Grassroots September 2016, Vol. 16, No. 3 | Page 21
Article
diverse as the Great Lakes, the east coast's
Chesapeake Bay and the Gulf of Mexico, the
severity of summer hypoxia has been linked to the
effects of weather on nutrient loading, watercolumn structure and water circulation. Although
these examples all relate to harmful algal blooms
and hypoxia, other types of water pollution are also
affected by weather conditions, which are altered
by climate change.
The challenge
Several factors explain the paucity of research.
First, the role of climate is difficult to pinpoint,
because changes in water quality result from a
delicate and complex interplay of human activities
across local, regional and global scales. Complex
chains of causative steps must be understood.
These start with how climate change affects factors
such as precipitation, temperatures and wind
patterns for given regions and watersheds. Next, we
must understand how these conditions alter the
flow of water, nutrients, contaminants and other
constituents to water bodies. Finally, we need to
assess how these inputs, combined with
meteorological conditions that influence freshwater
and coastal systems directly, will change water
quality. We do not yet know how to put the pieces
of this puzzle together.
For example, the harmful algal blooms in Lake
Erie are driven by excess phosphorus from
changing farming and land-management practices
in the region, but a summer 2011 bloom shattered
previous records. A forensic analysis9 revealed that
a series of intense rainstorms led to record
springtime discharge from rivers, which flooded
the lake with a record amount of nutrients flushed
from fields. Warmer-than-average summer
temperatures and low winds then accelerated the
growth of buoyant Microcystis cyanobacteria.
Unusually weak water circulation during the
summer kept nutrients in the lake for longer,
further feeding the bloom. How climate change
influences the occurrence of all these factors,
individually and together, needs to be elucidated to
predict the likelihood of similar events happening
more frequently in the future.
“There is disagreement about which variables
best capture water quality.”
Second, water-quality and climate scientists work
in disciplinary silos, and each tends to have a
different scale of focus. Whereas much of climate
science is global or concerned with large regions,
most hydrologists and limnologists study processes
in individual streams, lakes, watersheds or
estuaries. Similarly, water-quality impacts have
been treated mostly as local or regional issues,
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resulting from human activities in a particular basin
or watershed. Little attention has been given to the
local impacts of human action at global scales. For
example, strategies for preventing harmful blooms
and hypoxia often rightly focus on limiting nutrient
loads through land management, but should also
consider how a shifting climate will alter local
meteorology, and thus nutrient loads.
A clear understanding of the interplay between
climate and severe water-quality impairment events
is predicated on tracking cause and effect across a
cascading range of scales, from the globe to
individual watersheds and from decades to days.
Third, observational evidence to underpin a
global view of this interplay is lacking. Unlike for
weather variables such as temperature and
precipitation, no global network tracks water
quality. Existing monitoring of water quality is
sparse in space and time, and site-specific.
Satellite-based
observations
could
expand
coverage, but there are no widely accepted
approaches for doing so. There is even
disagreement about which variables best capture
water quality. For example, is the severity of a
harmful algal bloom best represented by its area,
the total mass of phytoplankton it contains, the
amount of toxins that it produces or the ecosystem
and human impacts that it engenders? Each brings a
different observational challenge.
Next steps
Researchers need to assess which meteorological
conditions, in what combination, make extreme
water-quality impairments most likely. In doing so,
they must also consider land use, land
management, population distributions and other
regional factors that compound the effects of
weather. An initiative such as Future Earth, which
provides a research platform for global
sustainability science, would be a good umbrella
for developing and integrating such knowledge
globally.
The first step should be a retrospective analysis
of past extreme events, to understand
commonalities and differences across types of
systems and impacts. The resulting conceptual
model will differ depending on the type of problem
— hypoxic dead zones and microbial outbreaks in
recreational waters will not link to climate in the
same ways. The water-quality and climate research
communities will have to work together to identify
key mechanisms and feedbacks.
Understanding meteorological drivers would
allow researchers to assess whether climate models
can accurately represent the occurrence of key
September 2016
Vol 16 No. 3