The purpose of this research was to investigate
the spatial and temporal patterns of unionid
bivalve assemblage size structure, distribution,
trophic status, and nutrient recycling. The
objectives of the first chapter were to: 1)
determine spatial and temporal variation in
assemblage structure at several scales; 2)
quantify the spatial and temporal variability in
size structure of populations; and 3) describe the
spatial patterns of distributions within and among
sites. Assemblages within a site were more
similar to each other than those found in
transects from other sites, and assemblages were
similar between years. Size structure was similar
at 3 of the 4 sites and was similar between
successive years. Unionid abundance and biomass
spatial dependence was variable within and among
sites. The objectives of the second chapter were
to: 1) determine the trophic status of 2 species
using stable isotopes and lipase-to-protease
ratios; 2) determine the potential food sources of
these species; and 3) identify seasonal patterns
in trophic status and potential food sources of
these species. Unionids were 2-4 ppt more depleted
in d13C and 1 trophic level above (2.6 ppt in d15N)
bulk fine particulate organic matter (FPOM).
Microbial C made up 35-86% of the total FPOM C in
the fall. Digestive fluid enzymes and stable
isotopes of unionids were spatially and temporally
stable across species. The objectives of the
third chapter were to: 1) describe and compare the
composition of stream seston using nutrient,
stable isotope, and microbial biomass and
composition analyses across sites, regions, and
seasons; 2) quantify nutrient recycling of
unionids by measuring shell, tissue, excretion,
and egestion nutrient concentrations and transfer
rates; and 3) determine the significance of
unionid excretion and egestion for nutrient
cycling across sites and seasons. Seston was
variable among sites, regions, and seasons.
Within a site, unionids were similar in nutrient
body composition and excretion. Fall Ouachita
unionid excretion represented 6-11% of the stream
discharge nutrient flux. Biodeposition may make a
large contribution to benthic nutrients as well.
Unionids represent large pools of nutrients, which
are temporally stable over one year, but are
spatially variable in terms of distribution and
size structure.