Ecological response to hydrological variability and catchment development: Insights from a shallow oxbow lake in Lower Mississippi Valley, Arkansas

Abstract

The ecological response of shallow oxbow lakes to variability in hydrology and catchment development in large river floodplain ecosystems (RFE) in Arkansas remains largely unknown. Investigating these responses will advance our understanding of ecological evolution of oxbow lakes in response to the major environmental drivers, which will establish baseline conditions required to develop effective management practices for RFE. In this pilot study, we examined the potential of using a dated surface sediment core from Adams Bayou, a floodplain lake located within the Cache-Lower White River Ramsar site in SE Arkansas. Stratigraphic records of diatoms and sediment geochemistry were used to ascertain variation in Adams Bayou's ecological condition. During 1968-2008, in response to hydrological and anthropogenic changes, Adams Bayou's diatom assemblages progressed from predominantly benthic (Gomphonema parvulum and Meridion circulare) to primarily planktonic assemblage (Aulacoseira granulata and Cyclotella meneghiniana), along with a decrease in magnetic susceptibility (k) and % silt. Statistical analyses reveled that during 1968-2000, higher hydrological connectivity and catchment alterations drove Adams Bayou's ecosystem. After 2000, lower hydrological connectivity and increase in cultivation were the major drivers. The potential impact of increasing air temperature was also noted. The shift in Adams Bayou from a connected, clear, mesotrophic state to a relatively isolated, turbid and nutrient enriched state is consistent with regime shift models and highlights its sensitivity to a combination of environmental stresses prevalent in the catchment. Although fluvial systems pose challenges in establishing clear chronologies, oxbow lake sediments can be a effective paleoecological archives. Our work provides clear evidence for the change in the ecological character of this wetland of international significance and flags the need for a wider assessment of water bodies across this site under obligations to the Ramsar Convention.

A 1600-year record of human impacts on a floodplain lake in the Mississippi River Valley

“…Prior work by Randsalu-Wendrup et al (2014 demonstrated that these alternative states-and shifts between them-can be inferred using diatom assemblages in sedimentary records because diatom taxa can be classified as planktonic or epiphytic. Similar state changes have been inferred using diatom records from shallow lakes, which show shifts from epiphytic to planktonic taxa in response to more eutrophic conditions, as aquatic macrophytes are replaced by planktonic algae in response to an increase in nutrient delivery to the lake (Bhattacharya et al 2016;Sayer et al 2010). At Horseshoe Lake, we interpret the prominent shift in diatom assemblages in the 14th century as a shift from a eutrophic to more mesotrophic state when prehistoric populations abandoned the area and nutrient inputs to the lake from settlements and agricultural fields in the watershed declined.…”

“…Sediments, diatoms, and other materials deposited in oxbow lakes are sourced from the lake itself (autochthonous) or its watershed (allochthonous), but during flood stages the main river channel may also deposit material in the lake (Toonen et al 2012;Bhattacharya et al 2016), which represents an extralocal source of allochthonous material. In a previous study of Horseshoe Lake's sedimentary record, Munoz et al (2015) used grain-size analysis to identify the timing of major overbank flood events of the Mississippi River (Fig.…”

“…In Adams Bayou, a floodplain lake in Arkansas (USA), 20th-century sediments are dominated by a group of Aulacoseira species including A. granulata, whereas Gomphonema parvulum and other epiphytic taxa were more abundant before this time. This change was interpreted as a change from a clear-water mesotrophic system to an enriched turbid system caused by an increase in local land clearance (Bhattacharya et al 2016). The dominance of A. granulata in Horseshoe Lake's diatom assemblages during diatom zone HORMD2 (610-1400 CE) indicates that the lake was more eutrophic during the prehistoric occupation of the area, as population densities and agricultural production increased (Milner 1998;Simon and Parker 2006;Pauketat 2009).…”

Potential anthropogenic regime shifts in three freshwater lakes in Tropical East Asia

“…However, small centric diatom species, such as D. stelligera , are also responsive to changes in nutrient availability, and an increased N:P ratio (Saros & Anderson, ). Moreover, Bhattacharya, Hausmann, Hubeny, Gell, and Black () link abundant Aulacoseira granulata , along with Cyclotella meneghiniana and Discostella spp., with nutrient‐enriched, turbid conditions in a Lower Mississippi floodplain lake in Arkansas, U.S.A. Thus, the co‐occurrence of relatively abundant A. granulata , C. meneghiniana and Discostella spp.…”

Hydrologic and anthropogenic influences on aquatic macrophyte development in a large, shallow lake in China

“…Diatoms are diverse and sensitive to a range of environmental factors, including water quality, hydrological conditions and trophic state, and their assemblages in sediments have been used to establish past ecological conditions in many shallow lakes (Bhattacharya, Hausmann, Hubeny, Gell, & Black, ; Wu et al., ). The abundance of epiphytic diatoms generally increases with the abundance of aquatic macrophytes and they are considered to be a useful indicator of changes in macrophyte abundance (Karst & Smol, ; Yang, Shen, Dong, Liu, & Wang, ).…”