Methodologies for Determining Empirical Critical Loads and Exceedances for California Ecosystems

Transcription

1 Methodologies for Determining Empirical Critical Loads and Exceedances for California Ecosystems M.E. Fenn 1, E.B. Allen, S. Jovan, S.B. Weiss, L.H. Geiser, A. Bytnerowicz, G.S. Tonnesen, and R.F. Johnson 1 USDA Forest Service, Forest Fire Laboratory, Pacific Southwest Research Station, Riverside, California mfenn@fs.fed.us

2 Objectives To provide an overview of methods for deriving empirical CL and CL exceedances in California, including: N deposition methods Ecological responders or parameters used to develop critical loads in 7 vegetation types in California Development of statewide CL exceedance maps

3 Briefly: Why Empirical Critical Loads? Uncertainty in modeled CL values As a real world check on computed CL Relationships between modeled CL (or thresholds for key input variables) and biological effects often poorly defined Models can t fully simulate complexities of ecological conditions and stressors

4 Limiting Factors in the Setting of Empirical Critical Loads Inadequate N input range (either as N addition or deposition) Lowest N input level too high (above the CL) N response variables measured at few points Confounding environmental factors across N gradients N addition treatments may be short term; need long term responses N deposition isn t known or well quantified Lack of an established N response threshold for setting an empirical CL Complex ecosystem responses (e.g., sustainability, multiple stress complexes, etc.)

5 Nitrogen Deposition Methodologies Ion exchange resin (IER) throughfall collectors USEPA, CMAQ simulated deposition: (Models- 3/Community Multiscale Air Quality) model Inferential method (dry dep) + NADP (wet dep) used for comparison with CMAQ at selected sites CMAQ used to develop statewide exceedance maps

6 Ion exchange resin (IER) throughfall collector. Ions in throughfall or precipitation samples are adsorbed by anion and cation exchange resin beads within the IER column. IER Column After exposure, ions of interest are extracted from the columns, analyzed and deposition fluxes calculated. Sampling frequency: typically 2x/yr Methods paper: Fenn & Poth, J. Env. Qual. 33:

7 Bulk Deposition: In Open Sites

8 Biological Challenges to Field Monitoring

9 Bear Damaged Collectors

10

11

12 Oil Sands Monitoring Network in N. Alberta, Canada

13 N and S Deposition Data: Oil Sands Region, N. Alberta, Canada 30 Deposition (kg/ha) 5/1 to 10/8, Throughfall SO4-S NH4-N NO3-N DIN Bulk Deposition 0 AMS 5 AMS 1 Lysimeter AMS 14 R2 AMS 15 AMS 13 AMS 9 AMS 10 AMS 5 AMS 1 Lysimeter AMS 14 AMS 15 AMS 13 AMS 9 AMS 10

14 CMAQ Simulated N Deposition for California 4 x 4 km grid scale over 2/3 of state; Rest is 36 km grid

15 Letharia vulpina; wolf lichen; In the Sierra Nevada of California concentrations of N in L. vulpina are correlated with N deposition and adverse changes in lichen community composition. Lichen-based CL developed for mixed conifer forests, chaparral and oak woodlands

16 Mixed Conifer Forest Throughfall N vs. N in L. vulpina Threshold N concentration = 1.0% N in L. vulpina; Corresponds with a CL of 3.1 kg N ha -1 yr -1 in the Sierra Nevada Mountains of California.

17 Indices of lichen N indicator groups (C) Acidophyte dominance shifts to neutrophyte dominance at 5.2 kg N ha -1 yr -1.

18 Streamwater Nitrate Leaching Critical Load: Forests and Chaparral Catchments Nitrogen Deposition Elevated NO 3 in runoff Deposition: Measured as throughfall; however chaparral and oak woodland lichen CL are based on CMAQ deposition estimates

19 Precipitation (mm) Nitrate Concentration (µmol L -1 ) SGW6 SGW7 SGW8 SGW9 SGW10 SGW11 SGW12 SGW Northern Sites Critical Value for Peak Runoff NO 3 Concentration Used for Estimating the Empirical CL: 14.3 µm or 0.2 mg N L -1 0 Precipitation (mm) Nitrate Concentration (µmol L -1 ) SGW1 SGW2 SGW3 SGW4 SGW5 SGW Southern Sites If peak NO 3 concentrations regularly exceed this threshold, the CL for incipient NO 3 leaching is exceeded by definition.

20 Empirical Throughfall CL for Mixed Conifer Forests: 17 kg N ha -1 yr -1 (Based on acceptable leaching value of 0.2 mg L -1 or 14.3 µeq L -1 ) Throughfall N Deposition (kg/ha/yr) y = x r 2 = Streamwater Nitrate (ueq/l)

21 Coastal Sage Scrub: CL based on invasion of exotic grasses and changes in mycorrhizal communities across a deposition gradient N deposition: CMAQ & Inferential method

22 Serpentine Grassland: CL based on exotic annual grass invasion N deposition: Inferential method using passive samplers for major N species and wet deposition

23 CL based on a roadside gradient at the Edgewood Natural Preserve: Transect at Highway 280, San Francisco Peninsula HNO3 NH3 NO2 kg-n/ha EW1 EW2 EW3 JR RC TH KC1 KC2

24 Desert Scrub: Joshua Tree NP CL based on exotic grass invasion with N additions Grass biomass leads to fuel buildup, increased fire frequency, and replacement of native species

25 N fertilizer study sites: Higher N deposition Covington Flat Lower N deposition Pine City West Wide Canyon Pinto Basin

26 Invasive Grass Fuel Buildup in Desert

27 Empirical CL Exceedance Maps: Overlay CMAQ N deposition and vegetation map and the empirical CL for each vegetation type California Vegetation Map CMAQ N Deposition Map

28 Critical load exceedance map for coniferous forest

29 Critical load exceedance map for coniferous forest

30 Empirical CL Exceedance for 7 Vegetation Types: Mixed conifer forest Oak woodlands Chaparral Coastal sage scrub Grassland Desert scrub Pinyon-juniper

31 We are steadily making good progress on critical loads development in the U.S.