Bioproductivity and biodiversity in shallow freshwater lakes

Abstract

To address the lake eutrophication problem, a research framework integrating molecular biotechnology with environmental engineering was developed. Initially, the lake-like microcosms (Trophic State-Classified Algal Reactors, TSCARs) were designed and constructed for using scenario assessment. As the results, several patterns of algal growth were observed under many replication experiments performed. By adjusting nutrient loading and hydraulic properties, TSCARs produced three classified trophic levels. The TSCARs' treatments, based on the Vollenweider model in conjunction with the practical works of environmental engineering, were conducted to investigate the relationships between lake biodiversity (LB) and algal bioproductivity (AB). The Chlorophyll-based estimation was developed for assessing the AB. Based on the estimate of AB, the time-varying algal populations were quantified. The relationships between LB and AB were clearly demonstrated by DGGE (Denaturing Gradient Gel Electrophoresis) fingerprints. Data showed that the relationships were in agreement with previous studies. The Shannon index (H') indicated that the eukaryotic biodiversity of mestrophic level was higher than that of oligo and eutrotrophic levels. The prokaryotic biodiversity of mestrophic level was lower than that of oligo and eutrotrophic levels. The similar trends were found in two sites of Lake Wilson under different trophic level. The phase-oriented concept of the algal growth is firstly proposed to explain the varying relationships between LB and AB by examining DGGE under time-varying analysis. Two relationships: positive relation following a hump shape pattern (eukaryotic assemblage) and negative relation following a U shape pattern (prokaryotic assemblage) were found and exhibited clear correlations between LB and AB. Results from time-varying analysis provided exciting insight into the lake biodiversity. These results showed that LB was deeply affected by the history of algal growth. Moreover, critical timing points of algal growth history in terms of Pr(t) predicted that a shift in LB was imminent. By conducting molecular cloning, four libraries were produced. The community structures sampled from the TSCARs were higher similarity in lakes. Finally, a minor finding is worthy of note in regard to the population dynamics of cryptophyta in lakes. It was found that the abundance of the cryptophyta was positively correlated with trophic levels in TSCARs.