N:P ratios,light limitation,and cyanobacterial dominance in a subtropical lake impacted by non-point source nutrient pollution

A long-term (28-year) data set was used to investigate historical changes in concentrations of phosphorus (P), nitrogen (N), N:P ratios, and Secchi disk transparency in a shallow subtropical lake (Lake Okeechobee, Florida, USA). The aim was to evaluate changes in the risk of N2-fixing cyanobacterial blooms, which have infrequently occurred in the lake's pelagic zone. Predictions regarding bloom risk were based on previously published N:P ratio models. Temporal trends in the biomass of cyanobacteria were evaluated using phytoplankton data collected in 1974, 1989-1992, and 1997-2000. Concentrations of pelagic total P increased from near 50 microg l-1 in the mid-1970s to over 100 microg l-1 in the late 1990s. Coincidentally, the total N:P (mass) ratio decreased from 30:1 to below 15:1, and soluble N:P ratio decreased from 15:1 to near 6:1, in the lake water. Published empirical models predict that current conditions favor cyanobacteria. The observations confirm this prediction: cyanobacteria presently account for 50-80% of total phytoplankton biovolume. The historical decrease in TN:TP ratio in the lake can be attributed to a decreased TN:TP ratio in the inflow water and to a decline in the lake's assimilation of P, relative to N. Coincident with these declines in total and soluble N:P ratios, Secchi disk transparency declined from 0.6 m to near 0.3 m, possibly due to increased mineral turbidity in the lake water. Empirical models predict that under the turbid, low irradiance conditions that prevail in this lake, non-heterocystous cyanobacteria should dominate the phytoplankton. Our observations confirmed this prediction: non-N2-fixing taxa (primarily Oscillatoria and Lyngbya spp.) typically dominated the cyanobacteria community during the last decade. The only exception was a year with very low water levels, when heterocystous N2-fixing Anabaena became dominant. In the near-shore regions of this shallow lake, low N:P ratios potentially favor blooms of N2-fixing cyanobacteria, but their occurrence in the pelagic zone is restricted by low irradiance and lack of stable stratification.     

A reevaluation of the cultural eutrophication of Lake Okeechobee using multiproxy sediment records.

Lake Okeechobee, the hydrological lynchpin of the Everglades ecosystem, is the subject of an ambitious, multiagency restoration effort aimed at reducing phosphorus inputs and resulting algal blooms and impaired water clarity. This restoration is predicated on returning the lake to something closer to its predisturbance condition, but that goal has been challenged on the premise that the lake has always been eutrophic. The resolution of this debate and the appropriateness of the nutrient reduction goals thus depend on obtaining a reliable sediment record of past limnological conditions--the aim of this study. Because of the potential for severe sediment mixing from tropical storms, this investigation used multiple dating tools to examine the integrity of the sediment record and then analyzed proxies for nutrient enrichment, phytoplankton composition, and paleoproductivity. Sediment profiles for atmospheric pollutants, fertilizer contaminants, and radiocesium from three widely spaced cores showed good preservation of stratigraphic detail and coherence with the 210Pb chronologies. These results demonstrated that sediment stratigraphy is largely intact and retains a reliable record of limnological change. Geochemical proxies provide strong evidence of increased nutrient loading beginning ca. 1950. Concentrations of sediment P double, and N:P and C:N ratios drop, while those for N isotopes (delta15N) increase. At the same time, tracers of phosphate fertilizers (uranium, vanadium, and arsenic) rise. These changes are synchronous among cores and constitute a robust, internally consistent record of increasing water-column P. Biotic responses are manifested in higher concentrations and in changing composition of fossil algal pigments, including (1) large increases in the concentrations of chemically robust carotenoids, (2) corresponding decreases in the ratios of pigments from diatoms to chlorophyte and cyanobacterial algae, and (3) increases in UVR-photo-protective compounds indicating greater prevalence of surface algal blooms. This study provides strong evidence that Lake Okeechobee has experienced accelerated eutrophication linked with post-1950s land use changes in its watershed, a conclusion consistent with the nutrient reduction goals of the Lake Okeechobee Protection Program. The results contradict recent claims that the lake's trophic state has not changed over time, as well as the assertion that sediments of large shallow lakes cannot support a reliable chronology of past events.     

Agenda 21 Realisierungsmöglichkeiten an Hochschulen

Chapter 36 from the Agenda 21 which was held at the Conference for the Environment and Development in 1992 provides suggestions for ?promoting education, public awareness and training“ and important contributions for continuing developments in the universities. The goals which have been mentioned here can only be realized on a long-term basis. A work group at the University in Furtwangen has concentrated on the adaptation of this theme since 1991. After five years, it is now possible to draw a provisional balance: The disciplines of the environment, technology, law and ecology are bound together through a reformed course of studies in the field of process engineering. The certification based upon the EC eco-auditing ordinance offers new prospects for increasing the integration of environmental aspects on a broad basis into the routine university life. The establishment of a regional environmental center provides a possibility for the exchange of knowledge as a joint venture.     

Langzeitmonitoring möglicher Auswirkungen gentechnisch veränderter Pflanzen auf Pflanzengesellschaften Konzeptentwicklung am Beispiel von Raps (Brassica napus)

Ecological monitoring of genetically engineered plants (GEPs) is being developed in the Bavarian Environmental Protection Agency. Focusing on oilseed rape (Brassica napus, Cruciferae), a method is being established to measure the impact of the commercial release of GEPs on plant communities. Oilseed rape is known to escape from cultures and to establish outside the fields. It also produces hybrid offspring with wild relatives of the European flora. The study site is located in Bavaria (Germany) and comprises an area of 5700 ha. It is characterized by a mosaic of protected natural habitats in close vicinity to intensively cultivated farmland. In this region species composition and population density of Cruciferae is documented prior to a possible commercial release of GEPs. Furthermore Cruciferae of the study site are tested for the presence of transgenes. Therefore, plant material of selected Cruciferae is randomly sampled. We also test oilseed rape honey from the study site and pollen from pollen traps for the presence of hybrid pollen. The molecular method used is the ‘real-time PCR’. In addition, an intensive monitoring program is established in two types of biotopes, which are located in the study site. Multivariate statistics are being used to correlate plant community data with soil parameters.     

Deponiesickerwässer: Bestimmung zytotoxischer Wirkungen mit dem Pollenschlauchwachstumstest

For risk assessment of environmental samples, rapid and sensitive screening assays for detection of toxic potencies are required. Using leachates from waste deposites in the industrial region Leipzig-Halle (Germany) as an example, we present a simple test procedure suitable for the detection of cytotoxic effects of samples. This method, the pollen tube growth test (PTG), works as follows: Pollen of tobacco (Nicotiana sylvestris Spegazz, & Comes) are suspended in mixtures of growth medium and buffered (pH 6,3 to 7,0) dumping ground leachates. After an 18h-incubation period, growth of pollen tubes is quantified by staining with Alcian blue and subsequent measurment of optical density in a photometer. Sample induced inhibition of pollen tube growth is calculated in relation to controls maintained in pure growth medium. The PTG test shows high sensitivity towards leachates of different chemical composition, and it shows good agreement with assay results from luminescent bacteria tests. We conclude that the PTG test is well suited to assess the hazardous potential of aqueous environmental samples.     

渔民的利益和合作:瑞典沿岸渔业共同管理的前提

本文在"共同管理"、"参与性管理"或"地方管理"等概念下用不同的理念探讨了渔民参与渔业管理的问题.瑞典渔业范围内的经验研究阐明了关于渔民参与渔业管理先决条件的新观点.在影响成败的重要因素中,我们这里着重探讨了其中两个:渔民利益的明确表达、组织及代表问题和通常参与资源管理合作的各群体即:渔民、政府管理人员以及研究人员之间的信任.本文所概述的研究论及了渔民在资源管理、地方渔业管理方面的利益以及渔民的参与.连接这三个主题的问题是:在渔业管理中如何更好地反映渔民的利益?利益与信任,即"软事实",对于渔业管理和参与的成败而言,可以犹如所有权、资源的数量和质量或资源的货币价值之类的"硬事实"一样的重要.