Coral reefs benefit from reduced land-sea impacts under ocean warming.

Coral reef ecosystems are being fundamentally restructured by local human impacts and climate-driven marine heatwaves that trigger mass coral bleaching and mortality1. Reducing local impacts can increase reef resistance to and recovery from bleaching2. However, resource managers lack clear advice on targeted actions that best support coral reefs under climate change3 and sector-based governance means most land- and sea-based management efforts remain siloed4. Here we combine surveys of reef change with a unique 20-year time series of land-sea human impacts that encompassed an unprecedented marine heatwave in Hawai'i. Reefs with increased herbivorous fish populations and reduced land-based impacts, such as wastewater pollution and urban runoff, had positive coral cover trajectories predisturbance. These reefs also experienced a modest reduction in coral mortality following severe heat stress compared to reefs with reduced fish populations and enhanced land-based impacts. Scenario modelling indicated that simultaneously reducing land-sea human impacts results in a three- to sixfold greater probability of a reef having high reef-builder cover four years postdisturbance than if either occurred in isolation. International efforts to protect 30% of Earth's land and ocean ecosystems by 2030 are underway5. Our results reveal that integrated land-sea management could help achieve coastal ocean conservation goals and provide coral reefs with the best opportunity to persist in our changing climate.

Trade-offs across values in cesspool management highlight challenges to policy making.

On-site Sewage Disposal Systems (OSDS) are globally common, and in Hawai'i they present a risk of contamination to drinking water sources and nearshore waters. State legislation has commanded that all cesspools are to be banned by 2050, thus requiring tens of thousands of systems to be converted in the coming decades. This project followed a participatory structured decision-making (SDM) approach to collaboratively design cost-effective and equitable solutions for thousands of cesspools in the high elevation areas of north Maui, Hawai'i. Participatory workshops with a diverse group of stakeholders set ten objectives and brainstormed 33 alternatives, for which the technical team then modeled groundwater nutrients, costs, and equity. All alternatives posed trade-offs, though composting toilets performed best across most objectives, albeit with high maintenance burden. Discounting innovative toilets, the multi-objective analysis suggests that the state should invest in cluster sewering of high-density communities, followed by incentivizing septic tank solutions in properties with the highest effluent flow first, then expanding across the area. The total project cost (installation and operation/maintenance) would be $183-258 million, depending upon the sewer-septic combination. An efficiency frontier reveals sub-par combinations, including aerobic treatment units and passive absorption systems, which cost much more and deliver lower mass flux reduction than more cost-effective alternatives. This study contributes a novel case of rural sanitation to the literature in which decision support tools are used to facilitate evidence-based, collaborative decision-making for sanitation planning. The state could use a similar participatory SDM process when approaching other communities to discuss their cesspool upgrade strategies. Broadening the use of decision analytic techniques can have wider ecological, economic, and social benefits for the state and contexts beyond Hawai'i, as SDM provides a transparent and rigorous, evidence-based decision-theoretic framework to explore multiple values and strategies to address difficult resource management problems.

Application of statistics to correlate groundwater chemistry with land use on O'ahu, Hawai'i.

This study compiles commonly available groundwater chemistry data from the Pearl Harbor Sole Source Aquifer (SSA), Hawai'i-O'ahu's primary drinking water source-and applies hierarchical clustering analysis (HCA), principal component analyses (PCA), piper diagrams, and box plots with geospatial analysis to better define groundwater regions and correlate groundwater chemistry in those regions with land use. Groundwater in this aquifer recharges and flows through chemically similar soil and rocks, such that anthropogenic activities are a primary influence on the chemical variability of the aquifer's differing regions. Our analyses link specific chemical species in groundwater to land use/cover categories: urban, agriculture, and natural and anthropogenically-induced saline water intrusion. To create distinct statistical groupings with different groundwater chemistry compositions, it was important that the suite of parameters used in the statistical analysis do not covary. In our case, Cl- covaried with several major ions; however, by including F-, alkalinity, and SiOx that do not covary with Cl- in the covariance matrix, we produced improved spatial grouping of HCA clusters and stronger affinities to land use designations. Results show that dominant groundwater chemistry changes with land use along flow paths. These results pertain to areas where groundwater flows from conservation land in high recharge areas of O'ahu's mountain ranges to urban and agricultural land use regions: groundwater retains its source characteristics until about 3-6 km into agricultural and urban zoned lands. Ultimately, this study outlines a simple method for water quality regulators to use groundwater chemistry to identify risks of target contaminants based on land use.

Understanding the origins of and influences on precipitation major ion chemistry on the Island of O'ahu, Hawai'i.

Precipitation is the primary groundwater source for the Island of O'ahu, Hawai'i, USA, and is an important source of terrestrial nutrients. Since Pacific Islands are particularly vulnerable to the impacts of climate change, they are important venues for studying the controls on and fluctuations in precipitation chemistry. Spatial variations in some of the dissolved rainfall ions can also be of value as natural geochemical tracers in examining surface and groundwater flow. This study collected and chemically analyzed bulk precipitation from 20 sites across the Island of O'ahu approximately quarterly between April 2018 and August 2021. The new precipitation chemistry data were integrated with previously published precipitation data to characterize major ion composition and examine the atmospheric processes controlling inorganic ion deposition. Linear regression and multivariate analysis were used to quantify the relationships among major ions and to assess the impacts of various environmental and meteorological factors on precipitation chemistry. Ordinary kriging and inverse distance weighted interpolations were conducted to help visualize spatial variations in major ion deposition. The results clearly indicate that ocean sea spray is the primary driver of precipitation inorganic chemistry, with marine sea salt aerosols accounting for more than 90% of the measured ion load. However, they also show that various weather patterns and nutrient sources impact inorganic deposition. Most notably, upper atmospheric transport of Asian continental dust during Hawaiian wet seasons, Ca2+ from local sedimentary deposits, and anthropogenic K+ from agricultural activity appear to be substantial non-marine deposition sources. This study synthesizes data from multiple sources into the most spatially and topographically diverse precipitation collector network on O'ahu to date. The findings from this effort help establish a baseline for assessing future fluctuations in inorganic ion deposition and lay important groundwork for examining connections between precipitation and groundwater chemistry within the study area.

Place-based management can reduce human impacts on coral reefs in a changing climate.

Declining natural resources have contributed to a cultural renaissance across the Pacific that seeks to revive customary ridge-to-reef management approaches to protect freshwater and restore abundant coral reef fisheries. We applied a linked land-sea modeling framework based on remote sensing and empirical data, which couples groundwater nutrient export and coral reef models at fine spatial resolution. This spatially explicit (60 × 60 m) framework simultaneously tracks changes in multiple benthic and fish indicators as a function of community-led marine closures, land-use and climate change scenarios. We applied this framework in Ha'ena and Ka'upulehu, located at opposite ends of the Hawaiian Archipelago to investigate the effects of coastal development and marine closures on coral reefs in the face of climate change. Our results indicated that projected coastal development and bleaching can result in a significant decrease in benthic habitat quality and community-led marine closures can result in a significant increase in fish biomass. In general, Ka'upulehu is more vulnerable to land-based nutrients and coral bleaching than Ha'ena due to high coral cover and limited dilution and mixing from low rainfall and wave power, except for the shallow and wave-sheltered back-reef areas of Ha'ena, which support high coral cover and act as nursery habitat for fishes. By coupling spatially explicit land-sea models with scenario planning, we identified priority areas on land where upgrading cesspools can reduce human impacts on coral reefs in the face of projected climate change impacts.

Technical commentary to: Direct aerobic NSZD of a basalt vadose zone LNAPL source in Hawaii, McHugh et al., JCH #235 (2020).

The subject Paper (McHugh et al., 2020) uses carbon dioxide and net thermal signatures to derive conclusions about the rates of natural source zone depletion (NSZD), as well as the location of residual fuel in the formation. We concur that both data sets are indicators of active fuel biodegradation, however, the simplifications of McHugh et al. render its estimates of NSZD rates uncertain and likely over-estimated. We cannot infer what role this degradation capacity may play in site management because: a) the biodegradation evidence is spatially limited and cannot be linked to LNAPL source zones; b) the LNAPL source zones are so poorly understood that we have no mass constraints or balances; and c) this is a very heterogeneous site, in terms of LNAPL source locations, masses, rates, and related subsurface properties. Consequently, much McHugh et al., 2020 amounts to speculative hypotheses and estimates of NSZD that are unbounded by confirmatory data. Several of the McHugh et al. authors prepared a conceptual site model (CSM) report that can be downloaded from the EPA website: https://www.epa.gov/sites/production/files/201907/documents/red_hill_conceptual_site_model_20190630-redacted.pdf. This CSM report incorporates the conclusions of McHugh et al., 2020 as part of a broader interpretation of a generally safe setting with regard to potential aquifer damages being caused by past and future fuel releases because of the assumed large fuel holding and assimilative capacities. Substantial impacts to the aquifer caused by recent fuel releases (May and November 2021) have contaminated drinking water and affected thousands of base residents. These aquifer impact events serve to highlight the importance of adequate technical detail in evaluations, particularly in complex settings like at the subject site. A partial synopsis of these recent fuel release events can be found at: https://www.hawaiipublicradio.org/local-news/2021-12-21/confused-about-the-timeline-for-the-red-hill-fuel-storage-facility-and-contaminated-water-read-this.

Algal bioassays detect modeled loading of wastewater-derived nitrogen in coastal waters of O'AHU, HAWAI'I.

Previous studies indicate coastlines are at risk of wastewater contamination from injection wells, cesspools, and septic systems. In this study, common marine algae were used to ground-truth modeled loading of wastewater-derived N to coastlines of O'ahu, Hawai'i. Macroalgae were collected and/or deployed at 118 sites and analyzed for tissue δ15N and N %. Wastewater source locations were used to estimate wastewater-derived N in groundwater with the modeling software MT3DMS/MODFLOW. Algal bioassays identified six coastal regions subjected to elevated wastewater-derived N loading. In a case study, submarine groundwater discharge (estimated by 222Rn mass balance) was related to wastewater loading from onsite sewage disposal systems (OSDS) and municipal wastewater injection wells in Waimanalo. The highest 222Rn-derived SGD rate and N flux were 21.4 m3/m/d and 62.6 g/m/d, respectively. The results of this study suggest that OSDS and injection wells discharge substantial volumes of wastewater and N across broad regions of coastal O'ahu.

Decision analysis to support wastewater management in coral reef priority area.

A cocktail of land-based sources of pollution threatens coral reef ecosystems, and addressing these has become a key management and policy challenge in the State of Hawai'i, other US territories, and globally. In West Maui, Hawai'i, nearly one quarter of all living corals were lost between 1995 and 2008. Onsite disposal systems (OSDS) for sewage leak contaminants into drinking water sources and nearshore waters. In recognition of this risk, the Hawai'i State Department of Health (DOH) is prioritizing areas for cesspool upgrades. Independently, we applied a decision analysis process to identify priority areas to address sewage pollution from OSDS in West Maui, with the objective of reducing nearshore coral reef exposure to pollution. The decision science approach is relevant to a broader context of coastal areas both statewide and worldwide which are struggling with identifying pollution mitigation actions on limited budgets.

A linked land-sea modeling framework to inform ridge-to-reef management in high oceanic islands.

Declining natural resources have led to a cultural renaissance across the Pacific that seeks to revive customary ridge-to-reef management approaches to protect freshwater and restore abundant coral reef fisheries. Effective ridge-to-reef management requires improved understanding of land-sea linkages and decision-support tools to simultaneously evaluate the effects of terrestrial and marine drivers on coral reefs, mediated by anthropogenic activities. Although a few applications have linked the effects of land cover to coral reefs, these are too coarse in resolution to inform watershed-scale management for Pacific Islands. To address this gap, we developed a novel linked land-sea modeling framework based on local data, which coupled groundwater and coral reef models at fine spatial resolution, to determine the effects of terrestrial drivers (groundwater and nutrients), mediated by human activities (land cover/use), and marine drivers (waves, geography, and habitat) on coral reefs. We applied this framework in two 'ridge-to-reef' systems (Ha'ena and Ka'upulehu) subject to different natural disturbance regimes, located in the Hawaiian Archipelago. Our results indicated that coral reefs in Ka'upulehu are coral-dominated with many grazers and scrapers due to low rainfall and wave power. While coral reefs in Ha'ena are dominated by crustose coralline algae with many grazers and less scrapers due to high rainfall and wave power. In general, Ka'upulehu is more vulnerable to land-based nutrients and coral bleaching than Ha'ena due to high coral cover and limited dilution and mixing from low rainfall and wave power. However, the shallow and wave sheltered back-reef areas of Ha'ena, which support high coral cover and act as nursery habitat for fishes, are also vulnerable to land-based nutrients and coral bleaching. Anthropogenic sources of nutrients located upstream from these vulnerable areas are relevant locations for nutrient mitigation, such as cesspool upgrades. In this study, we located coral reefs vulnerable to land-based nutrients and linked them to priority areas to manage sources of human-derived nutrients, thereby demonstrating how this framework can inform place-based ridge-to-reef management.

Wastewater injection, aquifer biogeochemical reactions, and resultant groundwater N fluxes to coastal waters: Ka'anapali, Maui, Hawai'i.

We utilize N and C species concentration data along with δ(15)N values of NO3(-) and δ(13)C values of dissolved inorganic C to evaluate the stoichiometry of biogeochemical reactions (mineralization, nitrification, anammox, and denitrification) occurring within a subsurface wastewater plume that originates as treated wastewater injection and enters the coastal waters of Maui as submarine groundwater discharge. Additionally, we compare wastewater effluent time-series data, injection rates, and treatment history with submarine spring discharge time-series data. We find that heterotrophic denitrification is the primary mechanism of N loss within the groundwater plume and that chlorination for pathogen disinfection suppresses microbial activity in the aquifer responsible for N loss, resulting in increased coastal ocean N loading. Replacement of chlorination with UV disinfection may restore biogeochemical reactions responsible for N loss within the aquifer and return N-attenuating conditions in the effluent plume, reducing N loading to coastal waters.

The high specificities of Phaseolus vulgaris erythro- and leukoagglutinating lectins for bisecting GlcNAc or beta 1-6-linked branch structures, respectively, are attributable to loop B.

Despite very similar tertiary structures based upon a common framework, legume lectins exhibit an amazing variety of sugar binding specificities. While most of these lectins recognize rather discrete sugar linkages, Phaseolus vulgaris erythroagglutinating and leukoagglutinating lectins (E(4)- and L(4)-PHA) are unique in recognizing larger structures. E(4)- and L(4)-PHA are known to recognize complex type N-glycans containing bisecting GlcNAc or a beta1,6-linked branch, respectively. However, the detailed mechanisms of molecular recognition are poorly understood. In order to dissect the contributions of different portions of each lectin, we carried out region-swapping mutagenesis between E(4)- and L(4)-PHA. We prepared six chimeric lectins by exchanging different combinations of loop B and the central portion of loop C, two of four loops thought to be important for the recognition of monosaccharides (Sharma, V., and Surolia, A. (1997) J. Mol. Biol. 267, 433-445). The chimeric lectins' sugar binding activities were evaluated quantitatively by surface plasmon resonance. These comparisons indicate that the high specificities of E(4)- and L(4)-PHA toward bisecting GlcNAc and beta1,6-linked branch structures are almost solely attributable to loop B. The contribution of the central portion of loop C to the recognition of those structural motifs was found to be negligible. Instead, it modulates affinity toward LacNAc residues present at the nonreducing terminus. Moreover, some of the chimeric lectins prepared in this study showed even higher specificities/affinities than native E(4)- and L(4)-PHA toward complex sugar chains containing either a bisecting GlcNAc residue or a beta1,6-linked branch.

A versatile planar QCM-based sensor design for nonlabeling biomolecule detection.

Despite high theoretical sensitivity, low-cost manufacture, and compactness potentially amenable to lab-on-a-chip use, practical hurdles have stymied the application of the quartz crystal microbalance (QCM) for aqueous applications such as detection of biomolecular interactions. The chief difficulty lies in achieving a sufficiently stable resonance signal in the presence of even minute fluctuations in hydrostatic pressure. In this work, we present a novel versatile planar sensor chip design (QCM chip) for a microliter-scale on-line biosensor. By sealing the quartz resonator along its edges to a flat, solid support, we provide uniform support for the crystal face not exposed to solvent, greatly decreasing deformation of the crystal resonator under hydrostatic pressure. Furthermore, this cassette design obviates the need for direct handling when exchanging the delicate quartz crystal in the flow cell. A prototype 27-MHz sensor signal exhibited very low noise over a range of flow rates up to 100 microL/min. In contrast, signals obtained from a conventional QCM sensor employing an O-ring-based holder were less stable and deteriorated even further with increasing flow rate. Additional control designs with intermediate amounts of unsupported undersurface yielded intermediate levels of stability, consistent with the interpretation that deformation of the crystal resonator under fluctuating hydraulic pressure is the chief source of noise. As a practical demonstration of the design's high effective sensitivity, we readily detected interaction between myoglobin and surface-bound antibody.