NWT RESEARCH DATABASE

Regions: Inuvialuit Settlement Region, Gwich'in Settlement Area

Tags: physical sciences, biogeochemical processes, Mackenzie Delta, Nitrate

Objective(s): To improve the understanding of biogeochemical cycling in arctic deltas and to characterize nitrate processing rates across a range of streams and lakes on the Mackenzie delta.

Project Description: This licence has been issued for the scientific research application No.4926. To improve the understanding of biogeochemical cycling in arctic deltas, the principal investigator (PI) propose fieldwork to characterize nitrate processing rates across a range of streams and lakes on the Mackenzie delta. This field expedition will primarily consist of the following three methods: 1) solute tracing experiments in rivers; 2) benthic chamber experiments in lakes; and 3) sediment incubation. These methods are described in detail below followed by an outline of how all the proposed research activities and their corresponding timeline. Solute Tracing Experiments: Solute spiraling experiments will be carried out in three streams of the Mackenzie River Delta to estimate nitrate removal rates (Vf) and elucidate relationships between Vf and stream size on the delta. Nutrient enrichment tracer injections will be conducted near Inuvik, NWT. Injection stations will be established at specified upstream and downstream locations of each stream reach. I will inject solutions consisting of nitrate (reactive tracer) and sodium chloride (stable tracer) dissolved in stream water. Nitrate solutions will not exceed the range of background levels. Sampling time will be 5 hours. Surface water and sediment pore water samples will be collected at the upstream and downstream locations. Samples will be collected as grab samples (with duplicates) at regular intervals before, during, and after injection. All samples will be immediately filtered on-site (0.45-micrometer nylon syringe filters). Channel width and depth will be measured. Nitrate removal (Vf) will be determined using standard protocols (Stream Solute Workshop 1990) based on a decrease in nitrate concentration along the reach, discharge, and channel width. Benthic Chamber Experiments: Thousands of lakes store and filter water in the Mackenzie delta. To incorporate removal processes occurring in adjacent lakes, a mesocosm study using open atmospheric benthic chambers will be conducted in three adjacent lakes. Open atmospheric benthic chambers (plastic drums with tops and bottom removed) are preferred in this setting because it will allow for surface water conditions within the chamber to remain near ambient conditions throughout the measuring period. Open atmospheric benthic chambers will be constructed from translucent polyethylene barrels. Upon installation, the bottom of each chamber will rest 10 cm below the sediment-water interface. Sodium Chloride (NaCl) will be added as a conservative tracer to monitor water exchange through the bottom of the chamber. Water samples will be collected immediately before and after NaCl addition. Samples will then be collected every few hours until significant nitrate removal is detected (48 to 72 hours). Samples will be filtered (0.45 micrometers) and placed on ice until analyses. Nitrate and Chloride will be measured by ion chromatography at West Virginia University. Open atmospheric benthic chambers are not designed to be used in deep water where overtopping of its sides would occur. Therefore, all sampling will only occur near shore assuming a well-mixed system. Sediment Incubation: Sediment cores will be obtained to estimate the denitrification potential of the riverbed and lakebed sediments using incubation methods. Six cores (and replicates) will be collected at one lake and one river location. Each core will be taken to a depth of 5 cm below the sediment using a 3.6 cm diameter Polyvinyl Chloride (PVC) corer. After collection in the field, microcosms will be prepared using Falcon Centrifuge Tubes (50 mL) in the lab. Sediment from each location will be added to the 10 mL line, surface water will be slowly added until it overflows allowing for the tubes to be capped with no headspace. Each microcosm will be incubated in darkness at 25°C and sampled at regular, predetermined intervals. Sampling will involve carefully collecting headspace water from each Falcon Tube using a syringe inserted below the upper 10 mL of the sample to avoid atmospheric contamination. Sampled headwater will be transferred to Exetainer 12 mL vials, water will be overflowed and capped without headspace. Zinc Chloride (ZnCl) (0.2 mL) solution will immediately be added to the vials to terminate all ongoing microbial activity. Each vial will be stored upside down in water at 4ºC until analysis. The samples would remain refrigerated until the conclusion of fieldwork and taken back to West Virginia University for further processing. Three months prior to research, the research team will reach out to communities in Inuvik. The team aim to make our research as collaborative as possible. The team understand that members of local communities have expert knowledge of the delta especially through a historical context. The team hope the field research will instill an exchange of ideas and experiences. Ideally, the team will share the expertise and experience studying similar processes in subtropical deltas of the Mississippi River Basin with the community in Inuvik and they can share theirs on the Mackenzie delta. During fieldwork, the team propose to give demonstrations on any of the field and lab techniques being used. Ideally, the team would have a field assistant to come out with us each day. Findings from the study would be made public and raw and processed data would be made available to the community government The fieldwork for this study will be conducted from July 18, 2022 to July 31, 2022