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USGS2021

Assessing cyanobacterial frequency and abundance at surface waters near drinking water intakes across the United States

This study presents the first large-scale assessment of cyanobacterial frequency and abundance of surface water near drinking water intakes across the United States. Public water systems serve drinking water to nearly 90% of the United States population. Cyanobacteria and their toxins may degrade the quality of finished drinking water and can lead to negative health consequences. Satellite imagery can serve as a cost-effective and consistent monitoring technique for surface cyanobacterial blooms in source waters and can provide drinking water treatment operators information for managing their systems. This study uses satellite imagery from the European Space Agency's Ocean and Land Colour Instrument (OLCI) spanning June 2016 through April 2020. At 300-m spatial resolution, OLCI imagery can be used to monitor cyanobacteria in 685 drinking water sources across 285 lakes in 44 states, referred to here as resolvable drinking water sources. First, a subset of satellite data was compared to a subset of responses ( n = 84) submitted as part of the U.S. Environmental Protection Agency's fourth Unregulated Contaminant Monitoring Rule (UCMR 4). These UCMR 4 qualitative responses included visual observations of algal bloom presence and absence near drinking water intakes from March 2018 through November 2019. Overall agreement between satellite imagery and UCMR 4 qualitative responses was 94% with a Kappa coefficient of 0.70. Next, temporal frequency of cyanobacterial blooms at all resolvable drinking water sources was assessed. In 2019, bloom frequency averaged 2% and peaked at 100%, where 100% indicated a bloom was always present at the source waters when satellite imagery was available. Monthly cyanobacterial abundances were used to assess short-term trends across all resolvable drinking water sources and effect size was computed to provide insight on the number of years of data that must be obtained to increase confidence in an observed change. Generally, 2016 through 2020 was an insufficient time period for confidently observing changes at these source waters; on average, a decade of satellite imagery would be required for observed environmental trends to outweigh variability in the data. However, five source waters did demonstrate a sustained short-term trend, with one increasing in cyanobacterial abundance from June 2016 to April 2020 and four decreasing.

Water Research↗

USGS2021

Freshwater cyanotoxin mixtures in recurring cyanobacterial blooms in Voyageurs National Park

Algal and cyanobacterial blooms can foul water systems, inhibit recreation, and produce cyanotoxins, which can be toxic to humans, domestic animals, and wildlife. Blooms that recur yearly present a special challenge, in that chronic effects of most cyanotoxins are unknown. To better understand cyanotoxin timing, possible environmental triggers, and inter-relations among taxa and toxins in bloom communities, recurring cyanobacterial blooms were investigated at three recreational sites in Kabetogama Lake in Voyageurs National Park from 2016-2019. Results indicated that peak neurotoxin concentrations occurred before peak microcystin concentrations and that toxin-forming cyanobacteria were present before visible blooms, which is a serious human health concern. Two cyanotoxin mixture models (MIX) and two microcystin (MC) models were developed using near-real-time environmental variables and additional comprehensive variables based on laboratory analyses. Comprehensive models explained more variability than the environmental models and neither MIX model was a better fit than the MC models. However, the MIX models produced no false negatives, indicating that all observations above human-health regulatory guidelines were simulated by the MIX models. The results show that a model based on a cyanotoxin mixture is more protective of human health than a model based on microcystin alone. In 2019, 7 of 19 toxins were detected in various mixtures. The potential toxin producing cyanobacteria, Microcystis , was significantly correlated with microcystin-YR, while Pseudanabaena sp. and Synechococcus sp. were negatively correlated to several toxins. Jaccard and Sorenson indices indicated strong same-day similarities among the three bloom communities. Nitrogen-fixing cyanobacteria were present at every site, and when combined with internal loading of phosphorus, might explain similarities among sites, and why seasonal differences, even in samples from the same site, were stronger. Information from this dissertation adds to the body of work on recurring blooms and under-studied toxins and toxin mixtures, providing a better understanding of future research options for freshwater cyanotoxins in and outside of Voyageurs National Park.

Minnesota↗

USGS2021

Simulated global coastal ecosystem responses to a half-century increase in river nitrogen loads

Coastal ecosystems are increasingly threatened by anthropogenic stressors such as harmful algal blooms and hypoxia projected to intensify through the combined effects of eutrophication and warming. As a major terrestrial nitrogen (N) source to the ocean, rivers play a critical role in shaping both coastal and global biogeochemical cycling. Combining an enhanced-resolution (1/4°), global ocean physical-biogeochemical model with dynamic river inputs, we estimate that elevated river nitrogen loads alone resulted in an increase of 16.6 Tg (+5.8%) in the global coastal nitrogen inventory (CNI) over the half century between 1961 and 2010. This change was accompanied by increases in coastal net primary productivity (NPP, +4.6%) and benthic detrital flux (BDF, +7.3%), the latter of which is indicative of an overall higher oxygen demand in coastal sediments. After normalization by area, the ecosystems most sensitive to added river nitrogen (g N m-2 yr-1) were those with long residence times and strong nitrogen limitation. While even enhanced-resolution global models remain limited in their capacity to resolve near-shore responses, these basic sensitivity factors provide two relevant axes for frameworks assessing the comparative susceptibility of globally distributed coastal ecosystems to enhanced nitrogen loading, and the effectiveness of mitigation strategies.

Geophysical Research Letters↗

USGS2006

Hurricanes, submarine groundwater discharge, and Florida's red tides

A Karenia brevis Harmful Algal Bloom affected coastal waters shallower than 50 m off west-central Florida from January 2005 through January 2006, showing a sustained anomaly of ???1 mg chlorophyll m-3 over an area of up to 67,500 km2. Red tides occur in the same area (approximately 26-29??N, 82-83??W) almost every year, but the intense 2005 bloom led to a widespread hypoxic zone (dissolved oxygen <2 mg L-1) that caused mortalities of benthic communities, fish, turtles, birds, and marine mammals. Runoff alone provided insufficient nitrogen to support this bloom. We pose the hypothesis that submarine groundwater discharge (SGD) provides the missing nutrients, and indeed can trigger and support the recurrent red tides off west-central Florida. SGD inputs of dissolved inorganic nitrogen (DIN) in Tampa Bay alone are ???35% of that discharged by all central Florida rivers draining west combined. We propose that the unusual number of hurricanes in 2004 resulted in high runoff, and in higher than normal SGD emerging along the west Florida coast throughout 2005, initiating and fueling the persistent HAB. This mechanism may also explain recurrent red tides in other coastal regions of the Gulf of Mexico. Copyright 2006 by the American Geophysical Union.

Geophysical Research Letters↗

USGS2018

Seafloor fluid seeps on Kimki Ridge, offshore southern California: Links to active strike-slip faulting

The Kimki Ridge fluid seeps are located in western Catalina Basin about 60 km southwest of the southern California mainland and at a water depth of approximately 1100 m. Multichannel seismic reflection profiles collected by the U.S. Geological Survey (USGS) in 2014 show acoustic transparency within the Kimki Ridge, suggesting the possibility of fluid seeps and possible sub-seafloor fluid pathways. Subsequent multibeam bathymetric and backscatter intensity data collected during a cooperative University of Washington/USGS cruise in early 2016 show subtle seafloor buildups with high acoustic backscatter (reflectivity) in three places along Kimki Ridge, supporting the existence of fluid seepage. A Remotely Operated Vehicle (ROV) dive, conducted as part of the Nautilus Exploration Program, took place in August 2016 to confirm the presence of these previously unknown seeps and document their characteristics as well as those of any associated biological communities. Two of the three seeps were explored by ROV, and showed abundant evidence of fluid seepage, including characteristic algal mats, chemosynthetic clams, and authigenic carbonate formation. The seeps are comprised of carbonate buildups 1–3 m thick and 300–500 m across. Within these areas, we interpret broad crater-like depressions 30–50 m across and 1–2 m deep to be individual seep vents. The seep areas appear to be broad zones of diffuse seepage that support chemosynthetic biologic communities; however, active venting was not observed. Geochemical analyses of rock samples collected from the seeps indicate microbially driven anaerobic oxidation of methane at or near the sediment water interface. Seismic-reflection profiles show chimney-like fluid pathways along the limbs and in the axis of the fold forming Kimki Ridge, and evidence of methane in shallow sediments can be traced into the adjacent Catalina Basin. A system of closely spaced faults located at the axis of the Kimki Ridge anticline may serve as pathways to allow fluid flow to the seafloor. Our data are consistent with other studies that suggest that transpression is an important component in the formation and localization of fluid seeps in a strike-slip setting, implying that seep formation may be a common occurrence at fault stepovers or transpressional bends in strike-slip systems.

California↗

USGS2013

Linkages between sea-ice coverage, pelagic-benthic coupling, and the distribution of spectacled eiders: observations in March 2008, 2009 and 2010, northern Bering Sea

Icebreaker-based sampling in the northern Bering Sea south of St. Lawrence Island in March of 2008, 2009, and 2010 has provided new data on overall ecosystem function early in the annual productive cycle. While water-column chlorophyll concentrations (<25 mg m −2 integrated over the whole water column) are two orders of magnitude lower than observed during the spring bloom in May, sea-ice algal inventories of chlorophyll are high (up to 1 g m −3 in the bottom 2-cm of sea-ice). Vertical fluxes of chlorophyll as measured in sediment traps were between 0.3 to 3.7 mg m −2 d −1 and were consistent with the recent deposition (days to weeks time scale) of chlorophyll to the surface sediments (0–25 mg m −2 present at 0–1 cm). Sediment oxygen respiration rates were lower than previous measurements that followed the spring bloom, but were highest in areas of known high benthic biomass. Early spring release of sedimentary ammonium occurs, particularly southeast of St. Lawrence Island, leading to bottom-water ammonium concentrations of >5 µM. These data, together with other physical, biological, and nutrient data are presented here in conjunction with observed sea-ice dynamics and the distribution of an apex predator, the Spectacled Eider (Somateria fischeri). Sea-ice dynamics in addition to benthic food availability, as determined by sedimentation processes, play a role in the distribution of spectacled eiders, which cannot always access the greatest biomass of their preferred bivalve prey. Overall, the data and observations indicate that the northern Bering Sea is biologically active in late winter, but with strong atmospheric and hydrographic controls. These controls pre-determine nutrient and chlorophyll distributions, water-column mixing, as well as pelagic-benthic coupling.

Deep-Sea Research Part II: Topical Studies in Ocea↗

USGS2023

Predicting daily river chlorophyll concentrations at a continental scale

Eutrophication is one of the largest threats to aquatic ecosystems and chlorophyll a measurements are relevant indicators of trophic state and algal abundance. Many studies have modeled chlorophyll a in rivers but model development and testing has largely occurred at individual sites which hampers creating generalized models capable of making broad-scale predictions. To address this gap, we compiled a large data set of chlorophyll a concentrations matched to other water quality, meteorological, and reach characteristic data for a diverse set of 82 streams and rivers across the United States. We used this data set and extreme gradient boosting, a tree-based machine learning algorithm, to predict daily chlorophyll a concentrations. Furthermore, we tested several practical considerations of broad-scale models, such as making predictions at sites not included in model training or the utility of in situ water quality data versus universally available remotely estimated model inputs. Predictions were very strongly correlated to observations when compared against a randomly withheld subset of days; however, the model had lower accuracy when applied to completely novel sites withheld from model training. Turbidity and total nitrogen were the two most important variables for predicting chlorophyll a . Although in situ variables improved modeled estimates and were identified as more important during model interpretation, using only remote inputs still resulted in highly correlated predictions with small bias. Testing a model across many sites allowed for identification of common variables relevant to chlorophyll a and highlighted several challenges for applying data-driven models to new sites or at larger spatial scales.

Water Resources Research↗

USGS2024

Assessing spatial variability of nutrients, phytoplankton, and related water-quality constituents in the California Sacramento–San Joaquin Delta at the landscape scale—2018 high resolution mapping surveys

Executive Summary This study examined the abundance and distribution of nutrients and phytoplankton in the tidal aquatic environments of the Sacramento–San Joaquin Delta (Delta) and Suisun Bay, comprising three spatial surveys conducted in May, July, and October of 2018 that used continuous underway high frequency sampling and measurements onboard a high-speed boat to characterize spatial variation across the extent of the Delta. The method used involves simultaneously collecting information about the concentration and spatial distribution of all major nutrient forms with analogous information about the major classes of phytoplankton and associated water-quality conditions. The results showed substantial variation across space and time, providing an unprecedented snapshot of the dynamic environmental processes that shape the ways nutrients interact with and affect aquatic habitats in the Delta. The purposes of this study were to improve our understanding of how hydrodynamics, landscape features, and aquatic primary productivity interact to drive nutrient cycling and transport in the Delta and to provide insights into the underlying processes most directly responsible for the conditions at the time of this study, and thus into the range of conditions that may be expected following the wide array of prospective future changes to the Delta. One major anticipated change at the time of this study was the planned upgrade to the Sacramento Regional Wastewater Treatment Plant, but the study also informs our understanding of potential effects from other changes to the Delta, such as those caused by other nutrient-management actions, flow actions, large-scale wetland restoration, drought, flood, levee failure, and changes to water management. Nutrient loading is the primary driver of nutrient concentrations in the Delta, but several other major drivers interact to shape their distribution and effects: geomorphology, hydrodynamics, landscape features, and aquatic productivity. Hydrodynamics affect timescales of transport and dilution of nutrient loads in the Delta. During transit through the system, channel geometry, tidal mixing, and water exports affect hydrodynamics in diverse ways that influence water-residence and transport times, thereby markedly affecting the range of times during which natural internal cycling can alter nutrient concentrations and forms. Channel geometry and location shape tidal energy and river currents into these observed dynamics. Interactions with Delta aquatic landscapes such as herbaceous tidal marsh, submerged aquatic vegetation, and large expanses of intertidal or subtidal sediments (all highly productive landscapes) exert demand on available nutrient supplies but can also simultaneously transform and generate nutrients. Finally, while phytoplankton require nutrients to sustain production and thus are a potential nutrient sink, the amount and form of nutrients also can influence the occurrence of harmful algal blooms (HABs) that adversely affect aquatic organisms as well as affect the occurrence of beneficial algal blooms that result in production of algae that are favorable for imperiled Delta pelagic aquatic food webs. The surveys revealed a complex mosaic of spatial variation, with nutrient concentrations varying from near zero to well above concentrations considered eutrophic; nutrient concentrations were more often related to the extent of hydrologic transport and mixing than to specific geographic locations or to specific landscape features. Similarly, the surveys identified phytoplankton abundance ranging from near detection to the level of large phytoplankton blooms, with large variation in phytoplankton community composition. Although the study occurred during a period of low bloom activity, phytoplankton productivity appeared to be the strongest potential sink for inorganic nutrients in the Delta, indicating that it is a larger control on nutrient concentrations and distribution than previously understood. Cycling and transformation within the water column only appeared to substantially lower total nutrient concentrations at the longest estimated transport timescales. Contrary to expectations, we did not observe substantial nutrient depletion near landscape-scale features such as open-water habitats, submerged aquatic vegetation beds, extensive wetlands, or exposed sediments, indicating that these habitat types did not act as major sinks for nutrients in the Delta during these surveys. These results indicated that nutrient reduction efforts may have the greatest effect on pelagic phytoplankton productivity in the more productive reaches of the Delta and estuary, but these effects are unlikely to be magnified by changes to nutrient loss within the Delta over conceivable changes in flow conditions, Delta water management actions, or large-scale wetland restoration activities. Nevertheless, local processes were shown to cause substantial loss, and thus integrating of nutrient effects with other indicators of aquatic habitat conditions will help inform planning future actions at specific sites. Finally, we note that the primary contribution of this study was intended to be the survey data themselves. Aside from the results highlighted in this report, the surveys are a benchmark against which future environmental change may be evaluated, including changes to nutrient management or water exports, drought, large-scale wetland restoration, and climate change. Further, although we highlight some of the main findings from the surveys in this report, the necessarily limited scope precludes examination of many topics for which these surveys may be highly informative. To facilitate the utility of these data to stakeholders, managers, and researchers, we have released the data online (Bergamaschi and others, 2020) and created an online data exploration portal ( https://ca.water.usgs.gov/bay-delta/2018-delta-wide-mapping-surveys.html ) where users may query the surveys in a variety of ways to test hypotheses, examine relationships, assess spatial trends, and download data. The data exploration portal is intended to be an immersive experience that allows users to gain greater understanding of the complex interactions that shape Delta aquatic environments. This report is intended as a companion to the portal, allowing the reader to challenge and further explore the highlighted findings. This study was a collaboration between the U.S. Geological Survey and the Delta Regional Monitoring Program, with additional funding provided from U.S. Geological Survey Cooperative Matching Funds Program.

California↗

USGS1976

An evaluation of methods for measuring algal growth

Algal growth was expressed as milligrams dry weight per litre with use of the electronic particle counter for determining cell number and cell volume. A gravimetric constant in milligrams dry weight per cubic micrometre was determined. This constant was applicable throughout the growth curve since there was a linear relationship between total cell weight and total cell volume. Cell volume must be considered in measuring growth because there is a change in average cell volume in addition to an increase in cell numbers throughout the growth curve. Chlorella vulgaris and Selenastrum capricornutum exhibited similar growth curves when growth was expressed as cells per litre or as milligrams dry weight per litre. Chlamydomonas reinhardtii appeared to have a lower algal growth potential when measured in cells per litre but had the same growth potential as C. vulgaris and S. capricornutum when expressed as milligrams dry weight per litre. The growth rate for Scenedesmus quadricauda was less than the other three, regardless of how the results were expressed. The image analysis system was used to count different types of algae in a mixed culture. C. reinhardtii , C. vulgaris , and Anacystis nidulans were not grossly distorted by the sample preparation method and could be distinguished from one another by variations in morphology. The counts could be separated by computing the ratio of area to length for each particle and by allowing the computer to sort and count each of the three types. Typical ratios ranged from 5 to 7 for G. reinhardtii , 2 to 4 C. vulgaris , and 0.2 to 1.3 for A. nidulans . The number of types to be counted in a mixture was limited only by the ability to apply shape factors without having an overlap between each type. Both the image analysis and electronic particle counter produced equal count and size measurements. Fluorescence was a sensitive measure of growth on a laboratory prepared medium since there was a logarithmic relationship between fluorescence and cells per millilitre for both C. vulgaris and S. capricornutum . Fluorescence measurements were not satisfactory for determining growth in samples of varying chemical composition (which occurs in natural samples) because the chlorophyll-to-cell ratio varied with media composition. This was especially pronounced with C. vulgaris .

Journal of Research of the U.S. Geological Survey↗

USGS2013

Burial and exhumation of temperate bedrock reefs as elucidated by repetitive high-resolution sea floor sonar surveys: Spatial patterns and impacts to species' richness and diversity

To understand how chronic sediment burial and scour contribute to variation in the structure of algal and invertebrate communities on temperate bedrock reefs, the dynamics of the substrate and communities were monitored at locations that experience sand inundation and adjacent areas that do not. Co-located benthic scuba-transect surveys and high-resolution swath-sonar surveys were completed on bedrock reefs on the inner shelf of northern Monterey Bay, CA, in early winter 2009, spring 2010, and summer 2010. Analysis of the sonar surveys demonstrates that during the 8 months over which the surveys were conducted, 19.6% of the study area was buried by sand while erosion resulted in the exposure of bedrock over 13.8% of the study area; the remainder underwent no change between the surveys. Substrate classifications from the benthic transect surveys correlated with classifications generated from the sonar surveys, demonstrating the capacity of high-resolution sonar surveys to detect burial of bedrock reefs by sediment. On bedrock habitat that underwent burial and exhumation, species' diversity and richness of rock-associated sessile and mobile organisms were 50–66% lower as compared to adjacent stable bedrock habitat. While intermediate levels of disturbance can increase the diversity and richness of communities, these findings demonstrate that burial and exhumation of bedrock habitat are sources of severe disturbance. We suggest that substrate dynamics must be considered when developing predictions of benthic community distributions based on sea floor imagery. These results highlight the need for predictive models of substrate dynamics and for a better understanding of how burial and exhumation shape benthic communities.

California↗

USGS2026

Groundwater nutrient contributions to surface water in the upper Maumee River basin

Harmful algal blooms triggered by nutrient loading have negatively affected Lake Erie water quality for decades, but the role groundwater plays in transporting nutrients to tributary streams is unclear. Here, we apply a multi-scale approach to investigate groundwater nitrogen (N) and phosphorus (P) dynamics at the field scale, along a groundwater flow path, and at the Maumee River basin scale. Unsaturated zone monitoring indicates that macropore flow is the primary mechanism for N and P leaching with nitrate and orthophosphate (OP) concentrations from macropore samplers more than double those from soil-matrix samplers. Shallow (< 4.5 m) groundwater nitrate concentrations indicate the timing of saturated-zone nitrate fluxes is crop dependent with more nitrate mobilized during the maize growing season whereas concentrations below soybeans can remain elevated (> 3 mg/L) through winter months. A three-end-member hydrograph analysis for the upper Maumee River basin indicates that tile drains transport most subsurface N and P with greater than 15,000 kg per day of nitrate transported between January and May. Orthophosphate concentrations in tile drainage at an edge-of-field site correlate well with concentrations in a nearby tributary of the Maumee River. While runoff is the dominant source of OP loading, tile drainage and groundwater discharge contributed an estimated 36% of OP load during a 2018–2022 analysis period with most subsurface loading occurring between January and March. These findings highlight how best management practices (such as cover crops and tile drainage control structures) can be used to help limit leaching and tile effluent during the nongrowing season.

Indiana↗

USGS2023

Agricultural conservation practices could help offset climate change impacts on cyanobacterial harmful algal blooms in Lake Erie

Harmful algal blooms (HABs) are a recurring problem in many temperate large lake and coastal marine ecosystems, caused mainly by anthropogenic eutrophication. Implementation of agricultural conservation practices (ACPs) offers a means to reduce non-point source nutrient runoff and mitigate HABs. However, the effectiveness of ACPs in a changing climate remains uncertain. We used an integrated biophysical modeling approach to predict how Lake Erie cyanobacterial HAB severity (bloom biomass) may change under several climate and ACP implementation scenarios, using western Lake Erie and its largely agricultural watershed as our study system. An ensemble of general circulation model projections was used to drive spatially explicit land use and hydrology models of the Maumee River watershed, the output of which informed a predictive model of Lake Erie HAB severity. Results show that, in the absence of changes in ACPs, the frequency of severe HABs is projected to increase during coming decades, owing to increased inputs of nutrients from the watershed. These anticipated increases are due to increased total precipitation and more frequent higher-magnitude rainfall events. While further implementation of ACPs appears capable of reducing severe HAB events, widespread implementation would be necessary to reduce HAB severity below current management targets. This study highlights how continued climate change will only exacerbate the need for land management practices that can reduce nutrient runoff in agriculturally dominated ecosystems, such as Lake Erie. It also shows how interdisciplinary, biophysical modeling approaches can help identify strategies to mitigate HABs in the face of anthropogenic stressors.

Lake Erie↗

USGS2010

Algal blooms and "Marine snow": Mechanisms that enhance preservation of organic carbon in ancient fine-grained sediments

Combined petrographic and geochemical methods are used to investigate the microfabrics present in thin sections prepared from representative organic carbon-rich mudstones collected from three successions (the Kimmeridge Clay Formation, the Jet Rock Member of the Whitby Mudstone Formation, and the pebble shale and Hue Shale). This study was initiated to determine how organic carbon-rich materials were being delivered to the sediment–water interface, and what happened to them after deposition, prior to deep burial. Analyses of the fabrics present shows that they exhibit many common attributes. In particular they are all: (1) highly heterogeneous on the scale of a thin section, (2) organized into thin beds (< 10 mm thick) composed mainly of mineral mixtures of fine-grained siliciclastic detritus and carbonate materials, and (3) contain significant concentrations of organic carbon, much of which is organized into laminasets that contain abundant organomineralic aggregates and pellets. In addition, framboidal pyrite (range of sizes from < 20 μm to < 1 μm) and abundant agglutinated foraminifers are present in some units. The individual beds are commonly sharp-based and overlain by thin, silt lags. The tops of many of the beds have been homogenized and some regions of the pelleted laminasets contain small horizontal burrows. The organomineralic aggregates present in these mudstones are interpreted to be ancient examples of marine snow. This marine snow likely formed in the water column, particularly during phytoplankton blooms, and was then transported rapidly to the seafloor. The existence of the thin beds with homogenized tops and an in-situ infauna indicates that between blooms there was sufficient oxygen and time for a mixed layer to develop as a result of sediment colonization by diminutive organisms using either aerobic or dysaerobic metabolic pathways. These textures suggest that the constituents of these mudstones were delivered neither as a continuous rain of sediment nor were the bottom waters persistently anoxic. In addition, the presence of thin lags and sharp-based beds suggests that the seafloor was being episodically reworked during deposition. These fabrics indicate that conditions in the water columns and at the seafloors while these rocks were being deposited were very dynamic, and episodic fluxes of high concentrations of organic carbon to the seafloor, during phytoplankton blooms, likely enhanced preservation of organic carbon.

Journal of Sedimentary Research↗

USGS2020

Dietary patterns in black abalone (Haliotis cracherodii Leach, 1814) as indicated by observation of drift algal and seagrass capture at San Nicolas Island, California USA, 1982‒2019

Black abalone Haliotis cracherodii Leach, 1814 are known to feed on drift plant macrodetritus moved about in the intertidal zone by waves and currents. Drift capture is a trait shared by at least several other abalone species. Drift materials are entrapped beneath the anterior foot and held for ingestion. The quantitative significance of feeding on entrapped drift macrodetritus for black abalone is unknown. Furthermore, there are no published data on the extent to which local and mesoscale spatial distributions of source plant populations influence the composition of drift plant material in black abalone diet as acquired by entrapment. From February 1982 through March 2019, occurrences of macrodetrital entrapment by black abalone were observed in nine rocky intertidal study plots, with a summed surface area of 2,054 m 2 , on the periphery of San Nicolas Island (SNI), California (Island centroid at ∼33.25°, –119.50°). A small preliminary survey and 27 complete surveys were performed during the study period (mean of ∼1.4 y between complete surveys). During the study, more than 1.5 × 10 5 black abalone were examined. The total likely included repeated observations of many individuals as a result of the known longevity and limited mobility of the species. Of those observed, ∼1.65 × 10 3 black abalone were recorded as apparently ingesting entrapped items. Frequency data were dominated (∼95% of all records) by three species of kelp Macrocystis pyrifera (Linnaeus) C. Agardh; commonly known as “giant kelp”, Egregia menziesii (Turner), and Eisenia arborea Areschoug. Of those, giant kelp was the most frequently observed entrapped category (∼76%). Living, attached giant kelp is rarely observed in intertidal habitats at SNI, and it follows that utilization of giant kelp by black abalone requires physical importation of the kelp from other locations. Frequencies of occurrence of giant kelp entrapment by individual study site were clearly associated with the relative surface canopy sizes and persistence patterns of offshore kelp forests adjacent (≤2 km) to the respective study sites. The pattern suggests that subsidies of drift giant kelp to black abalone diet involve mesoscale physical processes largely proximate to SNI but probably not subsidies from more distant locations such as other islands or the California mainland. Utilization of other frequently recorded kelps as food by black abalone likely involves spatial subsidies as well, but on smaller scales of distance (∼10–100 m for E. arborea ; ∼0–100 m for E. menziesii ). In the context of the imperiled status of black abalone, recovery actions may include outplants of captive-reared animals or transplantation of wild animals from other populations. For such actions, data from SNI suggest a need for consideration of scales of separation among release locations and nearby populations of the three apparently predominant kelp species in black abalone diet.

California↗

USGS2004

Holocene reef accretion: southwest Molokai, Hawaii, U.S.A.

Two reef systems off south Molokai, Hale O Lono and Hikauhi (separated by only 10 km), show strong and fundamental differences in modern ecosystem structure and Holocene accretion history that reflect the influence of wave-induced near-bed shear stresses on reef development in Hawaii. Both sites are exposed to similar impacts from south, Kona, and trade-wind swell. However, the Hale O Lono site is exposed to north swell and the Hikuahi site is not. As a result, the reef at Hale O Lono records no late Holocene net accretion while the reef at Hikauhi records consistent and robust accretion over late Holocene time. Analysis and dating of 24 cores from Hale O Lono and Hikauhi reveal the presence of five major lithofacies that reflect paleo-environmental conditions. In order of decreasing depositional energy they are: (1) coral-algal bindstone; (2) mixed skeletal rudstone; (3) massive coral framestone; (4) unconsolidated floatstone; and (5) branching coral framestone-bafflestone. At Hale O Lono, 10 cores document a backstepping reef ranging from ∼ 8,100 cal yr BP (offshore) to ∼ 4,800 cal yr BP (nearshore). A depauperate community of modern coral diminishes shoreward and seaward of ∼ 15 m depth due to wave energy, disrupted recruitment activities, and physical abrasion. Evidence suggests a change from conditions conducive to accretion during the early Holocene to conditions detrimental to accretion in the late Holocene. Reef structure at Hikauhi, reconstructed from 14 cores, reveals a thick, rapidly accreting and young reef (maximum age ∼ 900 cal yr BP). Living coral cover on this reef increases seaward with distance from the reef crest but terminates at a depth of ∼ 20 m where the reef ends in a large sand field. The primary limitation on vertical reef growth is accommodation space under wave base, not recruitment activities or energy conditions. Interpretations of cored lithofacies suggest that modern reef growth on the southwest corner of Molokai, and by extension across Hawaii in general, is controlled by wave-induced near-bed shear stress related to refracted North Pacific swell. Holocene accretion patterns here also reflect the long-term influence of wave-induced near-bed shear stress from north swell during late Holocene time. This finding is consistent with other studies (e.g., Grigg 1998; Cabioch et al. 1999) that reflect the dominance of swell energy and sea level in controlling modern and late Holocene accretion elsewhere in Hawaii and across the Pacific and Indian oceans. Notably, however, this result is refined and clarified for Hawaii in the hypothesis of Rooney et al. (2003) stating that enhancement of the El Niño Southern Oscillation beginning approximately 5000 years ago led to increased north swell energy and signaled the end to net accretion along exposed coastlines in Hawaii. The exposure of Hale O Lono to north swell and the age of sea floor there (ca. 4,800 cal yr BP), coupled with the lack of north swell incidence at Hikauhi and the continuous accretion that has occurred there over the last millennium, strongly supports the ENSO reef hypothesis as outlined by Rooney et al. (2003). Other factors controlling Holocene reef accretion at the study site are relative sea-level position and rate of rise, and wave sheltering by Laau Point. Habitat suitable for reef accretion on the southwest shore of Molokai has shrunk throughout the Holocene.

Hawai'i↗

USGS2014

Investigating the importance of sediment resuspension in Alexandrium fundyense cyst population dynamics in the Gulf of Maine

Cysts of Alexandrium fundyense , a dinoflagellate that causes toxic algal blooms in the Gulf of Maine, spend the winter as dormant cells in the upper layer of bottom sediment or the bottom nepheloid layer and germinate in spring to initiate new blooms. Erosion measurements were made on sediment cores collected at seven stations in the Gulf of Maine in the autumn of 2011 to explore if resuspension (by waves and currents) could change the distribution of over-wintering cysts from patterns observed in the previous autumn; or if resuspension could contribute cysts to the water column during spring when cysts are viable. The mass of sediment eroded from the core surface at 0.4 Pa ranged from 0.05 kg m −2 near Grand Manan Island, to 0.35 kg m −2 in northern Wilkinson Basin. The depth of sediment eroded ranged from about 0.05 mm at a station with sandy sediment at 70 m water depth on the western Maine shelf, to about 1.2 mm in clayey–silt sediment at 250 m water depth in northern Wilkinson Basin. The sediment erodibility measurements were used in a sediment-transport model forced with modeled waves and currents for the period October 1, 2010 to May 31, 2011 to predict resuspension and bed erosion. The simulated spatial distribution and variation of bottom shear stress was controlled by the strength of the semi-diurnal tidal currents, which decrease from east to west along the Maine coast, and oscillatory wave-induced currents, which are strongest in shallow water. Simulations showed occasional sediment resuspension along the central and western Maine coast associated with storms, steady resuspension on the eastern Maine shelf and in the Bay of Fundy associated with tidal currents, no resuspension in northern Wilkinson Basin, and very small resuspension in western Jordan Basin. The sediment response in the model depended primarily on the profile of sediment erodibility, strength and time history of bottom stress, consolidation time scale, and the current in the water column. Based on analysis of wave data from offshore buoys from 1996 to 2012, the number of wave events inducing a bottom shear stress large enough to resuspend sediment at 80 m ranged from 0 to 2 in spring (April and May) and 0 to 10 in winter (October through March). Wave-induced resuspension is unlikely in water greater than about 100 m deep. The observations and model results suggest that a millimeter or so of sediment and associated cysts may be mobilized in both winter and spring, and that the frequency of resuspension will vary interannually. Depending on cyst concentration in the sediment and the vertical distribution in the water column, these events could result in a concentration in the water column of at least 10 4 cysts m −3 . In some years, resuspension events could episodically introduce cysts into the water column in spring, where germination is likely to be facilitated at the time of bloom formation. An assessment of the quantitative effects of cyst resuspension on bloom dynamics in any particular year requires more detailed investigation.

Bay Of Fundy;Grand Manan Island;Gulf Of Maine;Jord↗