Kota Katsuki

Human-induced marine ecological degradation: micropaleontological perspectives

We analyzed published downcore microfossil records from 150 studies and reinterpreted them from an ecological degradation perspective to address the following critical but still imperfectly answered questions: (1) How is the timing of human-induced degradation of marine ecosystems different among regions? (2) What are the dominant causes of human-induced marine ecological degradation? (3) How can we better document natural variability and thereby avoid the problem of shifting baselines of comparison as degradation progresses over time? The results indicated that: (1) ecological degradation in marine systems began significantly earlier in Europe and North America (∼1800s) compared with Asia (post-1900) due to earlier industrialization in European and North American countries, (2) ecological degradation accelerated globally in the late 20th century due to post-World War II economic growth, (3) recovery from the degraded state in late 20th century following various restoration efforts and environmental regulations occurred only in limited localities. Although complex in detail, typical signs of ecological degradation were diversity decline, dramatic changes in total abundance, decrease in benthic and/or sensitive species, and increase in planktic, resistant, toxic, and/or introduced species. The predominant cause of degradation detected in these microfossil records was nutrient enrichment and the resulting symptoms of eutrophication, including hypoxia. Other causes also played considerable roles in some areas, including severe metal pollution around mining sites, water acidification by acidic wastewater, and salinity changes from construction of causeways, dikes, and channels, deforestation, and land clearance. Microfossils enable reconstruction of the ecological history of the past 102–103 years or even more, and, in conjunction with statistical modeling approaches using independent proxy records of climate and human-induced environmental changes, future research will enable workers to better address Shifting Baseline Syndrome and separate anthropogenic impacts from background natural variability.

Delta Formation in the Nakdong River, Korea, during the Holocene as Inferred from the Diatom Assemblage

ABSTRACT Cho, A.; Cheong, D.; Kim, J.C.; Shin, S.; Park, Y.-H., and Katsuki, K., 2017. Delta formation in the Nakdong River, Korea, during the Holocene as inferred from the diatom assemblage. The causes and succession of the Nakdong River delta formation related to sea-level change and precipitation in the early–middle Holocene were discussed based on diatom analysis. On the basis of ecology, stratigraphic changes of diatom flora were divided into five divisions, labeled zones I–V. According to the diatom assemblage, the first marine transgression occurred at about 10.5 ka at this research site. At that time, marine species gradually increased, and freshwater species had their highest values. This site was an estuary influenced by inputs of fresh and marine water until 9.8 ka (zone I). Zone II is dominated by bay and offshore species, meaning that sea level rose continuously after about 9.8 ka (zone II) when the Nakdong River mouth region was an inner bay. Then, the environment of this site changed to an outer bay after 8 ka (zone III) because of sea-level rise, which is supported by increasing numbers of oceanic species. At the end of this zone, at 6–7 ka, sea level highstand occurred. A prodelta began forming just after the highstand under slow sea-level rise (zone IV), and the delta front arrived at its present location at 5 ka by voluminous sediment input from the Nakdong River related to high precipitation during the Holocene Climate Optimum (zone V). After 5 ka, the delta front remained around its present site because of stable or decreasing sea level. Compared with other Asia deltas (Yangtze and Mekong), the initiation of the Nakdong River delta was delayed by about 1000–2000 years because of differences in relative sea-level changes.

Late Quaternary Environmental Changes of the Hwajinpo and Songjiho Lagoons on the Eastern Coast of Korea

The Hwajinpo and Songjiho lagoons, located 25 km apart on the mid-eastern coast of Korea, are known tectonically stable. Two core sediments were obtained from the Hwajinpo lagoon (HJ99) and Songjiho lagoon (SJ99). Lithologic, geochemical and paleontological data include grain size, water content, magnetic susceptibility, soft X-ray of core samples, TOC, TN, C/N, TS, C/S, assemblages of mollusc and palynomorphs remains. Based on multi-proxy data, six main lithological units were identified in both lagoons, indicative of paleoenvironmental changes during the Holocene, as well as the evolutionary histories of each lagoons related to Holocene sea level changes of the East Sea (Japan Sea). The environmental changes of both lagoons are considered mainly due to the lake/sea level fluctuation during the Late Quaternary because the mineral composition analysis does not show any provenance changes. Although the lithologic changes in the both lagoons do not show any temporal similarity, T-R (transgression and regression) trends based on the grain size variation shows simultaneity. T-R diagram presents three cycles clearly since 7,800 14C yr BP. Highstand sea levels (transgressions) are appeared at about 7,400, 5,500, and 2,200 14C yr BP, while lowstand sea levels (regressions) at about 6,500, 4,100, and 1,800 14C yr BP during the Holocene. Especially, the anthropogenic deposits in both lagoons since about 300 cal-yr BP show relatively very high sedimentation rate than previous depositional units. The rapid sedimentation was due to human activities, agricultural reclamation and/or deforestation in both lagoon-catchment areas.