Secchi Dip-In Results

The Transparency of North American Volunteer-Monitored Waterbodies 1994-2010

Most, but not all of the 41,000 records have been submitted from North America. Even within North America, the distribution of data is uneven. It is thought this is the result of lack of paraticipating monitoring programs in these regions and perhaps a scarcity of waterbodies.

The Dip-In database has been combined with one from the University of Florida, resulting in information on more than 13,000 waterbodies. This density of information gives us a better view of the regional distribution of transparency in North America.

Notice the concentration of waterbodies of greater transparency in the northern tier of US states and Canada. The agricultural heartland of the continent tends to have smaller transparencies, in part because of the fertile soils that make agriculture possible, in part because of agricultural practices, and, in part because of the predominance of reservoirs rather tan lakes.

Transparency Trends

By 2010, 2,019 waterbodies had 5 or more years of data. When the UF data are added, the number jumps to 4,800 waterbodies. Of these, 17% had significant changes in transparency; 9% had significant decreases in transparency and 8% had significant increases. Regional patterns related to land use might explain which lakes exhibited change.

Water Quality in North American Waterbodies

The Dip-In questionnaire has included questions of water quality. We hoped to gain some knowledge of the nature of problems as perceived by the volunteers. Although most people reported that they had little or no problems, more than 2,000 volunteers reported at least one problem severe enough to diminish enjoyment of the waterbody. Algal scums, weeds (aquatic macrophytes), and turbidity were the major problems reported.
	We have tracked what volunteers report as to the quality of their waterbody and compared their perception with the Secchi depth. It is interesting to note that there are strong regional differences in the average Secchi depth of waterbodies that volunteers consider to be in excellent condition (Left). The differences correspond to the distribution of transparency illustrated in the continental map (above)
	Conversely, volunteers from different regions have different perceptions of what constitutes an impaired waterbody. Again in the regions that have relatively clear waters the volunteers are less tolerant of smaller Secchi depths and more apt to consider the waterbody's use to be impaired.