Elsevier

CATENA

Volume 207, December 2021, 105660
CATENA

Linking sedimentological and spatial analysis to assess the impact of the forestry industry on soil loss: The case of Lanalhue Basin, Chile

https://doi.org/10.1016/j.catena.2021.105660Get rights and content

Highlights

  • Two approaches were used to evaluate soil loss: paleolimnology and USLE models.

  • Low sedimentation rates were discovered for the time prior to 1950 CE.

  • Organic/sand contents and total sediment increased after the arrival of forestry.

  • Forestry activity is the main cause of soil loss as compared to other land uses.

  • Priority restoration areas in the catchment have been proposed to control soil losses.

Abstract

Soil loss has become one of the main problems associated with global change over the last decades. New assessments are needed in order to improve our understanding of the real impacts of human productive activities on the natural dynamics linked to erosion in lake basins. We analyzed the recent and historical dynamics of soil loss in a coastal lake basin of central Chile (Lanalhue lake), evaluating land use impacts and proposing management changes to control erosion and restore the soil. We implemented two approaches: A) Using a high-resolution sedimentological proxy and a high-accuracy chronology of cores to determine the sediment accumulation rate, organic/inorganic matter and granulometry for the last 120 years; and B) applying the Universal Soil Loss Equation to estimate erosion of soil from hills during the last 32 years, considering a combination of satellite, climate, soil, and land-cover topographic data. We found that the sedimentation rates, as well as the concentration of organic matter in lake sediments, were relatively constant from 1900 to 1950; after that, they experienced a significant increase. The same pattern of rapid increase was found for sand content. We found that erosion during the last 30 years has been high and constant, especially in bare soil (mainly clear-cutting areas) and exotic forest plantations. Erosion has been significantly higher within exotic forest plantations, reaching 31 ton/ha/yr in clear-cutting areas. Three industrial forestry companies accounted for 61.5% of the basin surface where urgent erosion control is needed. Our findings support the indication that industrial forestry is the main activity affecting erosion dynamics in the basin; secondarily, earthquakes have been important modulators of the sediment dynamics in Lanalhue during these last 120 years.

Introduction

During the last decades, global change has generated a dramatic transformation of the land cover on the planet's surface. Among these effects, the increase in erosion stands out as a particularly concerning issue (Borelli et al., 2017), because soil is considered a non-renewable resource on a human time scale, and because the lost soil increases sedimentation and eutrophication in different bodies of water (Owens 2008). For this reason, a series of efforts has been developed globally to detect and control soil loss (Borrelli et al., 2017) as well as to develop new methodologies and frameworks for prioritizing areas for restoration (Geneletti et al., 2011, Crossman and Bryan, 2006). These methodologies include long-, medium-, and short-term analyses. Long-term studies are based on paleolimnology analysis, which reconstructs past environments by quantifying observed changes over time in factors like sedimentation rates, sedimentology, and biological proxies) (Larocque-Tobler, 2016). The medium-term analysis uses algorithms such as the Universal Soil Loss equation (USLE) to estimate the potential soil loss across a spatial expanse based on a series of hydrometeorological, physiographic, and land-cover factors (Wischmeier and Smith, 1978). This methodology can be applied by using satellite data in combination with edaphic cadasters to generate erosion assessments (Alewell et al., 2019). It is not possible to compare long- and medium-term methods directly, because USLE cannot estimate the total yield of sediment that enters into a lake, since part of it is retained in valleys or creeks. Boyle et al. (2011) discussed the SEDEM model, which was developed to estimate the fraction of soil that is not deposited in the lake, concluding that this method is difficult to apply because it requires high quantity and quality field information (short-term erosion studies), unlike the USLE method. Because of the lack of short−term erosion studies, Boyle et al. (2011) proposed an alternative approach based on the results of Vandenberghe et al. (1998) in Belgian lakes: discard that quantity of retained sediment, especially in the case of small catchments (< ~ 100 km2) because it is a small amount, and use USLE to estimate the sediment deposited in lakes (see Table 1).

One of the main sources of disturbance and soil loss is the replacement of natural land cover by forestry plantations (Grace, 2004, Huber et al., 2010). Chile has been one of the countries most affected by this type of land-cover change, especially in its south-central coastal area (Miranda et al., 2015, Miranda et al., 2017). In Chile, the species used for forestry plantations are mainly exotic; Pinus radiata was the first species to be massively planted, followed by Eucalyptus globulus. Forestry activity has been considered one of the most environmentally harmful activities in Chile since 1974, when the government offered subsidies for private owners to plant exotic species, producing an exponential expansion of plantations (Leyes de Chile, 2019). Industrial plantations use a clear-cutting system in which large stands of plantations are cut at once, leaving soil exposed to dramatic erosion by precipitation (Gayoso and Iroumé, 1995). In addition, the hydrophobic condition of Pinus species hinders water infiltration into soil, affecting water balance (Huber et al., 2010). Erosion is also promoted by the mountainous topography and heavy rain characteristic of south-central Chile (Oyarzun and Peña, 1995). The aim of this study is to estimate the impact of the forestry industry on soil loss by combining sedimentological and USLE methods in a medium-sized lake basin located in central Chile, and to propose priority sites for soil restoration and erosion control. Sedimentology allows us to estimate long-term changes of sedimentation rates before Pinus and Eucalyptus plantations (the background conditions), and comparing these results with the present soil loss obtained from the USLE model allows us to estimate the quantity of soil that is transported from nearby hills into the lake as well as the activity associated with soil loss.

We specifically address the following questions: A) Have sedimentation rates changed during the last 120 years in Lanalhue lake? B) What was the timing of these changes? C) Which of the factors of the USLE analysis had the greatest influence on erosion for each type of land cover? D) What type of land cover and property type has caused the greatest soil loss in the basin? E) Where is it most necessary to implement restoration actions? We propose that sedimentology and USLE models, working together, give us a powerful tool, because sediment analysis tells us the comparative quantity of sediment deposited in the bottom of the lake and its temporal changes through centuries and even decades, and the USLE method gives us information about the land use that produced this sediment, as well as the quantity of sediment in tons per area per year that arrived to the lake. The USLE model also tells us the origin (anthropogenic or not) and the land use that are producing the greatest amount of sediment. USLE models, validated by sedimentology, allow us to propose management actions to control soil loss. We also present a series of methodological advances which could be used to replicate USLE analysis.

Section snippets

Study area

Lanalhue basin is located in the Biobío Administrative Region, southwest of the Nahuelbuta coastal range (73° S, 37° W, Fig. 1). This coastal basin flows into the Pacific Ocean; it is surrounded by mountains composed of metamorphic rocks that rise from 500 to 800 m in the east (with minimum valley elevation of 21 m) and in the west rise up to 1065 m (SERNAGEOMIN, 2003). The average slope is 15° ± 9.9°, with a maximum of 63.3° . The basin has an area of 365.4 km2. The lake is 9 km long and

Sediment sampling and chronology

Fieldwork was carried out during January 2019 (austral summer). Lake bathymetry was explored with an echo sounder (Garmin echoTM100) and sediment cores were collected from four sites along the lake, following the principal streams and variable maximum depths (Licahue, 3 m; Lincuyin, 15 m; Huilquehue, 24 m and La Vaina, 24 m) (Fig. 1 and S1). At each site, four 1 m-long sediment cores were collected using an Uwitec gravity corer. Each core was sliced at 1-cm intervals, except for the La Vaina

Age model and radionuclide data

The age model created by Plum presented a good performance for the period 1960–2019 CE, which is the main temporal focus of this research. However, based on the basal radiocarbon ages from each core, we can extend the chronologies up to 1090 CE for Lincuyin, 330 CE for Huilquehue, 440 CE for Licahue, 1270 CE for La Vaina (Fig. S10, Table S4).

The mean unsupported 210Pb fluxes inferred by the Plum model were 58.7 Bq/m2 yr−1 for Lincuyin, 50.1 Bq/m2 yr−1 for Huilquehue, 22.5 Bq/m2 yr−1 for

Integrated insights from sedimentological analysis

Sedimentological proxies from Lanalhue lake presented here (sediment accumulation rates, organic matter content, and grain size) showed three main depositional phases over the last 120 years. From 1900 to 1950 CE, the lake had very low accumulation rates (<0.15 cm/year) in the four studied cores (Fig. 3). Although the accumulation rates from any core may differ greatly from the historical sedimentation of a lake, we have not found large differences between cores during this time period, as we

Assumptions, limitations and future potential

It has been found that USLE, RUSLE, and WEPP models may overestimate erosion in zones with high erosion (usually related to plots with high slope), and underestimate it in plots with low erosion (Tiwari et al., 2000, Aburto et al. 2010). The documented differences between real plots and models from previous studies suggest that WEPP models generate more uncertainty, while USLE and RUSLE produce more similar results in comparison with field plots (Tiwari et al., 2000). Since the Lanalhue basin

Concluding remarks

Our approach allowed us to estimate and map the dynamics of soil loss on historical (long-term) and recent (middle-term) time frames, helping to understand the trends and impacts of landscape transformations on the basin. The insight obtained from the sedimentological record can extend our understanding of landscape evolution developed from the USLE method previous 1985 CE, and is a useful and novel tool in ecosystem restoration planning. These approaches provided consistent results: the recent

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We are grateful to Violeta Tolorza for valuable conversations about soil erosion, and to Manuel Malibur for the local information he provided. We thank Manuel, Pedro Peña and Vivianne Claramunt for their field support. This study had the financial support of the Chilean Ministerio de Medio Ambiente FNDR-PRELA 608897-63-LP18 Project, the Instituto de Ecología y Biodiversidad (IEB) AFB 170008, and Fondecyt 1190398, 1201528 Projects. Alberto J. Alaniz was supported by ANID-PFCHA/ Doctorado

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