Petra Tallberg

Quantitative Real-Time PCR for Determination of Microcystin Synthetase E Copy Numbers for Microcystis and Anabaena in Lakes

ABSTRACT Cyanobacterial mass occurrences in freshwater lakes are generally formed by Anabaena, Microcystis, and Planktothrix, which may produce cyclic heptapeptide hepatotoxins, microcystins. Thus far, identification of the most potent microcystin producer in a lake has not been possible due to a lack of quantitative methods. The aim of this study was to identify the microcystin-producing genera and to determine the copy numbers of microcystin synthetase gene E (mcyE) in Lake Tuusulanjärvi and Lake Hiidenvesi in Finland by quantitative real-time PCR. The microcystin concentrations and cyanobacterial cell densities of these lakes were also determined. The microcystin concentrations correlated positively with the sum of Microcystis and Anabaena mcyE copy numbers from both Lake Tuusulanjärvi and Lake Hiidenvesi, indicating that mcyE gene copy numbers can be used as surrogates for hepatotoxic Microcystis and Anabaena. The main microcystin producer in Lake Tuusulanjärvi was Microcystis spp., since average Microcystis mcyE copy numbers were >30 times more abundant than those of Anabaena. Lake Hiidenvesi seemed to contain both nontoxic and toxic Anabaena as well as toxic Microcystis strains. Identifying the most potent microcystin producer in a lake could be valuable for designing lake restoration strategies, among other uses.

Seasonal succession of phytoplankton and zooplankton along a trophic gradient in a eutrophic lake – implications for food web management

The water quality and seasonal dynamics of phytoplankton and zooplankton in Lake Hiidenvesi were explored in order to evaluate the possibilites to improve the water quality by mass removal of fish. The four sampling stations were situated in basins representing a transition from hypertrophy to mesotrophy and maximum depths from 3 m to 33 m. The maximal phytoplankton biomasses ranged from 5 to 33 mg l-1 and the maximal zooplankton biomasses from 160 to 520 μg C l-1. Cyanophytes dominated the phytoplankton biomass in summer and the copepod biomass was higher than that of cladocerans at all the stations. No spring peak in the zooplankton biomass occurred and the average size of daphnids was below 1 mm. At present, the top-down control of phytoplankton biomass is thus ineffective. However, the water quality and morphometry of L. Hiidenvesi seem favourable for biomanipulation. The nutrient concentrations and external loading fall in the limits that facilitate successful restoration and the morphometry of the lake is favourable for the recolonization by submerged macrophytes. However, since stations 2 and 3 receive their nutrient loading mainly from station 1, restoration of station 1 may be crucial for the whole lake. This may not be achieved through food web management alone, but requires a reduction of the nutrient flow from River Vihtijoki.

Sedimentation and particulate nutrient dynamics along a coastal gradient from a fjord-like bay to the open sea

Seasonal changes of total particulate material (TPM), particulate organic carbon (POC), nitrogen (PON) and phosphorus (PTP) concentrations in the water column, in sediment traps and on the sediment surface were studied in the SW coast of Finland, Baltic Sea, from March to November 1992. Sampling was carried out along a coastal gradient from the fjord-like, semi-enclosed Pojo Bay to the outer archipelago and open sea area. In Pojo Bay, TPM sedimentation rates were high and relatively constant, and had low organic carbon contents throughout the seasonal cycle. Resuspension was estimated to contribute > 90% of total sedimentation of POC and PON. Clear seasonality in sedimentation with high settling rates of primary organic material in spring, low sedimentation rates during summer and a considerable increase of resuspension during autumn was found in the outer archipelago and open sea. The C:N:P ratios of suspended, settled and sediment surface material indicated greater sedimentary loss of N (as compared to P and C) and closer coupling between pelagial and benthos in the archipelago and open sea area than in Pojo Bay. The sedimentation of P was 20–50% more effective (as compared to N and C) in Pojo Bay than elsewhere. These results indicate that the shift of planktonic nutrient limitation (from P to N limitation) is enhanced due to the more efficient sedimentation of the main limiting element along the estuarine gradient. The primary sedimentation of organic carbon (approximating export flux from the pelagic system) during the whole study period was estimated to be 30–48% of the total net primary production. This indicates that despite the differences in the salinity, nutrient dynamics and planktonic community structure along the coastal gradient, a relatively constant fraction of the annual primary production is exported from the pelagic system by sedimentation.

A metalimnetic oxygen minimum indirectly contributing to the low biomass of cladocerans in Lake Hiidenvesi - a diurnal study on the refuge effect

The diurnal vertical migrations of smelt (Osmerus eperlanus), larvae of phantom midge (Chaoborus flavicans) and cladoceran zooplankton in eutrophic Lake Hiidenvesi were studied in order to clarify the factors behind the low zooplankton biomass. In the study area, an oxygen minimum occurred in the metalimnion in the 10–15 m depth. No diurnal fluctuations in the position of the minimum were observed. Cladocerans inhabited the epilimnion throughout the study period and their vertical movements were restricted to above the thermocline and above the oxygen minimum. C. flavicansconducted a diurnal migration. During the day, the majority of the population inhabited the 12 – 15 m depth just in the oxygen minimum, while during darkness they were found in the uppermost 8 m. Smelts started ascending towards the water surface before sunset and reached the uppermost 3 m around 23:00. During daytime, the majority of smelts inhabited the depth of 7–9 m, where the water temperature was unfavourably high for them (18 °C). Smelts thus probably avoided the steep oxygen gradient in the metalimnion, whereas Chaoborusused the oxygen minimum as a refuge against predation. Those smelts that were found in the same water layers as Chaoborusused the larvae as their main prey. The metalimnetic oxygen minimum thus seemed to favour the coexistence of vertebrate and invertebrate predators, leading to a depression of cladoceran zooplankton.

Nutrient fluxes and microbial activity in sediment enriched with settled seston

The chemical and microbiological responses of profundal surface sediment were monitored in sediment enriched with natural settled material collected in May, July or August, and with diatom or cyanobacteria cultures. The activation of the sediment microbial community was clearest after the addition of settled seston collected in May which was richer in organic matter than those collected later in the summer. N was released when the sediment was enriched with settled seston which had been collected in July and August and had C:N ratios lower than 10:1. The diatom-rich May-material enhanced the release of P to the interstitial water, obviously because of chemical competition between P and diatom-derived Si at the sediment surface. The July- and August-materials did not release P, nor did the diatom and cyanobacteria cultures. The results thus indicate that the seasonal variations in the quality and quantity of the settling phytoplankton affect the P dynamics at the sediment surface, both chemically and biologically.

Sea ice and primary production proxies in surface sediments from a High Arctic Greenland fjord: Spatial distribution and implications for palaeoenvironmental studies

Abstract In order to establish a baseline for proxy-based reconstructions for the Young Sound–Tyrolerfjord system (Northeast Greenland), we analysed the spatial distribution of primary production and sea ice proxies in surface sediments from the fjord, against monitoring data from the Greenland Ecosystem Monitoring Programme. Clear spatial gradients in organic carbon and biogenic silica contents reflected marine influence, nutrient availability and river-induced turbidity, in good agreement with in situ measurements. The sea ice proxy IP25 was detected at all sites but at low concentrations, indicating that IP25 records from fjords need to be carefully considered and not directly compared to marine settings. The sea ice-associated biomarker HBI III revealed an open-water signature, with highest concentrations near the mid-July ice edge. This proxy evaluation is an important step towards reliable palaeoenvironmental reconstructions that will, ultimately, contribute to better predictions for this High Arctic ecosystem in a warming climate.

Labile organic carbon regulates phosphorus release from eroded soil transported into anaerobic coastal systems

Abstract Coastal eutrophication is expected to increase due to expanding and intensifying agriculture which causes a large amount of soil-associated P to be transported into aquatic systems. We performed anaerobic long-term incubations on field soil to mimic the conditions that eroded soil encounters in brackish sediments. The release of P from soil increased with the amount of labile organic C (acetate) addition and decreased with the soil/solution ratio. We deduce that in less-productive brackish systems, microbial Fe reduction allows for the maintenance of the coupled cycling of Fe and P and restricts the amount of P entering the oxic water. In more eutrophic systems, the formation of Fe sulfides as a result of SO4 reduction inactivates Fe, and leads to a higher release of P, thus generating an adverse feedback effect. The dependence of the fate of soil-bound Fe and P on the trophic status of the receiving water should be recognized in eutrophication management.

Germanium-68 as a tracer for silicon fluxes in freshwater sediment.

The sorption of Si may decisively influence the P dynamics in surface sediment through competitive ligand exchange mechanisms. Many aspects of the process, such as the impact of Si dissolving from diatoms, are both insufficiently known and difficult to monitor by quantitative analyses due to the ubiquitousness of Si in sediment. Since the radioactive isotopes of Si have impractical half-times, the applicability of 68Ge as a tracer for Si additions in both inorganic and biogenic form to freshwater sediment (Lake Vesijärvi, Southern Finland) was studied in a 24-h laboratory experiment. The 68Ge-label was added to the sediment with either inorganic Si (940mg l(-1)) or diatoms (3.2 x 10(6) cellsl(-1)), and the distributions of the 68Ge-label and the different forms of added Si between the interstitial water and sequentially extracted, solid-phase sediment pools were critically examined. The inorganic Si addition significantly increased the amount of Si in the interstitial water and in the reversibly bound fraction, while the diatom addition had no discernible effects. The relative distribution of Si and 68Ge between the various sediment pools indicated that the first sorption phase of the added inorganic Si was similar to that reported for P. The high concentration of diatom-derived 68Ge-labelled Si in the interstitial water and in the easily soluble, reversibly bound pool indicated rapid dissolution of the added diatoms. The comparable distributions of the diatom-derived and inorganic Si-derived 68Ge-label within the studied pools indicated that the sorption of Si dissolving from diatoms in surface sediment closely resembles that of an inorganic addition of Si. Caution about the chemical speciation of the 68Ge-label is, however, advisable in sediment environments. Fractionation procedures designed for e.g. P may also be of limited use when applied to a different element, such as Si.

Separating Biogenic and Adsorbed Pools of Silicon in Sediments Using Bayesian Inference

There are several potentially mobile pools of silicon in sediment, e.g. biogenic Si (BSi), dissolved Si and adsorbed Si (AdSi) which makes the studying of a single pool very difficult because of the interference caused by other Si pools. In order to evaluate the impact that different Si pools have on the Si cycle of water ecosystems, it is important to have reliable estimates of the pool sizes. The objective of this study was to estimate the joint concentration distributions of two pools, AdSi and BSi, in, of a small catchment area in southern Finland. The potential correlation between BSi and AdSi was studied to find out if the AdSi pool can be inferred from the total pool (BSi + AdSi). The potential error caused by simultaneous extraction of AdSi in BSi determinations was also investigated. Because all extraction methods include variability due to measurement imprecision and inter-sample variation, the different sources of variation were explicitly separated to be able to infer the underlying true variation of AdSi and BSi within the study area. We have utilized Bayesian inference for this task.

Silicate Release from Sand-Manipulated Sediment Cores: Biogenic or Adsorbed Si?

The influence of an addition of either sand and/or spring-bloom algae on the efflux of nutrients from intact sediment cores from the Baltic Sea was studied in a flow-through experiment. The addition of sand significantly increased the efflux of silicon (Si) from sediment, but the algal addition did not. The effects on phosphorus (P) were not as clear, and fluxes of nitrogen (NH4 and NO2 + 3) remained relatively unaffected by the additions. The small effect of the algal addition was caused by the short time-period covered by the experiment and possibly by adsorption of released Si by the sediment. A follow-up bottle experiment showed that despite the apparently lower content of easily available Si and biogenic silica, BSi, in the sand, the sand-induced Si efflux was caused by release of Si from the sand itself, rather than by indirectly increasing the dissolution of BSi present in the sediment.