Search

Ecosystem structure and its heterogeneity shape ecosystem processes. Ecosystem heterogeneity has been characterized in smaller stream ecosystems dominated by benthic processes. However, in larger river ecosystems structured by water column characteristics including suspended sediment and phytoplankton, ecosystem heterogeneity has not been directly observed. We assessed flow‐dependent ecosystem structure along 230 km of a large, highly managed Great Plains river (The Kansas River) by analyzing 1‐dimensional, downstream color profiles across flow conditions derived from satellite imagery. River color is a robust metric that reflects the combined state of several important large‐river habitat features, specifically suspended sediment, chromophoric dissolved organic matter, and phytoplankton. We found that at flows above a flow threshold that we call Qpatch (240 m3 s−1), the entire river was uniformly yellow. At flows below Qpatch, the river was generally greener and often had patches of very green water that occurred upstream of run‐of‐river dams. Comparing color with in situ data showed the color patches were likely areas of elevated chlorophyll‐a concentrations from phytoplankton accumulation, indicating that the patches reflected biological processes. Flows were below Qpatch on 77% of days during the period of record (1985–present), indicating that the ecosystem spends significant time in a patchy state. Our findings uniquely demonstrate that the water column characteristics structuring temperate, large‐river ecosystems can be patchy. Plain Language Summary: An ecosystem represents a collection of smaller areas, or patches, that play different ecological roles. We can see and walk through patches in forests, however within flowing aquatic ecosystems like large rivers, it is difficult to see and characterize patches. Here, we present direct observations of downstream patches along a river and how they change across streamflow conditions. We measure spatial variation using satellite‐derived water color observations as a proxy for ecosystem properties along a highly managed Great Plains river, The Kansas River. Increases in algae floating in the river should make the river greener, while increases in sediment should make the river more yellow. We found that at high flows above a distinct threshold, the entire river was uniformly yellow. At flows below the threshold, the river was greener and often had particularly green patches behind small, in‐river dams. Comparing our color observations with in‐stream sensor measurements indicated that the green patches were likely caused by elevated algae accumulation and not a reduction in sediment. This work thus revealed a surprising feature of large rivers: they may have stable patches created largely by biological processes. Key Points: We use 1‐D profiles of water color on a large, managed Great Plains river to assess shifts in ecosystem structure across flow conditionsThe 77% percentile flow marked a threshold: above, the river was uniformly yellow. Below, the river was greener and showed green patchesIn situ data suggested these green patches were biologically driven, caused by increased phytoplankton growth upstream of run‐of‐river dams [ABSTRACT FROM AUTHOR]

Introduction Army recruits conducting BCT are among the most susceptible population of military personnel to experience exertional heat illness, a concern expected to become increasingly urgent due to steadily rising temperatures. In this study, we provide an empirical analysis of wet bulb globe temperature (WBGT) index trends at U.S. Army BCT installations and quantify the magnitude of these trends. Assuming these warming trends continue, the anticipated effects of increasing temperature trends are discussed in relation to potential impacts on recruit heat illness incidence and training disruption. Materials and Methods We obtained weather data beginning in the early 1960s, including WBGT index measurements derived by the U.S. Air Force 14th Weather Squadron. We apply these datasets to two classifications for high WBGT index days, including one classification accounting for heat illness susceptibility based on prior day heat exposure, to determine when recruits are most at risk of heat illness. The daily likelihood of extreme WBGT index values is described at each installation using a 30-year climatological average. Trends in the WBGT index are evaluated quantitatively during the warm season (May 1–September 30) and full year and compared between decades and by individual BCT classes. Results Trends in the WBGT index have increased at all four BCT installations. Between January 1960 and October 2022, the mean WBGT index value increased most quickly at Ft Jackson, SC (0.272°C decade−1, CI: 0.255–0.289) and least at Ft Moore, GA (0.190°C decade−1, CI: 0.170–0.210). Ft Moore experiences the greatest heat burden, with the daily likelihood of experiencing a "black flag" event (≥90°F WBGT index) peaking at nearly 50% in late July, while Ft Leonard Wood, MO, experiences the least heat burden. This heat burden is spread unevenly across installations and dependent on BCT class start date. Recruits beginning in mid-June will experience approximately 200 hours of hazardous heat during BCT at Ft Moore, GA; 100 hours at Ft Jackson, SC; 80 hours at Ft Sill, OK; and 61 hours at Ft Leonard Wood, MO. Conclusions Temperatures measured on the WBGT index have steadily increased at US Army basic training installations since at least 1960. In the future, adaptation to the BCT program will be required to maintain rigorous standards without incurring unacceptable risk of recruit heat illness. The analysis provided by this study can help inform medical, training, and policy implementations needed to ensure continued BCT in a warming world. [ABSTRACT FROM AUTHOR]

Vertical motion is an important driver of sunlight exposure in aquatic environments, shaping the growth and fate of materials and organisms. We derive a simple model accounting for turbulent depth fluctuations of particles to predict the depth that contributes the most sunlight exposure (effective depth) as well as the single depth that, if measured at one place over time, produces the same total sunlight exposure as a moving particle (functional depth). Field measurements of light and depth in rivers using neutrally buoyant drifters and buoys validate our model. Effective depth varied from 0.1 to 1.5 m below the water surface and was ~ 30% of the overall water depth on average. Functional depth varied from 0.67 to 2.3 m and was ~ 50% of the overall water depth on average. Functional and effective depth are physically based concepts incorporating turbulent motion, spatial variability, and water clarity offering new approaches to characterize light exposure in aquatic environments. [ABSTRACT FROM AUTHOR]

This pair of papers examines and describes the state action necessary to make markets function as environmental policy instruments and as strategies of governance. We do this through a detailed look at the mechanics of environmental credit compliance markets in the US states of Oregon, Ohio, and North Carolina in which stream credits are privately created and sold to developers who have impacted protected stream systems. In this paper, we observe that the governance of streams as water resources requires the state to create a scalar hierarchy that fixes certain characteristics of streams at certain scales of state action. These fixes attempt to resolve, bracket, or ignore the temporal and spatial variability of streams that can confound governance; however, these variabilities are essential to the scientific study of streams. At each of the four distinct scales, four different operations crucial to market function were observed; at each scale, elements of natural variability were fixed or confined to be expressed only within the given scale. These observations reveal principles of how scale functions within environmental governance, as well as failures where gaps and resistances appear that create unforeseen outcomes in market-led policy. In three different state settings, the establishment of a fixed scale of governance is made in different ways that depend on the local institutional and social context. However, they all act to render an unruly set of temporal and spatial flows as instead occurring within certain fixed scalar boundaries, and thus amenable to governance with markets. [ABSTRACT FROM AUTHOR]

This pair of papers examines and describes the state action necessary to make markets function as environmental policy instruments and as strategies of governance. They do this through a detailed look at the mechanics of environmental credit compliance markets in the US states of Oregon, Ohio, and North Carolina in which stream credits are privately created and sold to developers who have impacted protected stream systems. In this paper, we examine the tools, techniques, and people involved in the creation of a value-bearing stream credit out of a physical stream or river site. These observations reveal important principles of how science functions within governance, as well as where gaps and resistances appear that create unforeseen outcomes in market-led policy. We examine the construction and use of instruments that define natural processes as objects with value; these techniques and tools include databases and spreadsheets, algorithms, and field scoring tools that have been scavenged from a wide range of scientific and governance practices and are not themselves inherently capitalist or developed for capitalist purposes. In three different state settings, the move from measure to value is made in different ways that depend on the local institutional and social context. However, they all act to render a network of interacting ecological forces as a field of discrete ecosystem objects amenable to governance with markets. [ABSTRACT FROM AUTHOR]

The accuracy of discharge measurements derived from surface velocities are highly dependent on the accuracy of conversions from surface velocity u s to depth-averaged velocity U. This conversion factor is typically known as the 'velocity coefficient', 'velocity index', 'calibration factor', 'alpha coefficient', or simply 'alpha', where α = U / u s . At some field sites detailed in situ measurements can be made to calculate alpha, while in other situations (such as rapid response flood measurements) alpha must be estimated. This paper provides a review of existing methods for estimating alpha and presents a workflow for selecting the appropriate method, based on available data. Approaches to estimating alpha include: reference discharge and surface velocimetry measurements; extrapolated ADCP velocity profiles; log law profiles; power law profiles; site characteristics; and default assumed values. Additional methods for estimating alpha that require further development or validation are also described. This paper then summarises methods for accounting for spatial and temporal heterogeneity in alpha, such as 'stage to alpha rating curves', 'site alpha vs. local alpha', and 'the divided channel method'. Remaining challenges for the accurate estimation of alpha are discussed, as well as future directions that will help to address these challenges. Although significant work remains to improve the estimation of alpha (notably to address surface wind effects and velocity dip), the methods covered in this paper could provide a substantial accuracy improvement over selecting the 'default value' of 0.857 for alpha for every discharge measurement. [ABSTRACT FROM AUTHOR]

Both climate risk and race are factors that may affect municipal bond yields, yet each has received relatively limited empirical research attention. We analyzed > 712,000 municipal bonds representing nearly 2 trillion USD in par outstanding, focusing on credit spread or the difference between a debt issuer's interest cost to borrow and a benchmark "risk-free" municipal rate. The relationship between credit spread and physical climate risk is significant and slightly positive, yet the coefficient indicates no meaningful spread penalty for increased physical climate risk. We also find that racial composition (the percent of a community that is Black) explains a statistically significant and meaningful portion of municipal credit spreads, even after controlling for a variety of variables in domains such as geographic location of issuer, bond structure (e.g., bond maturity), credit rating, and non-race economic variables (e.g., per capita income). Assuming 4 trillion USD in annual outstanding par across the entire municipal market, and weighting each issuer by its percent Black, an estimated 19 basis point (bp) penalty for Black Americans sums to approximately 900 million USD annually in aggregate. Our combined findings indicate a systemic mispricing of risk in the municipal bond market, where race impacts the cost of capital, and climate does not. [ABSTRACT FROM AUTHOR]

Key Takeaways: The prevalence of low incomes in the United States is the primary driver for unaffordable water services. Minor rate increases or higher volumes of water usage can have a substantial impact on the pervasiveness of unaffordability. With the cost of water likely to continue increasing, utilities can play a role in protecting customers at all income levels through their rate structures. Affordability elasticity—the relationship of water bills to income distribution—is an important factor to consider in rate design. [ABSTRACT FROM AUTHOR]

Residential "Nonpayment risk" for water utilities — the risk of revenue loss from residential customers not paying water bills — is a financial risk for water service providers that remains poorly understood. Current rate setting strategies do not explicitly consider nonpayment risk and are generally informed by past payment histories. We develop a new heuristic model to categorize and evaluate water utility pricing (rate setting) strategies that are responsive to the effects of nonpayment (i.e., delinquency) on water utility revenues. The model is the first attempt, to our knowledge, to theorize the impact of residential nonpayment on utility revenues. The method draws on the theory behind the Kelly Criterion, a strategy developed in the mid-20th century now used by investors in portfolio management. The results of our thought exercise show that even excessive nonpayment levels (50% each year) do not negate the effectiveness of rate increases for revenue generation, but that nonpayment management can provide revenue benefits. Without political motives, utilities with high nonpayment may be inclined to continue raising water rates, unless higher water rates result in higher nonpayment levels. As such, we highlight the need to understand "nonpayment elasticity": the change in nonpayment due to changes in water rates. We illustrate how increased nonpayment elasticity can decrease the percent of potential revenue collected, particularly when water rates are increased substantially. The simple model provides a method to evaluate the financial sustainability of elevated nonpayment rates in water utility management and financial risk analysis. [ABSTRACT FROM AUTHOR]

Key Takeaways: Of 301 analyzed utilities in North Carolina, 51% reported operating revenues less than operating expenditures—operating ratios (ORs) less than 1. Affordability burden and OR were both affected by utilities' respective population size, population growth or loss rate, and median household income. Annual supplemental funding would be needed to provide all 301 utilities with sufficient revenue to cover operating expenses to ensure ORs are greater than 1. When evaluating consolidation of the utilities into a collective entity, the cumulative revenue of the 301 utilities well exceeded the sum of operating expenses. [ABSTRACT FROM AUTHOR]