Sediment Core Analysis of Max Lake Reveals Environmental Changes

0 cm 120 cm 270 cm 420 cm 460 cm 460 cm 120 cm 550 cm 270 cm 420 cm Figure 1. Photographs of the 5 drives from the Max Lake sediment core. The first 2 drives were largely uniform in color and mucky in texture. The third drive displayed more banding. The fourth drive was composed largely of clay material and was reddish brown in color. The fifth drive was composed largely of sand with some silt near the top and likely consists of material deposited as the glacier receded.

Max Lake Loss on Ignition 100 80 Organics (%) 60 40 20 0 Carbonates (%) 10 5 0 100 80 Ash/Silicates (%) 60 40 20 0 0 2000 4000 6000 8000 10000 12000 14000 16000 18000 Calibrated 14C yr BP Figure 2. Loss on ignition values are typical for many lakes in northern Wisconsin. Silicates/ash are high in the Late Glacial and Early Holocene due to detrital siliciclastics material in glacial meltwater and outwash. Ameliorating temperatures circa 11,000 yr BP resulted in increased in lake productivity and an elevated proportion of organic matter in the lake sediment throughout the Holocene.

Max Lake - Loss on Ignition 100 90 80 Percent (%) Water 70 Organics 60 Silicates/ash 50 40 30 1810.0 1830.0 1850.0 1870.0 1890.0 1910.0 1930.0 1950.0 1970.0 1990.0 2010.0 Year (Pb210) Figure 3. Loss on ignition values for the last two centuries, like the CHAR records for this period, also reflect an anthropogenic pattern of activity. An increase in silicates/ash are the likely result of land-disturbing activities that contribute slope- wash and soil to the lake basin. The decrease in organic matter is likely just relative to the increase in siliciclastic material and not reflective of reduced primary productivity in the lake.

1 2 3 4 5 0 Sample Date 445 516 623 761 922 1083 1196 1345 1685 1861 2046 2240 2444 2658 2881 3115 3615 3882 4160 4449 4843 5031 5355 5692 6077 6148 6403 6750 7207 7407 7611 7790 8028 8220 8907 9368 1 2 3 4 5 6 7 8 9 33 31 30 32 37 38 39 40 25 26 36 34 35 4 5 6 7 8 11 14 9 10 12 13 17 15 16 1 2 3 21 22 18 20 19 29 28 23 24 27 Group 1 Group 2 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 10334 38 10811 39 11338 40 12206 Group 3 Group 4 Figure 4. Cluster analysis of the diatom samples in the sediment core. The analysis used the Ward s clustering method with squared chord distance. The scale is the square root of the squared chord distance. The table on the right indicates calibrated 14C dates BP.

2=0.211 1.5 pH Phosphorus Group 1 Group 3 1= 0.361 Group 2 pH TP 31 32 30 Group 1 6.1 13.7 29 21 Group 2 6.4 13.9 Group 4 Group 3 5.4 10.7 Group 4 5.6 12.8 -1.0 -1.0 1.5 Figure 5. Principal Components Analysis ordination plot of downcore samples. Circled samples correspond with the 4 groups identfied with the cluster analysis. Groups 1 and 2 have higher pH and phosphorus values. The ordination plot shown in the inset is a Redundancy Analysis (RDA) illustrating the relationship between two environmental variables, pH and phosphorus.

0 4 1000 Group 3 2000 3000 4000 Group 4 5000 6000 7000 1 8000 9000 2 10000 1 11000 2 12000 0 20 0 20 40 60 20 20 40 20 20 20 20 20 20 20 0 20 20 20 0 20 0 20 20 40 0 20 40 20 20 20 0 20 20 Percentage of Total Diatoms Figure 6. Relative abundance of common diatom taxa. The four color groups are the 4 groups identified in the cluster analysis.

7.0 6.5 pH 6.0 5.5 5.0 0 2000 4000 6000 8000 10000 12000 14000 Calculated 14C BP 16 14 Phosphorus ( g L-1) 12 10 8 0 2000 4000 6000 8000 10000 12000 14000 Calculated 14C BP Figure 7. Diatom inferred pH and phosphorus for the portion of the core that was dated. Both pH and phosphorus levels declined after the mid-Holocene warming period.

Figure 8. Charcoal accumulation rates (CHAR) for Max Lake from the Late Glacial to the present. CHAR values are are lowest in the late-Glacial and early Holocene and highest in the last 2000 years.

Figure 9. Max Lake CHAR record excluding the last 2000 years to better illustrate charcoal variability in the early and mid-Holocene. The largest charcoal accumulation rates in the Holocene are centered on 10,000 years ago, 7000 years ago and 4000 years ago.

Figure 10. Max Lake CHAR values for the last 2000 years. During this interval the most wildfire activity in the Max Lake basin occurred between 1100 and 550 yrs BP, concurrent with the Medieval Warm Period and likely reflecting regional drought.

Max Lake CHAR 12 10 Charcoal pieces/cm2/yr 125 250 8 6 4 2 0 0 200 400 600 800 Calibrated 14C yr BP 1000 1200 1400 1600 1800 2000 Figure 11. Max Lake CHAR values for the same period of record as (previous figure) illustrating the relative contribution of charcoal pieces >250 m and those between 125 m and 250 m in diameter. An elevation of the finer charcoal during the Medieval Warm Period suggests that fires were regional in nature and consistent with drought, versus local, isolated phenomena.

Figure 12. Max Lake CHAR values for the same period of record as (previous two figures) showing the contribution charcoal derived from arboreal/canopy component of vegetation and charcoal from grasses and understory vegetation. During the Medieval Warm Period (1100 and 550 yrs BP) charcoal in Max Lake suggests fires were larger arboreal/canopy events.

Figure 13. In the last 200 years CHAR in Max Lake reflects human activities in the area. In the early and middle parts of the 19th Century very little charcoal accumulated in the lake, but logging at the turn of the 20th Century as well as settlement in the area has resulted in increased fire frequencies and elevated CHAR. A rise in CHAR values in the last two decades may reflect a period of sustained drought in the region.

Annual PDSI 4.00 3.00 2.00 1.00 PDSI Index 0.00 -1.00 -2.00 -3.00 -4.00 -5.00 -6.00 1890 1910 1930 1950 1970 1990 2010 Year Figure 14. Annual PDSI Index for the instrumental record for northern Wisconsin. Negative PDSI values represent drought conditions. Years with low regional precipitation and low PDSI values occur in the early 1930's and mid-1970's, both corresponding to episodes of increased CHAR (Figure 12).

Figure 15. Hypothesized extent of lake basin that Max Lake was a part of prior to the mid-Holocene warming period. At the present time most of this historical lake basin is a wetland.