Submarine groundwater discharge alters coral reef ecosystem metabolism.
Ontology highlight
ABSTRACT:
SUBMITTER: Silbiger NJ
PROVIDER: S-EPMC7779522 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description: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 (?15N, N %, and C:N) were compared with nutrient and ?15N-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 ?15N 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 ?15N 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.
| S-EPMC5094668 | biostudies-literature
Project description:Riverine and atmospheric inputs are often considered as the main terrestrial sources of dissolved inorganic nitrogen (DIN), phosphorus (DIP), and silicon (DSi) in the ocean. However, the fluxes of nutrients via submarine groundwater discharge (SGD) often exceed riverine inputs in different local and regional scale settings. In this study, we provide a first approximation of global nutrient fluxes to the ocean via total SGD, including pore water fluxes, by combining a global compilation of nutrient concentrations in groundwater and the SGD-derived 228Ra fluxes. In order to avoid overestimations in calculating SGD-derived nutrient fluxes, the endmember value of nutrients in global groundwater was chosen from saline groundwater samples (salinity?>10) which showed relatively lower values over all regions. The results show that the total SGD-derived fluxes of DIN, DIP, and DSi could be approximately 1.4-, 1.6-, and 0.7-fold of the river fluxes to the global ocean (Indo-Pacific and Atlantic Oceans), respectively. Although significant portions of these SGD-derived nutrient fluxes are thought to be recycled within sediment-aquifer systems over various timescales, SGD-derived nutrient fluxes should be included in the global ocean budget in order to better understand dynamic interactions at the land-ocean interface.
| S-EPMC5799265 | biostudies-literature
Project description:Despite the relevance of submarine groundwater discharge (SGD) for ocean biogeochemistry, the microbial dimension of SGD remains poorly understood. SGD can influence marine microbial communities through supplying chemical compounds and microorganisms, and in turn, microbes at the land-ocean transition zone determine the chemistry of the groundwater reaching the ocean. However, compared with inland groundwater, little is known about microbial communities in coastal aquifers. Here, we review the state of the art of the microbial dimension of SGD, with emphasis on prokaryotes, and identify current challenges and future directions. Main challenges include improving the diversity description of groundwater microbiota, characterized by ultrasmall, inactive and novel taxa, and by high ratios of sediment-attached versus free-living cells. Studies should explore microbial dynamics and their role in chemical cycles in coastal aquifers, the bidirectional dispersal of groundwater and seawater microorganisms, and marine bacterioplankton responses to SGD. This will require not only combining sequencing methods, visualization and linking taxonomy to activity but also considering the entire groundwater-marine continuum. Interactions between traditionally independent disciplines (e.g. hydrogeology, microbial ecology) are needed to frame the study of terrestrial and aquatic microorganisms beyond the limits of their presumed habitats, and to foster our understanding of SGD processes and their influence in coastal biogeochemical cycles.
| S-EPMC8498565 | biostudies-literature
Project description:Submarine groundwater discharge (SGD), a major component of the hydrological cycle, has significant impacts on the sustainable development of the marine environment. This study aimed to examine the literature characteristics and research hotspots of SGD based on Web of Science's citation database from 1998-2019. With systematic bibliometric analysis, insights were made into multiple aspects including research output, subject categories, journals, countries/territories, institutions, authors, and hotspots and research trends. Results showed that the current amount of publications on SGD has increased exponentially. The characteristics of multi-subject, active international and inter-institutional collaborations were identified. There were 11 core journals publishing the research on SGD, and the number of covered journals increased linearly from 1998. USA had distinct advantages in publication outputs and took the core position in international collaborations. At present, the research hotspots of SGD mainly include the following: dynamics process and estimation of SGD with hydrogeological methods, tracer techniques, geochemical process in subterranean estuary, and dissolved material inputs to coastal waters via SGD. Citation analysis implied much development space in carbon flux transported by SGD and the implement of head as groundwater tracer. These results provided an instructive perspective of the present situation and future research direction on SGD.
| S-EPMC7036937 | biostudies-literature
Project description:Near- and off-shore fresh groundwater resources become increasingly important with the social and economic development in coastal areas. Although large scale (hundreds of km) submarine groundwater discharge (SGD) to the ocean has been shown to be of the same magnitude order as river discharge, submarine fresh groundwater discharge (SFGD) with magnitude comparable to large river discharge is never reported. Here, we proposed a method coupling mass-balance models of water, salt and radium isotopes based on field data of (223)Ra, (226)Ra and salinity to estimate the SFGD, SGD. By applying the method in Laizhou Bay (a water area of ~6000 km(2)), we showed that the SFGD and SGD are 0.57 ~ 0.88 times and 7.35 ~ 8.57 times the annual Yellow River flux in August 2012, respectively. The estimate of SFGD ranges from 4.12 × 10(7) m(3)/d to 6.36 × 10(7) m(3)/d, while SGD ranges from 5.32 × 10(8) m(3)/d to 6.20 × 10(8) m(3)/d. The proportion of the Yellow River input into Laizhou Bay was less than 14% of the total in August 2012. Our method can be used to estimate SFGD in various coastal waters.
| S-EPMC4649716 | biostudies-literature
Project description:The Mediterranean Sea (MS) is a semienclosed basin that is considered one of the most oligotrophic seas in the world. In such an environment, inputs of allochthonous nutrients and micronutrients play an important role in sustaining primary productivity. Atmospheric deposition and riverine runoff have been traditionally considered the main external sources of nutrients to the MS, whereas the role of submarine groundwater discharge (SGD) has been largely ignored. However, given the large Mediterranean shore length relative to its surface area, SGD may be a major conveyor of dissolved compounds to the MS. Here, we used a (228)Ra mass balance to demonstrate that the total SGD contributes up to (0.3-4.8)⋅10(12) m(3) ⋅ y(-1) to the MS, which appears to be equal or larger by a factor of 16 to the riverine discharge. SGD is also a major source of dissolved inorganic nutrients to the MS, with median annual fluxes of 190⋅10(9), 0.7⋅10(9), and 110⋅10(9) mol for nitrogen, phosphorous, and silica, respectively, which are comparable to riverine and atmospheric inputs. This corroborates the profound implications that SGD may have for the biogeochemical cycles of the MS. Inputs of other dissolved compounds (e.g., iron, carbon) via SGD could also be significant and should be investigated.
| S-EPMC4386347 | biostudies-literature
Project description:We measured the magnitude of submarine fresh groundwater discharge (SFGD) and associated nutrient inputs to Jocheon harbor, on Jeju Island, Korea, during four sampling periods, in order to determine the link between SFGD and Ulva sp. green tide development. Good correlations among salinity, 222Rn, and dissolved inorganic nitrogen (DIN) in harbor seawater suggest that SFGD is the major source of DIN and fresh water since there are no surface runoffs. Using a 222Rn mass balance model, SFGD to the harbor was estimated to be 5.8?±?2.3?×?104?m3 d-1. The DIN inputs through SFGD enhanced DIN concentrations in harbor seawater approximately 10-fold of those in the open-ocean (outer harbor) seawater. Results from mesocosm experiments showed that the growth rate of U. pertusa increased by 160% on average due to the enhanced DIN concentrations (from 1 to 24?µM) through SFGD in this harbor. Thus, we conclude that DIN inputs through SFGD cause the green tide development in Jocheon harbor and perhaps in other green tide regions where river inputs are absent.
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Project description:Ocean acidification is expected to alter community composition on coral reefs, but its effects on reef community metabolism are poorly understood. Here we document how early successional benthic coral reef communities change in situ along gradients of carbon dioxide (CO2), and the consequences of these changes on rates of community photosynthesis, respiration, and light and dark calcification. Ninety standardised benthic communities were grown on PVC tiles deployed at two shallow-water volcanic CO2 seeps and two adjacent control sites in Papua New Guinea. Along the CO2 gradient, both the upward facing phototrophic and the downward facing cryptic communities changed in their composition. Under ambient CO2, both communities were dominated by calcifying algae, but with increasing CO2 they were gradually replaced by non-calcifying algae (predominantly green filamentous algae, cyanobacteria and macroalgae, which increased from ~30% to ~80% cover). Responses were weaker in the invertebrate communities, however ascidians and tube-forming polychaetes declined with increasing CO2. Differences in the carbonate chemistry explained a far greater amount of change in communities than differences between the two reefs and successional changes from five to 13 months, suggesting community successions are established early and are under strong chemical control. As pH declined from 8.0 to 7.8, rates of gross photosynthesis and dark respiration of the 13-month old reef communities (upper and cryptic surfaces combined) significantly increased by 10% and 20%, respectively, in response to altered community composition. As a consequence, net production remained constant. Light and dark calcification rates both gradually declined by 20%, and low or negative daily net calcification rates were observed at an aragonite saturation state of <2.3. The study demonstrates that ocean acidification as predicted for the end of this century will strongly alter reef communities, and will significantly change rates of community metabolism.
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Project description:Coral reefs are among Earth's best-studied ecosystems, yet the degree to which large predators influence the ecology of coral reefs remains an open and contentious question. Recent studies indicate the consumptive effects of large reef predators are too diffuse to elicit trophic cascades. Here, we provide evidence that such predators can produce non-consumptive (fear) effects that flow through herbivores to shape the distribution of seaweed on a coral reef. This trophic cascade emerged because reef topography, tidal oscillations, and shark hunting behaviour interact to create predictable "hot spots" of fear on the reef where herbivores withhold feeding and seaweeds gain a spatial refuge. Thus, in risky habitats, sharks can exert strong ecological impacts even though they are trophic generalists that rarely feed. These findings contextualize the debate over whether predators influence coral reef structure and function and move us to ask not if, but under what specific conditions, they generate trophic cascades.
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Project description: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 (Kīholo 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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