Analysis of Down-Core Pollen Assemblages

Transect "21"

Pollen Assemblage Zone 1: In cores from the ridge, slough, and transition zone (Figure 7, Figure 8, Figure 9), pollen zone 1, representing the base of the cores to approximately 1000 yr BP, is characterized by higher abundance of Nymphaea relative to Cladium pollen along with a low abundance to near absence of pollen from other plants. In the ridge core (Figure 7), marsh pollen and Chenopodiaceae-Amaranthaceae pollen are more abundant than in the adjacent transition (Figure 8) and slough (Figure 9) cores. In this zone, the pollen assemblages in the transition core are similar to those found in the slough core, rather than the ridge core. Assemblage data for these cores can be found in Appendix I, Appendix J, Appendix K.

Pollen Assemblage Zone 2: In zone 2, representing approximately 1000 yr BP - 1900 AD, plant species indicating drier conditions are more abundant throughout the transect. Fern spores, and the pollen of Cladium, the Asteraceae, and other marsh plants (including Polygonaceae, Apiaceae, Poaceae, Justicia, Typha, and Sagittaria) are more abundant than in zone 1 (Figure 7, Figure 8, Figure 9). In general, Nymphaea pollen is less abundant. The ridge and slough cores remain distinct in this zone, with fern spores more common in the ridge. The slough, along with the transition, has a higher abundance of marsh pollen during this interval than the ridge.

Pollen Assemblage Zone 3: Zone 3 encompasses the interval from approximately 1900 AD - present. Increased abundance of fern spores, Cladium, Myrica, and Asteraceae pollen in conjunction with decreased abundance of Nymphaea pollen (Figure 7 and Figure 8), characterize this zone. These increases also occur in the slough core (Figure 9), but Nymphaea abundance does not decrease. In general, the establishment of modern vegetation communities occurred midway through zone 3, which is approximately 1950.

Transect "20"

Pollen Assemblage Zone 1: Characterized by high abundances of Nymphaea relative to Cladium pollen, this zone represents the interval from approximately 2700 yr BP - 1000 yr BP (Figure 10, Figure 11). The ridge and slough cores are distinct from one another through this zone (Figure 10, Figure 11). Chenopodiaceae-Amaranthaceae pollen and fern spores are more abundant in the ridge core (Figure 10) than in the slough core (Figure 11). Assemblage data for these cores can be found in Appendix L, Appendix M.

Pollen Assemblage Zone 2: Pollen assemblages of zone 2 (~1000 yr BP - 1900 AD) are characterized by a greater abundance of fern spores, Cladium, and marsh pollen. The onset of zone 2 in the slough core is marked by a spike in the abundance of Chenopodiaceae-Amaranthaceae pollen, as occurred in slough cores from other transects (Figure 9, Figure 11, and Figure 13). The ridge and slough assemblages are distinct from each other throughout zone 2, primarily because of the great abundance of marsh pollen (Typha, Sagittaria, and Apiaceae).

Pollen Assemblage Zone 3: Pollen assemblages from zone 3 (~1900 AD - present) are characterized by high abundances of Chenopodiaceae-Amaranthaceae, Asteraceae, and woody vegetation pollen (Myrica and Cephalanthus) (Figure 10, Figure 11). Nymphaea pollen is nearly absent in the ridge core (Figure 10). In the slough core (Figure 11), Cladium, Myrica, and Asteraceae pollen are more abundant than in zone 2. Overall, the pollen assemblages in zone 3 indicate the shortest hydroperiod and shallowest water levels of the past 2700 years.

Transect "2000"

Pollen Zone 1: Pollen assemblages in zone 1 (base of core - 1000 yr BP) are difficult to characterize because of low diversity of pollen types (Figure 12, Figure 13). The ridge core (Figure 12) is characterized by a greater abundance of fern spores. The slough core (Figure 13) is characterized by a greater abundance of Nymphaea than Cladium pollen. Assemblage data for these cores can be found in Appendix N, Appendix O.

Pollen Zone 2: Between 1000 yr BP and 1900 AD, pollen assemblages contain greater abundances of ferns spores and marsh taxa than in zone 1. In the ridge core (Figure 12), Cladium pollen abundance is greater than in zone 1, and fern spores are more abundant. Pollen assemblages in the slough core (Figure 13) remain dominated by Nymphaea, but Myrica and Chenopodiaceae-Amaranthaceae pollen are more abundant than in zone 1.

Pollen Zone 3: In both cores, assemblages indicate drier conditions during the 20^th century (Figures 12, Figure 13). Fern spores comprise about 60-80% of assemblages within the ridge core (Figure 12); in the slough core, Nymphaea pollen abundance is noticeably reduced, and pollen from species indicative of dry conditions is more abundant (Figure 13).