Effects of sediment resuspension on phytoplankton production: teasing apart the influences of light, nutrients and algal entrainment

1. Wind‐induced sediment resuspension can affect planktonic primary productivity by influencing light penetration and nutrient availability, and by contributing meroplankton (algae resuspended from the lake bed) to the water column. We established relationships between sediment resuspension, light and nutrient availability to phytoplankton in a shallow lake on four occasions. 2. The effects of additions of surficial sediments and nutrients on the productivity of phytoplankton communities were measured in 300 mL gas‐tight bottles attached to rotating plankton wheels and exposed to a light gradient, in 24 h incubations at in situ temperatures. 3. While sediment resuspension always increased primary productivity, resuspension released phytoplankton from nutrient limitation in only two of the four experiments because the amount of available nitrogen and phosphorus entrained from the sediments was small compared with typical baseline levels in the water column. In contrast, chlorophyll a entrainment was substantial compared with baseline water column concentrations and the contribution of meroplankton to primary production was important at times, especially when seasonal irradiance in the lake was high. 4. Comparison of the in situ light climate with the threshold of light‐limitation of the phytoplankton indicated that phytoplankton in the lake were only likely to be light‐limited at times of extreme turbidity (e.g. >200 nephelometric turbidity units), particularly when these occur in winter. Therefore, resuspension influenced phytoplankton production mainly via effects on available nutrients and by entraining algae. The importance of each of these varied in time. 5. The partitioning of primary productivity between the water column and sediments in shallow lakes greatly influences the outcome of resuspension events for water column primary productivity.     

The role of sedimentation and resuspension for the transport of sediments and contaminants in the Skagerrak

An investigation was conducted in winter of 1997/1998 in the Skagerrak off southern Norway to collect data on the influence of sedimentation and resuspension on the transport of organic contaminants. Data from the water column and sediments, as well as on sedimentation and current regime near the sea floor, indicated that the deposition of contaminants is a continual process. Deposition is subject not only to seasonal biological processes such as growth and sedimentation of the spring phytoplankton bloom, but also to hydrographic events such as surges in near-bottom currents causing sediment resuspension. Contaminants at the sea floor may be transported considerable distances. It is suggested that in simplest terms, this transport can be envisaged as a conveyor belt skipping along the seabed. The dominant iterative processes regulating this near-bottom transport are sedimentation, resuspension and advection. In this way, particles and associated polycyclic aromatic hydrocarbons, as well as other hydrophobic contaminants, may be transported over hundreds of kilometers.     

The interaction between water movement,sediment dynamics and submersed macrophytes

Water movement in freshwater and marine environments affects submersed macrophytes, which also mediate water movement. The result of this complex interaction also affects sediment dynamics in and around submersed macrophyte beds. This review defines known relationships and identifies areas that need additional research on the complex interactions among submersed macrophytes, water movement, and sediment dynamics. Four areas are addressed: (1) the effects of water movement on macrophytes, (2) the effects of macrophyte stands on water movement, (3) the effects of macrophyte beds on sedimentation within vegetated areas, and (4) the relationship between sediment resuspension and macrophytes. Water movement has a significant effect on macrophyte growth, typically stimulating both abundance and diversity of macrophytes at low to moderate velocities, but reducing growth at higher velocities. In turn, macrophyte beds reduce current velocities both within and adjacent to the beds, resulting in increased sedimentation and reduced turbidity. Reduced turbidity increases light availability to macrophytes, increasing their growth. Additionally, macrophytes affect the distribution, composition and particle size of sediments in both freshwater and marine environments. Therefore, establishment and persistence of macrophytes in both marine and freshwater environments provide important ecosystem services, including: (1) improving water quality; and (2) stabilizing sediments, reducing sediment resuspension, erosion and turbidity.     

Additional observations of endobenthic behaviour in the early life history of Melanostigma atlanticum (Zoarcidae) in muddy bottom sediments of the Laurentian Trough,eastern Canada

Synopsis While adult Melanostigma atlanticum continue to be sporadically noted living within bottom sediments of the Laurentian Trough, the observation of late embryo/early juvenile stages has not previously been reported. The occurrence of 22 live specimens between 20–25 mm total length in the subsurface anoxic sediment in early May suggests that development of eggs and embryos may take place in such environments during the winter.     

Dynamics and ecological significance of daily internal load of phosphorus in shallow Lake Balaton, Hungary

1. As supported by field data, turbidity recorded by light scattering sensors could reliably be converted into concentration of suspended particulate matter (SPM) and coefficient of vertical light attenuation (K_d) in Lake Balaton. 2. Autocorrelation analysis revealed that proper determination of SPM concentration and K_d required daily sampling. To approximate daily rate of resuspension, 15 min or more frequent measurements were needed. Thus, routine monitoring provides very little insight into environmental variability of shallow lakes as habitats for phytoplankton. 3. The internal P load was estimated from daily rate of resuspension and P desorption capacity of sediments. The latter was assumed to be proportionate to the potentially mobile inorganic P content of SPM. A comparison with net primary production and nutrient status of phytoplankton showed that the proposed method of estimating time series of internal P load captured seasonal trends. 4. The daily rate of resuspension was high whereas that of internal P load was low in Lake Balaton relative to other shallow lakes. The latter reflects favourable behaviour of the calcite‐rich sediments. As a consequence, carrying capacity of Basin 1 of Lake Balaton was P‐determined. 5. The timing of external and internal loads was radically different. While the former showed mostly seasonal changes, large pulses characterised the latter. As a consequence, internal load may supply more P to phytoplankton growth during the critical summer months than external load. However, the relative importance of these sources may show substantial interannual variability. 6. Large resuspension events often followed each other during periods of 10–15 days. It has been shown that disturbances in this frequency range are of key importance in maintaining the diversity of phytoplankton. We propose that resuspension can be perceived not only as a disturbance factor but also as a factor that periodically relaxes nutrient stress. The former feature may dominate the instantaneous effect, whereas the latter may determine the persistent effect of resuspension on succession of phytoplankton.     

The benthic boundary layer approach and its application to Lake Päijänne,Finland

Resuspension of bottom sediments is the net result of a wide variety of different fluid mechanical processes with characteristic time and length scales that extend over six orders of magnitude. The sum of these effects is most heavily concentrated in a layer adjacent to the bottom called the benthic boundary layer (BBL). The physics of BBL must be understood before improved solutions to the resuspension problem are possible. Traditionally in lakes, sedimentation and resuspension have been modelled with the aid of equations which ignore the time and space variations of near bottom processes. This can lead to wrong estimates of material transport. With the exception of few recent studies, benthic boundary layer approach has been mainly applied to marine environments. The instrumentation has been a major problem for development of the theory and its applications, but during recent years some new instruments have been giving promising results. This paper discusses the applicability of the theory in Finnish lakes and presents results from Lake Päijänne.     

Are Antarctic suspension-feeding communities different from those elsewhere in the world?

This paper reviews the trophic ecology of benthic suspension feeders in Antarctic shelf communities, studied within SCAR's EASIZ Programme, in comparison with published information from other seas. Dense benthic suspension-feeder communities capture large quantities of particles and may directly regulate primary, and indirectly, secondary production in littoral food chains. Most work has been performed in temperate and tropical seas; however, little is known about suspension feeders in cold environments. Recent studies on Antarctic littoral benthic suspension feeders suggest the period of winter inactivity may last only a few weeks. This contrasts with the hypothesis that in Antarctic communities there is a prolonged period of minimal activity lasting at least 6 months during the austral winter. Results from other oceans may explain how dense benthic communities could develop under such conditions. Alternative food sources, i.e. the "fine fraction", sediment resuspension, lateral advection and efficient food assimilation may play a significant role in the development of suspension-feeder dominated, very diversified, high biomass and three-dimensionally structured communities on the Antarctic shelf.     

A bioassay to assess the potential effects of sediment resuspension on phytoplankton community composition

A laboratory assay (SAGA or Sediment Algal Growth Assay) was developed to assess the potential impact of sediment resuspension on the structure of phytoplankton communities, and to evaluate the effectiveness of various sediment treatments in decreasing the abundance of blue-green algae in the event of sediment resuspension during storms. In assays with sediment from eutrophic Akanoi Bay, Lake Biwa, Japan, 7–11 species of phytoplankton seeded from the sediments grew during the 3-week assay indicating that sediment resuspension has the potential to increase both phytoplankton biomass and species diversity. Treatment of sediments with Ca(NO3)2 substantially decreased phytoplankton biomass (measured as chlorophyll concentration) in assays with sediments from Akanoi Bay and the North Basin of Lake Biwa. Further, among various oxidation treatments of sediments, Ca(NO3)2 was most effective in decreasing or preventing filamentous blue-green algal growth in N- and P-replete media. In contrast, when sediments were added to P-limited phytoplankton dominated by green algae and diatoms, no growth of blue-green algae occurred regardless of sediment treatment. This revised version was published online in June 2006 with corrections to the Cover Date.     

The effect of wave-reduction engineering on sediment resuspension in a large, shallow, eutrophic lake (Lake Taihu)

Frequent resuspension of sediments is recognized as an important process in large shallow lakes, impeding the recovery of eutrophic lakes. A large-scale project, including a wave barrier (3.3 km long) and a soft enclosure, was implemented to reduce wave energy and sediment resuspension in Lake Taihu, eastern China. The effects of the wave-reduction engineering on sediment resuspension and internal nutrient loading were investigated. Results showed that sediment resuspension rates as well as suspended solids (SS) in the areas protected by the wave barrier and the soft enclosure were significantly lower than in the unprotected areas. There was a positive relationship between total phosphorus (TP) and SS; thus internal loading of phosphorus was significantly reduced by the wave-reduction structure. High nutrient levels and phytoplankton biomass persisted during the experiment period, suggesting that additional measures, such as re-establishment of the macrophyte community, must be included to help restore the water quality in such a large, shallow and eutrophic lake.     

Resting-egg hatching and early population development in rotifers: a review and a hypothesis for differences between shallow and deep waters

This paper reviews our very limited knowledge about resting-egg hatching and early population development in planktonic rotifers. Hatching of stem females from resting eggs may occur soon after resting eggs are produced, but perhaps usually it is delayed by a minimum obligate diapause, by a requirement for seasonal temperature changes, or by sinking to sediment environments that prevent hatching. In deep-water sediments, hatching probably is inhibited by low oxygen, darkness, or low temperature, so that eggs likely hatch following resuspension during water-column turnover. Populations should develop primarily by female parthenogenesis and have relatively low clonal diversity. By contrast, in shallow-water sediments, eggs are more likely to experience conditions conducive to hatching and to be resuspended into the water column. Populations may develop by massive emergence of stem females as well as by female parthenogenesis and thus have a very high clonal diversity. Stem females of some species are particularly fit for colonization of new habitat. First, compared to females hatched from parthenogenetic eggs, they can have a greater lipid reserve that enhances survival and reproduction. Second, amictic stem females can contain a transmissible factor that inhibits sexual reproduction and diapause for several to many successive generations, thus promoting rapid reproduction via female parthenogenesis.     

Deposition,resuspension, and decomposition of particulate organic matter in the sediments of Lake Itasca,Minnesota, USA

Sediment traps were used to investigate the settling, resuspension, and decomposition of particulate organic matter in Lake Itasca, MN (USA). Traps were deployed in the epilimnion and hypolimnion of the deepest basin during June, 1988, sampled twice during stratified conditions (August, September) and once after the lake had mixed (October). The downward flux of particulate material increased from summer to fall. The net sedimentation of organic matter ranged from 0.6 to 2.3 g m^–2 d^–1 at 4 m and increased to 2.1 to 3.2 g m^–2 d^–1 two meters above the bottom sediment indicating that resuspended sediment was at least 33% of the settling mass during all periods. The C:N ratios of captured particles (6.8–9.5) were between the ratios of plankton (5.8 to 6.8) and the sediments (9.9 to 10.2) but smaller than the ratios of terrestrial organic materials (13.5 to 222). The monosaccharide compositions of the entrapped particles were similar to plankton samples and different from the distinct composition of the sediments. Capture of rebound particles similar to the primary flux and not decomposition may have been responsible for this similarity. Total monosaccharide concentrations were lower in the sediments than in entrapped particles. Individual sugars exhibited different patterns of accumulation in the sediments. Glucose was lowest in sediments when the relative concentrations were compared to those in source materials and entrapped particles. In contrast, sediments had the highest rhamnose and fucose concentrations. Bacterial biomass could only account for small portions of these sugars in the sediment. The distinct monosaccharide composition of resuspended sediments was not strongly recorded in materials captured by the sediment traps even after the lake had mixed.     

The influence of an intermittent food supply on the feeding behaviour of Yoldia hyperborea (Bivalvia: Nuculanidae)

Yoldia hyperborea (Lovén) is a protobranch bivalve of circumboreal distribution and an important bioturbator of muddy sediments of cold-water embayments in Newfoundland, Canada, where it is exposed to a strong seasonal input of sinking phytoplankton during spring, sporadic events of sediment resuspension, and sediment of low nutritional value during winter. To explain field-observed patterns of population dynamics, we quantified the behavioural response of Y. hyperborea to pulses of settling algae and sediment resuspension events, and hypothesised that Y. hyperborea behaviour is modified during settling of nutrient-rich organic matter. Yoldia hyperborea responded rapidly to the arrival of settling microalgae by extending its siphons into the water column. Once the pulse of algal material reached the sediment the animals partially emerged, extended the palp proboscides over the sediment surface and maintained close contact with the area of highest algal concentration. In contrast, the activity of animals not exposed to settling algae or to resuspended sediment was primarily restricted to strata below the sediment surface. Thus the predominant subsurface feeding behaviour of Yoldia hyperborea is switched to surface deposit-feeding as a response to cues contained in microalgae. Results suggest active suspension-feeding during algal sedimentation events, although deposit-feeding resumes once the algae are no longer in suspension, and suspension-feeding is probably of little nutritional significance. The rapid behavioural response of Y. hyperborea to the influx of high quality food, such as fresh microalgae, is probably an adaptive foraging strategy to a food-limited environment and suggests higher bioturbation rates of surface sediments during spring, a key role being played by the protobranch in redistribution of labile phytodetritus within the benthos.     

Seasonal changes in eelgrass functions: current velocity reduction,prevention of sediment resuspension,and control of sediment–water column nutrient flux in relation to eelgrass dynamics

We assessed seasonal changes in eelgrass (Zostera marina) functions, i.e., reduction of current velocity, buffering of sediment resuspension, and control of dissolved inorganic nitrogen flux between the sediments and the water column, using field observations and experiments in the Akkeshi-ko estuary, Hokkaido, Japan. We also analyzed the relationships between eelgrass traits and functions. The efficiency of the reduction in current velocity increased with the development of the eelgrass canopy. Sediment resuspension was inhibited from May to August, during which time the eelgrass canopy developed. Eelgrass controlled the NH₄ ⁺ concentration of sediment porewater through root nutrient uptake, affecting NH₄ ⁺ flux between the sediments and the water column. Fluctuations in eelgrass functions and coincident changes in dynamics resulted in seasonal changes in the eelgrass environment, which may in turn affect the dynamics of organisms inhabiting eelgrass beds, e.g., mysids and epiphytic algae. Moreover, the developed eelgrass canopy trapped a large amount of material during spring and summer, which was resuspended into the surrounding ecosystem in autumn when the canopy and its functions (i.e., reduction of current and sediment resuspension) diminished. These results suggest that seasonal changes in eelgrass functions also affect communities within marginal coastal ecosystems through the control of allochthonous resources. Handling editor: P. Viaroli     

Studies of heavy metal sorption by Trenton Channel (Detroit River) sediments

Sediment resuspension plays a dominant physical role in downstream transport of sediment-bound, or in-place pollutants. During resuspension, however, numerous sorption reactions may alter contaminant phase distributions. Previous field resuspension studies on heavily contaminated sediments (Theis et al., 1988, J. Great Lakes Res. 14, 216) showed parallel trends in metal partitioning with pH and time for each of 7 metals (Cd, Co, Cr, Cu, Ni, Pb, Zn), when pH was < 7.5 during resuspension. To improve our ability to interpret follow-up laboratory partitioning experiments using sediments from the field sites, we conducted an evaluation of sediment sample storage as a potential factor leading to field-laboratory partitioning differences. Although metal sorption observed in the laboratory differed substantially from that observed in the field, sample storage effects, reported as holding time and changes in solid phase metal fractionation, gave minimal support for the hypothesis that sample storage caused the differences. It appears, rather, than our in vitro batch equilibrium systems incompletely replicated those attributes of a sediment-water system that are relevant to adsorption and desorption of heavy metals during a resuspension event. Accordingly, we conclude that a general improvement in the understanding of contaminant partitioning would result if future studies would assign greater importance to evaluating the effects of relevant physical phenomena on partitioning (e.g. particle interaction and shear stress), in addition to such widely studied chemical determinants as pH, time, and metal species.     

Sedimentary phosphorus fractions and bioavailability as influenced by repeated sediment resuspension

Concentrations of phosphorus (P) fractions and changes in their bioavailability in the sediments as influenced by repeated resuspension were determined by sequential fractionation in laboratory experiments. The water and sediment samples used were taken from the campus canal. Sequential fractionation indicated that the concentrations of the iron bound P (BD–P) were predominant, consisting of over 50% of total P (Tot-P) in the sediments that did and did not undergo resuspension. BD–P mobility was reduced due to resuspension resulting from the decline of the proportion ratio of non-occluded Fe–P and occluded Fe–P from 0.53 to 0.29. Therefore, under sediment resuspension conditions, using the sum of loosely sorbed P (NH₄Cl–P), BD–P, aluminium bound P (Al–P), and organic-P (NaOH–nrP) to estimate bio-available P (BAP) might be problematic. However, BAP could be accurately estimated by the sum of NH₄Cl–P, % BD–P (bio-available, non-occluded Fe–P), and NaOH–nrP. By this estimation, the amount of BAP in the sediments as influenced by repeated resuspension decreased by about 10% of Tot-P, compared with the initial state (raw sediments). The results suggest that repeated resuspension could accelerate the transformation of P from mobile fractions to refractory fractions, which can be attributed to the increase of occluded Fe–P, Al–P, and calcium bound P (HCl–P).     

Temporal distribution,source apportionment,and pollution assessment of metals in the sediments of Beas river,India

Metal pollution in the fluvial sediments of the rivers has become a severe problem throughout the world. Lower valleys with agricultural land are usually receiving diverse contaminants from various sources that are characterized by constant, bioaccumulative and harmful contaminants. One example is of the Beas river (India) which shows the distribution, contamination, and pollution status of metals in the sediments. In the present study, a cluster analysis and principal component analysis were conducted to assess the impact of anthropogenic activities in sediment metals. Results of contamination factor indicate that there is low contamination, whereas enrichment factor showed that 28.5% metals showed significant pollution during pre-monsoon season, 42.8% metals showed moderate to high pollution during post-monsoon season, and 42.8% metals showed moderate to extreme pollution during the winter season. Pollution index and modified pollution index showed that sediments in the winter season are slightly and critically polluted. The ecological risk factors indicate that 23.8% metals posed moderate to high ecological risk in the sediments.     

Storage,redistribution and net export of dissolved and sediment-bound nutrients,Vejle Fjord,Denmark

Sixty three percent of the nitrogen (total transported 2041 × 10³ kg y^–1) and 17% of the phosphorus (total 159 × 10³ kg y^–1) supplied from terrestrial sources to Vejle Fjord during the period September 1988 to October 1989 is exported to the Kattegat. The sediment nutrient concentrations in the estuary are mainly governed by hydrography and resuspension. The general wind-induced circulation consists of outgoing currents along the southern side and ingoing currents along the northern side of the estuary. The sediments in shallow water on the southern side had higher concentrations of nutrients.Resuspension resulted in large differences between gross sedimentation and net sedimentation, especially in shallow water. Gross sedimentation of total-N in shallow water was 819 × 10³ kg y^–1 compared to a net sedimentation of 19 × 103 kg y^–1. The shallow water areas in the estuary (10% of the area), had a net sedimentation of total-N which was less than 1% of the supply.Wave-induced resuspension only occurs in exposed parts of the deep water area, when wind velocities exceed 10 m s^–1. The concentration of nutrients in the sediments was found to increase with distance from the river (the source) and with increasing depth, as a result of resuspension near the river mouth in the inner part of the estuary. In sheltered parts of the estuary there was no wave-induced resuspension and the net sedimentation equals gross sedimentation. The rate of sedimentation in deep water areas was 12.2 g m^–2y^–1 for total-N and 2.1 gm^–2y^–1 for total-P.     

Distribution and survival of faecal indicator bacteria in the sediments of the Bay of Vidy,Lake Geneva,Switzerland

The purpose of this study was to determine the concentrations and the horizontal distribution of faecal indicator bacteria (FIB) including Escherichia coli and Enterococcus sp. in the bottom sediments of the Bay of Vidy, City of Lausanne, Switzerland. A vertical distribution of FIB in sediments near the municipal wastewater treatment plant (WWTP) outlet was evaluated and their persistence in those sediments was monitored for a period of 90 days. High FIB levels were measured in the sediments sampled near the WWTP outlet pipe and the mouth of the Chamberonne River, at concentrations ranging between 10⁵ and 10⁷ CFU 100 g^?1. FIB levels at 10 cm depth in the sediments near the WWTP outlet pipe ranged between 10⁴ and 10⁵ CFU 100 g^?1, and were still detected in the top 6 cm after 90 days. Results of this study indicate that freshwater sediments of the Bay of Vidy constitute a reservoir of faecal indicator bacteria, which can persist in certain areas of the bay. Possible resuspension of FIB and pathogens may affect water quality and may increase health risks to sensitive populations during recreational activities. FIB survival in sediments for long periods is of considerable significance for the understanding of microbial pollution in water and for the management of risk at specific recreational coastal sites.     

Arsenic transport between water and sediments

Arsenic discharged into the Moira River has accumulated in the sediments of Moira Lake during the past century. The chronology of arsenic concentrations in the sediments, established using Pb-210 dating, has a subsurface concentration maximum (> 1000 g g^–1) that reflects higher inputs to the lake 15 to 45 years ago. The distribution coefficient (K_d) of arsenic in the surficial sediments was low (4000–6000 L kg^–1) and decreased below the sediment water interface. Higher concentrations of exchangeable As also were extracted deeper in the sediments. As a result, arsenic is mobile in the sediment column and the flux of arsenic via diffusion and particle resuspension from the sediments into the water is greater than current external loading from the Moira River. Less than 20% of the external input of arsenic is buried in the lake sediments. Using these flux measurements and a one dimensional model of arsenic transport in the sediment column, we constructed the history of arsenic exchange between water and sediments throughout the past century. The simulations predict that arsenic input into the water from the sediments has been > 20 % of external loading for the past 25 years and will continue to be important in the future as diffusion and resuspension regenerate arsenic from the mixed layer of the sediments into the overlying water.     

Food availability and gut contents in the ascidian Cnemidocarpa verrucosa at Potter Cove, Antarctica

A high seasonality characterizes Antarctic environments, and generates marked differences in availability and composition of food for benthic filter feeders. During a year-round period at Potter Cove, Antarctica, algal pigment concentration (chlorophyll a) and organic matter were measured in water column and sediment samples. Chemical composition of gut contents of the ascidian Cnemidocarpa verrucosa was also analyzed. Despite the low standing stock, capture and absorption of organic matter were detected year-round, suggesting intake of other particles besides microalgae. The mechanism that provides food to the ascidians and epibenthic communities may be related to the supply of allochtonous particles, bottom resuspension events, and microbial community dynamics. Sea-ice cycles may affect food availability in terms of water-column mixing and benthic resuspension. The scarce primary production and the high amount of sedimented material are not limiting conditions in Potter Cove, which presents a rich ascidian community.