**5. Agri-environmental scenarios**

120 Studies on Water Management Issues

Water that enters the soil may move along one of the several different pathways. It may be removed by plant uptake or evaporation; it may percolate past the bottom of the soil profile or may move laterally in the profile. However, plant uptake removes the majority of water that enters the soil profile (Neitsch et al., 2005). The soil water content will be represented correctly if crops are growing at the expected rate and soils have been correctly parameterized. Figure 4 shows the average of HRU for both catchments, with a silt clay soils, with the prevailing surface runoff and slow lateral subsurface flow. Soils exit the field capacity in the spring and return to that state in the autumn (Fig. 4). Soils in the summer are

often completely dry with occasional increasing induced by storms.

**Soil Water Content (mm)**

**01/01/01**

**04/01/01**

(2001−2005)

**07/01/01**

**10/01/01**

presented on figure 5.

**01/01/02**

**04/01/02**

**07/01/02**

**10/01/02**

**01/01/03**

**04/01/03**

**Month/Day/Year**

**07/01/03**

**Soil Water Content HRU38 Precipitation Bilje (mm)**

**10/01/03**

**01/01/04**

**0 0.5 1 1.5 2 2.5 3**

**LAI (m2 m-2)**

HRU No. 38 in the river Reka catchment

**01/01/01**

**02/01/01**

**03/01/01**

**04/01/01**

**05/01/01**

**06/01/01**

Fig. 5. Simulated vineyard biomass growth (kg ha-1) and leaf area index (m2 m-2) for the

**07/01/01**

**Month/Day/Year**

**08/01/01**

**09/01/01**

**10/01/01**

**11/01/01**

**12/01/01**

**LAI Biomass**

**01/01/02**

**Biomass (kg ha-1)**

**04/01/04**

**07/01/04**

**10/01/04**

**01/01/05**

**04/01/05**

**07/01/05**

**Precipitation (mm)**

**Soil Water Content (mm)**

The plant growth component of SWAT is a simplified version of the plant growth model. Phenological plant development is based on daily accumulated heat units, leaf area development, potential biomass is based on a method developed by Monteith, a harvest index is used to calculate yield, and plant growth can be inhibited by temperature, water, N or P stress. (Neitsch et al., 2005). In the crop database a range of parameters can be changed to meet the requirements for optimal plant growth. We used default SWAT database parameters that were additionally modified (Frame, 1992). An example crop growth profile for development of leaf area index (LAI) and plant biomass (BIOM) for vineyard is

Fig. 4. Comparison of simulated soil water content (mm) for the HRU No. 38 (Reka) and HRU No. 182 (Dragonja) and observed precipitation (mm) in the calibration period

**01/01/01**

**04/01/01**

**07/01/01**

**10/01/01**

**01/01/02**

**04/01/02**

**07/01/02**

**10/01/02**

**01/01/03**

**04/01/03**

**Month/Day/Year**

**07/01/03**

**Soil Water Content HRU182 (mm) Precipitation Portorož (mm)**

**10/01/03**

**01/01/04**

**04/01/04**

**07/01/04**

**10/01/04**

**01/01/05**

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**07/01/05**

**Padavine (mm)**

The aim of this scenario was to investigate possible effects of the agri-environmental measures on the river water quality. To achieve the aim seven different scenarios were applied to the study area EVP, EKO20, EKO100, S35, S50, STV35, ETA.

The field erosion buffer strips scenario (EVP) is a function of how to minimize influences of diffuse pollution resulting from agricultural activities without drastic management changes. They are planted or indigenous bands of vegetation that are situated between source areas and receiving waters to reduce surface runoff velocities and to remove pollutants from surface and subsurface runoff. The effectiveness of strips is closely correlated with their slope and width (Dillaha et al., 1989). An option of 3 m wide strips was modelled on all arable (AGRC, AGRR), vineyard (VINE), orchard (ORCI, ORCE) in olive grove (OLEA) HRUs.

Organic farming scenarios on 20 % of the area (EKO20) and on the 100 % area (EKO100) aim to reduce the use of mineral fertilizers and to reduce the intensity of production. Special organic rotations with green manure and composted farmyard manure were created. The lack of P was compensated with the use of triple-superphosphate that is allowed in organic production. Both organic scenarios were designed to ensure normal production for the market.

Steep meadows, being an agricultural landscape, should be cut regularly, but due to the steep slopes and the associated costs and risks, are abandoned and overgrown. Scenarios having steep meadows with slope inclination above 35 % (S35) and 50 % (S50) should prevent overgrowth. To verify the effects of scenarios on water quantity and nutrients transport, meadows (TRAV) of both case studies located on slopes greater than 35 % and 50 % were changed into the forest (FRSD) (Fig. 6). In the S35 scenario 18 % (Reka) and 3.6 % (Dragonja) of grassland was changed into forest, which is equivalent to 1.43 % (Reka) and 0.67 % (Dragonja) of the total catchments. In the S50 scenario only 2 % (Reka) and 0.3 % (Dragonja) of grassland was changed into forest, which is equivalent to 0.16% (Reka) and 0.06% (Dragonja) of the total catchments.

Fig. 6. Hydrological response units with the grassland land use (TRAV) and slopes greater than 35 % and 50 % for the Reka and Dragonja catchment

Conservation of vineyards on steep slopes has proved to be difficult because of unprofitable production. Economic reasons were followed by a trend of wine production abandonment.

Modelling of Surface Water Quality by Catchment Model SWAT 123

Reka/8 0.57 0.56 0.21 0.27 1.00 Dragonja/14 0.80 0.78 0.21 0.42 1.11

Reka/8 1,844 1,576 1,075 571 4,185 Dragonja/14 4,804 4,934 1,576 1,917 7,734

Reka/8 88,728 74,260 63,255 33,376 278,227 Dragonja/14 163,763 134,801 98,949 59,922 406,330

Reka/8 3,489 2,729 2,993 947 11,742 Dragonja/14 2,420 1,950 1,447 896 6,009 Table 7. Average annual flow (m3 s-1) and river load of sediment (t year-1), total nitrogen and total phosphorus (kg year-1) for the Reka subcatchment 8 and Dragonja subcatchment 14

Changes in average annual flow between base and agri-environmental scenarios are minimal for both catchments for the research period. Maximum changes on an annual basis are less than 0.5 % (Table 8) and on a monthly basis close to 1% (Reka) and 5% (Dragonja) (Fig. 9). Student t-statistics for average annual flows reveal that the results of the agrienvironmental scenarios are not statistically different from the base scenario (Table 9).

**subcatchment EVP EKO20 EKO100 S35 S50 STV35 ETA** 

Reka/8 0.00 0.09 0.04 0.02 0.00 0.17 0.16 Dragonja/14 0.00 –0.32 0.36 0.00 0.00 0.00 0.09

Reka/8 –14.93 –4.95 –25.42 –0.85 –0.05 –2.28 –3.12 Dragonja/14 –31.95 –20.82 –20.92 –2.26 –0.05 –0.01 –52.96

Reka/8 –2.67 9.00 –1.91 –0.43 –0.02 –5.15 –2.32 Dragonja/14 –1.46 12.51 3.71 –0.22 –0.01 0.00 –6.63

Reka/8 –14.15 9.28 –26.15 –0.58 –0.04 –2.44 –3.45 Dragonja/14 –3.28 9.90 1.39 –0.29 0.00 0.00 –8.58 Table 8. Impacts (change in %) of agri-environmental scenarios on the river flow, sediment load, total nitrogen and total phosphorus load in the watercourse; compared to the baseline

**Catchment/ Average annual percentage change (%)** 

**deviation Min. Max.** 

**Catchment/subcatchment Average Median Standard** 

*Flow (m3 s-1)*

(1994−2008)

**6.1 River flow** 

*River Flow*

*Sediment*

*Total nitrogen* 

*Total phosphorus*

scenario

*Sediment (t year-1)*

*Total nitrogen (kg year-1)* 

*Total phosphorus (kg year-1)* 

In the steep vineyards scenario (STV35), all vineyards on the slopes greater than 35 % were changed into forest, to verify the environmental impact of abandonment of vineyards on steep slopes (Fig. 7). In the STV35 scenario, 17 % (Reka) and 1.4 % (Dragonja) of grassland is changed into forest, which is equivalent to 3.93% (River) and 0.06% (Dragonja) of the total catchments.

Fig. 7. Hydrological response units with the vineyard land use (VINE) and slopes greater than 35 % for the Reka and Dragonja catchment

Extensive grassland scenario (ETA) objective was to determine what would be the impact on water quantity and quality, if the whole grassland would be overgrown with forest. Extensive grassland use with one cutting is widespread in both areas. Whole grassland in the Reka (8 %) and Dragonja (18%) catchments area was turned into a forest (Fig. 8).

Fig. 8. Hydrological response units with the grassland land use (TRAV) and slope classes for the Reka and Dragonja catchment
