Use of selected anthropogenic pesticides, nutrients, and biomarkers to spatially and temporally characterize eutrophication dynamics at a shallow lake (Lake Seeburg)
von Sebastian Zeman-Kuhnert
Datum der mündl. Prüfung:2022-08-23
Erschienen:2022-11-09
Betreuer:Prof. Dr. Volker Thiel
Gutachter:Prof. Dr. Volker Thiel
Gutachter:Prof. Dr. Christine Heim
Dateien
Name:Doctoral thesis, Zeman-Kuhnert.pdf
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Format:PDF
Zusammenfassung
Englisch
Eutrophication of water bodies caused by high nutrient inputs, especially of phosphorus, is a global concern for a wide variety of ecosystems. To assess this problem, different monitoring approaches have been applied to a variety of water bodies worldwide. Its main focus is on the spatial monitoring of nutrient inputs, predominantly on allochthonous inputs. In contrast, the temporal monitoring of inputs is rarely considered. This includes possible variations of nutrient inputs within the seasons or due to extreme weather events. In addition, information on past eutrophication can be useful for retrospectively characterizing long-term changes in the organism composition of water bodies and reconstructing how the current eutrophic status arose. Lake systems can only be adequately understood when these factors are considered. The primary objective of this work is to develop different approaches for a better spatial and especially temporal characterization of eutrophication-relevant lake dynamics by using different substance classes. To this end, pesticides (using UPLC-MS/MS), bioavailable nutrients (using IC and photometry) and biomarkers (using GC-MS) were investigated in three different studies at the shallow (<4 m), eutrophic Lake Seeburg in southern Lower Saxony over a period of 1-3 years. In the first study (Warner et al., 2021), pesticides with their metabolites and selected nutrients were analyzed monthly for one year, to suggest improvements in current monitoring strategies based on spatial and temporal input patterns. Two different groups of pesticides were tested. The first group consisted of pesticides that have been used in large quantities in recent decades but are no longer allowed to be used today (e.g., the beet herbicide chloridazon and its degradation products). The second group consisted of pesticides that are still widely used today (e.g., the selective pre-emergence herbicide metazachlor). The pesticides of the first group, along with nitrate, show a relatively constant input into adjacent waters throughout the year. The results indicate that they are stored in large quantities in the soil and, although no longer applied, are slowly leached out over years. The pesticides of the second group, as well as dissolved reactive phosphate (SRP), show a strong seasonality. Their maximum input into surrounding waters occurs shortly after application, which indicates rapid leaching by precipitation. The results of this study confirm the undesired input of pesticides into surrounding waters, especially after rain events. In addition, it has been demonstrated that more targeted sampling not only saves costs, but also allows for more successful remediation efforts due to better detection of spatial and temporal pollution hotspots. The second study (Zeman-Kuhnert et al., 2022) focused on the effects of extreme weather events on the nutrient dynamics and cyanobacterial bloom composition in Lake Seeburg. Eutrophication-relevant parameters (water temperature, nitrate, ammonium, nitrite, and SRP) were studied monthly in the lake for three years (2017-2019) and supported with monthly SRP measurements in the sediment pore water for one year (2018). Following a three-day heavy rain event in July 2017, anoxic waters with high SRP levels entered the lake from the upstream flooded wetland. This exceptionally high allochthonous nutrient input resulted in a relatively short (≈3 weeks) but very intense and monospecific cyanobacterial bloom. During the hot and dry summer of 2018, strong internal SRP redissolutions from the sediment resulted in the longest (≈3 month) observed cyanobacterial bloom. The results of this study reveal high internal and external nutrient inputs and a severe loss of microorganism diversity following weather extremes. Despite similar negative impacts, the causes of cyanobacterial blooms are fundamentally diverse and thus must be considered differently in remediation strategies. In the third study (Zeman-Kuhnert et al., to be submitted), phytoplankton-related biomarkers, representative of allochthonous and autochthonous organism groups, were evaluated for their presence and conservation ability in the lake water and their transfer to the surface sediment. The primary objective was to study whether certain biomarkers can be used to reconstruct the eutrophication history of a lake. 26 biomarkers were clustered into 5 groups with similar characteristics using principal component analysis (PCA): (I) biomarkers discharged via the inflow, formed in the lake by (II) eukaryotes or (III) bacteria, (IV) compounds accumulating in the surface sediment, and (V) unsaturated C27 to C29 stenols with their saturated degradation products (C27 to C29 stanols) mainly present in lake water and sediment. The characteristics and seasonal distribution of the stenols showed potential to be used as a sedimentary eutrophication indicator. Therefore, they were additionally measured on two sediment cores to reconstruct the eutrophication history of the lake. The results show that autochthonously formed C27 and allochthonously formed C29 stenols, including their degradation products, contrast with sediment depth (highest C27 to C29 ratios at the surface, lowest with depth) and are thus considered as suitable biomarkers to qualitatively reconstruct the historical eutrophication trend. In summary, the results of this thesis provide further insights with regard to a more precise characterization of the overall lake dynamics relevant to eutrophication. Potential spatial and temporal pollution hotspots (whether due to constant or short-term inputs) need to be identified. Information on how eutrophication has evolved in the past may also be useful for a better overall understanding of the process. Due to the consequences of climate change and the growing world population, it will become increasingly important in the future to identify potential impacts and changes on water bodies in order to better assess their consequences and to develop adapted measures.
Keywords: pesticides; biomarker; eutrophication; shallow lake; cyanobacterial blooms; nutrient dynamics