Southwest Hokkaido Research Articles

The formation of schwertmannite colloids and natural remediation of toxic elements from Shojin River, Hokkaido, Japan

AbstractPassive treatment systems are a sustainable solution to mine drainage remediation, however, clarity lacks in the detailed understanding of the geochemical processes that govern the remediation processes. A study was carried out at Shojin River in Southwest Hokkaido, Japan, which has an acidic pH and is high in Fe, to represent the principal processes that occur in mine drainages of similar characteristics. At Shojin, Fe and S were mined from the Shojingawa mine, after which, wastewater contaminated by toxic elements such as Fe, As and Pb continue to flow from the underground. This wastewater flows through industrial and fishing areas, hence ensuring that the water meets environmental standards is important. In particular, the role of colloidal materials in transporting the toxic elements was investigated by analyzing the distribution of the elements (Fe, As and Pb) in the drainage as the dissolved and colloidal fractions, obtained from micro‐, and ultrafiltration respectively. Iron, particularly schwertmannite colloid formation was observed in the Shojin River system. Itwas present in the dissolved fraction in the wastewater like As, but after mixing with the uncontaminated river water, Fe in the colloid fraction gradually increased toward the downstream. Arsenic trends are similar to those of iron, indicating efficient sequestration by the schwertmannite colloids. Lead is dominantly in the dissolved fraction throughout the drainage and is comparatively less sequestered due to competitive adsorption with As and its pH dependence to be efficiently adsorbed. A detailed observation of the concentration trends suggests that pH 3.1 may efficiently allow colloid formation and subsequently, toxic element sequestration. The behavior of Fe colloids in Shojin River was compared to those of a circum‐neutral drainage system (Ainai mine drainage). The formation of the colloids in the acidic system was limited by the pH range, while colloids formed faster and more abundantly in the circumneutral system. The acidic and circum‐neutral systems are abundant in schwertmannite and ferrihydrite colloids respectively. The colloids in both systems were transported after their formation, however, the colloids in the Shojin (acidic) system were transported further than those of the circumneutral system. Aggregation is observed in both systems which results in a deposition of the colloid aggregates and hence an efficient removal of Fe and As, and minimally, Pb from the mine drainages.

Local Strategy for Managing the Impacts of Sea Cucumber Booms in the Global Market: A Study of Different Cases from South-West Hokkaido, Japan

Local Strategy for Managing the Impacts of Sea Cucumber Booms in the Global Market: A Study of Different Cases from South-West Hokkaido, Japan

Zircon U-Pb age of greenish tuff deposit distributed in the eastern base of Yotei Volcano, southwest Hokkaido, Japan

Zircon U-Pb age of greenish tuff deposit distributed in the eastern base of Yotei Volcano, southwest Hokkaido, Japan

Sedimentary rhythm of Mn-carbonate laminae induced by East Asian summer monsoon variability and human activity in Lake Ohnuma, southwest Hokkaido, northern Japan

Past and ongoing precipitations of Mn-carbonate (rhodochrosite) have occurred in the freshwater Lake Ohnuma, which is situated about 8 km south of the Hokkaido-Komagatake volcano, southwest Hokkaido (northern Japan). Lake sediments from a surface and a longer ∼4 m core contain the sedimentary rhythms of rhodochrosite laminae and volcanic deposits which were identified by nondestructive micro-XRF fluorescence analyses. The three tephra ash layers from the Hokkaido-Komagatake volcano, characterized by peaks of Al, Si, K, Ca, and Ti, correspond to regionally recognized tephras (1640, 1929 and 1996 CE) based on ashfall isopachs and 137Cs, 210Pb and 14C ages determined from the two cores. The sedimentation rate showed a drastic change around 1929 CE; ∼0.3 cm/yr for 1640–1929 CE and ∼2.7 cm/yr for 1929–2012 CE. The Mn content record of Lake Ohnuma sediments, composed of rhodochrosite laminae, showed a periodic variation with a decadal–centennial scale over the interval 1640–2012 CE. Sediment petrography and hydrochemical measurements suggest that the metastable phase of rhodochrosite was deposited during summer after being precipitated, followed by the crystal growth of rhodochrosite within the anoxic sediments. On the basis of these results, high Mn content is interpreted as an indicator of strengthened summer stratification associated with reduced rainfall runoff. The Ti/Si ratios are representative of the relative abundance of detrital inputs from the watershed. The combined signals of elevated Mn content and Ti/Si ratio for 1935–2012 CE indicate eutrophication and hypoxia in the lake and enhanced land erosion in the watershed, associated with the post-1970s intensive land use such as livestock farming. For 1640–1935 CE, the Lake Ohnuma record shows an antiphase relationship between the Mn content and Ti/Si ratio, which implies that the detrital inputs reflected the strength of the East Asian summer monsoon (EASM), and the reduced rainfall runoff resulted in weaker mixing, followed by depleted O2 in the water column. The antiphase variation in Mn content and Ti/Si ratio suggest weak EASM during the Little Ice Age (∼1850 CE), followed by strong EASM between 1860 and 1929 CE.

Reproductive cycle and growth of the sand dollar Scaphechinus griseus inhabiting Japanese surf clam Pseudocardium sachalinense fishing grounds in Tomakomai, southwest Hokkaido, Japan

Bioturbation by the sand dollar Scaphechinus griseus is suspected to inhibit the recruitment of Pseudocardium sachalinense, a commercially important bivalve. This study aimed to develop a standard method for the extermination of the sand dollar by examining its reproductive cycle, relationships between age and growth, and population structure in Tomakomai, southwest Hokkaido, Japan. Histological observations of the gonads indicated that the sand dollar has one spawning season per year, in June–August. Seasonal changes in the appearance of a dark band around the interambulacral plate suggested that the annual ring primarily forms in June–July, with the first ring forming at 1 year of age. Analysis of fitness by growth models showed that the Gompertz curve was better matched to the data than the von Bertalanffy and logistic curves; growth is fast until 1.6 years of age, then slows. The population density was 190–257 individuals/m2, and average test diameters were 39.0–40.9 mm. Three-year-olds comprised the highest percentage of the population; no individuals of 8 years of age or older were detected. In conclusion, to reduce the density of sand dollars efficiently and to prevent their reproduction, individuals with a test diameter of over 30 mm should be exterminated before the spawning season.

西南北海道洞爺湖東方の鮮新-更新統について : 堆積相・花粉層序・古地磁気層序

西南北海道洞爺湖東方の鮮新-更新統について : 堆積相・花粉層序・古地磁気層序

西南北海道における中新世玄武岩(馬場川層)のK-Ar年代

西南北海道における中新世玄武岩(馬場川層)のK-Ar年代

Stratigraphic records of tsunamis along the Japan Sea, southwest Hokkaido, northern Japan

AbstractThe stratigraphy of tsunami deposits along the Japan Sea, southwest Hokkaido, northern Japan, reveals tsunami recurrences in this particular area. Sandy tsunami deposits are preserved in small valley plains, whereas gravelly deposits of possible tsunami origin are identified in surficial soils covering a Holocene marine terrace and a slope talus. At least five horizons of tsunami events can be defined in the Okushiri Island, the youngest of which immediately overlies the Ko‐d tephra layer (1640 AD) and was likely formed by the historical Oshima‐Ohshima tsunami in 1741 AD. The four older tsunami deposits, dated using accelerator mass spectrometry 14C, were formed at around the 12th century, 1.5–1.6, 2.4–2.6, and 2.8–3.1 ka, respectively. Tsunami sand beds of the 1741 AD and circa 12th century events are recognized in the Hiyama District of Hokkaido Island, but the older tsunami deposits are missing. The deposits of these two tsunamis are found together at the same sites and distributed in regions where wave heights of the 1993 tsunami (Hokkaido Nansei‐oki earthquake, Mw = 7.7) were less than 3 m. Thus, the 12th century tsunami waves were possibly generated near the south of Okushiri Island, whereas the 1993 tsunami was generated towards the north of the island. The estimated recurrence intervals of paleotsunamis, 200–1100 years with an average of 500 years, likely represents the recurrence interval of large earthquakes which would have occurred along several active faults offshore of southwest Hokkaido.

A42 西南北海道,羊蹄火山の最近約5万年間のテフラ層序 : 古羊蹄火山起源テフラの発見と岩屑なだれの発生時期(火山発達史と地質,口頭発表)

A42 西南北海道,羊蹄火山の最近約5万年間のテフラ層序 : 古羊蹄火山起源テフラの発見と岩屑なだれの発生時期(火山発達史と地質,口頭発表)

ORE MINERALS FROM KUROKO TYPE DEPOSIT OF TOYA-TAKARADA MINE, HOKKAIDO, JAPAN

Toya-Takarada mine is Au- and Ag-rich Kuroko-type deposit located in Takarada, Toya-mura, southwest Hokkaido, Japan. The deposits were hosted in rhyolitic tuff and mudstone of Middle Miocene age. Ore samples of fine-grained black ore, vuggy black-yellow ore, granular vuggy black ore, quartz-sulfide ore and massive quartz-barite ore were studied to identify the ore minerals association in the Toya-Takarada mine. The ore minerals are dominated by sphalerite, galena, chalcopyrite and pyrite with fewer amounts of electrum, tetrahedrite-tennantite, and other sulfosalt minerals with secondary mineral of covellite.The quantitative chemical analysis of ore minerals by EPMA indicated that FeS contents in sphalerite is low (0.3-1.2 mol.%) in all kinds of ore samples. Small grains of electrum as inclusions in pyrite are identified in vuggy black-yellow ore with Ag content around 32-33 atm %.In general, the silver minerals in Kuroko-type deposits occurred mainly in the black and yellow ores zone dominantly composed of sphalerite, galena, pyrite, chalcopyrite and barite as a form of electrum and/or argentian tetrahedrite-tennantite series. Thus, the massive quartz-barite ore sample of Toya-Takarada mine are also contain some rare silver sulfosalt minerals such as proustite, Cu-rich pearceite, geocronite-jordanite and fizelyite. Those minerals were found together in association with sphalerite. It seems that sphalerite was crystallized first followed by proustite and Cu-rich pearceite, then geocronite-jordanite and fizelyite are crystallized later.Sphalerites from quartz-sulfide ore of Toya-Takarada contain some fluid inclusions and measured homogenization temperatures are in the range of 164-247°C (av. 208°C) with salinity ranging from 1.9 to 4.7 wt.% NaClequiv. (av. 3.9 wt.% NaClequiv.). The mineral assemblage, iron content in sphalerite and silver content in electrum were indicated that sulfur fugacity was slightly higher during ore mineralization in Toya-Takarada mine.

Explosive eruptive activity and temporal magmatic changes at Yotei Volcano during the last 50,000 years, southwest Hokkaido, Japan

To understand the eruptive history, structure, and magmatic evolution of Yotei Volcano, southwest Hokkaido, Japan, we investigated the geology and petrology of tephras located around the base of the volcano. We identified 43 tephra units interbedded with soils (in descending stratigraphic order, tephras Y1–Y43), and four widespread regional tephras. Ten radiocarbon ages were obtained from soils beneath the Yotei tephras. On the basis of petrologic differences and, the stratigraphic positions of thick layers of volcanic ash soil, indicative of volcanic stratigraphic gaps, the Yotei tephras are divided into four groups (in ascending stratigraphic order): Yotei tephra groups I, II-1, II-2, and II-3. We calculated the age of each eruptive deposit based on the soil accumulation rate, and estimated the volume of each eruption using isopach maps or the correlation between eruption volume and the maximum thickness at ~10km from the summit crater. The results regarding eruptive activity and the rate of explosive eruptions indicate four eruptive stages at Yotei Volcano over the last 50,000years. Stage I eruptions produced Yotei tephra group I between ca. 54cal.kaBP and up to at least ca. 46cal.kaBP, at relatively high average eruption rates of 0.07km3 dense-rock equivalent (DRE)/ky. After a pause in activity of ca. 8000years, Stage II-1 to II-2 eruptions produced Yotei tephra groups II-1 and II-2 from ca. 38 to ca. 21cal.kaBP at high average eruption rates (0.10km3DRE/ky), after a pause in activity of 2000–3000years. Finally, after another pause in activity of 4000–5000years, Stage II-3 eruptions produced Yotei tephra group II-3 from ca. 16.5cal.kaBP until the present day, at low average eruption rates (0.009km3DRE/ky). Whole-rock geochemical compositions vary within each tephra group over the entire eruption history. For example, group I and II-3 tephras contain the lowest and highest abundances, respectively, of K2O, P2O5, and Zr. Group II-1 has the highest abundances of Zr and Y. These trends indicate that the explosive activity was controlled by an evolving magma system. An understanding of these temporal changes in the chemical composition of the magma will enable future correlations of tephras with volcanic edifices, thereby revealing the full eruptive history and structure of Yotei Volcano, and constraining the timing of geological events in the region.

Floor conditions and the ecosystem of Fagus crenata forest in southwest Hokkaido

Floor conditions and the ecosystem of Fagus crenata forest in southwest Hokkaido

Strong Motion Estimation at Okushiri Port Landslide induced by the 1993 Southwest Hokkaido Earthquake based on the Empirical Site Amplification and Phase Effects

Strong Motion Estimation at Okushiri Port Landslide induced by the 1993 Southwest Hokkaido Earthquake based on the Empirical Site Amplification and Phase Effects

奥尻島住民による北海道南西沖地震後の復興の評価

奥尻島住民による北海道南西沖地震後の復興の評価

Spatial association between northern fur seal (Callorhinus ursinus) and potential prey distribution during the wintering period in the northern Sea of Japan

AbstractElucidating the response of marine predators to oceanographic features helps in understanding their foraging strategies and the cause of their spatial overlap and interference with fishery activities. Northern fur seal is a highly pelagic species during the wintering period. In recent years, fur seals have consistently been found distributed near the coast of southwest Hokkaido, Japan. Because interference by fur seals with coastal fishery activities has become a serious concern, an understanding is sought as to why fur seals come ashore in this area. We conducted ship‐based observations and estimated fur seal density. To elucidate the spatial and seasonal association of fur seal distribution and ocean environments, we constructed statistical models to describe how potential prey distribution and oceanographic features influenced the fur seal spatial distribution during the wintering period. Fur seal distribution corresponded markedly to potential prey distribution, and they tended to aggregate along the narrow continental shelf that is the main geographic feature of this area, which is 2000 m deep and approximately 10 km from the coast. Walleye pollock [Gadus chαlcogrαmmα(Theragra chαlcogrαmmα)] and arabesque greenling (Pleurogrammus azonus), which are one of the main prey for fur seals, move to the shallow area to spawn on the continental shelf seasonally, so potential prey abundance could be higher in coastal areas than offshore. Moreover, the absence of a mesopelagic biotic community may be one of the main factors in the coastal distribution of the fur seal.

Variation in regional diet and mandibular morphology in prehistoric Japanese hunter–gatherer–fishers

Previous research has identified a relationship between mandibular morphology and diet (e.g., coarse or tough diets result in more robust mandibles). Prehistoric Japan is an excellent place to explore the significance of this relationship in shaping mandibular morphology due to the pronounced regional dietary variation. South/West Honshu Jōmon engaged in broad spectrum foraging, Northeastern Honshu Jōmon were fisher–gatherers, Hokkaido Jōmon were maritime (sea mammal) foragers. We test the hypothesis that diet variation across temporal and spatial zones will be reflected in mandibular morphological traits. Metric measurements were utilized to test for regional differences with both archaeological time period and biological sex as covariants. ANOVA results for region with time period as a covariate indicates all variables except corpus height and breadth are significantly different among regions but for the time period covariate, only corpus breadth and dimensions of ascending ramus are significant. ANOVA for region with biological sex as a covariate indicates all variables except corpus height are significantly different. Biological sex as a covariate demonstrates significant p-values for chin height, bicondylar breadth and minimum ascending ramus breadth. Generally, North Hokkaido and Southwest Hokkaido, exhibit the largest mandibular ascending rami and tallest anterior mandibles, whereas Northeast and South/West Honshu have smaller mandibles. Multivariate analysis indicates a separation between North and Southwest Hokkaido and South/West Honshu, whereas Northeast Honshu partially overlaps these dietary zones. Differences in mandibular morphology are better explained by regional diets than by temporal trends and biological sex.

Petrology study of pyroclastic rocks of Yoneoka formation, Okushiri island, southwest Hokkaido

Petrology study of pyroclastic rocks of Yoneoka formation, Okushiri island, southwest Hokkaido

Fault outcrop at Neppu Genya in Kuromatsunai Lowland fault zone, southwest Hokkaido

Fault outcrop at Neppu Genya in Kuromatsunai Lowland fault zone, southwest Hokkaido

Holocene vegetation and climate on Hokkaido Island, northern Japan

Hokkaido is classified into five regions based on climatic features: the Japan Sea coast, the Pacific coast, the Okhotsk Sea coast, the inland region, and southwest Hokkaido. Holocene vegetation and climate changes at twelve sites selected from these regions are reviewed and compared. On the Japan Sea coast, Picea and Quercus pollen fluctuated at millennial scale, matching with pulses of the Tsushima Current revealed from diatom-based temperature reconstructions in the Japan Sea. A marine core obtained from off the Pacific coast revealed a maritime climate through increasing Betula pollen percentages during the last deglaciation and early Holocene. In summer, dense sea fog resulting from the Oyashio Cold Current and Ogasawara High caused a maritime climate on the Pacific coast. Pollen percentages of Betula ermanii, which is well adapted to the maritime climate in Northeast Asia, increased during this period. Vegetation changes on the Okhotsk Sea coast and in inland regions were similar, indicating similar climatic changes. In these regions, Quercus forests have been distributed steadily since 8000 BP under a warm and moist climate, except for the northern coast, at the Sea of Okhotsk, where Picea and Abies increased slightly since 2000 BP. In southwest Hokkaido, Quercus began to increase 1000 years earlier than in other regions. Fagus crenata migrated from Honshu Island to southernmost Hokkaido around 6000 BP and reached the current northern limit around 1000 BP. The period during which Quercus pollen percentages increased is recognized in almost all regions at around 8000–9000 BP. However, local factors, such as river flooding and local strong winds, also influenced the vegetation changes. Comparison of the vegetation changes in three neighboring regions of Northeast Asia indicate abrupt warming at around 8000–9000 BP and cooling at 2500 BP common to all regions, suggesting global climatic changes.

Sulfur isotopic study of ore minerals and altered host rocks of Neogene-Quaternary overprinting hydrothermal systems in the Toyoha-Muine area, southwest Hokkaido, Japan

Sulfur isotopic study of ore minerals and altered host rocks of Neogene-Quaternary overprinting hydrothermal systems in the Toyoha-Muine area, southwest Hokkaido, Japan