Sedimentary Pigment Concentrations Research Articles

In situ characterization of benthic fluxes and denitrification efficiency in a newly re-established mussel farm

Mussel farming has been proposed as a mechanism to mitigate eutrophication in coastal waters. However, localizing the intensive filtration of organic matter by mussels can cause a concomitant enrichment of organic matter in sediments below farms, which may influence biogeochemical processes and fates of nutrients in the system. In the context of mitigating eutrophication, it is important to quantify sedimentary changes induced at early life stages of mussel farms. Accordingly, this study investigated how a newly re-established mussel farm affected sedimentation rates, sediment characteristics, sediment-water solute fluxes and nitrate (NO3−) reduction rates (measured in situ) during the first year of production. Sedimentation rates were enhanced at the farm relative to a reference station, and both organic and inorganic carbon accumulated in the sediment with time. Increased organic matter input likely drove the slightly elevated sedimentary effluxes of ammonium (NH4+) and dissolved inorganic phosphorus (DIP) in the farm. Denitrification was the main NO3− reduction process, however, there was a relative increase in the remobilization of bioavailable nitrogen underneath the farm as dissimilatory nitrate reduction to ammonium (DNRA) rates were enhanced by >200% and the denitrification efficiency was 49% lower compared to the reference station. The sedimentary methane (CH4) release tended to be higher at the farm, but fluxes were not significantly different from reference conditions. Low sedimentary pigment concentrations indicated a reduced presence of benthic microalgae at the farm, which likely influenced sediment-water solute fluxes. Over the production cycle, the release of dissolved inorganic nitrogen (DIN) and DIP underneath the farm were respectively 426% and 510% relative to reference conditions. Impacts of the mussel farm were thus measurable already during the first year of establishment. These immediate changes to the sediment biogeochemistry, as well as long-term effects, should be considered when estimating the environmental impact of mussel aquaculture.

Holocene shifts in the primary producer community of large, shallow European Lake Peipsi, inferred from sediment pigment analysis

We used HPLC to identify and quantify pigments in a Holocene sediment record from large, shallow Lake Peipsi, Estonia. The aim of our study was to track the influence of long-term climate change (i.e. temperature fluctuations) on past dynamics of aquatic primary producers. Sedimentary pigments were separated and quantified in 182 samples that span the last ca. 10,000 years. There was an increasing trend in sedimentary pigment concentrations from basal to upper sediment layers, suggesting a gradual increase in lake trophic status through time. Using additive models, our results suggested that primary producer dynamics in Lake Peipsi were closely related to temperature fluctuations. We, however, identified two periods (early Holocene and after ca. 2.5 cal ka BP) when the relationship between primary producer composition and temperature was weak, suggesting the influence of additional drivers on the primary producer community. We postulate that: (a) the increase of primary producer biomass in the early Holocene could have been caused by input of allochthonous organic matter and nutrients from the flooded areas when water level in Lake Peipsi was increasing, and (b) changes in the abundance and structure of primary producer assemblages since ca. 2.5 cal ka BP was related to widespread agricultural activities in the Lake Peipsi catchment. These results suggest that human activities can disrupt the relationship between the primary producer community and temperature in large, shallow lakes.

Long-term diatom biodiversity responses to productivity in lakes of Fuxian and Dianchi

To date, productivity–diversity relationships (PDR) in terrestrial ecosystems have predominantly been examined across large spatial scales, while freshwater ecosystem studies typically focus on short-term field surveys. Here sediment records are used to examine the long-term patterns of PDR from two large lakes, Fuxian and Dianchi, which are currently oligo-mesotrophic and hyper-eutrophic, respectively. Changes in lake productivity and community structure were reconstructed based on sedimentary pigment concentrations (i.e. Chl-a) and diatom assemblages. Principal Component Analysis (PCA) of diatom community data showed that primary productivity was the most significant environmental gradient driving diatom community changes in both lakes. Lake productivity was positively correlated to diatom alphaand beta-diversity indices in Lake Fuxian but negative in Lake Dianchi. The relationship between the magnitude of productivity change and diatom beta-diversity was significantly negative in Lake Dianchi while no trend was found in Lake Fuxian. There was a significantly negative relationship between diatom species richness and community productivity in Lake Dianchi, suggesting the influence of increased species richness in enhancing community productivity was overridden by human disturbances. Disturbance associated changes in limnological properties 90 生 物 多 样 性 Biodiversity Science 第 23卷 not only caused the loss of biodiversity, but also directly promoted diatom production through intensive nutrient enrichment.

Sympagic-pelagic-benthic coupling in Arctic and Atlantic waters around Svalbard revealed by stable isotopic and fatty acid tracers

Stable isotope and fatty acid trophic markers (FATMs) were used to assess carbon flow and trophic structures of sympagic, pelagic and benthic communities in high-Arctic Svalbard. Three regions were sampled: Northwest Svalbard – dominated by Atlantic water (AtW) and limited seasonal sea ice; Northern Svalbard – dominated by AtW and perennial sea ice; and Northeast Svalbard – dominated by Arctic water (ArW) and extensive seasonal sea ice. Three to four trophic levels (TL) were found in the three habitats, with a dominance of omnivores (TL = 2.4–2.7). Ice fauna relied on phytoplankton and ice algae, zooplankton primarily on phytoplankton, while benthos relied on ice algae/refractory material. Ice fauna (mean 39%; range 17–62%) and benthos (mean 25%; range 11–65%) had high proportions of diatom-FATMs, while zooplankton had equally high diatom- and Phaeocystis/dinoflagellate-FATMs (mean 11% and 15%, respectively). Calanus-FATMs were prominent in carnivorous ice fauna (up to 28%) and zooplankton (up to 38%), but also in benthic invertebrates (up to 41%). Ice fauna biomass was low. Biomass of zooplankton and benthic infauna were variable, but positively correlated to each other (r 2=0.89; p<0.01) and sedimentary pigment concentrations (r 2>0.40; p<0.05). The coinciding peak biomasses of zooplankton and benthos in Northeast Svalbard can be explained by allochthonous organic matter of ice algal origin and highly specialized Arctic zooplankton utilizing both ice algae and phytoplankton carbon sources.

Spatial distribution of diatom and pigment sedimentary records in surface sediments in Doubtful Sound, Fiordland, New Zealand

Algal remains (pigment concentrations, diatom frustules) and organic matter sources (δ15N, δ13C) in surface sediments (0–2 cm) were quantified and related to environmental gradients in Doubtful Sound, Fiordland, New Zealand. Sedimentary pigment concentrations, in particular diatoxanthin and fucoxanthin (diatom biomarkers) were elevated near Malaspina Reach, which experiences greater incident irradiance and mixing of silica-rich freshwater with nutrient-rich marine water. In contrast, diatom frustules were recovered in low concentrations in deep basins including Malaspina Reach, most likely related to dissolution and grazing. Spatial variability in pigments in Doubtful Sound was mainly correlated with light conditions (incident irradiance, chromophoric dissolved organic matter). By contrast, diatoms were principally correlated with salinity gradients (effective freshwater depth) and water column stratification (mixing). This study highlights the importance of using complementary sedimentary proxies when reconstructing algal abundance and community composition in fjord environments.

Primary production in Lake La Cruz (Spain) over the last four centuries: reconstruction based on sedimentary signal of photosynthetic pigments

We analysed photosynthetic pigments in annually laminated sediment of meromictic Lake La Cruz, Spain, to cope with the timing and characterisation of primary productivity changes over the last four centuries. The photosynthetic pigments identified included chlorophyll a and b (and its derivatives) and specific carotenoids of different algal groups, such as zeaxanthin, lutein, alloxanthin, diadinoxanthin and diatoxanthin among others. Marker pigments of phototrophic sulfur bacteria were also observed, including bacteriochlorophyll a derivatives, homologue series of bacteriophaeophytins d and bacterial carotenoids okenone and chlorobactene. We investigated the diagenetic processes of pigment alteration in anoxic sediments and the possible implications for paleoproductivity reconstruction and interpretation. The lack of systematic down-core changes in diagenetic indicators suggests that variability of sedimentary pigment concentrations is the result of changes in lake productivity. The lower concentration of algal photosynthetic pigments in the bottom of sediment sequence corresponds to the onset of meromictic conditions. Before that, sediment was not continuously anoxic and the preservation of pigments was reduced. Regarding photosynthetic bacteria, green sulfur bacteria derivatives indicate that population growth was limited until the settled organic matter was sufficient to provide enough sulphide. Moreover, the presence of bacterioviridine, an oxidised derivative of bacteriochlorophyll a, suggest the competitive relation among photosynthetic bacteria. The high relative abundance of zeaxanthin indicates the dominance of picocyanobacteria in the primary productivity over the last centuries. Fluctuations of the pigment signal observed in the sediment sequence during the meromictic period were well correlated with fluctuations of solar activity.

Abrupt environmental change in Canada’s northernmost lake inferred from fossil diatom and pigment stratigraphy

[1] An analysis of diatoms and fossil pigments in a sediment core from perennially ice-covered Ward Hunt Lake at latitude 83°N in Nunavut, Canada revealed striking changes in diatom communities and sedimentary pigment concentrations during the last two centuries. Diatoms were found only in the upper 2.5 cm of the sedimentary record, and where present, diatom assemblages were composed almost entirely of Staurosirella pinnata. Photosynthetic pigments were present in low concentrations throughout the sedimentary profile, consistent with the ultra-oligotrophic nutrient status of the lake. Pigment concentrations varied slightly in the lower sections of the core, and began to increase gradually at the 4 cm horizon followed by an increase of two orders of magnitude in the uppermost 2.5 cm. The changes observed in the sedimentary record of Ward Hunt Lake had similar trajectories to those observed post-1850 elsewhere in the circumpolar Arctic, and imply that aquatic communities even in the most extreme northern lakes have been strongly impacted by recent climate warming.

Distribution and retention of effluent nitrogen in surface sediments of a coastal bay

Anthropogenic nitrogen (N) often causes coastal eutrophication, yet little is known about the fate and retention of effluent N in coastal waters and, hence, about the system’s ability to assimilate excess N loads. We used the spatial distribution of stable N isotope ratios and algal pigments in sedimentary organic matter from a Baltic bay receiving tertiary‐treated effluent to evaluate the extent of effects and the role of nearshore marine environments as sinks of anthropogenic N. Surface sediments (0–2 cm and 2–4 cm) exhibited a pronounced spatial gradient of δ15N, with the most elevated values (~8‰) near the outfall; values decreased linearly to values of ;4‰ outside the bay. Sedimentary pigment concentrations were consistent with water‐column data and showed that phytoplankton biomass was elevated in the inner reaches of the bay. In particular, diatoms were heavily labeled (δ15N ~ 10‰), reached maximum abundance near the effluent outfall, and were likely the main mechanism delivering effluent N to the sediments. Sediments within the bay removed ~5–11% of wastewater N inputs, with 50% of the sequestered effluent N buried in the basin nearest to the outfall. Magnitudes of N removal by sediments (23–26 x 104 kg N yr−1) were less than those estimated for denitrification (30–60 x 104 kg N yr−1), but they were substantially greater than biological uptake by macroalgae (~2 x 104 kg N yr−1). Taken together, these patterns demonstrate the idea that coastal sediments can be effective sinks of wastewater N, even after 30 yr of effluent input.

Benthic respiration and nitrogen release in Buzzards Bay, Massachusetts

The decomposition of organic matter and the regeneration of nitrogen in the sediments of Buzzards Bay, Massachusetts were examined by measuring benthic fluxes of oxygen and dissolved inorganic nitrogen (DIN). Benthic respiration (O 2 consumption) rates measured from one site yielded an estimate of 65-80 g C m −2 oxidized annually. Comparing the annual release of DIN with the consumption of O 2 led to an estimate of N loss from the benthicpelagic system, most likely as N 2 gas via denitrification, corresponding to 14-32% of the N remineralized from organic matter decomposition. Using path analysis, benthic flux rates of O 2 and DIN over a seasonal cycle in Buzzards Bay were determined to be related to water temperature and sediment photosynthetic pigments (chlorophyll a and phaeopigments). The rate of DIN release was also negatively related to the particulate organic N (PON) pool as well. The relationsbip of benthic fluxes to sedimentary pigment concentrations suggested that pigments were good indicators of labile organic matter input to sediments. Macrofauna appeared to have a direct negative effect, as well as a positive indirect effect on DIN release. Benthic respiration rates were not related to sedimentary particulate organic C (POC) or PON content, or macrofaunal abundances. Release rates of DIN were also unrelated to POC pools. Benthic flux rates measured at 12 sites in Buzzards Bay during August 1989 varied by less than a factor of 2 for benthic respiration and less than a factor of 3 for DIN release. The only environmental factor that emerged from path analysis as related (negatively) to the spatial pattern of benthic flux rates in August was water depth. Other factors, such as organic pools, pigment concentrations, macrofauna, and distance from the New Bedford sewage outfall were not related to the spatial patterns of benthic fluxes in Buzzards Bay. The combination of seasonal and spatial observations indicate that the processes oxidizing organic matter in Buzzards Bay sediments are controlled by temperature and the delivery of labile organic matter to the sediment surface. Benthic flux rates in Buzzards Bay were generally low, but N recycling efficiency was high, relative to similar coastal environments

An assessment of the sources of error in estimations of bulk sedimentary pigment concentrations and its implications for trophic status assessment

Pigment concentrations in surface sediments in two lakes were analysed on ten occasions over a year. Statistical analysis showed that mean concentrations varied through the year and the relative contribution of several sources of variability (analytical, spatial, temporal) to the total was estimated. Using this information, the relative cost-effectiveness of several alternative sampling strategies was investigated. Measurement of sedimentary pigment concentrations on single cores on two or three different occasions would reduce the standard error of the mean by 30% and 42% respectively and is very cost effective. However replicate cores taken on a single occasion appeared to be a workable compromise. The data also allowed a comparison of the ability of the different pigment determinands to resolve two lakes of very different trophic status. Total carotenoid concentrations were found to be the most effective.

Oscillaxanthin and myxoxanthophyll in two cores from Lake Wabamun, Alberta, Canada

A sedimentary blue-green algal record has been investigated through measurement of myxoxanthophyll and oscillaxanthin in two cores taken from deep and shallow sites in Lake Wabamun, Alberta, Canada (Longitudes 114° 26′ and 114° 44′ W; Latitudes 50° 30′ and 50° 35′ N). Blue-green algae have been a component of the algal flora of this lake throughout the Holocene period. Myxoxanthophyll and oscillaxanthin maxima occur in early Holocene sediments (ca. 9000 years BP), whereas oscillaxanthin concentrations are high between 7000 and 3800 years BP. High oscillaxanthin levels suggest that a phytoplankton assemblage, which included Oscillatoria spp., existed during this latter period and the lake was more eutrophic than at present. Decreases in the number of planktonic diatoms in the core from the deep site (Seba core) appear to be related to increased eutrophy, increased salinity, and sediment redistribution as well as possible competition with Oscillatoria. That the lake has been less productive during the last 2500 years in supported by the diatom record, the diatom: chrysophyte statospore (stomatocyst) ratio and concentrations of the blue-green algal pigments. In the core from the shallow site (Moonlight Bay) concentrations of blue-green algal pigments are initially high, which along with the diatom assemblage, indicates a younger basal age of the sediments. It is possible that benthic blue-green algae contributed significantly to sedimentary pigment concentrations in the Moonlight Bay core. Major fluctuations in the Osc: Myx ratio, particularly in the Seba core, casts some doubt upon the usefulness of this ratio, and suggests that it is not degradation-independent.

Fossil pigments in paleoecology and paleolimnology

For the past several decades scientists have been examining the nature of sedimentary chlorophylls and carotenoids from freshwater lakes for their value in paleoecology and paleolimnology. Unaltered chlorophyll molecules are rarely preserved for long periods, but the pheo-derivatives and chlorophyllides are common throughout lake sedimentary columns. Carotenoids tend to preserve largely unaltered from their conditions in living plant membranes, but degrade quickly to colorless derivatives when oxidized. Measurements of sedimentary pigment concentrations, ratios of chlorophyll derivatives to carotenoids and diversity, especially as regards prokaryote carotenoids, are most commonly published. This paper assesses the value of using sedimentary pigment data to provide paleoecological information on lake evolution and changing patterns of aquatic primary productivity. Factors that promote pigment preservation are contrasted to those that alter and cause destruction of organic molecules. The value of fossil pigments is considered in ascertaining the sources of organic matter to sediments and for providing clues to the changing diversity of aquatic flora, both rooted and planktonic. Consideration is given to recent investigations that have sought information from sedimentary pigments on the onset and intensity of cultural eutrophication, both in individual lakes and on a regional basis, and in the monitoring of progress toward lake restoration. A special case is made for the value of sampling meromictic lakes. In addition, this review provides information on the limitations of the sampling procedures, laboratory techniques, and interpretation of results, Discussion is made of the most valuable and easily obtainable data that can provide reliable, comparable and reproducible results. Special consideration is given to the value of the pigment data in supplementing additional paleoecological indicators such as sedimentary pollen grains, zooplankton, and various other sedimentary bio- and geochemical products.

Measurement and interpretation of sedimentary pigments

SUMMARY. The factors that control the concentrations of pigments in lake sediments are examined using data from (i) transects across lake basins, (ii) surface samples from logographic and atrophic lakes, and (iii) two 210Pb‐dated short cores. Methods for the rapid non‐chromatographic analysis of percent native chlorophyll and the blue‐green algal pigments oscillaxanthin and myxoxanthophyll are described. The concentrations of chlorophyll derivatives, total arytenoids, oscillaxanthin and myxoxanthophyll, and percent native chlorophyll, are higher under conditions along the transects favorable for preservation. Chlorophyll degrades at about the same rate as total carotenoids, and oscillaxanthin degrades at about the same rate as myxoxanthophyll. Therefore, both the ratio of chlorophyll to arytenoids (CD/TC) and the ratio of oscillaxanthin to myxoxanthophyll (OSC/MYX) are mostly determined by the quality of autochthonous production rather than by preservation conditions. CD/TC values are higher in logographic lakes than in atrophic lakes, apparently as a result of differences in production of the two pigment types. Calculations show that CD/TC shifts in these two cores cannot be a record of the allochthonous‐autochthonous Baltic in the systems. Instead, the CD/TC values shift with large changes in the kinds of plants dominating primary production. The stratigraphy of percent native chlorophyll appears to record the hypohmnetic oxygen concentrations at the time of deposition. No obvious reason exists why a eutrophic lake should produce more pigment per gram organic matter than should an oligotrophic lake. However, several correlated mechanisms tend to produce higher sedimentary pigment concentrations in eutrophic lakes. Most of these mechanisms, such as hypolimnetic oxygen consumption, indirectly translate greater primary productivity into greater sedimentary pigment concentration. Therefore, pigment concentrations are sometimes misleading, and pigment accumulation rate may be a better indicator of past primary production.