Suspended sediment supply dominated by channel processes in a low-gradient agricultural watershed, Wildcat Slough, Fisher, IL, USA

Nutrient loading in rivers in the Upper Sangamon River Basin has led to concentrations of nitrate that exceed EPA water quality standards and concentrations of phosphorous that promote algal growth. Nitrogen and phosphorous are primarily introduced by fertilization and transported via leaching through the soil profile and adsorption to fine sediments, respectively. This study estimates the relative contribution of suspended sediment from various land use types entering into the Wildcat Slough, a low gradient, intensively managed 61.3 km2 watershed in the Upper Sangamon River Basin in central Illinois, USA. The land is primarily used for agriculture, but forests, floodplains, banks, a restored prairie and grasslands, and a pasture are also present in the watershed. The majority of the river is retained within a deep, channelized ditch with a network of drainage tiles emptying into it as it flows through the farm fields. In the lowermost reaches, however, it is allowed to freely meander and has established point bars and outer banks. The relative contributions of sediment from each land type are estimated using geochemical fingerprinting. A suite of tracers showing significant variances between the different land types within the Wildcat’s watershed is statistically verified to distinguish between sources. An unmixing model uses the concentrations of these tracers from samples collected in suspension and from the different land types to estimate the fraction of the suspended load derived from each source. Sources adjacent to the meandering reaches, including banks, floodplains, and forests contribute significant fractions of the suspended load. During storm events, very little suspended sediment is derived from agricultural uplands, indicating a disconnection of the uplands from the channel, possibly due to the low relief of the uplands and the dominance of tile drainage in routing water to the channel. These findings indicate that management practices should focus on limiting sediment supply from near channel areas in meandering reaches to minimize the input of nutrients adsorbed to the sediment. Best practices may include installation of a buffer between a meandering channel and fertilized or farmed land, or requiring a minimum distance that fertilizer can be applied near channel banks. These practices would ensure that nutrients do not enter the river through natural channel migration.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Geology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Neal, Conor

Contributors dc:contributor

• Anders, Alison M.

• suspended sediment
• source sediment
• fingerprint

Statement dc:rights

• Copyright 2014 Conor Neal

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/49606

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/49606