Main authors: Birgitte Hansen, Hyojin Kim, Ingelise Møller, Abel Henriot, Marc Laurencelle, Tommy Dalgaard, Morten Graversgaard, Susanne Klages, Claudia Heidecke and Nicolas Surdyk
FAIRWAYiS Editor: Jane Brandt
Source document: Birgitte Hansen, Hyojin Kim, Ingelise Møller, Abel Henriot, Marc Laurencelle, Tommy Dalgaard, Morten Graversgaard, Susanne Klages, Claudia Heidecke and Nicolas Surdyk 2021. Evaluation of ADWIs: agri-drinking water quality indicators in three case studies (FAIRWAY Project Deliverable 3.2)

 

Contents table
1. Nitrogen indicators
2. Pesticide indicators

1. Nitrogen indicators

The statistical analyses and results from the three case sites regarding nitrogen is presented »Kim et al (2020) Lag Time as an Indicator of the Link between Agricultural Pressure and Drinking Water Quality State.

At these sites, various mitigation measures have been implemented since the 1980s at local to national scales, resulting in a decrease of soil surface N surplus, with long-term nitrate monitoring data also being available to reveal the water quality responses. The lag times continuously increased with an increasing distance from the N source in Tunø (from 0 to 20 years between 1.2 and 24 m below the land surface; mbls) and La Voulzie (from 8 to 24 years along downstream), while in Aalborg-Drastrup, the lag times showed a greater variability with depth—for instance, 23-year lag time at 9–17 mbls and 4-year lag time at 21–23 mbls.

These spatial patterns were interpreted, finding that in Tunø and La Voulzie, matrix flow is the dominant pathway of nitrate, whereas in Aalborg-Drastrup, both matrix and fracture flows are important pathways. The lag times estimated in at the two sites in Denmark were comparable to groundwater ages measured by chlorofluorocarbons (CFCs); however, they may provide different information to the stakeholders. The lag time may indicate a wait time for detecting the effects of an implemented protection plan while groundwater age, which is the mean residence time of a water body that is a mixture of significantly different ages, may be useful for planning the time scale of water protection programs. We conclude that the lag time may be a useful indicator to reveal the hydrogeological links between the agricultural pressure and water quality state, which is fundamental for a successful implementation of drinking water protection plans.

2. Pesticide indicators

The statistical analyses and results regaring pesticides are presented here.

In the first case study Island Tunø, DK, pesticides have been monitored since the 1990s for up to 28 compounds; however, none of them have been detected over the monitoring period (Figure 3.a).

In the second case study site Aalborg-Kongshøj, DK, at the beginning of the monitoring period, 5-6 compounds were measured, and it increased up to 31 compounds in 2010 (Figure 3.b). Pesticides were either not detected (16/34 monitoring points) or ranged at very low concentrations sporadically (<0.03 µg/L in 13/34 monitoring points; Figure 3.b).

D3.2R fig03
Figure 3

Atrazine is the main concern in La Voulzie, FR (Figure 3.c). This compound had been predominantly used in maize field. Use of atrazine has been banned since 2003. The pesticides monitoring has begun in 2001, and has been focusing on atrazine and its metabolite, desethylatrazine (DEA). Both compounds show decreasing trends: atrazine (0.1-0.2 µg/L to 0-0.1µg/L) and DEA (0.3-0.6 µg/L to 0.1-0.4 µg/L) over the monitoring period. The trends and the percentage of maize fields are shown in Figure 4, since atrazine was exclusively used in maize field.

D3.2R fig04
Figure 4

The relatively low impact of pesticides on the groundwater quality in the two Danish case studies makes further analyses of those indicators imposible. Therefore, the further analyses of pesticide indicators could be done only with data from La Voulzie in France because of the high impact of pesticides on the water quality, and their relatively high concentrations.

2.1 N surplus as a pressure indicator

Unlike in the case of nitrogen, time-series of the pesticide inputs are rarely available. Therefore, we tested the N surplus indicator to evaluate its applicability as a pesticides pressure indicator.

In La Voulzie, FR case study, the N surplus indicator and the annual average concentrations of atrazine showed statistically significant correlations using the CCF method. For the top and the bottom springs, the correlations were strong (0.85 for top and 0.83 for bottom springs) and statistically significant, and the estimated lag time was 20 year (Table 3). For the main spring, the correlation was 0.75 and the lag time is 15 years.

Table 3: Pesticide lag time (yr) estimation using N surplus pressure indicator in La Voulzie, France. Statistically significant at * p < 0.05; ** p < 0.005.

Sampling points N surplus
Lag year (correlation coefficient)
Top spring with annual average concentrations 20 (0.85)**
Main spring with annual average concentrations 15 (0.75)**
Bottom spring with annual average concentrations 20 (0.83)**

2.2 Area of main crop type as a pressure indicator

In La Voulzie, FR case study, the correlation between maize crop area and the atrazine concentrations in the main and bottom springs were 0.71 and 0.74, respectively, and both were statistically significant. The lag time for both springs were 10 years. For top spring, a shorter lag time was estimated but the result was statistically insignificant (Table 4).

In Derg catchment, IR a similar relationship was found between the area of main crop type and the application amounts of a specific pesticide. In this case the pesticide was MCPA and the area of main crop type was improved grassland infested by rush (Morton et al, 2021).

Table 4: Pesticide lag time (yr) estimation using area of main crop type indicator in La Voulzie, France. Statistically significant at * p < 0.05; ** p < 0.005.

Sampling points Lag year (correlation coefficient)
Top spring with annual average concentrations 7 (0.49)
Main spring with annual average concentrations 10 (0.71)*
Bottom spring with annual average concentrations 10 (0.74)*

2.3 Amounts of applied pesticides as a pressure indicator

In La Voulzie, FR, the applied amount of the pesticide atrazine is compared to the concentrations of atrazine in groundwater using the CCF method. The applied amount of pesticide is calculated by multiplying the recommended-application-rate for atrazine by the total area of maize fields in the study area. A highly significant correlation was found between the pressure indicator and the status indicator (Figure 5 and Table 5) indicating a lag time of 22-27 years. Thus, in the specific case of La Voulzie, the atrazine contamination of groundwater can directly be linked to the application of atrazine on the maize fields in the catchment.

D3.2R fig05
Figure 5
 

 

Table 5: Pesticide lag time (yr) estimation using application of pesticide indicator in La Voulzie, FR. Statistically significant at * p < 0.05; ** p < 0.005.

Sampling points Lag year (correlation coefficient)
Top spring with annual average concentrations 22 (0.94)**
Bottom spring with annual average concentrations 27 (0.85)*

Note: For full references to papers quoted in this article see

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