The fish biodiversity in the Congo River and its tributaries is extremely rich but the information on fish communities in the headwaters in terms of catch and biomass estimates is rare. Fishes in the running and stagnant waters in this region are of vital importance as a food resource for local residents. This study aimed to describe the fish community, catch, and biomass in the three headwater streams Bambou, Lebomo, and Bongo in the Lake Tumba Landscape (LTL) of the Democratic Republic of the Congo. Such information is of vital importance as a benchmark to understand the sustainability of the fish population for future generations of residents of the LTL. The field data were collected from 2007 through 2011, including dry and wet seasons. Here we present the results of this systematic, multi-annual study which was the first for fishes in streams of this region. In total, 50 species of 15 families were found in the nutrient-poor brown waters of these streams where high concentrations of humic acids cause a low pH. Among abundant species occurring in all three streams were the cyprinid Enteromius holotaenia (Boulenger, 1904), the mormyrid Marcusenius moorii (Günther, 1867), the alestids Clupeocharax schoutedeni Pellegrin, 1926 and Bryconaethiops boulengeri Pellegrin, 1900, and the clariid Clarias angolensis Steindachner, 1866. Bongo Stream was distinguished from the others by a rich abundance of Alestopetersius compressus (Poll et Gosse, 1963). The presence of several species at low pH (between 5.0 and 5.5) is new information that lowers the bottom of the pH interval for these species compared to earlier reports. The maximum total length (TL) of some other species was by 5–20 percentage points higher than those reported earlier. The median weight per unit effort (WPUE) in the streams varied between 30 and 115 g per hour during the dry seasons and between 18 and 86 g per hour during the wet seasons. The fish biomass in the streams varied between 0.05 and 0.7 g ⸱ m–2 with a median 0.14 g ⸱ m–2. This relatively low value compared to other tropical headwaters may be a result of the low pH and dark color of these headwaters. The results of the study serve as a reference point to which future monitoring of fish fauna can be compared for sustainable management of the LTL.

Background. Lake Tumba with a surface area of 830 km(2) is very humic (pH = 3.6-4.6). The fishery is important for the riparian population but there are concerns about overfishing. The objective of this study was to assess changes in the fish species composition by comparing the presently reported survey (2005-2010) with earlier studies carried out in 1938-1939, 1955-1956, and 1959 Our hypothesis was that Lake Tumba had been overfished. Materials and methods. Fishing was done in the pelagial with gillnet (25 and 30 mm) and line with hooks at three sites within 166 days in 2005-2006 and 2009-2010. Results. A total of 40 species were identified. Five species were caught all years and at all sites, namely Chrysichthys cranchii (Leach, 1818), Chrysichthys ornatus Boulenger, 1902, Chrysichthys punctatus Boulenger, 1899, Mormyrops anguilloides (Linnaeus, 1758), and Tylochromis lateralis (Boulenger, 1898). Twelve species were only caught once. Weight Per Unit Effort (WPUE) differed with site and season: ranging from 0 to 4200 g.day(-1) and the Number of fish Per Unit Effort (NPUE) varied from 0 to 27 fishes.day(-1). Conclusions. Out of 49 pelagic species caught by Matthes in 1959, we considered five as diminished in numbers or even missing. This may be attributed to high fishing pressure. The protected site Mabali hosted the majority of previously reported species of which two were noted in Matthes's list but not caught by him. Many parameters demonstrated a "positive" difference between Mabali (which is protected from fishing) and the other sites. This site should be a reference area for future monitoring if its status can be maintained. A trend in the fishery based on interviews with fishers indicated a change from larger species to smaller. This was deemed a result of fishing pressure and nine species were identified as diminishing. The presently reported survey introduced quantitative aspects while earlier studies were qualitative. This impairs the ability to draw strong conclusions about overfishing and other anthropogenic activities. The threat of overfishing calls for the need for consistent quantitative monitoring of the fish population, including monitoring of waters in the drainage area, to enable assessment of impact of anthropogenic pressure.

For more than 50 years, scientific insights from surface water monitoring have supported Swedish evidence-based environmental management. Efforts to understand and control eutrophication in the 1960s led to construction of wastewater treatment plants with phosphorus retention, while acid rain research in the 1970s contributed to international legislation curbing emissions. By the 1990s, long-time series were being used to infer climate effects on surface water chemistry and biology. Monitoring data play a key role in implementing the EU Water Framework Directive and other legislation and have been used to show beneficial effects of agricultural management on Baltic Sea eutrophication. The Swedish experience demonstrates that well-designed and financially supported surface water monitoring can be used to understand and manage a range of stressors and societal concerns. Using scientifically sound adaptive monitoring principles to balance continuity and change has ensured long-time series and the capability to address new questions over time.

When assessing the acidification status for a body of water, a reference value that describes the natural state is often estimated. One way to define this reference is to use the biogeochemical model MAGIC. However, MAGIC requires too many input parameters and modelling skills to use for operational application at a regional scale where hundreds or thousands of objects need to be assessed. Here we explore the possibility of complementing MAGIC with a simpler metamodel. The metamodel, metaMAGIC, was calibrated to 95 lakes with pre-industrial ANC predicted by MAGIC. The lakes constituted a diverse population, spread across a region stretching 1360 km in a N-S direction. MetaMAGIC proved capable of estimating the pre-industrial ANC calculated by MAGIC with a validated median error of 13.2 μeq/L, using contemporary concentrations of base cations, SO4 2- and Cl- as predictors. In comparison with the commonly used SSWC-model, MetaMAGIC reproduces the pre-industrial buffering capacity reconstructed with MAGIC more accurately. An advantageous feature of the metamodel is that it allows the reference value to vary in response to short-term hydroclimatological influences. Hence it provides a more stable assessment when few contemporary measurements of water chemistry are available. This metamodelling approach is suggested as a useful tool for acidification assessment purposes, and more generally, for extending the information from complex biogeochemical models.

Kalkningseffekter pa allman vattenkemi i sjoar inkl. mal och maluppfyllelse. Redovisning av delprojekt 2a.2 inom IKEU-utvarderingen 2008

The recovery from acidification has led to the demand for more precise criteria for classification of acidification. The Swedish Environmental Protection Agency has revised Sweden’s Ecological Quality Criteria for acidification to improve the correlation between the chemical acidification criteria and biological effects. This paper summarises the most relevant findings from several of the studies commissioned for this revision. The studies included data on water chemistry in 74 reference lakes in southern Sweden with data on fish in 61 of the lakes, as well as data on littoral fauna in 48 lakes. We found that the acidity variable most strongly correlated to the biota was the median pH from the current year. Our results probably do not reflect the mechanisms behind the negative effects of acidity on the biota, but are fully relevant for evaluation of monitoring data. The biogeochemical models used for predicting acidification reference conditions generate a pre-industrial buffering capacity. In order to get an ecologically more relevant criteria for acidification based on pH, we transferred the estimated change in buffering capacity into a corresponding change in pH. A change of 0.4 units was defined as the threshold for acidification. With this criterion a considerably lower number of Swedish lakes were classified as acidified when compared with the present Ecological Quality Criteria.

Trends from 160 lakes in Norway and Sweden for the period 1990–2004 reveal that Scandinavian lakes show clear signs of recovery from acidification. Sulphate has decreased and ANC, alkalinity and pH have increased. During the last 5a, the decline in SO4- has ceased, whereas ANC continues to increase. The results also show decreasing trends for Cl, while Na shows no or very small trends. The increase in the Na/Cl-ratio explains part of the increase in ANC. On average for the period 1990–2004 the decrease in Cl contributes 20–50% of the increase in ANC. The main cause of the trends in Cl in southern Sweden and Norway are probably due to declining seasalt inputs due to a higher frequency of heavy storms in the late 1980s and early 1990s. TOC exhibits increasing trends in regions with median TOC concentrations>3mgC/L, however, this does not contribute significantly to the observed increase in ANC.

Episodforsurning - Underlag till Naturvardsverkets handbok for kalkning av sjoar och vattendrag.

Brown waters There have been widespread reports of surface waters in many remote glaciated regions of North America and Northern Europe becoming browner as levels of dissolved organic carbon have increased. Several hypotheses have been proposed to explain the effect, including recent climate change, but the question remains controversial. A new survey of time series data from more than 500 remote lakes and streams, combined with a simple model, now shows that dissolved organic carbon concentrations are in fact closely related to the decline in the sulphate and seasalt content of atmospheric deposition. Dissolved organic carbon concentrations may therefore be returning towards levels that would have been typical prior to the first onset of acid rain during the nineteenth century.

Gradient analyses were used to correlatively determine the importance of acid-related variables for littoral macroinvertebrate assemblages. To better ascertain the effects of acidity on macroinvertebrate assemblages we removed sites judged to be affected by other stressors such as agriculture, urbanization and liming. PCA of land use and water chemistry confirmed the presence of an acidity gradient; several acidity variables (e.g. pH and buffering capacity) were strongly correlated with the first PC axis, which explained Ca 32% of the variance in the environmental data. Partial constrained ordination of littoral macroinvertebrate assemblages with water chemistry, after removing the effect of other confounding variables (e.g. land use/type), showed that acidity variables accounted for significant amounts of among-lake variability in assemblage structure. Regression of canonical scores (a metric of community composition) and diversity with pH and alkalinity was used to visually determine ecological breakpoints or threshold values. Five classes were established for pH: pH < 5 (extremely acid), 5 < pH ≤ 5.6 (very acid), 5.6 < pH ≤ 6.2 (acid), 6.2 < pH ≤ 6.8 (weakly acid) and pH > 6.8 (neutral-alkaline). Similarly, three classes were determined for alkalinity/acidity: <0.02, 0.02–0.1 and >0.1 meq/L.

Hosten 2005 genomfordes en riksomfattande sjoinventering som omfattade 2782 sjoar. Sjoinventeringen hade 2005 ett mer riktat syfte att folja upp de tva miljomalen”Bara naturlig forsurning” och ”Ing ...

The previous AMAP assessment of acidification of surface water in the Arctic focused on northern Fennoscandia and the Kola Peninsula (AMAP, 1998). There were no reports of acidified lakes and rivers in Arctic Canada and Alaska. Although lakes in some areas of North America were reported to be acid sensitive there were no indications of acidification. The geographical extent of surface water acidification was based on national lake surveys in Finland, Norway, and Sweden between 1986 and 1990 (Henriksen et al., 1992). These surveys showed that the impacts from high levels of sulfur deposition were mostly limited to a distance of about 50 km from the large pollution sources. Nitrate concentrations were very low over the whole area, due to very low nitrogen deposition. The border areas between Norway, Finland, and Russia were reported to be heavily polluted. Studies of lakes in the eastern parts of Finnmark in 1986 (Traaen, 1987) showed that the sulfate concentration had more than doubled since 1966 and was at the same stage of acidification as the most acidified lakes in southern Norway. Numerous small mountain lakes in the area were chronically acidic (pH<5). Even large lakes had little of their original buffering capacity left. Some small lakes, in particular at Jarfjordfjellet, were too acidic to support fish. Studies in 1987 to 1989 (Traaen, 1991) indicated that large areas in Sør-Varanger would become increasingly damaged, with a loss of fish stocks, if the acid deposition increased further. On the Kola Peninsula acidified lakes were reported around the industrial centers, and along the northern and eastern parts of the peninsula. However, at Kola, pollution from nickel and copper was a bigger problem in lakes than acidification (Moiseenko et al., 1995). An extensive inventory of small lakes in northern Finland between 1987 and 1991 showed that acidic and poorly buffered lakes were widely found in northeastern Lapland near the Norwegian and Russian borders. Sulfate concentrations here were generally higher than in other parts of Lapland (Kähkönen, 1996). A survey of small mountain lakes and brooks in northeastern Lapland in 1991 to 1993 found that the alkalinity of surface waters was lowest (mostly <50 μeq/L) in the Vätsäri area 40 to 50 km west of the Nikel smelter (Lappalainen et al., 1995). Areas sensitive to acidification and areas possibly acidified by acid deposition were quantified by calculating the critical loads for acidification of surface waters (see Box). Sulfur was regarded as the only acidifying agent as nitrate concentrations in lakes and streams in this area were very low. Critical loads for northern Fennoscandia, the Kola Peninsula, and the Spitsbergen Archipelago (Henriksen et al., 1994; Lien et al., 1995) were very variable, ranging from <300 to >1300 mg S/m2/yr. Most areas of Finland Definitions, terms, and calculations

To abate the severe acidification of Swedish lakes are about 7% directly limed (AL-lakes). These are important to include when assessing acidification. Consequently, we need to estimate their chemical status as if they were not lime-affected. We hypothesize that there is a spatial dependence for calcium (Ca) and magnesium (Mg) concentrations. Spatial variation is determined using variograms. We study lakes within two 150 ∗ 150 km quadrates (EMEP150-grid) in the middle and southern parts of Sweden. We model Ca in AL-lakes using the Ca and Mg concentrations in nearby, unaffected lakes (UL-lakes). The mean Ca/Mg for the three or seven closest UL-lakes is used. We assume that Ca/Mg is constant for UL-lakes and that Mg unaltered by liming. For UL-lakes, Ca and Mg are spatially dependent. For AL-lakes, there is a spatial dependence for Mg, but, as anticipated, not for Ca. The modeled Ca for UL-lakes show a good correspondence with measured Ca; r 2 > 0.6; slopes close to 1 and intercepts almost 0. Using three or seven nearby lakes when modeling Ca give similar results. Modeled Ca was higher than measured Ca for 36% (three closest lakes) and 38% (seven closest) of the modeled AL-lakes in the middle part of Sweden. The corresponding results for the southern part were 10% and 9%, respectively. This model is an acceptable estimator of Ca in limed lakes and for estimating critical loads and acidification status on an EMEP-scale.

Detta forslag till bedomningsgrunder for syrgaskoncentration i sjoar utgar fran effekter pa biota, framst fisk. Uppgifter har hamtats fran olika sammanstallningar av sadana effekter. Laga syrgashalter kan forekomma naturligt pa grund av humusamnens syretaring i bruna vatten och sedimentens syretaring, framst i grunda sjoar. De lagsta syrgaskoncentrationerna forekommer under sensommaren i sjons bottenvatten (hypolimnion) och under senvintern vid islaggning. For att skilja denna naturliga syretaring fran den antropogent orsakade foreslas en modell for berakning av den naturliga syretaringen. Om den naturliga syretaringen leder till laga syrgaskoncentrationer maste den antropogena paverkan begransas hardare an om den naturliga syretaringen ar liten. Darfor foreslas en klassning av status som tar hansyn till detta.