Constructed floating island is an eco-engineering solution applied for water restoration and creation of natural floating riverbanks in the cities. Wetland plants are supported by artificial buoyant mats. Nutrient rich water is treated by bacteria attached on the plant roots performing nitrification/denitrification (release of N₂ gas), biological breakdown and detoxification. Roots and installation itself enhance particle retention. As a result increased water clarity, reduced algae and cyanobacteria growth as well as reduced nutrient levels could be achieved. The increased habitat and food availability further enhances aquatic food chain and partly restores deteriorated biodiversity in turbid waters. In addition, floating wetlands provide habitats for aquatic and terrestrial fauna (insects, birds) as well as number of cultural aesthetic services.

Klaipeda city (Lithuania) contains fortification fragments (such as reconstructed Jonas Hill, Goldern’s bastion of 17^th century) that are nowadays used as popular visiting sites close to the old town and new built living houses. Enclosed embayment suffer from limited exchange of water with the main Dane River canal as well as accumulating nutrients and poor water quality. Therefore, the floating mats could be an extra space for plant growth with water restoration effects.

Nutrient removal by floating island would contribute to overall water quality management in the coastal areas of south-eastern Baltic Sea.

The floating island of the total area of ~28 m² would be installed in Dane River or river embayment. For an island we’ll need a sum of ~10 000 euros, which we have within LiveLagoons project funds (about the project: http://www.balticlagoons.net/livelagoons/). In addition, we need to collect 2000 euros as maintenance costs for 3 ys, which includes costs for mooring, planting, harvesting, replanting the damaged vegetation ect.). We have this price estimation as a result of experience based on the already installed islands in the Curonian Lagoon.

The quantified nutrient reduction/removal is 0.14 kg for 1 year(s).

The nutrient removal capacity of the island is the sum of nutrients accumulated in the aerial biomass (stems and leaves) and underwater biomass (roots), nitrogen loss by microbial activity, phosphorus uptake by microorganisms and sedimentation. Our estimates of plant biomass and nutrient content in the harvest from the 28 m² island installed in the Curonian Lagoon equals to 103g of N and 5g of P/m2. The aerial biomass could contribute only ~10% of nutrient removal while the rest is accounted for root-associated microbial community. Therefore we could assume that annual removal of 28 m² could be 2870g of N and 140g of P. For 3 ys respectively 8610g of N and 420g of P.

Timely harvesting of above ground tissues in September needs to be ensured before the start of vegetation decay. The construction could be kept in water year round, as freezing and thawing cycles do not seem to harm the islands. For annual plants especially ornamental species, the replanting costs are considered and this will need some labor work. The team of volunteers will be available at the Marine Research Institute, Klaipeda University for the installation and proper maintenance of the island. As the islands installation sites are enclosed embayment, waiving and water flow damage risk for the construction is low.

The installation of an island is in May, 2020. The maximum growth could be reached in ~July. The growth and succession of vegetation could be documented in pictures. The first harvest and weight recording is in late September 2020.  The cumulative harvest will be announced on the website.