Abstract
Streambank erosion may represent a significant source of sediment and phosphorus (P) to overall watershed loads; however, watershed-scale quantification of contributions is rare. In addition, streambanks are often comprised of highly variable stratigraphic source materials (e.g., alluvial deposits), which may differentially impact in-channel P dynamics once eroded. The objective of this study was to quantify sediment and total phosphorus (TP) losses from four materials comprising streambanks within a 5218 ha watershed in Iowa, USA. Streambank-face surveys, erosion pins, and soil analyses were used to quantify surface area representation, recession, and losses of sediment and TP over a two-year period. Cumulative, whole-bank gross mean recession totaled 18.6 cm over two years, and material-specific gross mean recession ranged from 15.5 to 64.1 cm. Cumulative, whole-bank mean gross mass losses totaled 0.28 Mg sediment and 0.7 × 10−5 Mg TP per meter channel length. Annual sediment losses equated to 4–44% of historic suspended sediment loads. Stratigraphy was significant in gross material erosion and losses, with lower materials (i.e., bank toe region) exhibiting the greatest recession rates and cumulative recession. Weathered/colluvial material dominated total bank face surface area (88.3%), and contributed the greatest proportion of sediment and TP mass loss (66, 68%, respectively) versus other streambank materials.
Highlights
Excessive loadings of sediment and phosphorus (P) to waterways are prime water quality impairments within both the agricultural Midwestern United States of America (USA) and globally [1,2]
The overall objective of this study was to quantify sediment and total phosphorus (TP) loading over a two-year period from four distinct Holocene materials comprising streambanks in Walnut Creek, Iowa, USA
This study provides a unique, high temporal resolution dataset of alluvial unit-specific erosion and potential contribution to suspended sediment (SS) and TP loads at the watershed scale
Summary
Excessive loadings of sediment and phosphorus (P) to waterways are prime water quality impairments within both the agricultural Midwestern United States of America (USA) and globally [1,2]. Phosphorus is often the limiting nutrient for algal primary production in freshwater systems [3], and excess loading may contribute to accelerated eutrophication, harmful algal blooms (HABs), and coastal hypoxic zones. In the Midwestern and southern USA, studies have documented a wide range of streambank contributions to annual. SS loads, with contributions ranging from 25–60% [5,6,7,8,9], up to 80–96% [10,11,12]. In Walnut Creek, Water 2018, 10, 111; doi:10.3390/w10020111 www.mdpi.com/journal/water
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