Conserving Freshwater and Coastal Resources in a Changing Climate

climate change, reductions in the levels of low flows are
expected as a result of earlier snowmelt and increased
summer temperatures and evapotranspiration
(Huntington 2003; Hayhoe et al., 2006). Also, more frequent
droughts combined with more intense and sporadic
precipitation events will result in more runoff and
therefore less of the water will recharge groundwater.
These climatic contributors to reduced flow would add
to the existing drivers of low flow (M. Kline, personal
communication, April 13, 2007).
9Photography by Bill Silliker Jr.
Altered River and Stream Flows
The timing and quantity of flow are important
components of river hydrology. Magnitude, frequency,
duration, timing, and rate of change are key attributes
of the flow regime and are considered the ‘master
driver’ of river systems (Poff, 1997). Changes to any
of these five components can have dramatic effects on
both aquatic and riparian species. As such, changes in
climate that affect the flow regime could have dramatic
effects on river ecosystems (Gibson et al, 2005).
Flows rise and fall seasonally with changes in precipitation,
evaporation, and snowmelt. In the northeast
and mid-Atlantic states, flow generally increases
in the spring as snow melts, and decreases in the late
spring and summer as trees and plants come out of
dormancy from evapotranspiration and the rising temperatures.
Although projections indicate that precipitation
is expected to increase during winter as a result of
Longer and more severe periods of low flow are
likely to affect species in a number of ways. Areas such
as the eastern United States that rarely experience periods
of no-flow naturally will be particularly susceptible
to ecological damage as no-flow conditions are a dramatic
change from normal conditions (Poff et al., 2002).
Small streams are especially vulnerable to low flow (P.
Angermeier, personal communication, April 5, 2007).
One study found that a 10% reduction in annual runoff
caused almost half of small streams with few groundwater
inputs to stop flowing in some years (Poff et al.,
2002). Another analysis estimated that flow could be decreased
in the New England and mid-Atlantic regions by
21-31% annually just from increased evaporation, with
the largest change felt in northern states (Moore et al.,
1997).
Decreases in flow have already been shown to cause
major species extinctions in some parts of the world.
Among freshwater fish, species that are adapted to live
only in flowing waters are anticipated to be the most
sensitive to climate change. Reduced flow and stream
miles will have a particularly deleterious effect on these
species (M. Bain, personal communication, March 22,
2007). Isolation also impedes migration and access to a
variety of habitat types.
Sensitive species such as amphibians can be exposed
to greater ultraviolet radiation (Poff et al.,
2002) which is especially problematic in clear, shallow
water bodies (Kling et al., 2005). In addition,
community composition, diversity, size, structure
of populations, spawning, and recruitment of fish
have all been documented to be significantly affected
by low flow and drought (Xenopoulos et al., 2005).
Conserving Freshwater and Coastal Resources in a Changing Climate