Quantifying Suspended Sediment Loading in a Mid-Missouri Urban Watershed Using Laser Particle Diffraction.

摘要

Soil erosion and suspended sediment is one of the most pervasive pollutants of freshwater impairment. High concentrations of suspended sediment can alter or damage physical, chemical, and biological status of aquatic ecosystems, which may lead to serious water quality issues. While suspended sediment is one of the most common sources of water impairment it is often difficult to quantify and characterize due to the expense and amount of labor associated with traditional sediment sampling techniques. New technologies have been developed to monitor suspended sediment in-situ, eliminating much of the labor and expense associated with traditional methods of suspended sediment monitoring. The following research used laser diffraction particle analyzers to quantify suspended sediment concentration (SSC) and particle size in an urbanizing, Mid-Western watershed during the spring of 2010. A nested-scale study design with three sub-basins was used to examine the effects of land-use on suspended sediment trends. Sub-basins were categorized as headwater (36% forested, 55% agriculture), suburban (36% forested, 36% agricultural), and urban (67% urban). Mean SSCs were estimated to be 66.0, 70.0, and 86.0 μl/l for the headwater, suburban, and urban sub-basins (respectively). Mean sediment size was estimated to be 151.0, 111.0, and 79.0 μm for the headwater, suburban, and urban sub-basins respectively. Total sediment loads measured at the headwater, suburban, and urban monitoring sites were 13,183, 27,369, and 42,854 tonnes (respectively). Sediment yield was approximately 170.0, 153.0, and 208.0 tonnes/km 2 for the headwater, suburban and urban sub-basins respectively. Mean suspended sediment concentrations were highest (86.0 μl/l) in the urban sub-basin and lowest (66.0 μl/l) in the headwater sub-basin. Mean sediment particle size decreased with linear distance of the stream from the headwater (151 μm), to the suburban (111.0 μm), and exited the watershed through the urban (79.0 μm) sub-basin. This pattern may indicate that as suspended particles are transported downstream they become physically weathered. Results also indicate that higher concentrations of smaller soil particles may be transported to the stream from urban terrestrial processes relative to headwater and suburban sub-basins. Total sediment yields were highest in the urban sub-basin and lowest in the suburban sub-basin. Total sediment yields decreased from the headwater to the suburban sub-basin possibly indicating that particles eroded in the upper portion of the watershed are deposited in the channel in the suburban reaches of the stream. Total sediment yield increased through the suburban to the urban sub-basin, which may be largely attributable to increased channel erosion between the suburban and urban gauging sites. Few studies have examined the relationships between land-use and sediment flux in the Mid-West. This study illustrates how land-use affects sediment trends. As land-use continues to change, the ability to protect and enhance water quality will depend on how well scientist, land managers, and policy makers understand the relationships between land-use and hydrological processes.