Timo Kairesalo

Biomanipulation as an Application of Food-Chain Theory: Constraints, Synthesis, and Recommendations for Temperate Lakes

ABSTRACT The aim of this review is to identify problems, find general patterns, and extract recommendations for successful biomanipulation. An important conclusion is that the pelagic food chain from fish to algae may not be the only process affected by a biomanipulation. Instead, this process should be viewed as the “trigger” for secondary processes, such as establishment of submerged macrophytes, reduced internal loading of nutrients, and reduced resuspension of particles from the sediment. However, fish reduction also leads to a high recruitment of young-of-the-year (YOY) fish, which feed extensively on zooplankton. This expansion of YOY the first years after fish reduction is probably a major reason for less successful biomanipulations. Recent, large-scale biomanipulations have made it possible to update earlier recommendations regarding when, where, and how biomanipulation should be performed. More applicable recommendations include (1) the reduction in the biomass of planktivorous fish should be 75% or more; (2) the fish reduction should be performed efficiently and rapidly (within 1–3 years); (3) efforts should be made to reduce the number of benthic feeding fish; (4) the recruitment of YOY fish should be reduced; (5) the conditions for establishment of submerged macrophytes should be improved; and (6) the external input of nutrients (phosphorus and nitrogen) should be reduced as much as possible before the biomanipulation. Recent biomanipulations have shown that, correctly performed, the method also achieves results in large, relatively deep and eutrophic lakes, at least in a 5-year perspective. Although repeated measures may be necessary, the general conclusion is that biomanipulation is not only possible, but also a relatively inexpensive and attractive method for management of eutrophic lakes, and in particular as a follow-up measure to reduced nutrient load.

Microbial community structure and activity in arsenic‐, chromium‐ and copper‐contaminated soils

Microbial community structure, potential microbial activity and As resistance were affected by arsenic (As), chromium (Cr) and copper (Cu) contamination in soils of abandoned wood impregnating plants. Contaminated soils differed in the concentrations of soil acid-soluble and total water-soluble As, Cr and Cu, and in the concentration of bioavailable As analyzed with a bacterial sensor. Phospholipid fatty acid (PLFA) and 16S rRNA gene terminal restriction fragment length polymorphism (t-RFLP) profiles indicated that exposure to high metal contamination or subsequent effects of this exposure permanently changed microbial community structure. The total number of colony forming units (CFU) was not affected by metal contamination and the As(V)-resistant bacterial ratio to total heterotrophic plate counts was high (0.5-1.1) and relatively independent of the concentration of As. In contrast, the proportion of As(III)-resistant bacteria was dependent on the concentration of As in the soils and a significant positive relationship was found between the bioavailability of As and the proportion of As(III)-resistant bacteria. Dominant As-resistant isolates from contaminated soils were identified by their fatty acid methyl ester (FAME) profiles as Acinetobacter, Edwardsiella, Enterobacter, Pseudomonas, Salmonella and Serratia species. No differences were noted in glucose mineralization among contaminated and control soil samples within sites. Based on [(14)C]glucose mineralization the community was able to compensate for the reduced diversity. According to t-RFLP results, this was not due to a reversion towards the unexposed community, but mainly due to the appearance of new dominating species. This study, combining complementary culture-dependent and -independent methods, suggests that microbes are able to respond to soil metal contamination and maintain metabolic activity apparently through changes in microbial community structure and selection for resistance.

Impact of Submerged Macrophytes on Fish-Zooplankton Interactions in Lakes

Fish have a major structuring impact on the Zooplankton communities in lakes (Hrbacek et al., 1961; Brooks and Dodson, 1965) that may cascade to the lower trophic levels and chemical environment (Carpenter et al., 1985; Carpenter and Kitchell, 1993). Ample evidence is available from enclosure experiments (e.g., Christoffersen et al., 1993), whole-lake experiments (e.g., Shapiro et al., 1975; Benndorf, 1987; Gulati et al., 1990; Carpenter and Kitchell, 1993), and empirical analyses (Jeppesen et al., 1990, 1997). More recently, it has become evident that 0+ fish may play a key role in Zooplankton population dynamics (Cryer et al., 1986; Mills et al., 1987), and some studies suggest that fish larvae are responsible for the midsummer decline in Zooplankton (Luecke et al., 1990; Jeppesen et al., 1997), a phenomenon that is often attributed to increased density of inedible phytoplankton such as cyanobacteria (e.g., De Bernardi and Guisanni, 1990). Whole-lake (Sondergaard et al., 1997) and enclosure (He and Wright, 1992) experiments support the structuring role of 0+ fish. How the importance of top-down control of Zooplankton by fish varies along a trophic gradient is debated extensively. McQueen et al. (1986) suggested that the cascading effect of zooplank-tivorous fish is stronger in oligotrophic lakes than in eutrophic lakes, but a growing body of literature argues that the cascading effect of fish is greater in eutrophic and hypertrophic lakes with respect to the food web in the classic sense

INFLUENCE OF MICROBES ON THE MOBILIZATION, TOXICITY AND BIOMETHYLATION OF ARSENIC IN SOIL

To understand the effects of microbial activity on the mobilization and speciation of arsenic in soil, the cycling of arsenic was studied in microcosm experiments under laboratory conditions. Particular attention was paid to the biomethylation of arsenic and to the toxicity of inorganic and organic arsenic species for microbes. Microbes enhanced mobilization of arsenic from soil by 19-24% compared to formaldehyde inhibited controls. Formation of dissolved methylated arsenic species by microbes was low (< 0.1%) during the 5-day incubation. Even though methylation may function as a detoxification method, it was of minor importance in the soil tested.

Effect of nutrient loading on bacterioplankton community composition in lake mesocosms.

Changes in bacterioplankton community composition were followed in mesocosms set up in the littoral of Lake Vesijärvi, southern Finland, over two summers. Increasing nitrogen and phosphorus concentrations in the mesocosms represented different trophic states, from mesotrophic to hypertrophic. In 1998, the mesocosms were in a turbid state with a high biomass of phytoplankton, whereas in 1999, macrophytes proliferated and a clear-water state prevailed. The bacterial communities in the mesocosms also developed differently, as shown by denaturing gradient gel electrophoresis profiling of partial 16S rRNA gene fragments and by nonmetric multidimensional scaling analysis. In 1998, nutrient treatments affected the diversity and clustering of bacterial communities strongly, but in 1999, the bacterial communities were less diversified and not clearly affected by treatments. Canonical correspondence analysis indicated that bacterioplankton communities in the mesocosms were influenced by environmental physicochemical variables linked to the increasing level of eutrophication. Nitrogen concentration correlated directly with the bacterioplankton composition. In addition, the high nutrient levels had indirect effects through changes in the biomass and composition of phyto- and zooplankton. Sequencing analysis showed that the dominant bacterial divisions remained the same, but the dominant phylotypes changed during the 2-year period. The occurrence of Verrucomicrobia correlated with more eutrophic conditions, whereas the occurrence of Actinobacteria correlated with less eutrophic conditions.

Do submersed plants enhance microbial activity in sediment

Abstract The effects of three submersed plant species ( Elodea canadensis Mixch., Myriophyllum alterniflorum L. and Lobelia dortmanna L.) on bacterial activity and microbial biomass in ambient sediment were measured under laboratory conditions with special reference to organic carbon release through the plant roots. The effect of Lobelia on denitrification potential in sediment was also assessed. Organic carbon was released into the sediment by all the three plant species: of the photosynthetically fixed 14 C-carbon, Elodea released 14%, Myriophyllum 4% and Lobelia 2% during the 7-day experiment. However, regardless of the carbon supply, Elodea and Myriophyllum did neither enhance the bacterial activity nor the microbial biomass in the sediment, whereas Lobelia had a positive influence on both the variables, as well as on denitrification potential within deeper root zone.

A fading recovery: the role of roach (Rutilus rutilus L.) in maintaining high phytoplankton productivity and biomass in Lake Vesijarvi, southern Finland

For 60 years, Lake Vesijärvi, especially the Enonselkä basin (2600 ha), received sewage water discharge from the City of Lahti. In 1976 the municipal sewage loading was diverted from the lake. Initially, the recovery of the lake proceeded well but after some years summer blooms of blue-green algae (Aphanizomenon, Microcystis) increased again. High biomass of roach (Rutilus rutilus L.) was considered to play an important role in maintaining high algal productivity and biomass in the lake water. Field experiments in mesocosms (22–24 m3) with different densities of roach suggested that fish biomass should be less than 30 g m−2, or 300 kg ha−1, to ensure a significant reduction in the current productivity and biomass of phytoplankton. Bioturbation of sediments and recycling of nutrients, rather than zooplanktivory, seemed to be the main factors linking roach to water quality in the mesocosms. The applicability of the mesocosm results to the management of Lake Vesijärvi is discussed.

Co-occurrence and potential chemical competition of phosphorus and silicon in lake sediment

Abstract Various chemical approaches were used to characterize P and Si in the surface sediment of Lake Vesijarvi, Southern Finland. The dynamic equilibrium between solid and solution P in aerobic and anaerobic sediment was investigated by means of desorption-sorption isotherms. The sediment material was rich in hydrated Al and Fe oxides and, accordingly, had a high P sorption capacity and a very low P concentration (5 μg l−1) in the interstitial water under aerobic conditions. Approximately 25–30% of total P and almost 90% of total Si were bound in mineral lattices, i.e. in a stable form not participating in biological and chemical transformations. Organic P comprised about 20–25% of total P and was mainly in practically insoluble form not extractable by dilute base or acid. Phosphorus participating in sorption-desorption reactions was considered to originate from reserves bound on oxide surfaces. When the oxide bound P reserves were determined by fractionation analysis, a large amount of Si (corresponding to about 30% of biogenic reserves) was also dissolved. Anaerobiosis increased distinctly the occurrence of both elements in the interstitial water. These dissolution patterns suggest that P and Si are bound to the same components and, therefore, compete with each other for the sorption sites. This chemical competition, in turn, may be of importance in the nutrient exchange between solid and solution phase in sediment.

Direct and indirect mechanisms behind successful biomanipulation

Lake Vesijärvi is a relatively large (length 25 km; total area 110 km2), shallow (mean depth 6 m), but stratified lake in southern Finland. The Enonselkä basin (26 km2), surrounded by the city of Lahti, received its sewage effluent, and changed from a clear water basin with flourishing fisheries from the 1940–50s to one of the most eutrophic lake systems in Finland thereafter. In 1976, the sewage effluent was diverted, resulting in a temporary recovery of water quality. However, in the 1980s, massive surface scums of cyanobacteria degraded the water quality and arrested the recovery of the lake. A restoration strategy providing an ecologically sound basis for the management of the lake was initiated in 1987. This strategy involved biomanipulation (mass removal of coarse fish) together with conventional pollution control measures on discharges to the lake. Biomanipulation was chosen instead of much more expensive chemical and/or technical methods, such as chemical treatment or dredging of the profundal sediment. The large-scale biomanipulation trial was carried out in the Enonselkä basin during 1989–93. Following the mass removal of coarse fish (1000 metric tons of fish; mainly roach and smelt), the biomass of cyanobacteria collapsed concomitantly with a decline of total phosphorus concentration from 45 to 35 mg P m−3, and with an increase of Secchi depth from 1 m to 3.5 m. These observed improvements in the water quality were matched with a large decline in roach-mediated phosphorus movement from littoral to pelagial, from 100 mg P m−2 in 1989 to 15 mg P m−2 in 1993. Year-to-year variation within the littoral communities, and in the recruitment of fish, could in this way cause large oscillations in the whole ecosystem. The involvement of local people (fishermen, farmers etc.) in controlling non-point nutrient loading and fish stock development, is of prime importance for the long term success of lake restoration.

Eutrophication and recovery of Lake Vesijärvi (south Finland): Diatom frustules in varved sediments over a 30-year period

Lake Vesijarvi was loaded by sewage from the City of Lahti for 60 years until 1976 when the discharge was diverted. Paleolimnological analyses of the varved bottom sediment indicate that the sedimentation rate within the Enonselka basin, the most eutrophic part of the lake, has been as high as 2 cm yr−1, and total phosphorus accumulation was 20–40 g P m−2 yr−1, during the last 20 years. Within the less eutrophic Laitialanselka basin, the sedimentation rate did not exceed 1 cm yr−1, and the formation of varved sediment only began at the end of the 1960s, i.e. about 10 years later than in Enonselka.