Sex‐dependent responses of perch to changes in water clarity and temperature

Rising temperatures and decreasing water transparency of lakes have strong wide ranging effects on fish. Fish responses to various changes in the environment are usually species‐dependent, but responses may also vary within species. In general, large individuals are considered to be more sensitive to environmental variation due to higher energy demand, than smaller individuals. Similarly, large individuals require more food to maintain bodily functions and are thus more sensitive to resource and food scarcity. These size‐specific responses to environmental gradients are also sex‐dependent in species that exhibit sexual size dimorphism (SSD). We studied in enclosures with short‐term experiments how rising temperatures and decreasing water transparency regulate the feeding rates of female and male European perch (Perca fluviatilis L.). To explore experimental results, we calculated perch SSD in nine lakes with varying environmental conditions using previously collected field data. The results of the experiments revealed that the combined effect of water transparency and temperature on the feeding rate of fish is gender‐dependent: feeding rate of females decreased more than that of males. The experimental results were also supported by field data that revealed a negative relation between water transparency and the magnitude of SSD in perch. Our results suggest that rising temperatures and decreasing water transparency may potentially decrease fish size in a sex‐dependent manner. As female size is one of the main demographic traits determining the reproductive success of a fish population, changing environments may have unexpected and far‐reaching consequences on fish population dynamics.     

Patterns in Water Quality and Fish Status of Some Acidified Lakes in Southern Finland During a Decade: Recovery Proceeding

Since the early 1980s, the acidic deposition in the northern Europe has decreased substantially. This has resulted in corresponding improvements of the water quality in some acid sensitive small lakes of southern Finland. Among the fish of these lakes, the first signs of recovery were recorded in the early 1990s, when the European perch (Perca fluviatilis L.) started to reproduce in some sparse populations. Since then, the reproduction of perch has been successful in several years. The appearance of strong year-classes in lakes earlier almost empty of fish indicates recovery. This development has resulted in increased population densities, decreased mean sizes of fish and decreased growth rates. In a more acid sensitive species, roach (Rutilus rutilus (L.)), no clear indications of recovery have been recorded this far. However, schools of small roach (age 1+) were observed in the summer of 1998 in two acidic lakes that were inhabited by sparse roach populations during 1985–1995.     

Responses of phyto- and zooplankton to liming in a small acidified humic lake

Liming resulted in an immediate and transitory decrease of plankton biomass and phytoplankton primary production in the limed part of an acidified humic lake. In the longer term liming has changed species composition and dominance of phyto- and zooplankton. Due to increased transparency and improved oxygen conditions plankton biomass peaked deeper in the water column after liming. During the three years post-liming period phyto- and zooplankton communities have changed less than reported in several other studies. This is largely because liming was carried out well before the collapse of perch population, which has controlled zooplankton both in the pre- and post-treatment period.     

Status of Zoobenthos and Fish Populations in Subarctic Rivers of the Northernmost Finland: Possible Effects of Acid Emissions from Russian Kola Peninsula

In 1990, a monitoring programme was initiated to survey the status of benthic invertebrate communities and fish populations over a wide range of subarctic rivers in northernmost Finnish Lapland (68°15′–70°N). A special emphasis was placed on detecting possible effects of acidification through sulfur emissions from Russian Kola Peninsula. Sampling in 13 rivers within four major river systems covered watercourses from small brooks to large 7th order rivers, and watersheds with different distances from the emission sources. The community structure of zoobenthos and the occurrence of acid-sensitive indicator species were assessed in 90 sampling sites. Sensitive fluvial fish species, including Atlantic salmon (Salmo salar), brown trout (Salmo trutta), European minnow (Phoxinus phoxinus) and burbot (Lota lota), were monitored by studying their occurrence, abundance and juvenile recruitment. No signs of acid-induced failure in juvenile recruitment were detected in salmonid populations. The occurrence of minnow and burbot covered all the systems studied. In parallell, the structure of benthic communities with relatively high species diversity and wide distribution of a highly acid-sensitive caddisfly indicated no effects of acidification.     

Acceleration of N mineralization by release of enzymes and substrates from soil mineral particles with phosphates

A study was conducted to develop an improved method for measuring organic N (net) mineralization in which chemical extraction takes place in combination with suspension incubation in ammonia-absorbing membrane bottles. To obtain direct evidence of the extent to which extracted organic N is mineralizable, the extraction suspension was further incubated immediately after the extraction procedure with mild and selective extractants. In this ‘extraction incubation’ method, extraction continues during the incubation but only relatively easily mineralizable organic matter is released. Standard incubation is usually carried out in sealed N₂-flushed bottles. However, when phosphate or pyrophosphate soil suspensions are incubated, mineralization is much higher than in soil water suspensions. Further, accumulation of ammonia+(ammonium) and other gases, i.e. CO_2, can affect the reaction rate and final reaction equilibrium in the sealed incubation flask. It was to avoid these effects that the membrane method was developed. With this procedure, the flask is closed with an ammonia-absorbing membrane permeable to other gases. Water, phosphate and pyrophosphate suspensions were incubated at 37 °C in sealed bottles (SB), in sealed N₂ gas-flushed bottles (SBN₂), and in bottles with ammonia-trapping filters (MB). The maximum amount of released during 10 days' incubation was 133.0 mg kg⁻¹ in the water, 208.0 mg kg⁻¹ in the phosphate and 454.1 mg kg⁻¹ in the pyrophosphate suspension (soil total C content 6.2% and N 0.25%). During incubation in phosphate and pyrophosphate suspensions, the mobilization was nearly linear in membrane bottles. The variation between replicates was also smallest in these bottles. It was concluded that membrane bottles were best suited to incubation when mobilization reactions were accelerated with phosphate or pyrophosphate extractants. The method was easy to perform and gave results with good replicability.     

The concentration of phenolics in brown-rot decay resistant and susceptible Scots pine heartwood

The concentrations of three individual stilbenes, pinosylvin (PS), pinosylvin monomethyl ether (PSM), and pinosylvin dimethyl ether (PSD), and the total concentration of phenolic compounds were determined in 34-year-old Scots pines which were known to have either decay-resistant or susceptible heartwood. The sample trees were selected from two progeny tests among 783 trees; the decay resistance of which had been screened earlier in vitro against a brown-rot fungus Coniophora puteana. Ten decay-resistant and ten susceptible trees from each of the progeny tests were analysed. In the heartwood of the resistant trees, the average total concentration of the stilbenes was 7.5 and 6.4 mg/g of dry weight, while in the heartwood of the susceptible trees the respective values were 5.0 and 4.7 mg/g. The difference between the decay resistant and susceptible trees was statistically significant in both progeny tests. The difference in concentration of total phenolics, analysed by the Folin-Ciocalteu method, was also significant. A high concentration of phenolics was connected to the low hygroscopicity of wood. The results support the argued hypothesis that the stilbenes make a contribution to the differences in the decay rate of natural wood substrate. On the other hand, the results show that the stilbenes alone do not explain the variation in decay rate.     

Effects of oral selenium supplementation on mastitis markers and pathogens in Estonian cows

The effects of selenium supplementation on mastitis parameters in milk and on glutathione peroxidase (GPx) levels in blood were evaluated. Fifty-five Estonian dairy cows were allocated to selenium-supplemented (n=39) and nonsupplemented (n=16) groups. The supplemented group received 0.2 ppm organic selenium in the form of selenium yeast in their diet daily for 8 weeks. The nonsupplemented cows received their standard diet with no selenium supplementation. Mastitis parameters (i.e., bacteriologic findings and somatic cell count, N-acetyl-beta-D-glucosaminidase, and bovine serum albumin concentration) and GPx levels were monitored. The increase in the activity of GPx was significantly (P<.001) greater in selenium-supplemented cows than in nonsupplemented ones. Milk samples from each quarter were examined before and 8 weeks after initiation of the study. The proportion of quarters still pathogen-free after 8 weeks was significantly (P<.01; odds ratio [OR]=9.7) higher in selenium-supplemented cows than in nonsupplemented cows. However, when quarters milk-tested as pathogen-infected at the start of the study were reexamined after 8 weeks, there was no significant (P=.14; OR 3.6) difference in the proportion of pathogen-free quarters between selenium-supplemented cows and nonsupplemented cows. Differential positive rate (Youden's index) revealed that individual quarters were more prone to be infected by pathogens when the blood GPx activities in cows were below the cutoff value of 3.3 microkat/g hemoglobin than when GPx activity was above this value. It was concluded that selenium supplementation in cows with low GPx activity seems to support udder defense mechanisms that favor reduction of the incidence of new mastitis cases.     

Chemical,biological and socio-economic approaches to the liming of Lake Alinenjärvi in southern Finland

The aim of this comprehensive study is to estimate the effects and usefulness of liming Lake Alinenjärvi based on chemical, biological and socio-economic studies. Methodological standpoints concerning the limestone dissolution rate, acidic surges and reacidification are also discussed. L. Alinenjärvi (0.4S km²) is located near the city of Nokia with a surrounding population of over 5 000 (< 2 km). Before liming, the lake had only a sparse crayfish (Astacus astacus L.) population left, because reproduction had been failing since the early 1980s. The most important effect of liming is that it should connect with the potential production of crayfish. The roach (Rutilus rutilus L.) population was also affected. The liming improved the chemical quality of the water, and decreased also the Al and Mn concentrations. The number of phytoplankton species increased, and the species composition of periphyton changed after liming. The a-chlorophyll concentration in water remained low. Furthermore, crustacean zooplankton and benthic animals increased in abundance in the first late summer after liming. The diet analysis of perch (Perca fluviatilis L.) gave comparable results suggesting a possible positive effect of liming on their food resources. The improved water quality seems to make the reproduction of the crayfish possible again, but recovery would take several years. To guarantee a recovery, the introduction of new crayfish individuals and supplementary neutralizing methods would be needed. The results of a mailed survey showed that L, Alinenjärvi is a valuable water source for the local people. The most usual forms of leisure around the lake and shores are, however, outdoor recreation and swimming, with only minor usage for fishing. Despite that, though the immediate benefits would be negligible, a majority of local residents supported the continuation of liming even though they would have to carry the costs in the future.     

Determining treatment frequency for controlling weeds on traffic islands using chemical and non‐chemical weed control

Many public authorities rely on the use of non‐chemical weed control methods, due to stringent restrictions on herbicide use in urban areas. However, these methods usually require more repeated treatments than chemical weed management, resulting in increased costs of weed management. In order to investigate the efficacy of four non‐chemical weed control methods and glyphosate treatment, experiments were carried out on traffic islands in the growing seasons 2005 and 2006. Three trial sites were each divided into six treatment areas, which were either treated with glyphosate, flame, steam, hot air/flame, hot water or left untreated. The treatments were carried out at regular, predetermined intervals throughout the growing season in 2004, whereas in 2005 and 2006 how many treatments that were required to keep weed cover below a predetermined acceptance level of 2% were investigated. Percentage weed cover was measured every second week using a 75 cm × 75 cm quadrat divided into 100 squares. On the control areas, a rapid increase in weed cover was observed, whereas weed cover could be kept below 2% by 2–7 treatments per year, depending on control method. On average, the following numbers of treatments per year were required: glyphosate 2.5, hot water 3, flames 5, hot air/flames 5.5 and steam 5.5 treatments. The results demonstrate that the weed control should be adjusted to the prescribed quality for the traffic islands by regularly assessing the need for weed control. They also show that tailored treatments can reduce the number of required non‐chemical treatments per year.