Laboratory and Field Protocol for Estimating Sheet Erosion Rates from Dendrogeomorphology

Summary

Characterizing erosion from dendrogeomorphology has usually focused on accurately finding the starting time of root exposure, by examining macroscopic or cell level changes caused by exposure. Here, we offer a detailed description of different novel techniques to obtain more precise erosion rates from highly accurate microtopographic data.

Abstract

Sheet erosion is among the crucial drivers of soil degradation. Erosion is controlled by environmental factors and human activities, which often lead to severe environmental impacts. The understanding of sheet erosion is, consequently, a worldwide issue with implications for both environment and economies. However, the knowledge on how erosion evolves in space and time is still limited, as well as its effects on the environment. Below, we explain a new dendrogeomorphological protocol for deriving eroded soil thickness (E_x) by acquiring accurate microtopographic data using both terrestrial laser scanning (TLS) and microtopographic profile gauges. Additionally, standard dendrogeomorphic procedures, dependent on anatomical variations in root rings, are utilized to establish the timing of exposure. Both TLS and microtopographic profile gauges are used to obtain ground surface profiles, from which E_x is estimated after the threshold distance (TD) is determined, i.e., the distance between the root and the sediment knickpoint, which allows defining the lowering of the ground surface caused by sheet erosion. For each profile, we measured the height between the topside of the root and a virtual plane tangential to the ground surface. In this way, we intended to avoid small-scale impacts of soil deformation, which may be due to pressures exerted by the root system, or by the arrangement of exposed roots. This may provoke small amounts of soil sedimentation or erosion depending on how they physically affect the surface runoff. We demonstrate that an adequate microtopographic characterization of exposed roots and their associated ground surface is very valuable to obtain accurate erosion rates. This finding could be utilized to develop the best management practices designed to eventually halt or perhaps, at least, lessen soil erosion, so that more sustainable management policies can be put into practice.

Introduction

Both economic and environmental impacts produced by sheet erosion makes this topic in a worldwide concern¹. Several methods, from direct techniques to physical-based and empirical approaches, are used to calculate soil erosion rates on a variety of temporal and spatial scales. Direct techniques use field measurements under natural conditions and are mainly based on the use of Gerlach troughs², water collectors³, erosion pins⁴ and profilometers⁵. Furthermore, models of soil erosion have been increasingly focused on representing in detail the real phys....

Protocol

1. Sampling Strategy

1. Geomorphic process identification
   1. Implement the Hydrologic Response Units approach (HRU)²¹. To this end, identify homogenous areas within the study site, comprising lithology and surface deposits, canopy cover, vegetative residue in contact with the soil surface and slope. Select among all the HRUs those in which the sheet erosion process is predominant.

Results

Samples of exposed roots suffer serious cambial deterioration due to the impact of exposure (e.g., modifications in temperature, incidence of light) plus the physical stress, due to trampling by hikers or animal grazing and browsing that the roots undergo after they are exposed. Determining the existence of discontinuous rings, as well as precisely dating the first year of response to exposure was accomplished in the lab as in Protocol 4 (steps 4.1.6 to 4.1.8). We chose the incre.......

Discussion

The protocol deployed demonstrates the value of detailed and proper characterization of ground surface microtopography, as it enables to measure trustworthy sheet erosion rates from dendrogeomorphology. Our methodological approach focuses on the importance of characterizing the microtopography in the surroundings of exposure roots to improve erosion rate estimation. This factor has been largely ignored in previous studies, resulting in a misinterpretation of soil erosion rates derived from dendrogeomorphology

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Topographic map, soil map, land cover map			To be obtained from public institutions or generate at the first phase of research
Single ring infiltometer	Turf-Tec International	IN16-W	http://www.turf-tec.com/IN16Lit.html
Handsaw			There is noy any specific characteristics to be considered regarding the model
Measuring tape			With accuracy of 1 mm
Terrestrial Laser Scanning (TLS)	Leica-Geosystems	Leica ScanStation P16	https://leica-geosystems.com/products/laser-scanners/scanners/leica-scanstation-p16
Microtopographic Profile Gauge	RS Online	Facom, 19	https://www.classic-conservation.com/es/herramientas-para-talla-y-escultura-en-madera/511-galga-medidora-de-perfiles.html
Sandpaper			from 80 to 400 grit
Scanner	EPSON	Perfection V800 Photo	https://www.epson.co.uk/products/scanners/consumer-scanners/perfection-v800-photo
Image analysis system	Regent Instruments Inc.	WinDENDRO	http://www.regentinstruments.com/assets/windendro_analysisprocess.html
Measuring table	IML		https://www.iml-service.com/product/iml-measuringtable/
Sliding microtome	Thermo Fisher SCIENTIFIC	Microm HM 450-387760	http://www.thermofisher.com/order/catalog/product/910020
Optical microscope	OLYMPUS	MX63/MX63L	https://www.olympus-ims.com/en/microscope/mx63l/
Digital camera for microscope	OLYMPUS	DP74	https://www.olympus-ims.com/en/microscope/dc/
Safranin			Empirical Formula (Hill Notation) C20H19ClN4
Astrablue			Empirical Formula C47H52CuN14O6S3
Alcohol			Alcohol by volume (50%, 75% and 100%)
Distilled water			H2O
Citrus oil clearing agent			https://www.nationaldiagnostics.com/histology/product/histo-clear
Coated slides	Thermo Fisher SCIENTIFIC		https://www.fishersci.com/us/en/products/I9C8JXMT/coated-glass-microscope-slides.html
Hardening epoxy	MERCK		https://www.sigmaaldrich.com/catalog/product/sial/03989?lang=es®ion=ES