Eutrophication,recovery and temperature in Lake Mjøsa: detecting trends with monitoring data and sediment records

1. How climate warming may interact with other pressures on aquatic ecosystems is an important issue for research and management. We combined lake monitoring data with a palaeolimnological study to explore the combined effects of eutrophication and subsequent oligotrophication with a long‐term temperature increase in epilimnetic waters. Our goals were (i) to evaluate how well sediment‐based reconstructions reflect the instrumental observations, (ii) to use the palaeo‐record to characterise a reference state for the lake and (iii) to explore whether data from the sediment record can aid in separating the effects of nutrient load and temperature in a large and deep lake. 2. Lake Mjøsa is a large and deep lake in south‐eastern Norway. Eutrophication symptoms peaked in the 1970s, which led to extensive measures to reduce the phosphorus load. A monitoring programme has run continuously from 1972. Monitoring has documented a marked decrease in phosphorus load and algal biomass and also revealed an increase in epilimnetic temperature and extended summer stratification. 3. Records of algal pigments and diatoms were extracted from sediment cores taken from 236 m depth. The pigment record documented dramatic changes in lake production consistent with the monitoring record. The diatom record reflected well the eutrophication history of the lake and also demonstrated that the assemblage of the recent recovery stage differs from that of the pre‐eutrophication period. 4. Ordination of diatom assemblages over time constrained by proxies for nutrient load and temperature indicated that the diatom assemblage correlated with both factors, which together accounted for 60% of the variation in diatom composition. No interaction was detected between these factors. The results suggest that the diatom assemblage has responded to varying nutrient loads as well as to changes in temperature and/or factors that correlate with temperature. 5. Reconstructions of algal biomass and total phosphorus content mirrored known changes through the monitoring period, although the absolute phosphorus estimates were too high relative to the instrumental record. The sediment record from Lake Mjøsa provides a baseline for lake production in terms of algal pigments and organic contents, and for the diatom assemblage composition in a pristine stage.     

Identifying from recent sediment records the effects of nutrients and climate on diatom dynamics in Loch Leven

1. Changes in nutrients and climate have occurred over approximately the same timescales in many European lake catchments. Here, we attempt to interpret the sedimentary diatom record of a large shallow lake, Loch Leven, in relation to these pressures using information gained from analysis of long‐term data sets of water quality, climate and planktonic diatoms. 2. The core data indicate the enrichment of Loch Leven starting in c. 1800–1850, most likely from agricultural practices in the catchment, with a more marked phase since c. 1940–1950 caused by increased phosphorus inputs from sewage treatment works, land drainage and a woollen mill. 3. While the recent diatom plankton remains are dominated by taxa associated with nutrient‐rich conditions, an increase in Aulacoseira subarctica relative to Stephanodiscus taxa since the mid‐1980s suggests that reductions in external catchment sources of nutrients (since 1985) may have resulted in partial recovery. This observation accords well with the long‐term monitoring series of water chemistry and phytoplankton. 4. On a decadal‐centennial scale, the eutrophication signal in the sediment record outweighs any evidence of climate as a control on the diatom community. However, at an inter‐annual scale, while the diatom data exhibit high variability, there are several changes in species composition in the recent fossil record that may be attributed to climatic controls. 5. The study highlights the value of a palaeolimnological approach, particularly when coupled with long‐term data sets, for developing our understanding of environmental change at a range of temporal scales. The diatom record in the sediment can be used effectively to track recovery from eutrophication, but requires greater understanding of contemporary ecology to fully interpret climate impacts. 6. The study illustrates the complexity of ecosystem response to synchronous changes in nutrients and climate, and the difficulty of disentangling the effects of these multiple, interacting pressures.     

The Effects of Red, Far-red, and Blue Light on the Geotropic Response of Coleoptiles of Zea mays

The effects of red, far-red, and blue light on the geotropicresponse of excised coleoptiles of Zea mays have been investigated.Seedlings were grown in darkness for 5 or 6 days, exposed tovarious light treatments, and then returned to darkness fordetermination of the geotropic response. The rate of response of the coleoptiles is decreased after theyhave been exposed to red light (620–700 mµ, 560ergs cm^–2sec^–1 for the 24 hrs, but not for the 4hrs, preceding stimulation by gravity. Furthermore, their rateof response is greatly reduced if they are exposed to red lightfor 10 min and then returned to darkness for 20 hrs before geotropicstimulation. At 25° C an interval of 6 to 8 hrs elapses between a 10-minexposure to red light and the first detectable decrease in thegeotropic response of the coleoptile. This interval can be lengthenedby exposing the seedlings to low temperatures (0° to 2°C) after the light treatment but cannot be greatly shortenedby increasing the duration of exposure to red light. Using a standard procedure of exposing 5-day-old etiolated seedlingsto light for various times, replacing them in darkness for 20hrs and then determining the response of the coleoptiles to4 hrs geotropic stimulation, it has been found that: (a) Exposureto red light for 15 sec significantly decreases the geotropiccurvature of the coleoptiles and that further reduction occurson increasing the length of the light treatment to 2 and 5 min.(b) Far-red light has no effect on the geotropic response ofthe coleoptiles but it can completely reverse the effect ofred light. After repeated alternate exposure to red and far-redlight the geotropic response of the coleoptile is determinedby the nature of the last exposure, (c) Complete reversal ofthe effect of red light by far-red radiation only occurs whenexposure to far-red follows immediately after exposure to red.The reversing effect of far-red radiation is reduced if a periodof darkness intervenes between the red and far-red light treatments,and is lost after a dark interval of approximately 2 hrs. The effect of red light on the rate of geotropic response ofthe coleoptiles is independent of their age and length at thetime of excision. Blue light acts in a similar way to red light, but the seedlingsare less sensitive to blue than to red light. Coleoptiles grown throughout in a mixture of continuous, weak,red, and far-red light have a lower rate of geotropic responsethan etiolated coleoptiles.     

The Immobilization Antigen of Paramecium aurelia is a Single Polypeptide Chain

The immobilization antigen (i-antigen) fraction of Paramecium aurelia syngen 4 is shown to contain a protease that is activated by mercaptoethanol. After the protease has been heat-inactivated, the molecular weight of the i-antigen (∼250,000 daltons) cannot be decreased by mercaptoethanol treatment. It is demonstrated that the i-antigen is a single polypeptide chain. Reasons are also given why low molecular weight subunits were previously reported by other authors.     

The Effect of Boron on the Breaking, and Possible Control of Dormancy of Seed of Themeda triandra Forsk

Dormancy of the caryopsis of Themeda triandra Forsk. was shownto be broken by the addition of boron to the germinating media.Further boron was found to stimulate the germination processes.This effect was specific for boron, as no response was observedwith zinc, copper, manganese, iron, cobalt, and molybdenum inthe germinating medium. Evidence is put forward suggesting thatdormancy is regulated by the state of the endogenous boron inthe caryopsis. Gibberellic acid was also found to break dormancy,but the effect of gibberellic acid was never as great as thatobserved with boron. Maximum effect was observed in the presenceof boron and gibberellic acid together in the medium. The relationships between boron and gibberellic acid are discussed.     

Nucleic Acid Conformation: Crystal Structure of a Naturally Occurring Dinucleoside Phosphate (UpA)

THEORIES of the molecular structure of nucleic acids have so far been based on evidence from the crystal structures of monomeric units such as nucleosides and mononucleotides, the interpretation of diffraction patterns of oriented nucleic acid fibres and molecular model building^1–6. Such approaches can help to suggest structures of periodic molecules such as helices, but they are insufficient for predicting and understanding nonrepetitive structures such as the loops in transfer RNA (tRNA), presumably associated with many of the functions of tRNA. To understand the geometry of nucleic acids and possible constraints on their conformation, it is therefore essential to know the detailed conformation of the sugar residues and the conformational relationship between the sugar residue, the base and the phosphate group^7–9. The simplest molecule which contains this information is a 3´5´-dinucleoside phosphate. We now report the structure of uridine-3´,5´-adenosine phosphate (UpA). This is the first naturally occurring dinucleoside phosphate whose crystal structure has been determined by X-ray diffraction. The only other dinucleoside phosphate with known crystal structure is adenosine-2´,5´-uridine phosphate¹⁰, but it does not have the naturally occurring 3´5´ sugar phosphate linkage.     

The Effect of Host Constitution on the Development of Plasmodium floridense*

More than 15,000 lizards from South Georgia were examined over a period of 16 years. Five percent of Sceloporus undulatus and 36% of Anolis carolinensis were found to harbor Plasmodium floridense. Development of 28 natural new infections was followed in detail as soon as they became patent and comparisons in the 2 host species made of intensity and duration of infections and of merozoite means during the periods of acute rise and decline. During the acute rise, the merozoite mean in Sceloporus was 10.6 ± 0.11 (8,495 segmenters counted), compared with 13.44 ± 0.15 in Anolis (3,805 counted); during the decline, the merozoite means were 8.55 ± 0.13 (3,305 counted) and 10.28 ± 0.09 (6,772 counted), respectively. It took an average of 150 (100–253) days for the infection to run its course in Sceloporus, compared with the average of 71 (60–90) days in Anolis; the peak of parasitemia in Sceloporus was 11,600 parasites/10,000 red cells, compared with 1,600 in Anolis. Both lizard genera produced 5–10% gametocytes.