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At least 91 records · Page 5Linked to original sources
USGS2022

Simple relationships between residence time and annual nutrient retention, export, and loading for estuaries

Simple mathematical models are derived from mass balances for water and transported substance to provide insight into the relationships between import, export, transport, and internal removal for nonconservative substances in an estuary. Extending previous work, our models explicitly include water and substance inputs from the ocean and are expressed in terms of timescales (i.e., mean residence time and the timescale for net removal). Steady-state, timescale-based expressions for ratios of export to import, retention to import, and net export to loading, as well as for loading and annually averaged concentration, are provided. The net export : loading model explains the underlying mechanisms for a well-known empirical relationship between fractional net export and residence time derived by other authors. Although our simplified models are first-order approximations, the relative importance of physical and biochemical processes influencing export or retention of a substance can be assessed using mean residence time and the timescale for net removal. Assumptions employed in deriving the simplified models (e.g., well-mixed, dynamic steady state) may not be met for real estuaries. However, model application to Chesapeake Bay for 1985–2012 demonstrates that interannual variations in total nitrogen (TN) net export : loading can be evaluated, and annual nutrient loadings can be well estimated using numerically modeled time-varying mean residence time, observation-based mean concentration, freshwater inflow, and an appropriately estimated removal timescale. Our model shows that net fractional export of TN loading ranges from 0.3 to 0.5 over the 28-yr period. The models can be employed for other substances and water bodies if the underlying assumptions are applicable.

Limnology and Oceanography↗
USGS2022

Warming in the upper San Francisco Estuary: Patterns of water temperature change from five decades of data

Temperature is a key controlling variable from subcellular to ecosystem scales. Thus, climatic warming is expected to have broad impacts, especially in economically and ecologically valuable systems such as estuaries. The heavily managed upper San Francisco Estuary supplies water to millions of people and is home to fish species of high conservation, commercial, and recreational interest. Despite a long monitoring record (> 50 yr), we do not yet know how water temperatures have already changed or how trends vary spatially or seasonally. We fit generalized additive models on an integrated database of discrete water temperature observations to estimate long-term trends with spatio-seasonal variability. We found that water temperatures have increased 0.017°C yr −1 on average over the past 50 yr. Rates of temperature change have varied over time, but warming was predominant. Temperature increases were most widespread in the late-fall to winter (November to February) and mid-spring (April to June), coinciding with the winter development of juvenile Chinook salmon and spring spawning window of the endangered delta smelt. Warming was fastest in the northern regions, a key fish migration corridor with important tidal wetland habitat. However, no long-term temperature trends were detected in October and were only observed in some regions in May, July, and August. These results can help identify optimal areas for restoration or refugia to buffer the effects of a warming climate, and the methods can be leveraged to understand the spatiotemporal variability in climate warming patterns in other aquatic systems.

California↗
USGS2022

Long-term change in metabolism phenology in north temperate lakes

The phenology of dissolved oxygen (DO) dynamics and metabolism in north temperate lakes offers a basis for comparing metabolic cycles over multi-year time scales. Although proximal control over lake DO can be attributed to metabolism and physical processes, how those processes evolve over decades largely remains unexplored. Metabolism phenology may reveal the importance of coherence among lakes and facilitate general conclusions about the controls on lake metabolism at regional scales. We developed a Bayesian modeling framework to estimate DO concentrations and metabolism in eight lakes in contrasting landscapes in Wisconsin, USA. We identify the DO and metabolism phenologies for each lake, and use those to compare how decadal patterns relate to trophic state and landscape setting. We show that lakes can be categorized by their hypolimnetic oxygen consumption dynamics, with oligotrophic lakes having a diverse set of patterns and eutrophic lakes having uniform trends of increased oxygen consumption over the last decade. Metabolism phenology is likewise diverse for oligotrophic lakes, whereas eutrophic lakes in southern Wisconsin share consistent long-term patterns of metabolic trends and seasonal DO consumption highlighting the importance of trophic state driving metabolism. Eutrophic lakes had higher magnitudes and more seasonal variation in net ecosystem production in contrast to oligotrophic lakes. Generally, long-term metabolic trends of north temperate lakes suggest a limited influence of climate on lake metabolism and that temporal coherence of long-term metabolism change is driven primarily by the landscape setting.

Wisconsin↗
USGS2022

Predicting larval alewife transport in Lake Michigan using hydrodynamic and Lagrangian particle dispersion models

Several species of fish in large lakes and marine environments have a pelagic larval stage, and are subject to variable transport that can ultimately regulate survival and recruitment success. Alewife, Alosa pseudoharengus , are subject to transport by complex coastal currents during their pelagic larval stage (~ 30 d). We assessed backward-trajectory simulations, consisting of a Lagrangian particle dispersion model linked to the Finite Volume Community Ocean Model, to estimate likely hatch locations of aged larval alewife collected from locations on both the eastern and western sides of Lake Michigan during July 2015. We used four deployments of three satellite-tracked drifter buoys in coastal waters to assess model skill in estimating the origin of a drifter from its final location. We found that the trajectories of drifters varied greatly, depending on wind events and associated coastal transport processes, including upwelling/downwelling and coastal jet currents. In 2 of 12 cases, the backward trajectory simulations failed to predict the drifter origin, associated with transport of 170 km in a narrow coastal jet current. In the remaining 10 cases, the known drifter origin was within 3.5 km of the spatial patch of predicted possible origins for a scenario of horizontal diffusivity (188 m 2 s −1 ) consistent with the offshore model grid resolution. Modeled backward trajectories estimated that alewife originated from the same side of the lake where they were collected, within ~ 100 km of the collection site. Our paper demonstrates the utility of hydrodynamic models to estimate a region of origin for aged larval fish.

Lake Michigan↗
USGS2022

Multiproxy paleolimnological records provide evidence for a shift to a new ecosystem state in the Northern Great Plains, USA

Wetlands in the Prairie Pothole Region of the North American Northern Great Plains perform multiple ecosystem services and are biodiversity hotspots. However, climatological changes can result in sudden shifts in these important ecosystems. For example, marked increases in precipitation in the last few decades have resulted in a widespread shift in wetlands across the Prairie Pothole Region to a new ecohydrological state. We used multiproxy analyses (diatom community composition and invertebrate stable isotopes) of 210 Pb-dated sediment cores from two adjacent, but morphologically and hydrologically different, prairie-pothole wetlands to assess the effects of hydroclimatic variability on these wetland ecosystems. Our results provide evidence that the recent ecohydrological shift in the region's wetlands is unprecedented over the past ca. 178 yr. Oxygen stable isotopes in chironomid head capsules provide a record of paleohydrology changes. The most recent sediments (i.e., those deposited after the state shift) from both wetlands revealed novel changes in diatom communities that differed greatly from earlier community compositions. In addition, a depleted signal in deuterium and 13 C carbon stable isotopes observed in chironomid head capsules and Daphnia ephippia, respectively, after 1993 is likely related to an increase in methane production in these wetlands. Our study highlights the importance of considering basin morphometry including whether a wetland has an overflow point, and multiple biological indicators to study climate-change influences on freshwater ecosystems. Research using these techniques can lead to an improved understanding of recent ecosystem shifts, an understanding that will be essential for future climate-change adaptation and mitigation in this ecologically important region.

North Dakota↗
USGS2022

Nonlinear multidecadal trends in organic matter dynamics in Midwest reservoirs are a function of variable hydroclimate

Dissolved organic matter (DOM) and particulate organic matter (POM) can influence biogeochemical processes in aquatic systems. An understanding, however, of the source, composition, and processes driving inland reservoir organic matter (OM) cycling at a regional scale over the long term is currently unexplored. Here, we quantify decadal patterns (> 20 yr) of DOM quantity and composition and POM in 40 reservoirs in the midcontinent United States. We built 184 Random Forest models to identify how the relative influence of watershed characteristics and limnological parameters on OM dynamics may vary over time and in synchrony with hydroclimatic anomalies. The reservoir OM quantity and composition varied nonmonotonically through time and in contrast to lake browning observed in the northern hemisphere. Reservoir DOM composition switched from humic and aromatic during wet summers to aliphatic, potentially autochthonous DOM during particularly prolonged dry summers in the mid-2000s. The shift in reservoir DOM quantity and composition could be attributed to the change in time-varying control of watershed and limnological factors mediated by the hydroclimatic conditions. Watershed control (e.g., percent crops) was predominant during wet summers, while the effect of reservoir morphology (e.g., maximum depth) and water quality parameters (e.g., Secchi depth, chlorophyll a ) were evident during dry summers. Thus, future predictions of drier conditions may promote “greening” with negative implications for reservoir water quality and treated drinking water. Considering the nonlinear nature of reservoir OM dynamics and its controls will help to better mitigate water quality issues in these constructed systems increasingly impacted by global changes.

Missouri↗
USGS2023

Glacial meltwater and sediment resuspension can be important sources of dissolved and total dissolvable aluminum and manganese to coastal ocean surface waters

The supply of aluminum (Al) and manganese (Mn) to the Gulf of Alaska from coastal sources is poorly constrained. Here, we investigate the seasonality of sources to better constrain Al and Mn cycling in the coastal Gulf of Alaska region and add to our understanding of seasonal and interannual inputs. We examine Mn and Al behavior over the shelf to distinguish between redox-induced release of dissolved trace metals (i.e., diffusion from sediments), sediment resuspension, and meltwater release. Data suggest that, prior to the onset of stratification in the spring, shelf sediment resuspension from deep mixing is an important mechanism for trace metal delivery to surface waters. As spring and summer ensue, increased meltwater discharge coupled with increased surface water temperatures result in stratification of the water column within the coastal Gulf of Alaska, and meltwater becomes a more important source of Al and Mn to the surface waters. The limited data available suggest that a redox-driven flux of Mn from shelf sediments is not as important as the meltwater flux during the summer. In addition, dissolved trace metal concentrations in meltwater-influenced plumes over the shelf exhibit conservative mixing, while particulate trace metal concentrations do not behave conservatively. This indicates that there are different physical controls (particle settling vs. mixing) on the spatial distributions of dissolved and particulate Al and Mn in coastal waters, the manifestation of which are likely highly variable and dependent on the trace metal composition of the river and the hydrodynamics governing this interaction at any given time.

Alaska↗
USGS2023

Spatial and temporal variability in summertime dissolved carbon dioxide and methane in temperate ponds and shallow lakes

Small waterbodies have potentially high greenhouse gas emissions relative to their small footprint on the landscape, although there is high uncertainty in model estimates. Scaling their carbon dioxide (CO 2 ) and methane (CH 4 ) exchange with the atmosphere remains challenging due to an incomplete understanding and characterization of spatial and temporal variability in CO 2 and CH 4 . Here, we measured partial pressures of CO 2 ( p CO 2 ) and CH 4 ( p CH 4 ) across 30 ponds and shallow lakes during summer in temperate regions of Europe and North America. We sampled each waterbody in three locations at three times during the growing season, and tested which physical, chemical, and biological characteristics related to the means and variability of p CO 2 and p CH 4 in space and time. Summer means of p CO 2 and p CH 4 were inversely related to waterbody size and positively related to floating vegetative cover; p CO 2 was also positively related to dissolved phosphorus. Temporal variability in partial pressure in both gases weas greater than spatial variability. Although sampling on a single date was likely to misestimate mean seasonal p CO 2 by up to 26%, mean seasonal p CH 4 could be misestimated by up to 64.5%. Shallower systems displayed the most temporal variability in p CH 4 and waterbodies with more vegetation cover had lower temporal variability. Inland waters remain one of the most uncertain components of the global carbon budget; understanding spatial and temporal variability will ultimately help us to constrain our estimates and inform research priorities.

Limnology and Oceanography↗
USGS2023

Mountain glaciers influence biogeochemical and ecological characteristics of high-elevation lakes across the northern Rocky Mountains, USA

Mountain glaciers are retreating rapidly due to climate change, leading to the formation of downstream lakes. However, little is known about the physical and biogeochemical conditions in these lakes across a range of glacial influence. We surveyed alpine lakes fed by both glacial and snowpack meltwaters and those fed by snowpack alone to compare nutrient concentrations, stoichiometry, water clarity, chlorophyll, and zooplankton communities. Total phosphorus (TP) and soluble reactive phosphorus were two times higher in glacial lakes than in non-glacial lakes, while nitrate concentrations were three times higher. However, organic carbon concentrations in glacial lakes were two times lower than in non-glacial lakes. The carbon-to-phosphorus ratio and the nitrogen-to-phosphorus ratio of lake seston increased with water clarity in glacial lakes, suggesting that turbidity from glacial flour increases light limitation and increases stoichiometric food quality for zooplankton in newly formed lakes. However, chlorophyll a concentrations did not differ between lake types. Through structural equation modeling, we found that glaciers exhibit a bidirectional association with nitrate and TP concentrations, perhaps mediated through landscape vegetation and lake clarity. Zooplankton communities in high-turbidity glacial lakes were largely composed of cyclopoid copepods and rotifers (i.e., non-filter feeders), while non-glacial lakes tended to be dominated by calanoid copepods and cladocerans (i.e., filter feeders). Our results show that glacier-influenced lakes have biogeochemical and ecological characteristics distinct from snow-fed mountain lakes. Sustained studies are needed to assess the dynamics of these unique features as the influence of the alpine cryosphere fades under ongoing climate change.

Montana↗
USGS2023

A continuous classification of the 476,697 lakes of the conterminous US based on geographic archetypes

A variety of classification approaches are used to facilitate understanding, prediction, monitoring, and the management of lakes. However, broad-scale applicability of current approaches is limited by either the need for in situ lake data, incompatibilities among approaches, or a lack of empirical testing of approaches based on ex situ data. We developed a new geographic classification approach for 476,697 lakes ≥ 1 ha in the conterminous U.S. based on lake archetypes representing end members along gradients of multiple geographic features. We identified seven lake archetypes with distinct combinations of climate, hydrologic, geologic, topographic, and morphometric properties. Individual lakes were assigned weights for each of the seven archetypes such that groups of lakes with similar combinations of archetype weights tended to cluster spatially (although not strictly contiguous) and to have similar limnological properties (e.g., concentrations of nutrients, chlorophyll a (Chl a ), and dissolved organic carbon). Further, archetype lake classification improved commonly measured limnological relationships (e.g., between nutrients and Chl a ) compared to a global model; a discrete archetype classification slightly outperformed an ecoregion classification; and considering lakes as continuous mixtures of archetypes in a more complex model further improved fit. Overall, archetype classification of US lakes as continuous mixtures of geographic features improved understanding and prediction of lake responses to limnological drivers and should help researchers and managers better characterize and forecast lake states and responses to environmental change.

conterminous United States↗
USGS2024

Deep learning of estuary salinity dynamics is physically accurate at a fraction of hydrodynamic model computational cost

Salinity dynamics in the Delaware Bay estuary are a critical water quality concern as elevated salinity can damage infrastructure and threaten drinking water supplies. Current state-of-the-art modeling approaches use hydrodynamic models, which can produce accurate results but are limited by significant computational costs. We developed a machine learning (ML) model to predict the 250 mg L −1 Cl − isochlor, also known as the “salt front,” using daily river discharge, meteorological drivers, and tidal water level data. We use the ML model to predict the location of the salt front, measured in river miles (RM) along the Delaware River, during the period 2001–2020, and we compare predictions of the ML model to the hydrodynamic Coupled Ocean–Atmosphere-Wave-Sediment Transport (COAWST) model. The ML model predicts the location of the salt front with greater accuracy (root mean squared error [RMSE] = 2.52 RM) than the COAWST model does (RMSE = 5.36); however, the ML model struggles to predict extreme events. Furthermore, we use functional performance and expected gradients, tools from information theory and explainable artificial intelligence, to show that the ML model learns physically realistic relationships between the salt front location and drivers (particularly discharge and tidal water level). These results demonstrate how an ML modeling approach can provide predictive and functional accuracy at a significantly reduced computational cost compared to process-based models. In addition, these results provide support for using ML models in operational forecasting, scenario testing, management decisions, hindcasting, and resulting opportunities to understand past behavior and develop hypotheses.

Limnology and Oceanography↗
USGS2024

Sight and blindness: The relationship between ostracod eyes, water depth, and light availability in the Arctic Ocean

Eye loss has been a long-standing interest in evolutionary biology. Many organisms that inhabit environments without light penetration, for example the deep sea, exhibit eye loss and thus become blind. However, water-depth distribution of eyes in marine organisms is poorly understood. Ostracods are widely distributed crustaceans, and many sighted marine ostracods have eye tubercles (lenses) on their shells. Since eye tubercles are visible on the shells illustrated in much literature, it is easy to determine their presence or absence via a literature survey. Here, we used a large Arctic-wide ostracod census dataset (Arctic Ostracode Database) to calculate the eye index (the percentage of species with eyes), and compare them with water depth and light availability. As water depth increases, eye index values decrease and become constantly zero in water deeper than 1000 m. Similar decline of sighted species with increasing depth is also known in isopods and amphipods, suggesting that it may be common in other crustaceans and perhaps in deep-sea organisms in general. We also show that eye index values increase as light availability increases. This study is the first to quantify how distributions of sighted and blind species change with light availability, giving baseline information on vision in the deep sea.

Limnology and Oceanography↗
USGS2024

Effect of a dense inflow on the stratification of a steep-side lake

We detail the effect of a small stream of dense inflow that significantly altered the stratification and water quality in a constructed water body in northern British Columbia, Canada. As the dense inflow passed through the epilimnion of the steep-sided lake, it entrained relatively large quantities of water. The resulting mixture of dense inflow and entrained epilimnetic water sank to the bottom of the lake. The removal of water from the epilimnion due to entrainment reduced the epilimnetic thickness. This opposes the normal process of epilimnetic deepening due to wind and convective cooling. The flux of fluid entrained into the dense inflow was calculated to be between 4 and 14 times the inflow, depending primarily on the thickness of the epilimnion. The entrainment had four major effects: (1) it reduced the residence time of the epilimnion from half a year to less than a month; (2) it removed the freshwater cap that resulted from spring ice melt; (3) it enabled fall turnover, which further enhanced deep oxygen content and helped to prevent meromixis from developing in the lake; and (4) it produced a rapid decline in contaminant (i.e., zinc) concentrations in the epilimnion, which received dissolved metals inputs from oxidized sulfide minerals exposed in the subaerial walls of the lake. Given the wide variety of inflows to inland water bodies, some of which are at least seasonally dense, an understanding of the mechanisms detailed here can inform lake management in general, and more specifically, management of water quality in mine-impacted water bodies.

British Columbia↗
USGS2024

Invertebrate trophic structure on marine ferromanganese and phosphorite hardgrounds

The Southern California Borderland hosts a variety of geologic and oceanographic features that allow for diverse habitats to occur in a restricted region with a strong oxygen minimum zone (OMZ) and hard substrates. These include ferromanganese (FeMn) crusts and phosphorites targeted for deep-seabed mining in other regions. Baseline studies regarding hardground macro- (> 0.3 mm) and megafaunal (> 2 cm) invertebrates are lacking, although they contribute to understanding nutrient cycling and resilience of deep-sea communities to ocean deoxygenation, fishing, or mineral extraction. With the goal of understanding how substrate type, depth, and dissolved oxygen concentration influence invertebrate trophic structure, we surveyed δ 13 C and δ 15 N values of invertebrates on hard substrates on the Southern California Borderland margin along a depth gradient (120–2400 m) through the OMZ at inshore (< 100 km from shore) and offshore (100–250 km from shore) sites, using generalized additive models and community-level metrics. Macrofaunal isotopic values correlate with substrate type, exhibiting higher trophic diversity on FeMn crusts and specialized communities on phosphorites. Megafaunal isotopic values correlate with proximity to shore; animals offshore seem to depend more on phytoplanktonic production than animals inshore. In general, δ 15 N increased with decreasing dissolved oxygen and increasing depth, possibly due to remineralization processes within the OMZ and with depth. We discuss how feeding modes and community composition might influence the observed patterns. This study elucidates the importance of the environmental context in shaping invertebrate trophic structure on continental margins and provides baseline knowledge that may be useful in regions where these minerals are targeted for extraction.

Limnology and Oceanography↗
USGS2024

Gulf Stream intrusion and deep current upwelling drive dynamic patterns of temperature and food supply within cold-water coral reefs

One of the most significant features of the Northwest Atlantic, the Gulf Stream influences high magnitude environmental fluctuations in deep habitats across the South Atlantic Bight. Amid this variability, the Blake Plateau harbors extensive reefs formed by cold-water corals that were previously assumed to rely on narrow ranges of temperature, currents, and particulate supply. A benthic lander collected near-bed conditions at the Richardson Reef Complex, a cold-water reef dominated by the scleractinian Desmophyllum pertusum at 830 m within the path of the Gulf Stream. Specific behavior of the Gulf Stream resulted in recurring environmental patterns at depth. During offshore meanders, deep stream components intruded onto the reef and caused rapid (3.74°C per hour) temperature increases up to 10.8°C (> 5°C above the site mean) and increased chlorophyll. Within 2 d of peak temperatures, intrusions were replaced by strong, turbid upwelling currents that rapidly cooled the site to temperature minima (4.13°C). While considerable environmental variability from the Gulf Stream may otherwise implicate a thermally stressful setting for corals, high-temperature events were likely mitigated by their short duration (< 37.4 h) and physical coupling with enhanced organic material. This hypothesis was supported by high-density clustering of D. pertusum occurrences within 50 km around the Gulf Stream's position along the South Atlantic Bight. This suggests that cold-water corals experiencing environmental variability can be sustained by relationships between food supply, temperature, and currents that vary in strength along stochastic time scales, shedding further light on the niche of cold-water corals.

Limnology and Oceanography↗
USGS2025

Ice thickness regulates heat flux in permanently ice-covered lakes

The permanently ice-covered lakes of Taylor Valley, Antarctica, are rare ecosystems where permanent ice cover and year-round vertically stable water columns provide critical redox zones for cold-adapted microorganisms. Using 30 yr of limnological data from the McMurdo Dry Valleys Long-Term Ecological Research program, we assessed the water column heat flux of four permanently ice-covered lakes in the context of global lake ice decline and lake warming. Our study reveals that heat flux in Taylor Valley lakes is driven by ice cover dynamics, both annual changes in ice thickness as well as overall ice thickness. During periods of ice thinning, like those observed from 2020 to 2023, the lakes accumulate heat. Lake Fryxell, Lake Hoare, and West Lake Bonney have repeatedly cooled and warmed over our record, with only East Lake Bonney cooling due to lake level rise. Ice thickness is largely synchronous among the four lakes, with periods of asynchronicity likely caused by lake-specific changes in surface albedo driven by changes in optical properties of the ice covers and in-ice sediment dynamics.

Limnology and Oceanography↗
USGS2025

The influence of mountain streamflow on nearshore ecosystem metabolism in a large, oligotrophic lake across a drought and a wet year

The influence of streamflow can be highly heterogeneous around lake edges, making it challenging to predict how benthic productivity in the littoral zone responds to hydroclimatic change. The degree to which streamflow affects nearshore productivity varies as a function of catchment characteristics, internal lake morphometry, and processes. This study investigates the relative influence of streamflow on nearshore metabolism (e.g., gross primary productivity [GPP], ecosystem respiration [ER], and net ecosystem productivity [NEP]) for shores with large, small, or no stream inflows (four locations across two shores) during two contrasting water years (one drought and one wet) in Lake Tahoe (Nevada/California, USA). Using Bayesian structural equation modeling, we found streamflow decreased water temperature, benthic light, and GPP across both years. Compared to the drought year, the subsequent wet year had 54% higher annual streamflow, 37% less light, and lower NEP at locations with large or small inflows (39% Δ −0.32 mmol O₂ m −3 d −1% and 49% Δ −1.19 mmol O₂ m −3 d −1 , respectively). During the wet year, we observed a 68% increase in the negative association between streamflow and nearshore GPP at the large inflow and a 62% decrease in the positive association between streamflow and GPP at the small inflow. This work demonstrates how oligotrophic littoral productivity varies across shorelines and in response to hydrological conditions, with streamflow and precipitation exerting contrasting effects depending on the proximity to inflowing streams. Our results suggest future lake responses to climate volatility depend on spatial and temporal hydrologic connectivity to catchments and upland processes.

California, Nevada↗
USGS2025

Seasonal variation in bay-marsh sediment exchange through a back-barrier salt marsh tidal creek

Salt marsh resilience to sea-level rise largely depends on the balance of sediment exchanges with surrounding bays. In this study, we investigate mechanisms that determine residual sediment fluxes using continuous measurements of bay-marsh sediment exchange conducted in a tidal creek spanning 13 months (753 tidal cycles) in an intertidal marsh recently subsidized with sediment via thin-layer placement. The maximum water level in each tidal cycle varied over seasonal and fortnightly timescales and was driven by a combination of the seasonal cycle in mean sea level (maximum in September, minimum in January) and the fortnightly spring-neap cycle. Residual water fluxes tended to be ebb-directed during overbank tides, possibly due to water crossing creekshed boundaries in the intertidal zone when water levels were sufficiently high. Sediment concentrations on the ebb of overbank tides exceeded those of their corresponding floods, but only for tidal cycles in which water temperatures exceeded 14°C. The interaction of these dynamics resulted in over 90% of the net sediment export from the creek occurring during overbank tides during warmer months—conditions met in 30% of the observed tidal cycles. These findings exemplify the importance of accounting for seasonality in sediment fluxes when assessing sediment budgets of salt marshes and illustrate how sediment budgets assessed with shorter duration datasets may exhibit seasonal bias. Additionally, they suggest that sediment retention for thin-layer sediment placement projects may be high over the course of the first year after sediment subsidies are deployed.

New Jersey↗