Regulating services

Pollination

Pollination by insects (mainly honeybees and bumblebees) is an essential ecosystem service for the cultivation of fruit (like apples, pears, cherries, strawberries), vegetables (like tomatoes, eggplant, paprika), for seed cultivation (eg. cabbage, lettuce, carrot, onion). For the supply of this service, the present habitat quality for pollinators is studied based on the biological index map. Positive aspects for qualitative habitat for pollinators are: open habitat (heath, natural grassland, shrubs) and flowery vegetation (eg. heath, robinia). Other positive aspects are the presence of green buffers and small landscape elements. To determine the demand for this service, the dependence of the production of cultivated crops from pollination is studied. When a demand for pollination is present in a certain area, the area of high qualitative habitat for pollinators in the vicinity is indicated to estimate the potential pollination. Based on numbers from literature and for Flemish crops, the economic importance of pollination in Flanders is estimated at 200 million euro for honeybees and 40 million euro per year for wild insects.

 

Denitrification

Biological denitrification is the process that converts nitrate (NO3-) to nitrogen (N). As a result, less nitrate will end up in ground and surface water which reduces the risk for eutrophication. Denitrification only takes place in badly drained soils of forests, grassland and agricultural areas, in partially to fully saturated soils, in seepage areas and riparian zones, in sediment of rivers, lakes and estuaries, etc. Nitrification (conversion of ammonia or organic nitrogen to nitrate or nitrite) and denitrification (conversion of nitrate to N2-gas) follow each other in time and/or space. Denitrification can take place when three fundamental conditions are fulfilled: i) nitrate is available, ii) oxygen concentration is limited, and iii) electron acceptors are available. Other factors that influence the denitrification efficiency are temperature (optimum temperature for bacterial denitrification species are 5<T(°C)<20), soil moisture content (> 60% water saturation), soil texture (clay soil shows the largest denitrification losses), vegetation, the supply of carbon and the presence of spatial variation or variation in structure (Liekens et al. 2009).

For the calculation of denitrification following factors are taken into account: groundwater supply (based on topography and soil type), nitrate concentration in ground water (based on nitrate leaching and groundwater refilling), residence time (based on soil type) and denitrification potential (based on groundwater levels). The nitrate concentration in shallow groundwater (mg N-NO3/liter) is multiplied with the ground water refilling (liter/m²) and denitrification rate. The denitrification rate is estimated based on the residence time (range 20-55%) and the average lowest and highest groundwater levels (range 0-100%).

 

Infiltration

Infiltration is an important ecosystem function to guarantee sufficient ground and surface water of good quality. Once deeply infiltrated in the soil, water continues slowly over a long time to deeper groundwater layers. The long residence time of groundwater contributes to the removal of pollutants and nutrients through adsorption, soil chemical processes and microbial denitrification processes. Groundwater will largely return to the surface in seepage zones and as such contribute to a stable and clean base discharge of our rivers. An important effect of infiltration is also the refilling of phreatic groundwater stocks. For Flanders, drainage classes from the soil maps of Flanders could be used as indicator for the infiltration potential of the soil. Based on topography, an index is estimated for each location which indicates the relative elevation compared to the surrounding area. This is repeated for different spatial scales. By combining these scales, we can indicate for each location if groundwater is delivered from the surrounding areas. Important additional factors which are also estimated are: potential soil infiltration (soil texture, soil permeability), compaction and cover of the soil with buildings and the presence of sewerage infrastructure with drainage of rainwater), and interception (retention of rainwater by vegetation by which rainwater evaporates without useful interaction).

 

Carbon in biomass and soil

To reduce the CO₂ concentration in the atmosphere, it is important to limit activities that emit carbon, but also natural carbon burial in ecosystems can contribute to reduce CO₂ in the atmosphere (by increasing net primary production or by reducing heterotrophic respiration). Terrestrial ecosystems sequester about 3 times more organic carbon (OC) than globally present in the atmosphere. The more atmospheric CO₂ is sequestered in biomass and soil organic matter, the less it could contribute to climate change.

In biomass: Plants absorb carbon from its environment for biomass production (primary production). Hence, the carbon is (temporarily) removed from the environment. All nature types absorb carbon. However, we assume that mainly forests with large, long-living biomass are important for carbon uptake. The annual carbon sequestration in biomass is calculated based on the annual growth of harvestable wood volume (m³/ha.year). This is multiplied with the biomass expansion factor to calculate the total biomass growth (m³/ha.year), including roots and branches. The total biomass growth is converted with the species specific density (kg C/m³) to the carbon sequestration per hectare (kg C/ha.year).

In soil: The capacity of carbon sequestration in the soil is determined by land use, soil moisture condition and clay content of the soil. Soil under natural ecosystems show usually higher carbon stocks compared to soils under intensive land use. Hence, carbon stocks are higher in forest soils and permanent grassland then in temporary grassland or arable soils. The wetter the soil and the higher the clay content, the more carbon could be sequestered. For the calculation of carbon sequestration in soils, a distinction is made between the potential maximal carbon sequestration (equilibrium (+ 100 year) with forest and natural or actual soil hydrology), and potential or actual carbon burial in soils with the present land cover and an assumed natural soil hydrology without drainage and groundwater extraction, or actual soil hydrology. Additional maps show the difference in carbon burial in soils between the actual situation (actual land use and actual groundwater level) and a potential maximal carbon burial in the soil (with natural groundwater levels and forest).

 

Air quality

Vegetation has in many different ways a positive influence on air quality. Besides the uptake of carbon dioxide and the production of oxygen gas (O2), it also limits the circulation of fine dust by increasing the dry deposition of particulate matter. This process is the ecosystem service. At locations with high concentrations of fine dust and a high health risk (eg. at traffic intersections in cities), fine dust capture by vegetation has the largest effect. However, vegetation has more complex effects on the concentration of precursors of secondary particulate matter and can even be a source of particulate matter such as pollen. For the quantification of the impact of green areas on the air quality, we build upon data of Oosterbaan, 2006. These numbers give the volume of fine dust capture for different land use types. Regarding the different vegetation types, trees are most effective in capturing harmful substances, followed by shrubs and herbaceous plants, and grass. The effect of coniferous forest is higher compared to deciduous forest. Effects of air pollution by fine dust for the public health form the most important cause of (known and quantified) effects of environmental pollution on health (MIRA-T, 2006). For the current concentrations in Flanders, the health effect is estimated at about 500 euro per inhabitant per year, of which 75% is attributed to PM2.5 (MIRA, distribution of fine dust 2007). A reduction of these effects will generate an important benefit which could be expressed in monetary values (euro/kg PM10 or PM2.5, and euro/ha per vegetation type).

 

Avoided erosion and nutrient burial in soils

Avoided erosion

Soil erosion is affected by erosive precipitation (with fine precipitation there is much less erosion then with hard rain), and by the characteristics of the soil and physical characteristics such as slope, length, etc. Soil cover and soil tillage have also an influence on infiltration and run-off and hence on soil erosion. Topography is one of the key factors that determines the sensitivity of soils for erosion. Mainly the slope length and slope angle are positively correlated with soil risk. The potential maximal erosion is estimated as the erosion that would occur in case the entire area is covered by arable land. The actual erosion is the erosion that occurs with the present soil cover. In addition, also the origin of and risk for mudslides are investigated. The eroded material will either run-off over a large area to downstream areas, or will concentrate in gullies. The latter case is called mudslides. Mudslides originate in erosion sensitive areas located at open slopes. The potential source locations of mudslides are mapped. Mudslides will only originate when a gully is present downstream of the source. Locations (gullies, valleys) that cause preferential streams for mudslides are investigated. The demand for erosion prevention is determined by the locations with a high risk for mudslides and a high population density. Avoided erosion is the reduction in the maximal potential erosion by the presence of vegetation. The avoided volume of erosion is estimated as the difference between the maximal potential erosion if everything is arable land and the actual erosion with the present soil cover. One of the most important benefits of protection against erosion is generated by the avoidance of sediment deposition in built-up areas. The higher the density of buildings, the greater the damage by mudslides (sediment deposition) and thus the risk of mudslides.

Nutrient burial in soils

The uptake of nitrogen, phosphorous and carbon in biomass, litter and organic matter in soils are linked to several ecosystem services. Soil and vegetation are closely related and certain vegetation types are highly adapted to certain soils. Furthermore, vegetation could also adapt certain soil characteristics. Ecosystems are capable of cycling nutrients and to enrich soils with organic matter. The ratio and availability of carbon, nitrogen and phosphorous in soils determines its productivity and species composition. Given certain hydrological conditions, ecosystems could filter ground and surface water by denitrification and/or uptake in organic matter (living, litter, humus). In this way, they improve the quality of ground and surface water and provide a number of direct (e.g. clean water) and indirect benefits (e.g. water related recreation).

The burial of nitrogen and phosphorous in soils in directly related to carbon burial in soils. The C/N/P ratio for forests and other land use/land cover are applied to estimate the potential and actual N and P burial in soils based on carbon burial in soils (see ES: carbon in biomass and soils).

 

Avoided N leaching

Land use and land cover determine the approved N-fertilising. Regulations relating to fertilising are complex. For the analysis, we consider the general fertilising rules from 2014 (Flanders is entirely a vulnerable water area). Leaching of nitrogen to the groundwater depends on many factors such as the type and amount of fertilising, and climate-, soil- and crop-dependent factors. To estimate the local nitrogen leaching to shallow groundwater, we consider nitrogen load and the sensitivity for leaching. The nitrogen load to groundwater is determined based on existing data and studies of the Flemish database for fertilising (‘Mestbank’), agricultural use map, the combined crop group and soil texture. The atmospheric nitrogen deposition is also added. For the sensitivity for nitrogen leaching, we consider following factors: texture, drainage, profile development, substrate, variation in source material (when peat is added), additional parameters (e.g. flow or seepage state (seepage, flow, infiltration)). A sensitivity score is given to each of these factors and added together to get a global score for nitrate leaching sensitivity.

 

Water retention

Water retention in shallow groundwater includes the (temporal) retention of water which is mainly important in case of drought (retention of water, sponge-effect). The long term retention of water in (upstream) ecosystems (natural depressions and valleys) could contribute to deep infiltration and the addition of groundwater resources. The volume of water that is available within a normal annual cycle to support crucial ecosystem functions, is estimated as the difference between average high groundwater level and average low groundwater level for areas with a shallow groundwater level. Water retention depends on soil characteristics, drainage and land cover (desired drainage). Water retention as supporting function is strongly determining for ecosystem services such as denitrification, carbon burial in soils and the associated nutrient retention. Several indicators for infiltration and retention could be derived from the estimation and combination of topographic indices (Ruhoff, 2011) with the digital elevation model and different scales. The TPI (topographic position index) is a simple indicator for how a site relates to its surroundings. It evaluates the elevation of a certain pixel in relation to the average elevation of the surrounding pixels. Evidently, this is a scale dependent indicator. Estimating and combining the TPI at different spatial scales could give a robust way to map infiltration-seepage patterns.