Assessing the Effectiveness of Various Riparian Buffer Vegetation Types (2003)

Abstract

Agricultural riparian buffer research has focused on examining water flow through native forest stands or grass filter strips (Sheridan et al. 1999), and has been conducted primarily in the Mid-Atlantic and southeastern United States (Jordan et al. 1993; Lowrance et al. 1984). Recently established riparian buffer strips, usually adjacent to crop fields, have become increasingly common in the Midwest. The climate, soils, and hydrology differ considerably between the Midwest and the eastern seaboard, thus the effectiveness of newly planted riparian buffers for filtering agricultural field runoff needs to be documented. The hydrology of Kansas surface water resources has been dramatically altered since settlement in the 1800s. Cropland tillage practices, urban and transportation development, channel straightening, and livestock grazing practices all have led to accelerated water movement through watersheds, which increases nonpoint source pollution and streambank erosion. In much of the state, native riparian area vegetative cover has been greatly reduced. Re-establishing riparian buffers along streams may reduce flood damage and streambank erosion, improve wildlife habitat, and filter pollutants, such as nutrients, pesticides, bacteria, and sediments. The strong filtering ability of the plots with natural weedy vegetation resulting from 7 years in fallow was surprising. To better understand these results vegetation characteristics were considered. Both the fallow and the seeded zones had over 98% vegetative ground cover, although there were differences in the type of vegetation. The fallow plots were dominated by cool season grasses (50%), primarily downy brome (Bromus japonicus), which, when combined with other annuals, accounted for over 60% of the vegetation points sampled. Conversely, the native grass area was dominated by the warm season perennial grasses (>80%) that were planted, such as Indian grass (Sorghastrum nutans) and switch grass (Panicum virgatum). The planted American plums had achieved crown closure, averaging almost 6 feet in both height and crown width, with numerous sucker sprouts appearing between the rows. DISCUSSION Runoff Components The reduction in TSS concentration was highly variable with the 2001 natural runoff, but uniformly high under the 2002 simulated runoff. This may have been due to the inherent natural variability in the 2001 runoff events, and, conversely, the uniformity of contaminants and flow rate applied in the simulated runoff collected in 2002. Total phosphorus would have a component bound to sediment. In fact, the reduction in concentration of runoff phosphorus was similar to reductions observed in TSS, when comparing buffer types and years, ranging from 40% to 60%. Total nitrogen concentration reduction was the least of the three components measured and also had the least variability by buffer type and year, with reductions ranging from 35% to 55%. Narrow riparian buffers were less effective in filtering a soluble nutrient like nitrogen because of the relatively short residence time and the direct flow paths through the narrow buffer. Vegetation The 7-year-old buffer plots all had well-established vegetation. The fallow and planted plots had complete ground cover, with annuals dominating the fallow plots, and warm season perennials and shrubs dominating the planted areas. The fallow plots had equal proportions of mostly annual cool and warm season grasses, which appeared to filter surface runoff quite effectively. Note: Trade names are used to identify products. No endorsement is intended, nor is any criticism implied of similar products not mentioned.