Paul Mayer

• PhD
• Research Ecologist at United States Environmental Protection Agency

Alongside global climate change, many freshwater ecosystems are experiencing substantial shifts in the concentrations and compositions of salt ions coming from both land and sea. We synthesize a risk framework for anticipating how climate change and increasing salt pollution coming from both land and saltwater intrusion will trigger chain reactions...

Impervious surface cover increases peak flows and degrades stream health, contributing to a variety of hydrologic, water quality, and ecological symptoms, collectively known as the urban stream syndrome. Strategies to combat the urban stream syndrome often employ engineering approaches to enhance stream-floodplain reconnection, dissipate erosive fo...

Anthropogenic salt inputs have impacted many streams in the U.S. for over a century. Urban stream salinity is often chronically elevated and punctuated by episodic salinization events, which can last hours to days after snowstorms and the application of road salt. Here, we investigated the impacts of freshwater salinization on total dissolved nitro...

Freshwater Salinization Syndrome (FSS) refers to groups of biological, physical, and chemical impacts which commonly occur together in response to salinization. FSS can be assessed by the mobilization of chemical mixtures, termed “chemical cocktails”, in watersheds. Currently, we do not know if salinization and mobilization of chemical cocktails al...

There are challenges in monitoring and managing water quality due to spatial and temporal heterogeneity in contaminant sources, transport, and transformations. We demonstrate the importance of longitudinal stream synoptic (LSS) monitoring, which can track combinations of water quality parameters along flowpaths across space and time. Specifically,...

Freshwater Salinization Syndrome (FSS) refers to the suite of physical, biological, and chemical impacts of salt ions on the degradation of natural, engineered, and social systems. Impacts of FSS on mobilization of chemical cocktails has been documented in streams and groundwater, but little research has focused on the effects of FSS on stormwater...

Nitrogen (N) retention is a common goal of stream-wetland restoration projects in systems with excess nitrate (NO3⁻), however N retention depends on habitats with high denitrification and uptake rates that interact with NO3⁻. Legacy sediments deposited along formerly impounded streams bury and disconnect historic floodplain-wetland systems. This di...

Nitrogen (N) fertilizer applications are important for agricultural yield, yet not all the applied N is taken up by crops, leading to surplus N storage in soil or leaching to groundwater and surface water. Leaching loss of fertilizer N represents a cost for farmers and has consequences for human health and the environment, especially in the souther...

We investigate impacts of Freshwater Salinization Syndrome (FSS) on mobilization of salts, nutrients, and metals in urban streams and stormwater BMPs by analyzing original data on concentrations and fluxes of salts, nutrients, and metals from 7 urban watersheds in the Mid-Atlantic U.S. and synthesizing literature data. We also explore future critic...

Stream restoration is a popular approach for managing nitrogen (N) in degraded, flashy urban streams. Here, we investigated the long-term effects of stream restoration involving floodplain reconnection on riparian and in-stream N transport and transformation in an urban stream in the Chesapeake Bay watershed. We examined relationships between hydro...

Riparian zones are a vital interface between land and stream and are often the focus of stream restoration efforts to reduce nutrient pollution in waterways. Restoration of degraded stream channels often requires the removal of mature trees during major physical alteration of the riparian zone to reshape streambank topography. We assessed the impac...

Factors driving freshwater salinization syndrome (FSS) influence the severity of impacts and chances for recovery. We hypothesize that spread of FSS across ecosystems is a function of interactions among five state factors: human activities, geology, flowpaths, climate, and time. (1) Human activities drive pulsed or chronic inputs of salt ions and m...

Nitrate contamination of groundwater is a concern globally, particularly in agricultural regions where decades of fertilizer nitrogen (N) use has led to a legacy of N accumulation in soils and groundwater. Linkages between current management practices and groundwater nitrate dynamics are often confounded by the legacy effect, and other processes un...

Stream restoration is a popular approach for managing nitrogen in degraded, flashy urban streams. Here, we investigated the long-term effects of geomorphic stream restoration on riparian and in-stream N transport and transformation in an urban stream in the Chesapeake Bay watershed. We examined relationships between hydrology, chemistry, and biolog...

Three of the primary functions of green roofs in urban areas are to delay rainwater runoff, moderate building temperatures, and ameliorate the urban heat island (UHI) effect. A major impediment to the survival of plants on an unirrigated extensive green roof (EGR) is the harsh rooftop environment, including high temperatures and limited water durin...

Increasing trends in base cations, pH, and salinity of freshwaters have been documented in U.S. streams over 50 years. These patterns, collectively known as Freshwater Salinization Syndrome (FSS), are driven by multiple processes, including applications of road salt and human-accelerated weathering of impervious surfaces, reductions in acid rain, a...

Green roofs are among the most popular type of green infrastructure implemented in highly urbanized watersheds due to their low cost and efficient utilization of unused or under-used space. In this study, we examined the effectiveness of green roofs to attenuate stormwater runoff across a large metropolitan area in the Pacific Northwest, United Sta...

Urbanization contributes to the formation of novel elemental combinations and signatures in terrestrial and aquatic watersheds, also known as ‘chemical cocktails.’ The composition of chemical cocktails evolves across space and time due to: (1) elevated concentrations from anthropogenic sources, (2) accelerated weathering and corrosion of the built...

One of the primary functions of green roofs in urban areas is to moderate rainwater runoff, and one of the major impediments to the survival of plants on an extensive green roof (EGR) is a lack of available water during dry periods. Runoff moderation and water storage are both influenced by the composition of the growing media. Here we present a fr...

Restoration and reconnection of floodplain systems provide multiple societal and ecosystem benefits, while providing municipalities the opportunity to attempt alternative approaches to maintain infrastructure protection and function. In some restored floodplains, treated wastewater effluent discharge is redirected over land instead of directly into...

In the Anthropocene, watershed chemical transport is increasingly dominated by novel combinations of elements, which are hydrologically linked together as ‘chemical cocktails.’ Chemical cocktails are novel because human activities greatly enhance elemental concentrations and their probability for biogeochemical interactions and shared transport alo...

Regenerative stormwater conveyance (RSC), a relatively new stormwater management approach, is extensively implemented throughout the mid-Atlantic for nutrient control, but little is known of its pollutant reduction capabilities and controlling factors. This study examined effects of organic carbon (C) quantity and quality on stream water quality an...

Decision-support tools (DSTs) are often produced from collaborations between technical experts and stakeholders to address environmental problems and inform decision making. Studies in the past two decades have provided key insights on the use of DSTs and the importance of bidirectional information flows among technical experts and stakeholders – a...

• Urban streams are degraded by a suite of factors, including burial beneath urban infrastructure, such as roads or parking lots, which eliminates light and reduces direct organic matter inputs to streams from riparian zones. These changes to stream metabolism and terrestrial carbon contribution will likely have consequences for organic matter meta...

Land use and climate change can accelerate the depletion of freshwater resources that support humans and ecosystem services on a global scale. Here, we briefly review studies from around the world, and highlight those in this special issue. We identify stages that characterize increasing interaction between land use and climate change. During the f...

Human-dominated land uses can increase transport of major ions in streams due to the combination of human-accelerated weathering and anthropogenic salts. Calcium, magnesium, sodium, alkalinity, and hardness significantly increased in the drinking water supply for Baltimore, Maryland over almost 50 years (p < 0.05) coinciding with regional urbanizat...

Poster Presented at Restore America’s Estuaries (RAE) 2016

Recent studies have shown that stormwater control measures (SCMs) are less effective at retaining phosphorus (P) than nitrogen. We compared P retention between two urban/suburban SCMs and their adjacent free-flowing stream reaches at the Baltimore Long-Term Ecological Study (LTER) site, and examined changes in P retention in SCMs across flow condit...

An improved understanding of sources and timing of water, carbon, and nutrient fluxes associated with urban infrastructure and stream restoration is critical for guiding effective watershed management globally. We investigated how sources, fluxes, and flowpaths of water, carbon (C), nitrogen (N), and phosphorus (P) shift in response to differences...

Woody plant expansion into grasslands and savannas is a global concern. Rapid expansion of Juniperus virginiana, a tree native to North America, has profound ecological consequences. We used transplanted J. virginiana seedlings to investigate the role of resource availability on J. virginiana expansion following the removal of fire, the factor hist...

Excess nitrogen (N) and phosphorus (P) from human activities have contributed to degradation of coastal waters globally. A growing body of work suggests that hydrologically restoring streams and rivers in agricultural and urban watersheds has potential to increase N and P retention, but rates and mechanisms have not yet been analyzed and compared a...

An improved understanding of sources and timing of water and nutrient fluxes associated with urban stream restoration is critical for guiding effective watershed management. We investigated how sources, fluxes, and flowpaths of water, carbon (C), nitrogen (N), and phosphorus (P) shift in response to differences in stream restoration and sanitary in...

Low impact development (LID), a comprehensive land use planning and design approach with the goal of mitigating land development impacts to the environment, is increasingly being touted as an effective approach to lessen runoff and pollutant loadings to streams. Broad-scale approaches for siting LID have been developed for agricultural watersheds,...

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...

Nitrogen (N) uptake in streams is an important ecosystem service that reduces nutrient loading to downstream ecosystems. Here we synthesize studies that investigated the effects of urban stream burial on N-uptake in two metropolitan areas and use simulation modeling to scale our measurements to the broader watershed scale. We report that nitrate tr...

Urbanization has resulted in the extensive burial and channelization of headwater streams, yet little is known about the impacts of stream burial on ecosystem functions critical for reducing downstream nitrogen (N) and carbon (C) exports. In order to characterize the biogeochemical effects of stream burial on N and C, we measured NO3 − uptake (usin...

Nitrogen (N) retention in streams is an important ecosystem service that may be affected by the widespread burial of streams in stormwater pipes in urban watersheds. We predicted that stream burial suppresses the capacity of streams to retain nitrate (NO3 −) by eliminating primary production, reducing respiration rates and organic matter availabili...

Road salts are a growing environmental concern in urban watersheds. We examined groundwater (GW) and surface water (SW) dynamics of Na+ and Cl- in Minebank Run (MBR), an urban stream in Maryland, USA. We observed an increasing salinity trend in this restored stream. Current baseflow salinity does not exceed water quality recommendations, but rapid...

Restoring urban infrastructure and man-aging the nitrogen cycle represent emerging chal-lenges for urban water quality. We investigated whether stormwater control measures (SCMs), a form of green infrastructure, integrated into restored and degraded urban stream networks can influence watershed nitrogen loads. We hypothesized that hydrologically co...

Nonpoint source pollution from agriculture and urbanization is increasing globally at the same time climate extremes have increased in frequency and intensity. We review >200 studies of hydrologic and gaseous fluxes and show how the interaction between land use and climate variability alters magnitude and frequency of carbon, nutrient, and greenhou...

We examined the effect of instream large wood on denitrification capacity in two contrasting, lower order streams — one that drains an agricultural watershed with no riparian forest and minimal stores of instream large wood and another that drains a forested watershed with an extensive riparian forest and abundant instream large wood. We incubated...

Recent identification of the widespread distribution of legacy sediments deposited in historic mill ponds has increased concern regarding their role in controlling land–water nutrient transfers in the mid-Atlantic region of the US. At Big Spring Run in Lancaster, Pennsylvania, legacy sediments now overlay a buried relict hydric soil (a former wetla...

Carbon and nutrient loading from urban stormwater and sanitary systems have well-known implications for freshwater quality and coastal eutrophication. The interactions between water quality and greenhouse gas (GHG) production within streams and rivers have not been fully explored in urban watersheds, however. The objective of this project is to det...

Because of nearly 8 years of pre-existing scientific research and hydrologic (surface and groundwater) monitoring data by the United States Geological Services (USGS), the BSR site was selected by PA Department of Environmental Protection (PADEP) in 2007 to evaluate a new approach to aquatic resources restoration. The Natural Floodplain, Stream, an...

Background/Question/Methods Due to the interactive effects of urbanization and climate variability, managing impacts on watershed hydrology and biogeochemical processing has become increasingly important, particularly due to the enhanced potential for eutrophication and hypoxia in downstream coastal ecosystems. We examined whether headwater manag...

Excess nitrogen (N) in freshwater systems, estuaries, and coastal areas has well-documented deleterious effects on ecosystems. Ecological engineering practices (EEPs) may be effective at decreasing nonpoint source N leaching to surface and groundwater. However, few studies have synthesized current knowledge about the functioning principles, perform...

A N-15-tracer method was used to quantify nitrogen (N) removal processes in two relict oxbow wetlands located adjacent to the Minebank Run restored stream reach in Baltimore County (Maryland, USA) during summer 2009 and early spring 2010. A mass-balance approach was used to directly determine the flow of (NO3)-N-15 (-) to plants, algae, and sedimen...

Organic carbon is important in regulating ecosystem function, and its source and abundance may be altered by urbanization. We investigated shifts in organic carbon quantity and quality associated with urbanization and ecosystem restoration, and its potential effects on denitrification at the riparian-stream interface. Field measurements of streamwa...

Background/Question/Methods Large river floodplains are poor nitrate pollution buffers when polluted groundwater moves beneath biogeochemically retentive zones prior to entering the main channel. However, in floodplain regions with extensive backwaters and organic carbon accumulation, surface waters may interact with groundwater to support enhance...

Data collected from 2002 through 2008 by the U.S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency, were used to assess geomorphic characteristics and geomorphic changes over time in a reach of Minebank Run, a small urban watershed near Towson, Maryland, prior to and after its physical restoration in 2004 and 2005. Da...

Managing the N cycle and restoring urban infrastructure represent major challenges for biogeochemistry and society. We investigated how stormwater management integrated into ecologically engineered stream networks may alter coupled N and C biogeochemical cycles. Stormwater management best management practices (BMPs) such as wetlands and ponds may s...

We measured nitrate (NO3-) and phosphate (PO4-) dynamics during eight discrete precipitation events in two relict oxbow wetlands created as a consequence of geomorphic stream restoration in Baltimore County, MD. Oxbow 1 (Ox1) received 1.6% to 4.2 % and Oxbow 2 (Ox2) received 4.2% to 7.4% of the cumulative stream flow during storm events from subsur...

There have been long-term changes in the quantity of organic carbon in streams and rivers globally. Shifts in the quality of organic carbon due to environmental changes may also impact downstream ecosystem metabolism and fate and transport of contaminants. We investigated long-term impacts of land use and hydrologic variability on organic carbon tr...

Background/Question/Methods The groundwater–surface water interface, consisting of shallow groundwater adjacent to stream channels, is a hot spot for nitrogen removal processes, a storage zone for other solutes, and a target for restoration activities. Characterizing groundwater-surface water interaction is difficult because of physical obstacles...

Riparian wetlands have been shown to be effective "sinks" for nitrate N (NO3-), minimizing the downstream export of N to streams and coastal water bodies. However, the vast majority of riparian denitrification research has been in agricultural and forested watersheds, with relatively little work on riparian wetland function in urban watersheds. We...

Stream restoration has increasingly been used as a best management practice for improving water quality in urbanizing watersheds, yet few data exist to assess restoration effectiveness. This study examined the longitudinal patterns in carbon and nitrogen concentrations and mass balance in two restored (Minebank Run and Spring Branch) and two unrest...

Background/Question/Methods Watersheds have a profound capacity to retain and remove nitrogen (N) inputs before entering coastal waters thereby minimizing eutrophication and hypoxia in estuarine waters. Research suggests that much of this N cycling occurs within aquatic ecosystems, e.g., lakes, streams and wetlands, which may become “hotspots” of n...

Background/Question/Methods Watersheds have a profound capacity to retain and remove nitrogen (N) inputs before entering coastal waters thereby minimizing eutrophication and hypoxia in estuarine waters. Research suggests that much of this N cycling occurs within aquatic ecosystems, e.g., lakes, streams and wetlands, which may become “hotspots” of...

Background/Question/Methods Increased nitrogen loading from watersheds can contribute to coastal eutrophication and harmful algal blooms. Despite significant recent investment in watershed restoration, there is a lack of data on ecosystem function associated with stream restoration and stormwater management projects. We chose to study the effects...

Background/Question/Methods Recently, resource managers have combined restoration strategies with wetland creation as a best management practice (BMP) in an effort to reduce the affects of increased nutrient loading in urban landscapes. Although, riparian wetlands have been shown to be particularly effective sinks for nitrogen, the vast majority of...

Background/Question/Methods: Historic land-use change can reduce water quality by impairing the ability of stream ecosystems to efficiently process nutrients such as nitrogen. We present study results from streams affected by urbanization, quarrying, agriculture, and impoundments in the Chesapeake Bay watershed in Maryland and Pennsylvania, USA....

Background/Question/Methods Increased delivery of nitrogen due to land-use change has contributed to increased coastal eutrophication. Improved knowledge of nonpoint sources and transformations of nitrogen will be critical in managing the nitrogen cycle in response to interactive land-use and climate change. We investigated effects of land use, hy...

In 2002, the mid-Atlantic region experienced record drought levels. In September 2003, Tropical Storm Isabel produced large amounts of rainfall in the Chesapeake Bay region, and freshwater flow into the Chesapeake Bay was 400% above the long-term monthly average (http://chesapeake.usgs.gov/isabelinfo.html). Record drought conditions followed by a v...

Few studies have quantified the impact of urbanization on the biogeochemistry of streams at the groundwater-surface water interface, a zone that may be critical for managing nitrogen transformations. We investigated the groundwater ecosystem of Minebank Run, a geomorphically degraded urban stream near Baltimore, Maryland in the Chesapeake Bay water...

Mayer, Paul M., Albert H. Todd, Judith A. Okay, and Kathleen A. Dwire, 2010. Introduction to the FeaturedCollection on Riparian Ecosystems & Buffers. Journal of the American Water Resources Association (JAWRA)46(2):207-210. DOI: 10.1111/j.1752-1688.2010.00425.xRiparian ecosystems, located at the interface of ter-restrial and aquatic systems, are of...

There is growing interest in rates of nitrate uptake and denitrification in restored streams to better understand the effects of restoration on nitrogen processing. This study quantified nitrate uptake in two restored and two unrestored streams in Baltimore, Maryland, USA using nitrate additions, denitrification enzyme assays, and a 15N isotope tra...

Background/Question/Methods Floodplain nitrate removal via denitrification in sediment provides an important ecosystem service that may be a valuable sink for nitrate pollution. At this time, much floodplain restoration is taking place with little consideration for in-situ nutrient processing, necessitating research to identify habitats for restor...

Predation selects against conspicuous colors in bird eggs and nests, while thermoregulatory constraints select for nest-building behavior that regulates incubation temperatures. We present results that suggest a trade-off between nest crypticity and thermoregulation of eggs based on selection of nest materials by piping plovers (Charadrius melodus)...