Odonates as indicators of shallow lake restoration by liming: comparing adult and larval responses

Published source details D'Amico F., Darblade S., Avignon S., Blanc-Manel S. & Ormerod S. J. (2004) Odonates as indicators of shallow lake restoration by liming: comparing adult and larval responses. Restoration Ecology, 12, 439-446.
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Summary

Odonata (dragonflies and damselflies) have been used as indicators of aquatic ecosystem quality for several reasons, including that they live in a wide range of aquatic habitats, are easy to record and identify to species level, and they respond clearly to environmental variation, caused for example by pollution. There is debate, however, about whether adults or larvae best reflect aquatic conditions. In this study, odonate assemblages were compared between replicate sets of shallow lakes, some of which had been treated with aqueous calcium carbonate to counter acidity. Both Odonate adults and exuviae were sampled to give a measure of the effects of this treatment.

Study area: The Réserve Nationale de Chasse et de Faune Sauvage d'Arjuzanx (44°01' N, 0°51' W), Auitaine, south west France, was a formerly forested area (2,700 ha) open-cast mined for lignite (coal) between 1959 and 1991. This mining resulted in newly created acidified lakes covering 550 ha, most less than 5 ha in area. Habitat restoration began in 1981 and included a return to agriculture and forestry, and also lake liming by the addition of aqueous calcium carbonate.

Odonate assemblages: Odonate assemblages were compared between replicate sets of shallow lakes. One set of five lakes was experimentally 'restored' by liming with calcium carbonate, whereas another set of five similar lakes were left untreated as reference lakes. Both odonate adults and exuviae were sampled bimonthly during May to August 1998.

Environmental data: Measures of pH, subsurface water temperature, conductivity, turbidity, and dissolved oxygen were made monthly at five different places in each lake, also between May and August, 1998. To further assess any natural deacidification after restoration, total water hardness and total organic matter was measured on 16 June 2000. Data on additional site attributes were collected to identify possible factors confounding the effects of past liming on dragonflies. In one 20 × 2 m quadrat at each lake, littoral vegetation was classified as: reed Phragmites spp. dominant; rush Juncus spp. dominant; or Phragmites and Juncus equally dominant. The presence or absence of Sphagnum moss and of floating or submerged aquatic vegetation and bank slope was also recorded. Surrounding land use was categorized as grassland, conifer (maritime pine Pinus maritimus) or mixed.

Odonate assemblages: Twenty-four and 19 odonate species occurred among adults and exuviae, respectively, but there were no significant differences in richness between limed and reference sites. Significantly, many more exuviae were collected from the reference sites (588 vs. 180), where their diversity and rank abundance indicated more evenly structured assemblages than those in the limed lakes. Adult assemblages differed significantly between restored and reference lakes, and varied highly significantly with lake turbidity. This occurred as five generally scarce species present as adults adults were characteristic of reference sites (i.e. willow emerald Chalcolestes viridis, small emerald damselfly Lestes virens, downy emerald Cordulia aenea, white-faced dragonfly Leucorrhinia albifrons and ruddy darter Sympetrum sanguineum). Exuviae of these same species were less abundant at restored sites, but exuvial assemblages overall did not discriminate between restored and reference lakes. We conclude that lake restoration by liming can reduce diversity and larval numbers among odonates and subtly affects adult assemblages.

Physicochemical characteristics: Elevated turbidity and conductivity was apparent in the five limed lakes. These were the only physicochemical characteristics measured that differed between these and the unlimed reference lakes, as deacidification occurred naturally, even in the reference lakes over the 17 years after the onset of the liming restoration attempts.

Conclusions: In this study, restoration by liming led to increased water turbidity and this might be considered adverse to some aquatic invertebrates. Adult Odonata assemblages discriminated best between the lake types, but important additional information came from exuviae abundance and structure. Results indicate that natural recovery after acidification in this formerly open-cast mined area, rather than intervention through liming, might actually lead to more preferable conservation outcomes.

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