Modeling the Effect of Algal Dynamics on Arsenic Speciation in Lake Biwa

Algae reduce and methylate arsenate and the end
product of the reaction is correlated to their growth rate.
At slow growth rates, dimethylarsinate (DMA) is produced,
and at fast growth rates arsenite (As(III)) is produced. Previous
work has linked this phenomenon to the phosphorus
luxury uptake mechanism of algae, and a model was
developed for the process (Hellweger et al. Limnol. Oceanogr.
2003, 48, 2275). This paper presents the integration of
that process model for arsenic transformation by algae into
a full ecological model and application to Lake Biwa,
Japan. The model application allows for a quantitative
analysis of the field data, consistent with the process model
and the ecological dynamics of the lake. The newly
developed ecological model includes a variable phytoplankton
composition, which is needed to simulate luxury uptake.
This is in contrast to most existing ecological models, which
typically assume a fixed “Redfield” composition. The
model adequately reproduces the observed ecology of
Lake Biwa, including the rapid uptake of phosphate by
phytoplankton without immediate growth (luxury uptake)
following lake overturn. The model also reproduces
the observed arsenic speciation, including the gradual
appearance of DMA during the summer and peaks in As(III)
concentration at the onset of spring and fall algal blooms.