D.W. Johnson and W.W. Miller

Transcription

1 Revised Work Plan: Spatial variability in the KREW watersheds: Effects on nutrient cycling and water quality D.W. Johnson and W.W. Miller Natural Resources and Environmental Science University of Nevada, Reno Tasks 1. Analysis of soil samples taken from the watershed grid system 2. Measurement of resin-based fluxes of N and P in conjunction with detailed soil moisture measurements 3. Pilot study of runoff in selected locations 4. Analysis of spatial variability in nutrient availability in the scale of meters or less Average soil carbon concentrations in KREW Watersheds. Note: Horizons 2, 3, and 4 are averages of genetic soil horizons that were not consistent from pit to pit for example, B1, BA, etc were lumped for averaging here if such horizons occurred at the second sampling depth. 1

2 Average soil nitrogen concentrations in KREW Watersheds. Note: Horizons 2, 3, and 4 are averages of genetic soil horizons that were not consistent from pit to pit for example, B1, BA, etc were lumped for averaging here if such horizons occurred at the second sampling depth. Bars not sharing the same letters were significantly different, post-hoc LSD tests. Average soil C:N ratios in KREW Watersheds. Note: Horizons 2, 3, and 4 are averages of genetic soil horizons that were not consistent from pit to pit for example, B1, BA, etc were lumped for averaging here if such horizons occurred at the second sampling depth. Average soil NH 4+ and NO - 3 concentrations in KREW Watersheds. Note: Horizons 2, 3, and 4 are averages of genetic soil horizons that were not consistent from pit to pit for example, B1, BA, etc were lumped for averaging here if such horizons occurred at the second sampling depth. Bars not sharing the same letters were significantly different, post-hoc LSD tests. 2

3 Initial results on soil C and N concentration There are significant differences in total N and mineral N but not C among watersheds NH 4+ levels are very high are we bordering on being N-saturated? Soil contents (kg ha -1 ) now being calculated from bulk density and rock content data and will be correlated with features like rock content, location, veg, etc. Hypotheses tasks 3 and 4 1. Because of the lack of rooting in the O horizons, runoff through the O horizons over the mineral soil will occur in KREW watersheds, as it does in eastern Sierran ecosystems 2. Runoff will have high concentrations of inorganic N and P, as in the eastern Sierran ecosystems 3. Infiltration of nutrient-rich runoff into preferential flowpaths will create hot spots of nutrient availability in O horizons and mineral soils. Nitrogen cycling in humid forest soils Abundant rooting in O horizons Intense competition between roots and microbes for N 3

4 Nitrogen cycling in Sierran forest soils No rooting in O or upper A horizons Spatial discoupling of roots and microbes No competition between roots and microbes for N in upper horizons High levels of mineral N are therefore possible in O horizons for leaching Inconspicuous nutrient-laden runoff Wally Miller and his students have been measuring interflow through the forest floor and above the mineral soil (which is typically hydrophobic in summer) Solutions collected have very high concentrations of NH 4+ and ortho-p, ions that would normally be strongly adsorbed to mineral soils and whose concentrations are very low in soil solutions We hypothesize that These interflow waters are nutrient laden because of the lack of root uptake in the O horizon When and where they enter soils at some point, they create hot spots of high nutrient availability Schematic of interflow collector Soil 45 cm HDPE Cover & Screen Sample Tube Flashing Funnel Vent Collection Bucket Organic Duff & Surface Litter 1 cm Soil 35 cm Lateral View 4

5 Top view of runoff collector Table 1. Ammonium, nitrate and ortho-p concentrations in typical interflow and soil solutions from Truckee, CA Source NH 4+ -N NO 3- -N ortho-p mg L Interflow 86.2 < Soil Solution 0.01 < Side view of runoff collector and installing the collector at KREW 5

6 The finished product Interflow collector in the field The actual entry hole for runoff is < 0.5 cm 2, but it collects many liters of water Layout of Hot spot sampling plots 2 m 2 m 0.67 m Central sub-plot is sampled on a 0.67 x 0.67 grid Sample points for resin capsules and PRS probes 6

7 At each sampling node: PRS anion and cation exchange membrane probes Unibest resin capsule Planned for after snowmelt: Litter sample Soil sample We are using the capsule only Western Ag Innovations, Saskatoon Canada 7

8 Locator wire and tag Unibest capsule PRS probes 8

9 At the Tree : Resin lysimeter at 10 of the twelve spokes Resin lysimeter (Susfalk and Johnson, 2002) Installing the Resin lysimeter Excavate small hole and tunnel Install under soil that is minimally disturbed in tunnel Bury all but locator line Remove and extract after snowmelt Gives cumulative nutrient flux but no water flux 9

10 Future Plans Fall/Winter 2008: Analyze KREW soils for exchangeable cations, extractable P, sulfate Spring 2009: Assess runoff data to see if hypothesis is supported or not Hot Spot Plots: Retrieve resins Sample litter and soil at sample nodes Analyze data and revise plans accordingly Retrieve resin lysimeters from the Tree, analyze data and decide how to proceed with next year s installation 10