groundwater discharge while that of the subsurface groundwater can be measured based on topographical information, and the actual catchment area for the bedrock groundwater is often different from that for the subsurface runoff. The model presented in this paper focuses on this _gdiscrepancy_h in the actual catchment area between the subsurface and bedrock groundwater runoff as an origin of the variability among the lo...
To clarify how hydrological processes affect biogenic methane (CH 4) production and emission from... more To clarify how hydrological processes affect biogenic methane (CH 4) production and emission from soil surfaces, we analyzed the d 13 C of CH 4 and CO 2 and chemical constituents dissolved in groundwater at a wetland in the headwater catchment of a temperate forest in Japan. We estimated the contribution of acetate fermentation using the d 13 C isotope mass balance of dissolved CH 4 and CO 2. CH 4 production pathways (e.g., acetate fermentation and carbonate reduction) changed temporally and spatially with hydrologically controlled redox conditions. The proportion of methanogenesis attributable to acetate fermentation usually decreased with temperature, suggesting that carbonate reduction dominated under conditions of high CO 2 concentration. In particular, the groundwater table and summer temperatures were key controlling factors in the interannual and intra-annual changes in CH 4 production pathways, controlling oxygen supply and consumption and, therefore, redox conditions in the soil. Under high temperature and high water table conditions during summer, the soil was strongly reduced and the proportion of carbonate reduction increased. Acetate fermentation also increased episodically, resulting in sporadic increases in d 13 C-CH 4. The calculated acetate contribution obviously decreased in periods of low water table and high temperature when the soil surface was relatively oxic, implying deactivation of acetoclastic methanogenesis under oxic conditions. Thus, hydrological processes control the supply of these electron donors and acceptors and therefore play an important role in determining the relative proportions of CH 4-producing pathways. Our results also indicate that an increase in acetate contribution under highly reducing conditions stimulates CH 4 production and emission from the soil surface.
The stable isotopic composition of dissolved inorganic carbon (υ 13 C-DIC) was investigated as a ... more The stable isotopic composition of dissolved inorganic carbon (υ 13 C-DIC) was investigated as a potential tracer of streamflow generation processes at the Sleepers River Research Watershed, Vermont, USA. Downstream sampling showed υ 13 C-DIC increased between 3-5‰ from the stream source to the outlet weir approximately 0Ð5 km downstream, concomitant with increasing pH and decreasing PCO 2. An increase in υ 13 C-DIC of 2Ð4 š 0Ð1‰ per log unit decrease of excess PCO 2 (stream PCO 2 normalized to atmospheric PCO 2) was observed from downstream transect data collected during snowmelt. Isotopic fractionation of DIC due to CO 2 outgassing rather than exchange with atmospheric CO 2 may be the primary cause of increased υ 13 C-DIC values downstream when PCO 2 of surface freshwater exceeds twice the atmospheric CO 2 concentration. Although CO 2 outgassing caused a general increase in stream υ 13 C-DIC values, points of localized groundwater seepage into the stream were identified by decreases in υ 13 C-DIC and increases in DIC concentration of the stream water superimposed upon the general downstream trend. In addition, comparison between snowmelt, early spring and summer seasons showed that DIC is flushed from shallow groundwater flowpaths during snowmelt and is replaced by a greater proportion of DIC derived from soil CO 2 during the early spring growing season. Thus, in spite of effects from CO 2 outgassing, υ 13 C of DIC can be a useful indicator of groundwater additions to headwater streams and a tracer of carbon dynamics in catchments.
Hydrology and biogeochemistry of forested catchments A Joint US-Japan Seminar on Forest Hydrology... more Hydrology and biogeochemistry of forested catchments A Joint US-Japan Seminar on Forest Hydrology and Biogeochemistry was held on 1-4 February 2000 at the East-West Center in Honolulu, Hawaii. The purpose of the seminar was to examine the similarities and differences in catchment hydrology research between Japan and the US and to highlight some of the recent and ongoing studies from both countries. A workshop component of the meeting facilitated informal exchange of ideas and approaches to educate the participants on activities in both regions. McDonnell and Tanaka (HPToday Commentary, this issue) synthesize the questions and discussions that emerged from the meeting, that provides the framework for a robust quantitative description of hydrological flowpaths that control biogeochemistry at the catchment scale in forested systems. Studies of catchment hydrology have evolved differently in the US and Japan. Much catchment research in the US has been motivated by interest in explaining stream water chemistry. In contrast, investigations on catchment hydrology in Japan have been more process oriented, initiated by geotechnical questions (Tsukamoto, 1963). As a result, the strengths of the two countries differ. Interdisciplinary approaches are common in the US but rarer in Japan. On the other hand, Japanese hydrologists have developed very sophisticated and novel hillslope and catchment monitoring approaches that aid in the interpretation of processes. Until recently, interactions between hydrological scientists in Japan and the US have not been extensive. The last formal exchange was the US-Japan Joint Seminar on Integration of Physical Insight Into New Approaches in Hydrology held in Hawaii in January 1987. Bras et al. (1988) synthesized these discussions and papers into a special issue of the Journal of Hydrology (Vol. 102). Since this 1987 seminar, the field of hydrology has grown rapidly and the scope of research within the two countries has also changed. Understanding the linkages between hydrology and biogeochemistry of small forested catchments has been highlighted in the US by recent National Research Council (NRC) reports as one of the most pressing needs in watershed research (Eagleson, 1991; Hornberger, 1997). Understanding the interactions between hydrology and biogeochemistry as a critical and under-recognized component of watershed research has also been emphasized (e.g. Cirmo and McDonnell, 1997). Several programmes at the US National Science Foundation (NSF) now promote research on these interactions. Japan has many instrumented headwater catchments (operated by various university researchers and the Japan Forestry and Forest Products Research Institute), several of which were highlighted during the 1987 meeting. Reports of research at these sites have appeared recently in international journals such as Water Resources Research (e.g.
Nematomorph parasites manipulate crickets to enter streams where the parasites reproduce. These m... more Nematomorph parasites manipulate crickets to enter streams where the parasites reproduce. These manipulated crickets become a substantial food subsidy for stream fishes. We used a field experiment to investigate how this subsidy affects the stream community and ecosystem function. When crickets were available, predatory fish ate fewer benthic invertebrates. The resulting release of the benthic invertebrate community from fish predation indirectly decreased the biomass of benthic algae and slightly increased leaf breakdown rate. This is the first experimental demonstration that host manipulation by a parasite can reorganise a community and alter ecosystem function. Nematomorphs are common, and many other parasites have dramatic effects on host phenotypes, suggesting that similar effects of parasites on ecosystems might be widespread.
To quantify the contributions of atmospheric nitrogen deposition and mechanisms of nitrate discha... more To quantify the contributions of atmospheric nitrogen deposition and mechanisms of nitrate discharge to stream, nitrogen chemistry and isotopes (delta 15N and delta 18O of NO3-) of streamwater were studied as part of an ongoing study of nutrient dynamics at the Sleepers River Research Watershed in Vermont, USA. We employed novel analytical procedures for high throughput of NO3- isotopic measurements. The denitrifier method for measurement of delta 15N and delta 18O of NO3- requires a smaller volume of water samples than previously applied methods, thus it enables fine resolution analysis of isotopes for stream, well, and soil water samples. Samples were collected throughout the spring 2003 snowmelt. Snowmelt runoff was initiated in the middle of March and peaked at the end of the month. Then, the runoff rate decreased gradually through April and May, and responded to several storm events. The highest concentration of NO3- in the stream was observed at the beginning of snowmelt (the end of March), and thereafter it declined continuously. The temporal course of NO3- discharge process during snowmelt period was divided into four phases based on changes in the relationship between runoff rate and NO3- concentration. During the earliest phase (very low runoff rate and highest NO3- concentration) isotope signatures, especially delta 18O of NO3-, indicated higher contribution of the atmospherically derived NO3-, meaning that the direct discharge from snow pack was the dominant source of NO3- to the stream. This also suggested that streamwater consisted only of a small volume of groundwater discharge and melt water of the in-stream snow pack and/or stream-covering snow pack. The delta 15N and delta 18O isotope compositions of NO3- during the middle phase of snowmelt indicated that the contribution of the NO3- generated by nitrifiers in soil increased gradually accompanied with increase of groundwater level. These detailed descriptions in the changes of NO3- discharge during snowmelt events were enabled by the dual-isotope analysis of NO3-. The fine resolution isotope analysis of NO3- in our experiment can provide advantages for elucidating the discharge mechanisms of nitrogen in forested watersheds with high atmospheric nitrogen depositions.
The denitrifier method to determine the dual isotopic composition (d 15 N and d 18 O) of nitrate ... more The denitrifier method to determine the dual isotopic composition (d 15 N and d 18 O) of nitrate is well suited for studies of nitrogen contributions to streams during runoff events. This method requires only 70 nmol of NO 3 À and enables high throughput of samples. We studied nitrate sources to a headwater stream during snowmelt by generating a high-temporal resolution dataset at the Sleepers River Research Watershed in Vermont, USA. In the earliest phase of runoff, stream NO 3 À concentrations were highest and stream discharge, NO 3 À concentrations, and d 18 O of NO 3 À generally tracked one another during diurnal melting. The isotopic composition of stream NO 3 À varied in-between atmospheric and groundwater NO 3 À end members indicating a direct contribution of atmospherically-derived NO 3 À from the snow pack to the stream. During the middle to late phases of snowmelt, the source shifted toward soil NO 3 À entering the stream via shallow subsurface flow paths.
To investigate the effects of bedrock permeability on the linkage between hillslope and riparian ... more To investigate the effects of bedrock permeability on the linkage between hillslope and riparian groundwater in a weathered granite headwater catchment, the groundwater dynamics were studied using intensive hydrometric and tracer observations. Water flow from the hillslope, through the hillslope/riparian interface, and into the riparian zone consists of two components: saturated through flow on the soil-bedrock interface during storms and groundwater flow within the permeable bedrock occurring year-round, except during the driest season. Most of the water, which will contribute to the stream, infiltrates the largest part of the catchment and the hillslope area and recharges the deeper groundwater body. Therefore bedrock permeability is an important factor in determining the hillslope-riparian linkage.
Uploads
Papers by N. Ohte