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Mitigating the global expansion of harmful cyanobacterial blooms: Moving targets in a human- and climatically-altered world

Mitigating the global expansion of harmful cyanobacterial blooms: Moving targets in a human-
and climatically-altered world
Hans W. Paerl
, Malcolm A. Barnard
Institute of Marine Sciences, University of North Carolina at Chapel Hill, 3431 Arendell St,
Morehead City, NC, USA, *Corresponding Author
© 2020 published by Elsevier. This manuscript is made available under the Elsevier user license
Version of Record:
Abstract 1
Cyanobacterial harmful algal blooms (CyanoHABs) are a major threat to human and environmental 2
health. As global proliferation of CyanoHABs continues to increase in prevalence, intensity, and 3
toxicity, it is important to identify and integrate the underlying causes and controls of blooms in 4
order to develop effective short- and long-term mitigation strategies. Clearly, nutrient input 5
reductions should receive high priority. Legacy effects of multi-decadal anthropogenic eutrophication 6
have altered limnetic systems such that there has been a shift from exclusive phosphorus (P) 7
limitation to nitrogen (N) limitation and N and P co-limitation. Additionally, climate change is 8
driving CyanoHAB proliferation through increasing global temperatures and altered precipitation 9
patterns, including more extreme rainfall events and protracted droughts. These scenarios have led to 10
the “perfect storm scenario”; increases in pulsed nutrient loading events, followed by persistent low-11
flow, long water residence times, favoring bloom formation and proliferation. To meet the 12
CyanoHAB mitigation challenge, we must: (1) Formulate watershed and airshed-specific N and P 13
input reductions on a sliding scale to meet anthropogenic and climatic forcings. (2) Develop 14
CyanoHAB management strategies that incorporate current and anticipated climatic changes and 15
extremes. (3) Make nutrient management strategies compatible with other physical-chemical-16
biological mitigation approaches, such as altering freshwater flow and flushing, dredging, chemical 17
applications, introduction of selective grazers, etc. (4) Target CyanoHAB toxin production and 18
developing management approaches to reduce toxin production. (5) Develop broadly applicable long-19
term strategies that incorporate the above recommendations. 20
Keywords: CyanoHABs; N and P Colimitation; Nutrient Legacies; Climate Change; Mitigation 22
Strategies 23
1. Introduction 25
Global expansion of harmful cyanobacterial blooms (CyanoHABs), is a major threat to safety and 26
sustainability of water supplies for human consumption, agriculture (irrigation), inland fisheries 27
resources, as well as recreational and aesthetic values of impacted waters (Burford et al., 2020; Paerl 28
et al., 2019a, b). Nutrient over-enrichment has been strongly linked to CyanoHAB expansion in 29
aquatic ecosystems (Paerl 1988). This link has a long history; going back at least to eutrophication 30
that spawned massive blooms during the Roman Empire (Haas et al., 2019). Historically, P over-31
enrichment associated with agricultural, urban and industrial development has been identified as a 32
key factor promoting this expansion (Elser and Bennett, 2011; Likens, 1972; Motew et al., 2017; 33
Schindler, 2012; Smith, 2003). As such, reduction of P inputs to CyanoHAB-impacted waters has 34
generally been prescribed as a key bloom mitigation step (Schindler, 2012). Because there are no 35
gaseous forms of P that can potentially escape aquatic ecosystems, P accumulates in both the water 36
column and sediments, leading to a “P legacy”, supporting persistent internal loading which can 37
sustain eutrophication and blooms (Lewis et al., 2011; Reddy et al., 2011). Lake and reservoir 38
systems can have lengthy water residence (or water age) times, often on the order of months to 39
multiple years. Therefore, even if P inputs are reduced, it will take appreciable time to naturally 40
“wean” these systems of internal P supplies (Havens, 1997; Paerl et al., 2016a, b). 41
The other major nutrient element controlling eutrophication, nitrogen (N), while also undergoing 42
excessive anthropogenic enrichment, has gaseous forms (e.g. N
, N
), that can readily 43
exchange with the atmosphere. Thus, even though anthropogenic N loading has increased at alarming 44
rates (Erisman et al., 2013; Galloway et al., 2002) and has been shown to be directly implicated in 45
both marine and freshwater eutrophication (Boesch et al., 2001; Conley et al., 2009; Elser et al., 46
2007; Lewis et al., 2011; Nixon, 1995; Ryther and Dunstan, 1971; Wurtsbaugh et al., 2019), there is 47
an “escape route” via gaseous transformation processes. Furthermore, natural inputs of “new” N via 48
fixation are generally exceeded by losses due to in-system denitrification, especially in bloom-49
prone eutrophic systems (Paerl et al., 2016b; Scott et al., 2019). As a result, chronic N limitation is 50
perpetuated, and external N inputs play a key role in maintaining eutrophic, bloom-prone conditions 51
(Paerl et al., 2016b). Furthermore, recent studies have stressed the need to reduce N inputs into 52
CyanoHAB-plagued systems due to the ties between N inputs, CyanoHAB growth and toxicity 53
(Gobler et al., 2016; Harke et al., 2016; Shatwell and Köhler, 2019). Clearly, there is good reason to 54
constrain external loads of both N and P, and impose more nutrient-limited conditions in order to 55
help mitigate the CyanoHAB problem (Chaffin and Bridgeman, 2014; Müller and Mitrovic, 2015; 56
Zohary et al., 2005). 57
Therefore, while P input reductions should be part of any long-term eutrophication and 58
CyanoHAB control strategy, in order to speed up the “de-eutrophication” or “oligotrophication” 59
process, parallel N input reductions are urgently needed, especially in light of global agricultural, 60
urban and industrial expansion (Paerl et al., 2019 a). 61
2. Legacy Effects of Nutrients in Freshwater Ecosystems 63
The term legacy effect entered the scientific literature in the late 1980s and early 1990s (Corbet, 64
1985; Molina and Amaranthus, 1991). Legacy effects are defined as the impacts that one generation 65
leaves on the environment for future generations to inherit (Button et al., 1999). In ecological terms, 66
legacy effects can be considered to be ecological inheritance (Cuddington, 2011). In freshwater 67
ecosystems, nutrient legacy effects add to the issues related to anthropogenic eutrophication (Duff et 68
al., 2009). A large portion of the nutrient legacy is driven by land use and land cover changes, which 69
have led to nutrient-enriched urban and agricultural runoff (Bain et al., 2012; Martin et al., 2011). 70
Since the rapid increases in chemical fertilizer use after WWII, nutrient loading has accelerated 71
dramatically (Haygarth et al., 2014). As mentioned earlier, P can mainly leave aquatic systems by 72
flushing or ending up in the sediments. Approximately 20−30% of P applied to agricultural land is
exported directly out of the watershed as crop and animal production. The remaining 70−80% of the 74
applied P ends up as stores in soils, river sediments, groundwater, wetlands, riparian floodplains, 75
lakes, and estuaries (Jarvie et al., 2013; Sharpley et al., 2013). Even though N can leave the aquatic 76
systems as gases, some N also end up leaving a legacy on water bodies. Anthropogenic loading of N 77
into agricultural soils can leach into groundwater, leading to an N legacy in aquifers (Puckett et al., 78
2011). A substantial fraction of accumulated CyanoHAB biomass is decomposed in the water 79
column and surface sediments, fueling hypoxia (< 2.0 mg O
) and anoxia (< 0.5 mg O
) 80
(Buzzelli et al., 2002; Paerl, 2014). The biomass fraction that is not immediately decomposed ends 81
up in the sediments as legacy organic carbon, organic N, and organic P. Legacy nutrients provide for 82
a positive feedback loop supporting CyanoHAB growth (Figure 1), and it is a key reason why 83
reversing the harmful effects of eutrophication can take a substantial amount of time, especially in 84
large, long water residence time aquatic ecosystems (Paerl et al., 2019b). 85
3. Climate Change Effects on Nutrient Loading in Freshwater Ecosystems 87
While nutrient input reductions represent the “bottom line” in mitigating eutrophication and 88
CyanoHAB expansion, there are additional, interacting drivers modulating this process, the most 89
prominent and challenging being climate change (Paerl and Paul, 2012). Global warming, changes in 90
precipitation patterns and amounts and altered wind speeds are strong modulators of eutrophication 91
and CyanoHAB expansion (Deng et al., 2018; Paerl et al., 2016a; Paerl and Huisman, 2009, 2008; 92
Weber et al., 2020). Both of these symptoms of climate change are increasing in frequency and 93
geographic distribution (Burford et al., 2020; Sinha et al., 2017; Trenberth, 2008; Wuebbles et al., 94
2013). Increasing temperatures, stronger vertical stratification, and salinization are also associated 95
with climate change and linked to CyanoHAB magnitudes, frequency, distribution and duration 96
(Chapra et al., 2017; Moore et al., 2008; Paerl, 2017; Paerl et al., 2011; Paerl and Huisman, 2009, 97
2008). As pointed out in Paerl et al., (2016a), the “perfect storm” scenario for CyanoHAB 98
development and proliferation is excessive episodic rainfall events, followed by droughts, which can 99
promote large nutrient input pulses followed by lengthy residence times, enabling blooms to develop 100
and proliferate. Increased temperatures and nutrient loading can also enhance CyanoHAB toxicity 101
(Botana, 2016; Gehringer and Wannicke, 2014; Lehman et al., 2013; Moe et al., 2013). Furthermore, 102
it is likely that these nutrient reduction thresholds will change with changing climatic conditions, 103
human watershed and airshed activities, as populations continue to change (Erisman et al., 2013; 104
Galloway et al., 2002; Moss et al., 2008; Peierls et al., 1991). Wildfires brought on by climate change 105
can also lead to nutrient loading due to increased mobility of sediment (Emelko et al., 2016), 106
especially when followed by extensive rainfall and flooding as has been the case in California and 107
most recently in Eastern and Southern Australia (Malmsheimer et al., 2008; Sharples et al., 2016). In 108
addition to enhancing P inputs associated with sediment mobilization, deforestation also leads to N 109
loading, as seen in N cycle shifts the Laurentian Great Lakes (Guiry et al., 2020). Therefore, changes 110
in these climatic drivers will need to be incorporated into the development of nutrient input 111
reductions that will effectively maintain bloom potentials below specific nutrient loading thresholds 112
for individual water bodies. Warming and nutrient loading and temperature synergistically increase 113
the intensity and recurrence of CyanoHABs, which amplify the feedback loop promoting CyanoHAB 114
growth (Figure 1). 115
Anthropogenic influences on the atmosphere are also modulating CyanoHABs. Increasing 116
atmospheric pCO
can enhance phytoplankton blooms, including CyanoHABs (Verspagen et al., 117
2014). The augmented pCO
will also favor CyanoHAB growth due to rapid adaptation to higher 118
environments as seen in microcosm and chemostat experiments (Sandrini et al., 2016; Shi et 119
al., 2017; Ji et al., 2020). While the effects of increased pCO
appear to promote CyanoHABs, much 120
less is known about the in situ mechanisms compared to the effects of temperature (Verspagen et al., 121
2014; Ji et al., 2020). In addition to atmospheric carbon emissions, N and P emissions also impact 122
CyanoHAB proliferation. Atmospheric deposition has been shown to be significant source of both N 123
and P into aquatic systems. For example, Paerl et al., (2002) estimated that from 20 to >35% of N 124
inputs to N-limited US Atlantic estuarine and coastal waters was attributed to atmospheric N 125
deposition, while 63% of total N and 42% of total P loading in Cultus Lake near Vancouver, BC, 126
Canada, come from atmospheric deposition (Putt et al., 2019). Atmospheric deposition also indirectly 127
impacts coastal systems, as an average of 64% of riverine N export to coastal ocean systems is 128
derived from NO
and NH
deposition (Church and Sickle, 1999; Jaworski et al., 1997). Groundwater 129
inputs of N and P, much of it due to human pollution, provide an additional source of nutrients 130
promoting eutrophication along the freshwater to marine continuum (Paerl, 1997). The combined 131
effect of increased anthropogenic surface, subsurface and atmospheric nutrient loading, in addition to 132
promoting eutrophication, has driven receiving waters into N and P co-limitation and N-limitation 133
(Chaffin et al., 2014; Dodds and Smith, 2016; Elser et al., 2007). 134
4. Management Recommendations 136
When reducing external N&P loading, both point-source and nonpoint-source nutrient inputs 137
need to be addressed. Point source pollution is the easiest target for N and P reduction, as this source 138
can be reduced by targeting readily identified and well-defined origins, such as effluents from 139
wastewater treatment plants and industrial discharge points (Hamilton et al., 2016; Wu et al., 2006). 140
Reduction in point source pollution generally involves diversion of sewage from waterbodies and 141
reduction in P and N concentrations in the wastewater discharge (Sedlak, 1991). N removal from 142
wastewater generally makes use of coupled nitrification–denitrification (US EPA, 2013). P removal 143
occurs either through burial or flushing of P bound in biomass out of the system (Downing, 1997). 144
Buried P can be removed by dredging (Reddy et al., 2007), although a short term P spike often 145
results from dredging (Smith et al., 2006). While P-based detergent bans have been successful at 146
reducing blooms (Dolan and McGunagle, 2005), there are cases where P from detergents continues to 147
be an important component of P in surface waters while also imposing a major burden on wastewater 148
treatment processes (Hamilton et al., 2016; Van Drecht et al., 2009). Greater attention needs to be 149
focused on nonpoint sources of nutrients, which in many watersheds is the largest source of nutrient 150
loading and is often dominated by agriculture (Hamilton et al., 2016). Furthermore, nonpoint-source 151
pollution continues to increase as a relative proportion of total loading as more advanced treatment of 152
point source pollution is implemented (Hamilton et al., 2016). Removing N and P from stormwater 153
runoff can be achieved by using combined wetlands and infiltration ponds to naturally filter N and P 154
(Marsalek and Schreier, 2009; Zheng et al., 2006). Retaining fertilizer-based N and P in agricultural 155
soils should receive high priority (Hamilton et al., 2016). Maintaining N and P in soils at levels close 156
to or below agronomic optima is critical and represents one of the simplest and most cost-effective 157
methods to reduce eutrophication in receiving waters (Drewry et al., 2006; Rasouli et al., 2014). 158
Where feasible, fertilizer should be directly injected into the soil to minimize nutrient-rich surface 159
runoff (Seo et al., 2005). 160
Another method of removing nutrients from non-point sources is through in situ biological 161
filtration, using non-harmful algal “scrubber” and “raceway” devices (Adey et al., 2013; Barnard et 162
al., 2017; Mulbry et al., 2010, 2008). Adding denitrifying bacteria can greatly speed up N removal 163
(Chen et al., 2017). Vegetated buffers are also a useful tool for remediating nonpoint source 164
pollution; trees, shrubs and grasses in the vegetated buffer have been shown to remove more than 165
85% of pollutants (Zhang et al., 2010), including 85% of N and 84% of P (Polyakov et al., 2005). 166
However, the biomass from buffers needs to be periodically harvested and exported in order to have 167
net nutrient removal effect, unless processes such as denitrification are additionally enhanced by this 168
approach (Hoffmann et al., 2009). Additionally, natural and constructed wetlands are very effective, 169
low cost solutions for removal of nonpoint source nutrients from aquatic systems (O’Geen et al., 170
2010; Ribaudo et al., 2001), with removal of over 80% of N loading and over 50% of P loading 171
(Braskerud, 2002a, 2002b; Kao and Wu, 2001). 172
There is a significant association between cyanobacterial blooms and land use types (i.e., 173
industrial, commercial, and transport areas) (Arthington, 1996; Soranno et al., 1996). These results 174
are relevant to landscape planning for mitigating future impacts of climate change on the drainage 175
network, surface runoff, nutrient loads and, ultimately, on the development of toxigenic 176
cyanobacteria (Hamilton et al., 2016). A better knowledge of the relationships between land use type 177
and discharge is essential to foresee the effects of climate change on drainage basins and therefore to 178
evaluate potential triggers of CyanoHABs (Jimenez Cisneros et al., 2014). 179
Higher amounts of freshwater runoff can enhance vertical density stratification (reduced vertical 180
mixing) in waters having appreciable salinity, including estuarine and coastal waters as well as saline 181
lakes and rivers; by allowing relatively light freshwater lenses to establish themselves on top of 182
heavier (denser) saltwater. The resultant enhanced vertical stratification will favor CyanoHABs 183
capable of rapid vertical migration to position themselves at physically-chemically favorable depths 184
in both freshwater and marine systems (Paerl, 2014; Paerl and Huisman, 2009) by rapidly altering 185
their buoyancy in response to varying light, temperature and nutrient regimes (Walsby et al., 1997). 186
The large biomass and long survival time of CyanoHABs in sediments can help explain the 187
delayed recovery of affected lakes after reduction of external nutrient loads (Brunberg and Boström, 188
1992; Paerl et al., 2016a). Sediment removal involves expensive dredging and disturbance of lake 189
bottoms, which can release additional nutrients (and potentially toxic substances) and adversely 190
affect benthic flora and fauna. However, CyanoHABs were eradicated successfully with this 191
approach in Lake Trummen, Sweden (1 km
, mean depth 1.6 m), which experienced CyanoHABs 192
and water quality degradation from domestic sewage and industrial nutrient inputs during the mid-193
1900s (Cronberg, 1982; Peterson, 1982). Suction dredging the upper half-meter of sediments over 194
two years led to significant decreases in nutrient concentrations and CyanoHABs (Cronberg, 1982; 195
Peterson, 1982). Lake Trummen’s rapid CyanoHAB eradication is attributed to its small size and the 196
ability to simultaneously reduce external nutrient loads effectively from its small size (13 km
) 197
(Cronberg, 1982; Peterson, 1982). Dredging is not a feasible solution for reducing internal P loading 198
in large lakes, where P-rich sediments are distributed over hundreds or thousands of square 199
kilometers and are highly mobile (James and Pollman, 2011). 200
CyanoHABs can be treated with chemical and/or biological agents to limnetic systems. Chemical 201
treatments, including precipitation and immobilization of phosphorus in bottom sediments (Phoslock, 202
alum, etc.), application of algaecides (Cu compounds, hydrogen
peroxide, permanganate, etc.), as 203
well as biological controls, such as the introduction of invertebrate and fish grazers, lytic bacteria, 204
and viruses, may temporarily halt the advance of CyanoHABs (Matthijs et al., 2012; Paerl et al., 205
2015; Pan et al., 2006; Robb et al., 2003). However, there are unintended negative impacts on flora 206
and fauna of the limnetic systems that make these chemical treatments potentially detrimental to 207
these systems (Bishop et al., 2018; Escobar-Lux et al., 2019; Paerl et al., 2015). Addition of selective 208
grazers is another option, but successful control of CyanoHABs by grazers is unlikely except in 209
specific cases (Paerl et al., 2001). This is due to cyanobacteria being generally considered to be 210
relatively low preference foods for marine and freshwater herbivores because of chemical and 211
structural defenses and poor nutritional quality (Cruz-Rivera and Villareal, 2006; DeMott and 212
Moxter, 1991; Paerl et al., 2001; Paerl and Paul, 2012). The addition of the grazers can also have 213
negative effects on the food webs through trophic cascades (Jeppesen et al., 2007; Wright and 214
Shapiro, 1984). Given the lack of feasibility, unpredictable and unintended effects of chemical and 215
biological additions, the most prudent and defensible approach is to prioritize nutrient input 216
reductions; however, if nutrient reduction is not enough to reduce the impacts of the blooms, then 217
reassessment of nutrient reduction thresholds as well as the use of any of the above mitigation 218
methods should be considered to manage the CyanoHABs. 219
Remote sensing technology can be useful for tracking and evaluating management of blooms as a 220
means of linking nutrient sources to bloom dynamics over varying temporal and spatial scales 221
(Dorigo et al., 2007; Field et al., 1995; Mishra et al., 2019). Using remote sensor networks, satellite 222
imagery, and machine learning, the extent and drivers of CyanoHABs can be remotely sensed and 223
analyzed (Davis et al., 2019; Mishra et al., 2018, 2019; Zhang et al., 2016). Satellite-based imagery 224
paired with Raspberry-Pi-based remote sensors (CyanoSense), cellular-phone-based application 225
CyanoTracker, and social networking services such as Twitter can document the progression and 226
proliferation of blooms (Boddula et al., 2017; Mishra et al., 2018, 2019; Page et al., 2018; Scott et al., 227
2016; Stumpf et al., 2016). While satellite imagery can measure biomass in CyanoHABs using the 228
different spectral properties of chlorophyll and phycocyanin (Binding et al., 2019), it cannot 229
accurately measure cyanotoxin production as CyanoHAB cellular toxin content can vary even on 230
short time scales and can persist extracellularly after bloom biomass is dissipated (Davis et al., 2019). 231
Therefore, remote sensing should be paired with long-term monitoring. On-lake long-term 232
monitoring of water quality parameters is also critical for protecting human exposure to cyanotoxins 233
during blooms (Davis et al., 2019). Management recommendations are outlined in Figure 2. 234
Anthropogenic forcing continues to alter natural systems and the climate, with major 235
ramifications for nutrient loading, hydrologic changes (e.g., more intense and larger rainfall and 236
flooding events), warming and changes in wind speed - all of which will alter the rates of 237
eutrophication and nutrient-bloom threshold relationships. This calls for the formulation of adaptive 238
nutrient management strategies aimed at maintaining bloom potentials and proliferation below 239
critical nutrient-bloom thresholds. Given the current trajectory of climate change (warming, more 240
extreme wet/dry cycles, reduced wind speed in many locations), it is likely that nutrient loading 241
threshold levels above which blooms will occur, will be lowered, because CyanoHABs will grow 242
more efficiently at elevated temperatures and persist longer under extreme wet/dry cycles (Paerl et 243
al., 2016a). Furthermore, with more extensive wet/dry cycles, both external and internal nutrient 244
cycling will be altered, and this will likely benefit CyanoHABs, which can affect internal cycling by 245
lasting longer during the growth season and can promote positive feedbacks on sediment-water 246
column nutrient cycling to maintain blooms (Fig. 1). This is especially true if CyanoHABs are not 247
effectively consumed by grazers and ultimately finfish or shellfish, which can be exported from the 248
system. More likely, CyanoHAB biomass will enter the detrital-microbial loop component of nutrient 249
cycling, enhancing microbial decomposition and recycling of nutrients more effectively during a 250
single growth season. Overall, this means that current nutrient loading targets aimed at controlling 251
CyanoHABs will need to be set at lower levels than currently prescribed for many regions. With 252
legacy nutrients and climate change leading to positive feedback loops of cyanoHAB proliferation, 253
we need to focus on watershed and airshed nutrient reductions that can help reduce and ultimately 254
break the loops. Lastly, we can complement these efforts with (where feasible and effective) 255
biological and chemical treatments, remote sensing technology, and routine monitoring to help 256
manage CyanoHABs into the future. 257
Acknowledgments 259
This work was supported by the USA National Science Foundation (1803697, 1831096), the 260
National Institutes of Health (1P01ES028939-01), a Grant-in-Aid of Research from Sigma Xi, The 261
Scientific Research Society (G201903158412545), and the NOAA/North Carolina Sea Grant 262
Program R/MER-43, R/MER-47. We would like to thank two anonymous reviewers for their 263
constructive feedback on the manuscript. 264
References 266
Adey, W.H., Laughinghouse, H.D., Miller, J.B., Hayek, L.-A.C., Thompson, J.G., Bertman, S., 267
Hampel, K., Puvanendran, S., 2013. Algal turf scrubber (ATS) floways on the Great 268
Wicomico River, Chesapeake Bay: productivity, algal community structure, substrate and 269
chemistry. J. Phycol. 49, 489–501. 270
Arthington, A.H., 1996. The effects of agricultural land use and cotton production on tributaries of 271
the Darling River, Australia. GeoJournal 40, 115–125. 272
Bain, D.J., Green, M.B., Campbell, J.L., Chamblee, J.F., Chaoka, S., Fraterrigo, J.M., Kaushal, S.S., 273
Martin, S.L., Jordan, T.E., Parolari, A.J., 2012. Legacy effects in material flux: structural 274
catchment changes predate long-term studies. Bioscience 62, 575–584. 275
Barnard, M.A., Porter, J.W., Wilde, S.B., 2017. Utilizing Spirogyra grevilleana as a 276
Phytoremediatory Agent for Reduction of Limnetic Nutrients and Escherichia coli 277
Concentrations. Am. J. Plant Sci. 8, 1148–1158. 278
Binding, C.E., Zastepa, A., Zeng, C., 2019. The impact of phytoplankton community composition on 279
optical properties and satellite observations of the 2017 western Lake Erie algal bloom. J. 280
Great Lakes Res. 45, 573–586. 281
Bishop, W.M., Willis, B.E., Richardson, R.J., Cope, W.G., 2018. The presence of algae mitigates the 282
toxicity of copper-based algaecides to a nontarget organism. Environ. Toxicol. Chem. 37, 283
2132–2142. 284
Boddula, V., Ramaswamy, L., Mishra, D., 2017. CyanoSense: A Wireless Remote Sensor System 285
using Raspberry-Pi and Arduino with Application to Algal Bloom, in: 2017 IEEE 286
International Conference on AI & Mobile Services (AIMS). IEEE, pp. 85–88. 287
Boesch, D., Burreson, E., Dennison, W., Houde, E., Kemp, M., Kennedy, V., Newell, R., Paynter, 288
K., Orth, R.J., Ulanowicz, R., 2001. Factors in the decline of coastal ecosystems. Science. 289
Botana, L.M., 2016. Toxicological perspective on climate change: aquatic toxins. Chem. Res. 290
Toxicol. 29, 619–625. 291
Braskerud, B.C., 2002a. Factors affecting nitrogen retention in small constructed wetlands treating 292
agricultural non-point source pollution. Ecol. Eng. 18, 351–370. 293 294
Braskerud, B.C., 2002b. Factors affecting phosphorus retention in small constructed wetlands 295
treating agricultural non-point source pollution. Ecol. Eng. 19, 41–61. 296 297
Brunberg, A.-K., Boström, B., 1992. Coupling between benthic biomass of Microcystis and 298
phosphorus release from the sediments of a highly eutrophic lake. Hydrobiologia 235, 375–299
385. 300
Burford, M.A., Carey, C.C., Hamilton, D.P., Huisman, J., Paerl, H.W., Wood, S.A., Wulff, A., 2020. 301
Perspective: Advancing the research agenda for improving understanding of cyanobacteria in 302
a future of global change. Harmful Algae, Climate change and harmful algal blooms 91, 303
101601. 304
Button, K., Stough, R., Arena, P., Comp, A., Casper, M., 1999. Dealing with environmental legacy 305
effects: the economic and social benefits of acid mine drainage remediation. Int. J. Environ. 306
Pollut. 12, 459. 307
Buzzelli, C.P., Luettich, R.A., Powers, S.P., Peterson, C.H., McNinch, J.E., Pinckney, J.L., Paerl, 308
H.W., 2002. Estimating the spatial extent of bottom-water hypoxia and habitat degradation in 309
a shallow estuary. Mar. Ecol. Prog. Ser. 230, 103–112. 310
Chaffin, J.D., Bridgeman, T.B., 2014. Organic and inorganic nitrogen utilization by nitrogen-stressed 311
cyanobacteria during bloom conditions. J. Appl. Phycol. 26, 299–309. 312 313
Chaffin, J.D., Bridgeman, T.B., Bade, D.L., Mobilian, C.N., 2014. Summer phytoplankton nutrient 314
limitation in Maumee Bay of Lake Erie during high-flow and low-flow years. J. Gt. Lakes 315
Res. 40, 524–531. 316
Chapra, S.C., Boehlert, B., Fant, C., Bierman, V.J., Henderson, J., Mills, D., Mas, D.M.L., Rennels, 317
L., Jantarasami, L., Martinich, J., Strzepek, K.M., Paerl, H.W., 2017. Climate Change 318
Impacts on Harmful Algal Blooms in U.S. Freshwaters: A Screening-Level Assessment. 319
Environ. Sci. Technol. 51, 8933–8943. 320
Chen, R., Deng, M., He, X., Hou, J., 2017. Enhancing Nitrate Removal from Freshwater Pond by 321
Regulating Carbon/Nitrogen Ratio. Front. Microbiol. 8. 322 323
Church, M.R., Sickle, J.V., 1999. Potential relative future effects of sulfur and nitrogen deposition on 324
lake chemistry in the Adirondack Mountains, United States. Water Resour. Res. 35, 2199–325
2211. 326
Conley, D.J., Paerl, H.W., Howarth, R.W., Boesch, D.F., Seitzinger, S.P., Havens, K.E., Lancelot, C., 327
Likens, G.E., 2009. Controlling Eutrophication: Nitrogen and Phosphorus. Science 323, 328
1014–1015. 329
Corbet, S.A., 1985. Insect chemosensory responses: a chemical legacy hypothesis. Ecol. Entomol. 330
10, 143–153. 331
Cronberg, G., 1982. Changes in the phytoplankton of Lake Trummen induced by restoration. 332
Hydrobiologia 86, 185–193. 333
Cruz-Rivera, E., Villareal, T.A., 2006. Macroalgal palatability and the flux of ciguatera toxins 334
through marine food webs. Harmful Algae 5, 497–525. 335 336
Cuddington, K., 2011. Legacy Effects: The Persistent Impact of Ecological Interactions. Biol. Theory 337
6, 203–210. 338
Davis, T.W., Stumpf, R., Bullerjahn, G.S., McKay, R.M.L., Chaffin, J.D., Bridgeman, T.B., 339
Winslow, C., 2019. Science meets policy: A framework for determining impairment 340
designation criteria for large waterbodies affected by cyanobacterial harmful algal blooms. 341
Harmful Algae 81, 59–64. 342
DeMott, W.R., Moxter, F., 1991. Foraging Cyanobacteria by Copepods: Responses to Chemical 343
Defense and Resource Abundance. Ecology 72, 1820–1834. 344
Deng, J., Paerl, H.W., Qin, B., Zhang, Y., Zhu, G., Jeppesen, E., Cai, Y., Xu, H., 2018. Climatically-345
modulated decline in wind speed may strongly affect eutrophication in shallow lakes. Sci. 346
Total Environ. 645, 1361–1370. 347
Dodds, W.K., Smith, V.H., 2016. Nitrogen, phosphorus, and eutrophication in streams. Inland Waters 348
6, 155–164. 349
Dolan, D.M., McGunagle, K.P., 2005. Lake Erie Total Phosphorus Loading Analysis and Update: 350
1996–2002. J. Gt. Lakes Res., Lake Erie Trophic Status Collaborative Study 31, 11–22. 351 352
Dorigo, W.A., Zurita-Milla, R., de Wit, A.J.W., Brazile, J., Singh, R., Schaepman, M.E., 2007. A 353
review on reflective remote sensing and data assimilation techniques for enhanced 354
agroecosystem modeling. Int. J. Appl. Earth Obs. Geoinformation, Advances in airborne 355
electromagnetics and remote sensing of agro-ecosystems 9, 165–193. 356 357
Downing, J.A., 1997. Marine nitrogen: Phosphorus stoichiometry and the global N:P cycle. 358
Biogeochemistry 37, 237–252. 359
Drewry, J.J., Newham, L.T.H., Greene, R.S.B., Jakeman, A.J., Croke, B.F.W., 2006. A review of 360
nitrogen and phosphorus export to waterways: context for catchment modelling. Mar. Freshw. 361
Res. 57, 757–774. 362
Duff, J.H., Carpenter, K.D., Snyder, D.T., Lee, K.K., Avanzino, R.J., Triska, F.J., 2009. Phosphorus 363
and nitrogen legacy in a restoration wetland, upper Klamath lake, Oregon. Wetlands 29, 12. 364 365
Elser, J., Bennett, E., 2011. A broken biogeochemical cycle. Nature 478, 29–31. 366 367
Elser, J.J., Bracken, M.E.S., Cleland, E.E., Gruner, D.S., Harpole, W.S., Hillebrand, H., Ngai, J.T., 368
Seabloom, E.W., Shurin, J.B., Smith, J.E., 2007. Global analysis of nitrogen and phosphorus 369
limitation of primary producers in freshwater, marine and terrestrial ecosystems. Ecol. Lett. 370
10, 1135–1142. 371
Emelko, M.B., Stone, M., Silins, U., Allin, D., Collins, A.L., Williams, C.H.S., Martens, A.M., 372
Bladon, K.D., 2016. Sediment-phosphorus dynamics can shift aquatic ecology and cause 373
downstream legacy effects after wildfire in large river systems. Glob. Change Biol. 22, 1168–374
1184. 375
Erisman, J.W., Galloway, J.N., Seitzinger, S., Bleeker, A., Dise, N.B., Petrescu, A.M.R., Leach, 376
A.M., de Vries, W., 2013. Consequences of human modification of the global nitrogen cycle. 377
Philos. Trans. R. Soc. B Biol. Sci. 368, 20130116. 378
Escobar-Lux, R.H., Fields, D.M., Browman, H.I., Shema, S.D., Bjelland, R.M., Agnalt, A.-L., 379
Skiftesvik, A.B., Samuelsen, O.B., Durif, C.M.F., 2019. The effects of hydrogen peroxide on 380
mortality, escape response, and oxygen consumption of Calanus spp. FACETS. 381 382
Field, C.B., Randerson, J.T., Malmström, C.M., 1995. Global net primary production: Combining 383
ecology and remote sensing. Remote Sens. Environ., Remote Sensing of Land Surface for 384
Studies of Global Chage 51, 74–88. 385
Galloway, J.N., Cowling, E.B., Seitzinger, S.P., Socolow, R.H., 2002. Reactive Nitrogen: Too Much 386
of a Good Thing? Ambio 31, 60–63. 387
Gehringer, M.M., Wannicke, N., 2014. Climate change and regulation of hepatotoxin production in 388
Cyanobacteria. FEMS Microbiol. Ecol. 88, 1–25. 389
Gobler, C.J., Burkholder, J.A.M., Davis, T.W., Harke, M.J., Johengen, T., Stow, C.A., Van de Waal, 390
D.B., 2016. The dual role of nitrogen supply in controlling the growth and toxicity of 391
cyanobacterial blooms. Harmful Algae. 392
Guiry, E.J., Buckley, M., Orchard, T.J., Hawkins, A.L., NeedsHowarth, S., Holm, E., Szpak, P., 393
2020. Deforestation caused abrupt shift in Great Lakes nitrogen cycle. Limnol. Oceanogr. n/a. 394 395
Haas, M., Baumann, F., Castella, D., Haghipour, N., Reusch, A., Strasser, M., Eglinton, T.I., Dubois, 396
N., 2019. Roman-driven cultural eutrophication of Lake Murten, Switzerland. Earth Planet. 397
Sci. Lett. 505, 110–117. 398
Hamilton, D.P., Salmaso, N., Paerl, H.W., 2016. Mitigating harmful cyanobacterial blooms: 399
strategies for control of nitrogen and phosphorus loads. Aquat. Ecol. 50, 351–366. 400 401
Harke, M.J., Steffen, M.M., Gobler, C.J., Otten, T.G., Wilhelm, S.W., Wood, S.A., Paerl, H.W., 402
2016. A review of the global ecology, genomics, and biogeography of the toxic 403
cyanobacterium, Microcystis spp. Harmful Algae. 404
Havens, K.E., 1997. Water Levels and Total Phosphorus in Lake Okeechobee. Lake Reserv. Manag. 405
13, 16–25. 406
Haygarth, P.M., Jarvie, H.P., Powers, S.M., Sharpley, A.N., Elser, J.J., Shen, J., Peterson, H.M., 407
Chan, N.-I., Howden, N.J.K., Burt, T., Worrall, F., Zhang, F., Liu, X., 2014. Sustainable 408
Phosphorus Management and the Need for a Long-Term Perspective: The Legacy 409
Hypothesis. Environ. Sci. Technol. 48, 8417–8419. 410
Hoffmann, C.C., Kjaergaard, C., Uusi-Kämppä, J., Hansen, H.C.B., Kronvang, B., 2009. Phosphorus 411
Retention in Riparian Buffers: Review of Their Efficiency. J. Environ. Qual. 38, 1942–1955. 412 413
James, R.T., Pollman, C.D., 2011. Sediment and nutrient management solutions to improve the water 414
quality of Lake Okeechobee. Lake Reserv. Manag. 27, 28–40. 415 416
Jarvie, H.P., Sharpley, A.N., Spears, B., Buda, A.R., May, L., Kleinman, P.J.A., 2013. Water Quality 417
Remediation Faces Unprecedented Challenges from “Legacy Phosphorus.” Environ. Sci. 418
Technol. 47, 8997–8998. 419
Jaworski, N.A., Howarth, R.W., Hetling, L.J., 1997. Atmospheric Deposition of Nitrogen Oxides 420
onto the Landscape Contributes to Coastal Eutrophication in the Northeast United States. 421
Environ. Sci. Technol. 31, 1995–2004. 422
Jeppesen, E., Meerhoff, M., Jacobsen, B.A., Hansen, R.S., Søndergaard, M., Jensen, J.P., Lauridsen, 423
T.L., Mazzeo, N., Branco, C.W.C., 2007. Restoration of shallow lakes by nutrient control and 424
biomanipulation—the successful strategy varies with lake size and climate. Hydrobiologia 425
581, 269–285. 426
Ji, X., Verspagen, J.M.H., van de Waal, D.B., Rost, B., Huisman, J., 2020. Phenotypic plasticity of 427
carbon fixation stimulates cyanobacterial blooms at elevated CO
. Sci. Adv. 6, eaax2926. 428 429
Jimenez Cisneros, B.E., Oki, T., Arnell, N.W., Benito, G., Cogley, J.G., Doll, P., Jiang, T., 430
Mwakalila, S.S., 2014. Freshwater resources, in: Field, C.B., Barros, V.R., Dokken, D.J., 431
Mach, K.J., Mastrandrea, M.D., Bilir, T.E., Chatterjee, M., Ebi, K.L., Estrada, Y.O., Genova, 432
R.C., Gimma, B., Kissel, E.S., Levy, A.N., MacCracken, S., Mastrandrea, P.R., White, L.L. 433
(Eds.), Climate Change 2014: Impacts, Adaptation and Vulnerability. Part A: Global and 434
Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the 435
Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, pp. 436
229–269. 437
Kao, C.M., Wu, M.J., 2001. Control of non-point source pollution by a natural wetland. Water Sci. 438
Technol. 43, 169–174. 439
Lehman, P.W., Marr, K., Boyer, G.L., Acuna, S., Teh, S.J., 2013. Long-term trends and causal 440
factors associated with Microcystis abundance and toxicity in San Francisco Estuary and 441
implications for climate change impacts. Hydrobiologia 718, 141–158. 442 443
Lewis, W.M., Wurtsbaugh, W.A., Paerl, H.W., 2011. Rationale for Control of Anthropogenic 444
Nitrogen and Phosphorus to Reduce Eutrophication of Inland Waters [WWW Document]. 445
URL (accessed 3.14.20). 446
Likens, G.E., 1972. Nutrients and eutrophication: the limiting-nutrient controversy: proceedings. 447
American Society of Limnology and Oceanography. 448
Malmsheimer, R.W., Heffernan, P., Brink, S., Crandall, D., Deneke, F., Galik, C., Gee, E., Helms, 449
J.A., McClure, N., Mortimer, M., Ruddell, S., Smith, M., Stewart, J., 2008. Forest 450
Management Solutions for Mitigating Climate Change in the United States. J. For. 55. 451
Marsalek, J., Schreier, H., 2009. Innovation in stormwater management in canada: The way forward. 452
Water Qual. Res. J. Canada 44, v–x. 453
Martin, S.L., Hayes, D.B., Rutledge, D.T., Hyndman, D.W., 2011. The land-use legacy effect: 454
Adding temporal context to lake chemistry. Limnol. Oceanogr. 56, 2362–2370. 455 456
Matthijs, H.C.P., Visser, P.M., Reeze, B., Meeuse, J., Slot, P.C., Wijn, G., Talens, R., Huisman, J., 457
2012. Selective suppression of harmful cyanobacteria in an entire lake with hydrogen 458
peroxide. Water Res. 46, 1460–1472. 459
Mishra, D., Ramaswamy, L., Kumar, A., Bhandarkar, S., Kumar, V., Narumalani, S., 2018. A Multi-460
Cloud Cyber Infrastructure for Monitoring Global Proliferation of Cyanobacterial Harmful 461
Algal Blooms, in: IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing 462
Symposium. Presented at the IGARSS 2018 - 2018 IEEE International Geoscience and 463
Remote Sensing Symposium, pp. 9272–9275. 464
Mishra, S., Stumpf, R.P., Schaeffer, B.A., Werdell, P.J., Loftin, K.A., Meredith, A., 2019. 465
Measurement of Cyanobacterial Bloom Magnitude using Satellite Remote Sensing. Sci. Rep. 466
9, 1–17. 467
Moe, S.J., Schamphelaere, K.A.C.D., Clements, W.H., Sorensen, M.T., Brink, P.J.V. den, Liess, M., 468
Toxicology and Chemistry. 471
Molina, R., Amaranthus, M., 1991. Rhizosphere biology: ecologi cal linkages between soil processes, 472
plant growth, and community dynamics. U.S. Department of Agriculture, Forest Service, 473
Intermountain Research Station. 474
Moore, S.K., Trainer, V.L., Mantua, N.J., Parker, M.S., Laws, E.A., Backer, L.C., Fleming, L.E., 475
2008. Impacts of climate variability and future climate change on harmful algal blooms and 476
human health. Environ. Health 7Suppl 2 S4.•069X•7•S2•S4 477
Moss, R., Babiker, W., Brinkman, S., Calvo, E., Carter, T., Edmonds, J., Elgizouli, I., Emori, S., 478
Erda, L., Hibbard, K., Jones, R., Kainuma, M., Kelleher, J., Lamarque, J.F., Manning, M., 479
Matthews, B., Meehl, J., Meyer, L., Mitchell, J., Nakicenovic, N., ONeill, B., Pichs, R., Riahi, 480
K., Rose, S., Stouffer, R., van Vuuren, D., Weyant, J., Wilbanks, T., vanYpersele, J.P., Zurek, 481
M., 2008. Towards New Scenarios for the Analysis of Emissions: Climate Change, Impacts 482
and Response Strategies. Intergovernmental Panel on Climate Change Secretariat (IPCC), 483
Geneva, Switzerland. 484
Motew, M., Chen, X., Booth, E.G., Carpenter, S.R., Pinkas, P., Zipper, S.C., Loheide, S.P., Donner, 485
S.D., Tsuruta, K., Vadas, P.A., Kucharik, C.J., 2017. The Influence of Legacy P on Lake 486
Water Quality in a Midwestern Agricultural Watershed. Ecosystems 20, 1468–1482. 487 488
Mulbry, W., Kangas, P., Kondrad, S., 2010. Toward scrubbing the bay: Nutrient removal using small 489
algal turf scrubbers on Chesapeake Bay tributaries. Ecol. Eng. 36, 536–541. 490 491
Mulbry, W., Kondrad, S., Pizarro, C., Kebede-Westhead, E., 2008. Treatment of dairy manure 492
effluent using freshwater algae: Algal productivity and recovery of manure nutrients using 493
pilot-scale algal turf scrubbers. Bioresour. Technol. 99, 8137–8142. 494 495
Müller, S., Mitrovic, S.M., 2015. Phytoplankton co-limitation by nitrogen and phosphorus in a 496
shallow reservoir: progressing from the phosphorus limitation paradigm. Hydrobiologia 744, 497
255–269. 498
Nixon, S.W., 1995. Coastal marine eutrophication: A definition, social causes, and future concerns. 499
Ophelia 41, 199–219. 500
O’Geen, A.T., Budd, R., Gan, J., Maynard, J.J., Parikh, S.J., Dahlgren, R.A., 2010. Chapter One - 501
Mitigating Nonpoint Source Pollution in Agriculture with Constructed and Restored 502
Wetlands, in: Sparks, D.L. (Ed.), Advances in Agronomy. Academic Press, pp. 1–76. 503 504
Paerl, H. W., 1988. Nuisance phytoplankton blooms in coastal, estuarine, and inland waters. 505
Limnol. Oceanogr. 33:823-847. 506
Paerl, H.W., 2017. Controlling harmful cyanobacterial blooms in a climatically more extreme world: 507
management options and research needs. J. Plankton Res. 39, 763–771. 508 509
Paerl, H.W., 2014. Mitigating harmful cyanobacterial blooms in a human- and climatically-impacted 510
world. Life Basel Switz. 4, 988–1012. 511
Paerl, H.W., 1997. Coastal eutrophication and harmful algal blooms: Importance of atmospheric 512
deposition and groundwater as “new” nitrogen and other nutrient sources. Limnol. Oceanogr. 513
42, 1154–1165. 514
Paerl, H.W., Dennis, R.L., Whitall, D.R., 2002. Atmospheric deposition of nitrogen: Implications for 515
nutrient over-enrichment of coastal waters. Estuaries 25, 677–693. 516 517
Paerl, H.W., Fulton, R.S., Moisander, P.H., Dyble, J., 2001. Harmful freshwater algal blooms, with 518
an emphasis on cyanobacteria. ScientificWorldJournal 1, 76–113. 519 520
Paerl, H.W., Gardner, W.S., Havens, K.E., Joyner, A.R., McCarthy, M.J., Newell, S.E., Qin, B., 521
Scott, J.T., 2016a. Mitigating cyanobacterial harmful algal blooms in aquatic ecosystems 522
impacted by climate change and anthropogenic nutrients. Harmful Algae, Global Expansion 523
of Harmful Cyanobacterial Blooms: Diversity, ecology, causes, and controls 54, 213–222. 524 525
Paerl, H.W., Hall, N.S., Calandrino, E.S., 2011. Controlling harmful cyanobacterial blooms in a 526
world experiencing anthropogenic and climatic-induced change. Sci. Total Environ. 409, 527
1739–1745. 528
Paerl, H.W., Havens, K.E., Hall, N.S., Otten, T.G., Zhu, M., Xu, H., Zhu, G., Qin, B., 2019a. 529
Mitigating a global expansion of toxic cyanobacterial blooms: confounding effects and 530
challenges posed by climate change. Mar. Freshw. Res. 531
Paerl, H.W. Havens, K.E., Xu, H., Zhu, G., McCarthy, M.J., Newell, S.E., Scott, J.T., Hall, N.S., 532
Otten, T.G., Qin, B. 2019b. Mitigating eutrophication and toxic cyanobacterial blooms in 533
large lakes: The evolution of a dual nutrient (N and P) reduction paradigm. Hydrobiologia 534 535
Paerl, H.W., Huisman, J., 2009. Climate change: a catalyst for global expansion of harmful 536
cyanobacterial blooms. Environ. Microbiol. Rep. 1, 27–37.
2229.2008.00004.x 538
Paerl, H.W., Huisman, J., 2008. Blooms Like It Hot. Science 320, 57–58. 539 540
Paerl, H.W., Joyner, A.R., Havens, K.E., 2015. in the Face of Climate Change. Clim. Change II 17–541
21. 542
Paerl, H.W., Paul, V.J., 2012. Climate change: Links to global expansion of harmful cyanobacteria. 543
Water Res., Cyanobacteria: Impacts of climate change on occurrence, toxicity and water 544
quality management 46, 1349–1363. 545
Paerl, H.W., Scott, J.T., McCarthy, M.J., Newell, S.E., Gardner, W.S., Havens, K.E., Hoffman, D.K., 546
Wilhelm, S.W., Wurtsbaugh, W.A., 2016b. It Takes Two to Tango: When and Where Dual 547
Nutrient (N & P) Reductions Are Needed to Protect Lakes and Downstream Ecosystems. 548
Environ. Sci. Technol. 50, 10805–10813. 549
Page, B.P., Kumar, A., Mishra, D.R., 2018. A novel cross-satellite based assessment of the spatio-550
temporal development of a cyanobacterial harmful algal bloom. Int. J. Appl. Earth Obs. 551
Geoinformation 66, 69–81. 552
Pan, G., Zhang, M.-M., Chen, H., Zou, H., Yan, H., 2006. Removal of cyanobacterial blooms in 553
Taihu Lake using local soils. I. Equilibrium and kinetic screening on the flocculation of 554
Microcystis aeruginosa using commercially available clays and minerals. Environ. Pollut. 555
141, 195–200. 556
Peierls, B.L., Caraco, N.F., Pace, M.L., Cole, J.J., 1991. Human influence on river nitrogen. Nature 557
350, 386–387. 558
Peterson, S.A., 1982. Lake Restoration by Sediment Removal. JAWRA J. Am. Water Resour. Assoc. 559
18, 423–436. 560
Polyakov, V., Fares, A., Ryder, M.H., 2005. Precision riparian buffers for the control of nonpoint 561
source pollutant loading into surface water: A review. Environ. Rev. 13, 129–144. 562
Puckett, L.J., Tesoriero, A.J., Dubrovsky, N.M., 2011. Nitrogen Contamination of Surficial 563
Aquifers—A Growing Legacy. Environ. Sci. Technol. 45, 839–844. 564 565
Putt, A.E., MacIsaac, E.A., Herunter, H.E., Cooper, A.B., Selbie, D.T., 2019. Eutrophication forcings 566
on a peri-urban lake ecosystem: Context for integrated watershed to airshed management. 567
PLOS ONE 14, e0219241. 568
Rasouli, S., Whalen, J.K., Madramootoo, C.A., 2014. Review: Reducing residual soil nitrogen losses 569
from agroecosystems for surface water protection in Quebec and Ontario, Canada: Best 570
management practices, policies and perspectives. Can. J. Soil Sci. 94, 109–127. 571 572
Reddy, K.R., Fisher, M.M., Wang, Y., White, J.R., James, R.T., 2007. Potential Effects of Sediment 573
Dredging on Internal Phosphorus Loading in a Shallow, Subtropical Lake. Lake Reserv. 574
Manag. 23, 27–38. 575
Reddy, K.R., Newman, S., Osborne, T.Z., White, J.R., Fitz, H.C., 2011. Phosphorous Cycling in the 576
Greater Everglades Ecosystem: Legacy Phosphorous Implications for Management and 577
Restoration. Crit. Rev. Environ. Sci. Technol. 41, 149–186. 578 579
Ribaudo, M.O., Heimlich, R., Claassen, R., Peters, M., 2001. Least-cost management of nonpoint 580
source pollution: source reduction versus interception strategies for controlling nitrogen loss 581
in the Mississippi Basin. Ecol. Econ. 37, 183–197.
8009(00)00273-1 583
Robb, M., Greenop, B., Goss, Z., Douglas, G., Adeney, J., 2003. Application of PhoslockTM, an 584
innovative phosphorus binding clay, to two Western Australian waterways: preliminary 585
findings. Hydrobiologia 494, 237–243. 586
Ryther, J.H., Dunstan, W.M., 1971. Nitrogen, phosphorus, and eutrophication in the coastal marine 587
environment. Science 171, 1008–1013. 588
Sandrini, G., Ji, X., Verspagen, J.M.H., Tann, R.P., Slot, P.C., Luimstra, V.M., Schuurmans, J.M., 589
Matthijs, H.C.P., Huisman, J., 2016. Rapid adaptation of harmful cyanobacteria to rising CO
. 590
Proc. Natl. Acad. Sci. U. S. A. 113, 9315–9320. 591
Schindler, D.W., 2012. The dilemma of controlling cultural eutrophication of lakes. Proc. R. Soc. B 592
Biol. Sci. 279, 4322–4333. 593
Scott, J.T., McCarthy, M.J., Paerl, H.W., 2019. Nitrogen transformations differentially affect 594
nutrient-limited primary production in lakes of varying trophic state. Limnol. Oceanogr. Lett. 595
4, 96–104. 596
Scott, M.D., Ramaswamy, L., Lawson, V., 2016. CyanoTRACKER: A Citizen Science Project for 597
Reporting Harmful Algal Blooms. 2016 IEEE 2nd Int. Conf. Collab. Internet Comput. CIC. 598 599
Sedlak, R.I., 1991. Phosphorus and Nitrogen Removal from Municipal Wastewater: Principles and 600
Practice, Second Edition. CRC Press. 601
Seo, Y., Lee, J., Hart, W.E., Denton, H.P., Yoder, D.C., Essington, M.E., Perfect, E., 2005. Sediment 602
loss and nutrient runoff from three fertilizer application methods. Trans. ASAE 48, 2155–603
2162. 604
Sharples, J.J., Cary, G.J., Fox-Hughes, P., Mooney, S., Evans, J.P., Fletcher, M.-S., Fromm, M., 605
Grierson, P.F., McRae, R., Baker, P., 2016. Natural hazards in Australia: extreme bushfire. 606
Clim. Change 139, 85–99. 607
Sharpley, A., Jarvie, H.P., Buda, A., May, L., Spears, B., Kleinman, P., 2013. Phosphorus legacy: 608
overcoming the effects of past management practices to mitigate future water quality 609
impairment. J. Environ. Qual. 42, 1308–1326. 610
Shatwell, T., Köhler, J., 2019. Decreased nitrogen loading controls summer cyanobacterial blooms 611
without promoting nitrogen-fixing taxa: Long-term response of a shallow lake. Limnol. 612
Oceanogr. 64, S166–S178. 613
Shi, X., Li, S., Wei, L., Qin, B., Brookes, J.D., 2017. CO
alters community composition of 614
freshwater phytoplankton: A microcosm experiment. Sci. Total Environ. 607–608, 69–77. 615 616
Sinha, E., Michalak, A.M., Balaji, V., 2017. Eutrophication will increase during the 21st century as a 617
result of precipitation changes. Science 357, 405–408. 618 619
Smith, D.R., Warnemuende, E.A., Haggard, B.E., Huang, C., 2006. Dredging of drainage ditches 620
increases short-term transport of soluble phosphorus. J. Environ. Qual. 35, 611–616. 621 622
Smith, V.H., 2003. Eutrophication of freshwater and coastal marine ecosystems a global problem. 623
Environ. Sci. Pollut. Res. 10, 126–139. 624
Soranno, P.A., Hubler, S.L., Carpenter, S.R., Lathrop, R.C., 1996. Phosphorus loads to surface 625
waters: A simple model to account for spatial pattern of land use. Ecol. Appl. 6, 865–878. 626 627
Stumpf, R.P., Johnson, L.T., Wynne, T.T., Baker, D.B., 2016. Forecasting annual cyanobacterial 628
bloom biomass to inform management decisions in Lake Erie. J. Gt. Lakes Res. 42, 1174–629
1183. 630
Trenberth, K.E., 2008. The Impact of Climate Change and Variability on Heavy Precipitation, 631
Floods, and Droughts, in: Encyclopedia of Hydrological Sciences. American Cancer Society. 632 633
US EPA, 2013. Biological Nutrient Removal Processes and Costs [WWW Document]. US EPA. 634
costs (accessed 3.14.20). 636
Van Drecht, G., Bouwman, A.F., Harrison, J., Knoop, J.M., 2009. Global nitrogen and phosphate in 637
urban wastewater for the period 1970 to 2050. Glob. Biogeochem. Cycles 23. 638 639
Verspagen, J.M.H., Van de Waal, D.B., Finke, J.F., Visser, P.M., Van Donk, E., Huisman, J., 2014. 640
Rising CO
levels will intensify phytoplankton blooms in eutrophic and hypertrophic lakes. 641
PLoS One 9, e104325. 642
Walsby, A.E., Hayes, P.K., Boje, R., Stal, L.J., 1997. The selective advantage of buoyancy provided 643
by gas vesicles for planktonic cyanobacteria in the Baltic Sea. New Phytol. 136, 407–417. 644 645
Weber, S.J., Mishra, D.R., Wilde, S.B., Kramer, E., 2020. Risks for cyanobacterial harmful algal 646
blooms due to land management and climate interactions. Sci. Total Environ. 703, 134608. 647 648
Wright, D.I., Shapiro, J., 1984. Nutrient reduction by biomanipulation: An unexpected phenomenon 649
and its possible cause. SIL Proc. 1922-2010 22, 518–524. 650 651
Wu, J., Yu, S.L., Zou, R., 2006. A water quality-based approach for watershed wide BMP strategies. 652
JAWRA J. Am. Water Resour. Assoc. 42, 1193–1204.
1688.2006.tb05294.x 654
Wuebbles, D., Meehl, G., Hayhoe, K., Karl, T.R., Kunkel, K., Santer, B., Wehner, M., Colle, B., 655
Fischer, E.M., Fu, R., Goodman, A., Janssen, E., Kharin, V., Lee, H., Li, W., Long, L.N., 656
Olsen, S.C., Pan, Z., Seth, A., Sheffield, J., Sun, L., 2013. CMIP5 Climate model analyses: 657
Climate extremes in the United States. Bull. Am. Meteorol. Soc. 95, 571–583. 658 659
Wurtsbaugh, W.A., Paerl, H.W., Dodds, W.K., 2019. Nutrients, eutrophication and harmful algal 660
blooms along the freshwater to marine continuum. WIREs Water 6, e1373. 661 662
Zhang, X., Liu, X., Zhang, M., Dahlgren, R.A., Eitzel, M., 2010. A review of vegetated buffers and a 663
meta-analysis of their mitigation efficacy in reducing nonpoint source pollution. J. Environ. 664
Qual. 39, 76–84. 665
Zhang, Y., Ma, R., Duan, H., Loiselle, S., Xu, J., 2016. Satellite analysis to identify changes and 666
drivers of CyanoHABs dynamics in Lake Taihu. Water Supply 16, 1451–1466. 667 668
Zheng, J., Nanbakhsh, H., Scholz, M., 2006. Case study: Design and operation of sustainable urban 669
infiltration ponds treating storm runoff. J. Urban Plan. Dev. 132, 36–41. 670 671
Zohary, T., Herut, B., Krom, M.D., Fauzi C. Mantoura, R., Pitta, P., Psarra, S., Rassoulzadegan, F., 672
Stambler, N., Tanaka, T., Frede Thingstad, T., Malcolm S. Woodward, E., 2005. P-limited 673
bacteria but N and P co-limited phytoplankton in the Eastern Mediterranean—a microcosm 674
experiment. Deep Sea Res. Part II Top. Stud. Oceanogr., On the Nature of Phosphorus 675
Cycling and Limitation in the Eastern Mediterranean 52, 3011–3023. 676 677
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Figure 1. Conceptual diagram, showing the feedback loops of climatic effects and nutrients on 681
CyanoHAB biomass. a) Climate change is causing more intense wet/dry cycles, widespread 682
wildfires, and warming, leading to an increase in CyanoHAB biomass. b) Increased CyanoHAB 683
biomass is involved in a positive feedback loop with legacy nutrients and regenerated nutrients 684
derived from the microbial loop. c) These feedback loops combined with climatic effects constitute a 685
key challenge to mitigating CyanoHABs. 686
Figure 2. Conceptual diagram, illustrating multiple, interacting controls in CyanoHAB management. 688
Climatic influences have led to the need to reduce nutrient loading below previous reduction 689
standards, putting additional pressure on reducing nutrient inputs from (a) point source pollution and 690
(b) non-point source pollution, (c) regenerated nutrients, and (d) legacy nutrients though various 691
mechanical, chemical, and biological means. (e) Short-term (several months) treatment, chemical and 692
biological approaches used. (f) Appropriate monitoring is essential for assessing the CyanoHAB 693
scales and the efficacy of management approaches. 694
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... Cultural eutrophication and harmful algal blooms (HABs) are increasingly prevalent issues globally (Ho et al., 2019;Leech et al., 2018;Moe et al., 2019) and have proven challenging and costly to address (Bramburger et al., 2022;Hamilton et al., 2014;Osgood, 2017). Within Elk/Beaver Lake (EBL) and many other lakes, acute impacts of eutrophication include increased frequency and duration of HAB events (Bullerjahn et al., 2016;Ho et al., 2019;Nordin, 2015;Nürnberg and Lazerte, 2016;Paerl and Barnard, 2020). HABs endanger the health of humans and pets, affecting the safe use of the lake for swimming and for pets and other animals (Carmichael and Boyer, 2016;Dodds et al., 2009). ...
... (Lewtas et al., 2015); 3 (CRD, 2020); 4 (Carvajal and Janmaat, 2016); 5 (van den Heuvel et al., 2017); 6 (Syslo et al., 2013) community, including the increased frequency and duration of HABs, and the impacts of degraded water quality and the spread of non-native species on biodiversity. These issues are of global importance-climate change and human activity are expected to contribute to the spread of non-native and invasive species (Pagnucco et al., 2015), as well as the worsening HABs in many lakes across the world (Moe et al., 2019;Paerl and Barnard, 2020). In EBL, the benefits of reducing the prevalence of HABs and improving the Canadian Water Quality Index score were $141-272 per household per year, while benefits of achieving the goals of the watershed management plan, including the management of HABs and invasive fish and macrophyte species, were $142-292 per household per year. ...
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Cultural eutrophication—the pollution of water bodies with nutrients such as nitrogen and phosphorus from human activities—and associated harmful algal blooms are key issues facing decision-makers, yet costs are often identified as a barrier to restoration. When designed in collaboration with impacted communities, economic valuation of lake ecosystem services can contribute to informed environmental decision-making by quantifying economic benefits of lake restoration and understanding the trade-offs people are willing to make. Here, we collaborate with the local community, stakeholders, and decision-makers to develop and implement a discrete choice experiment survey to estimate people’s preferences and willingness to pay for restoring Elk/Beaver Lake, Canada, which has been experiencing worsening harmful algal blooms and other water quality issues. Over half of survey respondents (66%) indicated that water quality issues impact their use of the lake, and many (52%) indicated they did not feel safe swimming in or allowing their pets to drink from the lake (64%). Responses to the choice experiment are analyzed using choice models which reveal that the annual economic benefits of lake restoration across different model specifications ranged from $141 to $292 CAD per household with substantial heterogeneity across people. The aggregate annual benefits of lake restoration are $27 to $55 million which is notably greater than the estimated costs of restoration plans. This study contributes to the growing literature suggesting that there are substantial benefits to society from restoring lakes, thus the perception of cost as an insurmountable barrier to restoration of bloom-affected lakes requires reconsideration.
... Recent decades have witnessed the global expansion of harmful cyanobacterial blooms, mainly in freshwater environments, in terms of frequency, intensity, and toxicity (Paerl and Barnard 2020). The toxic cyanobacterium Microcystis is one of the most pervasive species responsible for around 90% of the cyanobacterial bloom incidents reported in freshwater bodies (Preston et al. 1980;Chen et al. 2003;Paerl and Otten 2013). ...
The occurrence of toxic bloom-forming cyanobacteria, Microcystis aeruginosa, has been frequently reported worldwide. These colony forming toxic cyanobacteria harbour a wide range of heterotrophic bacterial communities. The present study has attempted to understand the bloom dynamics of M. aeruginosa along with isolating their colony-associated culturable heterotrophic bacteria from two freshwater ponds in south India with a persisting cyanobacterial bloom. The monthly monitoring of these study areas revealed the conducive role of warm, stagnant waters with high nutrients in forming M. aeruginosa bloom. The peak values of temperature, nitrate, and phosphate at station 1 reached up to 30.5 °C, 4.48 mg/L, 1.64 mg/L, and at station 2, 31 °C, 3.45 mg/L, and 0.62 mg/L, respectively. Twenty-eight bacterial isolates belonging to Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Actinobacteria, and Firmicutes were obtained during the study. Among these 28 isolates, Firmicutes was dominant with the M. aeruginosa bloom from both the study areas.
... A great matter of concern is the impact of climate change on water resources. Global warming, changes in rainfall patterns, and sea level rise represent shifts in stresses that affect water resource availability and quality (IPCC, 2021;Paerl and Barnard, 2020;Ryberg and Chanat, 2022;Komatsu et al., 2007;Nijhawan and Howard, 2022;Bertels and Willems, 2022;Lange, 2020). The main factors that can affect water quality on reservoirs are dilution and evaporation, surface runoffs in the hydrological catchment and changes in water demand. ...
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Climate change causes heavy rainfall incidents and sea level rise, which have serious impact on the availability and quality of water resources. These extreme phenomena lead to the rise of external and internal precursors in water reservoirs, and consequently affect the formation of disinfection by-products (DBPs). The aim of this study was to investigate the formation of nitrogenous_DBPs (N-DBPs) under extreme conditions caused by climate change. For this reason, two scenarios were adapted: a) sea level rise leading to increase of water salinity and b) heavy rainfall incidents leading to flooding events. The target-compounds were haloacetonitriles (HANs), haloacetamides (HAcAms) and halonitromethane (TCNM). Chlorination and chloramination were employed as disinfection processes under different doses (5 and 10 mg/L) and contact times (24 and 72 h). The results showed enhancement on the formation of N-DBPs and changes in their profile. Sea level rise scenario led to elevated concentrations of brominated species (maximum concentration of dibromoacetonitrile 23 μg/L and maximum concentration of bromoacetamide 57 μg/L), while flooding events scenario led to extended formation of chloroacetamide and bromochloroacetonitrile up to 58 μg/L and 40 μg/L, respectively. At the same time, changes in cytotoxicity and genotoxicity of the samples were observed.
Nutrient-induced blooms of the globally abundant freshwater toxic cyanobacterium Microcystis are the cause of worldwide public and ecosystem health concerns. The response of Microcystis growth and toxin production to new and recycled nitrogen (N) inputs, and the impact of heterotrophic bacteria in the Microcystis phycosphere on these processes are not well understood. Here, using microbiome transplant experiments, cyanotoxin analysis, and stable isotope tracing to measure N incorporation and exchange at single cell resolution, we monitored the growth, cyanotoxin production, and microbiome community structure of several Microcystis strains grown on amino acids and proteins as the sole N source. We demonstrate that 1) organic N availability shapes the microbiome community structure in the Microcystis phycosphere; 2) external organic N input leads to lower bacterial colonization of the phycosphere; 3) certain Microcystis strains can directly uptake amino acids, but with lower rates than heterotrophic bacteria; 4) biomass-specific microcystin production is not impacted by N source (i.e., nitrate, amino acids and protein) but rather by total N availability; and 5) some bacterial communities compete with Microcystis for organic N, but others remineralize organic N, in the process producing bio-available N for Microcystis. We conclude that organic N input can support Microcystis blooms and toxin production, and Microcystis-associated microbial communities play critical roles by influencing cyanobacterial succession through either decreasing (via competition) or increasing (via remineralization) N availability, especially under inorganic N scarcity.
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Blue-green algae, or cyanobacteria, may be prevalent in our rivers and tap water. These minuscule bacteria can grow swiftly and form blooms in warm, nutrient-rich water. Toxins produced by cyanobacteria can pollute rivers and streams and harm the liver and nervous system in humans. This review highlights the properties of 25 toxin types produced by 12 different cyanobacteria genera. The review also covered strategies for reducing and controlling cyanobacteria issues. These include using physical or chemical treatments, cutting back on fertilizer input, algal lawn scrubbers, and antagonistic microorganisms for biocontrol. Micro-, nano-and ultrafiltration techniques could be used for the removal of internal and extracellular cyanotoxins, in addition to powdered or granular activated carbon, ozonation, sedimentation, ultraviolet radiation, potassium permanganate, free chlorine, and pre-treatment oxidation techniques. The efficiency of treatment techniques for removing intracellular and extracellular cyanotoxins is also demonstrated. These approaches aim to lessen the risks of cyanobacterial blooms and associated toxins. Effective management of cyanobacteria in water systems depends on early detection and quick action. Cyanobacteria cells and their toxins can be detected using microscopy, molecular methods, chromatography, and spectroscopy. Understanding the causes of blooms and the many ways for their detection and elimination will help the management of this crucial environmental issue. Key Contribution: This article focuses on cyanobacteria, looking into their origins, how they spread, and any issues connected to this type of toxicity diffusion in water. Many strategies are also discussed to reduce these risks and secure drinking water.
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Although phenotypic plasticity is a widespread phenomenon, its implications for species responses to climate change are not well understood. For example, toxic cyanobacteria can form dense surface blooms threatening water quality in many eutrophic lakes, yet a theoretical framework to predict how phenotypic plasticity affects bloom development at elevated p CO 2 is still lacking. We measured phenotypic plasticity of the carbon fixation rates of the common bloom-forming cyanobacterium Microcystis . Our results revealed a 1.8- to 5-fold increase in the maximum CO 2 uptake rate of Microcystis at elevated p CO 2 , which exceeds CO 2 responses reported for other phytoplankton species. The observed plasticity was incorporated into a mathematical model to predict dynamic changes in cyanobacterial abundance. The model was successfully validated by laboratory experiments and predicts that acclimation to high p CO 2 will intensify Microcystis blooms in eutrophic lakes. These results indicate that this harmful cyanobacterium is likely to benefit strongly from rising atmospheric p CO 2 .
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Cyanobacterial harmful algal blooms (cyanoHABs) are a serious environmental, water quality and public health issue worldwide because of their ability to form dense biomass and produce toxins. Models and algorithms have been developed to detect and quantify cyanoHABs biomass using remotely sensed data but not for quantifying bloom magnitude, information that would guide water quality management decisions. We propose a method to quantify seasonal and annual cyanoHAB magnitude in lakes and reservoirs. The magnitude is the spatiotemporal mean of weekly or biweekly maximum cyanobacteria biomass for the season or year. CyanoHAB biomass is quantified using a standard reflectance spectral shape-based algorithm that uses data from Medium Resolution Imaging Spectrometer (MERIS). We demonstrate the method to quantify annual and seasonal cyanoHAB magnitude in Florida and Ohio (USA) respectively during 2003–2011 and rank the lakes based on median magnitude over the study period. The new method can be applied to Sentinel-3 Ocean Land Color Imager (OLCI) data for assessment of cyanoHABs and the change over time, even with issues such as variable data acquisition frequency or sensor calibration uncertainties between satellites. CyanoHAB magnitude can support monitoring and management decision-making for recreational and drinking water sources.
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Hydrogen peroxide (H2O2), a pesticide used in salmonid aquaculture, is released directly into the environment where nontarget organisms are at risk of exposure. We determined threshold concentrations for mortality of Calanus spp., the dominant zooplankton species in the North Atlantic, and assessed sublethal effects, focusing on the escape response and oxygen consumption rates (OCRs) as behavioral and physiological assays. One-hour exposure to 170 mg·L−1 (i.e., 10% of the recommended H2O2 treatment) was lethal to copepodite stage V (92% mortality) and adult females (100% mortality). The acute median lethal concentration (1h-LC50) was 214.1 (150.67–277.4) and 48.6 (44.9–52.2) mg·L−1 for copepodite V and adults, respectively. The 25-h LC50 was 77.1 (57.9–96.2) and 30.63 (25.4–35.8) mg·L−1 for copepodite V and adults, respectively. At concentrations of 0.5% and 1% of the recommended treatment level, Calanus spp. showed a decrease in escape performance and lower OCRs with increased concentration. At H2O2 concentrations of 5% of the recommended treatment levels (85 mg·L−1), exposed copepods showed no escape reaction response. These results suggest that sublethal concentrations of H2O2 will increase the risk of predation for Calanus spp. Furthermore, this study provides supporting evidence that theoretical “safe” values, traditionally used for predicting toxicity thresholds, underestimate the impact of H2O2 on the physiological condition of nontarget crustaceans.
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Cyanobacterial harmful algal blooms (CyanoHABs) are an increasingly common feature of large, eutrophic lakes. Non-N2-fixing CyanoHABs (e.g., Microcystis) appear to be proliferating relative to N2-fixing CyanoHABs in systems receiving increasing nutrient loads. This shift reflects increasing external nitrogen (N) inputs, and a > 50-year legacy of excessive phosphorus (P) and N loading. Phosphorus is effectively retained in legacy-impacted systems, while N may be retained or lost to the atmosphere in gaseous forms (e.g., N2, NH3, N2O). Biological control on N inputs versus outputs, or the balance between N2 fixation versus denitrification, favors the latter, especially in lakes undergoing accelerating eutrophication, although denitrification removal efficiency is inhibited by increasing external N loads. Phytoplankton in eutrophic lakes have become more responsive to N inputs relative to P, despite sustained increases in N loading. From a nutrient management perspective, this suggests a need to change the freshwater nutrient limitation and input reduction paradigms; a shift from an exclusive focus on P limitation to a dual N and P co-limitation and management strategy. The recent proliferation of toxic non-N2-fixing CyanoHABs, and ever-increasing N and P legacy stores, argues for such a strategy if we are to mitigate eutrophication and CyanoHAB expansion globally.
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Peri-urban lakes increasingly experience intensified anthropogenic impacts as watershed uses and developments increase. Cultus Lake is an oligo-mesotrophic, peri-urban lake near Vancouver, British Columbia, Canada that experiences significant seasonal tourism, anthropogenic nutrient loadings, and associated cultural eutrophication. Left unabated, these cumulative stresses threaten the critical habitat and persistence of two endemic species at risk (Coastrange Sculpin, Cultus population; Cultus Lake sockeye salmon) and diverse lake-derived ecosystem services. We constructed water and nutrient budgets for the Cultus Lake watershed to identify and quantify major sources and loadings of nitrogen (N) and phosphorus (P). A steady-state water quality model, calibrated against current loadings and limnological data, was used to reconstruct the historic lake trophic status and explore limnological changes in response to realistic development and mitigation scenarios. Significant local P loadings to Cultus Lake arise from septic leaching (19%) and migratory gull guano deposition (22%). Watershed runoff contributes the majority of total P (53%) and N (73%) loads to Cultus Lake, with substantial local N contributions arising from the agricultural Columbia Valley (41% of total N load). However, we estimate that up to 66% of N and 70% of P in watershed runoff is ultimately sourced via deposition from the nutrient-contaminated regional airshed, with direct atmospheric deposition on the lake surface contributing an additional 17% of N and 5% of P. Thus, atmospheric deposition is the largest single source of nutrient loading to Cultus Lake, cumulatively responsible for 63% and 42% of total N and P loadings, respectively. Modeled future loading scenarios suggest Cultus Lake could become mesotrophic within the next 25 years, highlighting a heightened need for near-term abatement of P loads. Although mitigating P loads from local watershed sources will slow the rate of eutrophication, management efforts targeting reductions in atmospheric-P within the regional airshed are necessary to halt or reverse lake eutrophication, and conserve both critical habitat for imperiled species at risk and lake-derived ecosystem services.
Managing and mitigating the global expansion of toxic cyanobacterial harmful algal blooms (CyanoHABs) is a major challenge facing researchers and water resource managers. Various approaches, including nutrient load reduction, artificial mixing and flushing, omnivorous fish removal, algaecide applications and sediment dredging, have been used to reduce bloom occurrences. However, managers now face the additional challenge of having to address the effects of climate change on watershed hydrological and nutrient load dynamics, water temperature, mixing regime and internal nutrient cycling. Rising temperatures and increasing frequencies and magnitudes of extreme weather events, including tropical cyclones, extratropical storms, floods and droughts, all promote CyanoHABs and affect the efficacy of ecosystem remediation measures. These climatic changes will likely require setting stricter nutrient (including both nitrogen and phosphorus) reduction targets for bloom control in affected waters. In addition, the efficacy of currently used methods to reduce CyanoHABs will need to be re-evaluated in light of the synergistic effects of climate change with nutrient enrichment.
Over the past decade, the global proliferation of cyanobacterial harmful algal blooms (CyanoHABs) have presented a major risk to the public and wildlife, and ecosystem and economic services provided by inland water resources. As a consequence, water resources, environmental, and healthcare agencies are in need of early information about the development of these blooms to mitigate or minimize their impact. Results from various components of a novel multi-cloud cyber-infrastructure referred to as "CyanoTRACKER" for initial detection and continuous monitoring of spatio-temporal growth of CyanoHABs is highlighted in this study. The novelty of the CyanoTRACKER framework is the collection and integration of combined community reports (social cloud), remote sensing data (sensor cloud) and digital image analytics (computation cloud) to detect and differentiate between regular algal blooms and CyanoHABs. Individual components of CyanoTRACKER include a reporting website, mobile application (App), remotely deployable solar powered automated hyperspectral sensor (CyanoSense), and a cloud-based satellite data processing and integration tool. All components of CyanoTRACKER provided important data related to CyanoHABs assessments for regional and global water bodies. Reports and data received via social cloud including the mobile App, Twitter, Facebook, and CyanoTRACKER website, helped in identifying the geographic locations of CyanoHABs affected water bodies. A significant increase (124.92%) in tweet numbers related to CyanoHABs was observed between 2011 (total relevant tweets = 2925) and 2015 (total relevant tweets = 6579) that reflected an increasing trend of the harmful phenomena across the globe as well as an increased awareness about CyanoHABs among Twitter users. The CyanoHABs affected water bodies extracted via the social cloud were categorized, and smaller water bodies were selected for the deployment of CyanoSense, and satellite data analysis was performed for larger water bodies. CyanoSense was able to differentiate between ordinary algae and CyanoHABs through the use of their characteristic absorption feature at 620 nm. The results and products from this infrastructure can be rapidly disseminated via the CyanoTRACKER website, social media, and direct communication with appropriate management agencies for issuing warnings and alerting lake managers, stakeholders and ordinary citizens to the dangers posed by these environmentally harmful phenomena.
Despite the longstanding significance of North America's Great Lakes, little is known about their preindustrial ecology. Here, we report on when and how humans first became a main driver of Lake Ontario's nutrient dynamics. Nitrogen isotope analyses of archaeological fish show that, prior to the 1830s, Lake Ontario's nitrogen cycle and the trophic ecology of its top predators had remained stable for at least 800 yrs, despite Indigenous and historical European agricultural land management across the region. An abrupt shift in the nitrogen isotope composition of Lake Ontario's fish community is evident in the early to mid‐19th century and reflects the initiation of industrial‐scale forest clearance. These data show how the nitrogenous nutrient regimes of even the world's largest freshwater ecosystems can be highly sensitive to short‐term watershed forest cover disturbances and indicate a profound shift in the relationship between humans and their environment.
The frequency and severity of cyanobacteria harmful blooms (CyanoHABs) have been increasing with frequent eutrophication and shifting climate paradigms. CyanoHABs produce a spectrum of toxins and can trigger neurological disorder, organ failure, and even death. To promote proactive CyanoHAB management, geospatial risk modeling can act as a predictive mechanism to supplement current mitigation efforts. In this study, iterative AIC analysis was performed on 17 watershed-level biophysical parameters to identify the strongest predictors based on Sentinel-2-derived cyanobacteria cell densities (CCD) for 771 waterbodies in Georgia Piedmont. This study used a streamlined watershed delineation technique, a 1-meter LULC classification with ~88% accuracy, and a technique to predict CyanoHAB risk in small-to-medium sized waterbodies. Landscape characteristics were computed utilizing the Google Earth Engine platform that enabled large spatio-temporal scope and variable inclusion. Watershed maximum winter temperature, percent agriculture, percent forest, percent impervious, and waterbody area were the strongest predictors of CCD with a 0.33 R-squared. Warmer winter temperatures allow cyanobacteria to be photosynthetically active year-round, and trigger CyanoHABs when warmer temperatures and nutrients are introduced in early spring, typically referred to as Spring Bloom in southeast U.S. The risk models revealed an unexpected significant linear relationship between percent forest and CCD. It is due to the fact that land reclamation via reforestation in the piedmont have left legacy sediment and nutrients which are mobilized as surface runoff to the watershed after rain events. A Jenks Natural Break scheme assigned waterbodies to CyanoHAB risk groups, and of the 771 waterbodies, 24.38% were low, 37.35% and 38.26% were medium and high risk respectively. This research supplements existing cyanobacteria risk modeling methods by introducing a novel, scalable, and reproducible method to determine yearly regional risk. Future studies should include factors such as demographic, socioeconomic, labor, and site-specific environmental conditions to create more holistic CyanoHAB risk outputs.
Agricultural, urban and industrial activities have dramatically increased aquatic nitrogen and phosphorus pollution (eutrophication), threatening water quality and biotic integrity from headwater streams to coastal areas world‐wide. Eutrophication creates multiple problems, including hypoxic “dead zones” that reduce fish and shellfish production; harmful algal blooms that create taste and odor problems and threaten the safety of drinking water and aquatic food supplies; stimulation of greenhouse gas releases; and degradation of cultural and social values of these waters. Conservative estimates of annual costs of eutrophication have indicated $1 billion losses for European coastal waters and $2.4 billion for lakes and streams in the United States. Scientists have debated whether phosphorus, nitrogen, or both need to be reduced to control eutrophication along the freshwater to marine continuum, but many management agencies worldwide are increasingly opting for dual control. The unidirectional flow of water and nutrients through streams, rivers, lakes, estuaries and ultimately coastal oceans adds additional complexity, as each of these ecosystems may be limited by different factors. Consequently, the reduction of just one nutrient upstream to control eutrophication can allow the export of other nutrients downstream where they may stimulate algal production. The technology exists for controlling eutrophication, but many challenges remain for understanding and managing this global environmental problem. This article is categorized under: Science of Water > Water Quality Water and Life > Stresses and Pressures on Ecosystems