수생태계 보호를 위한 토사관리 방안 = Sediment Management Plans for Protecting Aquatic Ecosystem

다국어 초록 (Multilingual Abstract)

Sediment significantly deteriorates the functions of aquatic ecosystems in streams. The main purpose of this study is to provide a detailed review of the impacts of sediment and sediment-oriented pollutants on the aquatic environment and to recommend a better sediment management strategy based on scientific proof and references. In Korea, large amounts of sediment detached from the soil structure are regarded as a natural or local problem during only the monsoon season. Nationwide research related to the impact of sediment primarily concentrated on the impact of turbid water because turbidity degrades the aesthetic quality of water and can disturb drinking water sources, such as large dams. Nevertheless, the Ministry of Environment (MOE) and other government groups recently agreed that to maintain their value, the health of streams and aquatic ecosystems should be restored. For example, MOE evaluates not only the characteristics in water quality in terms of physical and chemical measurement, but introduces biological assessments to observe aquatic and riparian ecosystems. Although environmental stressors for sediment come from point and/or nonpoint source pollution and intensive human activities, decision-makers have not employed sufficient sediment management strategies for conserving aquatic ecosystems. Numerous studies emphasize the importance of soil erosion and sediment control to manage the aquatic ecosystem. They also indicate that suspended and bedded sediments prohibit the growth of aquatic organisms and decrease ecological numbers and diversity, regardless of the streams size. Chemical-bounded sediment, in particular, may be harmful to benthic communities (e.g., macro-invertebrates and submerged plants) and fish. In this study, we focused on human activities that caused massive sediment yields generated by water erosion, how accelerated sediment processes alter overall aquatic ecosystems, and how to manage planning with regard to sediment before it enters the stream. As a result, sediment and aquatic ecosystems were defined based on previous references so that a regulatory definition may be used in the ``water quality and aquatic ecosystem protection`` law. Soil erosion potential was estimated using a soil loss prediction tool and the simulation was compared using the area-weighted ratio of mountain crops in each meso-scale watershed. In order to provide better management of sediment, several case studies identifying ecological disturbance in aquatic life were reviewed, and advanced control measures in other countries were examined. In conclusion, the following items were suggested: 1. It is important to recognize that soil is a valuable resource and that it ensures sustainability, but massive suspended and bedded sediments are classified as pollutants, especially with regard to the aquatic ecosystem. While soil is one of three essential assets (water and air being the other two), sediment and sediment-bound pollutants increase a degree of ecological risk when they enter streams. Therefore, a paradigm shift for ones should be made that massive sediments are regarded as serious pollutants because they decrease the river health. 2. The current standards (25 mg/L, moderate level) for suspended solids in streams should be further regulated. Some streams below the standards are required to maintain current concentrations and to reduce sediment yields based on indigenous charactieristics in aquatic ecosystem. In addition, developing the protocol of total maximum sediment loads may be demanded to protect aquatic species and other purposes in water resources management. 3. It is critical to survey the impact of bedded sediments on aquatic ecosystem. There were some reports for that of suspended sediments in Soyang and Imha dam watershed. However, it is very limited to evaluate how bedded sediments influence water quality and aquatic ecosystems in practice. After analyzing the relationship between pollutants in bedded sediments and changes in aquatic ecosystem, a new criteria for bedded sediments can be indroduced. 4. In the study, the group of human-induced sediments are classified to as agricultural, forest, surface soil disturbance, mining, urban and stream construction, etc. Best management practices help to reduce the risk posed by sediments. These practices should be parallel with non-structural measurements such as education, regulatory revisions, and stewardship. Above all, the most effective sediment management plan for protecting aquatic ecosystem is to keep soil particles in the soil structure using physical and regulatory efforts. 5. In order to connect the aquatic ecological heath up to downstream, sediment and pollution management at headwater or small streams is very significant. Management. Protecting small and/or shallow streams is obvious, as they are areas where abundant plant and animal life move downstream. Some aquatic habitats in small streams severely suffer from bedded sediment from crops, and these streams are usually located around watersheds upstream. Therefore, spatial extension for current water quality criteria should also cover small streams in order to maintain an integrated ecosystem. Also, the current small stream management regulations should adopt more ecological management guidelines. 6. In order to make sediment management decisions, the development of an advanced stream and soil database is recommended. Because sediments are transported by upland surface runoff to deposits downstream, an efficient Decision Support System (DSS) is crucial in order to estimate the risk of sediment to watersheds. Through DSS, the collection of related information, such as hydrology, geomorphology, and soil properties, is central to accurately predicting reactions and making reliable decisions. While there are a number of datasets for this information in various formats in Korea (Water Management Information System (WAMIS), and other government-supported institutions), they are limited in that they do not provide sufficient data on the management of sediments or soil erosion. Good examples of the frameworks necessary are the National Hydrography Dataset (NHD, http://nhd.usgs.gov) and the Soil Survey Geographic Dataset (SSURGO, http:// www.ncgc.nrcs.usda.gov/products/datasets/ssurgo/) This study was limited to analysis of the impact of rainfall intensity and soil moisture on sediment management. Sediment delivery ratios are inherently based on watershed conditions, and thus, the soil erosion rate was not precisely quantified using the prediction modeling. It is required to determine the relationship between both suspended and bedded sediment and other major factors, including dissolved oxygen, temperature, pH, and toxic pollutants with regard to the degradation of the aquatic ecosystem. Finally, we need to study the impact of disturbance to aquatic ecosystems on economic loss including general industries and culture & travel industries and to prepare changes from global weather changes whether our natural ecosystems respond to generate more or less sediment volume.