Abstract:
Ecosystem services (ES) are the benefits that humans gain from natural systems, either
directly or indirectly. The ES approach generally covers soil erosion as soil retention. Soil
erosion is one of the most crucial environmental problems confronting the globe today
affecting the fate of human societies and the achievement of sustainable development
goals that promote human and environmental well-being. Assessing soil erosion is crucial
for watershed management. Thus, this study estimated and mapped the soil erosion,
using the Integrated Valuation of Ecosystem Services and Trade-offs (InVEST 3.9.2)
Sediment Delivery Ratio (SDR) model, in the Samanalawewa watershed (SW) in Sri
Lanka, during 20 years (2000-2020) with five-year time intervals. Several models have
been used to assess soil erosion rates in watersheds. Due to its various advantages,
including high-accuracy predictions, the option to incorporate more input variables
for prediction, and flexibility for utilization, the InVEST SDR model is a frequently
used model for the assessment of soil erosion rates. Input data were obtained from
the Meteorological Department, Survey Department, USGS website, as secondary data
sources. According to the obtained results, the estimated mean annual soil erosion rates
were 53.2, 52.9, 69.7, 87.7, and 70.2 t ha−1 year−1, respectively for years 2000, 2005, 2010,
2015, and 2020. The resulting soil loss values of SW are 10 to 18 times higher than the
soil erosion tolerance (5 t ha−1 year−1) in Sri Lanka. The results show that the years 2015
and 2005 had the highest and the lowest total soil loss values, respectively. The upper
part of the watershed has the highest soil loss values, while the remaining parts of the SW
have relatively moderate soil loss values. Furthermore, the soil erosion distribution of SW
reveals that soil erosion is directly related to high precipitation values and inappropriate
land use practices (Chena and Tea cultivations). These results would support in the
development of watershed management policies and in the implementation of proper
soil and water conservation measures to mitigate soil erosion.
