Harmful algae
blooms (HABs) are considered to be a major environmental problem throughout the
U.S., in all 50 states, and throughout the world. These include so-called red tides and cyanobacteria
(blue-green algae). They can impact human and animal health, aquatic
ecosystems, and even economies. Not all algae blooms are harmful.
Harmful algae
blooms are overgrowths of algae in both freshwater and saltwater. Not all are
toxic but even the non-toxic ones can be harmful in other ways. The algae
blooms can produce toxins that can kill people or animals. They can create
“dead zones” in water bodies. They can increase water treatment costs and
damage industries that rely on clean water.
The
ingredients for harmful algae blooms are sunlight, slow-moving water, and
nutrients, notably nitrogen and phosphorus. The use of nitrogen and phosphorus
as fertilizers and the prevalence of fertilizer runoff make HABs occur more often
and with more severity. Both synthetic chemical fertilizers and natural
fertilizers like animal manure contribute to the problem. Agriculture also
produces gaseous nitrous oxides and ammonia that can end up in waterways and
eventually contribute to HABs. Agriculture is not the only source of nutrient
pollution that accumulates in waters. Stormwater runoff, wastewater from sewage
systems and septic tanks, fossil fuels combustion, industrial effluents, and
solid waste runoff, particularly agricultural waste from animals, also
contribute. The use of fossil fuels that emit nitrogen oxides into the air in
electricity generation, agriculture, and industry has led to more airborne
nitrogen that can later accumulate in waters.
Nutrient
pollution in the form of nitrogen and phosphorus runoff is considered to be
a major societal problem around the world. The excess nitrogen and phosphorus
that accumulates in waters feeds algae to the point where the algal growth rate
exceeds the ability of the water body to naturally regulate it. Water quality,
food resources, and habitats are affected. Eventually, the water can become
starved of oxygen. This can lead to fish kills and through time it can affect
potable water and groundwater. Nutrients can move through shallow groundwater
and end up in surface waters. Nitrates in potable water supplies can be elevated
to dangerous levels. The graphic below gives some good information and
statistics about the scope of the problem in the U.S. The Mississippi River
Basin is the third largest river basin in the world and drains quite a bit of
U.S. farmland. This has led to nutrient pollution in the Gulf of Mexico, often in the
form of red tides due to the type of algae that is prominent.
In the
temperate areas of the U.S. HABs often occur in the warmer months from mid-June
to early September. Laboratory analysis of water samples is required to
identify the bacteria responsible for an algae bloom. People are advised to
avoid water with possible HABs and especially to avoid letting their pets drink
from such water.
A harmful
algae bloom in Western Lake Erie in August 2014 led to difficulty of the water
treatment plant in Toledo, Ohio to treat the drinking water to a safe level and
residents were advised not to drink it. Another bloom returned there in 2015. HABs
have led to large fish kills. They have killed land animals and even whales in
some cases. Livestock and pet dogs that have drunk water affected by HABs have
died. People have been sickened and killed as well, largely due to eating saltwater
shellfish and fish that had accumulated toxins from HABs.
In the summer
of 2015, a wet spring followed by dry hot weather along the Ohio River led to a
clearing of the water and a slower-moving river. This was followed by hard
rains that washed fertilizer and sewage into the river. Cattle feedlots and
overloaded sewage systems were big contributors. These ideal conditions led to a
cyanobacteria algae bloom along 636 miles of the 981-mile river, from Wheeling,
West Virginia to Cannelton, Indiana. Oddly, the only other toxic algae bloom recorded in the river was in 2008 but by comparison that bloom only stretched
40 miles. Although I live less than 10 miles from the river I don’t seem to remember
this event.
Cyanobacteria Blooms
Cyanobacteria,
or blue-green algae, are microorganisms that can produce HABs in freshwater. Some
freshwater cyanobacteria blooms can produce highly potent toxins known as
cyanotoxins. There are several types of
cyanobacteria and some of these produce cyanotoxins. In the U.S. the most
common cyano are microcystins, cylindrospermopsin, anatoxins, and saxitoxins. Microcystis
is nearly always toxic. One type of cyanobacteria that produces microcystins is Dolichospermum, which forms “slimy summer blooms
on the surface of eutrophic lakes and reservoirs.” These blooms can occur
quickly. They look like green paint that accumulates along shores. I am
guessing that the image below depicts a Dolichospermum bloom. They are less
prevalent, forming smaller accumulations where nutrient loading
(eutrophication) is lower. According to
the U.S. EPA: “Microcystins are the most widespread cyanobacterial toxins
and can bioaccumulate in common aquatic vertebrates and invertebrates such as
fish, mussels, and zooplankton. Microcystins primarily affect the liver
(hepatotoxin), but can also affect the kidney and reproductive system. While
there is evidence of an association between liver and colorectal cancers in
humans and microcystins exposure and some evidence that microcystin-LR is a
tumor promoter in mechanistic studies, EPA determined that there is inadequate
information to assess carcinogenic potential of microcystins in humans due to
the limitations in the few available human studies (i.e., potential co-exposure
to other contaminants) and lack of long-term animal studies evaluating cancer
following oral exposure.” Another cyanotoxin, Cylindrospermopsin, is known
to promote liver and kidney damage and to be a possible carcinogen. It is
produced by a variety of cyanobacteria genera. Anatoxins are also produced by a
wide variety of cyanobacteria genera. They are a known neurotoxin since “they
bind to neuronal nicotinic acetylcholine receptors affecting the central
nervous system.” Saxitoxins are a large family of toxins that can
accumulate in shellfish and are referred to as Paralytic Shellfish Poisoning
(PSP) toxins. They mostly occur in saltwater but can also occur in freshwater.
Favorable
conditions that contribute to cyanobacteria blooms include light availability,
water temperature, alteration of water flow, vertical mixing, pH changes,
nutrient loading (both nitrogen and phosphorus), and trace metals. Human
activities contribute to the development of cyanobacteria blooms. EPA notes
that “point sources (which may include discharges from municipal and
industrial wastewater treatment plants, concentrated animal feeding operations
(CAFOs), Municipal Separate Storm Sewer Systems (MS4s), stormwater associated
with industrial activity, and other) and non-point sources (which may include
diffuse runoff from agricultural fields, roads and stormwater), may be high in
nitrogen and phosphorus and can promote or cause excessive fertilization
(eutrophication) of both flowing and non-flowing waters.”
Eutrophication
Eutrophication
refers to the condition of nutrient and mineral overloading in a body of water where
the overgrowth of algae, plankton, and plants. It is also known as nutrient
pollution. The excess of algae and plant growth creates problems when these
organisms consume oxygen when they decompose. The pH of the water is lowered
making it more acidic and oxygen supply is choked off in the water. This can
result in “dead zones.” It affects freshwater and saltwater. Marine water dead
zones from eutrophication are especially prominent in the Baltic Sea. There is
an enduring large dead zone in the Gulf of Mexico. These are due mainly to nitrogen
and phosphorus fertilizer runoff. In oceans, eutrophication also contributes to ocean
acidification. The graphs below show the anthropogenic contributions to
eutrophication in the Gulf of Mexico and the Chesapeake Bay. The second chart
below shows the contributions of different animal foods to eutrophication.
Source of Both: Wikipedia
Phosphate-containing detergents were once the main source
of phosphorous accumulating in water bodies until they were phased out in the
1970s. As the graphs above show, urban stormwater and municipal wastewater are
major sources of eutrophication in the Chesapeake Bay, especially from
phosphorous but also from nitrogen. Some eutrophication is natural,
particularly in lakes. Geology and climate variations can influence natural
eutrophication. In the geologic past, it is thought that volcanic eruptions producing
ash that lands in shallow ocean or inland sea waters has led to algae
proliferation. That algae decomposed in deoxygenated waters leading to deposits
of organic matter at the sea floors, Where the water was deep enough that
organic matter was preserved to form organic-rich black shales and mudstones,
many of which later became prominent oil & gas reservoirs after deep burial
created temperatures and pressures high enough to cook them into hydrocarbons.
Freshwater eutrophication
is mainly due to phosphorus. Eutrophication in marine waters is due more to nitrogen
and iron with phosphorus as a lesser contributor. Phosphate adheres tightly to
soil particles, resulting in a slower journey into the water itself. A 2014
book chapter abstract Eutrophication: Challenges and Solutions in the
book Eutrophication: Causes, Consequences and Control. Volume 2 explains
the whole eutrophication issue concisely as follows:
“On the hydrological map of the world eutrophication
has become the primary water quality issue. The excessive enrichment of waters
with anthropogenic sources of nutrients especially nitrogen (N) and phosphorus
(P) lead to the transformation of oligotrophic water bodies to mesotrophic,
eutrophic, and finally hypertrophic. Mesotrophic and eutrophic phases exhibit
intermediate and rich levels of nutrients and show increasing and serious water
quality problems, respectively. Eutrophication restricts water use for
fisheries, recreation, industry, and drinking because of increased growth of
undesirable algae and aquatic weeds and the oxygen shortages caused by their
death and decomposition. Associated periodic surface blooms of cyanobacteria
(blue-green algae) occur in drinking water supplies and may pose a serious
health hazard to animals and humans. Anthropogenic activities are the worst
culprit of nutrient enrichment and root cause of eutrophication of water
bodies. Excess nutrient inputs to water bodies usually come from sewage,
industrial discharges, agricultural runoff, construction sites, and urban
areas. Eutrophication can be minimized by regulating the nutrient sources,
reducing the use of fertilizers, proper soil management practices, implementing
mathematical models, phytoremediation etc. Among these, public awareness of
eutrophication can play an important role in preventing the eutrophication of
water bodies.”
Coastal eutrophication
is a serious issue in many places. Increased nutrient loads lead to changes in
biodiversity, proliferation of some species and suppression of others,
particularly phytoplankton. Changes in the ratio of nitrogen and phosphorous to
silica drive changes in phytoplankton proliferation. The map below shows areas
of ocean deoxygenation caused and/or exacerbated by human activities. Some water
bodies like the Baltic Sea and the Black Sea already naturally have low oxygen content
and thus are more susceptible to crossing deoxygenation thresholds.
The term “red
tides” refers mainly to the algae blooms of species of dinoflagellates, such as
Karenia brevis. The term is perhaps misleading since not all are red in
color. Some are also caused by other algal species, not just dinoflagellates. They
are not really associated with tides at all so the term is being used less and
less.
Efforts to Prevent and Reduce Harmful Algae Blooms
According to
Our World in Data: “…globally farmers apply around 115 million tonnes of
nitrogen to our crops every year. Only around 35% of this is used by them,
meaning 75 million tonnes of nitrogen runs off into our rivers, lakes, and
natural environments.” China has the highest levels of fertilizer runoff. The
U.S. also has high levels. Methods such as specific targeting of fertilizers
and better timing of applying fertilizers can reduce runoff.
Heavy rains are
the cause of much fertilizer runoff into rivers and lakes. One very important
way to prevent and reduce HABs resulting from fertilizers is to reduce
fertilizer run-off. Drip irrigation using tubes and emitters for injecting
fertilizer has been effective at reducing runoff. Drip irrigation is also effective
at reducing water use. Other proposals include creating buffer zones of plants
and wetlands that can help filter phosphorous, preventing some of it from
reaching key water bodies. Conservation tillage, changing crop rotations, and
wetlands restoration have also been proposed. Reduction of phosphorus
applications by farmers has been successful in managing and significantly reducing
dead zones in parts of the Baltic and Black Seas and the rivers that flow into
them. Reduction of phosphorous runoff in particular offers hope to keep HABs
under control. Chemical treatments such as algicides made from silver nitrate
or copper sulfate can be very successful at killing algae but may also be toxic
in themselves so care must be taken. Algae can also develop resistance to
copper sulfate. Some new methods with granular sodium percarbonate that allow
the algicide to float have been effective since they do not affect aquatic life
below the surface.
One of the
safest natural methods under consideration includes seaweed and other aquatic
plants, some of which have chemicals in them that suppress algae growth. Seaweed
and kelp aquaculture in coastal waters offers a good opportunity to decrease eutrophication.
“Some cultivated seaweeds have very high productivity and could absorb large
quantities of N, P, CO2, producing large amounts of O2 having an excellent
effect on decreasing eutrophication. It is believed that seaweed cultivation in
large scale should be a good solution to the eutrophication problem in coastal
waters.” This bioremediation process is referred to as nutrient
bioextraction.
Aluminum-modified clay is another
promising method of reduction of HABs, specifically HABs involving the species Aureococcus.
The aluminum ions create an electric charge on the surface of the clays on the
bottom that can attract the algae down onto the clay sediment rather than
leaving it in suspension. Studies have shown that the water can be pumped through
a hydrodynamic separator leaving less algae and less phosphorus. The captured
algal matter can then be biodigested for methane production.
There is an
urgent need for more sensors and monitoring devices to track algae blooms and
in particular to forecast HABs. Sensors deployed in the Gulf of Mexico have likely
led to a life-saving shutdown of shellfish harvesting in 2008. Satellite tracking
and early warning systems for HABs are also being developed.
Another method
to reduce eutrophication and deoxygenation (hypoxia), considered to be a kind
of geoengineering, involves simply pumping compressed air into the water to oxygenate
it. This is standard for small waters from fish tanks to aquaculture ponds. Phosphorous
can also be removed chemically by sorbents such as aluminum sulfate, which
falls to the bottom of the water body. This method has been effective in
shallow and deep lakes. It has been very effective in Finland.
A new
technology that may offer a solution involves hydrogels can sense nitrate
levels in farm runoff and capture it so that it can be reused. The same lab
that developed the technique also developed a hydrogel that allows soil to
effectively water itself. The researchers “made a copper-based hydrogel
that, when pulsed with electricity, provides a conductive reaction in a process
called ‘electrocatalysis’.” Experiments showed that the nitrate in the farm
field can be converted to ammonia at the surface when it runs over the gel. The
process can also be used to measure the amount of nitrate and ammonia in the
water and cue the farmers when fields need to be drained. The ammonia-rich
water can then be recycled back into the field. This could make fertilizer use
more efficiently and reduce runoff. Other potential benefits are higher plant
growth rates and reduced greenhouse gas emissions due to over-fertilization.
The key to the future success of the technique is “finding ways to properly
drain run-off into capture areas where the hydrogel can do its magic, and then
hook the ammonia-rich water up to irrigation systems.” It can be integrated
into existing irrigation systems and powered by solar panels or wind turbines. The
paper published in PNAS notes: “Electrocatalytic nitrate-to-ammonia
conversion has been recognized as an alternative strategy to produce nitrogen
fertilizer from polluted groundwater and industrial waste streams with high
environmental sustainability. This work reports an electrocatalysis-enabled
system for smart and precisely concentration-controlled nitrogen nutrient
recycling via electrifying nitrate-rich wastewaters.” They also note: “We
thus designed the Cu SAA {the hydrogel/aerogel} into a smart and sustainable
fertilizing system (SSFS), a prototype device for on-site automatic recycling
of nutrients with precisely controlled nitrate/ammonium concentrations. The
SSFS represents a forward step toward sustainable nutrient/waste recycling,
thus permitting efficient nitrogen utilization of crops and mitigating
pollutant emissions. This contribution exemplifies how electrocatalysis and
nanotechnology can be potentially leveraged to enable sustainable agriculture.”
They think that the process may become cost-competitive with the typical Haber-Bosch
process for nitrogen fertilizer production.
The paper's conclusions section summarizes the potential
for this technique: “This work further highlights the SSFS with Cu SAAs as
the functional unit allows on-demand ammonia production by utilizing
nitrate-rich wastewaters while precisely monitoring concentrations of NO3−/NH4+
in real time. We further assessed the feasibility of the SSFS for recycling of
fertigation water while controlling nitrogen nutrients with desired NO3−-N and
NH4+-N ratio. Under hydroponic conditions, the SSFS achieved unattended
operation with automation programs and displayed an impressive recovery rate of
nitrogen from nitrate wastewater for ammonia distributions. The study of crop
cultivation with the SSFS demonstrates the significantly enhanced efficiency of
nutrient uptake, thus benefiting the growth of plants and reducing nitrogen
losses. We believe that the SSFS with rationally designed multifunctional SAAs
may open up many opportunities to advance future agriculture by integrating
renewable energy and information technology.” Field trials are next on the
agenda for this technology.
The following is what I copied from Bing chat about an article in the Detroit Free Press that I can no longer find: According to a news article from Detroit Free Press, scientists at the Great Lakes Environmental Research Laboratory in Ann Arbor have created an uncrewed surface vehicle system that extracts algae samples and transmits data in real time. The surface vehicle, SHARC, short for Sea Harmful Algal Research Craft, will change the game for how scientists around the world understand algae in all bodies of water.
The SHARC system is designed to extract algae samples
from water bodies and transmit data in real-time. The system is expected to
help scientists understand why and when harmful algae blooms arise, which is
important as hundreds of thousands of people travel to dip their toes in the
state’s plentiful freshwater, which is a crucial economic driver for Michigan.
References:
Harmful
Algal Blooms. U.S. EPA. Harmful Algal Blooms | US EPA
What
are HABs? Pennsylvania Dept. of Environmental Protection. HABs (pa.gov)
Scientists
hope SHARC system takes a bite out of harmful algae. Audrey Richardson. Detroit
Free Press, September 5, 2023. Scientists hope SHARC system takes a
bite out of harmful algae (msn.com)
Two-thirds
of fertilizer is lost to run-off. This invention could recycle it. Emma Bryce.
Anthropocene Magazine. July 2023. Two-thirds of fertilizer is lost to
run-off. This invention could recycle it. (msn.com)
Nutrient
Pollution. U.S. EPA. Nutrient Pollution | US EPA
Cyanobacterial
Harmful Algal Blooms (CyanoHABs) in Water Bodies. U.S. EPA. Cyanobacterial Harmful Algal Blooms (CyanoHABs) in Water
Bodies | US EPA
Cyanobacterial
Harmful Algal Blooms and U.S. Geological Survey Science Capabilities. Jennifer
L. Graham, Neil M. Dubrovsky, and Sandra M. Eberts. USGS. Open-File Report
2016–1174. Ver. 1.1, December 2017. Cyanobacterial Harmful Algal Blooms
and U.S. Geological Survey Science Capabilities (usgs.gov)
Toxic
Algae Outbreak Overwhelms a Polluted Ohio River. Michael Wines, New York Times.
September 30, 2015. Toxic Algae Outbreak Overwhelms a
Polluted Ohio River - The New York Times (nytimes.com)
A
multifunctional copper single-atom electrocatalyst aerogel for smart sensing
and producing ammonia from nitrate. Panpan Li, Ling Liao, Zhiwei Fang, and
Guihua Yu. Edited by Catherine Murphy, University of Illinois at Urbana-Champaign,
Urbana, IL. June 20, 2023. PNAS. Vol. 120 | No. 26. A multifunctional copper single-atom
electrocatalyst aerogel for smart sensing and producing ammonia from nitrate |
PNAS
Excess
fertilizer use: Which countries cause environmental damage by overapplying
fertilizers? Hannah Ritchie. Our World in Data. September 7, 2021. Excess fertilizer use: Which
countries cause environmental damage by overapplying fertilizers? - Our World
in Data
Ocean deoxygenation.
Wikipedia. Ocean
deoxygenation - Wikipedia
Eutrophication.
Wikipedia. Eutrophication
- Wikipedia
Eutrophication:
Challenges and Solutions. M. Nasir Khan & Firoz Mohammad, Chapter in the
Book: Eutrophication: Causes, Consequences and Control. Volume 2. Editors: Abid
A. Ansari and Sarvajeet Singh Gill. Springer. 2014. Eutrophication:
Challenges and Solutions | SpringerLink
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