Geology Reports⌕ Search
Home/Archive/USGS

USGS · 70025175

Sediment DIN fluxes and preferential recycling of benthic microalgal nitrogen in a shallow macrotidal estuary

C. Tobias·A. Giblin·J. McClelland·J. Tucker·B. Peterson
View original source ↗Export metadata ↓

Abstract

Sediment -water fluxes of NH 4 + , NO 3 - , dissolved inorganic carbon, and O 2 were measured in cores collected from the upper Rowley River estuary , Massachusetts, and used to calculate rates of organic nitrogen (N) mineralization, nitrification, and coupled and direct denitrification (DNF). The cores contained 15 N label in benthic microalgae (BMA) and in NO 3 - in the overlying water as a result of an ongoing whole- estuary 15 NO 3 - enrichment study (NISOTREX II). The tracer allowed for estimation of gross NO 3 - regeneration in sediments and the contribution of BMA derived N to total mineralization. The mean mineralization rate between sites was 16.0 ± 2.0 mmol N m -2 d -1 . Approximately 13 to 56% of the mineralized N was nitrified at rates ranging from 1.8 to 10.1 mmol N m -2 d -1 . Total denitrification was dominated by direct DNF (3.6 mmol N m -2 d -1 ) furthest upstream, where NO 3 - concentrations were highest. Coupled DNF was most important (8.0 mmol N m -2 d -1 ) in the sediments with high nitrification and low water column NO 3 - . A gross NO 3 - flux from sediments to water of 0.9 to 2.1 mmol N m -2 d -1 was estimated from the isotope dilution of δ 15 NO 3 - in the overlying water of the cores. The isotope dilution seen in the cores was also detected as a deviation from conservative δ 15 NO 3 - mixing along estuarine transects. Incorporation of this NO 3 - regeneration into the DNF calculations effectively increased the estimate of direct DNF by up to 50% and decreased the coupled DNF estimate by up to 220%. Increasing δ 15 NH 4 + in the water of the cores indicated that the 15 N-labelled BMA were preferentially mineralized over bulk sediment organic N. Additional 15 N enrichments in the sediment bacterial biomarker diaminopimelic acid showed a link among 15 N-labeled BMA, active bacteria, and 15 NH 4 + released to the overlying water. Based on δ 15 NH 4 + enrichments in the cores, BMA accounted for approximately 50 to 100% of the N mineralized. An isotopic enrichment of δ 15 NH 4 + above background in the estuary was observed at a magnitude consistent with the core-based rates of BMA mineralization. These results provide further evidence that BMA are not unidirectional sinks for water column-dissolved organic nitrogen , but instead act to turn over N between sediments and estuarine water on the scale of days.

Explore related subjects

Marine Ecology Progress SeriesArticle

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

C. Tobias, A. Giblin, J. McClelland, J. Tucker, B. Peterson. 2003. Sediment DIN fluxes and preferential recycling of benthic microalgal nitrogen in a shallow macrotidal estuary. https://doi.org/10.3354/meps257025

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2025

Detection of the Diadema antillarum scuticociliatosis Philaster clade on sympatric metazoa, plankton, and abiotic surfaces and assessment for its potential reemergence

A ciliate belonging to the Diadema antillarum scuticociliatosis (DaSc)-associated Philaster clade (DaScPc) caused catastrophic long-spined urchin mass mortality in spring and summer of 2022. The ciliate can be grown in culture in both the presence and absence of D. antillarum tissues, suggesting that it may persist outside its host by consuming microorganisms or dissolved organic nutrients. We hypothesized that DaScPc was present outside its host during and after mass mortality and absent prior to 2022. We examined DaScPc in DNA extracted from 500 swabs of sym- patric metazoa and abiotic surfaces, and plankton samples, collected at 35 sites in the Caribbean in 2022 and 2023. DaScPc was detected on corals, turf algae, and a sponge, predominantly at sites with active or prior DaSc. We examined whether it was present prior to 2022 by surveying extracted DNA from Caribbean corals and water collected near corals by PCR and by mining publicly available transcriptomes and metagenomes for DaScPc rRNAs. These efforts yielded no DaScPc genes. We further hypothesized that DaScPc may recruit to the specific corals detected in field surveys, and that these may then infect naïve hosts. A mesocosm experiment to test DaScPc recruitment suggested that, while it recruited to corals, it did so inconsistently between coral species. Incubation of corals that recruited DaScPc with naïve urchins yielded inconclusive results since urchins died without characteristic DaSc signs. Overall, our results suggest that DaScPc may occur outside its urchin host, and that it may have been absent in the region prior to 2022.

Florida↗
USGS2024

Photogrammetry-based body condition for monitoring an Arctic marine mammal experiencing habitat loss

Monitoring animal body condition can provide insight on population responses to environmental change. Pacific walruses ( Odobenus rosmarus divergens ) are experiencing loss of their sea ice habitat which has decreased the time that females spend foraging during a critical period of pregnancy and lactation. Here we investigate the potential for body condition to track demographic change and be monitored via two-dimensional aerial imagery by (1) examining whether walrus somatic growth and body mass data tracked estimated historic demographic changes, (2) collecting morphometric and body mass data and aerial imagery of walruses in human care to determine if sex, age group, and body size and condition can be determined from imagery, and (3) examining aerial imagery from a large coastal haulout used primarily by females and young to estimate potential sample sizes of measurable walruses. Body mass and growth in body length decreased between the last 1970s and early 1980s concurrent with a period when the population apparently approached carrying capacity and subsequently declined. Measures from aerial imagery (1) accurately distinguished reproductive age females from subadults and adult males and (2) enabled body mass estimates with 6-7% error using either areal footprint or a combination of length and width. We found a mean of 216 ± 77 walruses appropriately positioned for measurement from aerial surveys of the haulout enabling measurements of ≥7000 individuals annually via repeated daily imagery. Our results suggest that body mass of reproductive age females and growth of dependent young may be useful indicators to augment monitoring of the Pacific walrus population and can be achieved via non-invasive aerial imagery collections.

Alaska↗
USGS2024

Assessing the population consequences of disturbance and climate change for the Pacific walrus

Climate change and anthropogenic disturbance are increasingly affecting wildlife at a global scale. Predicting how varying types and degrees of disturbance may interact to influence population dynamics is a key management challenge. Population consequences of disturbance (PCoD) models provide a framework to link effects of anthropogenic disturbance on an individual’s behavior and physiology to population-level changes. In the present study, we develop a Pacific walrus ( Odobenus rosmarus divergens ) PCoD model to encompass the population-level effects of both anthropogenic disturbance and climate change. As the Arctic becomes increasingly ice-free, walruses spend more time at coastal (vs. ice-based) haulouts, from which they must expend more energy to reach foraging areas and where they have an elevated risk of mortality. Concurrently, sea ice loss is increasing the anthropogenic footprint in the Arctic (e.g. fisheries, shipping, energy exploration), which creates additional disturbance. We applied the PCoD model to 4 scenarios (ranging from optimistic to pessimistic) which incorporate different global sea ice model projections along with varying degrees of anthropogenic disturbance. All scenarios indicated a decline in Pacific walrus vital rates by the end of the 21st century, but our results demonstrated that the intensity of that decline could be mitigated by global efforts to reduce carbon emissions, along with local management and conservation efforts to protect important coastal haulouts and foraging grounds. In summary, we introduce a flexible PCoD modeling framework in a novel context which will prove useful to researchers studying species threatened by rapid environmental change.

Marine Ecology Progress Series↗