Appendix

Impact of glacier cover data source on comparison of nitrate in GSF versus SF lakes

Analyses presented in the text used the PNW Gap ‘North American Alpine Ice Field’ land cover class to classify lakes as GSF or SF, and to compare nitrate concentrations between lake types. Nitrate concentrations were also compared between lake types using three other glacier coverages: a 1958 glacier coverage developed by Granshaw and Fountain (2006) by digitizing USGS glacier outlines on USGS topographic maps, which are based on 1958 aerial photography; a1998 glacier coverage developed by Granshaw and Fountain (2006) based on August 1998 1:12000 scale unrectified color vertical aerial photography, and a glacier coverage developed by Dick (2009) based on 2006 and 2009 orthorectified aerial photography. Park glacier area and the number of lakes classified as GSF varies across coverages (Table A1). Differences in the number of glaciers and glacier area across coverages results in part from the spatial scale and time of year associated with imagery, measurement errors associated with delineating margins of small glaciers in the North Cascades, difficulties distinguishing between snowfield and glacier boundaries, and inter-annual variation in snowpack across coverages (O’Neal et al. 2015). Lake classification and nitrate patterns were very consistent regardless of the coverage used.

Table A1. Comparison of NOCA glacier cover, lake classifications, and nitrate results across available glacier cover data sources. Units are mg NO3-N L-1.

Glacier Coverage / Imagery Period / NOCA Glacier Area (km2) / GSF / SF
N / Mean / SD / N / Mean / SD
PNW Gap / 1990-1993, 1999-2001 / 80 / 25 / 0.013 / 0.014 / 54 / 0.005 / 0.005
Granshaw & Fountain (2006) / 1958 / 117 / 24 / 0.011 / 0.011 / 55 / 0.006 / 0.008
Granshaw & Fountain (2006) / 1998 / 109 / 24 / 0.011 / 0.011 / 55 / 0.006 / 0.008
Dick (2009) / 2006 & 2009 / 94 / 23 / 0.011 / 0.011 / 56 / 0.005 / 0.009

Table A2. PNW GAP land cover classes present within study lakes, and class mean and range watershed percent area for GSF and SF lakes.

Land Cover Code / Description (ECOLSYS_LU) / GSF lakes % area / SF lakes % area
136 / East Cascades Mesic Montane Mixed-Conifer Forest and Woodland / 0.02 (0-0.58) / 0
147 / Northern Rocky Mountain Subalpine Woodland and Parkland / 2 (0-32) / 27 (0-99)
151 / Rocky Mountain Subalpine Dry-Mesic Spruce-Fir Forest and Woodland / 0 / 2 (0-21)
152 / Rocky Mountain Subalpine Mesic Spruce-Fir Forest and Woodland / 0.32 (0-3.3) / 4.6 (0-82)
167 / North Pacific Dry-Mesic Silver Fir-Western Hemlock-Douglas-fir Forest / 0.11 (0-2.1) / 0.23 (0-12)
177 / North Pacific Maritime Mesic Subalpine Parkland / 24 (0-63) / 27 (0-86)
178 / North Pacific Mountain Hemlock Forest / 2.5 (0-20) / 7.3 (0-53)
273 / North Pacific Hardwood-Conifer Swamp / 0.003 (0-0.07) / 0
308 / North Pacific Alpine and Subalpine Dry Grassland / 29 (9-68) / 12 (0-92)
311 / Northern Rocky Mountain Lower Montane, Foothill and Valley Grassland / 0.10 (0-2.6) / 1.1 (0-28)
430 / North Pacific Avalanche Chute Shrubland / 0.81 (0-13) / 0.25 (0-4.1)
432 / Temperate Pacific Freshwater Emergent Marsh / 0.06 (0-1.5) / 0.02 (0-0.47)
440 / Temperate Pacific Montane Wet Meadow / 0.12 (0-0.3) / 0.24 (0-11)
506 / North Pacific Dry and Mesic Alpine Dwarf-Shrubland, Fell-field and Meadow / 2.3 (0-16) / 3.4 (0-73)
507 / Rocky Mountain Alpine Tundra/Fell-field/Dwarf-shrub Map Unit / 0 / 1.6 (0-38)
529 / Rocky Mountain Cliff, Canyon and Massive Bedrock / 0 / 1.1 (0-35)
531 / North Pacific Montane Massive Bedrock, Cliff and Talus / 10 (0-26) / 6.8 (0-28)
549 / Rocky Mountain Alpine Bedrock and Scree / 0 / 0.34 (0-18)
551 / North Pacific Alpine and Subalpine Bedrock and Scree / 13 (0-48) / 0.77 (0-17)
554 / North American Alpine Ice Field / 12 (0.47-59) / 0
579 / Open Water (Fresh) / 2.7 (0-15) / 3.2 (0-18)

Figure A1. Annual net mass balance (m.w.e = meters of water equivalent) of NOCA glaciers monitored by NPS and USGS. Mass balances were negative for all monitored glaciers in 1994, 1998, and 2013.

Figure A2. Cell densities of phytoplankton phyla in GSF and SF lakes sampled in 2013.

Figure A3. Comparison of lake chemistry between GSF and SF lakes based on 89-99 lake means from Larson et al. (1999). Boxes indicate the inter-quartile range, horizontal lines are medians, diamonds are means, whiskers are 1.5 times the IQR, and dots are outliers. N = 24 for GSF lakes, and N = 52 for SF lakes.

Figure A4.Comparison of lake chemistry between GSF and SF lakes based on 1989 data from Larson et al. (1999). Box plots are structured the same as in Figure A1. N = 16 for GSF lakes, and N = 29 for SF lakes.

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