The role of charophytes in a Mediterranean pond created for restoration purposes

• An artificial pond was created to increase local charophyte diversity in a Natural Park.
• Five species grew from sediment oospores; C. hispida was dominant.
• The charophyte meadow played a key role in the maintenance of clear-water phases.
• The restoration plan was successful despite some factors that threaten charophyte growth.
• Countermeasures to retain charophyte presence in the system are proposed.

A small, shallow basin was created and flooded with groundwater in a Reserve Area in Albufera de València Natural Park (AVNP) under the scope of a restoration program intended to mimic typical environments such as freshwater springs, abundant in the past but currently suffering from deterioration (desiccation, pollution, etc.), with the ultimate goal of increasing local biodiversity of submerged macrophytes, particularly charophytes. In this study we have monitored, from April 2009 (a few months after its first flooding) to September 2012, the dynamics of charophyte growth and related physical, chemical and biotic variables to highlight the factors determining charophyte success. Just after flooding, five charophyte species grew spontaneously when oospores germinated in the sediments. Chara hispida populations largely dominated the community and developed dense meadows that covered virtually the entire pond floor. Charophytes exerted a negative influence on phytoplankton densities, increasing water transparency. C. hispida stands precipitated substantial CaCO3 in the form of incrustations on the plants, accompanied by coprecipitation of inorganic phosphorus, maintaining low concentrations of soluble P in the water. Reduced groundwater inflow, increased salinity, nutrient concentration, turbidity and augmented feeding pressure by waterfowl, separately or by synergistic effects, considerably reduced charophyte development during the final year of the study; however, charophytes still represent one of the most extensive and dense stands of submerged vegetation within AVNP, verifying the achievement of the goal of the restoration plan. The knowledge obtained has allowed us to recommend several measures to counteract the decrease of charophytes, which can also be applied in other regions affected by the same stressors.