The ice scour and flooding produced by river ice are Decreases in the frequency and/or severity of break-
known to be major reasons for the high biological produ- up flooding that may arise under future climates could
ctivity and diversity found in northern rivers, particularly threaten the ecosystem health of such river systems
29,42

along their margins and in deltas where break-up events (see box on maintaining delta pond ecosystems).
are also the key suppliers of water and nutrients
40,41
.
Maintaining delta pond ecosystems
The physical development and ecosystem health of river
deltas in cold regions are strongly controlled by ice proc-
esses and thus are highly susceptible to the effects of cli-
mate change. As an example, the photograph shows a
typical lake/pond and river network in the Peace-Athabasca
Delta (Canada), one of the largest freshwater deltas in the
world. The water budget and sediment-nutrient supply for
the multitude of lakes and ponds that dot the riparian zones
of such deltas depend strongly on the supply of floodwaters
produced by river-ice jams during the spring. These spring
floods usually exceed those from open-water flow events, as
illustrated in Figure 8.9(a). Studies of future climate condi-
tions for the Peace-Athabasca Delta indicate that a combi-
nation of thinner river ice and reduced spring runoff, due
to smaller winter snowpack, will lead to decreased ice-jam
flooding
42
. This, combined with greater summer evapora-
tion from warmer temperatures, will cause a decline in del-
ta-pond water levels
43
.
An adaptation strategy that has been successfully used to coun-
teract the effects of climatic drying of delta ponds involves the
use of flow enhancement through water releases from reser-
voirs. This increases the probability of ice-jam formation and
related flooding of the delta ponds (Figure 8.9(b)).
Peace-Athabasca Delta.
Photo: Dörte Köster
210 GLOBAL OUTLOOK FOR ICE AND SNOW