Academic journal article Estonian Journal of Ecology

Variability of Riparian Soil Diatom Communities and Their Potential as Indicators of Anthropogenic Disturbances

Academic journal article Estonian Journal of Ecology

Variability of Riparian Soil Diatom Communities and Their Potential as Indicators of Anthropogenic Disturbances

Article excerpt

INTRODUCTION

Soil is known for its high but still fairly unknown biodiversity. The decline of soil biodiversity due to anthropogenic influences has been recognized as an important ecological problem (e.g. Fierer et al., 2009). However, only some groups of organisms (e.g. earthworms) in soil are well understood, leaving a vast amount of biota and a number of habitats unresearched. Because the functions and services of the terrestrial ecosystem depend on soils and soil biodiversity, it is important to identify bioindicators for both natural and anthropogenic environmental trends and changes (Havlicek, 2012).

A number of different bioindicators (e.g. earthworms, microarthropods) are used to evaluate soil conditions (e.g. Ivan and Vasiliu, 2009), each with a different response to environmental changes. For example, in Estonia earthworms have been studied in flooded coastal grasslands, suggesting that species react differently to variable moisture conditions (Ivask et al., 2007). However, there are still many soil organisms with indicator properties that are understudied. An example of these is soil algae, which are among the first organisms to colonize soil (Starks et al., 1981). Among them are diatoms, eukaryotic single-celled algae, whose spatio-temporal distribution is constantly influenced by a combination of human activities and natural processes.

Although mostly known for their short response times to environmental changes and indicator abilities in water (e.g. Kobayasi and Mayama, 1982; Eloranta and Soininen, 2002; de la Rey et al., 2004; Levkov et al., 2007; Beyene et al., 2014), diatoms can also be found in soils and are considered to be potentially good environmental indicators of terrestrial ecosystem properties (van Kerckvoorde et al., 2000; Berard et al., 2004; Van de Vijver et al., 2008; Kabirov and Gaisina, 2009; Moravcova et al., 2009; Heger et al., 2012). For example, soil diatoms have been studied in relation to agricultural activities (Heger et al., 2012), oil pollution (Dorokhova, 2007), and in polar areas in the context of vegetation type (van Kerckvoorde et al., 2000; Van de Vijver et al., 2008) and animal perturbation (Moravcova et al., 2009).

Riparian zones are strongly affected by both aquatic and terrestrial environmental changes. Water-level fluctuations are often mediators of these changes and serve as a major source of nutrients, sediments, and water to the riparian soils (Grobbelaar, 1983; Weilhoefer and Pan, 2007). Therefore, not only do the riparian zones impact the development of the aquatic ecosystem and its trophic status, but the water body may also alter the physical and chemical parameters of the riparian habitat (e.g. floodwaters) (Weilhoefer and Pan, 2007). Through various alterations in their habitat, the riparian biota, including soil diatoms, are influenced by changes in the water body and on the catchment area. Understanding processes in riparian zones is a great challenge due to their variable environmental conditions. Therefore, exploring diatom variability in riparian areas can potentially enable us to explore the influence of anthropogenic disturbances on diatom communities.

Based on previous studies from aquatic (e.g. Dickman, 1998; Gudmundsdottir et al., 2013) and terrestrial environments (e.g. Kobayasi and Mayama, 1982; Zancan et al., 2006) together with earlier studies from Estonia where diatoms were studied on moist road-side soils (Vacht, 2012, 2014), the following hypotheses were formed: (1) the properties and structure of the riparian soil diatom community vary depending on the study area and site, soil and water body characteristics, and anthropogenic disturbances, but a partially common diatom community is maintained; and (2) diatom species richness and diversity decrease and community evenness increases with increasing human influence. Based on these hypotheses, the following goals were set: (1) to analyse diatom community parameters and structure taking into account both the variability of the sampling sites and the multiple types of anthropogenic disturbances they are subject to; (2) to discuss the potential of using riparian soil diatoms as bioindicators of anthropogenic disturbances. …

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