This thesis aims to investigate the influence of effluent from constructed wetlands (CW) on the structure of the macroinvertebrate community in the watercourses receiving treated water. Given that a large part of the catchment area of watercourses comprises of fertilized agricultural land, we were interested in the level of impact of effluents from CW. A macroinvertebrate community was used to evaluate this influence on watercourses, as they respond relatively quickly to such disturbances and other changes in the environment. Sampling took place in the southern part of Slovenske gorice, where 4 CWs were used to evaluate the impact on the macroinvertebrate community: CW Cvetkovci, Ivanjkovci, Sodinci, and Velika Nedelja. At all sampling sites we measured physical and chemical parameters and took water samples for chemical analyses. At each CW, one sampling point was upstream from the effluent, at the confluence, and two downstream at a distance of 50 and 200 m. An additional sample was on the effluent channel from the CW, through which the treated water flows into the watercourse. In the whole area, we found high concentrations of NO3-N, which increase slightly along watercourses. NH4-N concentrations increase much more (in places downstream the concentration is 3.24 times higher than upstream). Based on the S-W index, a decrease in value downstream from the effluent is observed in three cases, except at Sodinci. Based on the saprobic index, the deterioration of the watercourse is clear. In functional feeding guilds, the proportion of detritus feeders along the stream increases, and the proportion of shredders decreases. The impact of CW effluent is noticeable, but diffuse pollution, the source of which is agricultural land, affects the ecological status of watercourses in the wider area and thus should not be ignored.
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