Self-maintaining plankton: pelagic Cladocera in small microcosms with lake water

Monospecific and mixed populations of pelagic cladocerans, Daphnia galeata, Bosmina coregoni, and Diaphanosoma brachyurum of Lake Glubokoe (Moscow Region) were isolated in 0.6 litre flasks with their natural medium — epilimnion water. In the laboratory they persisted for more than 100 days without external additions of food until the experiment was stopped. In three-species cultures Diaphanosoma was outcompeted, but in the presence of only Bosmina it persisted. Daphnia coexisted with Bosmina in two- and three-species cultures the whole period of observations in spite of competition. Birth and death rates of animals in microcosms depended on their density indicating that experimental conditions did not spoil natural population regulation. Demographic time lags underlay the observed oscillations in numbers. Because the time of Cladocera persistence in the cultures was comparable with lake vegetational period I conclude that summer zooplankton is capable of existing solely at the expense of nutrient recycling within epilimnion. Density regulation of cladocerans reinforces the stability of the system herbivore — algae, but it is weakened by the demographic time lags.     

Benthic community response (primarily Chironomidae) to nutrient enrichment and alkalinization in shallow,soft water humic lakes

A comparison of the benthic fauna found in two shallow lakes in the New Jersey Pinelands (USA) illustrated the impact of elevated pH and nutrients caused by residential and agricultural disturbance on a naturally acidic, poorly buffered aquatic environment. Detailed community analysis suggested that change in community composition was a better indicator of response to disturbance than biological diversity indices. Chironomidae (insecta) were the predominant components of the benthic macroinvertebrate assemblage of both undisturbed Oswego Lake (low pH, low nutrients) and Nescochague Lake (fluctuating pH, elevated nutrients). The genera Procladius, Tribelos, and Pagastiella dominated Oswego Lake, where as Zalutschia zalutschicola, Procladius, Dicrotendipes, and Tanytarsus dominated Nescochague Lake. Glyptotendipes was a common and unique member of the Nescochague Lake assemblage. Cluster analysis indicated that the chemical differences between lakes were the most important community determinants, although, within each lake, depth and substrate affected the local communities. Oswego Lake exhibited a depauperate nonchironomid benthic fauna typical of low nutrient, acid lakes. In turn, Nescochague Lake exhibited an enriched nonchironomid fauna including mollusks and planaria which were not found in Oswego Lake.     

Response of lakes to the reduction of phosphorus load

On occasion of the publication of a book (H. SAS, ed.) a discussion of the predictability of the response of eutrofied lakes on a reduced external phosphorus loading is presented. Whereas the OECD study examines the correlations between nutrient loading and indicators for eutrofication for groups of lakes, the book discusses the direction of the response on reduction of the phosphorus loading for individual lakes. Although this is a valuable analysis that can increase the insight in the mechanisms controlling lake responses, neither the OECD study nor this book yield sufficiently unquestioned data that can be used directly in a a management framework. The relationships between loading and inlake concentration and between phosphate concentration and chlorophyll are discussed in some detail.     

Puddling in butterflies: sodium affects reproductive success in Thymelicus lineola*

ABSTRACT. Adults of many species of Lepidoptera, principally the males, frequent mud puddles, edges of streams, carrion and animal excreta where they imbibe moisture, an activity referred to as 'puddling' Sodium ions are the only known stimulus present which cause males of at least two lepidopteran species to drink for extended periods. In the European skipper Thymelicus lineola (Ochsenheimer) (Lepidoptera: Hesperiidae), only males puddle, even though they have concentrations of abdominal sodium 2–3 times that of females at emergence. During their first mating, males transfer 32% of their abdominal sodium to females. This could be of considerable importance given that an average egg complement contains >50% of the total body sodium of females at emergence. Virgin females, as well as having reduced fecundity, have reduced longevity. This is attributed to virgins not obtaining important nutrients which males transfer to females during mating. Access to sodium ions increases the total number of matings by c. 50% for males living >15 days. Access to sodium ions by once-mated males increases the percentage of males which re-mate on the day following first mating; the percentage of females, mated to the twice-mated males, which lay >50% fertile eggs; and the drought resistance of eggs laid by those females.     

Transport of phosphorus,nitrogen, and carbon by the Apure River,Venezuela

The concentrations and transport of carbon, nitrogen, and phosphorus were studied in the Apure River, Venezuela, over a period of 21 months. The drainage basin, which is in western Venezuela, encompasses 167,000 kM², most of which has low relief and supports tropical savanna vegetation. Average runoff for the period of study was 361 mm/year. Discharge-weighted mean concentrations were 188 ug/l for total P, 957 ug/l for total N, and 9.8 mg/l for organic C. Annual transport was 0.68 kg· ha^-1· year^-1 for total P, 3.45 kg · ha^-1· year^-1 for total N, and 35.4 kg · ha^-1 · year^-1 for organic C. Particulate matter accounted for 68% of P, 54% of N, and 37% of C transport. The yield of carbon from the Apure watershed agrees well with empirical predictions, based mostly on the temperate zone, for watersheds of similar size and water yield.Seasonal patterns in chemistry are tied strongly to the hydrologic cycle. When the wet season begins, rising water flushes organic matter from side channels and produces a sharp increase in particulate C and N. Particulate P, which is associated more with mineral material, also increases during rising water. All dissolved constituents except inorganic C also increase over the rising-water phase. As the river inundates the floodplain, the concentration of nitrate declines, whereas the concentrations of dissolved organic C and N continue to rise. At high water the floodplain appears to store sediments that are later remobilized. During low water, all fractions except dissolved inorganic C tend to be at minimum concentration.Soluble reactive P, total dissolved P, dissolved inorganic C, and dissolved organic C were successfully modelled as hyperbolic functions of discharge. No significant relationships were found between concentration and discharge for any particulate fraction because the flushing and storage mechanisms affecting these fractions occurred within specific hydrologic phases, rather than as a smooth function of discharge. No significant relationships were found for any nitrogen fraction. For nitrate, and thus for total dissolved N, of which nitrate is a major component, poor conformance to standard models is explained by association of key mechanisms (e.g. uptake) with specific hydrologic phases. Particulate components and nitrate in this sense violate the continuity assumptions implicit in the standard models.     

The effect of extracellular calcium elevation on morphology and function of isolated rat osteoclasts

Osteoclasts are large multinucleate cells unique in their capacity to resorb bone. These cells are exposed locally to high levels of ionised calcium during the process of resorption. We have therefore examined the effect of elevated extracellular calcium on the morphology and function of freshly disaggregated rat osteoclasts. Cell size and motility were quantitated by time-lapse video recording together with digitisation and computer-centred image analysis. In order to assess the resorptive capacity of isolated osteoclasts, we measured the total area of resorption of devitalised cortical bone by means of scanning electron microscopy and computer-based morphometry. The results show that elevation of the extracellular calcium concentration causes a dramatic reduction of cell size, accompanied by a marked diminution of enzyme release and abolition of bone resorption. We propose that ionised calcium might play an important role in the local regulation of osteoclastic bone resorption.     

Phosphorus and nitrogen retention in five Precambrian shield wetlands

Phosphorus and nitrogen mass balances of five wetlands (two beaver ponds, two conifer-Sphagnum swamps and one sedge fen) situated in three catchments in central Ontario, Canada, were measured. Monthly and annual input-output budgets of total phosphorus (TP), total nitrogen (TN), total organic nitrogen (TON), total inorganic nitrogen (TIN), ammonium ion (NH₄ ⁺ -N), nitrate (NO ₃ ^– -N) and dissolved organic carbon (DOC) were estimated for the five wetlands during the 1982–83 and 1983–84 water years. Except for the deepest beaver pond (3.2 m) which had annual TP retention of –44% (–0.030 ± 0.015 g m^–2 yr^–1), the wetlands retained < 0.001 to 0.015 g M^–2 yr^–1 ; however, this wasless than 20% of the inputs and the estimated budget uncertainties were equal to or greater than the retention rates. Annual TN retentions ranged from –0.44 to 0.56 g m^–2 yr^–1 (–12 to 4%) but were not significantly different from zero. The wetlands transformed nitrogen by retaining TIN (16 to 80% RT) and exporting an equivalent amount as TON (–7 to 102% RT). The beaver ponds, however, retained NO ₃ ^– while NH ₄ ⁺ was passed through or the outputs exceeded the inputs. In contrast, the conifer swamps retained both NH ₄ ⁺ and NO ₃ ^– . DOC fluxes into and out of the beaver ponds were equal (–18 and 4% RT) but output from the conifer swamps exceeded input by > 90%. Marked seasonal trends in nutrient retention were observed. Nutrient retention coincided with low stream flow, increased evapotranspiration and biotic uptake during the summer. Net nutrient export occurred during the winter and spring when stream flows were highest and biotic uptake was low.     

The application of algal growth potential tests (AGP) to the canals and lakes of western Netherlands

Four hundred and forty bioassays with Scenedesmus quadricauda (Turp.) Bréb. as a test organism have been carried out with samples from canals and lakes in the western part of the Netherlands. The results are used to assess the algal growth potential (AGP) and to determine the limiting nutrient(s) for maximum biomass production. Special attention has been paid to the effects of deep-freezing and autoclaving as pretreatment of water samples on pH and nutrient concentrations.The AGP ranged from very low in the relatively isolated polder lakes to very high in canals and lakes, which form part of the basin system of Rijnland. The lowest yields are observed in nitrogen and phosphorus co-limited waters, while the highest are found in waters limited by nitrogen alone. AGP proved to be primarily determined by the amount of nitrogen, especially nitrate, in the samples and only secondarily by the amount of phosphorus.The observed ranges indicating phosphorus limitation, > 50 for inorganic and > 30 for total N/P ratios, lie considerably higher than reported so far. It is concluded that, once the relations between AGP and nutrients are established, AGP tests do not have to be carried out routinely, but still can be very useful in special studies, e.g. in lake restoration projects.     

Transpiration/biomass ratio for carrots as affected by salinity,nutrient supply and soil aeration

The influence of salinity, nutrient level and soil aeration on the transpiration coefficient, defined as amount of water transpired/unit biomass produced (transpiration/biomass ratio) of carrots was investigated under non-limiting conditions with respect to water supply.Under optimum conditions and favorable nutrient supply, the transpiration coefficient amounted to 280–310 g H₂O g^–1 storage root dry weight (RDW). The transpiration coefficient did not change significantly up to salt concentration of 16 mS cm^–1 in the soil solution under otherwise optimum conditions. Higher salt concentrations or low nutrient levels increased the transpiration coefficient to values of 390–540 g H₂O g^–1 RDW. It is suggested that the transpiration coefficient is not affected by salinity as long as toxic effects and nutrient imbalances do not occur. The transpiration coefficient was not increased by impeded soil aeration. Biomass production was more negatively influenced by adverse soil conditions (salinity, low nutrient level, impeded soil aeration) than was the transpiration coefficient.