Dr. Drizo has 25 years of experience in research, development, implementation, and assessment of innovative technologies for sustainable water treatment and management. She pioneered passive filtration systems for phosphorus removal and harvesting from wastewater, and has led and managed projects in Europe, Canada, New Zealand, USA, Taiwan, and Brazil. She was an invited speaker for over 100 lectures and presentations speaking about solutions for eutrophication mitigation and control and other global environmental challenges.

Dr. Drizo held a number of academic positions across continents. She was an associate professor in sustainable water management at the University of Vermont, USA (2004–2012), a visiting professor at the Massey University, New Zealand (2004/2005), the Ecole des Mines de Nantes, France (2010) and National Pingtung University of Science and Technology (NPUST), Taiwan (2010). She was also a lecturer on Water/Energy Nexus and Global Water Issues at Singularity University, USA (2012 and 2014) and more recently, she worked as a full Professor in Water Technology at Heriot‐Watt University, UK (2014–2017).

Finding solutions to protect water resources from phosphorus pollution has occupied me throughout most of my professional life. I sincerely hope that this book will serve and inspire the next generation of phosphorus and water‐protection practitioners and regulators.

Foremost, I would like to express my sincere gratitude to my publisher, Wiley‐Blackwell, and their incredible team.

I am grateful most of all to Dr. Ian Francis, former Senior Commissioning Editor of the Wiley‐Blackwell New Analytical Methods in Earth and Environmental Sciences Series, for acknowledging the importance of the phosphorus pollution problem and for asking me to write this book.

Unforeseeably, from the beginning of writing the book, my life was also filled with the deep sorrows of losing my mother, my father, and my dearest friend and at times it was very difficult to find the strength to continue the work on it. In addition, I had to change jobs and move across continents.

For completing the work in spite of these difficult years, I wish above all to thank Ms. Sonali Melwani, Team Lead and Project Editor of Wiley‐Blackwell, for her patience, her constant encouragement, and kind understanding of my tardiness.

I would also like to thank the Production Editor, Ms. Priya Subbrayal and her team, Ms. Carol Thomas, Freelance Copyeditor, for her expertise and time in polishing the manuscript, and Mr. Andrew Harrison, Senior Commissioning Editor at Wiley‐Blackwell, for their help and assistance with the final stages of the book.

I owe warm thanks to Eamon Twohig, Program Manager at the Agency of Natural Resources, Department of Environmental Conservation, Vermont, USA, for the proofreading of Chapter 2 and for providing valuable input. He was also ‘my right hand’ and at the core of our research team during my time at the University of Vermont.

I would like to use this opportunity to thank my colleagues for reviewing and providing sources and permissions for the material described in the book: to Professor Gunno Renman, KTH Royal Institute of Technology, for his review of the Polonite‐based systems section and to Professor Tore Krogstad, Norwegian University of Life Sciences, for his review of the Filtralite P section; to Professor Paul Withers, Lancaster Environment Centre at Lancaster University, UK, for his permission to use the map presented in Figure 3.2.; to Mr. Karl‐Gustav Niska, Skandinavisk Ecotech AB, for providing pictures of Polonite phosphorus traps (Figure 3.3); to Professor Peter Jenssen, Norwegian University of Life Sciences, for the permission to use his photo of the Filtralite P system (Figure 3.4) and to Mr. Eric Fehlhaber, Conservation Manager at the Sheboygan County Planning & Conservation, Wisconsin, USA, for the permission to use the photos presented in Figure 3.6.

Last but not least, I would like to thank my sister Maja for always being there for me. And to Hugo, for years of happiness, for sharing my dreams and for being by my side.

1.1 Introduction

The word ‘eutrophic’ originates from a word eutrophy, from Greek eutrophia meaning nutrition and eutrophos which means well‐fed. Eutrophication has many different definitions depending on whether they describe solely the process of nutrient enrichment or whether they also include impacts and problems caused by such enrichment. In its simplest form eutrophication is defined as the over‐enrichment of receiving waters with mineral nutrients, phosphorus, and nitrogen. It results in excessive production and growth of autotrophs, in particular algae, cyanobacteria (Box 1.1), and aquatic macrophytes (Correll 1998; Ansari et al. 2011; van Ginkel 2011). The increased bacterial populations and vegetation abundance result in high respiration rates leading to hypoxia (oxygen depletion). Hypoxia and algal blooms (Figure 1.1) are the two most acute symptoms of eutrophication (Ansari et al. 2011; UNEP 2017).

Hypoxia or oxygen depletion in a water body often leads to ‘dead zones’ – regions where levels of oxygen in the water are reduced to a point that can no longer support living aquatic organisms (Figure 1.1). Hypoxia in the northern Gulf of Mexico is defined as a concentration of dissolved oxygen less than 2 mg/l (2 ppm). In other oceans of the world, the upper limit for hypoxia may be as high as 3–5 mg/l. The new knowledge on oxygen depletion (hypoxia) and related phenomena in aquatic systems has been recently reviewed by Friedrich et al. (2014).

1.2 Trophic Classes of Water Bodies

Since the beginning of twentieth century, water bodies have been categorized according to their trophic status, based on concentration of chlorophyll, the transparency of water, and phosphorus mean concentration (Foundation for Water Research 2006). For standing waters, the Organisation for Economic Cooperation and Development (OECD), proposed a classification scheme consisting of three main trophic classes: oligotrophic for nutrient poor waters, mesotrophic for waters slightly to moderately enriched with nutrients, and eutrophic for waters excessively enriched with nutrients (OECD 1982). In addition they also proposed two boundary classes, ultra‐oligotrophic class for the extreme nutrient deficiency and hypertrophic for extreme eutrophication (Table 1.1).

However, the classification for flowing waters according to their trophic status has been debated for the past few decades (Foundation for Water Research 2006). For example, Dodds et al. (1998) reviewed different classification systems for streams and proposed a simplified method based on frequency distribution of nutrients and chlorophyll to define three trophic categories.

The US EPA (2000a) proposed a two‐phase approach where streams are initially classified according to their physical parameters associated with regional and site specific characteristics, including climate, geology, substrate features, slope, canopy cover, water retention time, discharge and flow continuity, channel morphology, and system size.

The following phase involves further classifying by nutrient gradient. However, their trophic state classification focuses primarily on chemical and biological parameters including concentrations of nutrients, algal biomass as chlorophyll a, and turbidity, and may also include land use and other human disturbance parameters (US EPA 2000a). More recently, the European Council Directive 91/271/EEC concerning urban waste‐water treatment stated that if a river’s soluble Phosphorus (P) concentrations exceed 100 μg/l it is excessively enriched with phosphorus (European Commission 2016c).

1.3 The Role of Phosphorus in Eutrophication

Phosphorus (P) is an essential component of nucleic acids and as such it has a central role in nearly all biochemical functions of every living organism (Correll 1998; Wyant et al. 2013). P is vital for plants for the synthesis of genetic material, phospholipid membranes, and metabolism (Plaxton and Lambers 2015). In contrast to carbon and nitrogen, P has no gaseous phase; it is found in the atmosphere only in small particles of dust. Phosphorus is present in the environment as a variety of organic and inorganic compounds. In the aquatic systems it can be found in three forms, as the free ortho‐phosphate ion (HPO₄²⁻), as a polymer of phosphate compounds (‘polyphosphates’) or as part of an organic phosphorus molecule such as DNA (nucleic acid). However, of the three forms only ortho‐phosphate is bioavailable, e.g. it can cross the algal cell membranes and be assimilated by bacteria, algae, and plants (Correll 1998; Wyant et al. 2013).

In aquatic systems P is considered a ‘growth‐limiting’ factor (Box 1.3) because it is usually present in very low concentrations (Schindler 1977). Typical soluble P concentrations in unspoiled rivers are often bellow 30 μg/l. Therefore, the additions of very small quantities of P (0.01 to 0.02 mg P/l) are sufficient to induce harmful algae blooms (HABs) in surface waters (Heathwaite and Dils 2000).

The role of phosphorus in causing eutrophication was first demonstrated by Schindler and his research team, over four decades ago (Schindler 1974). In order to elucidate the primary cause of eutrophication, they conducted a series of whole‐lake experiments in the Experimental Lakes Area of north western Ontario, Canada. The lake was divided into two basins, of which one was fertilized with phosphorus, nitrogen, and carbon, and the other one only with nitrogen and carbon. Whilst the former one was covered by algal bloom within two months, in the later one there were no changes in species or algae quantity providing clear evidence that phosphorus has a vital role in eutrophication (Schindler 1974).

Schindler and co‐researchers continued the whole ecosystem experiment in which they investigated roles of carbon, nitrogen, and phosphorus in controlling eutrophication for nearly four decades. The results from this long‐term research corroborated their previous findings that the only way to reduce eutrophication is to decrease inputs of P (Schindler et al. 2008). However, despite evidence, scientists continued to debate the contribution of nitrogen and carbon to eutrophication, particularly in estuaries and coastal environments (e.g. Howarth and Marino 2006).

More recently, in the light of new European Union Water Framework legislation to control both nutrients (Chapter 3), Schindler (2012) revisited the controversy of which nutrient is the major cause of eutrophication. He discussed the common misconceptions and errors that affected scientific researchers’ recommendations including (i) the assumptions that results from the short‐term experiments where nutrients are added to small bottles or mesocosms can be extrapolated to whole ecosystems over long time periods; (ii) the investigations about strategies to reverse eutrophication are often made by adding instead of decreasing nutrients from water; and (iii) flawed logic and assumptions about ecosystem‐scale nutrient cycling. Furthermore, he pointed out that despite claims that reducing nitrogen is essential to decreasing estuarine eutrophication, there is no documented case history of where this measure has been successful. Regarding criticisms on the lack of response to P control measures in some estuaries, he underlined the well‐known fact that the largest human populations and the most intensive conversions of catchments have occurred in coastal areas. Therefore, in these catchments it may take decades to see the response to phosphorus reduction interventions and eutrified waters return to original, phosphorus‐limited state (Schindler 2012).

A recent report by the Lake Winnipeg Basin Initiative and published by Environment and Climate Change Canada (ECCC 2017) provided further evidence that nitrogen reduction measures have no or minimal impact on reducing P levels in lakes. The report revealed that after spending $18 million on nitrogen reduction measures between 2012 and 2017, the amount of phosphorus entering the lake fell by less than 1% (ECCC 2017).

1.4 Impacts of Eutrophication

Eutrophication has many detrimental impacts on the environment, health (animal and human), and the economy (Table 1.2).

1.5 The Extent of Eutrophication

The occurrence of cyanobacterial harmful algal blooms was first reported in an Australian lake 140 years ago (Francis 1878). During the past century and a half, the eutrophication of fresh and saline waters has been in continuous expansion across the globe (Vollenweider 1970; Schindler 1974; Selman et al. 2008; UNEP 2017; World Resources Institute 2018).

According to the World Resources Institute researchers the number of coastal areas worldwide experiencing symptoms of eutrophication and/or hypoxia increased 85% in just five years between 2008 and 2013 – from 415 to 762. Of the 762 sites, 479 were identified as experiencing hypoxia, whilst 228 sites showed other symptoms of eutrophication, including algal blooms, species loss, and negative impacts to coral reef congregations. The remaining 55 sites were systems in recovery from hypoxia (World Resources Institute 2018). It is estimated that as much as 78% of the assessed continental US coastal area and approximately 65% of Europe's Atlantic coast exhibit symptoms of eutrophication (Figure 1.3). The actual magnitude is most likely much greater given that in many regions of the world (e.g. Asia, Latin America, Africa) research and evidence collection on eutrophication is relatively recent (Le et al. 2010; Walton 2010; van Ginkel 2011; Kundu et al. 2015; World Resources Institute 2018).

In Europe, the European Environment Agency (EEA) declared eutrophication a pan‐European problem of a major concern more than 20 years ago (EEA 1995). Despite all the efforts and vast investments, it remains a major threat to achieving the good status of waters required by the Water Framework Directive (European Commission 2015a). The bottom of the Baltic Sea represents the world's largest hypoxic ‘dead zone’. Carstensten et al. (2014) recently reported a 10‐fold increase of hypoxia in the Baltic Sea in the past 115 years, from 5000 to about 60 000 km² which they attributed mainly to increased inputs of nutrients from land.

The second largest zone is located in the USA, in the northern Gulf of Mexico, just under the Midwestern Corn Belt. Over the past 30 years (1985–2014) it had an average size of about 13 650 km² (or 5300 mile²). However, in summer of 2017 the area of this dead zone increased 1.7 fold, to 22 730 km² or 8776 mile² (Charles 2017).