The current lack of monitoring and management capacity
leaves Amazon freshwater ecosystems largely vulnerable
to escalating degradation. Until the drivers of degradation
are curbed, many of the alterations in hydrology,
water chemistry, and food webs observed in the southeastern
Amazon can be expected to continue to spread
over the south and west regions of the basin (Figures
1 and 3). Although it is difficult to predict the cumulative
impacts of future degradation, ecological theory
predicts that the principal threat to freshwater ecosystems
is alteration of natural hydrology (Vannote et al.
1980; Junk et al. 1989). Hydrological alterations in the
Amazon basin stem mainly from three sources: largescale
deforestation, which significantly alters river discharge
and flood-pulse magnitude (Coe et al. 2009);
dams, which reduce flood-pulse amplitude (Poff & Hart
2002); and climate change, which is expected to decrease
regional rainfall and river discharge while increasing
the frequency of extreme droughts (Malhi et al. 2009).
Altogether, such hydrological alterations are expected to
significantly lower the magnitude of flood-pulses and increase
the frequency and severity of low-water events
(Costa et al. 2004). Among various impacts, these hydrological
alterations could threaten riverine livelihoods and
food security through disruptions of the lateral migration
of commercial fishes and their associated fishery yields,
as observed elsewhere in the world (Jackson & Marmulla
2001).