Existing water governance systems are proving to be quite ineffective in managing water scarcity, creating severe risk for many aspects of our societies and economies. Water markets are a relatively new and increasingly popular tool in the fight against growing water scarcity. They make a voluntary exchange possible between interested buyers and sellers of water rights. This paper presents direct evidence from seven water markets around the globe to document key economic and ecological challenges and achievements of water markets with respect to water scarcity. We specifically approach water markets as localized cap-and-trade systems, similar to those for carbon emissions. We examine whether water use remains within the set limits on use of water rights (i.e., under the cap), the degree to which water markets help protect the health of ecosystems and species, and whether (as predicted by economic theory) the explicit pricing of water is accompanied by improving efficiency, as less productive water users decide to sell water to more productive water users.

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Seafloor topography affects a wide range of physical and biological processes; therefore, collapsing the three‐dimensional structure of the bottom to roughness metrics is a common challenge in studies of marine systems. Here we assessed the properties captured by metrics previously proposed for the seafloor, as well as metrics developed to characterize other types of rough surfaces. We considered three classes of metrics: properties of the bottom elevation distribution (e.g., standard deviation), length scale ratios (e.g., rugosity), and metrics that describe how topography varies with spatial scale (e.g., Hölder exponents). The metrics were assessed using idealized topography and natural seafloor topography data from airborne lidar measurements of a coral reef. We illustrate that common roughness metrics (e.g., rugosity) can have the same value for topographies that are geometrically very different, limiting their utility. Application of the wavelet leaders technique to the reef data set demonstrates that the topography has a power law scaling behavior, but it is multifractal so a distribution of Hölder exponents is needed to describe its scaling behavior. Using principal component analysis, we identify three dominant modes of topographic variability, or ways metrics covary, among and within reef zones. Collectively, the results presented here show that coral reef topography is both multiscale and multifractal. While individual metrics that capture specific topography properties relevant to a given process may be suitable for some studies, many applications will require a set of metrics that includes statistics that capture how topography varies with spatial scale.

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In shallow water systems like coral reefs, bottom friction is an important term in the momentum balance. Parameterizations of bottom friction require a representation of canopy geometry, which can be conceptualized as an array of discrete obstacles or a continuous surface. Here, we assess the implications of using obstacle‐ and surface‐based representations to estimate geometric properties needed to parameterize drag. We collected high‐resolution reef topography data using a scanning multibeam sonar that resolved individual coral colonies within a set of 100‐m2 reef patches primarily composed of mounding Porites corals. The topography measurements yielded 1‐cm resolution continuous surfaces consisting of a single elevation value for each position in a regular horizontal grid. These surfaces were analyzed by (1) defining discrete obstacles and quantifying their properties (dimensions, shapes), and (2) computing properties of the elevation field (root mean square (rms) elevations, rms slopes, spectra). We then computed the roughness density (i.e., frontal area per unit plan area) using both analysis approaches. The obstacle and surface‐based estimates of roughness density did not agree, largely because small‐scale topographic variations contributed significantly to total frontal area. These results challenge the common conceptualization of shallow‐water canopies as obstacle arrays, which may not capture significant contributions of high‐wavenumber roughness to total frontal area. In contrast, the full range of roughness length scales present in natural reefs is captured by the continuous surface representation. Parameterizations of bottom friction over reef topography could potentially be improved by representing the contributions of all length scales to total frontal area and drag.

The seasonal occurrence of benthic hypoxia in western Long Island Sound (LIS) has been documented for decades by water quality cruise surveys and fixed mooring buoys. While previous studies have focused on factors modulating bottom dissolved oxygen (DO) at subtidal timescales, here we analyze continuous timeseries data from a moored buoy during summers 2021 and 2022 to examine factors controlling high-frequency fluctuations in surface and bottom DO at diurnal and semidiurnal timescales. Fluctuations in surface DO at diurnal timescales are associated with biological production, while fluctuations in bottom DO near semidiurnal timescales are associated with horizontal advection of DO by tides from the upper East River into western LIS. Results from timeseries analysis are supported by weekly cruise surveys that resolve horizontal and vertical DO gradients in the western narrows. However, inferences regarding the duration of hypoxia during a given summer vary across datasets in part because weekly survey data do not resolve dominant intraseasonal timescales of variability. While prior studies have illustrated the importance of nutrient loading, stratification, and wind in controlling the development of hypoxia, the results presented here demonstrate the role of tidal advection in modulating hypoxia in far western LIS. Despite stronger stratification in 2021, the duration of hypoxia was 11.1 days shorter compared to 2022 in part due to greater advection of DO by tidal currents that intermittently ventilated bottom waters near the buoy. While improvements in water quality have been observed in other areas of LIS, increasing hypoxic area in the western narrows highlights the spatially variable response of DO to nutrient load reductions. Future analysis of hypoxia in LIS should focus on leveraging high-frequency information contained in continuous datasets to improve estimates of hypoxia based on less temporally resolved water quality surveys.