Great Lakes algae -- an example of polluted data
In the 1970s there was considerable fuss over algal growth in the Great Lakes which might be stimulated by phosphorus pollution. There was reason for concern. But in one important case - that of Lake Michigan - the data generating such concern were themselves found to be ''polluted.''
Joseph Shapiro and Edward B. Swain, limnologists at the University of Minnesota, have studied the original data base. They find it to be of such poor quality that, they say, ''. . . it is not safe to conclude anything about long-term trends in Lake Michigan from these data.''
The story began in the 1960s, when studies of data from water treatment plants seemed to show a long-term decline of the silica (silicon dioxide) content of the lake. Phosphorus pollution from detergents, fertilizers, and other man-made sources was later suspected of stimulating diatoms to use up the silica faster than they normally would. Diatoms are microscopic algae that build silica shells. It was suggested that, as the water's silica content declined, diatoms would also decline and undesirable blue-green algae would eventually dominate the lake's algal population.
This hypothesis, which the water treatment data seemed to support, was widely accepted. It was included in limnology textbooks and cited in litigation. Shapiro and Swain say they cited it repeatedly themselves until they took a detailed look at the supposedly supporting data.
As they explain recently in Science, they found these data to be deceptive. For example, water analysis data taken at Chicago seem to show a significant decline in silica content from 1926 to 1962. But the data, in fact, are not continuous. There is an abrupt drop in average silica content around 1948 which coincides with a change in the laboratory that made the analyses. Looking at data from other points, Shapiro and Swain find they were not well calibrated against each other so as to form a compatible data set.
They say that ''the 1948-49 (silica) change was probably 'in the laboratory' and not in the lake.'' Taking the data as a whole, Shapiro and Swain find they don't support the popular hypothesis of a silica decline in Lake Michigan which led to blooms of blue-green algae and was linked to pollution. The data simply aren't good enough to substantiate any conclusion about long-term trends in the lake.
This is unfortunate. If the data had been gathered carefully, the limnologists say, the Lake Michigan analyses could have been ''an unparalleled environmental record.'' As it is, they generated a spurious theory which spread through the scientific literature and was cited in making polution-control policy.
The problem, the two scientists say, is that the data were gathered for purposes of monitoring water quality on a year-by-year basis and by different authorities. There was no thought of combining them to form a data base with which to study environmental trends.
Yet Shapiro and Swain note, ''Those agencies doing analyses . . . year after year, for whatever reason, have a largely unrecognized obligation (and opportunity) to carry out monitoring of long-term trends.'' Indeed they do. And since such environmental trends may be important for the public, those agencies should make sure their data are up to the standard needed for scientific analysis. Volcanic harvests
People suspect that volcanoes affect weather. But proof is usually lacking. Now two oceanographers have found a definite correlation between volcanic eruptions and delays in the European grape harvest.
The oceanographers - Henry Stommel of the Woods Hole (Mass.) Oceanographic Institution and John C. Swallow of Britain's Institute of Oceanographic Sciences - say their results do ''not imply that all volcanoes lead to late grape harvests, only that a substantial number do.'' Nevertheless, they do appear to have come up with an intriguing correlation, which they report in the Bulletin of the American Meteorological Society.
The oceanographers took advantage of two data sets that have become available in the past two years. A listing of European grape harvest dates has been prepared by French scientists Emmanuel Le Roy Ladurie of the College de France and Micheline Baulant of the Centre National de la Recherche Scientifique. They have worked grape harvest data into a single composite date for each year from 1484 to 1879. Those harvest dates were matched with relevant eruption dates in a list of known volcanic outbursts occurring over the past 10,000 years, which has been issued by the Smithsonian Institution.
The eruptions are ranked according to a Volcanic Explosivity Index (VEI), running from 0 through 7. There was only one great eruption with a VEI of 7 during the period covered by the harvest dates - that of Mt. Tambora in 1815. The 1816 grape harvest was indeed delayed. Stommel and Swallow note that this was the famous ''Year Without a Summer,'' marked by an excessively cold, wet summer and many crop failures in Europe as well as parts of North America.
There were no VEI 6 eruptions during the relevant period. But there were eight in the VEI 5 category and 44 with a rank of VEI 4. Matching these up with the corresponding grape harvest dates, Stommel and Swallow find ''positive results'' indicating that volcanic debris, thrown into the atmosphere and circling Earth, does indeed affect weather. It affects it enough to delay Europe's grape harvest by several days to as much as a fortnight from average.
The oceanographers do not speculate about the mechanisms of the volcanic weather influence. Many climatologists suspect that the veil of dust and, especially, of acid particles thrown into the stratosphere by major eruptions may dim sunshine reaching the lower atmosphere. This could induce at least a slight cooling in some regions.
