Temporal development of biodiversity of macrophytes in newly established lakes

Abstract

Abstract Every year, a vast number of wetlands are constructed to restore ecosystem function and biodiversity, thus counteracting massive historical losses by reclamation to farmland. However, our knowledge of the long‐term effects on biodiversity, particularly of large systems such as lakes, is very limited. Our objective was to follow the development of macrophytes over 3–4 decades in 24 new, shallow, eutrophic lakes in order to test the hypotheses that: (1) species richness reaches a maximum after some years and then declines; and (2) species composition changes substantially from small early colonisers to taller, competitive later colonisers, which causes ongoing high β‐diversity. A generalised linear mixed‐effect model showed that species richness was related to lake size, phosphorus concentration and spatial setting, which are known to influence natural lakes as well. Moreover, species composition and richness were affected by lake age. Species colonised rapidly and richness peaked at an intermediate age and then declined. Temporal species turnover within lakes was high in three lake age groups of ≤10, 11–20 or >20 years since establishment, although lowest after 11–20 years. Species replacement tended to contribute most to β‐diversity in the youngest lakes, whereas richness fluctuated in older lakes and appeared to contribute most to temporal turnover there. Early colonisers in ≤10‐year‐old lakes were commonly replaced by tall canopy‐forming species in 11–20‐year‐old lakes, probably as a result of increasing competition for light and space over time. After 20 years, rootless Ceratophyllum submersum as well as species with floating and emergent leaves became dominant, potentially due to the gradual accumulation of more organic sediment difficult to root and grow in, along with gradually reduced light penetration in the water. Establishing new lakes for biodiversity remains a challenge because of the falling richness and continuous species turnover with lake age, but our results suggest that constructing large, nutrient‐poor lakes in species‐rich landscapes ensures the best prerequisites for obtaining diverse communities.