Impacts of Agricultural Management Systems on Economic, Environmental, and Wildlife Values of Altered and Unaltered Wetland Areas

Impacts of Agricultural Management Systems on Economic, Environmental, and Wildlife Values of Altered and Unaltered Wetland Areas

Summary

In the Prairie Pothole Region of eastern South Dakota, wetlands are an integral part of the agricultural landscape. Our multidisciplinary research project investigated wildlife, water quantity/quality, economic, and agronomic interactions between farm management systems and wetlands. A model farm was developed in order to generalize results from the case study farms to more widespread applications. The case study farms included organic (ORG), transitional no-till (TNT) and conventional (CON) management systems on similar soil types. Wetlands classified as semipermanent, seasonal, and temporary were located on each case study farm. All farm fields were surveyed for selected avian and invertebrate abundance and richness. Twelve selected wetland and adjacent upland sites were instrumented and monitored for water quantity/quality studies. On-farm interviews and detailed field measurements were conducted 1992-1995 to obtain information about each system.

Effects of the three management systems on waterfowl, wetland and upland breeding birds, and wetland invertebrates were difficult to demonstrate. Waterfowl breeding pair species richness was highest in the ORG system in all years. Other differences were relatively minor and can be ascribed to habitat factors. Water budgets indicated that approximately 60 percent of the wetland water input was runoff from adjacent fields and thus a potential for wetland pollution from agricultural management existed. Of the total wetland water budget, wetland storage and recharge to soil moisture or groundwater was nearly 40 percent. Nitrate concentrations were less in wetland surface water than the discharging groundwater, and were influenced by wetland classification. Seasonal wetlands were more efficient at removing nitrates than semipermanent wetlands. Groundwater samples from wells near the wetland margin contained higher concentrations of ortho-phosphate than groundwater sample at upland sites. Soil microbiological assays indicated that denitrification values and populations of sulfate reducing bacteria were higher for lowlands than adjacent upland areas. Wetlands are frequently cited as nutrient filters for surface and groundwater. Although this function helps reduce contamination, it represents a loss of nutrients from the agricultural system.

Yield measurements collected as a base for economic comparisons established zones of increasing grain yield progressing outward from the wetland. The relative ranking of net returns by management system was consistently TNT>CON>ORG, unless organic premiums were a major component of gross cash receipts. Overall, the major differences in net returns per crop acre were attributed to differences in reported average yields, production costs per acre, crop mix, organic premiums, and amount of wetlands in each farming system. Managing agricultural fields with wetlands can challenge both economic and environmental goals. A major conclusion is that all three systems are profitable and can be managed in an environmentally sound manner.