WHAT...Floating islands as a promising solution

ADVANCING TOWARDS A SOLUTION

There are many possible solutions that would help to decrease phosphorous concentrations in Hicklin lake. Such treatments include: alum treatment, lake water dilution, storm water diversion, retention and treatment of lake water, sediment treatment (to deal with internal contributions of phosphorous), dredging and watershed education (Sims). Here I will to focus on two solutions that have been implemented in Hicklin Lake with mixed results.

I. ALUM TREATMENT 

As a result of the Microcystin detection in Hicklin Lake in 2004 action was taken through financing of alum treatments aimed at reducing available phosphorous (Abella). Alum is a substance that binds to excess phosphorous in the water and is therefore an effective method of temporarily decreasing phosphorous levels and containing algal growth (Abella). However, this treatment is a short-term solution and only managed to keep cyanobacteria populations at bay for four years. Algal blooms resurfaced in Hicklin Lake in 2010. Another alum treatment was financed in response. Algal blooms were only held off for one year after this treatment (Abella). Blooms and their toxic repercussions are a huge concern for this community and the long-term solution will not be found in financing more and more frequent alum treatments. This treatment has short-term benefits and long-term repercussions in terms of plant and animal health.  

II. FLOATING WETLANDS

Floating islands are vegetated rafts engineered in such a way that plant roots dangle into the water and absorb nutrients and pollutants from the water (Abella). In addition to removing detrimental pollutants from the lake, plant roots provide a home for biofilm development (roots provide a surface to which microorganisms can bind) . Biofilm presence increases water treatment and provides nutrition for the bottom of the food chain (Abella).  Highlighting the extreme importance of biofilm formation, it has been estimated that up to 80% of the nutrient removal occurring by floating wetlands can be attributed to bacteria that attach to the wetland plants while 20% is being taken up by the plants themselves (Reinsel).  Plants are removed from the islands after they die to ensure that nutrients consumed by the plant aren't re-released into the water.

The above model provides an image of all the important components of a floating wetland (Reinsel)

III. STUDIES ON THE EFFECTIVENESS OF FLOATING WETLANDS

Although there are limited studies looking at the effectiveness of floating wetlands in Washington state, there have been many experiments done around the country that support the effectiveness of floating wetlands in removing unwanted substances from polluted waters. (DeBusk)

Floating wetland study done in Florida (DeBusk)

In this study a floating wetland was deployed in a Floridian lake in August of 2003 (DeBusk). The performance of the introduced wetland was then monitored for the next year. It is important to note that in this study, Alum was injected beneath the wetland to stabilize the Phosphorous that accumulates in the sediment (DeBusk). Had this not been done, researches predicted there would be little net removal of phosphorous (DeBusk).

 Success of this floating wetland project was quantified through comparisons of different nutrient/pollutant concentrations in water sampled from wetland inflow (water which had not yet been exposed to filtration from the wetland) and wetland outflow (water surrounding the wetland which had benefitted from wetland filtration) areas of the lake. This data shows a general trend of decreased nutrients in outflow water (DeBusk). It should be noted that coliform concentrations are shown to be extremely high in wetland outflow due to heavy utilization by birds. This issue has been accounted for in floating wetlands installed in Hicklin Lake. 

List of alternate studies proving the effectiveness of floating wetlands: 

1.) http://www.bluewing-env.com/docs/NIWA_Study.pdf

2.) http://www.bluewing-env.com/docs/MBRCT_Study.pdf

3.) http://www.stormwater.ucf.edu/chemicaltreatment/documents/DeBusk%20et%20al%202005b.pdf

IV. FLOATING WETLANDS IN HICKLIN LAKE

In 2013, two 600 square foot islands were installed in Hicklin Lake (Abella). Each island has been planted with 18 wetland shrubs and 500 rushes and sedges. There are fences set up around small plants in order to protect them from ducks that frequent the area. To mitigate effects of bird feces on the lake, the islands have been outfitted with sparkling mylar tape which should deter them. These islands have only been established recently so there is no data to support their success at this point (Abella). Due to past studies, we have hope that they will be beneficial to the health of Hicklin lake.