The use of rarefaction and extrapolation as methods of estimating the effects of river eutrophication on macrophyte diversity

Anna Budka,Agnieszka Łacka,Krzysztof Szoszkiewicz

doi:10.1007/s10531-018-1662-3

Anna Budka, Agnieszka Łacka + Show 1 more

Open Access

https://doi.org/10.1007/s10531-018-1662-3

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Abstract

A study was carried out to estimate the effect of trophic degradation on the diversity of aquatic plants in rivers, with the application of rarefaction and extrapolation. The purpose of rarefaction was to standardise the uneven number of samples, while extrapolation enabled prediction of the real diversity considering the expected number of species undetected by the sampling effort. Both methods were based on three Hill’s numbers: q = 0 (species richness), q = 1 (Shannon index) and q = 2 (inverse Simpson index). The macrophyte survey was carried out at 96 river sites of a uniform abiotic type (medium lowland rivers with sandy substrate). Macrophyte diversity was evaluated based on survey data (the reference sample) as well as using a dataset standardised by rarefaction and extrapolation. Trends in species richness along the trophic gradient were depicted differently by analysis based on the reference sample and on the extrapolated dataset. Based on the reference sample, the increases of river trophy led to diminishing macrophyte richness, whereas use of the extrapolated dataset revealed that the highest plant diversity can be found in mesotrophic rivers. The extrapolated dataset showed that most oligotrophic pristine rivers were poorer in species than mesotrophic watercourses, and the most limited pool of macrophytes was found in highly eutrophic watercourses. Rarefaction/extrapolation methods enable the precise comparison of plant diversity across sites, by predicting the occurrence of rare species. Moreover, the extrapolation method allows assesses of the total biodiversity basing on a smaller number of trials (survey samples).

Highlights

Biological diversity, i.e. variety of ecosystems, species and genes, is one of the Earth’s natural resources which is currently under severe threat from human activities
All three diversity metrics decrease along the trophic gradient, and the lowest values of the calculated three metrics were found in the last class: 71 0Δ, 48.43 1Δ and 37.86 2Δ (Table 2)
The change in the order of quality classes based on extrapolated samples, relative to the reference samples, confirms the hypothesis that data standardisation can modify the picture of macrophyte diversity change along the trophic gradient

Summary

Introduction

Biological diversity, i.e. variety of ecosystems, species and genes, is one of the Earth’s natural resources which is currently under severe threat from human activities. Its effective conservation requires appropriate methods for the identification and monitoring of existing natural resources (Loreau et al 2001; Cardinale et al 2012). Biodiversity metrics are widely used in nature conservation and are utilised as a tool of ecological policy in various countries. The EU countries have developed numerous indices for estimating the diversity of freshwater organisms, which may be used in monitoring or play a fundamental role in the environmental impact assessment (EIA) of water engineering systems (Furse et al 2006; Freni et al 2008). It is important to estimate biodiversity precisely, since incorrect evaluation may lead to wrong decisions in natural resource monitoring and management (Gotelli and Colwell 2001; Hurlbert 1971; Simberloff 1979; Palmer 1990; Colwell and Coddington 1994; Colwell et al 2004; Ulrich and Ollik 2005)

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