William H McDowell

William H McDowell
University of New Hampshire | UNH · Department of Natural Resources & the Environment

PhD

About

388
Publications
126,425
Reads
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34,607
Citations
Introduction
I am focusing on understanding watershed-scale biogeochemistry and stream nutrient cycles across environmental gradients. My approach uses both long-term observations and experiments. Study sites include New England, Puerto Rico, Czech Republic, and Siberia.
Additional affiliations
September 1989 - December 2012
University of New Hampshire
Position
  • Professor (Full)
May 1985 - August 1989
November 1982 - June 1985
University of Puerto Rico at Rio Piedras
Position
  • Researcher

Publications

Publications (388)
Article
Streams and rivers are important sources of nitrous oxide (N2O), a powerful greenhouse gas. Estimating global riverine N2O emissions is critical for the assessment of anthropogenic N2O emission inventories. The indirect N2O emission factor (EF5r) model, one of the bottom‐up approaches, adopts a fixed EF5r value to estimate riverine N2O emissions ba...
Article
Full-text available
Wet deposition of dissolved inorganic nitrogen (N) is declining nationally, accompanied by a shift in stoichiometry from predominantly oxidized to reduced forms of N. Stoichiometric trends that include the organic fraction of N wet deposition have yet to be assessed in light of anthropogenic pressures and global change, including shifting seasonali...
Article
Full-text available
Previous studies have evaluated how changes in atmospheric nitrogen (N) inputs and cli- mate affect stream N concentrations and fluxes, but none have synthesized data from sites around the globe. We identified variables controlling stream inorganic N concentrations and fluxes, and how they have changed, by synthesizing 20 time series ranging from 5...
Article
Full-text available
Plain Language Summary The entire global N budget remains out of balance, with total N inputs exceeding N losses. Streams and rivers serve as substantial recipients and processors of reactive N transported from terrestrial landscapes. The benthic zone is traditionally identified as a hotspot for N processing in fluvial systems. However, the role of...
Article
Urbanization can result in multiple stres-sors for freshwater ecosystems including altered flow regimes, higher sediment loads and increased inorganic nutrient supply. The effects of urbanization on ecosystem processes including organic matter decomposition are poorly understood. Relationships between decomposition and nutrient levels are inconsist...
Article
Hurricanes and other extreme events are increasing in many regions, yet their long‐term impacts on ecosystem function are uncertain. In forested ecosystems, soil solution chemistry provides an important tool to assess the impacts of disturbance on nutrient cycling and dissolved organic carbon dynamics. Here, we address the dependence of soil soluti...
Article
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Dissolved organic matter (DOM) is a heterogeneous mixture of organic compounds that is produced through both microbial degradation and abiotic leaching of solid phase organic matter, and by a wide range of metabolic processes in algae and higher plants. DOM is ubiquitous throughout the hydrologic cycle and plays an important role in watershed manag...
Article
While tropical cyclone regimes are shifting with climate change, the mechanisms underpinning the resistance (ability to withstand disturbance‐induced change) and resilience (capacity to return to pre‐disturbance reference) of tropical forest litterfall to cyclones remain largely unexplored pantropically. Single‐site studies in Australia and Hawaii...
Article
Full-text available
Meteoric waters move along pathways in the subsurface that differ as a function of lithology because of the effects of chemical and physical weathering. To explore how this affects stream chemistry, we investigated watersheds around an igneous intrusion in the Luquillo Mountains (Puerto Rico). We analyzed streams on 1) unmetamorphosed country rock...
Chapter
The scientific discipline of biogeochemistry is inherently interdisciplinary. The name alone evokes principles across the physical and biological sciences.
Article
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Extreme rainfall events in the humid-tropical Luquillo Mountains, Puerto Rico export the bulk of suspended sediment and particulate organic carbon. Using 25 years of river carbon and suspended sediment data, which targeted hurricanes and other large rainstorms, we estimated biogenic particulate organic carbon yields of 65 ± 16 tC km−2 yr−1 for the...
Article
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Tropical cyclones drive coastal ecosystem dynamics, and their frequency, intensity, and spatial distribution are predicted to shift with climate change. Patterns of resistance and resilience were synthesized for 4138 ecosystem time series from n = 26 storms occurring between 1985 and 2018 in the Northern Hemisphere to predict how coastal ecosystems...
Article
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Significance This paper provides a comprehensive analysis of the annual patterns of ecosystem productivity and respiration for more than 200 rivers, comparing the magnitude and phenology of river metabolic regimes with annual estimates from more than 150 terrestrial ecosystems. Although mean annual temperature and mean annual precipitation explain...
Technical Report
We identified variables controlling stream nitrogen concentrations and fluxes, and how they have changed over time, by synthesizing 20 time series ranging from 5 to 51 years of data collected from forest and grassland dominated watersheds across Europe, North America, and East Asia and across four climate types (tropical, temperate, Mediterranean,...
Article
Full-text available
Catchment‐scale assessments of nitrogen retention and loss rarely account for soil and landscape heterogeneity and are, thus, unable to account for the suite of nitrogen cycling processes that ultimately affect the export of nitrate via stream water. Long‐term study at the Hubbard Brook Experimental Forest, NH has generated a unique data set that f...
Article
Full-text available
Lithium isotopes are used to trace weathering intensity, but little is known about the processes that fractionate them in highly weathered settings, where secondary minerals play a dominant role in weathering reactions. To help fill this gap in our knowledge of Li isotope systematics, we investigated Li isotope fractionation at an andesitic catchme...
Article
Full-text available
Urbanization can result in multiple stressors for freshwater ecosystems including altered flow regimes, higher sediment loads and increased inorganic nutrient supply. The effects of urbanization on ecosystem processes including organic matter decomposition are poorly understood. Relationships between decomposition and nutrient levels are inconsiste...
Article
Full-text available
We examined how climate variability affects the mobilization of material from six watersheds. We analyzed one to seven years of high‐frequency sensor data from a temperate ecosystem and a tropical rainforest. We applied a windowed analysis to correlate concentration‐discharge (C‐Q) behavior with climate anomalies, providing insight into how hydrolo...
Article
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Dissolved organic carbon (DOC) and nitrogen (DON) are important energy and nutrient sources for aquatic ecosystems. In many northern temperate freshwater systems DOC has increased in the past 50 years. Less is known about how changes in DOC may vary across latitudes, and whether changes in DON track those of DOC. Here we present long‐term DOC and D...
Article
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Inland waters can be significant sources of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) to the atmosphere. However, considerable uncertainty remains in regional and global estimates of greenhouse gas (GHG) emissions from freshwater ecosystems, particularly streams. Controls on GHG production in streams, such as water chemistry and s...
Article
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Monitoring the temporal variation of solute concentrations in streams at high temporal frequency can play an important role in understanding the hydrological and biogeochemical behavior of catchments. UV-Visible spectrometry is a relatively inexpensive and easily used tool to infer those concentrations in streams at high temporal resolution. Howeve...
Preprint
Full-text available
The forests of central Europe have undergone remarkable transitions in the past 40 years as air quality has improved dramatically. Retrospective analysis of Norway spruce ( Picea abies ) tree rings in the Czech Republic shows that air pollution (e.g. SO 2 concentrations, high acidic deposition to the forest canopy) plays a dominant role in driving...
Data
A global compilation of stream chemistry data was synthesized to evaluate spatial and temporal trends in solutes with a particular focus on dissolved organic matter and nitrogen (inorganic and organic forms). Data span a global array of streams and rivers ranging from the tropics to the arctic. Data include concentrations of dissolved organic nitro...
Article
Full-text available
A comprehensive cross‐biome assessment of major nitrogen (N) species that includes dissolved organic N (DON) is central to understanding interactions between inorganic nutrients and organic matter in running waters. Here, we synthesize stream water N chemistry across biomes and find that the composition of the dissolved N pool shifts from highly he...
Article
Mountain ponds in the northeastern US have undergone acidification and subsequent recovery due to changes in atmospheric deposition, and also reflect physical and biological responses to climate change. These ponds are distinct from other lakes and ponds in the region as they are higher in elevation, relatively small, and have little direct impact...
Article
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...
Article
Accurately inferring erosion rates from cosmogenic isotope concentrations in river sand assumes temporally steady concentrations; few studies test this assumption. Following Hurricane María in Puerto Rico, we quantified temporal variability in meteoric and in situ ¹⁰Be (¹⁰Bem, ¹⁰Bei) on sand-sized grains of riverine transported material in landslid...
Article
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Carbon dioxide (CO2) emissions to the atmosphere from running waters are estimated to be four times greater than the total carbon (C) flux to the oceans. However, these fluxes remain poorly constrained because of substantial spatial and temporal variability in dissolved CO2 concentrations. Using a global compilation of high-frequency CO2 measuremen...
Article
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Catchments in the Luquillo Experimental Forest (LEF) of Puerto Rico are warm, wet, and tropical with steep elevational relief creating gradients in temperature and rainfall. Long‐term objectives of research at the site are to understand how changing climate and disturbance regimes alter hydrological and biogeochemical processes in the montane tropi...
Article
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Streams and rivers of the Luquillo Experimental Forest, Puerto Rico, have been the subject of extensive watershed and aquatic research since the 1980s. This research includes understanding stream export of nutrients and coarse particulate organic matter, physicochemical constituents, aquatic fauna populations and community structure. However, many...
Article
The Lamprey River Hydrological Observatory (LRHO) is a lowland coastal watershed in southeastern New Hampshire (USA). The LRHO offers a platform to investigate the effects of suburbanization and changing seasonality on watershed hydrology, biogeochemistry, and nutrient export to an estuarine ecosystem. The LRHO utilizes a nested‐watershed design to...
Article
Anthropogenic increases in nitrogen (N) and phosphorus (P) concentrations can strongly influence the structure and function of ecosystems. Even though lotic ecosystems receive cumulative inputs of nutrients applied to and deposited on land, no comprehensive assessment has quantified nutrient‐enrichment effects within streams and rivers. We conducte...
Article
Full-text available
The biogeochemical cycles of carbon (C) and nitrogen (N) are inextricably linked for a range of reactions. For coupled reactions such as denitrification to occur, however, solutes must be found together in space and time. Using the framework of concentration-discharge (c-Q) relationships, we examine the frequency of synchronous C and N export (i.e....
Presentation
Full-text available
In-situ monitoring of the temporal variation of solutes' (nutrients and metals) concentrations as tracers can enhance knowledge of the hydrological and biogeochemical behavior of catchments. UV-Visible spectrometry represents a relatively inexpensive and easily used tool to explore how those concentrations vary in time at high temporal frequency. H...
Article
The Hubbard Brook Experimental Forest (HBEF) was established in 1955 by the U.S. Department of Agriculture, Forest Service out of concerns about the effects of logging increasing flooding and erosion. To address this issue, within the HBEF hydrological and micrometeorological monitoring was initiated in small watersheds designated for harvesting ex...
Conference Paper
Full-text available
While tropical cyclones are intensifying and occurring at higher latitudes in recent decades, the mechanisms underpinning the resistance (ability to withstand disturbance-induced change) and resilience (pace of return to pre-disturbance reference) of tropical forest canopies to cyclone disturbance remain largely unexplored at the pantropical scale....
Article
Stream solute monitoring has produced many insights into ecosystem and Earth system functions. Although new sensors have provided novel information about the fine‐scale temporal variation of some stream water solutes, we lack adequate sensor technology to gain the same insights for many other solutes. We used two machine learning algorithms – Suppo...
Article
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At a “clean air” trade winds site in northeastern Puerto Rico, we found an apparent paradox: atmospheric total mercury (THg) deposition was highest of any site in the USA Mercury Deposition Network, but assimilation into the local food web was quite low. Avian blood THg concentrations (n = 31, from eight species in five foraging guilds) ranged wide...
Article
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High‐frequency in situ sensors have enabled researchers to measure solute concentrations at a time scale that captures the variability in stream discharge. We analyzed discrete samples and high‐frequency time series of solutes to characterize how nitrate (NO3⁻) and fluorescent dissolved organic matter (fDOM; a proxy for dissolved organic carbon) re...
Article
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Tropical cyclones play an increasingly important role in shaping ecosystems. Understanding and generalizing their responses is challenging because of meteorological variability among storms and its interaction with ecosystems. We present a research framework designed to compare tropical cyclone effects within and across ecosystems that: a) uses a d...
Article
Full-text available
The Central Siberian Plateau is undergoing rapid climate change that has resulted in increased frequency of forest fires and subsequent alteration of watershed carbon and nutrient dynamics. Across a watershed chronosequence (3 to >100 years since wildfire) we quantified the effects of fire on quantity and composition of dissolved organic matter (DO...
Article
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Global climate change predictions include decreased precipitation and more frequent droughts in many world regions. In the aseasonal wet tropics, predicting potential impacts is particularly challenging because droughts are rare and therefore poorly understood. In 2015, the Caribbean islands experienced the most severe drought within the past 5 dec...
Chapter
Throughfall is the incoming precipitation that passes through a vegetative canopy. Because it represents the major fraction of incident precipitation that is delivered to the forest floor, it is central to understanding forest hydrology. The quantity of throughfall in a forest stand is related to canopy architecture and leaf morphology, because can...
Article
Percentile-Range Indexed Mapping and Evaluation (PRIME) is a new tool to visualize and quantifying spatio-temporal dynamics of long-term datasets. PRIME is based on categorical partitioning of magnitude based on user defined indices assigned to ranges of percentile and mapping subsets of data at selected percentiles of long-term data. Indices can r...
Article
Full-text available
The Lotic Intersite Nitrogen eXperiments (LINX I and II) were a series of replicated in situ manipulations of 15 N across biomes and land-uses designed to assess the factors that control the removal, retention, and ultimate fate of inorganic nitrogen in stream ecosystems. By studying streams at the continental scale, the lessons learned provide som...
Article
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Concentration-discharge relationships are a key tool for understanding the sources and transport of material from watersheds to fluvial networks. Storm events in particular provide insight into variability in the sources of solutes and sediment within watersheds, and the hydrologic pathways that connect hillslope to stream channel. Here we examine...
Conference Paper
Full-text available
Dissolved organic matter (DOM) is an important component of the carbon (C) and nutrient cycles in terrestrial and aquatic systems. In rivers and streams draining forested catchments DOM often constitutes the largest component of organic matter, since particulate loads are often relatively low. Dissolved organic carbon (DOC) and dissolved organic ni...
Article
Full-text available
Background: Fire plays an important role in controlling the cycling and composition of organic matter and nutrients in terrestrial and aquatic ecosystems. In this study, we investigated the effects of wildfire severity, time since fire, and site-level characteristics on (1) concentration of multiple solutes (dissolved organic carbon, DOC; total dis...
Article
Full-text available
Understanding the drivers of variability in the concentration and composition of dissolved organic matter (DOM) in running waters is a fundamental challenge for aquatic biogeochemistry. Although multiple conceptual frameworks have been proposed to quantify expected changes in DOM within a river network, few studies have collected data to document t...