Water Column Research Articles

Numerical modelling of dispersal of Ampelisca (Amphipoda Gammaridae) during their diel migration

The aim of this study is to analyse and model the dispersal of Ampelisca, a benthic genus of amphipod crustaceans, in the fine sand community of the Bay of Morlaix (western English Channel), during their nocturnal migration in the water column. Based on sampling of the suprabenthos (in the water column adjacent to the bottom) and surface plankton on 17 June 1994, Dauvin and Zouhiri (1996) studied the vertical distribution of Ampelisca during a spring swarming reproductive period. Statistical modelling techniques and specific numerical models were combined to simulate the effects of tidal currents, wind direction and speed on Ampelisca dispersal. As an illustration to constant pluriannual seasonal pattern, the dispersion of Ampelisca individuals considered as passive particles was studied at two reproductive periods, on a short night (17th-18th June 1994) during a neap tide, and on long night (7th-8th September 1994) during a spring tide. These models are used to investigate whether Ampelisca can be dispersed beyond the fine sand community in the immediate area of their small-scale benthic habitat (only 6 km²) during their diel vertical migration. According to the results, the speed and direction of currents will determine the trajectory of Ampelisca and the degree of dispersal outside their benthic habitat during a nighttime pelagic sortie. These simulations, particularly during spring tides, are incompatible with population stability, as they appear to be excessively dispersive. Short-term dispersal simulations for twenty minutes in the plankton allow the optimal return of individuals to the fine sand benthic habitats. We hypothesize there is an adaptative advantage for Ampelisca over time to short diel migrations. However, we currently do not know whether each individual makes a single migration, or several migrations in the water column during a night.

Impact of wave action on the entrainment rate and droplet size of oil

Oil dispersed on the water surface undergoes fragmentation into droplets, subsequently entering the water column under wave action. The oil entrainment rate and the droplet size distribution (DSD) significantly influence the subsequent migration and transformation of oil in the water column. A wave tank system was employed to investigate the impact of wave action on oil entrainment rate and DSD. The experimental results revealed that increased wave height and wave frequency facilitated the entry of oil into the water column and fragmented it into dispersed droplets. Relationships between oil entrainment rate and energy dissipation, as well as DSD, were established and supported by mathematical regression analyses. Non-linear regression analysis indicated that the cumulative frequency distribution of DSD adhered to the Log-Normal and Rosin-Rammler distributions. These findings contribute to a comprehensive understanding of natural oil dispersion and subsea transport, valuable for estimating the origin of oil spills.

Using machine learning techniques in inverse problems of acoustical oceanography

AbstractThe goal of the work presented here is to study a novel approach for inverting acoustic signals recorded in the marine environment for the estimation of environmental parameters of the water column and/or the seabed. The proposed approach is based on signal feature extraction using a discrete wavelet packet transform, applied to the measured signal, and hidden Markov models that exploit the sequential patterns of the signals. The signal feature is thereafter used in the framework of a mixture density network, which, after training with sets of simulated signals calculated within a predefined search space, provides conditional posterior distributions of the recoverable parameters. The technique is tested with two test cases corresponding to different types of inverse problems. The first case corresponds to a simple problem of geoacoustic inversion, while the second is referred to a, rather unusual, still interesting problem of recovering the shape of a seamount using long‐range acoustic data. Both test cases are based on simulated experiments. The inversion results obtained using the proposed scheme are compared with inversion results using statistical features of the acoustic signal, which is another inversion approach well documented in the literature and is also based on the wavelet packet transform of the measured signal.

Recurring seasonality exposes dominant species and niche partitioning strategies of open ocean picoeukaryotic algae

Ocean spring phytoplankton blooms are dynamic periods important to global primary production. We document vertical patterns of a diverse suite of eukaryotic algae, the prasinophytes, in the North Atlantic Subtropical Gyre with monthly sampling over four years at the Bermuda Atlantic Time-series Study site. Water column structure was used to delineate seasonal stability periods more ecologically relevant than seasons defined by calendar dates. During winter mixing, tiny prasinophytes dominated by Class II comprise 46 ± 24% of eukaryotic algal (plastid-derived) 16S rRNA V1-V2 amplicons, specifically Ostreococcus Clade OII, Micromonas commoda, and Bathycoccus calidus. In contrast, Class VII are rare and Classes I and VI peak during warm stratified periods when surface eukaryotic phytoplankton abundances are low. Seasonality underpins a reservoir of genetic diversity from multiple prasinophyte classes during warm periods that harbor ephemeral taxa. Persistent Class II sub-species dominating the winter/spring bloom period retreat to the deep chlorophyll maximum in summer, poised to seed the mixed layer upon winter convection, exposing a mechanism for initiating high abundances at bloom onset. Comparisons to tropical oceans reveal broad distributions of the dominant sub-species herein. This unparalleled window into temporal and spatial niche partitioning of picoeukaryotic primary producers demonstrates how key prasinophytes prevail in warm oceans.

Stratified water columns: homogenization and interface evolution

Stratified water columns are often found in lakes and oceans. Stratifications result from differences in density due to salt concentration, temperature, solid content and oxygenation. The stability of stratifications affects bioactivity, sedimentation, contaminant transport and environmental remediation. This study investigates the evolution of 6 stratified water columns created by differences in salinity, suspended minerals and the presence of a bottom heat source. We use acoustic wave reflection, photography, and both electrical conductivity and temperature profiles to track changes in stratification. Results show that multiple concurrent processes emerge across layers in otherwise quiescent water bodies. Dissimilar chemo-thermo conditions give rise to chemical and thermal diffusion, convection, and double-diffusion convection. When stratification involves suspended particles, interlayer processes include diffusiophoresis, flocculation/aggregation, sedimentation, osmosis, and chemo-consolidation; in this case, the specific surface and surface charge of suspended particles, and the salt concentration in contiguous layers determine aggregation-sedimentation-consolidation patterns. The interlayer transition zone acts as a high-pass filter that preferentially reflects low-frequency long-wavelength P-waves; invasive thermal and electrical conductivity probes provide complementary information and may identify stratification even when it is undetected by acoustic signals.

Changes in the limiting nutrients and dominant phytoplankton communities of three major European rivers: Response to catchment lithologies and human activities

Catchment lithologies and human activities can cause variations in riverine carbon (C), nitrogen (N), and phosphorus (P) loads, and the ratio of these nutrients may affect the primary productivity of rivers and their phytoplankton communities. We conducted a comparative study of biogeochemical variations in three major European rivers—the Rhine, Danube, and Seine—which reveals the impacts of different carbonate outcrops and human impacts (agricultural activities and sewage input) on the changes in the limiting nutrients and phytoplankton community compositions of flowing water systems. N limitation was observed in the Rhine and Danube owing to their low average NO3– loads (4.04–6.45 mg/L). Although the extensive outcrops of carbonate rocks in the Seine catchment result in high average HCO3– concentrations of ∼ 4.68 mmol/L, the elevated inorganic C input did not match the high average NO3– loads (∼19.38 mg/L), driven by intensive agricultural activity and urban sewage input, demonstrating a potential C limitation on productivity. Our results show that the productivity of the Seine River, determined by the chlorophyll-a concentration, was significantly related to the dissolved inorganic carbon (DIC) concentration (coefficient of determination: R2 = 0.68, P < 0.05). Our results demonstrate that changes in DIC content can significantly alter the dominant phytoplankton species in the water column. The high inputs of DIC and aqueous CO2(aq) to the Seine lead to Bacillariophyta proportions that are 3.96–8.81 % and 19.87–22.56 % higher than those of the Rhine and Danube in the wet and dry seasons, respectively. This can be explained by the difference in the efficiency of carbon concentrating mechanisms (CCMs) among phytoplankton species. Therefore, to mitigate river eutrophication and improve the quality of the aquatic environment, we suggest that future water–carbon management in the flowing water systems with abundant nutrients should consider C-limitation alleviation and its potential effect for reducing the abundance of harmful algae.

Transport and separation behaviors of crosslinked GO/PVA sponge with high porosity

Separation materials (technology) with high efficiency and high precision is a goal that researchers are relentlessly pursuing. Here, crosslinked graphene oxide and polyvinyl alcohol (GO/PVA) sponges with high porosity are reported, which were constructed by crosslinking a dilute solution of GO/PVA. The structure and transport characteristics of the sponges were investigated. It was found that it took 150 days for 30 mg/L methylene blue (MB) to diffuse from the side of crosslinked GO/PVA sponge (10 mm thickness) to the other side (breakthrough) even though the porosity of sponge was up to 92.9 %, while it needed only 2 days in PVA sponge and 13 days for methyl orange (MO) in the sponge. Hence, the transport and separation behaviors of more substances were explored and it is found that not only a precise separation of more than 99 % was achieved for MB/MO (similar molecular weight) mixed solution due to the extremely wide difference of transport rate, but also a water permeability of (4.3 × 105 L·m−2·h−1·Mpa-1) was reached under 10 cm height of water column pressure (0.01 bar), which is three orders of magnitude higher than that of nanofiltration membrane. The extremely high selectivity and efficiency to MB are attributed to the structural features of the sponge, i.e., the fully dispersed GO nanosheets and their crosslinking structure with PVA. Thus, the adsorption amount, adsorption rate, and adsorption strength to MB were greatly improved due to a synergistic effect of GO and PVA, and the highly efficient, precise, and rapid separation of MB was realized. In addition, the structural characteristics of the sponges favor the slow transport of many substances, which will extend their applications to the controlled release field.

Source rock assessment and organic matter characterization of the Oligocene upper Shahejie and Dongying formations in the Nanpu Depression of the saline lacustrine Bohai Bay Basin, China: Geochemical, palynological, and mineralogical perspectives

The Bohai Bay Basin, located in eastern China, is a significant petroliferous, non-marine rift basin, underwent intricate tectonic activities throughout the Cenozoic. The Nanpu Depression in the Huanghua sub-basin in the northern part of the basin was controlled by Paleogene rifting and increased subsidence. These geological processes resulted in the deposition of the Shahejie and Dongying formations, which exhibited varying quantities and qualities of organic matter. Eighty drill cuttings samples of the Paleogene First Member (Es1) and the overlying Third (Ed3) and Second (Ed2) members of the Shahejie and Dongying formations, respectively, were investigated. An integrated approach including organic and inorganic geochemistry, palynology, and mineralogy was employed to assess the paleoredox and marine incursion conditions, source rock quality and levels of thermal maturity, and factors that governed organic matter accumulation. Results indicated that the Es1 Member was deposited under anoxic conditions, resulting in the accumulation of organic matter-rich mudstones in the Nanpu Depression. Abundant pollen grains and acritarchs were found in the Es1 Member yielded along with minor occurrences of dinoflagellate cysts, freshwater algae, and spores. Terrestrial palynomorph composition provided evidence of increased terrestrial runoff, while the high abundance of acritarchs, accompanied by some dinoflagellate cysts, confirmed episodes of marine incursion and deposition under hypersaline conditions in the lacustrine Bohai Bay Basin. The Ed2 Member exhibited poor to fair amounts of organic matter and a limited potential of hydrocarbon generation with a variety of kerogen Types, including IV, III, II/III, and II. The Ed3 Member shows fair to good organic matter richness and hydrocarbon potential of kerogen Types III, II/III, and II. The Es1 Member emerged as the most promising source rock within the studied interval, boasting good to excellent organic matter richness, and fair to good hydrocarbon generation potential of kerogen Types III and II/III. Evaluating the thermal maturity of organic matter, based on Tmax and VRo-Eq% and related cross-plots, revealed that the Shahejie and Dongying formations are still in the immature to the early stage of the oil window. The mineralogical composition of the Es1 Member primarily consists of clay and quartz with some carbonate and accessory minerals, such as epigenetic halite, dolomite, and plagioclase. Weak correlations observed between the total organic carbon (TOC) and mineral components indicated that the availability of organic matter was primarily controlled by enhanced production and preservation rather than limited dilution under saline lacustrine, oxygen-deprived, and well-stratified water column conditions. Regional investigations of the Es1 Member confirmed the widespread anoxia and deposition of organic-rich source rocks in the Bohai Bay Basin during the Oligocene.

Substrate uptake patterns shape niche separation in marine prokaryotic microbiome.

Marine heterotrophic prokaryotes primarily take up ambient substrates using transporters. The patterns of transporters targeting particular substrates shape the ecological role of heterotrophic prokaryotes in marine organic matter cycles. Here, we report a size-fractionated pattern in the expression of prokaryotic transporters throughout the oceanic water column due to taxonomic variations, revealed by a multi-"omics" approach targeting ATP-binding cassette (ABC) transporters and TonB-dependent transporters (TBDTs). Substrate specificity analyses showed that marine SAR11, Rhodobacterales, and Oceanospirillales use ABC transporters to take up organic nitrogenous compounds in the free-living fraction, while Alteromonadales, Bacteroidetes, and Sphingomonadales use TBDTs for carbon-rich organic matter and metal chelates on particles. The expression of transporter proteins also supports distinct lifestyles of deep-sea prokaryotes. Our results suggest that transporter divergency in organic matter assimilation reflects a pronounced niche separation in the prokaryote-mediated organic matter cycles.

Light Intensity of Phosphorescent-Netting Pots and Determining Their Visibility to Snow Crab (Chionoecetes opilio) Using Visual Modeling Techniques

This study explores the visibility of phosphorescent-netting pots to snow crab (Chionoecetes opilio) using visual modeling techniques. Light emitted from such pots increases catch per unit effort, yet little is understood about the factors driving these higher catch rates. In this study, we measure pot light emission and snow crab visual acuity. Combining these data with estimates obtained in the literature for other biotic and abiotic factors, we model snow crab vision in relation to the pots. Utilizing these factors and environmental conditions, we derive a contrast ratio between the pot light and the ambient light. Findings reveal that the visibility of pot lights at 200-m depth depends primarily on solar angle (time of day) and time elapsed post-deployment. Additional factors influencing the vision of the pots include water column quality and benthic boundary layer turbidity. This study is the first to model the visual ecology of snow crab and the first to estimate snow crab visual acuity. These insights into snow crab visual ecology can potentially enhance fishing techniques, promote catch efficiency and sustainability, and help provide a path forward for visual ecology research in the fisheries science field.

Microplastic Contamination of the Seawater in the Hamsilos Bay of the Southern Black Sea

The marine ecosystem is severely threatened by microplastics. The entire marine environment of the Black Sea is contaminated with both macro- and microplastics but the contamination of the water column with this pollutant has received less attention. This study aims to obtain data on the microplastic abundance, and vertical and temporal distribution of the microplastics in the water column of Hamsilos Bay which is a natural protected area, and an important area for fishery and tourism on the Sinop coast in the Black Sea. This study was carried out for 12 months in 7 stations. Microplastic abundance varied among 5.58 ± 6.12–8.12 ± 9.17 pieces/m3 in and 1.74 ± 0.80–21.07 ± 3.84 pieces/m3 in stations. The dominant microplastics were fibre by shape (73.92%), 1–2 mm (28.35%) by size class, and blue (37.98%) by colour. The synthetic polymers in the examined microplastic samples of this study were PET (47%), PE (34%), HDPE (10%), PVC (7%) and PS (2%). The results of this study show that the coastal area is widely contaminated with microplastics. Microplastic pollution is an increasingly significant environmental issue that poses a threat to the Black Sea which is particularly vulnerable to microplastic pollution. The region is an important ecological hotspot in the Black Sea and this study can provide valuable insights into the extent of microplastic pollution and will contribute to the literature on the evaluation of microplastic pollution in marine ecosystems. These types of investigations; efforts to address the environmental challenges facing the Black Sea, including the development of programs to reduce pollution, increase sustainability, and support the protection of the region's natural resources, are crucial to its continuity.

Methylmercury cycling in the Bohai Sea and Yellow Sea: reasons for the low system efficiency of methylmercury production

Coastal seas contribute the majority of human methylmercury (MeHg) exposure via marine fisheries. The terrestrial area surrounding the Bohai Sea and Yellow Sea (BS and YS) is one of the mercury (Hg) emission “hot spots” in the world, resulting in high concentrations of Hg in BS and YS seawater in comparison to other marine systems. However, comparable or even lower Hg levels were detected in seafood from the BS and YS than other coastal regions around the word, suggesting a low system bioaccumulation of Hg. Reasoning a low system efficiency of MeHg production (represented by MeHg/THg (total Hg) in seawater) may be present in these two systems, seven cruises were conducted in the BS and YS to test this hypothesis. MeHg/THg ratios in BS and YS seawater were found to be lower than that in most coastal systems, indicating that the system efficiency of MeHg production is relatively lower in the BS and YS. The low system efficiency of MeHg production reduces the risk of Hg in the BS and YS with high Hg discharge intensity. By measuring in situ production and degradation of MeHg using double stable isotope addition method, and MeHg discharge flux from various sources and its exchange at various interfaces, the budgets of MeHg in the BS and YS were estimated. The results indicate that in situ methylation and demethylation are the major source and sink of MeHg in the BS and YS. By comparing the potential controlling processes and environmental parameters for MeHg/THg in the BS and YS with the other coastal seas, estuaries and bays, lower transport efficiency of inorganic Hg from water column to the sediment, slower methylation of Hg, and rapid demethylation of MeHg were identified to be major reasons for the low system efficiency of MeHg production in the BS and YS. This study highlights the necessity of monitoring the system efficiency of MeHg production, associated processes, and controlling parameters to evaluate the efficiency of reducing Hg emissions in China as well as the other countries.

Intercontinental invasion dynamics of Cercopagis pengoi, an IUCN-listed planktonic invasive species

Predicting the spread of invasive species and understanding the role of niche dynamics in niche transferability are critical challenges in the management of biological invasions, both theoretically and practically. We used complementary species distribution modelling approaches, such as multivariate niche analysis and reciprocal distribution models, to test the niche conservatism hypothesis and to predict the potential distribution of the fishhook waterflea, Cercopagis pengoi. Our analysis indicated a significant similarity between its native and invasive ranges, suggesting that a subset of the Ponto-Caspian propagules may have been the founders of European populations. However, our results contradict the niche conservatism hypothesis, showing that C. pengoi has not fully occupied the available niche within its current invasive ranges. Moreover, we observed a notable niche expansion, reflecting a significant shift in niche following its intercontinental introduction in North America. Given the suitability of new environments for the expansion of C. pengoi and its tendency to evade detection prior to population surges, we recommend a focus on early detection through monitoring of both water columns and bottom sediments. This should be complemented by strict enforcement of ballast water regulations to curtail its spread in North America, Europe, and other suitable non-native regions globally.

Ediacaran marine animal forests and the ventilation of the oceans.

The rise of animals across the Ediacaran-Cambrian transition marked a step-change in the history of life, from a microbially dominated world to the complex macroscopic biosphere we see today.1,2,3 While the importance of bioturbation and swimming in altering the structure and function of Earth systems is well established,4,5,6 the influence of epifaunal animals on the hydrodynamics of marine environments is not well understood. Of particular interest are the oldest "marine animal forests,"7 which comprise a diversity of sessile soft-bodied organisms dominated by the fractally branching rangeomorphs.8,9 Typified by fossil assemblages from the Ediacaran of Mistaken Point, Newfoundland,8,10,11 these ancient communities might have played a pivotal role in structuring marine environments, similar to modern ecosystems,7,12,13 but our understanding of how they impacted fluid flow in the water column is limited. Here, we use ecological modeling and computational flow simulations to explore how Ediacaran marine animal forests influenced their surrounding environment. Our results reveal how organism morphology and community structure and composition combined to impact vertical mixing of the surrounding water. We find that Mistaken Point communities were capable of generating high-mixing conditions, thereby likely promoting gas and nutrient transport within the "canopy." This mixing could have served to enhance local-scale oxygen concentrations and redistribute resources like dissolved organic carbon. Our work suggests that Ediacaran marine animal forests may have contributed to the ventilation of the oceans over 560 million years ago, well before the Cambrian explosion of animals.

The effects of bathymetry on the long-term carbon cycle and CCD

The shape of the ocean floor (bathymetry) and the overlaying sediments provide the largest carbon sink throughout Earth's history, supporting ~one to two orders of magnitude more carbon storage than the oceans and atmosphere combined. While accumulation and erosion of these sediments are bathymetry dependent (e.g., due to pressure, temperature, salinity, ion concentration, and available productivity), no systemic study has quantified how global and basin scale bathymetry, controlled by the evolution of tectonics and mantle convection, affects the long-term carbon cycle. We reconstruct bathymetry spanning the last 80 Myr to describe steady-state changes in ocean chemistry within the Earth system model LOSCAR. We find that both bathymetry reconstructions and representative synthetic tests show that ocean alkalinity, calcite saturation state, and the carbonate compensation depth (CCD) are strongly dependent on changes in shallow bathymetry (ocean floor ≤600 m) and on the distribution of the deep marine regions (>1,000 m). Limiting Cenozoic evolution to bathymetry alone leads to predicted CCD variations spanning 500 m, 33 to 50% of the total observed variations in the paleoproxy records. Our results suggest that neglecting bathymetric changes leads to significant misattribution to uncertain carbon cycle parameters (e.g., atmospheric CO2 and water column temperature) and processes (e.g., biological pump efficiency and silicate-carbonate riverine flux). To illustrate this point, we use our updated bathymetry for an Early Paleogene C cycle case study. We obtain carbonate riverine flux estimates that suggest a reversal of the weathering trend with respect to present-day, contrasting with previous studies, but consistent with proxy records and tectonic reconstructions.

Wave Breaking Eddies And Transient Rip Current Dynamics In Large-Scale Wave Basin Experiments

Wave Breaking Eddies And Transient Rip Current Dynamics In Large-Scale Wave Basin Experiments

Risk assessment of e-waste - Liquid Crystal Monomers re-suspension caused by coastal dredging operations

The Pearl River Estuary (PRE), one of the primary e-waste recycling centers in the world, has been suffering from the pollution of Liquid Crystal Monomers (LCMs), critical materials with persistent, bio-accumulative, and toxic substances used in electronic devices. It has been detected in seabed sediment with both high frequency and concentration near PRE - Hong Kong (HK) waters. In the same area, dredging operations with in-situ sediment have been frequently used in the last decades for coastal land reclamation projects. Dredging is known to cause a huge amount of sediment re-suspension into water columns, with potential damage to marine ecosystems and biodiversity.In this study, we proposed a new risk assessment strategy to estimate the secondary pollution due to the re-suspension sediment highly contaminated by LCMs. We formulate a robust and reliable probabilistic approach based on unsupervised machine learning and hydrodynamic and sediment transport numerical simulation. New risk indexes were also proposed to better quantify the impact of contaminated sediments. We applied the methodology to assess the potential impact of dredging operations in the PRE and Hong Kong waters on the local marine ecosystem. The results of the analysis showed how the potentially contaminated areas depended on the dredging locations.

Long-term declines in chlorophyll a and variable phenology revealed by a 60-year estuarine plankton time series

Long-term ecological time series provide a unique perspective on the emergent properties of ecosystems. In aquatic systems, phytoplankton form the base of the food web and their biomass, measured as the concentration of the photosynthetic pigment chlorophyll a (chl a), is an indicator of ecosystem quality. We analyzed temporal trends in chl a from the Long-Term Plankton Time Series in Narragansett Bay, Rhode Island, USA, a temperate estuary experiencing long-term warming and changing anthropogenic nutrient inputs. Dynamic linear models were used to impute and model environmental variables (1959 to 2019) and chl a concentrations (1968 to 2019). A long-term chl a decrease was observed with an average decline in the cumulative annual chl a concentration of 49% and a marked decline of 57% in winter-spring bloom magnitude. The long-term decline in chl a concentration was directly and indirectly associated with multiple environmental factors that are impacted by climate change (e.g., warming temperatures, water column stratification, reduced nutrient concentrations) indicating the importance of accounting for regional climate change effects in ecosystem-based management. Analysis of seasonal phenology revealed that the winter-spring bloom occurred earlier, at a rate of 4.9 ± 2.8 d decade-1. Finally, the high degree of temporal variation in phytoplankton biomass observed in Narragansett Bay appears common among estuaries, coasts, and open oceans. The commonality among these marine ecosystems highlights the need to maintain a robust set of phytoplankton time series in the coming decades to improve signal-to-noise ratios and identify trends in these highly variable environments.

Determining the main driver of hypoxia potential in freshwater inland lakes

This study aimed to determine the potential for hypoxia in inland freshwater lakes via examining water quality variables, mainly dissolved oxygen (DO). To this end, field studies including environmental surveying and water column sampling at six stations along two routes in Lake Zarivar, Iran, together with laboratory analysis were conducted. Then, a stepwise multivariate regression analysis was employed to identify existing patterns and effects among variables. To secure the evolved model generalizability, the range of data was adjusted using available measurements from several similar lakes/wetlands with respect to their climate and sampling season. Finally, the evolved models’ reliability was examined using validation samples as well as a comparative performance appraisal with a benchmark model attained by the least squares regression technique. The results indicated that NH4 and pH have the most significant effect on DO. The greater amount of DO on the lake surface, i.e., wind effect, and its effect on both nitrification and ammonification processes ensure the absence of hypoxia in surface layers. Therefore, in water column monitoring programs, measuring NH4 and pH would be sufficient. Our results also demonstrated that the potential of hypoxia increases if the amount of NH4 increases in the lower layers of the water column despite releasing DO with nitrate. Strong relations between DO, as the main factor of hypoxia, with NH4 and pH, gives us the opportunity to predict the hypoxia potential and its level. Using time delay between nitrification and ammonification processes, one may predict the changes in the amount of oxygen from the changes in nitrogen.

Short wave attenuation by a kelp forest canopy

AbstractGiant kelp (Macrocystis pyrifera) forests are common along the California coast. Attached on the rocky bottom at depths of approximately 5–25 m, the kelp, when mature, spans the water column and develops dense, buoyant canopies that interact with waves and currents. We present two novel results based on observations of surface gravity waves in a kelp forest in Point Loma, California. First, we report short wave (1–3 s) attenuation in kelp, quantified by an exponential decay coefficient —comparable to the dampening effect of sea ice. Second, we identify seasonal and tidal changes in attenuation, peaking mid‐summer with maximum kelp cover, and during low tide when a greater proportion of the fronds are at the surface. Thus, the naturally occurring surface canopies of kelp forests can act as temporally varying, high‐frequency filters of wave energy.