Targeted Conservation Can Improve Water Quality
A study on water quality in the Saginaw Bay basin found that targeted conservation on agricultural land can significantly improve fish habitat.
The purpose of the study was to determine the effects of conservation on water quality and especially how much conservation is needed and where it does the most good in terms of water quality, said Mary Fales, Saginaw Bay Watershed project director for The Nature Conservancy.
The Nature Conservancy, in collaboration with Michigan State University, studied the relationship between fish community health and water flow and water quality in four Saginaw Bay basin watersheds. The model showed that fish communities are typically limited by nutrients and summer levels of sediment. Other studies conducted in the region have shown evidence that runoff from row cropped-land is the major source of pollution (nutrient and sediment) limiting fish communities. The resulting model allowed The Conservancy to run conservation implementation scenarios on agricultural land in these watersheds. Model results indicate that if conservation practices are implemented on targeted areas of agricultural land, major improvements in the health of the local fish communities can result.
The study, part of the NRCS Conservation Effects Assessment Project, focused on the Cass, Pigeon/Pinnebog, Rifle, and Shiawassee River watersheds. The final report, Assessing the Costs and Benefits of Conservation Practices to Restoring Biological Integrity in Agricultural Watersheds was completed on March 31, 2013.
The selected watersheds had different levels of agricultural activity, ranging from 25 percent of land in the Rifle, to 80 percent in the Pigeon Pinnebog Watershed. The outlets of all four watersheds had at least one environmental factor limiting fish populations. Some of the limiting factors included phosphorus, nitrates and sediment, largely from agricultural land.
The study judged water quality by examining the fish populations of streams within the watersheds. Important data included the number of fish species present, including the presence of fish species that are most sensitive to water quality. “Healthy streams should include a variety of fish species”, said Fales. Carp and stickleback are examples of species tolerant of poor water quality while rock bass and black redhorse are much less tolerant and are indicators of good water quality.
The study advocates strategic conservation on agricultural land to improve aquatic habitat in the Great Lakes region. Strategic conservation is described as getting the right conservation practices to the right places in the right amount to achieve the desired ecological goals. An advisory panel that included local conservation professionals compiled a list of conservation practices to include in models on the impact of conservation practices on water quality. The list of practices included:
• Nutrient Management/Waste Utilization
• Conservation Crop Rotation
• Filter Strip
• Conservation Cover
• Residue and Tillage Management, No-Till/Strip Till/Direct Seed
• Mulch Till (Residue Mgt, Mulch Till; Residue and Tillage Mgt, Mulch Till)
• Residue Management, No-Till/Strip Till
• Cover Crop
• Pasture and Hay Planting
• Wetland Creation/Restoration
The study modeled the impact of implementing the selected conservation practices on 25 percent and 50 percent of the agricultural land in the four watersheds. The study showed dramatic water quality improvements at both levels but that the most significant improvements came at the 25 percent level.
“With the 25 percent conservation practice scenario, the entire Rifle River watershed is unlimited. In addition, several subwatersheds within the Shiawassee and Cass watersheds are unlimited—including the outlet of both rivers, and the Pigeon-Pinnebog has improved substantially, though no individual subwatershed became unlimited… Under the current scenario, most subwatersheds outside of the Rifle River watershed were limiting by three or more water quality variables. In fact, many subwatersheds were limited by five or more, and most Pigeon-Pinnebog watersheds were limited by all seven variables.”
Conservation practices had the greatest impact on limiting nutrients, like phosphorus and nitrates, in surface water. Sediment was the most difficult limiting factor to reduce. The number of subwatersheds with no limiting factors on fish populations was most pronounced at the 25 percent level.
“Before this study we didn’t best know where to apply conservation practices and how much conservation were needed,” said Fales. “We realize that 25 percent is still a tall order.”
The estimated cost to implement conservation practices on 25 percent of the agricultural land in the selected watersheds was about $22 million. The cost would double to put the conservation practices on 50 percent of agricultural land.