Land use impacts on sediment and water phosphorus concentrations in selected Eagle Creek reservoir tributaries

Candiss Omehl Williams, Purdue University

Abstract

Phosphorus (P) is generally the nutrient that most limits the productivity of freshwater ecosystems. It is unclear how management practices and seasonal patterns influence P concentrations in watersheds when point source inputs are limited. Our objectives were to evaluate (1) seasonal patterns in stream and ditch water P concentrations among 4 different land use types, (2) sediment physical and chemical properties related to sediment P status, and (3) the relationship between sediment P and water column P concentrations within the Eagle Creek Reservoir watershed located in central Indiana. Stream and drainage ditch water and sediment samples were collected monthly from 8 selected locations within the Eagle Creek watershed for two consecutive years (2005 and 2006). Our results indicated a seasonal trend where P concentrations were greatest during warmer summer, base flow period, but the greatest mass of P loss occurred during the winter, high flow period. Urbanizing areas had greater P losses than row crop agriculture, livestock agriculture and established urban areas. The EPA Nutrient Criteria Limit for total P (TP) in streams and rivers in Ecoregion VI is 0.076 mg TP L-1. Total P concentrations exceeded the EPA Nutrient Criteria limit for all seasons and land use types in 2005, while in 2006 TP exceeded the EPA Nutrient Criteria limit only during the summer and fall. The overall mean mass of TP lost from the 8 sub-catchments studied was 0.54 kg ha-1, and approximately two thirds of the TP exported was water soluble reactive P (SRP). Sediment P status was evaluated using Mehlich-3, ammonium oxalate, calcium chloride and TP. The Mehlich-3 derived P saturation ratio (PSRM3) was related to oxalate derived PSR (PSROX) (r = 0.62), calcium chloride extractable P (Ex-P) (r = 0.77), total P (TP) (r = 0.38), equilibrium P concentration (EPC0) (r = 0.69) and P sorption maximum (Smax) (r = 0.35). Sediment TP and PSROX were both positively correlated to water column SRP, total reactive P (TRP), and total P (P<0.0001). Overall sediment EPC0 concentrations were not related to water column SRP, however, when sediments were separated as ‘P sinks’ or ‘P sources’, a positive correlation was found between sediment EPC 0 and water column SRP (r = 0.49 and 0.64, respectively, P<0.0001). The relatively high correlation between PSRM3 and EPC0 and the widespread use of the Mehlich-3 soil tests suggests that the Mehlich-3 soil test has immediate potential for assessing the ability of sediments to sorb P from, or desorb P to, overlying water.

Degree

Ph.D.

Advisors

Joern, Purdue University.

Subject Area

Biogeochemistry|Soil sciences|Water Resource Management

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