Shifts from Clear to Turbid State in a Small Semi-Artificial Headwater Wetland Following Macrophyte Removal

ABSTRACT

Wetlands in Bulgaria have been altered, degraded or lost due to a wide range of human activities. The main objective of the study was to restore a densely overgrown semi artificial headwater wetland through macrophyte removal. Since the mid 80s rapid macrophyte invasion has taken place in the lake and by the end of the 90s it has been completely overgrown by pondweed. In 2005, 70% of the pondweed was removed and the effects of the restoration activities were monitored. The reduced amount of organic matter and increased circulation of the water led to increased oxygen content, reduced amounts of phosphates and chlorophyll-a and increased amounts of dissolved inorganic nitrogen. The small size and the shelter from the trees, as well as the incorporation of nutrients in newly developing macrophytes biomass, have helped to maintain the clear water state of the lake throughout the first year after the restoration activities. Subsequently, a shift to phytoplankton dominated state was established after introduction of grass-carp.

Keywords:

• Alternative states
• eutrophication
• headwater wetlands
• macrophyte removal