| Abstract |
Samples of water and sediment were taken from Bramiana dam-lake once a month or seasonally, in order to record and study spatial and temporal variation of physico-chemical parameters and invertebrates which live there. Because of great water fluctuation during a year, in Bramiana dam-lake, greatest attempt was made to study the marginal zone of the dam-lake. The following physico-chemical parameters were determined: temperature, pH, dissolved oxygen, chloride, chlorinity, salinity, sulphate, magnesium, calcium, total hardness, potassium, sodium, conductivity, total dissolved solids, nitrate, nitrite, phosphate, total alkalinity, total organic carbon (in water) and particulate organic carbon (in sediment). The macroinvertebrates basically were identified up to a family taxonomic level. A list of mactoinvertebrates which dwell in Bramiana dam-lake was drawn up and abundance, taxa/L of sediment, diversity ( Shannon index, H'), eveness index J΄ of macrophauna were determined too. Data analysis was made using the statistical methods: cluster analysis, non parametric ANOVA, Principal Component Analysis, regression and correlation. We estimate that sea water was inflowed into dam-lake during warm period and that the dam-lake water was oligotrophic to mesotrophic. We believe that organic carbon had been introduced into the dam-lake from Korakas (or Bramianos) stream, after the first rainfall in November 1999, while it was biologically produced in the dam-lake, during the spring-summer-autumn period. It was recorded a thermocline-oxycline zone at a depth of between 12 and 13 m, in May 2000. We consider that evaporation, sea water inflow as well as photosynthesis were the major factors which had caused an increase in concentration of Cl-, Na+, Br+, K+, Mg2+ ions and a decrease in concentration of Ca2+, NO3-, and HCO3- ions during the warm period. 28 different taxa of macroinvertebrates were recorded in the dam-lake, but one of these is not refered in bibliography, so we were named Pleidae O, because of similarities-differences with members of Pleidae family. Furthermore, 4 taxa were recorded only in the dam-lake inflows (Nematoda, Amphipoda, Asselus and Lumbricidae). Baetidae, Orthocladiinae and Hydrobiidae were the major taxa of marginal (shore-line) phauna, while Ostracoda, Orthocladiinae and Hydrobiidae in deeper regions. Oligochaeta, Orthocladiinae, Hydrobiidae and Sphaeriidae are most often present taxa in marginal zone, while the above taxa with Chironomus genus as well as, are the most often present taxa in deeper regions. The abundance as well as, biomass of macrophauna were high, but diversity (Shannon index H΄) was relatively low in Bramiana dam-lake. The employed non-parametric analyses of variance led to the conclusion that macroinvertebrates prefer to live in deeper regions during winter, because this environment is more constant and familiar for benthos. When the water level of the dam-lake go up, Oligochaeta and Diptera are more abundant in the deeper zone. Ostracoda live only in the deeper zone and they are absent from the littoral. In contrary, Libellulidae, Coleoptera, Hydrobiidae and Sphaeriidae dwell in shore-line zone and in deeper zone too. Baetidae, some Hemiptera (Pleidae, Pleidae O, Notonectidae) and some Coleoptera (Berosus, Colymbetinae), were found only in the littoral zone (to a depth of 2,5 m), during warm period. The decrease of total abundance due to low numbers of Baetidae and Hemiptera were correlated with DO decrease in July 2000. The Odonata absence were correlated with lower concentrations of DO in water, at station C on August of 2000 too. Total abundance were decreased in winter, while it was increased during warm period. Diversity (H΄) as well as taxa/L were increased during warm period. According to statistical analysis: 1. Taxa/L variance was statistically significant only between winter and summer for every sampling station. 2. Taxa/L variance was not statistically significant between sampling stations for every season. Marginal biomass was higher in August 2000 than January 2000. In conclusion, abundance, diversity and biomass of macroinvertebrates were increased at all marginal stations during warm period, showing a health system.
|
Καταγραφή και μελέτη μεταβολής φυσικοχημικών παραγόντων και μακροασπονδύλων σε σχέση με το χρόνο και το χώρο στη φραγμολίμνη Μπραμιανών Λασιθίου
