Updating the Lake Champlain Basin Land Use Data to Improve Prediction of Phosphorus Loading. LCBP Technical Report #54

Capen, D., Troy, A., and Wang, D. (2007). Updating the Lake Champlain Basin Land Use Data to Improve Prediction of Phosphorus Loading (Technical Report No. 54). Grand Isle, VT: Lake Champlain Basin Program

This report updated land use maps in the Lake Champlain watershed and the corresponding phosphorus loading estimates to the Lake for urban, agricultural, and forested lands.

The study created a new map of the basin using 2001 satellite imagery— the most recent comprehensive and complete data for this region. New satellite data interpretation methods and ancillary datasets were also used to improve a 1992 land use map from an earlier study. The analysis found that the 1992 study underestimated large-lot suburban development and that there has been growth in suburban development over the last decade.

The study indicated that forest areas comprise about 66% of the watershed’s land use. “Agricultural” areas, which include fields and brush, comprise about 14% of the land-use. “Urban” areas, including densely developed downtowns, as well as all roads, suburbs, and large-lot residential development, comprise about 5% of the basin land-use. Water and wetlands cover the remaining area in the Basin. When the 2001 data was compared to the 1992 data, urban areas grew by almost 2% and agricultural lands decreased by about 5%.

The study also updated the phosphorus loading estimates for the entire Lake Champlain Basin and by sub-watershed. According to the new study, urban and suburban land contributed about 46% of the phosphorus runoff basin-wide to Lake Champlain and agricultural lands contributed about 38% in 2001 (using the loading method). These proportions, however, varied greatly among the various sub-watersheds. For example, agricultural land use was still the greatest contributor of phosphorus (about 70%) in the Missisquoi Bay watershed.

The new study is a shift from previous research based on 1992 data which attributed 51% of the basin-wide phosphorus load to agriculture and 37% to urban sources (Hegman et al, 1999). Factors that contributed to the increased proportion of the load attributed to urban sources included corrections for previous underestimates of urban land cover and more years of water quality and precipitation data from the Lake Champlain monitoring program. The increase in urban and suburban development in some areas of the Lake Champlain Basin between 1992 and 2001 was also a contributor. Chittenden County, near the broad lake, and the St. Albans watersheds are good examples of where this has happened.