A study was conducted to evaluate the ability of a multispecies riparian buffer (MRB) to remove sediment, nitrogen, and phosphorus from cropland runoff. Simulated rainfall was applied to 4.1‐ by 22.1‐m bare cropland source areas paired with either no buffer, a 7.1‐m‐wide switchgrass (Panicum virgatum L. cv. Cave‐n‐Rock) buffer, or a 16.3‐m‐wide switchgrass‐woody plant buffer. Each treatment plot combination had three replicates. The switchgrass buffer trapped 70% of the incoming sediment, while the switchgrass‐woody buffer trapped more than 92%. In general, these buffers retained 93% of sand and silt particles and 52% of clay particles. During a 2‐h rainfall simulation at 25 mm h−1, the switchgrass buffer removed 64, 61, 72, and 44% of the incoming total N, NO3−N, total P, and PO4‐P, respectively. The switchgrass‐woody buffer removed 80, 92, 93, and 85% of the incoming total N, NO3−N, total P, and PO4‐P, respectively. During a 1‐h rainfall simulation at 69 mm h−1, the switchgrass buffer removed 50, 41, 46, and 28% of the incoming total N, NO3−N, total P, and PO4‐P, respectively. The switchgrass‐woody plant buffer removed 73, 68, 81, and 35% of the incoming total N, NO3−N, total P, and PO4‐P, respectively. The switchgrass buffer was effective in trapping coarse sediment and sediment‐bound nutrients. But the additional buffer width with high infiltration capacity provided by the deep‐rooted woody plant zone was effective in trapping the clay and soluble nutrients.

A simplified method of clearing and staining large numbers of plant roots for vesicular-arbuscular (VA) mycorrhizal assay is presented. Equipment needed for handling multiple samples is described, and two formulations for the different chemical solutions are presented. Because one formulation contains phenol, its use should be limited to basic studies for which adequate laboratory exhaust hoods are available and great clarity of fungal structures is required. The second staining formulation, utilizing lactic acid instead of phenol, is less toxic, requires less elaborate laboratory facilities, and has proven to be completely satisfactory for VA assays.

Phosphorus and sediment are major nonpoint source pollutants that degrade water quality. Streambank erosion can contribute a significant percentage of the phosphorus and sediment load in streams. Riparian land-uses can heavily influence streambank erosion. The objective of this study was to compare streambank erosion along reaches of row-cropped fields, continuous, rotational and intensive rotational grazed pastures, pastures where cattle were fenced out of the stream, grass filters and riparian forest buffers, in three physiographic regions of Iowa. Streambank erosion was measured by surveying the extent of severely eroding banks within each riparian land-use reach and randomly establishing pin plots on subsets of those eroding banks. Based on these measurements, streambank erosion rate, erosion activity, maximum pin plot erosion rate, percentage of streambank length with severely eroding banks, and soil and phosphorus losses per unit length of stream reach were compared among the riparian land-uses. Riparian forest buffers had the lowest streambank erosion rate (15-46 mm ⁄ year) and contributed the least soil (5-18 tonne ⁄ km ⁄ year) and phosphorus (2-6 kg ⁄ km ⁄ year) to stream channels. Riparian forest buffers were followed by grass filters (erosion rates 41-106 mm ⁄ year, soil losses 22-47 tonne ⁄ km ⁄ year, phosphorus losses 9-14 kg ⁄ km ⁄ year) and pastures where cattle were fenced out of the stream (erosion rates 22-58 mm ⁄ year, soil losses 6-61 tonne ⁄ km ⁄ year, phosphorus losses 3-34 kg ⁄ km ⁄ year). The streambank erosion rates for the continuous, rotational, and intensive rotational pastures were 101-171, 104-122, and 94-170 mm ⁄ year, respectively. The soil losses for the continuous, rotational, and intensive rotational pastures were 197-264, 94-266, and 124-153 tonne ⁄ km ⁄ year, respectively, while the phosphorus losses were 71-123, 37-122, and 66 kg ⁄ km ⁄ year, respectively. The only significant differences for these pasture practices were found among the percentage of severely eroding bank lengths with intensive rotational grazed pastures having the least compared to the continuous and rotational grazed pastures. Row-cropped fields had the highest streambank erosion rates (239 mm ⁄ year) and soil losses (304 tonne ⁄ km ⁄ year) and very high phosphorus losses (108 kg ⁄ km ⁄ year).(KEY TERMS: riparian areas; streambank erosion; soil and phosphorus losses; best management practices; grazing practices; nonpoint source pollution.) Zaimes, George N., Richard C. Schultz, and Thomas M. Isenhart, 2008. Streambank Soil and Phosphorus Losses Under Different Riparian Land-Uses in Iowa. Journal of the American Water Resources Association (JAWRA) 44(4):935-947.

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A new theoretical and experimental framework that permits an accurate determination of aggregate-size stability distribution is presented. The size-stability distribution in addition to estimating aggregate-size distribution distinguishes between amounts of stable and unstable macroaggregates (>250 μm). The determination of aggregate-size stability distribution involves the assumptions that soil aggregates can be categorized in terms of their size and water stability (slaking resistance). Experimentally this procedure involves the slaked and capillary-wetted pretreatments; and a subsequent slaking treatment of aggregates >250 μm in size. We also propose the stable aggregates index (SAI) and the stable macroaggregates index (SMaI) for studying soil stability based on aggregate resistance to slaking. These indices account for the total weighted average of stable aggregates and the total weighted average of stable macroaggregates, respectively. Both the SAI and the SMaI indices were shown to be sensitive to the effects of vegetation on soil stability under different riparian buffer communities. The SAI and the SMaI indices were higher in surface soils under coolseason grass than any of the other treatments. These soils samples are well aggregated with SAI = 74% and SMaI = 56% followed by SAI = 55% and SMaI = 37% under existing riparian forest, SAI = 40% and SMaI = 21% under 7-yr switchgrass and SAI = 36% and SMaI = 18% under cropped system. (Kemper and Rosenau, 1986). Several studies have used capillary-wetted and slaked pretreatments (Elliott, 1986; A new theoretical and experimental framework that permits an ABSTRACT