From a tree to a stand in Finnish boreal forests: biomass estimation and comparison of methods

There is an increasing need to compare the results obtained with different methods of estimation of tree biomass in order to reduce the uncertainty in the assessment of forest biomass carbon. In this study, tree biomass was investigated in a 30-year-old Scots pine (Pinus sylvestris) (Young-Stand) and a 130-year-old mixed Norway spruce (Picea abies)-Scots pine stand (Mature-Stand) located in southern Finland (61º50' N, 24º22' E). In particular, a comparison of the results of different estimation methods was conducted to assess the reliability and suitability of their applications. For the trees in Mature-Stand, annual stem biomass increment fluctuated following a sigmoid equation, and the fitting curves reached a maximum level (from about 1 kg/yr for understorey spruce to 7 kg/yr for dominant pine) when the trees were 100 years old. Tree biomass was estimated to be about 70 Mg/ha in Young-Stand and about 220 Mg/ha in Mature-Stand. In the region (58.00-62.13 ºN, 14-34 ºE, ≤ 300 m a.s.l.) surrounding the study stands, the tree biomass accumulation in Norway spruce and Scots pine stands followed a sigmoid equation with stand age, with a maximum of 230 Mg/ha at the age of 140 years. In Mature-Stand, lichen biomass on the trees was 1.63 Mg/ha with more than half of the biomass occurring on dead branches, and the standing crop of litter lichen on the ground was about 0.09 Mg/ha. There were substantial differences among the results estimated by different methods in the stands. These results imply that a possible estimation error should be taken into account when calculating tree biomass in a stand with an indirect approach.

Use of biomass fuels in the brick-making industries of Sudan: Implications for deforestation and greenhouse gas emission

The study focuses on the potential roles of the brick making industries in Sudan in deforestation and greenhouse gas emission due to the consumption of biofuels. The results were based on the observation of 25 brick making industries from three administrative regions in Sudan namely, Khartoum, Kassala and Gezira. The methodological approach followed the procedures outlined by the Intergovernmental Panel on Climate Change (IPCC). For predicting a serious deforestation scenario, it was also assumed that all of wood use for this particular purpose is from unsustainable sources. The study revealed that the total annual quantity of fuelwood consumed by the surveyed brick making industries (25) was 2,381 t dm. Accordingly, the observed total potential deforested wood was 10,624 m3, in which the total deforested round wood was 3,664 m3 and deforested branches was 6,961 m3. The study observed that a total of 2,990 t biomass fuels (fuelwood and dung cake) consumed annually by the surveyed brick making industries for brick burning. Consequently, estimated total annual emissions of greenhouse gases were 4,832 t CO2, 21 t CH4, 184 t CO, 0.15 t N20, 5 t NOX and 3.5 t NO while the total carbon released in the atmosphere was 1,318 t. Altogether, the total annual greenhouse gases emissions from biomass fuels burning was 5,046 t; of which 4,104 t from fuelwood and 943 t from dung cake burning. According to the results, due to the consumption of fuelwood in the brick making industries (3,450 units) of Sudan, the amount of wood lost from the total growing stock of wood in forests and trees in Sudan annually would be 1,466,000 m3 encompassing 505,000 m3 round wood and 961,000 m3 branches annually. By considering all categories of biofuels (fuelwood and dung cake), it was estimated that, the total emissions from all the brick making industries of Sudan would be 663,000 t CO2, 2,900 t CH4, 25,300 t CO, 20 t N2O, 720 t NOX and 470 t NO per annum, while the total carbon released in the atmosphere would be 181,000 t annually.

The effects of environmental factors on biomass and microcystin production by the freshwater cyanobacterial genera Microcystis and Anabaena

Several cyanobacterial genera produce the hepatotoxins, microcystins. Microcystins are produced only in cells that have microcystin synthetase gene (mcy) clusters, which encode enzyme complexes involved in microcystin biosynthesis. Microcystin-producing and nonmicrocystin-producing genotypes of single cyanobacterial genus may occur simultaneously in situ. Previously, the effects of environmental factors on the growth and microcystin production of cyanobacteria have mainly been studied by means of isolated cyanobacteria cultures in the laboratory. Studies in the field have been difficult, owing to the lack of methods to identify and quantify the different genotypes. In this study, genus-specific microcystin synthetase E (mcyE) gene primers were designed and a method to identify and quantify the mcyE copy numbers was developed and used in situ. Microcystis and Anabaena mcyE genes were observed in two Finnish lakes. Microcystis appeared to be the most abundant microcystin producer in Lake Tuusulanjärvi and in one basin of Lake Hiidenvesi. Because the most potent microcystin-producing genus of a lake can be identified, it will be possible in the future to design genus-targeted strategies for lake restoration. Effects of P and N concentrations on the biomass of microcystin-producing and nonmicrocystin-producing Microcystis strains and an Anabaena strain were studied in cultures. P and N concentrations and their combined effect increased cyanobacterial biomass of all Microcystis strains. The biomass of microcystin-producing Microcystis was higher than that of nonmicrocystin-producing strains at high nutrient concentrations. The P concentration increased Anabaena biomass, but the effect of N concentration was statistically insignificant for growth yield, probably due to the ability of the genus to fix molecular N2. P and N concentrations and combined nutrients caused an increase in cellular microcystin concentrations of the Microcystis strain cultivated in chemostat cultures. Cyanobacteria are able to hydrolyse nutrients from organic matter through extracellular enzyme activities. Leucine aminopeptidase (LAP) activity was observed in an axenic N2-fixing Anabaena strain grown in batch cultures. The P concentration caused a statistically significant increase in LAP activity, whereas the effect of N concentration was insignificant. The highest LAP activities were observed in the most eutrophic basins of Lake Hiidenvesi. LAP activity probably originated mostly from attached heterotrophic bacteria and less from cyanobacteria.

Forest inventory-based large-scale forest biomass and carbon budget assessment: new enhanced methods and use of remote sensing for verification

In recent years, concern has arisen over the effects of increasing carbon dioxide (CO2) in the earth's atmosphere due to the burning of fossil fuels. One way to mitigate increase in atmospheric CO2 concentration and climate change is carbon sequestration to forest vegeta-tion through photosynthesis. Comparable regional scale estimates for the carbon balance of forests are therefore needed for scientific and political purposes. The aim of the present dissertation was to improve methods for quantifying and verifying inventory-based carbon pool estimates of the boreal forests in the mineral soils. Ongoing forest inventories provide a data based on statistically sounded sampling for estimating the level of carbon stocks and stock changes, but improved modelling tools and comparison of methods are still needed. In this dissertation, the entire inventory-based large-scale forest carbon stock assessment method was presented together with some separate methods for enhancing and comparing it. The enhancement methods presented here include ways to quantify the biomass of understorey vegetation as well as to estimate the litter production of needles and branches. In addition, the optical remote sensing method illustrated in this dis-sertation can be used to compare with independent data. The forest inventory-based large-scale carbon stock assessment method demonstrated here provided reliable carbon estimates when compared with independent data. Future ac-tivity to improve the accuracy of this method could consist of reducing the uncertainties regarding belowground biomass and litter production as well as the soil compartment. The methods developed will serve the needs for UNFCCC reporting and the reporting under the Kyoto Protocol. This method is principally intended for analysts or planners interested in quantifying carbon over extensive forest areas.

Harmful algae in the planktonic food web of the Baltic Sea

This study deals with algal species occurring commonly in the Baltic Sea: haptophyte Prymnesium parvum, dinoflagellates Dinophysis acuminata, D. norvegica and D. rotundata, and cyanobacterium Nodularia spumigena. The hypotheses are connected to the toxicity of the species, to the factors determining toxicity, to the consequences of toxicity and to the transfer of toxins in the aquatic food web. Since the Baltic Sea is severely eutrophicated, the fast-growing haptophytes have potential in causing toxic blooms. In our studies, the toxicity (as haemolytic activity) of the haptophyte P. parvum was highest under phosphorus-limited conditions, but the cells were toxic also under nitrogen limitation and under nutrient-balanced growth conditions. The cellular nutrient ratios were tightly related to the toxicity. The stoichiometric flexibility for cellular phosphorus quota was higher than for nitrogen, and nitrogen limitation led to decreased biomass. Negative allelopathic effects on another algae (Rhodomonas salina) could be observed already at low P. parvum cell densities, whereas immediate lysis of R. salina cells occurred at P. parvum cell densities corresponding to natural blooms. Release of dissolved organic carbon from the R. salina cells was measured within 30 minutes, and an increase in bacterial number and biomass was measured within 23 h. Because of the allelopathic effect, formation of a P. parvum bloom may accelerate after a critical cell density is reached and the competing species are eliminated. A P. parvum bloom indirectly stimulates bacterial growth, and alters the functioning of the planktonic food web by increasing the carbon transfer through the microbial loop. Our results were the first reports on DSP toxins in Dinophysis cells in the Gulf of Finland and on PTX-2 in the Baltic Sea. Cellular toxin contents in Dinophysis spp. ranged from 0.2 to 149 pg DTX-1 cell-1 and from 1.6 to 19.9 pg PTX-2 cell-1 in the Gulf of Finland. D. norvegica was found mainly around the thermocline (max. 200 cells L-1), whereas D. acuminata was found in the whole mixed layer (max. 7 280 cells L-1). Toxins in the sediment trap corresponded to 1 % of DTX-1 and 0.01 % PTX-2 of the DSP pool in the suspended matter. This indicates that the majority of the DSP toxins does not enter the benthic community, but is either decomposed in the water column, or transferred to higher trophic levels in the planktonic food chain. We found that nodularin, produced by Nodularia spumigena, was transferred to the copepod Eurytemora affinis through three pathways: by grazing on filaments of small Nodularia, directly from the dissolved pool, and through the microbial food web by copepods grazing on ciliates, dinoflagellates and heterotrophic nanoflagellates. The estimated proportion of the microbial food web in nodularin transfer was 22-45 % and 71-76 % in our two experiments, respectively. This highlights the potential role of the microbial food web in the transfer of toxins in the planktonic food web.

Fluorescence properties of Baltic Sea phytoplankton

To obtain data on phytoplankton dynamics with improved spatial and temporal resolution, and at reduced cost, traditional phytoplankton monitoring methods have been supplemented with optical approaches. In this thesis, I have explored various fluorescence-based techniques for detection of phytoplankton abundance, taxonomy and physiology in the Baltic Sea. In algal cultures used in this thesis, the availability of nitrogen and light conditions caused changes in pigmentation, and consequently in light absorption and fluorescence properties of cells. In the Baltic Sea, physical environmental factors (e.g. mixing depth, irradiance and temperature) and related seasonal succession in the phytoplankton community explained a large part of the seasonal variability in the magnitude and shape of Chlorophyll a (Chla)-specific absorption. The variability in Chla-specific fluorescence was related to the abundance of cyanobacteria, the size structure of the phytoplankton community, and absorption characteristics of phytoplankton. Cyanobacteria show very low Chla-specific fluorescence. In the presence of eukaryotic species, Chla fluorescence describes poorly cyanobacteria. During cyanobacterial bloom in the Baltic Sea, phycocyanin fluorescence explained large part of the variability in Chla concentrations. Thus, both Chla and phycocyanin fluorescence were required to predict Chla concentration. Phycobilins are major light harvesting pigments for cyanobacteria. In the open Baltic Sea, small picoplanktonic cyanobacteria were the main source of phycoerythrin fluorescence and absorption signal. Large filamentous cyanobacteria, forming harmful blooms, were the main source of the phycocyanin fluorescence signal and typically their biomass and phycocyanin fluorescence were linearly related. Using phycocyanin fluorescence, dynamics of cyanobacterial blooms can be detected at high spatial and seasonal resolution not possible with other methods. Various taxonomic phytoplankton pigment groups can be separated by spectral fluorescence. I compared multivariate calibration methods for the retrieval of phytoplankton biomass in different taxonomic groups. Partial least squares regression method gave the closest predictions for all taxonomic groups, and the accuracy was adequate for phytoplankton bloom detection. Variable fluorescence has been proposed as a tool to study the physiological state of phytoplankton. My results from the Baltic Sea emphasize that variable fluorescence alone cannot be used to detect nutrient limitation of phytoplankton. However, when combined with experiments with active nutrient manipulation, and other nutrient limitation indices, variable fluorescence provided valuable information on the physiological responses of the phytoplankton community. This thesis found a severe limitation of a commercial fast repetition rate fluorometer, which couldn t detect the variable fluorescence of phycoerythrin-lacking cyanobacteria. For these species, the Photosystem II absorption of blue light is very low, and fluorometer excitation light did not saturate Photosystem II during a measurement. This thesis encourages the use of various in vivo fluorescence methods for the detection of bulk phytoplankton biomass, biomass of cyanobacteria, chemotaxonomy of phytoplankton community, and phytoplankton physiology. Fluorescence methods can support traditional phytoplankton monitoring by providing continuous measurements of phytoplankton, and thereby strengthen the understanding of the links between biological, chemical and physical processes in aquatic ecosystems.

Phytoplankton ecology of subarctic lakes in Finnish Lapland

Climate is warming and it is especially seen in arctic areas, where the warming trend is expected to be greatest. Arctic freshwater ecosystems, which are a very characteristic feature of the arctic landscape, are especially sensitive to climate change. They could be used as early warning systems, but more information about the ecosystem functioning and responses are needed for proper interpretation of the observations. Phytoplankton species and assemblages could be especially suitable for climate-related studies, since they have short generation times and react rapidly to changes in the environment. In addition, phytoplankton provides a good tool for lake classifications, since different species have different requirements and tolerance ranges for various environmental factors. The use of biological indicators is especially useful in arctic areas, were many of the chemical factors commonly fall under the detection limit and therefore do not provide much information about the environment. This work brings new information about species distribution and dynamics of arctic freshwater phytoplankton in relation to environmental factors. The phytoplankton of lakes in Finnish Lapland and other European high-altitude or high-latitude areas were compared. Most lakes were oligotrophic and dominated by flagellated species belonging to chrysophytes, cryptophytes and dinoflagellates. In Finnish Lapland cryptophytes were of less importance, whereas desmids had high species richness in many of the lakes. In Pan-European scale, geographical and catchment-related factors were explaining most of the differences in species distributions between different districts, whereas lake water chemistry (especially conductivity, SiO2 and pH) was most important regionally. Seasonal and interannual variation of phytoplankton was studied in subarctic Lake Saanajärvi. Characteristic phytoplankton species in this oligotrophic, dimictic lake belonged mainly to chrysophytes and diatoms. The maximum phytoplankton biomass in Lake Saanajärvi occurs during autumn, while spring biomass is very low. During years with heavy snow cover the lake suffers from pH drop caused by melt waters, but the effects of this acid pulse are restricted to surface layers and last for a relatively short period. In addition to some chemical parameters (mainly Ca and nutrients), length of the mixing cycle and physical factors such as lake water temperature and thermal stability of water column had major impact on phytoplankton dynamics. During a year with long and strong thermal stability, the phytoplankton community developed towards an equilibrium state, with heavy dominance of only a few taxa for a longer period of time. During a year with higher windiness and less thermal stability, the species composition was more diverse and species with different functional strategies were able to occur simultaneously. The results of this work indicate that although arctic lakes in general share many common features concerning their catchment and water chemistry, large differences in biological features can be found even in a relatively small area. Most likely the lakes with very different algal flora do not respond in a similar way to differences in the environmental factors, and more information about specific arctic lake types is needed. The results also show considerable year to year differences in phytoplankton species distribution and dynamics, and these changes are most likely linked to climatic factors.

The role of phosphorus as a regulator of bloom-forming diazotrophic cyanobacteria in the Baltic Sea

Eutrophication favours harmful algal blooms worldwide. The blooms cause toxic outbreaks and deteriorated recreational and aesthetic values, causing both economic loss and illness or death of humans and animals. The Baltic Sea is the world s only large brackish water habitat with recurrent blooms of toxic cyanobacteria capable of biological fixation of atmospheric nitrogen gas. Phosphorus is assumed to be the main limiting factor, along with temperature and light, for the growth of these cyanobacteria. This thesis evaluated the role of phosphorus nutrition as a regulating factor for the occurrence of nitrogen-fixing cyanobacteria blooms in the Baltic Sea, utilising experimental laboratory and field studies and surveys on varying spatial scales. Cellular phosphorus sources were found to be able to support substantial growth of the two main bloom forming species Aphanizomenon sp. and Nodularia spumigena. However, N. spumigena growth seemed independent of phosphorus source, whereas, Aphanizomenon sp. grew best in a phosphate enriched environment. Apparent discrepancies with field observations and experiments are explained by the typical seasonal temperature dependent development of Aphanizomenon sp. and N. spumigena biomass allowing the two species to store ambient pre-bloom excess phosphorus in different ways. Field experiments revealed natural cyanobacteria bloom communities to be predominantly phosphorus deficient during blooms. Phosphate additions were found to increase the accumulation of phosphorus relatively most in the planktonic size fraction dominated by the nitrogen-fixing cyanobacteria. Aphanizomenon sp. responded to phosphate additions whereas the phosphorus nutritive status of N. spumigena seemed independent of phosphate addition. The seasonal development of phosphorus deficiency is different for the two species with N. spumigena showing indications of phosphorus deficiency during a longer time period in the open sea. Coastal upwelling introduces phosphorus to the surface layer during nutrient deficient conditions in summer. The species-specific ability of Aphanizomenon sp. and N. spumigena to utilise phosphate enrichment of the surface layer caused by coastal upwelling was clarified. Typical bloom time vertical distributions of biomass maxima were found to render N. spumigena more susceptible to advection by surface currents caused by coastal upwellings. Aphanizomenon sp. populations residing in the seasonal thermocline were observed to be able to utilise the phosphate enrichment and a bloom was produced with a two to three week time lag subsequent to the relaxation of upwelling. Consistent high concentrations of dissolved inorganic phosphorus, caused by persistent internal loading of phosphorus, was found to be the main source of phosphorus for large-scale pelagic blooms. External loads were estimated to contribute with only a fraction of available phosphorus for open sea blooms. Remineralization of organic forms of phosphorus along with vertical mixing to the permanent halocline during winter set the level of available phosphorus for the next growth season. Events such as upwelling are important in replenishing phosphate concentrations during the nutrient deplete growth season. Autecological characteristics of the two main bloom forming species favour Aphanizomenon sp. populations in utilising the abundant excess phosphate concentrations and phosphate pulses mediated through upwelling. Whilst, N. spumigena displays predominant phosphorus limited growth mode and relies on more scarce cellular phosphorus stores and presumably dissolved organic phosphorus compounds for growth. The Baltic Sea is hypothesised to be in an inhibited state of recovery due to the extensive historical external nutrient loading, extensive internal phosphorus loading and the substantial nitrogen load caused by cyanobacteria nitrogen fixation. This state of the sea is characterised as a vicious circle .

Fast- and drift-ice communities in the Bothnian Bay and the impact of UVA radiation on the Baltic Sea ice ecology

The aim of this thesis was to study ecology of Baltic Sea ice from two perspectives. In the first two studies, sea-ice ecology from riverine-influenced fast ice to drift ice in the Bothnian Bay was investigated, whereas the last two studies focus on the sensitivity of sea-ice bacteria and algae to UVA examined in situ. The seasonal sea ice cover is one of the main characteristics of the Baltic Sea, and despite the brackish parental water, the ice structure is similar to polar ice with saline brine inclusions, the sea ice habitat. The decreasing seawater salinity from the northern Baltic Sea to the Bothnian Bay translates to decreasing brine volumes along the gradient, governing the size and community structure of the food webs in ice. However, the drift and fast ice in the Bothnian Bay may differ greatly in this sense, as drift ice may have been formed at more southern locations. Rafting and the formation of snow ice are common processes in the ice field of the Bothnian Bay. As evidenced in this thesis, rafting altered the vertical distribution of organisms and snow-ice formation provided habitable space in the better-illuminated, nitrogen-rich surface layer. The divergence between fast and drift ice became apparent at the more advanced stages, and chlorophyte biomass decreased from fast to drift ice, while the opposite held true for protozoan and metazoan biomass. The brine volumes affected the communities somewhat, and a higher percentage of flagellate species was generally linked to lower brine volumes, whereas chain-forming diatoms were mostly concentrated in layers with larger brine volumes. These results add to knowledge of the ecological significance of the ice cover lasting up to 7 months per year in this area. Sea-ice food webs are generally light-limited, but while increasing light irradiances typically enhance the primary production and further, the secondary production in sea ice, any increase in solar radiation also includes an increase in harmful UVA radiation. The Baltic Sea ice microbial communities were clearly sensitive to UVA and the responses were strongly linked to the earlier light history, as well as to the solar irradiances they were exposed to. The increased biomass of chlorophytes and pennate diatoms, when UVA was excluded, indicates that their normally minor contribution to the biomass in the upper layers of sea ice might be partly dictated by UVA. The effects of UVA on bacterial production in Baltic Sea ice mostly followed the responses in algal growth, but occasionally the exposure to UVA even enhanced the bacterial production. The dominant bacterial class, Flavobacteria, seemed to be UVA-tolerant, whereas all the Alpha-, Beta- and Gammaproteobacteria present in the surface layer showed UVA sensitivity. These results indicate that changes in the light field of ice may alter the community structure and affect the functioning of ice food webs, and are of importance when the effects of thinning of the ice cover are assessed.