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Hypoxia and cyanobacteria still occur occasionally in large, mesotrophic Lake Simcoe, and total phosphorus (TP) concentration has remained relatively constant despite external nutrient load reduction. This may indicate a potential internal P source. Internal load as redox-dependent P release from bottom sediments is hard to determine in such a relatively shallow and mostly mixed lake. This study represents the first attempt to quantify internal P loading over many years for the three main sections of Lake Simcoe. Internal load was determined (a) as in situ estimate based on TP increases between July and October and (b) as gross estimate from the product of experimentally determined P release rates and hypoxic extent of sediment surfaces in space and time. Hypoxic extent was quantified (1) as the hypoxic factor determined from dissolved oxygen profiles below the level of 3.5 mg/L, and (2) as active sediment area release factor (AA) modeled from summer euphotic TP concentration, which is especially useful in the mixed sections. Annual internal load for the whole lake was determined as a near constant 62.2 metric tonnes/yr (86 mg/m2/yr) for 1980-2011 using the gross estimates of the AA approach and 88 t/yr before and 53 t/yr after external load abatement and zebra mussel invasion using in situ estimates. Means of in situ and AA-based estimates for 2000-2011 are in close agreement except for polymictic Cook's Bay. These estimates are 45 to 89% of external load, which suggests that internal loading is an important source of P in Lake Simcoe. [ABSTRACT FROM AUTHOR]

Hypoxia and cyanobacterial blooms were extensive in Lake Simcoe during the 1980s and are still a problem to a lesser degree despite extensive nutrient load reduction from the catchment basin. The continuing signs of productivity indicate a potential internal phosphorus (P) source. Internal P load, as a redox-dependent release from bottom sediments, is hard to determine in a large, relatively shallow and partially unstratified lake such as Lake Simcoe. Of the lake's three major basins, only Kempenfelt Bay stratifies long enough to develop hypoxia in the stagnant summer hypolimnion. The following indications of sediment P release are available from historic data: 1) hypolimnetic hypoxia still occurs in Kempenfelt Bay although the hypoxic factor (number of days that an area equal to the bay's surface area is overlain by water of ⩽2 mg/L dissolved oxygen, DO) has decreased substantially and significantly from 15.8 d/yr (1980-1994) to 4.0 d/yr (1995-2011); 2) hypoxic factors for other lake sections and at different DO levels also indicate widespread hypoxia; 3) concentrations of redox dependent metals, Fe and Mn, increase with depth; and 4) euphotic zone P and chlorophyll concentrations increase and water clarity decreases during fall turnover. Cyanobacterial blooms appear to occur in response to internal load as supported by occasional cyanobacteria counts. These indicators provide evidence that internal loading is likely occurring and affecting the water quality in Lake Simcoe. We expect that further monitoring, specific for internal load, will corroborate these results [ABSTRACT FROM AUTHOR]

A recessive hairless mutation arose spontaneously in a congenic line of spontaneously hypertensive rats SHR.BN-(D1Mit3-Igf2)/Ipcv. The mutant rats develop generalized alopecia except for partial hair growth on their heads. Affected animals of the congenic line were crossed with LEW rats and randomly bred for several generations. A genome scan in 74 affected and 75 unaffected offspring localized the mutant gene on rat chromosome 18p12, near the marker D18Rat107, which is closely linked to the desmosomal cadherin gene cluster, syntenic to mouse chromosome 18 and human chromosome 18q12. Recently, the mouse and rat phenotypeslah/lah(lanceolate hair) andlahJ/lahJ(lanceolate hair-J) were found to be caused by mutations in the desmoglein 4 (Dsg4) gene. Direct sequencing of theDsg4gene in the SHR revealed a homozygous C-to-T transition generating a premature termination codon within exon 8 in the affected animals. Further studies on the skin histology in affected rats demonstrated features consistent with alanceolate hairmutation, providing further support for the crucial role of desmoglein 4 in hair shaft differentiation. [ABSTRACT FROM AUTHOR]