High Organic Sediments Research Articles

Eelgrass Genetic Diversity Influences Resilience to Stresses Associated with Eutrophication

Eelgrass (Zostera marina L.), an underwater marine flowering plant, has a high degree of morphological plasticity that allows it to survive and adapt to environmental changes. To test the effect of eelgrass genetic diversity (measured as allelic richness and observed heterozygosity) on resilience to stresses associated with eutrophication, eelgrass from ten genetically differentiated populations was studied in outdoor mesocosms. In a full factorial experiment lasting 3 months, eelgrass was subjected to two light levels (100 and 58% ambient) and two sediment treatments (1 and 8% organic content). Some populations of eelgrass showed higher resilience, measured as a combination of productivity and survival, when exposed to the stress of high sediment organic matter and, to a lesser extent, reduced light. Overall, eelgrass resilience correlated positively with eelgrass source population genetic diversity. The findings show that eelgrass resilience to stress typical of eutrophic estuaries (low light, high organic sediment) is improved by genetic diversity, with implications for transplantation, conservation, and management.

Utilisation of XRF core scanning on peat and other highly organic sediments

XRF core scanning (XRF-CS) is a valuable tool, which allows for the rapid, non-destructive geochemical analysis of sediment cores at extremely high (sub-millimetre) resolution. Peat sediments, due to their near-worldwide distribution, high organic content allowing for reliable radiocarbon chronology development, and typically autochthonous nature, have long been used for palaeoenvironmental reconstructions. However, XRF-CS methods have been utilised on peat sediments relatively rarely. This is due in part to analytical uncertainty relating to high water content, uneven sediment surfaces and high organic matter contents negatively impacting the ability of the approach to reliably reproduce elemental compositions. Here we provide evidence from Mohos peat bog record in central Romania, and, by comparing to ICP measurements, indicate the ability of XRF-CS to consistently investigate the elemental geochemistry of peat sediments for major elements such as Fe and Ti. However, trace element (Cu, Ni and Sc) measurements appear to be unreliable, due in part to measurements approaching detection limits, and the diluting nature of the peat. Further, we investigate the usefulness of the Incoherent/Coherent (inc/coh) scattering ratio as a proxy for organic matter content, concluding that within high-organic sediment such as peat, the ratio does not pick up small shifts (<5%) in organic content. Finally, we present a review of approaches applied to investigating peat sediments via XRF-CS to date, with a number of suggestions for future avenues of research.

Dynamics of surface elevation and microtopography in different zones of a coastal Phragmites wetland

Surface elevation and microtopography of coastal wetlands are important attributes with respect to the adaptation to sea level change. While the total increase in elevation determines if a wetland can keep up with sea level rise, microtopography impacts, inter alia, hydrological patterns, which again drive surface elevation changes. We analyzed the dynamics of surface morphology during the course of one year at five locations along a transect from land (interior zone) to sea (fringe zone) in a coastal Phragmites wetland at the Darss-Zingst Bodden Chain (Southern Baltic Sea) using a modified Surface-Elevation Table. Landwards this wetland is confined by a dyke while the seaward boundary of the wetland is formed by a micro-cliff. A small strip between the interior and the fringe zone is characterized by small basins (basin zone). Surface elevation changes in the wetland interior are mainly driven by its own productivity. Litter accumulation by the dense Phragmites stands is high, but a combination of high organic sediments and water scarcity led to compaction and counteracted vertical accretion. While the surface elevations of the measurement location in the basin zone and one of the locations in the interior zone remained fairly stable (intra-annual changes<±0.8mm), the other location in the interior showed a drastic decrease in surface elevation (−3.3cmyear−1). This large deviation may have been caused by the high spatial variability of sediment organic matter. The micro-cliff eroded constantly (−3.7cmyear−1); its steepness and surface roughness increased making it more vulnerable to the forces of the sea. The micro-cliff protects the wetland interior from flooding but at the same time suppresses allogenic sediment input. The simple approach to use freely available water level data to predict morphological changes in the fringe zone did not yield significant model results. However, the strong intra-annual variability in elevation change especially in the fringe zone showed that short-term changes may often mask long-term trends. Although we cannot predict long-term developments from our relatively short-term measurements, our results indicate that wetland evolution in such squeezed environments is threatened. In dyked wetlands sediment supply from the land is suppressed and lateral erosion at the seaward edge leads to marsh retreat. None of the measuring locations is currently keeping up with local sea level rise.

THE EARLY JURASSIC OIL SHALES IN THE QIANGTANG BASIN, NORTHERN TIBET: BIOMARKERS AND TOARCIAN OCEANIC ANOXIC EVENTS

In the Qiangtang Basin, northern Tibet, the most complete and extensive marine sedimentary strata outcropped in the Shuanghu-Sewa-Amdo area during the Jurassic, especially the Early Jurassic. The organic-rich marine sediments - commonly referred to as black shales - were deposited in the Early Jurassic, therefore, many petroleum geologists have been focusing on them for many years. Although achievements in geological investigations and petroleum resource assessments during recent years have been remark- able, the environmental conditions, mechanics, and process that resulted in the deposition of high-organic sediments during the Early Toarcian (183- 176.5 Ma, Early Jurassic) Oceanic Anoxic Event are still a matter of dis- cussions. In this paper, we deal with the biomarker distributions of Lower Jurassic oil shales in the Biluo Co section, Shuanghu area of northern Tibet. The oil shales are characterized by a marked predominance of short chain n- alkanes with a maxiumun at C16 or C17, nC17/nC31 ratio values between 9.4 and 17.8, and low Pr/Ph ratios. Furthermore, a series of C27 and C29-C35 hopanes with minor amounts of gammacerane are present in all samples, as indicated by gammacerane/C30-17α-hopane values from 0.06 to 0.12 and the steranes C27/C29 ratios higher than 1 in the three samples. The above- mentioned parameters indicate that the organic matter source is attributed to an algal/bacterial contribution. According to maturity parameters, all the homohopane 22S/(22S+22R) values in this study are > 0.58 and the sterane 20S/(20S+20R) values are all between 0.48 and 0.59, which is consistent

Distinguishable root plaque on root surface of Potamogeton crispus grown in two sediments with different nutrient status

The properties of plaques were different on the root surface of Potamogeton crispus planted in sediments from two different shallow lakes. Lake Tangxunhu sediment, with low pH, contained low organic matter, whereas Lake Yuehu sediment, with high pH, had high calcium deposits mixed with high organic matter. The contents of mineral elements in sediment of Lake Tangxunhu was lower than that of Lake Yuehu, except for iron (Fe) content, but the contents of mineral elements extracted by sodium dithionite–sodium citrate–sodium bicarbonate (DCB) from root plaques were higher in Lake Tangxunhu than those in Lake Yuehu, except for Fe. These element distributions on P. crispus root plaques were characterized by scanning electron microscope combined with energy-dispersive X-ray spectrometer and were consistent with the contents of mineral elements in sediment. The root plaque of P. crispus planted in Lake Tangxunhu sediment mainly contained silicon (Si) and Fe, and the content of Si was greater than Fe, which may be contributed to the formation of poly-silicic-ferric in the natural conditions. However, the root plaque of P. crispus planted in the sediment with higher calcium content of Lake Yuehu was rich in Fe, Si, phosphorus (P), and calcium (Ca). Due to oxygen secretion by plant roots, the root plaque has more Fe3(PO4)2 and a certain amount of Ca3(PO4)2. The ratio of magnesium (Mn) to Fe extracted by DCB from root plaque in Lake Tangxunhu sediment was 0.031 and 0.010 in Lake Yuehu sediment. In Lake Tangxunhu sediment, lower content of organic matter results in weak reducibility. Enhanced oxidation ability by oxygen secretion of P. crispus root could oxidize low-valent Fe and Mn into iron–manganese oxide, which leads to formation of iron–manganese plaque on the root surface. However, this case is different in Lake Yuehu sediment, where Fe and Mn can be reduced in high organic sediment and low-valent Mn can precipitate in the sediment in which pH is >8. Thus, low-valent Fe in Lake Yuehu sediment moves to the root surface of P. crispus, where it oxidizes into Fe oxide, i.e., Fe plaque.

A high‐resolution record of vegetation and climate through the last glacial cycle from Caledonia Fen, southeastern highlands of Australia

AbstractA blocked tributary has provided a rare site of long‐term sediment accumulation in montane southeastern Australia. This site has yielded a continuous, detailed pollen record through the last ca. 140 000 years and revealed marked vegetation and environmental changes at orbital to sub‐millennial scales. Radiocarbon and optically stimulated luminescence (OSL, or optical) ages provide some chronological control for the last ca. 70 000 years. Most of the sediment is inorganic but with well preserved pollen that accumulated under unproductive and probably largely ice‐covered lake conditions. The lake was surrounded by low‐growing plants with an alpine character. Exceptions include three discrete periods of high organic sedimentation in the basin and forest development in the surrounding catchment. The two major periods of forest expansion are related to the last interglacial and the Holocene, with the third, shorter period considered to represent an interstadial in the early part of Marine Isotope Stage (MIS) 3. The latter part of the last glacial period is characterised by abrupt sub‐millennial, amelioration events that may relate to documented global oscillations emanating from the North Atlantic. There are systematic changes through the record that can be partly attributed to basin infilling but the progressive reduction and regional extinction of some plant taxa is attributed to a long‐term trend towards climatic drying. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Oxygen stress and reduced growth of Lobelia dortmanna in sandy lake sediments subject to organic enrichment

Summary1. Lobelia dortmanna is a common representative of the small isoetid plants dominating the vegetation in nutrient‐poor lakes in Europe and North America. Because of large permeable root surfaces and continuous air lacunae Lobelia exchanges the majority of O2 and CO2 during photosynthesis across the roots. This leads to profound diel pulses of O2 and CO2 in sandy sediments with low microbial O2 consumption rates. The ready radial root loss of O2 may, however, make Lobelia very susceptible to more reducing sediments. Therefore, we grew Lobelia for 6 months on natural and organically enriched sandy sediments to test how: (i) root oxygenation influenced degradation of organic matter and depth profiles of N and C; (ii) Lobelia and microbial O2 consumption rates influenced pool size and depth penetration of O2 in the sediments; and (iii) sediment enrichment influenced growth and mineral nutrition of Lobelia.2. Naturally low‐organic sediments (0.32% DW) accumulated organic C and N during the experiment as a result of growth of Lobelia and surface micro‐algae. In contrast, surface layers of enriched sediments (0.58, 0.87 and 2.46% DW) lost organic C and N because of enhanced mineralisation rates because of oxygen availability. In deeper layers of enriched sediments no significant differences in organic C and N pools were found between plant‐covered and plant‐free sediments probably because faster organic degradation because of root oxygenation was balanced by release of organic matter from the plants and because short roots with dense Fe‐Mn coatings in the most enriched sediments constrained O2 release.3. Depth‐integrated O2 pools were much higher in light than darkness, higher in plant‐covered than plant‐free sediments and higher in sandy than in organically enriched sediments. All sediments had a primary O2 maximum 1–2 mm below the sediment surface in light because of photosynthesis of micro‐algae. Plant‐covered sediments of low organic content (0.32 and 0.58% DW) also had a secondary deep maximum (2–4 cm) because of higher O2 release from Lobelia roots than microbial O2 consumption. Nitrification occurred here resulting in depletion of NH and accumulation of NO. In low organic sediments, oxygen pools increased with higher plant biomass both in light and darkness. The deep O2 and NO3 maxima disappeared in high organic sediments of greater O2 consumption rates and smaller O2 release rates.4. Lobelia was stressed by increasing O2 consumption rate of the sediments. Plant weight and leaf number declined twofold and maximum root length declined fourfold suggesting severe problems maintaining sufficient axial O2 transport to the root tips because of rapid radial O2 loss. Despite markedly higher nutrient concentrations in the enriched sediments, leaf‐N declined twofold and leaf‐P declined fourfold to growth‐limiting levels. These responses can be explained by constrains on mycorrhisal activity, root metabolism and vascular transport because of O2 depletion. Management efforts to stop the decline and ensure the recovery of the isoetid vegetation should therefore focus on improving water quality as well as sediment suitability for growth.

Sulfate reduction in lake sediments inhabited by the isoetid macrophytes Littorella uniflora and Isoetes lacustris

Sulfur cycling was examined in sediments inhabited with the isoetids Littorella uniflora and Isoetes lacustris in the oligotrophic soft-water Lake Kalgaard, Denmark. Based on short-term tracer incubations sulfate reduction was measured along a transect from the shore (0.6 m) to profundal sediments (4.6 m). The sulfate reduction rates were low (0.008–0.8 mmol m −2 d −1) in the sandy shallow sediments with low organic content (<1.3 mmol C g −1 sed DW) and high redox potentials (>100 mV), whereas sulfate reduction was higher at the deeper sites (2.7–4.6 mmol m −2 d −1) with high organic content (max. 11.5 mmol C g −1 sed DW) and lower redox potentials (<100 mV). High concentrations of dissolved organic carbon (DOC) were found in the low particulate organic sediments (up to 18.4 mM), and most of the DOC pool consisted of acetate (40–77%). Reoxidation of sulfides due to root oxygen release was probably important at all sites and a positive efflux of sulfate across the sediment–water interface was measured, attaining rates (up to 4.8 mmol m −2 d −1) similar to the sulfate reduction rates. Reoxidation of sulfides was also manifested by high fraction (>80%) of reduced sulfides being accumulated as elemental sulfur or pyrite (chromium reducible sulfur, CRS). The largest pools of CRS were found in high organic sediment with vertical distributions resembling those of the sulfate reduction rates. The overall effect of isoetid growth on sulfur cycling in the rhizosphere is a suppression of sulfate reduction in low organic sediments and the governing of sulfide reoxidation in sediments with higher organic content.

Interferences between root plaque formation and phosphorus availability for isoetids in sediments of oligotrophic lakes

Freshwater isoetids exchanges a high proportion of the photosynthetically produced oxygen over the extensive root system and, therefore, they influence the redox potential (Eh) and phosphorus (P) availability in their sediments. Because isoetids rely on the sediment for P uptake, P may be a key element in controlling the distribution of isoetids. We investigated biomass and P availability to isoetids (Littorella uniflora and Isoetes lacustris) in a transect of five stations across the littoral zone in oligotrophic Lake Kalgaard, Denmark. At the two shallowest stations (0.6 and 1.0 m depth) the redox potential in the low organic rhizosphere sediment was high (>300 mV) and low concentrations of reduced exchangeable iron (Fe) and manganese (Mn) compounds in the sediment and of precipitated Fe and Mn oxides on isoetid roots (plaques) were found. The concentration of sediment P pools was low and so was isoetid P content and isoetid biomass. At intermediate water depth (1.8 m) sediment Eh was high (∼300 mV) and isoetids showed low root plaque concentrations. However, higher concentration of P pools in the rhizosphere was found at 1.8 m and isoetids showed the highest P content and biomass. At deeper stations (2.8 and 4.6 m depth) Eh was low (<100 mV) in the high organic rhizosphere and high concentrations of plaques were found. The P content in the sediment was high, however, isoetids showed low biomass and low P content. We suggest that the low P content in isoetids growing on P rich organic sediments is partly due to inhibition of the P uptake because of adsorption of P to the oxidized Fe and Mn plaques. However, ratios between oxidized Fe and Fe-bound P, 150 for plaques and 40 for sediment, suggest the isoetids are able to access some of the P that is bound in the plaques. The pools of dissolved P in the porewater were 25–1100 times lower than the estimated annual P requirement for net growth of isoetids while solid fraction P pools were 20–260 times higher than the estimated annual P requirement. Clearly, the oxygen release from isoetid roots decreases the availability of P either by keeping the entire rhizosphere oxidized (low organic sediments) or by the formation of root plaques (high organic sediments).

Oligochaetes, organic sedimentation, and trophic state: how to assess the biological recovery of sediments in lakes?

Oligochaete communities were used to assess the biological recovery of sediments after the abatement of eutrophication in Lake Geneva (Switzerland). In 1995, mean relative abundance of oligotrophic worm species (OS) was around 30% in areas of low organic sedimentation (LOS) whereas, in areas of high organic sedimentation (HOS), it was below 15%. The abundance of OS observed in LOS areas was close to values predicted from total phosphorus (TP) concentrations in the water. Recovery from eutrophication proceeded at the same pace in the water (TP) and in the sediment (OS) of LOS areas, whereas it was delayed in the sediment of HOS areas. Lake Geneva was mesotrophic according to the oligochaete communities of LOS areas, but it was meso-eutrophic according to those of HOS areas.

Sedimentation rates measurements in former channels of the upper Rhône river using Chernobyl 137Cs and 134Cs as tracers

Former river channels are aquatic ecosystems with a different geomorphology generated by fluvial dynamics more or less linked to the main channel. They present different ecological successions to become terrestrial ecosystems and are thus supposed to have different sedimentation rates. The aim of this paper is to assess this sedimentation rate using radioactive tracer methodology commonly used in lake studies. Chernobyl impacts, expressed in 137Cs concentration and 137 Cs 134 Cs ratio, were determined in sediment cores. Sites (21) were sampled in the alluvial plain of the Upper Rhône River from 1989 to 1994. The contamination presented a high spatial heterogeneity. The maximum values encountered by site ranged between 34 and 541 Bq/kg of dry matter. The method generally gave good core profiles. Sedimentation rate ranged between 0.14 and 0.70 cm/year for the former meanders and between 0.14 and 2.86 cm/year for the braided channels. The sediment accumulation rates ranged from 0.03 to 0.25 g/cm 2 per year and 0.03 to 2.26 g/cm 2 per year, respectively. These values are similar to those found for Lake Geneva. The importance of the former channels in relation to the main channel is enhanced by the higher contamination and radionuclides retention. The sediment accumulation rate is related to the organic carbon content in the sediment. A comparison between two former channels with different productivity showed that the the allogenous driven system presents a high organic sediment accumulation rate with a low organic content in the sediment and inversely, a low organic sediment accumulation rate with a high organic carbon content was found for the autogenous driven system.

Larval habitat choice in still water and flume flows by the opportunistic bivalve Mulinia lateralis

Competent pediveligers of the coot clam Mulinia lateralis (Say) clearly preferred an organically-rich mud over abiotic glass beads in 24-h flume experiments, and often demonstrated the same choice in still-water experiments. We hypothesize that peediveligers with characteristic helical swimming paths above the bottom can exercise habitat choice in both still water nad flow, but that the limited swimming ambits of physiologically older periveligers require near-bottom flows to move the larvae between sediment patches so that they can exercise habitat choice. Although M. lateralis larvae are planktotrophic, their ability to delay metamorphosis in the absence of a preferred sediment cue is limited to about five days, a shorter time than the lecithotrophi larvae of the opportunistic polychaete species, Capitella spp. I and II. Field distributions of all three opportunistic species may result, at least in part, from active habitat selection for high-organic sediments by settling larvae.

Preliminary experiments on the development of extensive culture methods for juvenile sole, Solea solea (L.)

. The effect of different levels of organic enrichment on benthic productivity was studied over a 16-week period in trays of sediment placed in a fertilized seawater pond. Primary and secondary planktonic production were also monitored. The exploitation of these sources of food by juvenile sole and their growth and survival over an 8-week period were assessed. The colonization of the sediments showed a marked succession. Nematodes were numerically the most abundant group and reached a peak after about 8 weeks. This was followed by a peak in the abundance of epibenthic copepods after 11 weeks. The maximum numbers of poiychaetes and larger Crustacea (mainly amphipods) occurred at the end of the trial (15 weeks). The high-organic sediment supported fewer polychaetes and copepods than either the low- or medium-organic sediments. The species composition of the benthos varied both with the level of organic enrichment and with time. Peaks of zooplankton concentrations of 23 to 25 organisms/l occurred during the spring and late summer. There was some evidence of an inverse relationship between zooplankton abundance and standing crop of algae, as indicated by chlorophyll a concentrations. Harpacticoid copepods were the dominant food item consumed by small (21-50mm total length) sole. Polychaetes, amphipods and Crangon spp. were exploited by large (61-90mm total length) sole to a much greater extent, though harpacticoid copepods were also commonly taken. The percentage increase in length of the juvenile sole at low-, medium- and high-organic levels was 108, 146 and 152 respectively. Survival, however, was highest (100%) on the untreated sediment and lowest (57%) at the medium-organic level.

Accumulation of PCBs, mercury and cadmium by Nereis virens, Mercenaria mercenaria and Palaemonetes pugio from contaminated harbor sediments

Accumulation of polychlorinated biphenyls (PCBs), mercury, and cadmium by sandworms ( Nereis virens), hard clams ( Mercenaria mercenaria) and grass shrimp ( Palaemonetes pugio) exposed to contaminated sediments from four sites in New York Harbor was studied for a 100-day period. Of the three contaminants monitored, only PCBs were found to bioaccumulate above background (control) concentrations. Small increases in PCB body burden were detected in M. mercenaria and P. pugio, whereas higher concentrations were measured in N. virens. Uptake was affected by the organic content of the sediment. Bioaccumulation factors (concentration in tissue/concentration in sediment) for N. virens ranged from 1.59 in a low organic sediment to 0.15 in a high organic sediment. Results from this study support the contention that sediment concentration alone does not reflect bioavailability and that toxicity tests (bioassays) and field monitoring remain the most direct method for estimating bioaccumulation potential of sediment-bound contaminants.