66 research outputs found
Metal-bound carbon and nutrients across hydrologically diverse boreal peatlands
No full textBoreal peatlands store abundant carbon (C) belowground because of saturated conditions and cold temperatures, which inhibit the enzymatic release of dissolved organic carbon (DOC) from organic matter. However, metals may also bind DOC, as well as nitrogen (N) and phosphorus (P), and their impact may vary among peatlands with differing hydrology. To assess variation of metal-C-nutrient interactions within and among peatlands and with depth, we sampled cores from seven peatlands in the Marcell Experimental Forest, Minnesota, including bogs, poor fens, and a rich fen. We extracted peat with sodium sulfate to release elements bound with exchangeable metals such as calcium (Ca) or aluminum (Al), and with sodium dithionite to release elements bound with the redox-active metals iron (Fe) and manganese (Mn). We compared extracted elements to long-term peat porewater measurements. Mean DOC extracted by sulfate or dithionite in the bogs and poor fens was 5 or 8 times greater, respectively, than porewater DOC, and in the rich fen it was 8 or 38 times greater. Similarly, N and P extracted by sulfate and dithionite were 10–24 times higher than porewater in the bogs and poor fens and 7–55 times higher in the rich fen. The ratio and absolute values of redox-sensitive and ion-exchangeable elements varied by element among peatland types and with peat depth and values were not always greater in fens than bogs. We conclude that both redox-active (Fe) and non-redox-active (Ca and Al) metals bind important pools of peatland C and nutrients regardless of peatland hydrologic type and despite the very low total mineral content of these boreal peats.This article is published as Curtinrich, H.J., Sebestyen, S.D. & Hall, S.J. Metal-bound carbon and nutrients across hydrologically diverse boreal peatlands. Biogeochemistry 168, 7 (2025). https://doi.org/10.1007/s10533-024-01199-z.This research was partially supported by grants to HJC from the Department of Ecology, Evolution, and Organismal Biology at Iowa State University and the Center for Global and Regional Environmental Research at the University of Iowa. The contributions of SDS and the collection, analysis, and curation of porewater chemistry data were funded by the Northern Research Station of the USDA Forest Service
Coupled hydrological and biogeochemical processes that control stream nitrogen and dissolved organic carbon at the Sleepers River Research Watershed
No full textTo investigate how hydrological and biogeochemical processes control the forms and concentrations of stream nutrients in upland forests affected by elevated atmospheric nitrogen deposition, I traced sources of water, nitrogen, and dissolved organic carbon (DOC) at the Sleepers River Research Watershed (northeastern Vermont, USA). To augment long-term weekly hydrochemical data that have been collected at the site since 1991, I collected high-frequency stream water samples over multiple storm flow events from 2002 to 2005. During autumn, baseflow nitrate concentrations decreased by an order of magnitude during leaf fall and dissolved organic nitrogen briefly became the dominant form of stream nitrogen. Quantifying terrestrial to aquatic linkages revealed how coupled hydrological and biogeochemical processes affected stream nutrient variation during autumn including the "nitrate crash" and rebound. A mass balance showed that a stream reach during baseflow was a net sink for nitrate while a net source of DOC and DON. Nitrate concentrations rebounded from this "nitrate crash" during storm flow events. Isotopic signatures and end-member mixing analysis revealed when nitrate and dissolved organic nitrogen (DON) were flushed to the stream from terrestrial source areas and that up to 30% of the stream nitrate was directly contributed from atmospheric sources. Results from snowmelt studies showed when solutes entered the stream and that variable source areas were linked to the stream by preferential shallow subsurface and overland flowpaths. The highest stream nutrient concentrations occurred when nitrate originated from atmospheric sources as well as nitrified sources and terrestrial organic matter was the dominant source of DOC and DON. In the third component of my work, I examined the long-term record of stream hydrochemistry to explore the relationship between catchment wetness and stream nutrient loadings and to assess how stream nutrient loadings may respond to climate change. Model results suggest that leaching of nitrate and DOC will seasonally shift due to anthropogenic climate forcing and affect the timing and magnitude of annual stream loadings in the northeast USA during the next century. Net annual stream runoff (+8%) and DOC flux (+9%) increases were primarily affected by increased winter precipitation. In contrast, decreased annual flux of stream nitrate (-2%) reflected a greater effect of growing season controls on stream nitrate that resulted as days shifted to the longer growing seasons. Overall, these studies identified hydrological transport processes, source variation, and biogeochemical transformations as key processes that influenced stream nutrient variation
Daily water and TOC yields for studies of the biodegradability of dissolved organic matter in peatland catchments at the Marcell Experimental Forest: 2009-2011
No full textEvent runoff volume data and daily runoff data for the S2 and S6 catchments at the Marcell Experimental Forest
No full textCo-simulation of energy transition in residential sectors of Chinese lower-tier cities
No full textChina is undergoing large changes to tackle carbon dioxide emissions and air pollution. While the top-down governance allows for clear setting of emission reduction targets for industrial sectors and major cities, reducing emissions in residential sectors in smaller (the so-called low-tier) cities remain challenging and often unaddressed. This paper studies policy options to reduce emissions in residential sectors in low-tier Chinese cities. We conducted interviews and surveys in the city of Jingmen in the Hubei province and developed simulation models with feasible policy options and realistic consumption choice preferences. The simulation provided insights to the policies on reducing household coal consumption and ensuing emissions. Our research found that top-down restrictive policies such as coal ban and coal tax are effective in reducing emissions. They, however, restrict access to affordable energy for heating and cooking, especially within rural areas. They hence need to be combined with supportive policies such as electricity subsidy to yield long-term positive impact.System Engineerin
The influence of metals on carbon and nutrient cycling in boreal peatlands
No full textNorthern peatlands have historically been a carbon (C) sink and contain a considerable proportion of terrestrial organic matter, but it is unclear if that C will become vulnerable with climate change. Therefore, it is important to understand controls on C and nutrient stabilization and loss in peatlands. The main controls on the solubilization of dissolved organic carbon (DOC) and loss of C through decomposition or stream export are generally thought to be: limited oxygen due to saturated conditions, cold temperatures, and, in bogs, acidity. In addition to those controls, metals may also impact C and nutrient cycling in peatlands by binding organic matter and also releasing DOC to the pore water when metal-C associations are disrupted. I examined the role of metals on C and nutrient cycling and release and how these roles vary among peatlands with differing hydrology in the Marcell Experimental Forest in Minnesota. I extracted peat cores from four bogs, two poor fens, and a rich fen with salt solutions (sodium dithionite and sodium sulfate) and found the chemical reduction of Fe(III) and ion exchange led to the release of C and nutrients such as phosphorus, particularly near the peat surface. This release of C and nutrients indicates Fe and Ca were likely bound to organic matter in the peat and protected elements were solubilized when bonds were disrupted. I found much greater concentrations of dithionite-extracted DOC and sulfate-extracted DOC compared to concentrations of DOC present in the porewater in all peatland types, but the predicted ratio of redox-sensitive to ion-exchangeable elements varied among peatland types and also varied among the various bogs for some elements. The ecological importance of the metal-bound C observed in the extractions was corroborated by positive correlations between Fe and DOC and Ca and DOC in near-surface pore water samples from one of the bogs and in water samples collected from the outflow of experimental enclosures in Spruce and Peatland Responses Under Changing Environments (SPRUCE), an ecosystem-scale warming experiment. The correlation between metals and C may be due in part to the solubilization of Fe-C and Ca-C associations. The concentration of Fe(II) increased with increasing temperature in the SPRUCE samples but stabilized at the highest temperature treatments as water depth declined, suggesting Fe(III) reduction may increase with warmer temperatures, contingent on water table depth, and may release more Fe(II) and elements bound to it. The correlation between TOC and metals present in the surface water samples was also documented at the watershed scale in streams draining catchments including five bogs and one fen. Overall, concentrations of TOC were more strongly correlated with Fe than temperature or H+, but TOC was more correlated with Ca than Fe, temperature or H+ in streams draining some of the bogs. Concentrations of Ca and Fe may be an important component for predicting TOC concentrations in streams draining peatland watersheds but can only explain some of the variation. Overall, I conclude that metals such as Fe and Ca are important for influencing the cycling of DOC and nutrients in addition to the factors traditionally accepted to control these processes in peatlands
Responses of stream nitrate and DOC loadings to hydrological forcing and climate change in an upland forest of the northeastern United States
No full textControls on decadal, annual, and seasonal concentration-discharge relationships in the Sleepers River Research Watershed, Vermont, northeastern United States
No full textPast studies on concentration-discharge (C-Q) relationships have focused on short-term or low-temporal resolution data. While advancing understanding of catchment processes, these studies provided limited insight on catchment response over time or to climate change. Using 15 solutes from 1992 to 2015 at Sleepers River Research Watershed, Vermont, we compared C-Q relationships over decades, years, and seasons to elucidate controls on stream chemical variation. We applied end-member mixing analysis (EMMA) to identify solute sources and flow path routing. EMMA identified three end-members: near-surface runoff (NSR), riparian groundwater, and hillslope hollow groundwater. Shifting mixing proportions of these end-members accounted for the temporal variability of conservative (no chemical reaction en route from source to stream) solutes in streamflow. For example, an increase in NSR fraction, typical of high flow, caused flushing (increased concentrations) of NO3−, DOC, Al, and Fe, which were greatest in NSR, dilution of specific conductance and base cation, SO42−, Si, Sr, Ba, and Mn concentrations, which were greatest in the two groundwater end-members. This behaviour is reflected in the b-coefficient of the C-Q relation (C = aQb), which indicates the strength of dilution (b \u3c −0.1) and flushing (b \u3e 0.1) effects. For conservative solutes, the b-coefficient decreased significantly (p \u3c 0.01) with an increase in the groundwater to NSR concentration ratio. Solutes that are conservative and have relatively constant concentrations in end-members over time showed consistent annual C-Q patterns over years and decades. Furthermore, the strength of dilution or flushing was stronger during the snowmelt period, when the NSR fraction peaked, than during the dormant and growing seasons. With shorter snowmelt periods and snow to rain shifts, the flushing or dilution power of snowmelt runoff will weaken and alter catchment response to climate change. These insights provide more tools for the interpretation of catchment processes and responses to climate change
New Insights on Ecosystem Mercury Cycling Revealed by Stable Isotopes of Mercury in Water Flowing from a Headwater Peatland Catchment
No full textStable isotope compositions of mercury (Hg) were measured in the outlet stream and in soil cores at different landscape positions in a 9.7-ha boreal upland-peatland catchment. An acidic permanganate/persulfate digestion procedure was validated for water samples with high dissolved organic matter (DOM) concentrations through Hg spike addition analysis. We report a relatively large variation in mass-dependent fractionation (delta Hg-202; from -2.12 to -1.32 parts per thousand) and a smaller, but significant, variation of mass independent fractionation (Delta Hg-199; from -0.35 to -0.12 parts per thousand) during two years of sampling with streamflow varying from 0.003 to 7.8 L s(-1). Large variations in delta Hg-202 occurred only during low streamflow (<0.6 L which suggest that under high streamflow conditions a peatland lagg zone between the bog (3.0 ha) and uplands (6.7 ha) becomes the dominant source of Hg in downstream waters. Further, a binary mixing model showed that except for the spring snowmelt period, Hg in streamwater from the catchment was mainly derived from dry deposition of gaseous elemental Hg (73-95%). This study demonstrates the usefulness of Hg isotopes for tracing sources of Hg deposition, which can lead to a better understanding of the biogeochemical cycling and hydrological transport of Hg in headwater catchments
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