Earth surface environmental changes printed in lacustrine sediments are introduced for the two time-windows (the long interval after the middle Pleistocene and the short one after the little ice age). Lake Baikal and Lake Biwa systems are picked up for the long interval discussion; temperature-related proxies for the two systems indicate similar fluctuations synthesized with solar insolation. Precipitation (discharge)-related proxy for Baikal system shows a similar fluctuation to the temperature-related proxies while the proxy for Lake Biwa shows a fluctuation different a little from the insolation related one, with different periods. Sediment information from Oshima-Onuma lake catchment system picked up for the short interval discussion shows clear cold period in the Maunder minimum period and more precipitation in the late little ice age (till the end of 19^th century).

Lake Onuma and the adjoined lakes, Konuma and Junsainuma are believed to be dammed lakes caused by the volcanic activities of Mt. Komagatake in geological and historical ages. The debris avalanche deposit located at the eastern part of Lake Onuma, which had blocked the water flow of the Oritogawa River, was studied in detail from the aspects of geology and topography. The study showed that the Oritogawa River flow was crammed with a large amount of debris from avalanche deposits about 25m thick that originated in the A.D. 1640 volcanic activity in the eastern area of Lake Onuma. This resulted in the formation of the modern Lake Onuma and the associated lakes. The precise volume of the A.D.1640 debris avalanche deposits, estimated by means of the mass calculated method, was 0.64 km³. Meanwhile, the old debris from avalanche deposits from around 3.2-3.9ka were not observed at all in this area. The water level, that was higher than the present level by about 1 to 2m between A.D.1600 and A.D.1856, was traced from some field research evidences - such as a sedimentary formation located above the present lake water level of 130m at the type locality, two steps of the terrace in the Oritogawa River and erosion cliffs located1 2m above the present lake water level in the eastern corner of Lake Onuma. A particle size change from 3φ to 7φ recorded in the sediment of the type locality covering an age span between 1640 and 1856 at the type locality might have informed us of a lake water level change associated with a precipitation variation in this region. The pumice products 30-50cm thick (a volume of 0.03 km) sourced in the Ko-c1 (A.D.1856) and Ko c2 (A.D.1694) volcanic activities newly found in the wide area of the southern foot of the Mt. Komagatake Volcano. Those intense volcanic events would cause severe damage to the natural environment in Lake Onuma and its surroundings.

This study investigated recent environmental changes in the catchment of Lake Onuma, Japan, based on a physical and geochemical analysis of sediment cores obtained in 2011. Fluctuations in the sediment density, mineral grain size, and C/N ratio of the sediment cores indicate that the sediment yield in the catchment increased between the 1950s and 1970s, with this increase attributed to the artificial land transformation during this period. Clear mineral grain size peaks correspond to heavy rainfall events that caused local flooding and landslides in the catchment. The C/N ratio and δ¹³C values of the sediment core are within both the planktonic material and river sediment ranges, which suggest that the lacustrine sediment is an almost constant mixture of these two sources. However, the δ¹⁵N values have increased in the core since the 1950s, which reflects recent and ongoing anthropogenic nitrogen inflow into the lake.

The chemical speciation of major inorganic elements and arsenic in the 1 m length sediment core obtained Lake Onuma, Hokkaido were examined by means of chemical extraction technique. The obtained core recorded the environmental history from the eruption of Hokkaido Komagatake volcano at 1929 to present. The arsenic contents in the sediment were low at 5-15 mg/kg. However, those at top 40cm layer of the sediment exceeded the background level of arsenic in the catchment area. This suggests that the arsenic is accumulated in the surface sediments of Lake Onuma. The arsenic in the sediment was mainly associated with iron/manganese oxide and iron sulfide. The contributions with the iron sulfide increased with depth, while those with iron/ manganese oxide decreased with depth. The systematic trends with depth indicate that the sedimented arsenic must be mobile via redox reactions in the sediments. The arsenic concentration in the lake water (0.4 μg/L) was almost twice higher than those from the inflow rivers. This may suggest that very small amount of arsenic in the surface sediments has been continuously released to the lake water.

Lake Onuma, Hokkaido, has a history of eutrophication accompanied by the developments of agriculture and cattle breeding in the catchment area. Non-point source loadings of nutrients caused the eutrophication and resultantly frequent occurrences of nuisance cyanobacterial blooms there. The existence of cyanobactericidal bacteria and growth-inhibiting bacteria against the toxic cyanobacterium Microcystis aeruginosa was newly discovered on the water plants such as the reed Phragmites australis and floating plant Trapa japonica in Lake Onuma. These effective bacteria were found with densities of the order of 10⁵-10⁷ CFU (colony-forming units) g^－1 wet weight, and 10³-10⁴CFU mL^－1 in the adjacent waters. The absence and/or lower densities of M.aeruginosa was closely related to the abundant presence of these effective bacteria detected from the water and biofilms of water plants. These facts provide new insights into the ecology of cyanobactericidal bacteria and growth-inhibiting bacteria, and suggest that the water plants provide an environment that reduces the abundance of cyanobacterial blooms in freshwater ecosystems. The Sato-Umi concept was proposed to maintain good conditions of Lake Onuma with decreased incidents of nuisance cyanobacterial blooms under the adequate control managements of biomass and diversity (species composition) of water plants.

Specific amount of sediment deposition in dam reservoirs is a useful index to appraise the degree of sediment production from the catchments. We examined the relationships between the amount and geomorphic and geological characters of catchments of various sizes in Hokkaido, Japan, by analyzing annual sedimentation records in 105 reservoirs. The 28 of the reservoirs were situated in mountainous areas, and the annual specific sediment yield from the catchments was 178m³/km²/year on average. Sediment yield from the catchments underlain by sedimentary rocks was 8 times larger than those underlain by volcanic rocks, and rainfall pattern was strongly reflected in the sedimentation record. On the other hand, specific sediment yield rates became more dependent on dam utilization by human activities for larger catchments. The data revealed that annual specific sediment yield increased with the size in catchments smaller than 100 km², while the relationship is reversed for those larger than the size.