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Composition and sources of particulate and dissolved matter in stream and groundwater of the Honeysuckle Creek watershed

Project Abstract: 
An important function of watersheds is the transport of organic matter from terrestrial to aquatic ecosystems. In order to better understand this function, and predict the impacts of climate change, more information is needed on the sources of terrestrial organic matter, the partitioning among particulate and dissolved forms, and the influence of precipitation events. In this investigation, we are looking at the dissolved and particulate matter distribution in stream water and shallow water wells along the Honeysuckle Creek watershed, a 120 ha, first-order watershed in northern Michigan. We are taking water samples during base flow and after a rain event. This water can be filtered to isolate the particulate matter, which is then weighted before and after ignition to obtain total suspended solids. The filtrate can be analyzed for carbon (C), nitrogen (N) concentrations, and stable isotope signatures; as well as for total mercury (THg) concentration. The dissolved matter can be analyzed for organic carbon content using an OI Analytical Aurora TOC (total organic carbon) analyzer. This is providing information about potential sources of the material transported by the water, and giving the opportunity to survey the flow path of material through the watershed. In order to explore the source of this material, we ball mill soil samples from upland and wetland sites into fine powder which is then analyzed for C and N concentrations, and stable isotope signatures, and THg in the same manner as the particulate matter in water.
Years Active: 
In-progress Soil samples and analysis Soil samples were collected as per Nave et al. (2017) , Conley (2016), and Thompson (2015) from upland and wetland areas in the Honeysuckle Creek watershed, a 120 ha, first-order watershed located within the 4000 ha University of Michigan Biological Station (UMBS), USA (45. 6°-84.7°). Soil samples from the upland were separated by their density into heavy fractions (HF), free light fractions (FLF), and free occluded fractions (OCC) using methods described by Crow et al. (2007) with sodium polytungstate. The soil samples were analyzed for their carbon (C), and nitrogen (N) content; and stable isotopes (C, N) signatures (Costech Analytical CHN analyzer coupled with a Finnigan Delta Plus XL isotope ratio mass spectrometer). Then, their total mercury (THg) concentration was analyzer using U.S. EPA method 7473 on a Milestone DMA-80 automated mercury analyzer. Next, a known amount (~0.1 g) of these samples was mixed with 0.1 M sodium pyrophosphate (pH 10), and placed on a sonicator for approximately 15 minutes for extraction. These solutions were diluted accordingly for UV-VIS spectroscopic analysis (Lambda 35 spectrometer, PerkinElmer, Shelton, CT, USA). Absorbance measurements were collected at wavelengths 254, 365, 465, and 665 nm in order to calculate approximations of the degree of molecular condensation as a way to investigate the water flow path. Water samples and analysis Using acid-washed (50% HCl) nalgene bottles, water samples were collected from six locations within the Honeysuckle Creek watershed. Three shallow groundwater wells were chosen that flowed near the creek. The water was collected using a vacuum pump. The other three locations were along the creek; here the water was collected using the acid-washed nalgene bottles. The bottles were transported to UMBS - Lakeside Lab in a cooler, and immediately transferred to a refrigerator for later analysis. Once at the lab, the pH and conductivity of the water samples was measured. Then, the samples were filtered in previously ashed and weighed 42.5 mm glass microfibre filters in order to isolate the particulate matter. The filtration apparatus was acid-washed before use. One liter per location were filtered, and the isolated particulate matter was burned at 500 C for 12 hours, and the percent loss on ignition (%LOI) was calculated. 100 mL of the filtrated water from each location was separated in 125mL nalgene bottles, and refrigerated for later analysis. The particulate matter and filter were ball milled to homogenize the samples - for some locations we had more than one filter. These ball milled samples were then prepared for C, N, Hg, and stable isotope content analysis as described above. The 100 mL of filtrated water was analyzed for dissolved organic carbon (DOC) using an OI Analytical Aurora TOC (total organic carbon) analyzer, and their UV/VIS absorbances at wavelengths 254, 365, 465, and 665 nm were measured. In order to compare baseflow and temporal variation, water samples at the same locations were collected and analyzed as previously stated after rain events.