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Chlorophyll has long been used as a natural indicator of plant health and photosynthetic efficiency. Laser-induced fluorescence (LIF) is an emerging technique for understanding broad spectrum organic processes and has more recently been used to monitor chlorophyll response in plants. Previous work has focused on developing a LIF technique for imaging moss mats to identify metal contamination with the current focus shifting toward application to moss fronds and aiding sample collection for chemical analysis. Two laser systems (CoCoBi a Nd:YGa pulsed laser system and Chl-SL with two blue continuous semiconductor diodes) were used to collect images of moss fronds exposed to increasing levels of Cu (1, 10, and 100 nmol/cm2) using a CMOS camera. The best methods for the preprocessing of images were conducted before the analysis of fluorescence signatures were compared to a control. The Chl-SL system performed better than the CoCoBi, with dynamic time warping (DTW) proving the most effective for image analysis. Manual thresholding to remove lower decimal code values improved the data distributions and proved whether using one or two fronds in an image was more advantageous. A higher DTW difference from the control correlated to lower chlorophyll a/b ratios and a higher metal content, indicating that LIF, with the aid of image processing, can be an effective technique for identifying Cu contamination shortly after an event.

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The ability to detect, measure, and locate the source of contaminants, especially heavy metals and radionuclides, is of ongoing interest. A common tool for contaminant identification and bioremediation is vegetation that can accumulate and indicate recent and historic pollution. However, large-scale sampling can be costly and labor-intensive. Hence, non-invasive in-situ techniques such as laser-induced fluorescence (LIF) are becoming useful and effective ways to observe the health of plants through the excitation of organic molecules, e.g., chlorophyll. The technique presented utilizes images collected of LIF in moss to identify different metals and environmental stressors. Analysis through image processing of LIF response was key to identifying Cu, Zn, Pb, and a mixture of the metals at nmol/cm2 levels. Specifically, the RGB values from each image were used to create density histograms of each color channel's relative pixel abundance at each decimal code value. These histograms were then used to compare color shifts linked to the successful identification of contaminated moss samples. Photoperiod and extraneous environmental stressors had minimal impact on the histogram color shift compared to metals and presented with a response that differentiated them from metal contamination.

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Resource-constrained island populations have thrived in Hawai'i for over a millennium, but now face aggressive new challenges to fundamental resources, including the security and sustainability of water resources. Characterizing the microbial community in groundwater ecosystems is a powerful approach to infer changes from human impacts due to land management in hydrogeological complex aquifers. In this study, we investigate how geology and land management influence geochemistry, microbial diversity and metabolic functions. We sampled a total of 19 wells over 2-years across the Hualalai watershed of Kona, Hawai'i analyzing geochemistry, and microbial communities by 16S rRNA amplicon sequencing. Geochemical analysis revealed significantly higher sulfate along the northwest volcanic rift zone, and high nitrogen (N) correlated with high on-site sewage disposal systems (OSDS) density. A total of 12,973 Amplicon Sequence Variants (ASV) were identified in 220 samples, including 865 ASVs classified as putative N and sulfur (S) cyclers. The N and S cyclers were dominated by a putative S-oxidizer coupled to complete denitrification (Acinetobacter), significantly enriched up to 4-times comparatively amongst samples grouped by geochemistry. The significant presence of Acinetobacter infers the bioremediation potential of volcanic groundwater for microbial-driven coupled S-oxidation and denitrification providing an ecosystem service for island populations dependent upon groundwater aquifers.

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Groundwater is a vital resource for humans and groundwater dependent ecosystems. Coastal aquifers and submarine groundwater discharge (SGD), both influenced by terrestrial and marine forces, are increasingly affected by climate variations and sea-level rise. Despite this, coastal groundwater resources and discharge are frequently poorly constrained, limiting our understanding of aquifer responses to external forces. We apply traditional and novel time-series approaches using an SGD dataset of previously unpublished resolution and duration, to analyze the dependencies between precipitation, groundwater level, and SGD at a model site (Kiholo Bay, Hawai'i). Our objectives include (1) determining the relative contribution of SGD drivers over tidal and seasonal periods, (2) establishing temporal relationships and thresholds of processes influencing SGD, and (3) evaluating the impacts of anomalous events, such as tropical storms, on SGD. This analysis reveals, for example, that precipitation is only a dominant influence during wet periods, and otherwise tides and waves dictate the dynamics of SGD. It also provides time lags between intense storm events and higher SGD rates, as well as thresholds for precipitation, wave height and tides affecting SGD. Overall, we demonstrate an approach for modeling a hydrological system while elucidating coastal aquifer and SGD response in unprecedented detail.

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Untreated and minimally treated wastewater discharged into the environment have the potential to adversely affect groundwater dependent ecosystems and nearshore marine health. Addressing this issue requires a systems approach that links land use and wastewater management decisions to potential impacts on the nearshore marine environment via changes in water quality and quantity. To that end, a framework was developed to assess decisions that have cascading effects across multiple elements of the ridge-to-reef system. In an application to Kona (Hawai'i, USA), eight land use and wastewater management scenarios were evaluated in terms of wastewater system upgrade costs and wastewater related nutrient loads in groundwater, which eventually discharge to nearshore waters, resulting in potential impacts to marine habitat quality. Without any upgrades of cesspools or the existing wastewater treatment plant (WWTP), discharges of nutrients are expected to increase substantially with permitted development, with potential detrimental impacts to the marine environment. Results suggest that converting all of the existing cesspools to aerobic treatment units (ATU) and upgrading the existing WWTP to R-1 quality provide the highest protection to nearshore marine habitat at a cost of $569 million in present value terms. Other wastewater management options were less effective but also less costly. For example, targeted cesspool conversion (a combination of septic and ATU installation) in conjunction with the WWTP upgrade still provided a substantial reduction in nutrients and potential impacts to marine habitat quality relative to the present situation at a price point roughly $100 million less than the entirely ATU option. Of note, results were more sensitive to the inclusion of the WWTP upgrade option than they were to assumptions regarding the efficiency of the cesspool conversion technologies. The model outputs also suggest that the spatial distribution of potential impacts should be carefully considered when comparing different wastewater management scenarios. When evaluated separately, the WWTP option reduced total nutrients by more than the targeted cesspool conversion option at a fraction of the cost. However, potential improvements in marine habitat quality only occurred in the immediate vicinity of the WWTP, whereas the benefits under targeted cesspool conversion were more evenly distributed along the coast.

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Submarine groundwater discharge (SGD) is rarely considered as a pathway for contaminants of emerging concern (CECs). Here, we investigated SGD as a source of CECs in Sydney Harbour, Australia. CEC detection frequencies based on presence/absence of a specific compound were >90% for caffeine, carbamazepine, and dioxins, and overall ranged from 25 to 100% in five studied embayments. SGD rates estimated from radium isotopes explained >80% of observed CEC inventories for one or more compounds (caffeine, carbamazepine, dioxins, sulfamethoxazole, fluoroquinolones and ibuprofen) in four out of the five embayments. Radium-derived residence times imply mixing is also an important process for driving coastal inventories of these persistent chemicals. Two compounds (ibuprofen and dioxins) were in concentrations deemed a high risk to the ecosystem. Overall, we demonstrate that SGD can act as a vector for CECs negatively impacting coastal water quality.

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As urban areas expand around the world, there are growing efforts to restore and protect natural and agricultural systems for the multitude of ecosystem services they provide to urban communities. This study presents a researcher-farmer collaboration in a highly urbanized area of O'ahu focused on understanding the historical and current challenges and opportunities faced by a culturally and socially valued spring-dependent urban farm, Sumida Farm, which produces the majority of the state of Hawai'i's watercress. We conducted a long-term trend analysis (25 years) of factors identified by the farmers to be important historical drivers of crop yield, including groundwater pumping, pest outbreaks, temperature, Oceanic Niño Index, and precipitation. We combined this analysis with a year of intensive spring water sampling on the farm to evaluate nutrient and contaminant composition and flow to understand water-related stressors, as well as evaluate the potential of the farm to provide nutrient retention services. We found negative correlations between historical crop yields and increases in the Oceanic Niño Index, temperature thresholds, and pest outbreaks. Despite the surrounding urbanization, we found on-farm water quality to be very high, and microbial analyses revealed an abundance of denitrifiers (nirS gene) suggesting that the farm provides a nutrient retention service to downstream systems. Finally, we found that socio-cultural values including heritage value, aesthetic value, and educational value are increasingly important for the Sumida family and surrounding community. These socio-cultural benefits alongside highly valued local food production and nutrient retention services are essential for continued community and political support. Collectively, our study demonstrates that challenges facing urban agricultural systems shift through time, and that recognition of the beyond crop-yield benefits of these systems to urban communities is essential to their long-term survival.

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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.

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Groundwater-surface water interactions drive water quality in both streams and the coastal ocean, where groundwater discharge occurs in streams as baseflow and along the coastline as submarine groundwater discharge (SGD). Groundwater contributions to streams and to the coastal ocean were quantified in three urban streams in Kane'ohe Watershed, Hawai'i. We used radon as a groundwater tracer to show that baseflow contributions to streams ranged from 22 to 68% along their reaches leading to the coast of Kane'ohe Bay. Total SGD was 4,500, 18,000, and 23,000 m3/day for the northwest, central, and southern sectors of the bay, respectively. Total groundwater (stream baseflow + SGD) dissolved nutrient fluxes were significantly greater than those sourced from stream surface runoff. The studied streams exhibited increasing nutrient levels downstream from groundwater inputs with high nutrient concentrations, negatively impacting coastal water quality. SGD dynamics were also assessed during the anomalously high perigean spring tides in 2017, where SGD was four times greater during the perigean spring tide compared to a spring tide and resulted in strong shifts in N:P ratios, suggesting that rising sea level stands may disrupt primary productivity with greater frequency. This study demonstrates the importance of considering baseflow inputs to streams to coastal groundwater budgets and suggests that coastal water quality may be improved through management and reduction of groundwater contaminants.

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Several reactors at the Fukushima Dai-ichi Nuclear Power Plant suffered damage on March 11, 2011, resulting in the release of radiocesium (134Cs and 137Cs), as well as other radionuclides, into the atmosphere. A week later, these isotopes were detected in aerosols over the state of Hawai'i and in milk samples analyzed on the island of Hawai'i. This study estimated the magnitude of cesium deposition in soil, collected in 2015-2016, resulting from atmospheric fallout. It also examined the patterns of cesium wet deposition with precipitation observed on O'ahu and the island of Hawai'i following the disaster. Fukushima-derived fallout was differentiated from historic nuclear weapons testing fallout by the presence of 134Cs and the assumption that the 134Cs to 137Cs ratio was 1:1. Detectable, Fukushima-derived 134Cs inventories ranged from 30 to 630 Bq m-2 and 137Cs inventories ranged from 20 to 2200 Bq m-2. Fukushima-derived cesium inventories in soils were related to precipitation gradients, particularly in areas where rainfall exceeded 200 mm between March 19 and April 4, 2011. This research confirmed and quantified the presence of Fukushima-derived fallout in the state of Hawai'i in amounts higher than predicted by models and observed in the United States mainland, however the activities detected were an order of magnitude lower than fallout associated with historic sources such as the nuclear weapons testing in the Pacific. In addition, this study showed that areas of highest cesium deposition do not overlap with densely populated or agriculturally used areas.

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Generally unseen and infrequently measured, submarine groundwater discharge (SGD) can transport potentially large loads of nutrients and other land-based contaminants to coastal ecosystems. To examine this linkage we employed algal bioassays, benthic community analysis, and geochemical methods to examine water quality and community parameters of nearshore reefs adjacent to a variety of potential, land-based nutrient sources on Maui. Three common reef algae, Acanthophora spicifera, Hypnea musciformis, and Ulva spp. were collected and/or deployed at six locations with SGD. Algal tissue nitrogen (N) parameters (δ15N, N %, and C:N) were compared with nutrient and δ15N-nitrate values of coastal groundwater and nearshore surface water at all locations. Benthic community composition was estimated for ten 10-m transects per location. Reefs adjacent to sugarcane farms had the greatest abundance of macroalgae, low species diversity, and the highest concentrations of N in algal tissues, coastal groundwater, and marine surface waters compared to locations with low anthropogenic impact. Based on δ15N values of algal tissues, we estimate ca. 0.31 km2 of Kahului Bay is impacted by effluent injected underground at the Kahului Wastewater Reclamation Facility (WRF); this region is barren of corals and almost entirely dominated by colonial zoanthids. Significant correlations among parameters of algal tissue N with adjacent surface and coastal groundwater N indicate that these bioassays provided a useful measure of nutrient source and loading. A conceptual model that uses Ulva spp. tissue δ15N and N % to identify potential N source(s) and relative N loading is proposed for Hawai'i. These results indicate that SGD can be a significant transport pathway for land-based nutrients with important biogeochemical and ecological implications in tropical, oceanic islands.

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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.

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