SEARCH · Search USGS

Results for “Carbon Balance and Management”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources

USGS2023

Blue carbon in a changing climate and a changing context

Blue carbon, a convenient term to encompass the climate mitigation value of coastal carbon dynamics, has received global policy attention and growing datasets to support management actions. Carbon stock assessments in mangroves, seagrass, and tidal marshes document significant carbon storage in soils. Models illustrate significant downward fluxes of carbon dioxide and limited methane emissions, making tidal wetland preservation and restoration notably potent for carbon dioxide removal (CDR). Natural variation in different carbon stocks and fluxes has led to prioritization efforts to characterize coastal lands across physical and biological gradients. However, a larger concern beyond upscaling carbon dynamics is the resilience of these stocks and fluxes with global changes. Data-informed models have greatly improved our assessments of the vulnerability of soil and biomass stocks, greenhouse gas (GHG) balance, and spatial extents. Accelerated sea-level rise is increasingly concerning, but its impacts vary by resilience context, as very few coastal lands are without direct human impact. As the landscape context has changed, blue carbon fluxes have also shifted in terms of importance and distribution. New incentives for tidal ecosystem management are expanding boundaries to include algal carbon and tidal transport of alkalinity, which bring additional co-benefits to coastal waters. Using examples from the conterminous USA on blue carbon stocks, radiative balance, and extent, this chapter explores timelines of physical and biogeochemical stressors and their application to past, current, and future climate mitigation functions of coastal ecosystems.

Book chapter↗

USGS2021

Linking decomposition rates of soil organic amendments to their chemical composition

The stock of organic carbon contained within a soil represents the balance between inputs and losses. Inputs are defined by the ability of vegetation to capture and retain carbon dioxide, effects that management practices have on the proportion of captured carbon that is added to soil and the application organic amendments. The proportion of organic amendment carbon retained is defined by its rate of mineralisation. In this study, the rate of carbon mineralisation from 85 different potential soil organic amendments (composts, manures, plant residues and biosolids) was quantified under controlled environmental conditions over a 547 day incubation period. The composition of each organic amendment was quantified using nuclear magnetic resonance and mid- and near-infrared spectroscopies. Cumulative mineralisation of organic carbon from the amendments was fitted to a two-pool exponential model. Multivariate chemometric algorithms were derived to allow the size of the fast and slow cycling pools of carbon to be predicted from the acquired spectroscopic data. However, the fast and slow decomposition rate constants could not be predicted suggesting that prediction of the residence time of organic amendment carbon in soil would likely require additional information related to soil type, environmental conditions, and management practices in use at the site of application.

Soil Research↗

USGS2017

Human footprint affects US carbon balance more than climate change

The MC2 model projects an overall increase in carbon capture in conterminous United States during the 21st century while also simulating a rise in fire causing much carbon loss. Carbon sequestration in soils is critical to prevent carbon losses from future disturbances, and we show that natural ecosystems store more carbon belowground than managed systems do. Natural and human-caused disturbances affect soil processes that shape ecosystem recovery and competitive interactions between native, exotics, and climate refugees. Tomorrow's carbon budgets will depend on how land use, natural disturbances, and climate variability will interact and affect the balance between carbon capture and release.

Book chapter↗

USGS2013

An integrated model of environmental effects on growth, carbohydrate balance, and mortality of Pinus ponderosa forests in the southern Rocky Mountains

Climate-induced tree mortality is an increasing concern for forest managers around the world. We used a coupled hydrologic and ecosystem carbon cycling model to assess temperature and precipitation impacts on productivity and survival of ponderosa pine ( Pinus ponderosa ). Model predictions were evaluated using observations of productivity and survival for three ponderosa pine stands located across an 800 m elevation gradient in the southern Rocky Mountains, USA, during a 10-year period that ended in a severe drought and extensive tree mortality at the lowest elevation site. We demonstrate the utility of a relatively simple representation of declines in non-structural carbohydrate (NSC) as an approach for estimating patterns of ponderosa pine vulnerability to drought and the likelihood of survival along an elevation gradient. We assess the sensitivity of simulated net primary production, NSC storage dynamics, and mortality to site climate and soil characteristics as well as uncertainty in the allocation of carbon to the NSC pool. For a fairly wide set of assumptions, the model estimates captured elevational gradients and temporal patterns in growth and biomass. Model results that best predict mortality risk also yield productivity, leaf area, and biomass estimates that are qualitatively consistent with observations across the sites. Using this constrained set of parameters, we found that productivity and likelihood of survival were equally dependent on elevation-driven variation in temperature and precipitation. Our results demonstrate the potential for a coupled hydrology-ecosystem carbon cycling model that includes a simple model of NSC dynamics to predict drought-related mortality. Given that increases in temperature and in the frequency and severity of drought are predicted for a broad range of ponderosa pine and other western North America conifer forest habitats, the model potentially has broad utility for assessing ecosystem vulnerabilities.

Jemez Mountains, Rocky Mountains↗

USGS2022

Streambank and floodplain geomorphic change and contribution to watershed material budgets

Stream geomorphic change is highly spatially variable but critical to landform evolution, human infrastructure, habitat, and watershed pollutant transport. However, measurements and process models of streambank erosion and floodplain deposition and resulting sediment fluxes are currently insufficient to predict these rates in all perennial streams over large regions. Here we measured long-term lateral streambank and vertical floodplain change and sediment fluxes using dendrogeomorphology in streams around the U.S. Mid-Atlantic, and then statistically modeled and extrapolated these rates to all 74 133 perennial, nontidal streams in the region using watershed- and reach-scale predictors. Measured long-term rates of streambank erosion and floodplain deposition were highly spatially variable across the landscape from the mountains to the coast. Random Forest regression identified that geomorphic change and resulting fluxes of sediment and nutrients, for both streambank and floodplain, were most influenced by urban and agricultural land use and the drainage area of the upstream watershed. Modeled rates for headwater streams were net erosional whereas downstream reaches were on average net depositional, leading to regional cumulative sediment loads from streambank erosion (−5.1 Tg yr −1 ) being nearly balanced by floodplain deposition (+5.3 Tg yr −1 ). Geomorphic changes in stream valleys had substantial influence on watershed sediment, phosphorus, carbon, and nitrogen budgets in comparison to existing predictions of upland erosion and delivery to streams and of downstream sediment loading. The unprecedented scale of these novel findings provides important insights into the balance of erosion and deposition in streams within disturbed landscapes and the importance of geomorphic change to stream water quality and carbon sequestration, and provides vital understanding for targeting management actions to restore watersheds.

Chesapeake Bay watershed↗

USGS2019

Social equity shapes zone-selection: Balancing aquatic biodiversity conservation and ecosystem services delivery in the transboundary Danube River Basin

Freshwater biodiversity is declining, despite national and international efforts to manage and protect freshwater ecosystems. Ecosystem-based management (EBM) has been proposed as an approach that could more efficiently and adaptively balance ecological and societal needs. However, this raises the question of how social and ecological objectives can be included in an integrated management plan. Here, we present a generic model-coupling framework tailored to address this question for freshwater ecosystems, using three components: biodiversity, ecosystem services (ESS), and a spatial prioritisation that aims to balance the spatial representation of biodiversity and ESS supply and demand. We illustrate this model-coupling approach within the Danube River Basin using the spatially explicit, potential distribution of (i) 85 fish species as a surrogate for biodiversity as modelled using hierarchical Bayesian models, and (ii) four estimated ESS layers produced by the Artificial Intelligence for Ecosystem Services (ARIES) platform (with ESS supply defined as carbon storage and flood regulation, and demand specified as recreation and water use). These are then used for (iii) a joint spatial prioritisation of biodiversity and ESS employing Marxan with Zones, laying out the spatial representation of multiple management zones. Given the transboundary setting of the Danube River Basin, we also run comparative analyses including the country-level purchasing power parity (PPP)-adjusted gross domestic product (GDP) and each country's percent cover of the total basin area as potential cost factors, illustrating a scheme for balancing the share of establishing specific zones among countries. We demonstrate how emphasizing various biodiversity or ESS targets in an EBM model-coupling framework can be used to cost-effectively test various spatially explicit management options across a multi-national case study. We further discuss possible limitations, future developments, and requirements for effectively managing a balance between biodiversity and ESS supply and demand in freshwater ecosystems.

Science of the Total Environment↗

USGS2026

VegET evapotranspiration for Africa: Continental-scale simulation, multi-product evaluation, and drought assessment

Study region Continental Africa, encompassing diverse climatic zones—tropical, arid, and temperate—and spanning major transboundary river basins such as the Nile, Niger, Congo, Volta, and Zambezi River Basins. The region exhibits pronounced hydroclimatic gradients and heterogeneous land use systems ranging from rainfed croplands and rangelands to dense tropical forests and irrigated schemes. Study focus Actual evapotranspiration (ETa) is a central component of the terrestrial water balance, governing the redistribution of water and energy between the land surface and the atmosphere. Accurate estimation of ETa at continental scale is critical for hydrological monitoring, water resource management, and climate adaptation, as well as for quantifying water, energy, and carbon fluxes that underpin sustainable development. In this study, we applied the agro-hydrologic VegET v2 model to simulate a new, high-resolution, continental-scale ETa dataset for Africa (2000–2021). The model results were benchmarked against four widely used remote sensing-based products—MODIS16 v6.1, SSEBop v6.1, WaPOR v3, and GLEAM v4.1a—across major climate zones, land use types, and River Basins, providing a comprehensive multi-product evaluation of evapotranspiration dynamics across the continent. New hydrological insights for the region Validation against eddy covariance flux tower observations at eight representative sites confirmed that VegET v2 accurately reproduces the seasonal dynamics of observed ETa, achieving a correlation (r) of 0.8 and an RMSE of 25 mm month⁻¹ —accuracy that is comparable to or higher than accuracies of satellite-based products MODIS16, SSEBop, and GLEAM. This study represents one of the first Africa-wide hydrological simulations of ETa, extending the VegET model beyond basin-scale applications. Intercomparisons reveal that VegET aligns closely with MODIS16, SSEBop, and GLEAM in humid and tropical regions (r = 0.80–0.90; RMSE < 20 mm month⁻¹), while greater discrepancies appear in arid and semi-arid zones, where WaPOR tends to overestimate ETa (RMSE ≥ 28 mm month⁻¹). Despite these differences, VegET effectively captures spatial and temporal ETa variability across rainfed croplands, forests, and savannas, supporting its utility in regional water balance assessments, water accounting, and drought monitoring. A key application of VegET v2 is the Evapotranspiration Deficit Index (ETDI), derived by integrating VegET-based ETa with potential evapotranspiration (PET) to quantify water stress. ETDI successfully captured major drought episodes across Africa, including persistent Sahelian and southern African dry spells, the 2020–2021 winter drought in the Maghreb, and the 2018–2019 austral summer drought in southern Africa, while identifying positive anomalies over central Africa indicative of recurrent wetness. These results underscore VegET’s capability as a hydrologically consistent, operational tool for continental ETa monitoring and drought assessment, offering support for basin-scale water balance studies, food security planning, and climate resilience across Africa’s diverse hydrological environments.

Journal of Hydrology: Regional Studies↗

USGS2003

Soil organic carbon on lands of the Department of the Interior

The stocks of soil organic carbon (SOC) on the landscape are an important element in the global carbon cycle. Changes in soil carbon can change the concentrations of greenhouse gases in the atmosphere. If carbon dioxide from the atmosphere, captured through photosynthesis, is ultimately stored in the soil to an enhanced degree, the resulting soil carbon sequestration may help delay some of the undesirable consequences of global warming. If the conditions affecting the balance of photosynthesis and decomposition are changed to favor decomposition, then soil carbon can be released to the atmosphere as carbon dioxide or methane, contributing to greenhouse warming. The Department of the Interior (DOI) is the largest land management agency in the United States, with jurisdiction influencing more than 2 million square kilometers of land--about 22 percent of the total land area of the country. Estimates using available data indicate that the DOI lands have nearly 18 petagrams (Pg; 1 Pg = 1015 g = 1 gigaton) of SOC, which is about 22 percent of the estimate for the country (81 Pg). The distribution is not uniform, and few areas of DOI lands reflect “average” conditions. Large areas of land with low biological productivity occur in the conterminous U.S. part of the DOI lands, and substantial areas with high SOC occur in Alaska. About 74 percent of the SOC on DOI lands is in Alaska. Details on amounts of SOC by DOI Bureau and location are shown in a series of tables and maps. For the conterminous United States, statistics are given by land cover type and soil depth ranges.

Open-File Report↗

USGS2003

Calibration of remotely sensed, coarse resolution NDVI to CO2 fluxes in a sagebrush–steppe ecosystem

The net ecosystem exchange (NEE) of carbon flux can be partitioned into gross primary productivity (GPP) and respiration ( R ). The contribution of remote sensing and modeling holds the potential to predict these components and map them spatially and temporally. This has obvious utility to quantify carbon sink and source relationships and to identify improved land management strategies for optimizing carbon sequestration. The objective of our study was to evaluate prediction of 14-day average daytime CO 2 fluxes ( F day ) and nighttime CO 2 fluxes ( R n ) using remote sensing and other data. F day and R n were measured with a Bowen ratio–energy balance (BREB) technique in a sagebrush ( Artemisia spp.)–steppe ecosystem in northeast Idaho, USA, during 1996–1999. Micrometeorological variables aggregated across 14-day periods and time-integrated Advanced Very High Resolution Radiometer (AVHRR) Normalized Difference Vegetation Index (iNDVI) were determined during four growing seasons (1996–1999) and used to predict F day and R n . We found that iNDVI was a strong predictor of F day ( R 2 =0.79, n =66, P <0.0001). Inclusion of evapotranspiration in the predictive equation led to improved predictions of F day ( R 2 =0.82, n =66, P <0.0001). Crossvalidation indicated that regression tree predictions of F day were prone to overfitting and that linear regression models were more robust. Multiple regression and regression tree models predicted R n quite well ( R 2 =0.75–0.77, n =66) with the regression tree model being slightly more robust in crossvalidation. Temporal mapping of F day and R n is possible with these techniques and would allow the assessment of NEE in sagebrush–steppe ecosystems. Simulations of periodic F day measurements, as might be provided by a mobile flux tower, indicated that such measurements could be used in combination with iNDVI to accurately predict F day . These periodic measurements could maximize the utility of expensive flux towers for evaluating various carbon management strategies, carbon certification, and validation and calibration of carbon flux models.

Idaho↗

USGS2021

Carbon fluxes and potential soil accumulation within Greater Everglades cypress and pine forested wetlands

In forested wetlands, accumulation of organic matter in soil is partly governed by carbon fluxes where photosynthesis, respiration, lateral advection of waterborne carbon, fire-derived carbon emissions, and methanogenesis are balanced by changes in stored carbon. Stored carbon can eventually accumulate as soil over time if net primary productivity exceeds biomass decomposition. For this study, potential soil accumulation was estimated based on four years of continuous daily carbon cycling data and a one-dimensional mass-balance model of landscape-atmospheric exchange for cypress and pine forested wetlands in the Greater Everglades of south Florida. The mass-balance model was driven by eddy-covariance estimates of vertical net ecosystem exchange of carbon dioxide and methane. Key findings include confirmation of a basic premise of the historic Everglades restoration project; specifically, more water either from rainfall or water management encourages soil carbon accumulation and thus conservation of soils that support biologic activity and ecosystem services. For example, an anomalous wet season for south Florida that flooded the forested wetlands through the traditional dry season was followed by the most productive year for photosynthetic carbon uptake and potential soil accumulation. On the other hand, methane emissions were enhanced by the anomalous wet season and extended flooding – which confirmed a complex tradeoff to consider if wetlands are managed for both soil conservation and reduction of greenhouse gas emissions. Potential soil accumulation rates were about 1.7, 2.8, and 18 millimeters per year at the Dwarf Cypress, Cypress Swamp, and Pine Upland ecosystems, assuming soil C density values of 0.07, 0.09, and 0.02 grams of carbon per cubic centimeter, respectively. For these values of soil C density, the accumulation rates are considered a “best-case” upper limit because the lateral export of carbon in the canals and creeks that drain the study area were assumed negligible.

Florida↗

USGS2023

Finding a GEM: The Grassland Effectiveness Monitoring (GEM) protocol provides a tiered approach for habitat treatment assessment across private lands incentive programs

The soil store carbon dioxide from the atmosphere through different processes, depending on the use and management of the land. For the Maderas del Carmen and Ocampo natural protected areas, one of the main conservation goals is to preserve natural habitats, ensuring an ecological balance and making a sustainable. The main productive activity in the region is extensive livestock. Different strategies have been explored for producers to modify their practices to ensure sustainable management. In this study, we established the baseline of sustainable management indicators according to the sustainable management protocol. Soils showed a low activity and low C with a high bulk density. Establishing this baseline will allow a starting point for a long-term evaluation different from those traditionally used when evaluating the productivity of the rangeland.

Conference Paper↗

USGS2011

How reservoirs alter drinking water quality: Organic matter sources, sinks, and transformations

Within reservoirs, production, transformation, and loss of dissolved organic matter (DOM) occur simultaneously. While the balance between production and loss determines whether a reservoir is a net sink or source of DOM, changes in chemical composition are also important because they affect DOM reactivity with respect to disinfection by-product (DBP) formation. The composition of the DOM pool also provides insight into DOM sources and processing, which can inform reservoir management. We examined the concentration and composition of DOM in San Luis Reservoir, a large off-stream impoundment of the California State Water Project. We used a wide array of DOM chemical tracers including dissolved organic carbon (DOC) concentration, trihalomethane and haloacetic acid formation potentials (THMFP and HAAFP, respectively), absorbance properties, isotopic composition, lignin phenol content, and structural groupings determined by 13 C nuclear magnetic resonance (NMR). There were periods when the reservoir was a net source of DOC due to the predominance of algal production (summer), a net sink due to the predominance of degradation (fall–winter), and balanced between production and consumption (spring). Despite only moderate variation in bulk DOC concentration (3.0–3.6 mg C/L), changes in DOM composition indicated that terrestrial-derived material entering the reservoir was being degraded and replaced by aquatic-derived DOM produced within the reservoir. Substantial changes in the propensity of the DOM pool to form THMs and HAAs illustrate that the DBP precursor pool was not directly coupled to bulk DOC concentration and indicate that algal production is an important source of DBP precursors. Results suggest reservoirs have the potential to attenuate DOM amount and reactivity with respect to DBP precursors via degradative processes; however, these benefits can be decreased or even negated by the production of algal-derived DOM.

California↗

USGS2026

Prioritizing resource protection and understanding potential susceptibility of springs to surficial changes in a low-temperature geothermal system

Geothermal systems are vulnerable to changes in water budget and composition, requiring science-based management. This study uses a dataset of spring water temperatures, time series of groundwater residence time tracers (tritium and carbon-14), and stable isotopes of water to understand geothermal flow in a low-temperature geothermal system in north west Colorado, United States (Steamboat Springs). The geothermal system is bisected by the Yampa River, necessitating a stream mass balance approach to quantify total discharge. Time series analysis of water temperature data provides a ranked list of features more susceptible to surficial changes, which is corroborated using time series of tritium which indicate spatially distinct patterns of mixing between modern and pre-modern groundwater. All springs contain a portion of pre-modern groundwater that is thousands to tens of thousands of years old, a period coinciding with melting of extensive Pleistocene glaciers that was likely one of the recharge sources to the geothermal system. Stream mass balance indicates that greater than 80% of the total geothermal discharge is derived from diffuse or small springs, highlighting the extensive nature of the geothermal outflow zone and the association with local geologic structures. This study provides baseline data to support management of the Steamboat Springs geothermal system and indicates the utility of these approaches in developing science-based geothermal management.

Colorado↗

USGS2016

Impact of carbon dioxide level, water velocity, and feeding regimen on growth and fillet attributes of cultured rainbow trout (Oncorhynchus mykiss)

Production and management variables such as carbon dioxide (CO 2 ) level, water velocity, and feeding frequency influence the growth and fillet attributes of rainbow trout ( Oncorhynchus mykiss ), as well as cost of production. More information is needed to determine the contributions of these variables to growth and fillet attributes to find the right balance between input costs and fish performance. Two studies, of 84 and 90 days duration, were conducted to determine the effects of CO 2 level, water velocity, and feed frequency on rainbow trout growth, fillet yield, and fillet quality. In the first study, two CO 2 levels (30 and 49 mg/L) and two velocity levels (0.5 and 2.0 body lengths/s) were tested. In the second study two CO 2 levels (30 and 49 mg/L) and two feeding regimens (fed once daily to satiation or three times daily to satiation) were tested. In the first study, after 84 days, fillet weight from high CO 2 tanks was 13.5% lower than the fillet weights of fish from low CO 2 tanks. Percent fat of fillets was higher in low CO 2 fish ( P = 0.05) after 84 days and, fish from the low CO 2 treatment were larger ( P < 0.01). Both studies had similar results in regards to fat content and weight of fillets in response to elevated CO 2 levels. Velocity had little affect on either whole wet weight or fillet attributes of rainbow trout in this study. Muscle tissue contained more ( P < 0.01) fat when fish were fed three times daily (7.3%; day 90) compared to once daily (5.4%; day 90). Also, fish were larger (P < 0.05) when fed 3 times per day (1079 g; day 90) in comparison to only one daily feeding (792 g; day 90). Fish in high feed/high CO 2 tanks were larger and had more fillet fat than fish from low feed/low CO 2 tanks. To maximize rainbow trout growth at aquaculture facilities, management strategies should attempt to keep CO 2 levels below 30 mg/L when cost efficient. However, feeding 2–3 times daily should reduce production losses if CO 2 cannot be minimized. The effect of strain and velocity were minimal over the range we tested in comparison to the effects of CO 2 and feeding regimen.

Book chapter↗

USGS2017

Disrupted carbon cycling in restored and unrestored urban streams: Critical timescales and controls

Carbon fixation and respiration in flowing waterways play significant roles in global and regional carbon budgets, yet how land use and watershed management interact with temporal disturbances (storms) to influence metabolism remains poorly understood. Here, we combine long-term with synoptic sampling of metabolism and its variable controls in neighboring watersheds of the Chesapeake Bay to resolve limiting factors and critical timescales associated with recovery from disturbance. We found that, relative to predictions of the river continuum concept, focal streams have “disrupted” carbon cycles, with carbon balances closer to zero, and, in some cases, tighter coupling between gross primary production (GPP) and ecosystem respiration (ER), attributable to carbon limitation. Carbon became limiting to ER where flashy storm hydrographs and simplified channel geomorphology inhibited accumulation of fine sediment. Shannon entropy analysis of timescales revealed that fine sediment served as a time-release capsule for nutrients and carbon over 4–6 months, fueling biogeochemical transformations. Loss of fines through hydraulic disturbance had up to 30-d impacts on GPP and 50-d impacts on ER in the stream with carbon limitation. In contrast, where GPP and ER were not tightly coupled, recovery occurred within 1 d. Results suggest that a complex interplay between nutrient and carbon limitation and mechanical and chemical disturbance governs patterns and consequences of disrupted carbon cycling in urban streams. Carbon limitation and tight GPP/ER coupling enhance the vulnerability of stream ecosystem functions, but best management practices that target stormflow reduction and channel geomorphic diversity can break that coupling and minimize carbon cycle disruptions.

Limnology and Oceanography↗

USGS2024

Urbanization and water management control stream water quality along a mountain to plains transition

Urbanization can have substantial effects on water quality due to altered hydrology and introduction of constituents to water bodies. In arid and semi-arid environments, streams are further stressed by dewatering as a result of diversions. We conducted a high-resolution synoptic survey of two streams in Colorado, USA that transition abruptly from granitic/metamorphic forested mountains to sedimentary urbanized plains and are both highly managed for water supply, yet differ in degree of urbanization. A synoptic mass balance approach developed for mine drainage applications was adapted to elucidate effects of urbanization, geology, and diversions on stream chemistry during baseflow conditions. Urbanization was a more important driver of stream concentrations than geology. The urban area was a strong source of bromide, calcium, chloride, and manganese, while lanthanum and dissolved organic carbon were primarily sourced from the mountains. A majority of streamflow was removed by diversions near the mountains/plains interface. Groundwater accounted for 31% of the subsequent flow increase to the urbanized stream, and delivered at least 33% of chloride loading. Constituents that were primarily urban-derived (bromide, calcium, chloride, and manganese) were 2–3 times higher in the urban region due to diversions; without diversions, stream water quality would have largely retained characteristics of forested streams through the urban reach. This study provides insights into processes that affect water quality in highly managed streams of the semi-arid western USA.

Colorado↗

USGS2010

Methylmercury cycling, bioaccumulation, and export from agricultural and non-agricultural wetlands in the Yolo Bypass

This 18-month field study addresses the seasonal and spatial patterns and processes controlling methylmercury (MeHg) production, bioaccumulation, and export from natural and agricultural wetlands of the Yolo Bypass Wildlife Area (YBWA). The data were collected in conjuntion with a Proposition 40 grant from the State Water Resources Control Board in support of the development of Best Management Practices (BMP's) for reducing MeHg loading from agricultural lands in the wetland-dominated Yolo Bypass to the Sacramento-San Joaquin River Delta. The four managemenr-based questions addressed in this study were: 1. Is there a different among agricultural and managfed wetland types in terms of Me Hg dynamic (production, degradation, bioaccumulation, or export)? 2. Does water residence time influence MeHg dynamics? 3. Does the application of sulfate-based fertilizer impact MeHg production rates? 4. Does the presence (or absence) of vegetation influence MeHg production rates? Measurements of MeHg concentrations in sediment, water, and biota (plants, invertebrates, and fish) were made to assess management-level patterns in five wetland types, which included three type of shallowly-flooded agricultural wetlands (white rice, wild rice, and fallow) and two types of managed wetlands (permanently and seasonally flooded). To strengthen our understanding of the processes underlying the seasonal and spatial patterns of MeHg cycling, additional exploratory factors were measured including ancillary sediment and water quality parameters, stable isotope fractionation (oxygen, sulfur, carbon, and nitrogen), photodemethylation rates, and daily-integrated hydrologic budgets. Samples and field data were collected from May 2007 to July 2008, and nearly all sample analyses were completed by September 2008 as per the Quality Assurance Program Plan (QAPP) requirements. Although wetland type was a major factor that drove the study design, within-field hydrology also proved to be an important factor controlling aqueous MeHg and total mercury (THg) concentrations and export. Overall, agricultural wetlands exhibited higher MeHg concentrations in overlying water, sediment, and biota than did managed seasonal and permanent wetlands. This appears to be partly due to higher rates of sediment in microbial production of MeHg on agricultural wetlands during the fall through spring period. Both sulfate- and iron-reducing bacteria have been implicated in the MeHg production process, and both were demonstrably active in all wetlands studied; however, sulfate-reducing bacteria were not stimulated by the addition of sulfate-based fertilizer to agricultural wetlands, suggesting that easily-degraded (labile) organic matter, rather than sulfate, was limiting their activity in these field types. The data suggest that agriculturally-managed soils promoted MeHg production through 1) enhanced microbial activity via higher temperatures and larger pools of labile carbon, and 2) enhanced pools of microbially available inorganic divalent mercury (Hg(II)) resulting from a decrease in reduced-sulfur, solid-phase minerals under oxic or only mildly reducing conditions. MeHg mass balances were assessed by comparing filed-specific MeHg loads for inlets vs. outlet flows. The overall mass balance for MeHg in surface water during the summer irrigation period (June - September 2007) indicated little to no net MeHg export from the six agricultural wetlands taken as a whole. Of the six agricultural wetlands, there was net overall MeHg export from two fields (one fallow and one white rice) during August, and from four of the six fields (one fallow, one white rice, and two wild rice) during September) Over the entire summer irrigation period, two of the fields (one fallow and one wild rive) showed net MeHg export, and the other four fields showed wither net import or no significant change. Rates of measured photomethylation and exchange between sediment and water pools suggest that both processes may be responsible for the lack of MeHg export. Despite significant differences during winter months between fields in surface water concentrations of MeHg, MeHg loads were not calculated in mid-winter because flood waters had overtopped field boundaries and field fidelity could not be established. During the summer 2007 irrigation season, surface water out-flows from agricultural wetlands were 9%-36% of inlet flows, and evaporation rates explained most of this water loss, with infiltration likely accounting for the remainder. Unfiltered aqueous MeHg concentrations increased from <1 ng L -1 in source waters to up to 10 ng L -1 in agricultural wetland drains during the summer irrigation period. Increases in solute concentration caused by evapoconcentration were estimated by determining concentration factors (outflow/inflow) for chloride (a conservative dissolved constituent) and by measuring oxygen isotope ratios ( 18 O/ 16 O, expressed as δ 18 O) in water. Increases in MeHg concentration from inflows-to-outflows exceeded those caused by evapoconcentration on several fields during the summer irrigation season. This was especially true when initial surface water MeHg concentrations were low, as seen in the southern block of fields receiving irrigation water directly from the Toe Drain. The northern block of fields received irrigation water from Greens Lake, which included Toe Drain water plus recirculated drain water from other agricultural fields within the Yolo Bypass and west of the Yolo Bypass; as such, the northern fields showed a smaller percentage increase in MeHg concentration because initial MeHg concentrations in surface water inflows were greater than in inputs to the southern fields. Mercury concentrations in fish were greater in agricultural wetlands white rice and wild rice) than in the two permanently flooded wetlands. Additionally, Hg concentrations in biota showed a general increase from inlets to outlets withing agricultural wetlands, but not within permanent wetlands. This was particular evident in white rice fields where caged western mosquitofish at the outlets had Hg concentrations that were more than 4 times higher than in caged fish held at the inlets. Similar spatial patterns in Hg bioaccumulation in agricultural and permanent wetlands were seen for wild populations of western mosquitofish and Mississippi silversides. In contrast to fish, invertebrates, such as water-boatman (Corixidae) and back swimmers (Notonectidae), had greater Hg concentrations in permanent wetlands than in tempoarirly flooded agricultural wetlands, Fish THg concentrations were weakly correlated with water MeHg,a and not correlated with sediment MeHg. In contrast, invertebrate MeHg concentrations were more strongly correlated with sediment MeHg than with water MeHg concentrations. These results illustrate the complexity of MeHg bioaccumulation through food webs and indicate the importance of simultaneously using multiple biosentinels when monitoring MeHg production and bioaccumulation. Despite high sediment production rates and water concentrations in agricultural wetlands, MeHg export was physically limited by hydrologic export for all wetlands studied. We suggest that load reduction is maximized by limiting water throughout, but that on-site biota exposure is maximized by this loner water residence time. While field-specific hydrologic loads could not be fully quantified during flood conditions in February 2008, we suggest that the primary period of MeHg export from Yolo Bypass Wildlife Area is during those winter flooding periods when overall microbial activity and MeHg production in agricultural soils is fueled by the decomposition of rice straw, and when hydrologic flowthrough is maximal. Local stakeholders participated in two workshops related to this study, demonstrating an interest in understanding factors controlling MeHg production, export, and bioaccumulation. The results of this field study show that permanently flooded, naturally vegetated wetlands are unlikely to a large source of MeHg production within the YBWA, in contrast with agriculturally-managed wetlands. MeHg loading to Toe Drain waters of the Yolo Bypass may be reduced by lowering rated of hydrologic export from agricultural wetlands during the growing season and especially during rice harvest, However, under these water-holding conditions, biota living within agricultural wetlands may thus be exposed to higher MeHg concentrations in surface water, As observed in this study, rapid bioacculumaltion over a 2-month period led to MeHg concentrations in invertebrates and fish more than 6 and 11 times higher, respectively, than proposed TMDL target values to protect wildlife (0.03 ppm ww). The results of this field study, together with the information from YBWA stakeholders, provide a more definitive understanding of how MeHg cycling and bioaccumulation respond to habitat differences and specific management practices. These results directly address 4 core components of CBDA's Mercury Strategy for the Bay-Delta Ecosystem (Wiener et al., 2003a): a) Quantification and evaluation of THg and MeHg sources, b) Quantification of effects of ecosystem restoration on MeHg exposure, c) Assessment of ecological risk, and d) Identification and testing of potential management approaches for reducing MeHg contamination. In addition, the quantitative results reported here assess the effect of current land use practices in the Yolo Bypass MeHg production, bioaccumulation and export, and provide process-based advice towards achieving current goals of the RWQCB-CVR's Sacramento -- San Joaquin Delta Estuary TMDL for Methyl & Total Mercury (Wood et al., 2010b). Further work is necessary to evaluate biotic exposure in the Yolo Bypass Wildlife Area at higher trophic levels (e.g. birds), to quantify winter hydrologic flux of MeHg to the larger Delta ecosystem, and to evaluate rice straw management options to limit labile carbon supplies to surface sediment during winter months. In summary, agricultural management of rice fields -- specifically the periodic flooding and production of easily degraded organic matter -- promotes the production of MeHg beyond rates seen in naturally vegetated wetlands, whether seasonally or permanently flooded., The exported load from MeHg from these agricultural wetlands may be controlled by limiting hydrologic export from fields to enhance on-site MeHg removal processes, but the tradeoff is that this impoundement increases Me Hg exposure to resident organisms.

California↗

USGS2015

Terrestrial Carbon Sequestration in National Parks: Values for the Conterminous United States

Lands managed by the National Park Service (NPS) provide a wide range of beneficial services to the American public. This study quantifies the ecosystem service value of carbon sequestration in terrestrial ecosystems within NPS units in the conterminous United States for which data were available. Combining annual net carbon balance data with spatially explicit NPS land unit boundaries and social cost of carbon estimates, this study calculates the net metric tons of carbon dioxide sequestered annually by park unit under baseline conditions, as well as the associated economic value to society. Results show that, in aggregate, NPS lands in the conterminous United States are a net carbon sink, sequestering more than 14.8 million metric tons of carbon dioxide annually. The associated societal value of this service is estimated at approximately $582.5 million per year. While this analysis provides a broad overview of the annual value of carbon sequestration on NPS lands averaged over a five year baseline period, it should be noted that carbon fluxes fluctuate from year to year, and there can be considerable variation in net carbon balance and its associated value within a given park unit. Future research could look in-depth at the spatial heterogeneity of carbon flux within specific NPS land units.

Natural Resource Report↗