Invasion of<i>Dreissena Polymorpha</i>(Pallas, 1771) to Reservoirs in the Struma River Basin (Aegean Sea Drainage Basin, Southwest Bulgaria)

Zooplankton is not included as a biological quality element, even though it is a key component of pelagic food webs. The data on zooplankton community structure can be used to evaluate the trophic state of lakes through an RCC Index, based on quantitative proportions between the main zooplankton groups. As previous investigations have related the index only to the Secchi disc transparency, the aim of this study was to compare the Index to a set of water quality parameters and trophic state indices. Two sandpit lakes with contrasting characteristics were selected as model lakes for the study. A total of 57 samples were collected simultaneously with the physicochemical water quality parameters between 2016 and 2020. Carlson’s trophic state indices were used to assess the trophic state of the lakes. Pearson correlation coefficient and Principal Component Analysis were used to assess the observed correlations between the measured parameters and to distinguish what factors regulate zooplankton community structure. Overall, 86 zooplankton taxa were identified. RCC Index ranged from 2 in the small sandpit lake to 87 in the big sandpit lake. A highly significant negative correlation was found between the RCC Index and the values of TP and COD. The results complement the arguments for the inclusion of zooplankton as a BQE for the assessment of the status of lakes.

Section: Species Compositionmentioning

confidence: 97%

Comparison of the zooplankton-based RCC to Carlson’s trophic state indices and water quality parameters

Stanachkova,

Dashinov,

Traykov

2024

“…The lake is no longer used for sand and gravel extraction and has a maximum depth of 12 m and an elevation of 551 m. The bottom substrate in the lake is mostly sand, gravel and stones in the shallow part, and silt-clay and sandy in the deeper part. Zebra mussels were found attached to the stems of aquatic plants and to a concrete structure at a depth of about 1 m [18]. On the sand pit Lake Kazichene's territory there is a hydro park for water sports such as wakeboarding and water skiing.…”

Section: Sampling Areamentioning

confidence: 99%

“…Adult zebra mussels were sampled by the use of hand bottom drag with an entrance of 17.5 cm, a fine scraping edge, and a handle length of 1.70 m [19]. Samples were taken from the littoral part of the lake, at about 1 to 2 meters underwater.…”

Section: Sample Collection and Primary Processing Of Biological Samplesmentioning

confidence: 99%

Accumulation of microplastics in Zebra mussel (Dreissena polymorpha, Pallas, 1771) in the sand pit lake Kazichene, Bulgaria

Hongyu,

Rozdina,

Kozuharov

et al. 2024

In recent years, microplastic contamination has received worldwide distribution and specific attention. As a result, detecting sensitive bioindicators is crucial to establish the pollution. The aim of the present study is to investigate the accumulation of microplastics in zebra mussels (Dreissena polymorpha, Pallas, 1771) from the sand pit lake Kazichene. The natural range of the zebra mussel in Bulgaria includes the Danube River delta, the Black Sea rivers and coastal lakes. However, it is considered a wide spread invasive species to inland freshwaters. The use of invasive species as bioindicators over native species is advisable in order to protect the local biodiversity. In total 20 mussels of D. polymorpha were used for the analysis. The biological tissues of the mussels were digested with the aid of 30% H2O2 at 65°C for 24 - 48 hours. Microplastics (772 pcs. in total) were detected in all zebra mussel samples, indicating microplastic contamination in Lake Kazichene. Three main shapes have been identified: fragments, fibres and pellets, with the highest proportion of the fragments. The colours of the microplastic particles found were black, red, yellow and transparent, dominated by those of black colour, followed by red. The length of the fibres found in the zebra mussels ranged from 0.25 to 5 mm. There was no strong correlation between the body length/meat weight of zebra mussels with the degree of microplastic accumulation in the mussels.

“…At the beginning of the 20th century, at the place of the Small Negovan Lake (SNL), there was "Negovansko blato", which was a natural riverside wetland of high importance for the biological diversity and was part of the so-called "Swampy Triangle". In the 1930s, the drainage of wetland began, and later the correction of the Lesnovska River was made and lakes were dug for the extraction of aggregates, sand and gravel [1]. As a result of deforestation, extraction of aggregates, illegal dumping of waste and the corrections of the Lesnovska River, the riverside ecosystems have lost their natural character.…”

Section: Introductionmentioning

confidence: 99%

Ecological evaluation of the Small Negovan Lake after habitat restoration

Tosheva,

Traykov

2024

The study presents result on the changes in the ecological status of the sandpit lake during first six years after its restoration. The lake is located on the remnants of an extensive wetland with high biodiversity and conservation value, which was drained in mid 30s of the 20th century. Later canalization and embankment of the river resulted in the hydrological cut-off and complete drying up of the wetland. Fortunately, the territory was simultaneously exploited for aggregate production, thus retaining water and providing refuge to a number of the original flora and fauna of the wetland. After the exploitation of bottom material was ended, the sandpit lake regained a semi natural appearance, partly due to a series of projects. The most recent and complete restoration took part in the period 2013-2015 with the aim to restore and improve the ecological conditions in the lake. Subsequently (2016-2020), a monitoring program was launched, to assess the effect of the restoration activities on the macrophytes community (hydrophytes and helophytes), part of which are presented here. The results suggest pronounced deterioration of the status after the interventions, but the impacts are overcome in the next two to three years.