2021-08-172021-08-172020-082020-08August 202https://hdl.handle.net/2346/87638Contaminated sediments serve as the sink and source of contaminants, and pose one of the most difficult and cost-effective remediation challenges. Continued metal inputs from stormwater discharges may result in significant discharges into receiving waters and remediating sediments; presenting a challenge from both regulatory and assessment perspective. Metals, like cadmium (Cd), copper (Cu), mercury (Hg), lead (Pb), zinc (Zn), nickel (Ni), and the metalloid arsenic (As), are non-degradable and toxic, posing biological risks by accumulation on living organisms entering the food chain. Stormwater sources are difficult to understand due to the poor characterization of the irregular, event-driven inputs, and the difficulty of managing these diffuse sources of large volumes. Effective means of evaluating the significance of stormwater inputs is particularly important when examining the long-term effectiveness of sediment remedial efforts. This dissertation presents improved approaches for assessing the impact of metals in stormwater on receiving sediments at Paleta Creek in San Diego Naval Base, USA. First aim of the study presents the stormwater assessment and characterization and the exploration of useful indicators for associating metal discharges to sediment recontamination. Second goal presents the evaluation of seasonal storm effects to biologically available metals and biota accumulation in sediments as well as to bulk sediment chemistry. Intensive stormwater and receiving waters sampling was coupled with sediment trap and seasonal sediment core collections, ex situ bioassays, and porewater passive sampling via DGTs during the wet and dry seasons. The first part identified that the most successful indicators of stormwater impacts on sediment recontamination were the size segregated stormwater discharges both in water and on suspended solids, total (>0.45 μm), sand (>63 μm), coarse silt (20-63 μm), fine silt (5-20 μm), clay (0.45-5 μm), as well as the dissovled phase (<0.45 μm) combined with sediment traps in the receiving waters. The stormwater concentrations, characterized by particle size distribution, provided the potential of the discharged mass and resulting deposition on sediments. The sediment traps provided an indication of the short-term sediment deposition and recontamination resulting from the storm events. The comparison of these various indicators allowed the estimation of the proportion of sediment recontamination likely due to stormwater and the proportion that might be caused by other sources, including resuspension of sediment in the receiving waters. Among the metals studies, Cd was clearly associated with large (>63 µm) particles and was found to settle quickly into locations immediately downstream. Cu, however, was associated with a range of particle sizes and was found in all sediment traps, even those located with some distance from the stormwater discharge. Other constituents, like Pb, Zn, Ni, Hg, and As, showed behavior intermediate to these two extremes suggesting both stormwater and other sources were likely important for these metals. In the second part, the synthesis of multiple lines of evidence successfully evaluated the biota accumulation due to contamination of sediments by stormwater heavy metals. The metal uptake in Macoma nasuta in bioaccumulation assays using sediments collected after the storm seasons were reduced with statistical certainty relative to pre-storm season samples for all measured metals, Cd, Hg, Cu, Pb, Zn, Ni, and the metalloid As; suggesting deposition of stormwater contaminants in low bioavailable forms. Similar reductions were observed after the storms in porewater of sediments measured by DGTs for all measured metals. Interestingly, sediment recontamination as indicated by stormwater loads and bulk chemistry of the receiving sediments did not indicate biological impacts as indicated by bioaccumulation. Moreover, the bulk sediment chemistry did not correlate with bioaccumulation with the exception of Pb. Analysis of the metal biota accumulation and DGT measured porewater concentrations showed statistically significant positive correlations (p<0.05, α=0.05) for most metals; suggesting that porewater concentrations can successfully indicate metal availability. In conclusion, sediment recontamination should be assessed by the combination of size-segregated stormwater discharges and settling traps to identify short term deposition resulting from those storms. Any observed sediment recontamination should also be subjected to bioassays or other bioavailability assessments because bulk sediment recontamination may not lead to negative impacts on benthic organisms.application/pdfengSedimentStormwaterHeavy MetalsBioaccumulationThesis2021-08-17Access restricted until August 2021.