Situated in Estonia, the earlier alkaline fen Läänemaa-Suursoo (over 3400 ha), as autonomous part of the Suursoo-Leidissoo mire complex (over 23 000 ha), was drained in the 1880s. Shallow streams were straightened and cut deeper – becoming ditches – to remove water from the area and allow mowing of hay. During that period milk production and export of butter had become very good business, which is why hay was in such high demand.
The digging of these ditches was done by hand. Before the ditches, the water level was either on the fen surface or very near it. As the area dried out, the vegetation started to change and peat started to decompose, adding continuous CO2 to the atmosphere.
In the 1930s, the plan was to ameliorate the fen for agricultural and peat excavation (required for the power plant) purposes in the northern and southern parts, respectively. However, the plan was not realized due to political reasons. Later, in the 1960s, the old ditches were simply dredged. Due to the incomplete amelioration, the prevailingly open alkaline fen degraded from semi-drained Pinus-Sphagnum to deeply drained mixed peatland forest communities.
Tallinn University’s (TLU) initial plan, as part of the LIFE Peat Restore project, was to raise the water level in ditches/streams by building around 300 peat dams. However, at the same time that LIFE Peat Restore officially started (01.07.2016) the Minister of Environment signed a decree that designated new flowing water bodies as protected spawn sites for salmon and trout. Within the decree’s list are two streams flowing through the project’s fen site, which actually are just corridors for fishes to reach to their spawning places upstream.
The old ditches (or straightened streams) had become “fish streams”, and according to fish conservationists, they should not be impacted, because fish cannot jump over dams. TLU was facing a nature protection conflict as, on the one hand, the importance of restoring damaged or destroyed peatlands into vital mires is prioritized legislatively; on the other hand, there is a prohibition by legislators to dam water bodies and raise the water level, in order to protect the spawn places for these fish species under threat After a year and half of lively discussions with ichtyologist-conservationists, a compromise was reached: no dams in the two salmon streams, but dams will be on the two sides parallel to the two streams.
With this compromise, the surface waters cannot reach the stream, but stay on the peatland. As the hydraulic conductivity of the sedge dominated peat is rather low the waters can hardly infiltrate into streams. Nevertheless, TLU must prevent the rapid runoff of spring high water into the ditches. It is important to make the peatland wet again, which means we have to keep the spring high water longer on peatland. So the dams parallel to the ditches protect it from extra water inflow and water will stand also on the peatland longer; thus, allowing the water to be absorbed slowly into the peat. This will prevent a dry summer period (i.e. drop-down of mire water) and will keep water close to peatland surface. The measures will be favourable to mire plants and to peat formation.
The technical plan to restore the hydrology regime on the Läänemaa-Suursoo was completed by the corresponding bureau in the end of January 2020. Thereafter, the tender opened for blocking ditches. On April 8, 2020 the contract with the company was signed.
The restoration measures will begin on July 16 after the end of the “bird-peace” time, which allows peace and quiet for birds to mate without disturbances. Fortunately, the grave circumstances – with the Corona virus affecting nearly all human activities – have not impacted our plans. The works are foreseen to be finished for February 15, 2021.