Distribution of submerged macrophytes along environmental gradients in large, shallow Lake Balaton (Hungary)

Abstract Distribution of submerged macrophytes was assessed at 15 littoral sites in large, shallow Lake Balaton using the echo sounding technique. Sites represented the conspicuous longitudinal and transverse environmental gradients. Absence/presence of plants, water depth, bottom consistency and distance from the shore have been derived from echo sounding data. Turbidity and meteorological variables were recorded at a single site from 2004 to 2006. Site-specific variability in underwater light conditions (an indicator of stress) and exposure to breaking waves (an indicator of disturbance) were estimated by simple models. Light deficiency was the prime factor that determined the distribution and colonization depth of submerged macrophytes. The influence of light and exposure on plants could be distinguished by considering the complex interplay of site-specific morphometry and the stochastic wind field in a highly simplified manner. Unlike in the wind protected northern littoral, wave disturbance limited the distribution of plants along the offshore portion of the nearly horizontal southern plateau. Due to the long (in the order of several kilometres) fetch in the direction of the dominant winds, establishment of a macrophyte dominated stable state can only be expected at a local scale in spite of the shallow mean depth of Lake Balaton. Relative frequency of plants was the highest at the same bottom consistency in both the muddy northern and the sandy southern littoral. Preference of submerged macrophytes towards relatively firm bottoms could be demonstrated along the northern shore. The observed pattern suggested that preference was not driven by nutrient availability.