Historical changes in epilimnetic phosphorus concentrations in six rural lakes in Northern Ireland

1. Sediment cores were taken from six lakes in Northern Ireland: Loughs Heron, Ballywillin, Corbet, Patrick, Brantry and Creeve. The present-day total phosphorus (TP) concentrations of these lakes range from around 30 to 400 μg TP l^–1. None of the lakes have sewage point-sources disposing into them, and all have primarily agricultural catchments. 2. Sediment cores were dated using ²¹⁰Pb. The cores cover time periods ranging from about 100 years at Lough Corbet to periods considerably greater than the range of ²¹⁰Pb (more than 150 years), Lough Patrick. 3. Diatom stratigraphies indicate considerable ecological change at all the lakes, regardless of their current nutrient status. Epilimnetic phosphorus concentrations were inferred using weighted averaging regression and calibration. Diatom-inferred TP values for the core surface samples agreed reasonably well with the contemporary values. Pre-1900 TP concentrations range from about 10 μg TP l^–1 at Lough Patrick to 80 μg TP l^–1 at Lough Corbet. The higher values prior to 1900 are assumed to relate to land-clearance activities and the expansion of agriculture associated with the Plantation period. 4. Although there are increasing diatom-inferred TP concentrations between 1850 and 1900 at some sites, there is a final and more marked increase at all lakes after 1950. Phosphorus concentrations have increased at all lakes, by between a factor of three to five, over an average 50-year period. At four of the lakes, TP concentrations have been increasing linearly from around 1950 to the present day, suggesting that, in general, there is little sign of amelioration of the eutrophication problem. 5. The post-1950 increases are assumed to relate to changes in agricultural activity within their catchments, notably the continued improvement in field drainage, which has facilitated transfer of nutrients to water courses and lakes and increasing soil-P concentration due to a positive annual-P balance. Another factor, probably associated with increased animal grazing densities and improvement of grassland, is the application of animal slurries, which appears to be a largely unquantified factor.     

Effects of Calcitonin on <Superscript>85</Superscript>Sr Whole Body Retention in the Dog

BECAUSE of its inhibitory action on bone, long term administration of calcitonin could be beneficial to humans who have high rates of bone turnover. Nearly all experiments involving calcitonin have been of the order of only a few days or less; we now report a longer study of the effects of calcitonin on the whole body retention of strontium-85 by normal and thyroparathyroidectomized pure bred beagle dogs.     

The Control of the Reptilian Gonad

In reptiles, there is adequate evidence to indicate environmentalcontrol of the ovarian cycle through hvpothalamic pathways andthe subsequent release of tropic hormone (s) from the anteriorpituitary. The role of the pineal-parietal complex still remainsto be elucidated. In the hypothalamus there appear to be steroidsensitive areas and both progesterone and estrogen appear tohave important feedback influences upon gonadal growth ovulation,and ovarian steroid production. Cytological studies of the reptilianpituitary indicate similar cell types to those observed in mammalianpituitaries, but thus far, two gonadotrophs cannot be identifiedwith any certainty. Chemical and biological studies of the actionof mammalian gonadotropuis suggest that in reptiles hormoneswhich are FSH-like in mammals are able to stimulate gonadaldevelopment, ovulation, and steroid biosynthesis under certainconditions. Preliminary studies of the chemistry of turtle gonadotropuishave so far demonstrated only one active principle, which ischemically similar to mammalian LH, but is far more active thanthe latter hormone in reptilian systems. Further, the hormonealso has FSH-like activity in the reptile. Thus reptilian gonadaldevelopment can be stimulated by treatment with a variety ofmammalian gonadotropins. Recent studies have indicited an importantrole for growth hormone, acting in concert with gonadotropinand estrogen in the regulation of vitellogenesis and ovariangrowth. Piolactin appears to be an antigonadal agent in reptiles,as does progesterone. The exact manner in which these hormonesexert their antigonadal action remains to be clarified, butat least one site of action is the central nervous system; othersites maybe the liver and the fat depot. Ovarian tissue from reptiles is able to synthesize and secretesteioid hormones by pathways similar to those present in mammalianovaries. Circulating levels of estrogen have not been measured,but progesterone levels in the blood show distinct changes assocntedwith pregnancy and the presence of corpora lutea in the ovary.     

Utility of a set of microsatellite primers developed for the massasauga rattlesnake (Sistrurus catenatus) for population genetic studies of the timber rattlesnake (Crotalus horridus)

I tested six microsatellite DNA primer pairs developed for the massasauga rattlesnake (Sistrurus catenatus) on a sample population of the timber rattlesnake (Crotalus horridus). It had been speculated in a previous publication that cross‐species amplification would not be worthwhile across the two rattlesnake genera. However, for this primer set (the only one currently published for the genus Sistrurus), successful amplification at each locus was accomplished for all loci with an annealing temperature of 57 °C and locus‐specific buffer conditions. Each locus was polymorphic, with the number of alleles per locus ranging from two to 12. Significant heterozygote deficits were detected for three loci (Scu01, Scu05 and Scu07). For Scu01, all individuals were homozygous for the same allele except one female who was homozygous for a different allele. This same female was also homozygous for a rare allele at Scu07. When this female was removed from the data set, the number of observed heterozygotes at Scu01 and Scu07 did not differ significantly from random expectations. However, a large heterozygote deficit persisted at Scu05 (despite subsampling), suggesting that this locus may not be useful for population genetic studies of timber rattlesnakes. Despite some limitations, this set of primers may be a useful complement to those already developed for the genus Crotalus. Moreover, the results of this study seem to provide new justification for further studies of cross‐species amplification of microsatellite loci across the two rattlesnake genera.     

Nutrient limitation of Myriophyllum spicatum growth in situ

SUMMARY. 1. The hypothesis that the submersed macrophyte biomass in natural weedbeds is nutrient limited was tested in situ by an enrichment experiment.
2. The response of Myriophyllum spicatum was significant and positive for N-enrichment, resulting in a 30–40% increase in biomass over controls. There was no response to phosphorus or to potassium enrichment.
3. Plant length and number of shoots per rephcate were also significantly increased by nitrogen additions but again showed no response to phosphorus and potassium.
4. Water depth differences were also found to affect the plant responses in some cases.
5. The macrophyte response to fertilization was similar to that recorded for emergent macrophytes and terrestrial crops but much smaller than for phytoplankton.