The influence of hydrological and land use indicators on macrophyte richness in lakes - A comparison of catchment and landscape buffers across multiple scales

In biogeography it is well established that environmental variables often have scale-dependent effects on abundance and distribution of organisms. Here we present results from a study on scale-dependency of macrophyte (aquatic plant) richness to hydrology and land use indicators. Hydrological connectivity and land use within the landscape surrounding 90 UK lakes, at nine buffer sizes varying from 0.25 km to 10 km from the shoreline, with (catchment buffer) and without (landscape buffer) adherence to the catchment boundary, were constructed using GIS. These variables were used to explain variation in macrophyte richness derived from field surveys. The results revealed strong scale-dependency. The effects of land use were most apparent at small buffer sizes and grossly outweighed the importance of hydrology at all spatial scales. The total richness of macrophytes was most strongly determined by land use and hydrology within 1 km of the lake for landscape buffers and 500 m for catchment buffers. The nature of the scale-dependent effect also varied with macrophyte growth habit. In terms of growth form composition, the effects of hydrological connectivity were stronger than those of land use, being greatest at an intermediate distance (∼5 km) from the lake. Our results indicate the value of maintaining some lake catchments with less intensive land use, at least within 1 km of the lake shore, while also minimising alterations to catchment hydrology (e.g. through drainage or impoundment) over distances extending at least 5 km from the lake shore.