Plants need phosphorus to grow. The Red Cedar
Watershed has plenty of excess phosphorus in the summer months, which promotes
the growth of the green layer of cyanobacteria that residents have learned to
see and smell so well. Why not use this phosphorus to promote the growth of a
different plant, one that adds cultural significance to the water, rather than
to fuel the growth of a slimy, green layer? Wild rice, a native aquatic plant
to Wisconsin, should be this plant. Wild rice would add value to the Red Cedar
Watershed as a natural and ecological approach to phosphorus mitigation.
Wild rice has the potential to thrive and support
native wildlife in the Red Cedar Watershed due to its historic presence. To
better understand the dynamics of a wild rice ecosystem, my team and I went
straight to the source. We found and surveyed five sites in the Red Cedar and
surrounding watersheds that had healthy wild rice stands. These visits alone
were enough to prove that wild rice can both grow and thrive in north-western
Wisconsin, so why not throughout Red Cedar Watershed too? Before jumping right
into planting and seeding of this plant, it is important to understand how wild
rice growth affects phosphorus in the water and sediment.
To study how wild rice growth impacts phosphorus
concentration and deposition along the bed, we took samples from the start to
end of the wild rice bed. There was a noticeable difference in the sediment as
we sampled throughout the zones just by the appearance of the muck as it oozed
out of the corer. The sediment before the bed was barely penetrable sand while throughout
the stand, the sediment was a black-brown, fibrous muck. There was an obvious
difference in the sediment along the wild rice bed- a complex environment
connected with wild rice that was waiting to be explored.
To quantify the
apparent differences in the sediment, my team and I took to the lab where we
analyzed phosphorus concentrations and texture of the sediment from the samples.
The phosphorus was measured as soluble reactive phosphorus (SRP), a form of
phosphorus readily available to plants. There was an increase in SRP
concentration in the downstream direction of the bed. Increasing SRP levels are
likely related to high levels of nutrient sediment as well as decaying plant
matter from previous years. In addition, the sediment with the highest sand
content was found before the bed began and the sediment with the highest
content of fine particles, like clay and silt, was found in the most upstream
portion of the bed. This expected sedimentation from coarse to fine particles
in the downstream direction is most likely caused a decrease in flow velocity
due to the presence of wild rice. Since phosphorus is attached to particles
floating in the water, sedimentation allows for the settling of phosphorus.
The increasing SRP levels in the sediment along the
length of the wild rice bed and evidence of sedimentation provide initial data
to phosphorus dynamics among the plant, water, and sediment. An increasing
concentration of phosphorus in the sediment may be sourced from the water
column. A decrease in phosphorus in the water column would lead to decreased
phosphorus available for algae growth. To further understand the transport of
SRP at the sediment-water interface, water measurements of SRP concentration
along wild rice beds should be investigated. Data that revealed a decrease in
SRP in the water column as the SRP in the sediment decreased would better
support that wild rice removes phosphorus from the water column.
Wild rice nutrient uptake throughout the growing
season is also important to understand because the plant takes up and released
varying levels of phosphorus throughout the year to support growth. For instance, wild rice holds the most
nutrients in the sediment in mid-July to August so that the nutrients are ready
to support the later stage of grain formation in late-August to September.
Since the maximum nutrient uptake of wild rice occurs at the same time of algae
blooms, wild rice may be an optimal plant for eutrophication mitigation.
Further studies may measure SRP concentrations in the sediment throughout the
year to understand phosphorus intake by the growing plant and phosphorus
release by the decaying plant.
This study provides the initial evidence that wild
rice affects phosphorus levels at the water-sediment interface and can be a
part of the solution to decreasing algae blooms. Members of the community have
asked me, “Why not just throw some scum suckers on the lake to clean up the
mess?” While this machine and other forms of artificial technology may seem
like the desired quick fix for algae blooms, they are by no means a long-term
solution. Human activity and change to the landscape of Dunn County has led to
the disruption of the lakes, but a natural process like plant growth can be
used to balance the nutrients in the water bodies. It is time for us to rely on
the restoration of wild rice, an ecosystem approach, to return the lakes their
historic, clean state.
I spent much of this summer driving around with my research partner, Lucia, listening to NPR and sharing our favorite playlists as we shuffled around the Red Cedar Watershed on our way to interviews. As someone who takes a keen interest in the experiences of others, I joined the LAKES REU to partake in qualitative research, which is a fancy way of saying research that focuses on ideas, opinions, and motivations rather than hard numbers. For our research, Lucia and I interviewed twenty-three stakeholders across the watershed: nine farmers and 23 property owners.