Paleolimnological evidence of the effects on lakes of energy and mass transfer from climate and humans

Abstract

The premise of this article is that climate effects on lakes can be quantified most effectively by the integration of process-oriented limnological studies with paleolimnological research, particularly when both disciplines operate within a common conceptual framework. To this end, the energy (E)-mass (m) flux framework (Em flux) is developed and applied to selected retrospective studies to demonstrate that climate variability regulates lake structure and function over diverse temporal and spatial scales through four main pathways: rapid direct transfer of E to the lake surface by irradiance, heat, and wind; slow indirect effects of E via changes in terrestrial development and subsequent m subsidies to lakes; direct influx of m as precipitation, particles, and solutes from the atmosphere; and indirect influx of water, suspended particles, and dissolved substances from the catchment. Sedimentary analyses are used to illustrate the unique effects of each pathway on lakes but suggest that interactions among mechanisms are complex and depend on the landscape position of lakes, catchment characteristics, the range of temporal variation of individual pathways, ontogenetic changes in lake basins, and the selective effects of humans on m transfers. In particular, preliminary synthesis suggests that m influx can overwhelm the direct effects of E transfer to lakes, especially when anthropogenic activities alter m subsidies from catchments.The structure and function of lake ecosystems is regulated by complex interactions among climate, humans, ecosystem morphology, and catchment characteristics, each of which varies in time and space (Schindler 2001). For example, climatic controls range from daily meteorological variations in local irradiance, temperature, and water fluxes (Keller 2007) through to large-scale interactions of the atmosphere and oceans (Trenberth and Hurrell 1994;Hurrell 1995;Mantua et al. 1997) and millennium-long changes in energy (E) and mass (m) flux around the planet (Williams et al. 1997;Diffenbaugh et al. 2006). Within this framework, chemical, physical, and ecological processes combine to determine the production and composition of aquatic communities, both uniquely and in consort with other mechanisms (Carpenter 1999). In addition, lakes are affected both by human disturbance of biotic communities and biogeochemical cycles (e.g., land use, urbanization, fisheries management) and by creation of novel stressors (e.g., acidic precipitation, toxicants, ozone loss). However, because these factors interact over diverse spatial and temporal scales, it is difficult to determine the relative importance of regulatory processes using only traditional site-based observation and experimentation. Instead, it is the premise of this article that the combined use of limnology and paleoecology represents the best means to quantify and scale interactions between climate and other control mechanisms and to develop a hierarchical understanding of how these regulatory processes are likely to influence lakes pres...

Magnitudes and controls of organic and inorganic carbon flux through a chain of hard‐water lakes on the northern Great Plains

“…In contrast, external inputs of IC appear to regulate the C content of hard-water lakes at all timescales (Table 2) (Stets et al 2009), while mainly chemical mechanisms (pH, precipitation) provide the weak linkage between IC and OC fluxes Finlay et al 2009). Although this weakly coupled dual flux model is tentative and requires validation, we note that it is consistent with predictions of the Em flux framework of Leavitt et al (2009) in which the relative effects of energy (E) or mass (m) influx on ecosystem function are greatest when influx composes a high proportion of lake content.…”

“…R. Leavitt unpubl. data) and longer cores spanning up to 250 yr (Hall et al 1999;Leavitt et al 2006) reveal that C deposition varies , 25% among profundal sites, a range that is similar to observed spatial variation within other lakes . Together, these findings suggest that comparisons of C efflux within and among lakes are robust to measurement errors, particularly when averaged over the 13 yr of study.…”

“…Each section was freeze-dried, and subsamples were acidified using 0.3 mol L 21 HCl. Each organic (acidified) and bulk (unacidified) sample was analyzed for C stable isotope ratios (d 13 C) and content (% dry weight) using isotope ratio mass spectrometry at the University of Regina following Leavitt et al (2006). Sediment chronology was based on 210 Pb activity measured by gamma spectrometry using an Ortec highpurity germanium (HPGe) coaxial well photon detector system following standard procedures (Appleby et al 1986;Schelske et al 1994).…”

A spatiotemporal investigation of varved sediments highlights the dynamics of hypolimnetic hypoxia in a large hard‐water lake over the last 150 years

“…Climate variability was measured as changes in air temperature and precipitation (Leavitt et al 2009). Annual and seasonal air temperature were extracted from the historical instrumental climatological surface time series of the Alpine region database (www.zamg.ac.at/histalp/), according to lake geographical coordinates (Auer et al 2007).…”

Deciphering the effect of climate change and separating the influence of confounding factors in sediment core records using additive models

“…Indeed, far more interesting questions may be addressed where independent data on forcing variables are available covering the same time period as the observed samples (Leavitt et al 2009). For example, given independent temperature measurements for a recent sediment core sequence covering the past 1-200 yr, one could model the effect of temperature variations on species composition recorded in the sediment samples.…”