Timothy T. Eaton

Data-based perfect-deficit approach to understanding climate extremes and forest carbon assimilation capacity

Several lines of evidence suggest that the warming climate plays a vital role in driving certain types of extreme weather. The impact of warming and of extreme weather on forest carbon assimilation capacity is poorly known. Filling this knowledge gap is critical towards understanding the amount of carbon that forests can hold. Here, we used a perfect-deficit approach to identify forest canopy photosynthetic capacity (CPC) deficits and analyze how they correlate to climate extremes, based on observational data measured by the eddy covariance method at 27 forest sites over 146 site-years. We found that droughts severely affect the carbon assimilation capacities of evergreen broadleaf forest (EBF) and deciduous broadleaf forest. The carbon assimilation capacities of Mediterranean forests were highly sensitive to climate extremes, while marine forest climates tended to be insensitive to climate extremes. Our estimates suggest an average global reduction of forest CPC due to unfavorable climate extremes of 6.3 Pg C (~5.2% of global gross primary production) per growing season over 2001–2010, with EBFs contributing 52% of the total reduction.

Heavy Metal Distribution in an Urban Wetland Impacted by Combined Sewer Overflow

The heavy metal content and distribution in an urban wetland affected by combined sewer overflow (CSO) discharge during dry conditions was evaluated. Metals identified in the CSO discharge were also measured upstream and downstream of the CSO. Metals were detected in the acid-extractable fraction of the wetland sediments and the roots of Phragmites australis plants. Sediment from the banks of a pool created by the CSO, and from a clay bed upstream were found to be moderately contaminated with Cu, Pb and Zn. Micro X-ray fluorescence (μ-XRF) of Phragmites roots from the CSO banks showed a correlation in the spatial distribution of Fe and Mn, attributed to the formation of mineral plaques on the root surface. Micro X-ray absorption near edge spectroscopy (μ-XANES) revealed that Cu and Zn were complexed with the organic ligands phytate and cysteine. The findings indicated that continuous discharge from the CSO is a source of heavy metals to the wetland. Metals bound to sediments are susceptible to remobilization and subsequent transport, whereas those associated with Phragmites roots may be more effectively sequestered. These observations provide insight into the behavior of heavy metals in urban areas where CSOs discharge into wetlands.

Is one an upper limit for natural hydraulic gradients

Hart et al. (2008) discuss the often confusing presence of unusually high vertical hydraulic gradients in some layered aquifer systems. By assuming a priori steady-state flow conditions and specifying an overall gradient less than or equal to 1, however, they bypass the role of broader hydrodynamic processes and other controls on vertical hydraulic gradients. Analysis of any vertical hydraulic gradient (hydrodynamically, a value of 1 has no inherent physical significance) depends on whether the flow system is transient or steady state, and the geometry, head difference, and elevations of the layered system in question. So, no, 1 is not an upper limit for “natural” hydraulic gradients. In addition, because of storage changes, simple notions of mass balance do not apply over periods on the order of the time constant (T∗ = SsLc/K) of transient systems (Alley et al. 2002). Thus, a more complete analysis would consider transient conditions also. Although the thought experiment presented by Hart et al. (2008) may represent near-surface soils, heads in confined systems are commonly much greater than the physical elevations of the boundaries of the aquifer system layers (e.g., Taylor et al. 2003). Under transient stresses, not limited to pumping (see below), there is no physical reason why an aquifer hydraulic head value cannot be changed by a magnitude greater than the adjacent aquitard thickness to generate a vertical gradient greater than 1 across the aquitard (Figure 1). This situation has occurred notably in the Cambrian–Ordovician system in the upper Midwest (Fetter 1981), where the pumped aquifer system is under transient conditions, and a nonlinear profile of hydraulic head was measured across the aquitard (Eaton and Bradbury 2003; Eaton et al. 2007). A linear, steadystate vertical head gradient greater than 1 could have

Approach and case-study of green infrastructure screening analysis for urban stormwater control

Urban stormwater control is an urgent concern in megacities where increased impervious surface has disrupted natural hydrology. Water managers are increasingly turning to more environmentally friendly ways of capturing stormwater, called Green Infrastructure (GI), to mitigate combined sewer overflow (CSO) that degrades local water quality. A rapid screening approach is described to evaluate how GI strategies can reduce the amount of stormwater runoff in a low-density residential watershed in New York City. Among multiple possible tools, the L-THIA LID online software package, using the SCS-CN method, was selected to estimate relative runoff reductions expected with different strategies in areas of different land uses in the watershed. Results are sensitive to the relative areas of different land uses, and show that bioretention and raingardens provide the maximum reduction (∼12%) in this largely residential watershed. Although commercial, industrial and high-density residential areas in the watershed are minor, larger runoff reductions from disconnection strategies and porous pavement in parking lots are also possible. Total stormwater reductions from various combinations of these strategies can reach 35-55% for individual land uses, and between 23% and 42% for the entire watershed.

Recirculation over complex terrain

This study generated eddy covariance data to investigate atmospheric dynamics leeward of a small, forested hillside in upstate New York. The causes and effects of recirculation eddies were examined to support the larger goal of improving measurement of the exchange of energy, moisture and trace gases between the terrestrial biosphere and the atmosphere over complex terrain. Sensors operated at five different altitudes on two separate towers – one at the top of the hill and one down the slope to the east – for approximately eight weeks in the spring of 2013. During the experiment, the vertical potential temperature gradient was found to be the primary factor for determining whether winds interacting with the terrain features caused a recirculating eddy leeward of the hill. The study found evidence that the recirculation influenced carbon dioxide flux and caused the air column to be vertically well-mixed.

Single-Indicator Strategies Treat Symptoms, Not Sources of Sewage Contamination, Hampering Water Quality Improvement in Urban Areas

Infrastructure challenges and water pollution are endemic to major urban centers worldwide [1], causing eutrophication [2], hypoxia [3], and infection risk from fecal pathogens in coastal waters. In New York City, coastal water quality is still unacceptable because nearly 100 billion liters of untreated sewage-contaminated waste are delivered to receiving waters each year. Sewage pollution is even worse in cities with less developed infrastructure, and has been exacerbated by the global trend toward urbanization. The roots of this problem lie in the challenges of modernizing aging sewage infrastructure: both increasing capacity and overcoming a legacy of delivering untreated sewage directly to waterways. As public expectations and regulatory requirements have improved, driven by enforcement of the Clean Water Act in the USA, an increasing fraction of this sewage is now being captured for modern secondary and tertiary treatment in many regions. However, retrofitting of infrastructure to address water quality deficiencies is difficult, and failure to restore healthy waterways remains common in urban settings. In New York City, and in many other older cities, major progress has occurred by updating existing wastewater treatment plants, including expanded capacity and increasing efficiency of microbial and nutrient removal. Water quality is monitored using indicators such as selected fecal bacteria and dissolved oxygen which are proxies for a wide variety of pollutants, not all of which can be measured. These indicators have been essential in identifying pollution sources and assessing environmental quality. Average water quality across the waterways of New York City has significantly improved since the 1970s. However, conditions are still unacceptable in locations where most untreated sewage is delivered. Most of the city is serviced by a combined sewer system, designed with hundreds of Combined Sewer Overflow (CSO) pipes that discharge to waterways following precipitation. Managers face consent orders to limit these CSOs that bypass treatment plants several dozen times a year when capacity of the delivery system is exceeded. The challenge to restore clean waterways and control CSOs is enormous. When managers are faced with a challenge of this magnitude, difficult decisions are made to best use public funds for maximizing sustainable environmental improvements. The constraints on decision-making include using approved monitoring approaches (e.g., indicators) to assess environmental conditions, meeting current and evolving (usually stricter) regulatory standards, while also efficiently using limited public funds. Independent scientists and an engaged public have the responsibility to comment on public environmental management projects. Academics sometimes avoid advocacy on regulatory issues in society, but their feedback can positively contribute to management agency actions and decisions. This is not a call for antagonistic interactions with management agencies but instead greater public involvement to support these agencies and policymakers in making more forward-looking decisions that will result in accelerating sustainable environmental gains. Independent scientists can often contribute insight and a broader perspective on management decisions and their unrecognized environmental implications, as well as highlight potential future emerging contaminants that are not yet regulated. Agency decisions on mitigation strategies often come down to oversimplified cost-benefit analyses, where leastcost options targeting violations based on monitoring data for single indicators are often selected. But managing for * Gregory D. O’Mullan gomullan@qc.cuny.edu