Kibuye, Henry, Agricultural and Biological Engineering, The Pennsylvania State University, 436 Shortlidge Rd, University Park, Pennsylvania, 16802, hjk5236@psu.edu; Veith, Tamie, L, Pasture Systems and Watershed Management Research Unit, USDA Agricultural Research Service, 532 Curtin Rd, University Park, Pennsylvania, 16802, Groh, Tyler, A Ecosystem Science and Management The Pennsylvania State University 160 Curtin Rd University Park Pennsylvania, 16802; Preisendanz, Heather, E, Agricultural and Biological Engineering; Institute of Sustainable, Agricultural, Food and Environmental Science, College of Agricultural Sciences, Pennsylvania State University, 436 Shortlidge Rd, University Park, Pennsylvania, 16802, heg12@psu.edu.
Even at trace levels, emerging contaminants (ECs), in surface water resources pose potential adverse ecological and human health impacts. The assessment of monitoring approaches used in tracking spatial-temporal patterns of ECs is key in the development of cost-effective monitoring networks. In this study, a nested watershed monitoring approach was implemented to quantify 24 ECs over the 2023-2024 growing seasons at five sampling sites within an agriculturally impaired headwatershed with no point sources of ECs. Using grab sampling and polar organic chemical integrative samplers (POCIS), both active and passive stream samples were collected every two weeks to (1) compare the effectiveness of the methods in documenting spatial-temporal patterns of ECs, and (2) examine the relationship between estimated POCIS time-weighted average (TWA) and grab sample concentrations over the monitoring period. POCIS sampling detected ECs at equal or higher frequencies than grab sampling did. Atrazine, simazine, clothianidin and caffeine were the most frequently detected ECs in at least 68% of grab and POCIS samples. At seasonal scales, grab samples showed highest detection frequencies for most ECs in summer while POCIS samples had higher detection frequencies in both spring and summer. However, grab samples showed seasonal variability that was within or exceeded the range captured by POCIS. Both methods were effective in identifying hotspot sites for the different ECs, giving insights into contamination levels at different site sub-catchments that would have been missed by single-site monitoring. However, only caffeine, clothianidin and carbamazepine showed statistically significant differences in concentration between the sampling sites in both methods. PERMANOVA analysis revealed that POCIS captured differences in EC profiles between sites while grab samples documented within site variability. ECs that remain in their neutral state at environmental pH including atrazine, simazine, clothianidin and caffeine, sorbed better to POCIS and had higher estimated POCIS TWA than grab samples concentration. However, this was not true for carbamazepine which is relatively persistent in water and had estimated POCIS TWA largely within the range of grab sample concentration. Ionic ECs such as Sulfamethoxazole may not sorb well to HLB POCIS indicated by the estimated POCIS TWA being lower or within the range of grab sample concentration. Overall, the findings of this study enhance understanding of the extent of ECs contamination in agricultural watersheds and the relationship between the sampling methods that would guide monitoring approaches.