The process of eutrophication in form of intense plant growth has been observed in some lakes and water streams at the Plitvice Lakes National Park in central Croatia. Here we investigate whether this phenomenon is a consequence of anthropogenic pollution or due to naturally produced organic matter in the lakes. We applied chemical analysis of water at two springs and four lakes (nutrients, dissolved organic carbon (DOC), trace elements) and measurements of surface lake sediments (mineral and organic fraction analyses, trace elements) in four different lakes/five sites. The chemical composition of water does not indicate recent anthropogenic pollution of water because the concentrations of most trace elements are below detection limits. The concentrations of DOC and nutrients are slightly higher in the area of increased eutrophication-plant growth. Also the content of organic matter in the sediment is at the highest level in areas with highest C/N ratio indicating that the organic fraction of this sediment is mainly of terrestrial origin. There is no significant difference among the trace element concentration in the upper segment of all cores, deposited approximately during last 50 years when higher anthropogenic influence is expected due to development and touristic activity, and the lower part of the cores, corresponding to the period approximately 100-200 years before present. The content of trace elements and organic matter in sediments decreases from the uppermost lake downstream. According to our results there is no indication of recent anthropogenic pollution in water and sediment. Higher concentrations of DOC in water as well as phosphorus and some other elements in the lake sediment can be a consequence of input of natural organic matter to the lake water.

The puddles Slatina and Pecena Slatina are the old meanders of the river Tamis. These ecosystems are periodicity fill with moderate salt and high alkaline water. The paper gives a review of qualitative and quantitative analysis of the algal compositions. Cyanoprokaryota and Euglenophyta are more common. All investigated parameters like compositions of lagal communities, their abundace, biomass and chlorphyll-a showed a high level of nature eutriphication in these ecosystems.

In this paper the results of zooplankton investigations (and its dominant group Copepoda) were presented from the part of the Boka Kotorska Bay with more intensive circulation with the open sea, from summer of 2005. Some results from the open South Adriatic were given, too - from the frontal zone exposed to anthropogenic eutrophication of Bojana and Drim rivers, and the impact of oligotrophic South Adriatic, simultaneously.

In this paper, results of phytoplankton investigations were performed in June 2005. The investigated positions are located near the entrance of Boka Kotorska Bay: two positions in the outer part (Zanjica and Mamula island) and two positions in the inner part of the Bay (Njivice and Tivat bay). In this area the influences of the open sea and the land are expressed to the phytoplankton community. As a consequence of that quantities of phytoplankton are lower in the outer part and higher in the inner part. The most dominant species is diatom Pseudo-nitzschia delicatissima which is very frequent in the eutrophic area.

Investigation of the nutrients and chlorophyll a concentrations, as indicators of trophic level, in the period from September 2003 to August 2004 in three sampling locations in the inner part of Boka Kotorska Bay varied widely. Nitrate concentration ranged from 0.0 to 2.42 mg/l at the surface and from 0.02 to 3.88 mg/l at the bottom, nitrate concentration from 0.02 to 0.21 mg/l at the surface and from 0.01 to 0.6 mg/l at the bottom, phosphate concentration from 0.03 to 0.18 mg/l at the surface and from 0.01 to 0.22 mg/l at the bottom, silicate concentration from 0.0 to 1.42 mg/l at the surface and 0.45 mg/l at the bottom respectively. Value of phytoplankton biomass, as represented by chlorophyll a, ranged from 1.02 to 8.68 mg/cubic meter and from 0.49 to 5.23 mg/cubic meter at the bottom. According to the UNEP criteria during the investigated period it can be concluded that the area in question is mesotrophic with the exception of December when it is eutrophic.