Mapping drainage ditches in agricultural landscapes using LiDAR data

R. Melniks¹², J. Ivanovs¹, A. Lazdins¹ and K. Makovskis¹

¹Latvian State Forest Research Institute ‘Silava’, Riga street 111, LV-2169 Salaspils, Latvia
²University of Latvia, Faculty of Geography and Earth Sciences, Jelgava street 1, LV-1004 Riga, Latvia
*Correspondence: mailto:raitis.melniks@silava.lv

Abstract:

The aim of this study is to develop a method for identification of the drainage ditch network, which can be used for surface runoff modeling and to increase accuracy of estimation of greenhouse gas (GHG) emissions in croplands and grasslands, using remote sensing data. The study area consists of 11 objects throughout Latvia with a total area of 145 km². Digital elevation models (DEMs) in two resolutions, which were created using three different interpolation methods, were used for the analysis. Several multi-level data filtering methods were applied to identify ditch network, including flow patterns, which can be used in surface runoff process. The method we developed correctly identified 85–89% of ditches, depending on the DEM used, in comparison to the reference data. Mapped ditches are located within 3 m range of the reference data in 89–93% of cases. The elaborated model is robust and uses openly available source data and can be used for large scale ditch mapping with sufficient accuracy necessary for hydrological modelling and GHG accounting in the national inventories.

Key words:

Evaluation of greenhouse gas emissions and area of organic soils in cropland and grassland in Latvia – integrated National forest inventory data and soil maps approach

G. Petaja*, M. Okmanis, K. Polmanis, J. Stola, G. Spalva and J. Jansons

Latvian State Forest Research Institute “Silava” Rigas street 111, LV–2169 Salaspils, Latvia
*Correspondence: guna.petaja@silava.lv

Abstract:

The aim of the research was to assess distribution of organic soils in farmlands for the time period between 1990 and 2015, as well as to carry out a recalculation of GHG emissions from organic soils in grassland and cropland. We evaluated the area of typical organic soils using digitized soil maps created between 1960s and 1980s there were 183,000 ha of cropland and grassland on organic soils. A selected number of areas on organic soils intersecting with the National forest inventory (NFI) plots were surveyed. We found that 66 ± 10% of surveyed plots still conforms to criteria for organic soils according to Intergovernmental Panel on Climate Change (IPCC) guidelines; in the rest of plots soil organic matter has been mineralized and these areas do not conform to IPCC criteria of organic soils. The following distributionof organic soils was estimated in cropland – 6.3 ± 3.3% in 1990 and 4.1 ± 3.4% in 2015, but in grassland – 11.6 ± 3.6% in 1990 and 7.7 ± 3.9% in 2015. The annual reduction of GHG emissions due to reduction of area of organic soils in cropland in 2015 corresponds to 1,400,000 tonnes CO₂ eq. in comparison to 1990 and in grassland – to 1,100,000 tonnes CO₂ eq. The estimated reduction of the GHG emissions due to conversion of organic soils into mineral soils, comparing the average value in 2005–2009 with the projection for 2021–2030 on average will correspond to 313,000 tonnes CO₂ eq. annually, however LULUCF sector still won’t become a net CO₂ sink according to the GHG inventory data on other land use categories and carbon pools.

Key words:

cropland, GHG emissions, grassland, organic soil