wAbstract
@The effect of eutrophication on particulate amorphous silica
(ASi) sequestration was isolated and quantified in Lake St. Croix
and Lake Pepin, two natural, human-impacted impoundments of the
upper Mississippi River. In contrast to impoundments behind engineered
dams, where silica (Si) fluxes may be changed by various aspects
of dam construction, these two riverine lakes have long (9,000+
years) sedimentary sequences that record the entire span of cultural
eutrophication and the resulting silica sequestration. The concentrations
of dissolved silicate (DSi) and ASi in the lake inflows were measured
for 1 year to obtain the total flux of biavailable silica (TSib = DSi + ASi) to each impoundment. Historical
rates of Si sequestration in each lake were determined using ASi
burial in multiple sediment cores and modeled estimates of historical
TSib fluxes. The Si trapping efficiency of
each lake was found to have increased exponentially with cultural
eutrophication (estimated two- to five-fold increase in Lake St.
Croix and 9- to 16-fold increase in Lake Pepin over the last 100
years), indicating the degree to which eutrophication of impoundments
can reduce silica export to downstream coastal and marine ecosystems.
Because these two lakes presently exhibit different degrees of
eutrophication, together they depict a relationship between phosphorus
concentration and Si trapping efficiency that may be applied to
other impoundments, including human-made reservoirs.
Keywords: Biogenic silica; Trapping efficiency; Mississippi River;
Eutrophication; Riverine lakex
Introduction
Site descriptions
Methods
Results
@Trapping efficiency
Discussion
@ASi burial
@ASi burial through time
@Effects of eutrophication
Conclusions
Acknowledgments
References