Odonata - Entomological Society of Latvia - Latvijas Daba

2.3. RESEARCH OF THE OCCURRENCE AND POPULATION DENSITY OF GOMHIDAE LARVAE IN RIVER
GAUJA
Sampling. Gomphidae larvae were collected during implementation of the project
„Establishment of long-term pollution in water of Gauja” in 1998. In total 280 quantitative samples
of macrozoobenthos were collected at 32 sampling sites in the river Gauja from village Taurene
upstream to village Carnikava downstream. Standardized methods were used for collecting and
processing the Gomphidae material (Standart… 1992). At each sampling site 2-4 quantitative
macrozoobenthos samples were collected. At most of the sites the samples were collected during
three seasons. An Ekmans–Berdge type grab (0.025 m 2 ) was used for collecting quantitative
samples. 1-2 qualitative samples were collected at each sampling site, using a hydrobiological handnet.
In total 65 qualitative samples were obtained. In each sample spot the substrate composition
and the speed of the stream (using a floating object, by formula: speed of the stream (v) = distance
(s) / time (t)) were determined. The vegetation was described using Braun-Blanquet scale (Kent,
Coker 1996). The ground composition was evaluated visually, registering the percentage of ground
composition: cobbles (>256 mm), pebbles (64-256 mm), gravel (2-64 mm), sand (0.06-2 mm), mud
and detritus.
Additionally, a survey of Ophiogomphus cecilia imagos was performed in Gauja, July 29-30,
2003 in the section from Cēsis to Sigulda (45 km), where all adult individuals near the river and its
banks were recorded. The survey was performed in sunny conditions, from 11:00 till 16:00. The
observation places were recorded by GPS and marked in a map.
Data analysis For the analysis and the interpretation the data from the observations of adult
individuals were used, including literature and unpublished observations from 1993-2005 (basic
data base). The density of larvae was estimated from the total number of collected samples and the
number of the Gomphidae samples. In this way, the total density of the Gomphidae larvae in Gauja
and the density of the individuals in the Gomphidae habitats were obtained. The imago observations
were used to describe the distribution of the species in Gauja area.
2.4. RESEARCH OF THE REGIONAL DIFFERENCES OF THE EUROPEAN ENDANGERED AND
PROTECTED DRAGONFLY SPECIES IN LATVIA
All species. For the analysis of species distribution and populated habitats the basic data from
data bases were used. Data on the relation of the species to specific habitats and vegetation were
obtained by using:
• information from data base;
• descriptions of localities in literature;
• descriptions of localities and photos obtained during inventories;
• orthophotomaps, thematic data layers (Latvian Geospatial Information Agency, Envirotech,
Ltd.);
• data from http://www.ezeri.lv (2011).
Additional data were obtained during the research by describing and taking photographs of research
locations on various scales (landscape, habitat, micro habitat, plant species).
The area and distance measurements were performed by using the first (1994-1999), second
(2003-2005) and third (2007-2008) cycle othophotomaps on a scale of 1:10 000 available for the
specific location and time (Latvian Geospatial Information Agency) and Arc GIS 9 program
package.
Nehalennia speciosa. In order to identify the species the habitats (lakes with fens and bogmoss,
poor fens and raised bogs with water bodies of various sizes) and micro habitats potentially
suitable for the species (imagos) were searched for the individual imagos using an insect net. The
micro habitats (vegetation where individual imagos were observed) were described, accounting for
the vegetation, the area and shape of the micro habitat and its location in the habitat. The
individuals observed in each micro habitat were counted. The inventory was carried out on the
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