The pitfalls of transfer functions (and how to avoid them!)

By Erin Hayes-Pontius

Paleoecology, or the study of organisms and their environments in past times, has a specific branch known as paleolimnology, which deals with records left by lakes. Beyond being pleasant places for swimming, fishing, and other recreation, lakes are particularly valuable for paleo records. Not only do lakes archive the goings-on within themselves, but they also archive goings-on within their drainage basins. In the case of Lake Champlain, it has a drainage basin nearly 17 times that of its surface area (21,326 km2 : 1,269 km2), making it extra sensitive to changes in climate (Fig. 1).

Due to lakes’ positions at low points on the landscape, they integrate everything that happens within their drainage basin and are therefore important “sentinels of change” (Williamson et al. 2009).

Figure 1. Lake Champlain’s drainage basin. From Wikimedia Commons

Over time, a variety of things fall into lakes, such as diatoms (single-celled algae), pollen, chironomid midges, or needles, to name a few, and these things get buried by sediment. In some lakes- some, certainly not most- sediment deposits occur quickly enough to leave annual layers; if this interests you, definitely check out Rob’s post from a little while back. Unfortunately, this does not happen most of the time, and we’re left with a much coarser resolution to deal with. Rather than knowing about the diatom species every year, we may only know ‘who’ was there every few years, every decade, or even every few decades. Despite these challenges, lakes are still- and will continue to be- widely used in paleoecology.

Through the looking glass: how diatoms can reconstruct wind

By Kelsey

Few object are more beautiful than the minute siliceous cases of the diatomaceae: were these created that they might be examined and admired under the high powers of the microscope? ~ Charles Darwin

As Darwin remarks, diatoms are beautiful.  They have unique, intricate cell walls that help in their identification, because in addition to their beauty, they can tell a lot about past environmental conditions.  My research uses diatoms as a proxy (a preserved item that acts as a ‘natural archive,’ capable of telling us something about climate in the past) to explore past environmental conditions in lakes.  Diatoms are a type of single celled organisms called algae.  These organisms are found in many wet environments including soils, but I focus on diatoms in lakes.

Figure 1: Images of various species of diatoms. Image from Wikimedia Commons.

Diatoms are unique from other types of algae because they have siliceous or glass-like cell walls, and therefore are well preserved in lake sediments.  This makes them good proxies of past climates.  Additionally, diatom species, like other algae have a variety of environmental preferences.  These preferences can range from mixed or stable water conditions, to high nutrient or light levels and provide the basis for climate inferences.

What proxies can tell us about drought

By Kelsey

We are all familiar with the images.  The barren landscape.  Brown, dead vegetation spanning as far as the eye can see.  Lakes and rivers shrinking in size, their relict banks cracked and dry.

These dryspells or droughts can last from days to years and they occur when a region receives below average precipitation.  Droughts are generally said to arise from insufficient precipitation amounts over an extended period of time.  This shortage in precipitation occurs typically in one season or more, and results in a water shortage for an environmental region.  The impact of the drought arises from the interaction between the natural events (less precipitation than expected) and the demand on the water supply (both from the environment and humans), which can exacerbate the impacts of the drought. Because of these factors that can influence the magnitude of the drought, they need to be taken into consideration when working to define a drought (National Drought and Mitigation Center). Frequently the definitions can vary from location to location as certain areas are less adapted to low water conditions than others.  But it can also dependent on timing.  For example, in the desert a month without rain doesn’t have the same effect as it would in the rainforest.  However, if the month without rain in the desert came during the period designated as the rainy season, the impacts would be drastically different.

Depending on how long these dryspells last there can be a huge impact on the ecosystem and economies associated with them.  One prime example is the Dust Bowl.