# Soils are linked along hillslopes ## The concept of a catena as linked soils Soil scientists separate soils into distinct units by necessity. The [[Soils form in profiles and horizons|soil profile]] is where we often start. We need to put boundaries on what and where a soil is in space in order to study it. But in reality, soils exist in a continuum across a landscape. I like to think of soils like a blanket resting over the rocks underneath. This blanket is quilted with patches representing different soil types. Some patches are overlapping, some areas crumpled or folded, and other areas are haphazardly stitched together. The patches are connected and interacting in many different ways. The blanket of soil as a whole hugs the shape of the landscape. Soils exist as a natural mosaic. While distinct soil types and features do exist, soils are physically connected across space and so too, are their properties. Soil scientists have devised a concept to help us visualize and study soils that are interdependent with one another within a landscape. The term "catena", Italian for "chain", is used to describe a group of soils that occur on a continuous hillslope. A catena is a chain of soils that exist on different topographic positions on the same hillslope and therefore are connected by hillslope processes. But unlike a [[Soil scientists study groups of soils in sequence|toposequence]] where topography is the only soil forming factor that varies between a group of soils, a catena includes soils that may vary in their parent material and biotic communities. ![[catena sketch photo.jpg]] *An example of a catena of soils forming along a continuous hillslope in San Luis Obispo, CA. We have a series of soils we study for my class on the side of the hill where I am taking the photo, but you can see similar hillslope positions from this view across the valley.* ## Soil processes and properties vary across catenas The shape of a hillslope will influence how water, rocks, sediment, and soil material move across a catena. Water flows downhill. As it does, water picks up and transports soil particles, drives chemical reactions, and dissolves Earth materials. This movement of water results in soil processes and properties that occur predictably at different hillslope positions[^scha]. Soils along the shoulders and backslopes of a hill see higher runoff and erosion rates. This leads to shallower soils because the rate at which material is lost is greater than the rate at which soil material can accumulate. We find the opposite in soils at the bottom of the hill. These footslope and toeslope soils receive more water and material, and tend to be thicker. Of course, as is always the case, these general patterns vary depending on where the catena is located. The climate will impact how much precipitation falls, and not all geologic materials weather and erode at the same rate. Even so, knowing where a soil is on a landscape can tell us a lot about the kinds of processes that impact its formation and ultimately the many features we observe that make soils beautiful. [^scha]: For a great description of hillslope processes, check out this reading: Schaetzl, R.J., 2013. Catenas and soils. In: Shroder, J. (Editor in Chief), Pope, G.A. (Ed.), Treatise on Geomorphology. Academic Press, San Diego, CA, vol. 4, Weathering and Soils Geomorphology, pp. 145–158. ## Take home message Soils do not form in isolation. They are linked together across hillslopes and landscapes. These interconnections, in combination with the [[Soil scientists study groups of soils in sequence|soil forming factors]], create unique soil forms. There's also a greater lesson embedded within the catena concept. In a time when we must constantly bear witness to the destruction of the natural world and a changing climate, the catena concept teaches us that we are inextricably connected to our neighbors, both in space and time. The strength of our communities will help us endure the challenges of the climate crisis that we are already facing[^bill]. The collective actions we take today stem from our past and have consequences for our future. [^bill]: Bill McKibbon recently shared some thoughts about the importance of community for weathering the storms (literal and metaphorical) brought on by the climate crisis. https://billmckibben.substack.com/p/where-should-i-live Thanks for making the time to care about soil. #### Postscript > This essay is part of [[One thing about soil - an educational series]] created by Dr. Yamina Pressler. The essay was originally shared on substack. *created August 23, 2023*