Windows into the past: lake sediment phosphorus trajectories act as integrated archives of watershed disturbance legacies over centennial scales

Abstract

Historic land alterations and agricultural intensification have resulted in legacy phosphorus (P) accumulations within lakes and reservoirs. Internal loading from such legacy stores can be a major driver of future water quality degradation. Yet, little is known about the magnitude and spatial patterns of legacy P accumulation in lentic systems, and how watershed disturbance trajectories drive these patterns. Here, we used a meta-analysis of 113 paleolimnological studies across 124 lakes and 4 reservoirs (referred here on as lakes) in 20 countries to quantify the linkages between the 100-year trajectories of P concentrations in lake sediments, watershed inputs, and lake morphology. We find five distinct clusters for lake sediment P trajectories, with lakes in the developing and developed world showing distinctly different patterns. Lakes in the developed world (Europe and North America) with early agricultural intensification had the highest sediment P concentrations (1,176-1,628 mg/kg), with a peak between the 1970-1980s and a decline since then, while lakes in the developing world, specifically China, documented monotonically increasing sediment P concentrations (857-1,603 mg/kg). Sediment P trajectories reflected watershed disturbance patterns and were driven by a combination of anthropogenic drivers (fertilizer input and population density) and lake morphology (watershed to lake area ratio). Specifically, we found the largest legacy accumulation rates to occur in shallow lakes experiencing long-term land-use disturbances. These links between land-use change and P accumulation in lentic systems can provide insights about inland water quality response and help to develop robust predictive models useful for resource managers and decision-makers.

Contrasting Impacts of Agricultural Intensification and Urbanization on Lake Phosphorus Cycling and Implications for Managing Eutrophication

“…After entering a lake, the supplied P undergoes further biogeochemical transformations in the water column and bottom sediments, including uptake into biomass, mineralization, adsorption‐desorption, and dissolution‐precipitation reactions (Katsev et al., 2006; Markelov et al., 2019; Orihel et al., 2017; Van Cappellen & Berner, 1988). A lake's sediment core can therefore serve as a historical archive of the changes in external P loading and in‐lake cycling (Bhattacharya et al., 2022; Moyle et al., 2021; O'Connell et al., 2020; C. Wang et al., 2013). In addition, sediment accumulation rates measured using dating techniques, such as the 210 Pb method, provide information about historical changes in soil erosion and runoff (Dearing, 1991).…”

Comparing Drivers of Spatial Variability in U.S. Lake and Stream Phosphorus Concentrations

“…In addition, recent work has emphasized the importance of considering lake-specific characteristics, particularly lake depth, when looking to explain the variability in lake nutrient concentrations and dynamics (King et al, 2019;Oliver et al, 2017;Read et al, 2015), so this important contextual variable was also included in our analysis. Likewise, a global analysis of P in sediment cores across the globe highlights the potential importance of considering legacy phosphorus stored within lake sediments when evaluating the potential responsiveness of lentic systems to shifts in contemporary pollution sources (Bhattacharya et al, 2022). While we do not have lake sediment core data available for the NARS sampling sites, we have incorporated watershed average estimates of agricultural soil erodibility and legacy agricultural P surplus to approximate long-term P loading and sediment to lakes (Sabo et al, 2021a(Sabo et al, , 2021b (Tables 1 and 2).…”