Wilfred M. Wollheim

• University of New Hampshire

Hyporheic zones regulate biogeochemical processes in streams and rivers, but high spatiotemporal heterogeneity makes it difficult to predict how these processes scale from individual reaches to river basins. Recent work applying allometric scaling (i.e., power‐law relationships between size and function) to river networks provides a new paradigm fo...

Restoring wetlands will reduce nitrogen contamination from excess fertilization but estimates of the efficacy of the strategy vary widely. The intervention is often described as effective for reducing nitrogen export from watersheds to mediate bottom-level hypoxia threatening marine ecosystems. Other research points to the necessity of applying a s...

River networks play a crucial role in the global carbon cycle, as relevant sources of carbon dioxide (CO 2) to the atmosphere. Advancements in high-frequency monitoring in aquatic environments have enabled measurement of dissolved CO 2 concentration at temporal resolutions essential for studying carbon variability and evasion from these dynamic eco...

Anthropogenic nitrogen (N) inputs to the landscape have serious consequences for inland and coastal waters. Reservoirs are effective at mitigating downstream N fluxes but measurements have generally focused on large reservoirs and have not considered seasonal variability or all N forms. In this study, we conducted an N mass balance in eight small r...

We utilize a coupled economy–agroecology–hydrology modeling framework to capture the cascading impacts of climate change mitigation policy on agriculture and the resulting water quality cobenefits. We analyze a policy that assigns a range of United States government’s social cost of carbon estimates ($51, $76, and $152/ton of CO 2 -equivalents) to...

Headwater stream networks contribute substantially to the global carbon dioxide terrestrial flux because of high turbulence and coupling with terrestrial environments. Heterogeneity within headwater stream networks, both spatially and temporally, makes measuring and upscaling these emissions challenging because measurements of carbon dioxide in str...

This paper describes the University of New Hampshire Water Balance Model, WBM, a process-based gridded global hydrologic model that simulates the land surface components of the global water cycle and includes water extraction for use in agriculture and domestic sectors. The WBM was first published in 1989; here, we describe the first fully open-sou...

The period of disrupted human activity caused by the COVID-19 pandemic, coined the "anthropause," altered the nature of interactions between humans and ecosystems. It is uncertain how the anthropause has changed ecosystem states, functions, and feedback to human systems through shifts in ecosystem services. Here, we used an existing disturbance fra...

This paper describes the University of New Hampshire Water Balance Model, WBM, a process-based gridded global hydrologic model that simulates the land surface components of the global water cycle and includes water extraction for use in agriculture and domestic sectors. WBM has a long publication history; here we describe the first fully open sourc...

River networks regulate carbon and nutrient exchange between continents, atmosphere, and oceans. However, contributions of riverine processing are poorly constrained at continental scales. Scaling relationships of cumulative biogeochemical function with watershed size (allometric scaling) provide an approach for quantifying the contributions of flu...

Fecal contamination is a significant source of water quality impairment globally. Aquatic ecosystems can provide an important ecosystem service of fecal contamination removal. Understanding the processes that regulate the removal of fecal contamination among river networks across flow conditions is critical. We applied a river network model, the Fr...

Inland waters are the largest natural source of methane (CH4) to the atmosphere, yet the contribution from small streams to this flux is not clearly defined. To fully understand CH4 emissions from streams and rivers, we must consider the relative importance of CH4 emission pathways, the prominence of microbially-mediated production and oxidation of...

Headwater streams are known sources of methane (CH4) to the atmosphere, but their contribution to global scale budgets remains poorly constrained. While efforts have been made to better understand diffusive fluxes of CH4 in streams, much less attention has been paid to ebullitive fluxes. We examine the temporal and spatial heterogeneity of CH4 ebul...

Rapid changes in land use, pollution inputs, and climate are altering the quantity, timing, and form of materials delivered from watersheds to estuaries. To better characterize these alterations simultaneous measurements of biogeochemical conditions in watersheds and estuaries over a range of times scales are needed. We examined the strength of wat...

Over the past 30 plus years, the Arctic has warmed at a rate of 0.6°C per decade. This has resulted in considerable permafrost thaw and alterations of hydrological and biogeochemical processes. Coincident with these changes, recent studies document increases in annual fluxes of inorganic nutrients in larger Arctic rivers. Changing nutrient fluxes i...

The capacity of headwater streams to transform and retain organic matter and nutrients during base flow conditions has been largely demonstrated in the literature. Yet, most solute exporting occurs during storms, and thus, it becomes essential to understand the role of in-stream processes in regulating solute concentrations and exports during storm...

Flooding is a major disturbance that impacts aquatic ecosystems and the ecosystem services that they provide. Predicted increases in global flood risk due to land use change and water cycle intensification will likely only increase the frequency and severity of these impacts. Extreme flooding events can cause loss of life and significant destructio...

Chloride contamination of rivers due to nonpoint sources is increasing throughout developed temperate regions due to road salt application in winter. We developed a river‐network model of chloride loading to watersheds to estimate road salt application rates and investigated the meteorological factors that control riverine impairment by chloride at...

Streams play a key role in the global carbon cycle. The balance between carbon intake through photosynthesis and carbon release via respiration influences carbon emissions from streams and depends on temperature. However, the lack of a comprehensive analysis of the temperature sensitivity of the metabolic balance in inland waters across latitudes a...

Accurate quantification of ecosystem services (ES) at regional scales is increasingly important for making informed decisions in the face of environmental change. We linked terrestrial and aquatic ecosystem process models to simulate the spatial and temporal distribution of hydrological and water quality characteristics related to ecosystem service...

Nonpoint pollution sources are strongly influenced by hydrology and are therefore sensitive to climate variability. Some pollutants entering aquatic ecosystems, e.g., nitrate, can be mitigated by in-stream processes during transport through river networks. Whole river network nitrate retention is difficult to quantify with observations. High freque...

Scaling aquatic ecosystem processes like nutrient removal is critical for assessing the importance of streams and rivers to watershed nutrient export. We used pulse NH4⁺ enrichment experiments and measured net NH4⁺ uptake in 7 streams throughout a mountainous tropical river network in Puerto Rico to assess spatial variability in NH4⁺ uptake and to...

Ecological functions are coupled to the physical transport of water and solutes in streams. Transport of conservative tracers in lotic systems is subject to the processes of advection, dispersion, transient storage, and mass loss to groundwater. Stream tracer experiments and the simulation of observed tracer breakthrough curve (BTC) data with 1-D n...

Quantifying the role that freshwater ecosystems play in the global carbon cycle requires accurate measurement and scaling of dissolved organic carbon (DOC) removal in river networks. We reviewed reach-scale measurements of DOC uptake from experimental additions of simple organic compounds or leachates to inform development of aquatic DOC models tha...

Climate change has resulted in warmer soil temperatures, earlier spring thaw and later fall freeze-up, resulting in warmer soil temperatures and thawing of permafrost in tundra regions. While these changes in temperature metrics tend to lengthen the growing season for plants, light levels, especially in the fall, will continue to limit plant growth...

Context Spatial scaling of ecological processes is facilitated by quantifying underlying habitat attributes. Physical and ecological patterns are often measured at disparate spatial scales limiting our ability to quantify ecological processes at broader spatial scales using physical attributes. Objective We characterized variation of physical strea...

The spatial distribution of land use and associated nutrient inputs may influence the efficacy of in-stream nutrient removal however, the effect of source location on N removal and watershed N export has not been quantified. We present the skewness index, a metric to quantify the spatial distribution of land use within watersheds. Using this index...

The structure, function, and services of urban ecosystems evolve over time scales from seconds to centuries as Earth’s population grows, infrastructure ages, and sociopolitical values alter them. In order to systematically study changes over time, the concept of “urban evolution” was proposed. It allows urban planning, management, and restoration t...

Surface waters play a potentially important role in the global carbon balance. Dissolved organic carbon (DOC) fluxes are a major transfer of terrestrial carbon to river systems, and the fate of DOC in aquatic systems is poorly constrained. We used a unique combination of spatially distributed sampling of three DOC fractions throughout a river netwo...

River-borne inputs of alkalinity influence the pH and pCO2 of coastal ocean waters, and changes in alkalinity inputs also have implications for responses to climate-driven ocean acidification. Recent work has shown that alkalinity fluxes from rivers are not always dominated by inorganic carbon species, and can instead be composed somewhat or mostly...

Demand for locally-produced food is growing in areas outside traditionally dominant agricultural regions due to concerns over food safety, quality, and sovereignty; rural livelihoods; and environmental integrity. Strategies for meeting this demand rely upon agricultural land use change, in various forms of either intensification or extensification...

This overview and synthesis paper focuses on the evolution of urban biogeochemical cycles across time. We synthesize empirical data and review existing literature, including papers in this special issue, and we propose the concept of ''urban evolu-tion.'' The built environment often changes quickly in response to human activities, thus contributing...

Piped streams, or streams that run underground, are often associated with urbanization. Despite the fact that they are ubiquitous in many urban watersheds, there is little empirical evidence regarding the ecological structure and function of piped stream reaches. This study measured ecosystem metabolism, nutrient uptake, and related characteristics...

Suburbanization negatively impacts aquatic systems by altering hydrology and nutrient loading. These changes interact with climate and aquatic ecosystem processes to alter nutrient flux dynamics. We used a long term data set (1993-2009) to investigate the influence of suburbanization, climate, and in-stream processes on nitrogen and phosphorus expo...

River systems are important regulators of anthropogenic nitrogen flux between land and ocean. Nitrogen dynamics in small headwater streams have been extensively measured, whereas less is known about contributions of other components of stream networks to nitrogen removal, including larger streams or fluvial wetlands. Here, we quantified nitrate rea...

Land use influences the distribution of non-point nitrogen (N) sources in urbanizing watersheds and storm events interact with these heterogeneous sources to expedite N transport to aquatic systems. In situ sensors provide high frequency and continuous measurements that may reflect storm-event N variability more accurately compared to grab samples....

Controls on the fate of ~ 277 Pg of soil organic carbon (C) stored in permafrost peatland soils remain poorly understood despite the potential for a significant positive feedback to climate change. Our objective was to quantify the temperature, moisture, organic matter, and microbial controls on soil organic carbon (SOC) losses following permafrost...

Extreme weather continues to preoccupy society as a formidable public safety concern bearing huge economic costs. While attention has focused on global climate change and how it could intensify key elements of the water cycle such as precipitation and river discharge, it is the conjunction of geophysical and socioeconomic forces that shapes human s...

Earth System model development is becoming an increasingly complex task. As scientists attempt to represent the physical and bio-geochemical processes and various feedback mechanisms in unprecedented detail, the models themselves are becoming increasingly complex. At the same time, the surrounding IT infrastructure needed to carry out these detaile...

The demand for ecosystem services and the ability of natural ecosystems to provide those services evolve over time as population, land use, and management practices change. Regionalization of ecosystem service activity, or the expansion of the area providing ecosystem services to a population, is a common response in densely populated coastal regio...

The electricity sector is dependent on rivers to provide ecosystem services that help regulate excess heat, either through provision of water for evaporative cooling or by conveying, diluting and attenuating waste heat inputs. Reliance on these ecosystem services alters flow and temperature regimes, which impact fish habitat and other aquatic ecosy...

Major strategic issues facing the global thermoelectric sector include environmental regulation, climate change and increasing electricity demand. We have addressed such issues by modeling thermoelectric generation in the Northeastern United States that is reliant on cooling under five sensitivity tests to evaluate losses/gains in power production,...

Understanding the processes controlling the transfer and chemical composition of dissolved organic carbon (DOC) in freshwater systems is crucial to understanding the carbon cycle and the effects of DOC on water quality. Previous studies have identified watershed-scale controls on bulk DOC flux and concentration among small basins but fewer studies...

Humans have dramatically altered nutrient cycles at local to global scales. We examined changes in anthropogenic nutrient inputs to the northeastern United States (NE) from 1930 to 2000. We created a comprehensive time series of anthropogenic N and P inputs to 437 counties in the NE at 5 year intervals. Inputs included atmospheric N deposition, bio...

Spatial and temporal patterns of runoff generation are poorly understood in watersheds throughout the world, though this is particularly true in Arctic watersheds underlain by permafrost. Approximately 24% of land in the northern hemisphere is underlain by continuous or discontinuous permafrost. In these regions of the world, the presence of permaf...

River transport of dissolved organic carbon (DOC) to the coastal zone is a major component of the global carbon cycle. By scaling the results from small, watershed based studies, we have developed a model to simulate and aggregate DOC export to the mouths of 17 large rivers across the continental United States. DOC was partitioned into hydrophilic...

Over the last two decades, long-term ecological research in the United States has expanded to urban sites. Cities, despite the dominance of built structures, utilize unexpected amounts of human-generated nutrients. Additionally, cities can both intensify and weaken local impacts of processes such as climate. Challenges remain at these sites, as pro...

Changes to nutrient loads may affect the stoichiometry of urban or suburban stream food webs. We quantified foodweb stoichiometry in 9 detritus-based headwater streams draining forested or suburban watersheds in northeastern, coastal Massachusetts (USA). We measured C, N, and P content (%C, %N, %P) and relative ratios (C∶N∶P) of basal food resource...

Improvements in hydrological modeling and new satellite sensors for ocean color and salinity are poised to provide data that will enable major advances in our understanding of biogeochemical processes at the land sea interface. These data streams will include information from two new salinity sensors currently in orbit, proposed polar orbiting ocea...

Salt marshes are highly productive coastal wetlands that provide important ecosystem services such as storm protection for coastal cities, nutrient removal and carbon sequestration. Despite protective measures, however, worldwide losses of these ecosystems have accelerated in recent decades. Here we present data from a nine-year whole-ecosystem nut...

Legacy effects of past land use and disturbance are increasingly recognized, yet consistent definitions of and criteria for defining them do not exist. To address this gap in biological- and ecosystem-assessment frameworks, we propose a general metric for evaluating potential legacy effects, which are computed by normalizing altered system function...

Highly resolved time series data are useful to accurately identify the timing, rate, and magnitude of solute transport in streams during hydrologically dynamic periods such as snowmelt. We used in situ optical sensors for nitrate (NO3 −) and chromophoric dissolved organic matter fluorescence (FDOM) to measure surface water concentrations at 30min i...

The spatiotemporal scales, controls, and biogeochemical consequences of zone specific transient storage in Arctic headwater streams is currently unclear. We propose that surface and hyporheic transient storage at the reach scale in streams underlain by continuous permafrost is a function of both seasonally changing thaw depth and more rapidly chang...

Numerous types of heterogeneity exist within river systems, leading to hotspots of nutrient sources, sinks, and impacts embedded within an underlying gradient defined by river size. This heterogeneity influences the downstream propagation of anthropogenic impacts across flow conditions. We applied a river network model to explore how nitrogen satur...

Dissolved organic carbon (DOC) in rivers is a critical component of the global carbon cycle and both its quantity and quality are important water quality parameters in numerous fields of study, from drinking water quality to coastal oceanography. Some previous studies have considered the variability of DOC quantity through time, but little such wor...

Water quality monitoring using continuous in-situ sensors can improve our understanding of biogeochemical variability in urban watersheds. In New Hampshire, the Lamprey River drains an urbanizing watershed and discharges to the nitrogen (N)-impaired Great Bay estuary. Multiple instruments (Satlantic Submersible Ultraviolet Nitrate Analyzer, Turner...

One of the primary expressions of climate change in the arctic is a change in "seasonality"; i.e., changes in the timing, duration, and characteristics of the traditional arctic seasons. These changes are most likely to affect temperature and precipitation patterns but will have relatively little effect on the annual light regime. Temperature, prec...

Stream ecosystem processes in the Arctic are poorly understood in the spring and fall 'shoulder' seasons. We hypothesize that seasonal changes in solar radiation, hydrologic conditions, and landscape inputs are all reflected in the seasonal patterns of Gross Primary Productivity (GPP) and Community Respiration (CR). We continuously monitored the GP...

Despite the importance of spring and fall "shoulder" seasons for biogeochemical processes in arctic ecosystems, relatively little field research on land-water interactions has been done during these times of the year. Within arctic ecosystems, the zone of thawed soils and stream sediments expand and contract seasonally (influenced by temperature an...

Transient storage (TS) zones are important areas of dissolved inorganic nitrogen (DIN) processing in rivers. We assessed sensitivities regarding the relative impact that the main channel (MC), surface TS (STS), and hyporheic TS (HTS) have on network denitrification using a model applied to the Ipswich River in Massachusetts, United States. STS and...

Agricultural and urban development alters nitrogen and other biogeochemical cycles in rivers worldwide. Because such biogeochemical processes cannot be measured empirically across whole river networks, simulation models are critical tools for understanding river-network biogeochemistry. However, limitations inherent in current models restrict our a...

1] Little is known about the impact of surface transient storage (STS) zones on reach-scale transport and the fate of dissolved nutrients in streams. Exchange with these locations may influence the rates of nutrient cycling often observed in whole-stream tracer experiments, particularly because they are sites of organic matter collection and lower...

Nitrous oxide (N(2)O) is a potent greenhouse gas that contributes to climate change and stratospheric ozone destruction. Anthropogenic nitrogen (N) loading to river networks is a potentially important source of N(2)O via microbial denitrification that converts N to N(2)O and dinitrogen (N(2)). The fraction of denitrified N that escapes as N(2)O rat...

Biogeochemical fluxes in human dominated streams and rivers are highly impacted, but effects can be attenuated downstream through natural ecosystem processes. We deployed in situ nitrate, fdom, and chlorophyll sensors to characterize biogeochemical fluxes draining a suburban catchment, and modifications by a channel-floodplain system located immedi...

This study was carried out to support and enhance a series of global studies assessing contemporary and future changes in nutrient export from watersheds (Global Nutrient Export from Watersheds (NEWS)). Because hydrography is one of the most important drivers in nutrient transport, it was essential to establish how climatic changes and direct human...

Stream-groundwater interactions are critical to ecosystem structure and function and water quality in many streams. Hence it is desirable to quantify exchange rates/amounts, lateral gains, and/or losses of water (and coincident mass/energy balances). Interpretations from investigations of stream-groundwater interactions, however, are influenced by...

Reach scale water balances along Arctic tundra streams have rarely if ever been previously studied, yet may have significant influences on stream biogeochemical dynamics. Channel water balances of contiguous reaches can provide quantitative insight on surface - subsurface hydrologic interactions within Arctic stream networks. During summer and fall...

The concept of nitrogen saturation, or when nitrogen supply exceeds demand, stems from terrestrial ecosystems. The concept has recently entered the aquatic domain and been applied to understand nutrient dynamics in stream reaches. Nitrogen supply generally exceeds demand in river reaches, but at network scales, demand may approach supply. We demons...

Transient storage of stream water and associated solutes is expected to vary along stream networks in response to related changes in stream hydraulic conditions and morphologic gradients. These spatial changes are relevant to a wide variety of processes (e.g., biogeochemical cycling), yet data regarding these dynamics are limited and almost exclusi...

Streams are potential hotspots for retention and removal of NO3−, and understanding the mechanisms that enhance NO3− reactivity in stream systems is critical for predicting and preventing eutrophication. Both dissolved organic C (DOC) and dissolved O2 (DO) influence NO3− removal processes. Assessing the individual impacts of NO3−, DO, and DOC conce...

Human demands for ecosystem services (e.g. provision of food and water; regulation of waste) change over space and time as society, economy, and environment evolve. The distribution of population relative to watershed boundaries determines supply and demand of ecosystem services, which in turn affects watershed water and nutrient budgets. A watersh...

Increasing beaver populations within low gradient basins in the northeastern United States are fundamentally changing the way water and dissolved nutrients are exported through these stream networks to the coast. Beaver dams can increase water residence time and contact with organic material, promote anoxic conditions and enhance both surface and h...

Water is an essential component in the successful development and economic growth within a region. Throughout recorded history, civilizations have been modifying and controlling local environments in the pursuit of maximizing water benefits. These efforts include the creation of large waterworks to reduce the uncertainties caused by adverse climati...

Humans can affect the amount and quality of dissolved organic carbon (DOC) inputs to aquatic ecosystems by altering land use (e.g. by agricultural uses and impervious surfaces) and by the production of sewage and animal waste. These changes may affect stream ecosystem metabolism and contribute to the eutrophication of downstream ecosystems. The pre...

Characteristic time scales are useful and simple descriptors of geophysical and socio-economic system dynamics. Focusing on the integrative nature of the hydrologic cycle, new insights into system couplings can be gained by compiling characteristic time scales of important processes driving these systems. There are many examples of changing charact...

Nitrogen provides a fundamental building block for life. However, some nitrogen species (e.g., NO~3~) cause water quality degradation and contribute to climatic warming as a greenhouse gas (e.g., N~2~O). Denitrification is a central process in the nitrogen cycle, transforming water-soluble nitrogen to gaseous nitrogen, thereby removing nitrogen fro...

Slow moving, transient storage zones of streams and rivers have been identified as critical habitats and locations of enhanced biogeochemical processing of stream and groundwater borne nutrients and pollutants. Stream tracer experiments provide a useful approach to characterizing the transport and fate of dissolved stream loads. However, the retard...

This study examines the role of fluvial wetlands (those connected to the stream via floodplains) in controlling DOC quality and export in urban systems. Human activity in urban basins may impact both DOC quality and export, but river-wetland complexes may dampen this signature. These dynamics are important to understand because the processing of DO...

Hyporheic zones of streams and rivers have been identified as important ecotones, harboring critical habitat and serving as locations of enhanced biogeochemical cycling of stream and groundwater borne nutrients and pollutants. Stream tracer experiments provide a useful approach to characterizing the transport and fate of dissolved stream loads. How...

The importance of lotic systems as sinks for nitrogen inputs is well recognized. A fraction of nitrogen in streamflow is removed to the atmosphere via denitrification with the remainder exported in streamflow as nitrogen loads. At the watershed scale, there is a keen interest in understanding the factors that control the fate of nitrogen throughout...

Human activities have greatly increased the transport of biologically available nitrogen (N) through watersheds to potentially sensitive coastal ecosystems. Lentic water bodies (lakes and reservoirs) have the potential to act as important sinks for this reactive N as it is transported across the landscape because they offer ideal conditions for N b...

Earth System model development is becoming an increasingly complex task. As scientists attempt to represent the physical and bio-geochemical processes and various feedback mechanisms in unprecedented detail, the models themselves are becoming increasingly complex. At the same time, the complexity of the surrounding IT infrastructure is growing as w...

The importance of lotic systems as sinks for nitrogen inputs is well recognized. A fraction of nitrogen in streamflow is removed to the atmosphere via denitrification with the remainder exported in streamflow as nitrogen loads. At the watershed scale, there is a keen interest in understanding the factors that control the fate of nitrogen throughout...

In comparison to the main channel of a stream, transient storage zones provide increased opportunity for flowing water and dissolved solutes to interact with microbial communities, both by extending residence times and by facilitating contact with biogeochemically active sediments. Our current understanding of transient storage has been limited by...

River networks are comprised of a wide array of linked aquatic ecosystem types (e.g. channels of different sizes with associated transient storage zones, ponds, lakes, reservoirs, and floodplains). Recent field and modeling results demonstrate that river channels become less effective at retaining nutrients under high flow conditions when most nutr...

Little is known about the impact of surface transient storage (STS) zones on reach-scale transport and fate of dissolved nutrients in streams. Exchange with these locations may influence the rates of nutrient cycling often observed in whole-stream tracer experiments, particularly because they are sites of organic matter collection and lower flow ve...