Geology topics

P.A. Raymond

Publications and source records attributed to P.A. Raymond.

7 recordsLinked to original sources

USGS2021

Evaluating streamwater dissolved organic carbon dynamics in context of variable flowpath contributions with a tracer-based mixing model

This study focuses on characterizing the contributions of key terrestrial pathways that deliver dissolved organic carbon (DOC) to streams during hydrological events and on elucidating factors governing variation in water and DOC fluxes from these pathways. We made high-frequency measurements of discharge, specific conductance (SC), and fluorescent dissolved organic matter (FDOM) during 221 events recorded over 2 years within four Vermont (USA) watersheds that range in area from 0.4 to 139 km 2 . Using the SC measurements, together with statistical information on discharge, we separated the event hydrographs into contributions from three terrestrial pathways, which we refer to as riparian quickflow, subsurface quickflow, and slow-flow groundwater. The pathway discharges were used as input to a mixing model that closely approximated sub-hourly streamwater DOC concentrations as measured with the FDOM sensors. Subsurface quickflow, comprised of pre-event water, was the leading contributor to streamwater DOC fluxes, while riparian quickflow, comprised of event water, was the second-leading contributor to streamwater DOC fluxes, despite comprising the smallest proportion of streamflow yield among the three end-member pathways. Fixed-effects regression analysis revealed that the relationship between DOC fluxes from the end-member pathways and event magnitude was consistent across the four watersheds. This analysis also showed that DOC fluxes from the quickflow pathways increased significantly with temperature and varied inversely, but weakly, with catchment antecedent wetness. We believe that our approach, which leverages in-stream sensors that enable high-frequency measurements over extended periods, may be applicable for evaluating controls on DOC export from other watersheds within and beyond our study region.

New Hampshire, Vermont↗

USGS2020

Source switching maintains dissolved organic matter chemostasis across discharge levels in a large temperate river network

Dissolved organic matter (DOM) helps regulate aquatic ecosystem structure and function. In small streams, DOM concentrations are controlled by transport of terrestrial materials to waterways, and are thus highly variable. As rivers become larger, the River Continuum Concept hypothesizes that internal primary production is an increasingly important DOM source, but direct evidence is limited. Recently, the Pulse-Shunt Concept postulated that terrestrial DOM concentrations in larger rivers increase with flow and temperature, which seemingly contradicts previously reported DOM chemostasis in large rivers. This study estimates daily gross primary production (GPP) in 13 streams and rivers across the Connecticut River watershed (watershed areas 0.4–25,019 km 2 ) from 2015 through 2017. Chemostasis of DOM concentrations is maintained by a switch from autochthonous sources of DOM at low flows to terrestrial sources of DOM at high flows in a large temperate river and to a lesser degree in smaller tributaries. At low flow, autochthonous DOM linked to aquatic GPP is the dominant fraction of the DOM pool in large rivers. This autochthonous DOM maintains chemostasis in the main stem and to a lesser extent upstream. Thus, in larger rivers, low-flow autochthonous production stabilizes DOM concentrations during the summer, a critical time for riverine ecology. Consistent with the Pulse-Shunt Concept, terrigenous DOM is the dominant fraction of DOM during higher flow periods and about 70% of annual DOM fluxes to the coast are terrestrial. This pattern of DOM switching is potentially widespread in temperate watersheds with implications to both inland waters and coastal ecosystems.

Ecosystems↗

USGS2011

Development of pan-Arctic database for river chemistry

More than 10% of all continental runoff flows into the Arctic Ocean. This runoff is a dominant feature of the Arctic Ocean with respect to water column structure and circulation. Yet understanding of the chemical characteristics of runoff from the pan-Arctic watershed is surprisingly limited. The Pan- Arctic River Transport of Nutrients, Organic Matter, and Suspended Sediments ( PARTNERS) project was initiated in 2002 to help remedy this deficit, and an extraordinary data set has emerged over the past few years as a result of the effort. This data set is publicly available through the Cooperative Arctic Data and Information Service (CADIS) of the Arctic Observing Network (AON). Details about data access are provided below.

Eos, Transactions, American Geophysical Union↗

USGS2010

Land-use controls on sources and processing of nitrate in small watersheds: Insights from dual isotopic analysis

Studies have repeatedly shown that agricultural and urban areas export considerably more nitrogen to streams than forested counterparts, yet it is difficult to identify and quantify nitrogen sources to streams due to complications associated with terrestrial and in-stream biogeochemical processes. In this study, we used the isotopic composition of nitrate (??15N-NO3- and ??18O- NO3-) in conjunction with a simple numerical model to examine the spatial and temporal variability of nitrate (NO3-) export across a land-use gradient and how agricultural and urban development affects net removal mechanisms. In an effort to isolate the effects of land use, we chose small headwater systems in close proximity to each other, limiting the variation in geology, surficial materials, and climate between sites. The ??15N and ??18Oof stream NO 3- varied significantly between urban, agricultural, and forested watersheds, indicating that nitrogen sources are the primary determinant of the ??15N-NO3-, while the ??18O-NO3- was found to reflect biogeochemical processes. The greatest NO3- concentrations corresponded with the highest stream ??15N-NO3- values due to the enriched nature of two dominant anthropogenic sources, septic and manure, within the urban and agricultural watersheds, respectively. On average, net removal of the available NO3- pool within urban and agricultural catchments was estimated at 45%. The variation in the estimated net removal of NO3- from developed watersheds was related to both drainage area and the availability of organic carbon. The determination of differentiated isotopic land-use signatures and dominant seasonal mechanisms illustrates the usefulness of this approach in examining the sources and processing of excess nitrogen within headwater catchments. ?? 2010 by the Ecological Society of America.

Ecological Applications↗

USGS2009

Inputs of fossil carbon from wastewater treatment plants to U.S. Rivers and oceans

Every day more than 500 million cubic meters of treated wastewater are discharged into rivers, estuaries, and oceans, an amount slightly less than the average flow of the Danube River. Typically, wastewaters have high organic carbon (OC) concentrations and represent a large fraction of total river flow and a higher fraction of river OC in densely populated watersheds. Here, we report the first direct measurements of radiocarbon ( 14 C) in municipal wastewater treatment plant (WWTP) effluent. The radiocarbon ages of particulate and dissolved organic carbon (POC and DOC) in effluent are old and relatively uniform across a range of WWTPs in New York and Connecticut. Wastewater DOC has a mean radiocarbon age of 1630 ?? 500 years B.P. and a mean ?? 13 C of -26.0 ?? 1???. Mass balance calculations indicate that 25% of wastewater DOC is fossil carbon, which is likely derived from petroleumbased household products such as detergents and pharmaceuticals. Thesefindings warrant reevaluation of the "apparent age" of riverine DOC, the total flux of petroleum carbon to U.S. oceans, and OC source assignments in waters impacted by sewage. ?? 2009 American Chemical Society.

Environmental Science & Technology↗

USGS2007

Flux and age of dissolved organic carbon exported to the Arctic Ocean: A carbon isotopic study of the five largest arctic rivers

The export and Δ 14 C-age of dissolved organic carbon (DOC) was determined for the Yenisey, Lena, Ob', Mackenzie, and Yukon rivers for 2004–2005. Concentrations of DOC elevate significantly with increasing discharge in these rivers, causing approximately 60% of the annual export to occur during a 2-month period following spring ice breakup. We present a total annual flux from the five rivers of ∼16 teragrams (Tg), and conservatively estimate that the total input of DOC to the Arctic Ocean is 25–36 Tg, which is ∼5–20% greater than previous fluxes. These fluxes are also ∼2.5× greater than temperate rivers with similar watershed sizes and water discharge. Δ 14 C-DOC shows a clear relationship with hydrology. A small pool of DOC slightly depleted in Δ 14 C is exported with base flow. The large pool exported with spring thaw is enriched in Δ 14 C with respect to current-day atmospheric Δ 14 C-CO 2 values. A simple model predicts that ∼50% of DOC exported during the arctic spring thaw is 1–5 years old, ∼25% is 6–10 years in age, and 15% is 11–20 years old. The dominant spring melt period, a historically undersampled period, exports a large amount of young and presumably semilabile DOC to the Arctic Ocean.

Global Biogeochemical Cycles↗

USGS2005

A decrease in discharge-normalized DOC export by the Yukon River during summer through autumn

Climate warming is having a dramatic effect on the vegetation distribution and carbon cycling of terrestrial subarctic and arctic ecosystems. Here, we present hydrologic evidence that warming is also affecting the export of dissolved organic carbon and bicarbonate (DOC and HCO 3 − ) at the large basin scale. In the 831,400 km 2 Yukon River basin, water discharge (Q) corrected DOC export significantly decreased during the growing season from 1978–80 to 2001–03, indicating a major shift in terrestrial to aquatic C transfer. We conclude that decreased DOC export, relative to total summer through autumn Q, results from increased flow path, residence time, and microbial mineralization of DOC in the soil active layer and groundwater. Counter to current predictions, we argue that continued warming could result in decreased DOC export to the Bering Sea and Arctic Ocean by major subarctic and arctic rivers, due to increased respiration of organic C on land.

Geophysical Research Letters↗