Water Column In Response Research Articles

Sediment Evolution and Habitat Function of Organic-Rich Muds within the Albemarle Estuarine System, North Carolina

The analyses of 248 samples have revealed that the composition and distribution patterns of sediments within the Albemarle estuarine system (AES) represent a complex interaction between multiple sediment sources, basin morphology and evolution, and associated estuarine processes. Three sediment end-member types are dominant: sand, peat, and organic-rich mud (ORM). Throughout the AES, shallow perimeter platforms and associated sediment-bank shorelines are eroded into Pleistocene units. Shoreline recession supplies sand to the platforms and mud to the central basins; these sediments mix with suspended sediment from the fluvial drainages. Swamp forest-peat and marsh-peat shorelines are actively eroding and supply fine organic detritus to produce the dominant ORM sediment in the central basins. Perimeter platform sands grade into ORM on the platform slope. ORM constitutes about 70% of the benthic habitats within the AES and has an average composition of 76.2% inorganic mud, 13.1% sand, and 10.7% organic matter. The characteristics of ORM greatly affect the benthic community structure, chemical quality of the sediments, and the water quality of the estuary. ORM readily moves in and out of the water column in response to natural and anthropogenic activities, affecting water column turbidity and trace and major element geochemistry. Organic matter and clay minerals in ORM are chemically reactive and interact with the water column to adsorb or release contaminants, nutrients, and gases. Thus, ORM acts as both a sink and source for many different chemical constituents in the water column and plays important, but poorly understood, functions in the physical and chemical dynamics of estuarine ecosystems.

Experimental Evidence for Aggregation of Salmon Louse Copepodids (Lepeophtheirus Salmonis) in Step Salinity Gradients

The copepod Lepeophtheirus salmonis Krayer (Copepoda: Caligida), the salmon louse, is a parasite of salmonids. The vertical distribution of the infective stage, the copepodid, was studied in salinity gradients with one step increase of 15‰ (154%e> on top of 304‰), 5‰ (25–4‰ on top of 30–4‰) and 2%> (28–4‰ on top of 304‰) in 1-m perspex columns. Copepodid distribution in a linear gradient, where the salinity increased from 154‰ at 0 cm depth to 304‰ at 87–5 cm, was also recorded. Homogeneous 304‰ salinity columns served as the control. In these, the animals gathered in the top section of the water column in response to 1 h of light from above, and spread downwards in response to 4 h of darkness. In columns with a 15‰ step increase in salinity with depth, copepodids aggregated just underneath the discontinuity irrespective of light conditions. In step salinity gradients of 5‰ and 2‰ S, under both light regimes, animals were significantly more numerous in the step sections compared with the control. In the linear gradient, significant numbers of copepodids accumulated at approximately 20‰ salinity when subjected to 1 h of light. In the dark, there were no significant aggregations. Copepodids were found in 15–17–2‰ salinity in all linear gradient experiments.

Field evidence for copper mobilization by dissolved organic matter

Fluxes of copper from the sediments to the water column in response to the presence of dissolved organic matter were measured in field enclosures placed on the floor of the Contrary Creek arm of Lake Anna, Virginia. Experimental chambers received a spike input of either sodium humate or phytoplankton; unamended chambers served as controls. Over the subsequent five days, water samples were withdrawn from the chambers and analyzed for total and dissolved copper, total and dissolved organic carbon (DOC) Eh, pH, dissolved oxygen, dissolved sulfides and heterotrophic microbial activity. Chambers amended with phytoplankton did not experience a rise in dissolved copper concentrations. Furthermore, the concentrations of dissolved copper in these chambers were not well-correlated with DOC concentrations (r = 0.1175, P = 0.642). Dissolved copper concentrations in chambers amended with sodium humate rose approximately 500% and remained elevated for the duration of the experimental trial (5 days). In this treatment, dissolved copper concentrations were well-correlated with DOC concentrations (r = 0.798, P < 0.005). The increase in dissolved copper in the chambers amended with sodium humate was observed to persist despite reducing conditions which were confirmed by redox measurements and the occurrence of dissolved sulfides. The addition of sodium humate to the chamber water resulted in a net mobilization of copper to the water column from the sediments. In contrast, dissolved organic carbon generated by the decomposition of phytoplankton did not appear to mobilize copper over the time interval examined. None of the changes in soluble copper concentrations could be related to Eh or pH effects. Supplementary laboratory experiments corroborated the field trials. The results suggest that long term (but not short term) products of decomposition processes may enhance the concentration of dissolved copper in the water column by the formation of soluble organometallic complexes.

Patterns in Algal Recruitment from Sediment to Water in a Dimictic, Eutrophic Lake

In the large, dimictic, and highly productive Lake Mendota (Wisconsin, USA), the recruitment rates from sediment to water were determined for some characteristic and dominating algal species during a 1-yr cycle. Quantifying recruitment in relation to abundance in the water on a whole-lake basis revealed that recruitment usually accounted for less than 1% of the total standing stock of each species per day, indicating that recruitment may not be an important population variable in Lake Mendota, but may instead function as an inoculum for future growth in the water column. The recruitment of Cryptomonas erosa and Ceratium hirundinella showed a dephasing among sites, suggesting that algae on the sediment surface rise into the water column in response to some depth-related cue. With the exception of one recruitment period for Aphanizomenon, no recruitment was recorded below the thermocline during the stratification period, indicating that a variable associated with stratified conditions affected algal movements from the hypolimnion to the euphotic zone. We argue that the understanding of recruitment patterns from sediment to water is a key factor in managing algal blooms in highly productive lakes.

The influence of species composition on behaviour in mixed‐species cyprinid shoals

Adult dace, minnows and gudgeon (50 of each) were studied in a fluvarium. Each possible paired‐and three‐species combination was compared with single‐species controls. Species position in the fluvarium and the behaviour of marked individuals were used to measure interactions. Individual behaviours were standardized for day‐to‐day changes in activity level. The presence of a second species caused significant increases in the frequency and total time of behaviours associated with positional change. Such behavioural changes may reduce competition by adjusting individual position within the shoal. Minnows moved higher in the water and downstream in the presence of dace. Gudgeon moved lower in the water and downstream in the presence of dace and of minnows. Dace made slight, but significant, movements downstream and higher in the water column in response to both minnows and gudgeon. These shifts were very distinct, and the resulting shoal structure mirrors the positions occupied in mixed‐species shoals of these species in the wild.

Holocene carbonate sedimentation in Lake Manitoba, Canada

ABSTRACTThe carbonate mineral suite of the modern offshore bottom sediment of the South Basin of Lake Manitoba consists mainly of high magnesian calcite and dolomite with minor amounts of low‐Mg calcite and aragonite. The high‐Mg calcite is derived from inorganic precipitation within the water column in response to supersaturation brought about by high levels of organic productivity in the basin. Both dolomite and pure calcite are detrital in origin, derived from erosion of the surrounding carbonate‐rich glacial deposits. Aragonite, present only in trace amounts in the offshore sediments, is bioclastic in origin. The upward increase in the amount of magnesian calcite in the post‐glacial sediment record is attributed to increasing photosynthetic utilization of CO2 in the lake. Stratigraphic variation in the amount of magnesium incorporated into the calcite lattice is interpreted as reflecting a variable magnesium input to the lake from ground water and surface runoff, and possibly variable calcium removal in the precipitating lake water. The effects of long‐term chemical weathering at the source and size segregation explain the changes in dolomite content throughout the section.

A laboratory investigation into the effects of hydrostatic pressure on the vertical migration of planktonic Crustacea

A laboratory-scale vertical migration, using adult Daphnia magna, was observed within an observational pressure vessel. The animals exhibit a clearly defined movement along the water column in response to an overhead light regime. The hydrostatic pressure was increased to 41.5 bar (600 psi) during the course of a migration. a short lived increase in swimming rate was observed, but the pattern of the migration was quickly restored; the migration continued at the high ambient pressure. The response of D. magna to light does not appear to be affected by high pressure.