Volume 41 Issue 1 Page 1 - February 1999
Oxygen supply and the adaptations of animals in groundwater
F. Malard* and F. Hervant
1. The first part of this review focuses on the oxygen status of natural groundwater
systems (mainly porous aquifers) and hyporheic zones of streams. The second part
examines the sensitivity of groundwater organisms, especially crustaceans, to low
oxygen concentrations (<3.0mgL1O2).
2. Dissolved oxygen (DO) in groundwater is spatially heterogeneous at macro-
(km), meso- (m) and micro- (cm) scales. This heterogeneity, an essential feature of
the groundwater environment, reflects changes in sediment composition and
structure, groundwater flow velocity, organic matter content, and the abundance
and activity of micro-organisms. Dissolved oxygen also exhibits strong temporal
changes in the hyporheic zone of streams as well as in the recharge area of aquifers,
but these fluctuations should be strongly attenuated with increasing distance from
the stream and the recharge zone.
3. Dissolved oxygen gradients along flow paths in groundwater systems and
hyporheic zones vary over several orders of magnitude (e.g. declines of 9105 to 1.5
102mgL1O2m1 in confined aquifers and 2102 to 1mgL1O2m1 in parafluvial water).
Several factors explain this strong variation. Where the water table is close to the
surface, oxygen is likely to be consumed rapidly in the first few metres below the
water table because of incomplete degradation of soil-generated labile dissolved
organic carbon (DOC) in the vadose zone. Where the water table is far from the
surface, strong oxygen depletion in the vicinity of the water table does not occur,
DO being then gradually consumed as groundwater flows down the hydraulic
gradient. In unconfined groundwater systems, oxygen consumption along flow
paths may be compensated by down-gradient replenishment of DO, resulting either
from the ingress of atmospheric oxygen or water recharge through the vadose zone.
In confined groundwater systems, where replenishment of oxygen is impossible, the
removal time of DO varies from a few years to more than 10000years, depending
mainly on the organic carbon content of the sediment. Comparison of the hyporheic
zones between systems also revealed strong differences in the removal time and
length of underground pathways for DO. This strong variability among systems
seems related to differences in contact time of water with sediment.
4. Although groundwater macro-crustaceans are much more resistant to hypoxia
than epigean species, they cannot survive severe hypoxia (DO<0.01mgL1O2) for
very long (lethal time for 50% of the population ranged from 46.7 to 61.7h). In
severe hypoxia, none of the hypogean crustaceans examined utilized a high-ATP
yielding metabolic pathway. High survival times are mainly a result of the
combination of three mechanisms: a high storage of fermentable fuels (glycogen and
phosphagen), a low metabolic rate in normoxia, and a further reduction in metabolic
rate by reducing locomotion and ventilation. It is suggested here that the low
metabolic rate of many hypogean species may be an adaptation to low oxygen and
not necessarily result from an impoverished food supply.
5. An interesting physiological feature of hypogean crustaceans is their ability to
recover from anaerobic stress and, more specifically, rapidly to resynthesize
glycogen stores during post-hypoxic recovery. A high storage and rapid restoration
of fermentable fuels (without feeding) allows groundwater crustaceans to exploit a
moving mosaic of suboxic (<0.3mgL1O2), dysoxic (0.3-3.0mgL1O2) and oxic (>3
6. It is concluded that although hypogean animals are probably unsuited for life in
extensively or permanently suboxic groundwater, they can be found in small or
temporarily suboxic patches. Indeed, their adaptations to hypoxia are clearly suited
for life in groundwater characterized by spatially heterogeneous or highly dynamic
DO concentrations. Their capacity to survive severe hypoxia for a few days and to
recover rapidly would explain partly why ecological field studies often reveal the
occurrence of interstitial taxa in groundwater with a wide range of DO.
Биология пресных вод: о науке.
Freshwater Biology Volume 39 Issue 4 Page 741 - June 1998
The state of freshwater ecology
Colin S. Reynolds
1. The case is advanced that freshwater ecologists need to champion the relevance
of their work to the development of ecological theory and to the understanding of
ecosystem function and behaviour, not least for its importance in addressing
pressing applications to the stewardship of the biosphere. An essential step is to
review, and update where necessary, the paradigms of aquatic ecology.
2. It is proposed that the major constraint on the organisms, their attributes and
adaptations are related first to the physical properties of the medium in which they
live. The drives to grow and reproduce relate to the trophic transfer of reduced
carbon with important microbial interventions. General principles of emergy apply.
The supportive capacities of given environments may be set by chemical
constraints, but it is suggested that, with the exception of chronically resource
deficient waters, population dynamics relate to opportunities incumbent upon
system variability and the consequent pulsation of resources.
3. Variability affects diversity, through frequent revision of the thermodynamic
base. Frequent structural change promotes species diversity and, because function
is maintained, it appears that efficient function is dependent upon high diversity.
Caution is necessary because high productivity and high diversity are both products
of the disturbances consequent upon external forcing and manifestly nonequilibrium
4. Reactions to these statements are canvassed.