Freshwater Ecosystems - Freshwater Ecology: Concepts and Environmental Applications - page 454

Some of the best data for functional separation of ecosystem processes
related to biodiversity derive from studies of two shrimp species that break
down leaf litter in Puerto Rican streams (Covich, 1999). The two species
( Xiphocaris elongata and Atya lanipes ) can both degrade leaf litter, but
breakdown is significantly more efficient and the streams are more reten-
tive of organic particles when both species are present. Atya does not break
down intact leaves as rapidly as does Xiphocaris, but it scrapes microbes
from the leaves and filters fine particles from the water column more effi-
ciently. Particulate transport is highest in streams in which both species of
shrimp are rare because predatory fishes are present (Pringle et al., 1999).
Such a relationship between biodiversity and ecosystem function may oc-
cur in mainland streams as well (Jonsson et al., 2001).
GROUNDWATER ECOSYSTEMS
Groundwater ecosystems often rely on organic material derived from
surface habitats (Gibert et al., 1994). Alternatively, chemoautotrophic
processes, such as sulfide oxidation (e.g., Sidebar 13.2), ammonium oxi-
dation, or use of iron or manganese as electron donors, can form the ba-
sis of autotrophic production in some systems. Investigation of respiration
rates of groundwater sediments suggests that respiration rates decrease
with depth (Fig. 22.5). Deep groundwater sediments have the slowest rates
of biological activity of any known habitats.
Groundwater ecosystems can be classified on a continuum of perme-
ability and average interstitial space. The size and connectivity of the pores
or channels through an aquifer can control the transfer of materials through
the aquifer and limit the size of the organisms that inhabit the aquifer.
10 2
10 -1
10 -4
10 -7
10 -10
10 -13
FIGURE 22.5 Ranges of documented respiration rates from various types of sediments
(data from Kieft and Phelps, 1997).