Hazardous Substance Load Estimation in a Small Catchment Using Baseflow Separation and Composite Sampling

The pollution of our natural waters is an increasingly urgent and crucial problem.Both point and diffuse pollution can enter the river basin from a variety of sources.The streamflow - and the resulting pollutant loads - exhibit abrupt changes in behavior influenced by rainfall and surface run-off.A significant portion of the  pollution is associated with short-duration event flows, which cause sudden, substantial increases in streamflow. The primary objective of my thesis is to refine the load estimation method using baseflow separation methods, specifically the Lyne-Hollick (L-H.) and Eckhardt methods. The methods were applied at two measuring stations of the Koppány stream in Somogy County, Törökkoppány and Tamási.

In addition to hourly water flow measurements, electrical conductivity and turbidity are continuously monitored in the area at five-minute intervals. A permanent point source of pollution is the treated wastewater of Balatonlelle, which is discharged into the Koppány stream as a contribution to the baseflow load. The calculation process benefited significantly from the stratified sampling method used, in which an automatic sampler is activated at a defined water flow threshold. This enables separate treatment of samples from baseflow and high flow, allowing better estimations of contaminant concentrations during high flow conditions and providing a more accurate load estimation.

The estimated baseflow-index for Törökkoppány is 0.60 (L-H.) and 0.57 (Eckhardt) while for Tamási, it is 0.86 (L-H.) and 0.57 (Eckhardt). In terms of micropollutants, metals and pesticides dominate the mass for both methods, associated with high flow events.Meanwhile, pharmaceuticals, phenols, and PFAS compounds, linked to anthropogenic sources, are more prominent in the baseflow load. Based on the L-H. filter, Törökkoppány receives 91.7% of its annual 4634 kg metal compound load during high flow events. The total pesticide load is 87 kg per year, with 98% attributed to high flow events. Results from the Eckhardt filter align closely with the aforementioned findings. Based on the L-H. method at Tamási, the estimated annual metal load is 3488 kg, with 62% from high water events. while the Eckhardt method reports an annual metal load of 7408 kg (88% from high flow). Total pesticide emissions are 63kg/year (L-H.), predominantly from high flow (88%), and 171 kg (Eckhardt) with 97% attributed to high flow.  Phenols, PAH and PFAS compounds are baseflow-related and do not exceed 1-2kg/year.

To understand why the two methods show such different results for Tamási, the Rimmer-Hartmann method could be an appropriate solution.

Funding: The research presented in the article was carried out within the framework of the Széchenyi Plan Plus program with the support of the RRF-2.3.1-21-2022-00008 project. The research was co-financed by the National Research Development and Innovation Office (NKFIH) through the OTKA Grant SNN 143868 and by the European Union through the RRF-2.3.1-21-2022-00004 Artifical Intelligence National Laboratory project.