Nutrient Retention in Ecologically Functional Floodplains: A Review

Brad A. Gordon,Christian F. Lenhart,Olivia Dorothy

doi:10.3390/w12102762

Brad A. Gordon, Christian F. Lenhart + Show 1 more

Open Access

https://doi.org/10.3390/w12102762

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Journal: Water	Publication Date: Oct 4, 2020
Citations: 27	License type: CC BY 4.0

Affiliation: American Rivers, University of Minnesota

Abstract

Nutrient loads in fresh and coastal waters continue to lead to harmful algal blooms across the globe. Historically, floodplains—low-lying areas adjacent to streams and rivers that become inundated during high-flow events—would have been nutrient deposition and/or removal sites within riparian corridors, but many floodplains have been developed and/or disconnected. This review synthesizes literature and data available from field studies quantifying nitrogen (N) and phosphorus (P) removal within floodplains across North America and Europe to determine how effective floodplain restoration is at removing nutrients. The mean removal of nitrate-N (NO3−-N), the primary form of N in floodplain studies, was 200 (SD = 198) kg-N ha−1 year−1, and of total or particulate P was 21.0 (SD = 31.4) kg-P ha−1 year−1. Based on the literature, more effective designs of restored floodplains should include optimal hydraulic load, permanent wetlands, geomorphic diversity, and dense vegetation. Floodplain restorations along waterways with higher nutrient concentrations could lead to a more effective investment for nutrient removal. Overall, restoring and reconnecting floodplains throughout watersheds is a viable and effective means of removing nutrients while also restoring the many other benefits that floodplains provide.

Highlights

Despite global efforts to reduce nutrient loads, harmful algal blooms (HABs) and hypoxic zones are occurring more often, in new places, for longer durations, and at different toxicities [1]
The proportions of each form of these nutrients are in constant flux, and the occurrence of each algal bloom depends on the algal species, environmental conditions, other organisms creating those conditions, and the nutrient concentrations and forms present [1]
In addition to toxicity from HABs, high concentrations of NO3 − in drinking water are a risk to human health and NO3 − has been prioritized for nutrient removal efforts in many areas, especially in the Mississippi River Basin [4,15,16,17]

Summary

Introduction

Despite global efforts to reduce nutrient loads, harmful algal blooms (HABs) and hypoxic zones are occurring more often, in new places, for longer durations, and at different toxicities [1]. Most are caused by nutrient pollution [1] The impacts of these algal blooms can be devastating for human and animal health, wildlife habitat, and economics. Nutrient loads have been increasing, especially from nitrogen (N) and phosphorus (P) fertilizer use, river alterations, field and bank erosion, human and animal waste, and expanding aquaculture practices [1,2,3,4,5,6,7,8,9]. In addition to toxicity from HABs, high concentrations of NO3 − in drinking water are a risk to human health and NO3 − has been prioritized for nutrient removal efforts in many areas, especially in the Mississippi River Basin [4,15,16,17]

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