Spatial and temporal variations of nutrients and heavy metals in legacy sediments for Mid-Atlantic streams
Date
2019
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Stream bank legacy sediments can make up a large fraction of the annual watershed sediment exports in Mid-Atlantic streams. However, the corresponding nutrient contributions are not well known since legacy sediment chemistry is understudied. The following thesis consists of two novel studies that investigate variations in stream bank legacy sediment chemistry in space and time. Legacy sediments in stream banks were sampled across 15 sites in northern Delaware, eastern Maryland, and southeastern Pennsylvania. Solid phase chemical analyses and nutrient extractions were performed on the sediments to determine nutrient and heavy metal contents. ☐ The first study focused on differences in legacy sediment stream bank chemical content across multiple land uses, bank depths, and particle sizes. Fifteen legacy sediment stream banks were sampled at multiple depths from sites that were located within four land use categories. Legacy sediments were sieved into coarse (> 63μm) and fine (< 63μm) fractions and analyzed for a suite of heavy metals and nutrients. Stream water and deionized water extractions were also completed. Analyses indicated that legacy sediment chemistry was influenced by land use and particle size, but trends with bank depth were not as strong. Results from this study highlight the complexity of legacy sediment stream bank chemical composition, while also providing insight to the potential water quality impacts of legacy sediments. ☐ The second study investigated how legacy sediment nutrient content varied with particle size and season, and specifically focused on how freeze-thaw cycles impact legacy sediment chemistry. Surficial sediments from two legacy sediment stream banks were sampled on a bi-weekly basis for approximately one year, and solid phase nutrient analyses as well as deionized water nutrient extractions were performed on both coarse and fine sediments. Results showed little seasonal variation in organic nutrient concentrations, but inorganic nutrient concentrations varied based on the presence or absence of freeze-thaw cycles. ☐ This thesis provides important new insights into legacy sediment chemistry and how it varies with space, season, and particle size. Findings from this study will be of interest to soil and water quality scientists, watershed managers and modelers, and natural resource agencies.