Global mapping of freshwater nutrient enrichment and periphyton growth potential

R W Mcdowell,L M Mosley,B E Haggard,P Pletnyakov,A Noble

doi:10.1038/s41598-020-60279-w

R W Mcdowell, L M Mosley + Show 3 more

Open Access

https://doi.org/10.1038/s41598-020-60279-w

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Abstract

Periphyton (viz. algal) growth in many freshwater systems is associated with severe eutrophication that can impair productive and recreational use of water by billions of people. However, there has been limited analysis of periphyton growth at a global level. To predict where nutrient over-enrichment and undesirable periphyton growth occurs, we combined several databases to model and map global dissolved and total nitrogen (N) and phosphorus (P) concentrations, climatic and catchment characteristics for up to 1406 larger rivers that were analysed between 1990 and 2016. We predict that 31% of the global landmass contained catchments may exhibit undesirable levels of periphyton growth. Almost three-quarters (76%) of undesirable periphyton growth was caused by P-enrichment and mapped to catchments dominated by agricultural land in North and South America and Europe containing 1.7B people. In contrast, undesirable periphyton growth due to N-enrichment was mapped to parts of North Africa and parts of the Middle East and India affecting 280 M people. The findings of this global modelling approach can be used by landowners and policy makers to better target investment and actions at finer spatial scales to remediate poor water quality owing to periphyton growth.

Highlights

Periphyton growth in many freshwater systems is associated with severe eutrophication that can impair productive and recreational use of water by billions of people
Www.nature.com/scientificreports in support of threshold concentrations of N and P derived in the US, Europe, China, South America, Africa and Australasia to prevent periphyton growth[15,21]
We review these studies to determine if there is a consistent threshold in N or P that can be used globally in conjunction with estimates of N and P concentration to predict the likelihood of undesirable periphyton growth in catchments where little or no data exist

Summary

Introduction

Periphyton (viz. algal) growth in many freshwater systems is associated with severe eutrophication that can impair productive and recreational use of water by billions of people. Some species of cyanobacterial algae can be toxic, while the excessive growth and subsequent death and decay of toxic and non-toxic species can deplete oxygen, clog the hyporheic zone and alter pH1 These changes can impair the reproductive capacity or even kill fish and bottom-dwelling animals, taint potable water supply and reduce the aesthetic and recreational quality of streams and rivers[2]. Investigations of the public perception of ‘good’ and ‘bad’ water quality suggest that water quality is deemed to be undesirable when the percentage of periphyton cover was >25–30%, equivalent to a chlorophyll-a concentration of 120–200 mg m−2 16–20 These chlorophyll-a concentrations have been used www.nature.com/scientificreports in support of threshold concentrations of N and P derived in the US, Europe, China, South America, Africa and Australasia to prevent periphyton growth[15,21]. TN:TP ratios are used to describe stressor-response relationships in slow-flowing rivers and standing water with long water residence times where particles settle and can be accessed by microbes which facilitate nutrient dissolution[24]

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