Grassroots September 2016, Vol. 16, No. 3 | Page 20
Article
Study role of climate change in extreme threats to water quality
Anna M. Michalak
Department of Global Ecology, Carnegie Institution for Science, Stanford, California, USA
Record-breaking harmful algal blooms and
other severe impacts are becoming more
frequent. We need to understand why, says
Anna M. Michalak
W
ith concerns about climate 'extremes'
growing1, water is often the focus —
either too much or too little. That is no
coincidence: climate and the hydrological cycle are
tightly coupled, and water is essential to
ecosystems and societies. But it is not just the
quantity of water that matters. So does its quality.
Last year, Lake Erie, one of the US Great Lakes
(which contain one-fifth of the world's fresh
surface water), experienced its biggest recorded
harmful algal bloom. At its peak, the bloom spread
some 200 kilometres across most of the lake2.
Meanwhile, off the continent's west coast, another
record harmful bloom stretched from Baja
California in Mexico up to Alaska, probably
triggered by unusually warm water in the Pacific
Ocean3. Both blooms were dominated by species
of phytoplankton that produce powerful toxins.
Such episodes can wreak havoc. During a
previous bloom, in 2014, 500,000 people living
near Lake Erie were ordered not to drink tap water,
because it contained levels of hepatotoxins
produced by the cyanobacterium Microcystis that
were 2.5 times higher4 than the World Health
Organization's safe standard. The 2015 west-coast
bloom of the diatom algae Pseudo-nitzschia shut
down fisheries. The Dungeness crab fishery, one of
the most valuable on the west coast, opened four
months late owing to toxic levels of the neurotoxin
domoic acid in the crabs. Brain damage in sea lions
has also been documented as a result of exposure to
this toxin5.
Impaired water quality is a global and growing
problem, limiting resources for drinking, domestic
use, food production and recreation, as well as
harming ecosystems. The types and causes range
from excess nutrients feeding harmful algal blooms
and hypoxic 'dead zones', to bacterial, viral and
chemical contamination, to pollution by personalcare products and pharmaceuticals. Cases of
extreme impairment often lead to disproportionate
human and ecosystem impacts. The costs can be
huge. More than US$4 billion are lost each year in
Grassroots
the United States alone as a result of harmful algal
blooms6.
Because the most severe water-quality impacts
are exacerbated by weather, climate plays a part.
Runoff of nutrients from farmland spikes after
heavy rains; warm temperatures accelerate the
growth of bacteria and phytoplankton. As climate
change alters weather patterns and variability,
conditions conducive to severe water impairment
are likely to become more frequent.
Yet there has been scant study of how climate
will affect the occurrence of the extreme events that
relate to water quality rather than quantity. We do
not know how to relate water-quality extremes,
their causes, their severity or their occurrence
directly to changes in climate. It is time to plug this
knowledge gap.
Complex chain
Scientific understanding of extreme storms,
droughts and rising sea levels has improved
markedly over the past decade. The impacts of
extreme weather events are integral to discussions
about climate-change mitigation and adaptation.
The expected rise in the frequency and severity of
such events is well established, and even individual
episodes have been linked probabilistically to
climate change1.
Not so for water quality. Researchers have
explored trends in water quality with climate, but
the science of projecting and attributing the
occurrence of extremes is in its infancy. This is
despite evidence of strong links with climate.
Regional studies reveal how multiple factors
often conspire to create conditions ripe for dire
water quality. For example, summer toxic blooms
in Lake Taihu, the third-largest freshwater lake in
China, are more intense after tropical cyclones,
because the associated rains wash more nutrients
into the lake, and the subsequent warmer
temperatures and lower wind speeds further
encourage the growth of blooms7. In 1999, a series
of hurricanes triggered severe hypoxia in Pamlico
Sound, North Carolina (part of the United States'
second-largest estuarine system) by delivering huge
amounts of nutrients, organic carbon and fresh
water to the estuary8. In North American regions as
September 2016
Vol 16 No. 3