Nutrient (P, N) dynamics in the southwestern Kattegat, Scandinavia: sedimentation and resuspension effects

 The yearly nutrient supply from land and atmosphere to the study area in SW Kattegat is 10 900 tons of N and 365 tons of P. This is only few percent of the supply from adjacent marine areas, as the yearly transport through the study area is 218 000 tons of N and 18 250 tons of P. Yearly net deposition makes up 1340 tons of N (on average 2.5 g m^–2 yr^–1) and 477 ton of P (on average 0.9 g m^–2 yr^–1). Shallow-water parts of the study area have no net deposition because of frequent (>35% of the year) resuspension. Resuspension frequency in deep water is <1% of the year. Resuspension rates, as averages for the study area, are 10–17 times higher than net deposition rates. Because of resuspension, shallow-water sediments are coarse lag deposits with small amounts of organic matter (1.1%) and nutrients (0.04% N and 0.02% P). Deep-water sediments, in contrast, are fine grained with high levels of organic matter (11.7%) and nutrients (0.43% N and 0.15% P). Laboratory studies showed that resuspension changes the diffusive sediment water fluxes of nutrients, oxygen consumption, and penetration into the sediment. Fluxes of dissolved reactive phosphate from sediment to water after resuspension were negative in organic-rich sediments (13.2% organic matter) with low porosity (56) and close to zero in coarse sediments with a low organic matter content (2.3%) and high porosity (73). Fluxes of inorganic N after resuspension were reduced to 70% and 0–20% in relation to the rates before resuspension, respectively. Received: 10 July 1995 · Accepted: 19 January 1996     

First record of 1.2 Ga quartz dioritic magmatism in the Archaean Yilgarn Craton,Western Australia,and its significance

Farming of southern bluefin tuna in South Australia currently contributes to more than 30% of the value of the aquaculture production in Australia. This study investigated the natural sedimentary setting of the area designated for this important industry in coastal waters off Port Lincoln, and explored the links between the natural distribution of sediments and potential environmental effects and risks to the industry. Sediments were mostly composed of poorly sorted silts and fine sands, predominantly skeletal remains of carbonate-secreting organisms. The contribution of plankton to the organic matter remaining in the sediments was calculated to be in excess of 80% using concentration-dependent stable-isotope mixing models. An erosional area was identified south of Rabbit Island where sediments contained up to 50% siliciclastic material, grainsize distributions were better sorted and coarser, and organic carbon and total nitrogen contents were very low. In contrast, deeper waters north of Cape Donington were identified as a depocentre for fine sediments, which contained organic matter levels twice those elsewhere in the region despite the extremely high carbonate contents (>80%). The heavier stable isotopic signature of nitrogen suggested that this organic matter comprised a greater fraction of weathered components, probably advected to the area by suspended and bedload transport. This local variability of sediment characteristics in the farming zone suggests that the benthic assimilative capacity of farmed sites will depend on their location. Wastes from pens located south of Rabbit Island in particular are likely to be quickly winnowed out by wave and tidal action. These pens are also less likely to be affected by resuspension of fine sediments that might be associated with unusually severe storms.     

Paleoceanographic Setting and Preservation of Buried Manganese Deposits in DSDP/ODP Cores

Abstract. The occurrence, lithology, and stratigraphic setting of buried manganese deposits and associated host sediments in cores obtained on Legs 123–210 of the Ocean Drilling Program (ODP) are examined in order to establish the formative environment and conditions of preservation. Fossil manganese nodule and crusts are found to have formed or deposited throughout the period from 100 Ma to the present, with an additional example of formation near 137 Ma, suggesting that the deep-sea environment has been oxic and suitable for the formation of manganese nodules and crusts since the Cretaceous. Many manganese nodules and crusts occur on horizons corresponding to hiatuses in sedimentation or periods of slow sedimentation, consistent with the environment in which modern nodules form (sedimentation rate less than 10 m/m.y.). Sediments overlying the fossil nodules and crusts are oozes or biogenic sediments with sedimentation rates of 1–18 m/m.y. Low total organic carbon (<0.1 wt%) in the overlying sediments and high sulfate content (>25 mM) in interstitial water around the manganese horizon suggest that no strong reduction occurred within the overlying sediments. Coverage by biogenic sediments containing only small amounts of organic matter is therefore considered important for the preservation of manganese nodules and crusts. Manganese carbonate occurs sporadically as nodules, concretions or thin layers in various host sediments, including clay, calcareous ooze and siliceous ooze with sedimentation rates of 6–125 m/m.y. Hiatuses are rare around the host sediments of manganese carbonate. Higher total organic carbon (0.2–1.8 wt%) in the host sediments and lower sulfate content (0–25 mM) in interstitial water around the manganese carbonate horizon suggest that reduction in association with decomposition of organic matter would have proceeded in the host sediments.     

Signature and timing of the Kattegat Ice Stream: onset of the Last Glacial Maximum sequence at the southwestern margin of the Scandinavian Ice Sheet

At the end of the Middle Weichselian (30–25 ka BP) a glacier advance from southern Norway, termed the Kattegat Ice Stream, covered northern Denmark, the Kattegat Sea floor and the Swedish West Coast during onset of the Last Glacial Maximum (LGM) at the southwest margin of the Scandinavian Ice Sheet. The lithostratigraphic unit deposited by the ice stream is the till of the Kattegat Formation (Kattegat till). Because morphological features have been erased by later glacial events, stratigraphic control and timing are decisive. The former ice stream is identified by the dispersal of Oslo indicator erratics from southern Norway and by glaciodynamic structures combined with glaciotectonic deformation of subtill sediments. Ice movement was generally from northerly directions and the flow pattern is fan-shaped in marginal areas. To the east, the Kattegat Ice Stream was flanked by passive glaciers in southern Sweden and its distribution was probably governed by the presence of low permeability and highly deformable marine and lacustrine deposits. When glaciers from southern Norway blocked the Norwegian Channel, former marine basins in the Skagerrak and Kattegat experienced glaciolacustrine conditions around 31–29 ka BP. The Kattegat Ice Stream became active some time between 29 ka BP and 26 ka BP, when glaciers from the Oslo region penetrated deep into the shallow depression occupied by the Kattegat Ice Lake. Deglaciation and an interlude with periglacial and glaciolacustrine sedimentation lasted until c. 24–22 ka BP and were succeeded by the Main Glacier Advance from central Sweden reaching the limit of Late Weichselian glaciations in Denmark around 22–20 ka BP, the peak of the LGM. This was followed by deglaciation and marine inundation in the Kattegat and Skagerrak around 17 ka BP.     

A sediment chronology of the eutrophication of Chesapeake Bay

Chesapeake Bay sediments were examined for biogeochemical evidence of eutrophication trends using two mesohaline sediment cores. Measurements of ²¹⁰Pb geochronology and sediment profiles of organic carbon, nitrogen, organic phosphorus, inorganic phosphorus, and biogenis silica (BSi) were used used to develop temporal concentration trends. Recent sediments have 2–3 times as much organic carbon and nitrogen as sediments from 80 to 100 yr ago, but the increases result from both changes in organic matter deposition and time-dependent changes in organic matter decomposition rates. Despite increases in phosphorus loading, no major changes in phosphorus concentration were noted throughout most of the century; anthropogenic phosphorus deposition, though not evident in sulfidic mid-bay sediments, must occur in more oxidizing sediment environments in both the northern and southern bays. Temporal trends in BSi concentrations are much less evident and the lack of substantial increases in this century suggest that BSi inputs may be capped by late spring-summer Si limitation.     

Suspended sediment transport,sedimentation, and resuspension in Lake Houston,Texas: Implications for water quality

Lake Houston is a man-made reservoir located northeast of Houston, Texas. The purpose of this investigation was to document suspended sediment transport, sedimentation, and resuspension in the lake with a view towards estimating the influence of sedimentation on water quality. Sediment traps were placed in strategic locations in the lake to collect suspended sediments. Samples were analyzed for bulk density, grain size, organic carbon, and a number of trace elements. These data were analyzed along with meteorological data to examine those factors which regulate suspended sediment input and dispersal, and the role of suspended sediments in controlling water quality within the lake. Sediment input to the lake depends primarily on the intensity of rainfall in the watershed. Sediment movement within the lake is strongly influenced by wave activity, which resuspends sediments from shallow areas, and by wind-driven circulation. The increased residence time of suspended sediments due to resuspension allows greater decomposition of organic matter and the release of several trace elements from sediments to the water column. Virtually all samples from sediment traps suspended between 1 and 5 m above the lake bottom contain medium to coarse silt, and even some very fine sand-sized material. This implies that circulation in Lake Houston is periodically intense enough to transport this size material in suspension. During winter, northerly winds with sustained velocities of greater than 5 m/sec provide the most suitable condition for rapid (<1 d) transport of suspended sediment down the length of the lake. Fluctuations in current velocities and the subsequent suspension/deposition of particles may explain variations in the abundance of coliform bacteria in Lake Houston.     

Organic carbon burial rates,and carbon and sulfur relationships in coastal sediments of the southern Baltic Sea

Organic C burial rates and C–S relationships were investigated in the Holocene sediment sequences of 3 shallow polymictic coastal lagoons in the southern Baltic Sea to better understand the biogeochemical cycling of C and S in these environmental systems. The results show that these lagoons may have a considerable influence on the environmental status of the southern Baltic Sea area in having the potential to act as a temporary sink or source for heavy metals. High organic C accumulation rates (C_org-AR) can be observed in the sediments due to a high organic matter supply from land and a high productivity of the water bodies as a result of eutrophication. However, organic C burial does not increase as a result of increasing sediment accumulation rates (SAR). Even when high sedimentation rates do occur, there appears to be a thorough recycling and resuspension of the sediment enhancing the biological decay of organic matter before burial or the removal of organic matter from the system by transport. That is why high SAR in the coastal lagoons do not enhance pyrite formation, and thereby permanent fixing of heavy metals in the sediments, to the extent that could be expected from their magnitude. Initially there is a high potential for a temporary binding of heavy metals, but the latter are likely to be subject to mobilization and redistribution within the sediments and the water column. The patterns of burial of organic and mineral matter are different from those observed in the present-day Baltic Proper, implying possible important links in deposition between the central and coastal areas of the Baltic Sea and implications for C cycling in the ecosystem of the Baltic Sea.     

太平洋西部深海沉积物中有机质、氮、磷的初步研究

本文通过对太平洋西部(南纬2°-8°,东径170°-173°20')水深在3800-5200米7个站位柱状样中有机质、氮、磷的含量分析,并与沉积物中粒度、微古、底栖生物、矿物资料的对比研究,指出了太平洋西部深海沉积物中有机质、氮、磷的分布规律,控制因素及地球化学特征。资料研究表明:有机质、氮主要来自海水的化学作用及生物作用的沉淀物,而磷同时又有火山喷发时颗粒无机磷的加入;有机质、氮的含量分布与沉积物类型密切有关,在某种程度上,对太平洋西部的沉积环境起了标志作用。     

Benthic Phosphorus Dynamics in the Gulf of Finland, Baltic Sea

Benthic fluxes of soluble reactive phosphorus (SRP) and dissolved inorganic carbon (DIC) were measured in situ using autonomous landers in the Gulf of Finland in the Baltic Sea, on four expeditions between 2002 and 2005. These measurements together with model estimates of bottom water oxygen conditions were used to compute the magnitude of the yearly integrated benthic SRP flux (also called internal phosphorus load). The yearly integrated benthic SRP flux was found to be almost 10 times larger than the external (river and land sources) phosphorus load. The average SRP flux was 1.25?±?0.56?mmol?m^?2?d^?1 on anoxic bottoms, and ?0.01?±?0.08?mmol?m^?2?d^?1 on oxic bottoms. The bottom water oxygen conditions determined whether the SRP flux was in a high or low regime, and degradation of organic matter (as estimated from benthic DIC fluxes) correlated positively with SRP fluxes on anoxic bottoms. From this correlation, we estimated a potential increase in phosphorus flux of 0.69?±?0.26?mmol?m^?2?d^?1 from presently oxic bottoms, if they would turn anoxic. An almost full annual data set of in situ bottom water oxygen measurements showed high variability of oxygen concentration. Because of this, an estimate of the time which the sediments were exposed to oxygenated overlying bottom water was computed using a coupled thermohydrodynamic ocean?Csea and ecosystem model. Total phosphorus burial rates were calculated from vertical profiles of total phosphorus in sediment and sediment accumulation rates. Recycling and burial efficiencies for phosphorus of 97 and 3%, respectively, were estimated for anoxic accumulation bottoms from a benthic mass balance, which was based on the measured effluxes and burial rates.     

Composition and diagenesis of neutral carbohydrates in sediments of the Baltic-North Sea transition

The distribution and composition of neutral carbohydrates in the solid phase and porewater, and their role in carbon cycling were investigated in contrasting marine sediments of the Baltic-North Sea region. Depth-invariant profiles of particulate carbohydrates (PCHO) and low PCHO yields (PCHO/organic carbon) indicated that a small inert carbohydrate fraction deposits on the sediment at the deeper stations in the northern Kattegat and Skagerrak compared to the shallower stations further South. This was supported by long-term sediment incubations, in which the PCHO concentrations remained unchanged during 480 days, revealing that neutral carbohydrates play a minor role in carbon mineralization at the deeper sites. In contrast, the reactivity of PCHO was high (first-order rate constant of 3.2 yr⁻¹) at one shallow site in the Belt Sea. Monosaccharide spectra were uniform with sediment depth and between sites with the exception of the shallowest site in the middle of Kattegat, where glucose dominated the polymers at the surface. This was likely due to benthic diatoms. Addition of fresh algae to surface sediment from the deeper sites resulted in a preferential mineralization of particulate glucose polymers. The addition of algae also resulted in an initial pulse of glucose in the porewater pools of total hydrolyzable carbohydrates (THCHO), indicating a faster hydrolysis of glucose polymers in the particulate phase than the subsequent hydrolysis and bacterial consumption of oligo- and polymers of glucose in the porewater. This study shows that some carbohydrates such as glucose polymers are selectively utilized by heterotrophic bacteria during the settling of organic particles through the water column, and a relatively inert fraction arrives to the sediments where much of it escapes mineralization and becomes permanently buried. In shallow coastal environments, where the degradation in the water column is less extensive and where benthic algae may represent a local carbohydrate source, neutral carbohydrates appear to be more important in organic matter mineralization.     

Surface sediments of transboundary Lake Peipsi: composition, dynamics and role in matter cycling

To describe and analyse the role of sediments in the matter cycling in large shallow transboundary Lake Peipsi (L. Peipsi) in north-eastern Europe, detailed surface-sediment mapping was conducted. On the basis of grain size the surface sediments fall into three groups: coarse-grained sediments (prevailingly sands in the lake’s southern part), fine-grained sediments (mainly silts) and silty sands, both in the central deeper part within the 8-m depth contour. The groups of deposits have a distinct spatial distribution, determined mainly by the current system in the lake. The main source of bottom sediments is the erosion of the lake floor and shores, the role of the river input seems to be limited. Fine-grained organic-rich sediments are very cohesive, playing the main role in the circulation of various inorganic and organic pollutants like nutrients and xenobiotics. Due to the cohesive character of the sediments their physical and chemical properties are extremely diverse and if the near-bottom shear stress increases (extreme meteorological events, changes in the water level, etc.), the lake floor may be subjected to episodic erosion and resuspension, which may cause remobilisation of impurities in muddy sediments and their return to the food chain.     

The West Bornholm basin in the Baltic Sea: geological structure and Quaternary sediments

KÖgler, F.-C. & Larsen, B. 1979 03 01: The West Bornholm basin in the Baltic Sea: geological structure and Quaternary sediments. Boreas . Vol. 8, pp. 1–22. Oslo. ISSN 0300–9483.
The West Bornholm basin is an approx. 1000 km² subbasin of the Bornholm basin just north of Bornholm. The basin has been mapped by acoustic profiling and sampling of the sea floor. The basin is eroded down into Mesozoic sediments which are downfaulted between basement horsts in the Fennoscandian Border Zone. The development of the Quaternary morphology is illustrated by maps of the surface of the bedrock, the glacial landscape beneath the varved clays, the recent topography combined with isopach maps of late Glacial and Holocene formations. Quaternary formations are defined and described. The brown, very fine grained varved clay is deposited as a conformable cover on the substratum. It is probably deposited from suspensions carried in the whole water body, while turbidity currents were of minor importance. The recent sedimentary environment is an example of a restricted, but not totally anoxic basin. The recent sediment is chiefly mud rich in organic matter (ca. 4% C_org). According to a rough estimate, the long-term mean sedimentation rate of organic carbon is 6 g/m²/year.     

潮白河中游沉积物氮磷和有机质分布特征及评价

潮白河是京津冀地区的重要河流。本研究以潮白河中游段为研究区,针对该区段沉积物有机质、氮磷污染程度不明的问题,通过对研究区130个采样点表层沉积物中有机质(OM)、总氮(TN)和总磷(TP)的测定,分析了表层沉积物中有机质和氮磷的分布特征及污染来源,将有机指数和有机氮污染指数评价法相结合开展污染及生态风险评价。结果表明:(1)潮白河中游表层沉积物中OM含量变化范围为0.17%~13.15%,平均含量为5.32%; TN的含量为0.005~1.028 g/kg,平均含量为0.192 g/kg;TP的含量为0.367~4.825 g/kg,平均含量为1.662 g/kg。(2)相关性分析表明,OM与TP、OM与TN均呈弱相关,而TN与TP呈强相关。这是因为TN和TP来源相近,主要来自外源,与OM来源有一定差异。根据TOC/TN特征分析,OM主要受藻类、浮游植物和非纤维束植物等影响。(3)有机指数评价结果显示,潮白河中游段表层沉积物监测点中60%为清洁,33.85%为较清洁,4.62%为尚清洁,1.54%为有机污染。有机污染点主要位于运潮减河入潮白河口和田贾庄排干渠入潮白河口。区域有机氮评价结果以清洁级别为主,整体较好。     

近海沉积物中氮磷的同时测定及其在胶州湾沉积物中的应用

通过实验优化确定了近海自然粒度下沉积物中氮和磷同时浸取并测定的条件，其中无机态氮和无机态磷用0．1moL／L盐酸浸取后测定；总氮、总磷采用氢氧化钠与过硫酸钾混合氧化剂进行氧化浸取后测定。用这种方法研究了胶州湾沉积物中的氮与磷，探讨了其沉积物中氮和磷的地球化学分布特征，发现胶州湾沉积物中有机氮可占总氮的50％～70％，而有机磷所占总磷的比例低于40％，从湾内到湾外这一比例有降低的趋势；与其他海区相似，胶州湾表层沉积物中无机氮和无机磷的相对含量随着深度的增加而增大，在次表层则趋于稳定或变化较小；而有机氮和有机磷的垂直变化与其相反。结果表明，这种沉积物氮、磷的同时测定方法，具有操作简单、精密度高等特点，可用于近海沉积物氮、磷生态学功能及过量氮、磷生态毒理的研究。     

Theoretical post-glacial sedimentation rates for a semi-enclosed sea; example of the Kieler Bucht, Western Baltic

The theoretical rates of deposition for fine sediments over the last 10 ka have been deduced and plotted for the Kieler Bucht. Assumptions are that the bay has remained as a closed sedimentary system, and that the fine sediments deposit in water deeper than 10 m. A sharp peak of sedimentation activity is indicated between 7.5 and 8.5 ka B.P. with low rates prior to 9.5 ka and since 6 ka. Comparison of rates obtained from dated cores extracted from different parts of the Kieler Bucht with the theoretical curve shows general conformity, and confirms that peak sedimentation rates exceeding 3 mm/a, as averaged over 100–200 years, occurred between 8 and 9 ka, with the suggestion of a minor activity peak between 3 and 4 ka. The overall consistency supports the view that the bay has acted essentially as a closed sedimentary basin during the Holocene marine transgression and subsequently.     

Distributions of total,inorganic and organic phosphorus in surface and recent sediments of the sub-tropical and semi-pristine Guaratuba Bay estuary,SE Brazil

This study addresses the distribution of total phosphorus (TP) and its inorganic (IP) and organic (OP) fractions, grain-size and organic matter of surface and recent sediments, coupled to the behavior of total and dissolved inorganic phosphorus (TP and DIP) of the water column, of the semi-pristine Guaratuba Bay estuary, SE Brazil. Surface sediment samples were taken at 43 sites spread along the estuarine gradient and recent sediments from 3 short (35 cm long) cores from the upper, central and lower portions of the estuary, respectively. Highest TP and IP concentrations of surface sediments were detected within the upper sector and the transition zone between the upper and central sectors, all characterized by fine sediments, low salinities and water depths. In contrast, the lower sector and its narrow and deep tidal channel, subject to more intense tidal forcing, exhibited a higher fraction of sandy sediments with lower TP, IP and OP contents. In spite of the spatial variability in sediment grain size, IP corresponded to the major fraction of TP in all estuarine sectors and both TP and IP correlated significantly with the fine sedimentary (silt + clay) grain-size fraction. The fine surface sediments acted as a trap for IP at the fresh water–low salinity interface, which also corresponded to the region of a DIP sink in surface waters. In general, the short sediment cores showed that TP and IP contents increased from 15 cm depths to the top layer. Published sedimentation rates from additional cores taken at the sites of the short cores of this study, implied that depositional alterations of TP and IP increased during the early 1970s, which corresponded to the onset of anthropogenic disturbances from crop plantations in the lowland plains of the river end-member and urbanization at the estuary’s mouth and along the adjacent coast.     

Sediment resuspension and transport in Lake Michigan during the unstratified period

Instrumented moorings were deployed during the winter of 1994–95 at three depths (28, 58 and 101 m) in southern Lake Michigan. Storms during the observation period were not unusually severe, so the processes observed are typical of those that occur during an average winter. Time series observations of water temperature, beam attenuation coefficient (a measure of water transparency) and current velocity show that local resuspension of bottom sediment occurred frequently after the breakdown of the thermocline. Resuspension was most frequent close to the shore but was also observed at the 58 m station. Local resuspension did not occur at the 101 m station, but advection to the site of material resuspended at shallower sites was observed. These observations do not support the hypothesis proposed by previous investigators that local resuspension at depths of 100 m or greater occurs during the unstratified period. It is more likely that fine-grained material resuspended by storm action in intermediate water depths (≈ 30–60 m) is transported into the deeper parts of the lake by the general lake circulation.     

北黄海沉积物中氮的地球化学特征及其早期成岩作用

本文首次报道对北黄海沉积物中氮的形态及其早期成岩作用的研究成果。结果表明 ,北黄海沉积物中占主导地位的是细粒度组分 ,其结构和性质直接影响着沉积物中化学元素的形态、含量与分布 ,使自然粒度沉积物中各形态氮的垂向分布与细粒度组分中各形态氮的分布非常相近。在氮的早期成岩过程中 ,粒度也起着非常重要的作用 ,沉积物的粒度越细 ,沉积物中有机氮的分解速率越小 ,即细粒度沉积物中有机氮的分解矿化速率最小 ,易于富集有机氮。对于不同站位的沉积物来说 ,因其沉积速率的差异 ,致使沉积物中各形态氮的埋藏通量有很大差异 ,沉积速率越大 ,沉积物中各形态氮的埋藏通量越大 ,在沉积速率最大的 C4站位 ,各形态氮的埋藏通量最大。     

Biogeochemical cycling in an organic-rich coastal marine basin. 5. Sedimentary nitrogen and phosphorus budgets based upon kinetic models,mass balances,and the stoichiometry of nutrient regeneration

The rapid rates of sediment accumulation (~ 10–20 cm/yr) in the recently formed Cape Lookout Bight, North Carolina, have resulted in the deposition of approximately 157 moles of carbon, 14 moles of nitrogen and 1.3 moles of phosphorus, per square meter annually. The metabolism of the organic matter in these anoxic sediments is dominated by sulfate reduction and fermentation reactions. Sedimentary nitrogen and phosphorus budgets are estimated using 3 related approaches: 1) a kinetic model of solid phase diagenesis; 2) direct measurements of nutrient burial and regeneration; and 3) nutrient recycling rates estimated from annual rates of sulfate reduction and the SO₄:NH₄ and SO₄:PO₄ stoichiometry of nutrient regeneration. The mass balances derived agree reasonably well and indicate that approximately 30% of the total nitrogen and 15% of the total phosphorus deposited in these sediments are recycled. The kinetics of nutrient regeneration are rapid. The mean residence time for recycled nutrients within the sediment is 4 to 6 months for nitrogen and 1.5 to 2 years for phosphorus. Nearly 60% of the total nitrogen regeneration and 90% of the total phosphorus regeneration occur during the 4 month summer period of June through September. Nitrogen regeneration, like carbon, appears to be controlled by the microbially-mediated metabolism of labile organic matter. The greater asymmetry and lower percent turnover in phosphorus cycling is apparently due to changes in its solubility under oxidized and reduced conditions and selective regeneration prior to deposition.