Soil respiration within riparian buffers and adjacent crop fields

3 We quantified rates of soil respiration among sites within an agricultural 4 landscape in central Iowa, USA. The study was conducted in riparian cool-season grass 5 buffers, in re-established multispecies (switchgrass + poplar) riparian buffers and in 6 adjacent crop (maize and soybean) fields. The objectives were to determine the 7 variability in soil respiration among buffer types and crop fields within a riparian 8 landscape, and to identify those factors correlating with the observed differences. Soil 9 respiration was measured approximately monthly over a two-year period using the soda- 10 lime technique. Mean daily soil respiration across all treatments ranged from 0.14-8.3 g 11 C m-2 d-1. There were no significant differences between cool-season grass buffers and 12 re-established forest buffers, but respiration rates beneath switchgrass were significantly 13 lower than those beneath cool-season grass. Soil respiration was significantly greater in 14 both buffer systems than in the cropped fields. Seasonal changes in soil respiration were 15 strongly related to temperature changes. Over all sites, soil temperature and soil moisture 16 together accounted for 69 % of the seasonal variability in soil respiration. Annual soil 17 respiration rates correlated strongly with soil organic carbon (R =0.75, P<0.001) and fine 18 root (<2 mm) biomass (R=0.85, P<0.001). Annual soil respiration rates averaged 1140 C 19 m-2 for poplar, 1185 g C m-2 for cool-season grass, 1020 g C m-2 for switchgrass, 750 g 20 C m-2 for soybean and 740 g C m-2 for corn. Overall, vegetated buffers had significantly 21 higher soil respiration rates than did adjacent crop fields, indicating greater soil biological 22 activity within the buffers

Biomass, carbon and nitrogen dynamics of multi-species riparian buffers within an agricultural watershed in Iowa,USA

This study was conducted to determine biomass dynamics, carbon sequestration and plant nitrogen immobiliza- tion in multispecies riparian buffers, cool-season grass buffers and adjacent crop ?elds in central Iowa. The seven-year-old multispecies buffers were composed of poplar (Populus × euroamericana ‘Eugenei’) and switch- grass (Panicum virgatum L.). The cool-season grass buffers were dominated by non-native forage grasses (Bro- mus inermis Leysser., Phleum pratense L. and Poa pratensis L). Crop ?elds were under an annual corn-soybean rotation. Aboveground non-woody live and dead biomass were determined by direct harvests throughout two growing seasons. The dynamics of ?ne (0–2 mm) and small roots (2–5 mm) were assessed by sequentially col- lecting 35 cm deep, 5.4 cm diameter cores (125 cm deep cores in the second year) from April through Novem- ber. Biomass of poplar trees was estimated using allometric equations developed by destructive sampling of trees. Poplar had the greatest aboveground live biomass, N and C pools, while switchgrass had the highest mean aboveground dead biomass, C and N pools. Over the two-year sampling period, live ?ne root biomass and root C and N in the riparian buffers were signi?cantly greater than in crop ?elds. Growing-season mean biomass, C and N pools were greater in the multispecies buffer than in either of the crop ?elds or cool-season grass buffers. Rates of C accumulation in plant and litter biomass in the planted poplar and switchgrass stands averaged 2960 and 820 kg C ha-1 y-1, respectively. Nitrogen immobilization rates in the poplar stands and switchgrass sites averaged 37 and 16 kg N ha-1 y-1, respectively. Planted riparian buffers containing native perennial species therefore have the potential to sequester C from the atmosphere, and to immobilize N in biomass, therefore slow- ing or preventing N losses to the atmosphere and to ground and surface waters

Source-Pathway Separation of Multiple Contaminants during a Rainfall-Runoff Event in an Artificially Drained Agricultural Watershed

A watershed\u27s water quality is influenced by contaminant-transport pathways unique to each landscape. Accurate information on contaminant-pathways could provide a basis for mitigation through well-targeted approaches. This study determined dynamics of nitrate-N, total P, Escherichia coli, and sediment during a runoff event in Tipton Creek, Iowa. The watershed, under crop and livestock production, has extensive tile drainage discharging through an alluvial valley. A September 2006 storm yielded 5.9 mm of discharge during the ensuing 7 d, which was monitored at the outlet (19,850 ha), two tile-drainage outfalls (total 1856 ha), and a runoff flume (11 ha) within the sloped valley. Hydrograph separations indicated 13% of tile discharge was from surface intakes. Tile and outlet nitrate-N loads were similar, verifying subsurface tiles dominate nitrate delivery. On a unit-area basis, tile total P and E. coli loads, respectively, were about half and 30% of the outlet\u27s; their rapid, synchronous timing showed surface intakes are an important pathway for both contaminants. Flume results indicated field runoff was a significant source of total P and E. coli loads, but not the dominant one. At the outlet, sediment, P, and E. coli were reasonably synchronous. Radionuclide activities of (7)Be and (210)Pb in suspended sediments showed sheet-and-rill erosion sourced only 22% of sediment contributions; therefore, channel sources dominated and were an important source of P and E. coli. The contaminants followed unique pathways, necessitating separate mitigation strategies. To comprehensively address water quality, erosion-control and nitrogen-management practices currently encouraged could be complemented by buffering surface intakes and stabilizing stream banks