Abstract
In North America, land use practices of the last two centuries have strongly influenced aquatic communities and freshwater quality, but the impacts of prehistoric land use on freshwater resources remain poorly documented. Here we investigate the influence of prehistoric and historical land use on Horseshoe Lake, Illinois, USA, an oxbow lake in a floodplain of the Mississippi River that is adjacent to Cahokia, the largest prehistoric indigenous population center north of Mexico. Diatom assemblages from Horseshoe Lake’s sedimentary record track shifts in aquatic environmental conditions over the last ca. 1600 years. During the period of prehistoric population growth and agricultural intensification associated with Cahokia’s emergence (ca. 600–1200 CE), the relative abundance of Aulacoseira granulata—a planktonic diatom associated with shallow eutrophic lakes—increased. Following the abandonment of Cahokia in the 14th century CE, the diatom flora of the lake shifted from planktonic Aulacoseira taxa to the epiphytic taxa Cocconeis and Gomphonema. This shift in diatom assemblages is consistent with a reduction of nutrient inputs to the lake and/or reduced fishing pressure as prehistoric populations abandoned the area. Following the intensification of historic settlement after 1800 CE, diatom assemblages shift to epipelic species of small Staurosira and Fragilaria, indicating a reduction in aquatic macrophytes and increased turbidity. Our results document prehistoric indigenous impacts on a freshwater system beginning nearly 1000 years before European colonization of the Americas and demonstrate the antiquity of human impacts on freshwater resources in North America.
Highlights
Human activities exert a fundamental control on aquatic ecosystems and freshwater quality (Smith et al 1999; Jackson et al 2001; Dudgeon et al 2006)
We present diatom assemblages in a sedimentary record from Horseshoe Lake, Illinois (USA)—an oxbow lake that is adjacent to Cahokia, the largest prehistoric indigenous settlement north of Mexico
Diatom assemblages are present throughout most of Horseshoe Lake’s sedimentary record (Figs. 4, 5), but we encountered poor diatom preservation in sections that were identified by Munoz et al (2015) as sediment deposited during major flood events of the Mississippi River (Fig. 3)
Summary
Human activities exert a fundamental control on aquatic ecosystems and freshwater quality (Smith et al 1999; Jackson et al 2001; Dudgeon et al 2006). Despite the abundance of evidence documenting recent historical degradation of freshwater resources, paleolimnological records of prehistoric human impacts on aquatic ecosystems in North America are scarce. Paleolimnological evidence from South and Central America demonstrates that indigenous populations in those regions influenced freshwater ecosystems thousands of years before European colonization (Haberyan and Horn 2005; Slate et al 2013; Bush et al 2016), but were similar impacts north of Mexico confined to the relatively recent past? Prehistoric populations in some areas of eastern North America, in the Midwest and Southeast, were large, sedentary, and cultivated a variety of plant foods for thousands of years prior to European colonization (Smith 2009; Milner 2005), but their influence on freshwater ecosystems remains poorly documented Paleolimnological evidence from South and Central America demonstrates that indigenous populations in those regions influenced freshwater ecosystems thousands of years before European colonization (Haberyan and Horn 2005; Slate et al 2013; Bush et al 2016), but were similar impacts north of Mexico confined to the relatively recent past? Prehistoric populations in some areas of eastern North America, in the Midwest and Southeast, were large, sedentary, and cultivated a variety of plant foods for thousands of years prior to European colonization (Smith 2009; Milner 2005), but their influence on freshwater ecosystems remains poorly documented
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