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Zabieg krótkoterminowej biomanipulacji ekologicznej zastosowany w trzech śródleśnych płytkich jeziorach

Czerniawski R., Sługocki Ł, Domagała J., Pilecka-Rapacz M.

Rocznik Ochrona Środowiska

2015

Tom 17, cz. 2

1207--1223

A crucial factor affecting the rate of eutrophication is the characteristics of the catchment area of lakes. The most visible result of excessive eutrophication is rapidly deteriorating transparency of waters in the summer which is caused by rapid development of planktonic algae. Another symptom of this process is gradual overgrowth of water reservoirs and watercourses by macrophytes. Hence, in order to improve the quality of water in these lakes the renovation treatment is applied. Lakes restoration can be made in many ways: physical, chemical and biological. The chemical and physical methods of lakes restoration are invasive and controversial. However, one of the relatively not invasive methods of lakes restoration is ecological biomanipulation. The goal of biomanipulation is to reduce the concentration of harmful phytoplankton, by the stocking of predatory fish triggers a trophic cascade with decreases in the biomass of smaller-bodied fish, e.g. cyprinids, increases in the biomass of herbivorous zooplankton, and decreases in the biomass of harmful phytoplankton. In some cases plankton-eating fish have been removed directly by lake managers. In addition, the removal of bottom-feeding fish from shallow lakes leads to increases in rooted vegetation and increased water clarity as the rooted plants stabilize the sediments. This transition involves a trophic cascade, as herbivorous zooplankton increase in biomass and consume phytoplankton, but also involves the direct effects of rooted vegetation on sediment stability and nutrient cycling. The most frequent cause of fast eutrophication is the runoff of untreated sewage directly into the waters of lakes and rivers or the excessive runoff of biogenic compounds from agricultural catchment areas. Forest lakes because of far distance from agglomeration and agricultural areas are in lesser extent exposed on the human pressure. Generally, one unfavorable variable affected these lakes is angling pressure. Thus, due to the lack of pollution and the relative stabilization of the mid-forest lakes they are a good place to conduct the ecological biomanipulation. The aim of the present study was to determine the short-term biomanipulation effectiveness in three shallow forest lakes. Biomanipulation was performed by stocking in 2012 to these lakes a summer fry of pike (200 ind. ha-1) and zander (150 ind. ha-1). Before the biomanipulation (in 2011) a control study of physic-chemical parameters, ichthyofauna and zooplankton composition were made. After the biomanipulation (in 2014) the same control study were conducted. Before and after the biomanipulation period significant changes in values of physic-chemical variables were not observed. Similarly, a slight changes in ichthyofauna composition between these two period occurred. The roach and bream were the biomass dominants. Only the zooplankton composition obtained pronounced changes, but statistically not significant. The most visible differences in zooplankton abundance concerned cladocerans – group that the most affect the phytoplankton decreasing. After the biomanipulation abundance of cladocerans increased from 31% to 67%. According to the results, it can be concluded that the biomanipulation time in study lakes was too short to make significant changes. To get a better effect of biomanipulation a successive stocking with summer or autumn fry of pike and zander should be conducted, even in 1000 ind. ha-1. Finally, we can assume that in the forest, shallow, highly eutrophic lakes a biomanipulation with predatory fish may be sufficient for their effective restoration.

Restoration of subalpine species-rich grasslands: short-term vs long-term changes in the density and diversity of above-ground insects

Karg J., Kujawa K., Manhart C., Marschalek H., Neugebauer K. R., Sachteleben J.

Polish Journal of Ecology

2015

Vol. 63, nr 1

142--158

Due to decrease in the area of extensively managed, semi-natural grasslands, that contribute to high biodiversity level preservation, the conversion of highly productive meadows to extensively managed, species-rich grasslands is now regarded as an important task for nature conservation. The aim of this long-term study was to assess the significance of restoration measures for diversity and trophic structure of above-ground insect community. That study challenges some weaknesses of previous studies as it was conducted with the use of suction trap enabling quantitative analyses of the changes in most insect taxa, and in a long time-span (1992–2005) in a set of permanent plots. The study area was located in a subalpine zone in Bavaria, near Laufen (Germany). The restoration process was initiated in 1996 by a cessation of fertilization and reduction of number of mowing to 1–2 per year. The changes in insect density and diversity (number of families) were monitored in ten restored and two reference plots with the aid of a suction trap. The changes in the insect community recorded during 14 years support findings from other studies that response of insect community to restoration process is usually slow on average. The short-term comparison in 2004–2005 between the restored and reference plots show that the first ones were characterized by more diverse (in term of family number) insect communities (as a whole as well as in guilds of predatory and parasitic species). From the other side, the long-term trend analysis shows that since 1998–2000 insect diversity and abundance was declining. Also trophic structure is fluctuating without clearly defined trend. These findings are in line with the results of the analyses of taxonomic composition similarity. They did not support the expectations neither that difference between initial and current taxonomical composition in a restored plot increases in time (mainly because of incoming new species), nor that spatial heterogeneity of insect assemblages should increase. However, spatio-temporal insect interactions between sample plots (located close to each other), linked to high movement ability of many insect taxa, could mask the changes in insect community caused by restoration.