Temporal trends in amount and placement of conservation practices in the South Fork of the Iowa River watershed

Conservation practices (CP) for erosion prevention include contour buffers, terraces, grassed waterways, water and sediment control basins, and ponds. Quantifying the amount and placement of CP in watersheds is one step in assessment of their potential effectiveness at the watershed scale. We used geographic information system (GIS) mapping techniques and aerial photography to document installation and removal of these CP from the 1930s to 2016.The study was performed in the South Fork of the Iowa River in central Iowa as part of the Conservation Effects Assessment Program (CEAP). Installation of CP increased in each decade from the 1930s to 2002 and then increased only slightly from 2,169 CP in 2002 to 2,282 in 2016. Grassed waterways were the most numerous and treated the largest area within the watershed. In the 1980s through 2010, sonic grassed waterways were removed as water and sediment control basins (V/ASCOBs) were installed. The mean duration of 1,696 grassed waterways installed before 2007 was 31.6 +/- 18.6 years, and the duration of WASCOBs averaged 24 years, suggesting that farmers are making long-term commitments to these CP. Land areas treated with CP tended to be greater in the HUC12 subwatersheds where estimated erosion was greater. Land areas treated by existing grassed waterways (21,609 ha) tended to match areas identified for that CP by the Agricultural Conservation Planning Framework (ACPF) tool: 20,866 ha of existing grassed waterways overlapped with the area predicted by the ACPF However, the ACPF identified an additional 20,866 ha where grassed waterways could be installed, primarily in the western part of the watershed. Mapping of CP and the land areas treated illustrates some of the potential utility of these techniques at the watershed scale. The application of these techniques, which integrate CP amounts and placement in relation to potential placement of CP, provide a different perspective on conservation planning that may interest soil conservationists.