Environmental control and limnological impacts of a large recurrent spring bloom in Lake Washington, USA.

A series of statistical analyses were used to identify temporal and spatial patterns in the phytoplankton and nutrient dynamics of Lake Washington, an mesotrophic lake in Washington State (USA). These analyses were based on fortnightly or monthly samples of water temperature, Secchi transparency, ammonium (NH(4)), nitrate (NO(3)), inorganic phosphorus (IP), total nitrogen (TN), total phosphorus (TP), dissolved oxygen (DO), pH and chlorophyll a (chl a) collected during 1995-2000 from 12 stations. Lake Washington has a very consistent and pronounced annual spring diatom bloom which occurs from March to May. During this bloom, epilimnetic chl a concentrations peak on average at 10 microg/L, which is 3 times higher than chl a concentrations typically seen during summer stratified conditions. The spring bloom on average comprised 62% diatoms, 21% chlorophytes and 8% cyanobacteria. During summer stratification, diatoms comprised 26% of the phytoplankton community, chlorophytes 37% and cyanobacteria 25%. Cryptophytes comprised approximately 8% of the community throughout the year. Overall, 6 phytoplankton genera (i.e., Aulacoseira, Fragilaria, Cryptomonas, Asterionella, Stephanodiscus, and Ankistrodesmus) cumulatively accounted for over 50% of the community. These analyses also suggest that the phytoplankton community strongly influences the seasonality of NO(3), IP, DO, pH and water clarity. According to a MANOVA, seasonal fluctuations explained 40% of the total variability for the major parameters, spatial heterogeneity explained 10% of variability, and the seasonal-spatial interaction explained 10% of variability. Distinctive patterns were identified between offshore and inshore sampling stations. The results of our analyses also suggest that spatial variability was substantial, but much smaller than temporal variability.

Outcome of women referred to colposcopy for persistently inadequate smears.

The outcome of referral to colposcopy of 240 women who had persistently inadequate smears was investigated. Of 232 women who attended colposcopy, 214 (92.2%) had a normal outcome, 12 (5.2%) had low grade abnormalities, and six (2.6%) had high grade abnormalities. This group of women therefore has a negligibly increased risk of harbouring cervical neoplasia. Although not directly comparable, women with a history of previous abnormal cytology did not have a higher risk than those without such a history. Unnecessary colposcopy could have been avoided in the majority of cases if a good quality repeat smear had been taken. Improved smear taker training could decrease the number of referrals. A hospital cytology clinic is proposed as a cost-effective alternative to colposcopy at the first attendance.