Mark D. Tomer

Riparian buffers can improve water quality, but watershed‐scale evaluations of riparian buffering opportunities are rare. A landscape discretization tool called riparian catchments, part of the Agricultural Conservation Planning Framework (ACPF) version 3, was applied to evaluate functional riparian settings for 32 headwater watersheds representing three major land resource areas (MLRAs) in Iowa. Riparian settings of 250‐m length were classified based on height above channel and upslope contributing area to show where to place buffers primarily designed to intercept runoff, treat nitrate in shallow groundwater, and/or protect streambanks. Riparian zones found below small riparian catchments were common, typically occupying >50% of streambank lengths in MLRA 103 (northern Iowa) and MLRA 108 (southeast Iowa). In these settings, narrow (6–10 m wide) buffers provide a buffer/contributing area ratio of >0.02 to filter surface runoff, while providing streambank protection. This similarity occurred despite these two MLRAs having contrasting landscapes. Whereas the narrow buffers suggested are associated with ditches and flat terrain in MLRA 103, they occur below short slopes along streams that have well dissected the watersheds in MLRA 108. In MLRA 104 of east‐central Iowa, headwater alluvial streams often had broad low‐lying riparian zones, where wide buffers (>25 m) may be placed to help mitigate nitrate transport in shallow groundwater. The ACPF riparian catchments approach enabled cross‐watershed analyses of riparian settings, while providing spatial data to inform watershed‐scale riparian planning efforts.

This paper presents the case of a voluntary watershed project that addressed the need for improving water quality by reducing agricultural nutrient loss. The Beargrass Creek Watershed Approach Project in Wabash County, Indiana aimed to demonstrate that it is possible to achieve ambitious water quality goals and maximize the effectiveness of conservation funding through locally‐led efforts that bring together multiple stakeholders throughout the process. The project focused on implementing the “right practices” in the “right places” through a goal‐oriented, science‐based, and locally‐adapted approach to voluntary conservation. We examine and evaluate all three phases of the project and discuss successes and lessons learned from the point of view of both agricultural producers and agency staff from the local Soil and Water Conservation District and the Natural Resources Conservation Service.

The Neal Smith National Wildlife Refuge was established as a tallgrass prairie ecosystem reconstruction in the Walnut Creek watershed (5238 ha), Jasper County, Iowa, with >1200 ha of prairie plantings initiated between 1993 and 2006. This study updates the documented decreases in watershed NO₃–N losses that accompanied this change in land cover to a 20‐yr record. Annual flow‐weighted NO₃–N concentrations declined by 0.15 mg NO₃–N L⁻¹ yr⁻¹, which was not significantly different from the rate of 0.07 mg NO₃–N L⁻¹ yr⁻¹ reported after the first decade of monitoring. There was also evidence (p < 0.1) that prairie reconstruction led to a declining trend in annual watershed water yield, which would have contributed to the trend of decreasing NO₃–N loads. However, variability in climate, including 2 yr with significant flooding events followed by a major drought during the second decade of monitoring, challenged any notion that a watershed water quality record will stabilize even >10 yr after a substantial change in land cover, in this naturally drained watershed underlain by fine grained glacial deposits that exhibit multidecadal groundwater transport times. Efforts to document progress toward water quality goals will need to consider dominant flow paths and associated travel times, uncertainty in the effectiveness of management changes, and a changeable climate.Core Ideas: Nitrate in streamflow draining a prairie reconstruction was tracked for 20 yr. Nitrate loss decreased with time, at a slow rate of only 0.15 mg NO₃–N L⁻¹ yr⁻¹. Even with substantial land use change, water quality response may take decades.

Streambank erosion may represent a significant source of sediment and phosphorus (P) to overall watershed loads; however, watershed-scale quantification of contributions is rare. In addition, streambanks are often comprised of highly variable stratigraphic source materials (e.g., alluvial deposits), which may differentially impact in-channel P dynamics once eroded. The objective of this study was to quantify sediment and total phosphorus (TP) losses from four materials comprising streambanks within a 5218 ha watershed in Iowa, USA. Streambank-face surveys, erosion pins, and soil analyses were used to quantify surface area representation, recession, and losses of sediment and TP over a two-year period. Cumulative, whole-bank gross mean recession totaled 18.6 cm over two years, and material-specific gross mean recession ranged from 15.5 to 64.1 cm. Cumulative, whole-bank mean gross mass losses totaled 0.28 Mg sediment and 0.7 × 10⁻⁵ Mg TP per meter channel length. Annual sediment losses equated to 4–44% of historic suspended sediment loads. Stratigraphy was significant in gross material erosion and losses, with lower materials (i.e., bank toe region) exhibiting the greatest recession rates and cumulative recession. Weathered/colluvial material dominated total bank face surface area (88.3%), and contributed the greatest proportion of sediment and TP mass loss (66, 68%, respectively) versus other streambank materials.

Core Ideas: Long‐term databases are important for assessing soil change. The USDA Soil Survey Characterization Database provides long‐term soil data. Methods of analysis used have changed and soils were sampled only once. Changes in methods must be accounted for in soil change studies and trends. Recently, the USDA–NRCS National Cooperative Soil Survey Soil Characterization Database (NSCD) was reported to provide evidence that total nitrogen (TN) stocks of agricultural soils have increased across the Mississippi basin since 1985. Unfortunately, historical changes in methods used to measure TN were not fully accounted for in that report. We used NSCD archives to calibrate between wet (pre‐1995) and dry (post‐1995) digestion methods used in measuring TN and soil organic carbon (SOC), then evaluated temporal trends in SOC and TN stocks with data from 423 Alfisol and 900 Mollisol profiles representing the US Corn Belt. Data were grouped by moisture regime, farming history (presence of Ap horizon), and depth (0–20, 20–60, and 60–100 cm). Regressions showed geographic and textural influences on SOC, and that SOC increased with time among farmed soils, particularly at 20 to 60 cm. Soil TN was dependent on SOC, especially at the surface ( R ² > 0.71), and decreasing TN trends with time were found among farmed soils above 60‐cm depth. Increases in C to N ratios further suggested TN has been slowly stabilizing within soils of the US Corn Belt. However, C to N ratios 60% frequency), indicating large TN stores remain in these soils. An increasing trend in SOC, TN, and C to N ratios among non‐farmed, aquic Mollisols suggested SOC and TN accumulations in wet soils typically located below croplands. Results suggest slow improvement in agricultural soils. However, resampling has not been broadly undertaken for NSCD soil profiles, hence use of this database to detect soil change should be approached cautiously.

Conservation planning information is important for identifying options for watershed water quality improvement and can be developed for use at field, farm, and watershed scales. Translation across scales is a key issue impeding progress at watershed scales because watershed improvement goals must be connected with implementation of farm‐ and field‐level conservation practices to demonstrate success. This is particularly true when examining alternatives for “trap and treat” practices implemented at agricultural‐field edges to control (or influence) water flows through fields, landscapes, and riparian corridors within agricultural watersheds. We propose that database structures used in developing conservation planning information can achieve translation across conservation‐planning scales, and we developed the Agricultural Conservation Planning Framework (ACPF) to enable practical planning applications. The ACPF comprises a planning concept, a database to facilitate field‐level and watershed‐scale analyses, and an ArcGIS toolbox with Python scripts to identify specific options for placement of conservation practices. This paper appends two prior publications and describes the structure of the ACPF database, which contains land use, crop history, and soils information and is available for download for 6091 HUC12 watersheds located across Iowa, Illinois, Minnesota, and parts of Kansas, Missouri, Nebraska, and Wisconsin and comprises information on 2.74 × 10⁶ agricultural fields (available through http://northcentralwater.org/acpf/). Sample results examining land use trends across Iowa and Illinois are presented here to demonstrate potential uses of the database. While designed for use with the ACPF toolbox, users are welcome to use the ACPF watershed data in a variety of planning and modeling approaches.Core Ideas: Water quality improvement must meet watershed goals through farm‐level measures. Planning data can help better connect farm implementation and watershed outcomes. We developed a database to help develop watershed plans through farm‐level options. The database is available for >6000 HUC12 watersheds in the US Midwest.