In the course material, you will find In Class pop - assignment #2 - 29 November 2019 Page ; follow those steps before continuing here.

Objective: analyse the Nitrogen emission from agricultural practices in Veneto Region, using samples of pollutant in rivers as proxies.

How: use the table with sampled pollutants for each river (in dataset c0408100 LIMECO) - aggregate this table to get a single reading for sampled rivers and then join them to the spatial layer representing rivers.

Question to be answered: which area is more vulnerable? How polluted are rivers ? Which is the more polluted river segment - is there any correlation with the degree of Used Agricultural Area (Superficie Agricola Utilizzata - SAU) that we downloaded from assignment #2 ?

  • You should have a layer representing Veneto's municipalities with a  theme from white to red for the SAU_HA column, which is the Used Agricultural Area (Superficie Agricola Utilizzata - SAU) from the previous excercies
  • SAU is an absolute value, but we are interested to know the % of SAU - Let's create a new column called SAU_perc and divide the SAU by the area in HA and convert to percentage... what is the formula?
  • Load rivers using WFS
  • Load the excel table with c0408100_LIMECO which has concentration values of pollutants (direct link) - you can also search for it in the portal with keyword "Livello di Inquinamento dei fiumi" which means "Pollution level of rivers"
  • Aggregate the table (look-up "aggregate") in processing toolbox. Select "aggregating column" which is the "Group by expression" tab, and select which aggregating function you want to use for which columns - we want the average sampled pollutant concentration, and want to keep some other information, like the code (ID) of the river segment (Codice Corpo Idrico) - see image below

You now have 383 rows derived from the initial 2574 because each river segment had its pollutant values form different sampling campaigns aggregated.


  • Make  a table join (Performing Table Joins (QGIS3)) between rivers and pollutants using the code (ID) of the river segment (Codice Corpo Idrico) and the ID in the spatial layer of the rivers
  • You will then be able to assign color scales according to pollutant concentration! Which river segment is the most polluted??
  • Create a spatial join, to assign to each river  the SAU of the municipality that it intersects - this will provide a new river layer with SAU of the town it intersects - look-up the tool in the processing toolbox!
NB - many tools allow to save results in a temporary layer - remember to make it permanent if you are interested in not loosing it.

  • Create a scatter plot of SAU vs Pollution level in the river... any relationship? Not at first glance (bottom left image), but because SAU is an area, if we rescale it to LOGn using "field calculator" in our table, we see a relationship (bottom right)



Tutorials


Ultime modifiche: venerdì, 6 dicembre 2019, 14:30