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Small Lake (small + lake)
Selected AbstractsLand cover change and land degradation in parts of the southwest coast of NigeriaAFRICAN JOURNAL OF ECOLOGY, Issue 2009Mayowa Fasona Abstract Frequent alteration in land cover often leads to decreased stability of ecosystems which can also increase the vulnerability of rural communities to externalities of environmental change. This study carried out in parts of the coast of southwestern Nigeria utilized topographic base maps and two-time Landsat TM imageries to assess the trend in land cover changes and ecosystems degradation for the three time periods 1965, 1986 and 2001. Remote sensing, geographic information systems and landscape pattern analysis were employed for data processing and analysis. The focus of the analysis was on land cover change, land degradation, and changes in landscape pattern resulting from interplay of natural and anthropogenic drivers. The results show increased trend in human-induced land cover change with concomitant severe negative impacts on ecosystems and livelihoods. About 98,000ha (30% of the area) was seriously degraded as at 2001. About 33,000ha (10%) was under permanent saline water inundation with about 21 communities already dislocated. Loss of fragile ecosystems including marshland (from 7.7% in 1965 to 1% in 2001) and mangrove (from 14.6% in 1965 to 3.1% in 2001) was intense, while over 300 ponds/small lakes which are important for the local fishing economy have disappeared. About eighteen communities were also dislocated by erosion in a section around the southeastern parts of the coastline. Landscape metrics generated, suggested increased ecosystems perturbation and landscape fragmentation. The paper also discussed the implications of these rapid changes for ecosystems stability, food security and sustainable rural livelihoods in the area. [source] CRYPTIC BARRIERS TO DISPERSAL WITHIN A LAKE ALLOW GENETIC DIFFERENTIATION OF EURASIAN PERCHEVOLUTION, Issue 8 2007S. Bergek Gene flow between coexisting or nearby populations normally prevents genetic divergence and local adaptation. Despite this, there are an increasing number of reports of sympatric sister taxa, indicating potential divergence and speciation in the face of gene flow. A large number of such reported cases involve lake-dwelling fish, which are expected to run into few physical barriers to dispersal within their aquatic habitat. However, such cases may not necessarily reflect sympatric speciation if cryptic dispersal barriers are common in lakes and other aquatic systems. In this study, we examined genetic differentiation in perch (Perca fluviatilis L.) from nine locations in a single, small lake (24 km2), using microsatellites. We detected significant genetic differentiation in all but two pairwise comparisons. These patterns were not consistent with divergence by distance or the existence of kin groups. Instead, they suggest that cryptic barriers to dispersal exist within the lake, allowing small-scale genetic divergence. Such an observation suggests that allopatric (or parapatric) divergence may be possible, even in small, apparently homogenous environments such as lakes. This has important consequences for how we currently view evidence from nature for sympatric speciation. [source] Modelling the effects of changing retention time on abundance and composition of phytoplankton species in a small lakeFRESHWATER BIOLOGY, Issue 6 2007I. D. JONES Summary 1. The phytoplankton community model, PROTECH, was used to model the algal response to changing annual mean retention time in a small lake. 2. Simulations of short retention time with a fixed nutrient load resulted in a reduced chlorophyll concentration. A similar relationship was observed when the simulations were repeated but with inflowing nutrients increased in proportion to river discharge. 3. Longer retention time caused the spring bloom to start earlier and the autumn bloom to persist longer. 4. Changes in discharge of the inflowing river also caused a change in the thermal structure of the lake. This change in thermal structure, in turn, influenced the magnitude and composition of the phytoplankton population, particularly those in the CS-functional group, such as Aphanizomenon. [source] HYDROLOGY AND GEOMORPHIC EFFECTS OF A HIGH-MAGNITUDE FLOOD IN AN ALPINE RIVERGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2007DAVID MORCHE ABSTRACT. The catchment of the River Partnach, a torrent situated in a glacial valley in the Northern Calcareous Alps of Bavaria/Germany, was affected by a high-magnitude flood on 22/23 August 2005 with a peak discharge of more than 16 m3s -1 at the spring and about 50 m3s -1 at the catchment outlet. This flood was caused by a long period of intense rainfall with a maximum intensity of 230 mm per day. During this event, a landslide dam, which previously held a small lake, failed. The flood wave originating from the dam breach transported a large volume of sediment (more than 50 000 m3) derived from bank erosion and the massive undercutting of a talus cone. This caused a fundamental transformation of the downstream channel system including the redistribution of large woody debris and channel switching. Using terrestrial survey and aerial photography, erosional and depositional consequences of the event were mapped, pre- and post-event surfaces were compared and the sediment budget of the event calculated for ten consecutive channel reaches downstream of the former lake. According to the calculations more than 100 000 tonnes of sediment were eroded, 75% of which was redeposited within the channel and the proximal floodplain. A previous large flood which occurred a few weeks prior to the August 2005 event had a significant effect on controlling the impact of this event. [source] An Early Bronze Age Logboat from Degersee, Southern GermanyINTERNATIONAL JOURNAL OF NAUTICAL ARCHAEOLOGY, Issue 1 2009Martin Mainberger In 2004 the remains of a logboat were discovered in Degersee, a small lake near Lake Constance, southern Germany. Dating to the beginning of the 2nd millennium BC, it is an important find from a period with scarce archaeological evidence and only a few previously-known logboats. The vessel was situated in lake sediment and documented in situ. Our investigations can be linked to palaeo-environmental studies carried out at Degersee and adjacent lakes, and to palaeo-climatic research in the northern Alpine region. After investigation by underwater archaeologists the boat was moved to a sheltered place in deeper water. © 2008 The Author [source] Rapid Holocene chemical weathering on a calcitic lake shoreline in an alpine periglacial environment: Attglųyma, Sognefjell, southern NorwayPERMAFROST AND PERIGLACIAL PROCESSES, Issue 1 2006Geraint Owen Abstract A small lake (Attglųyma) at an altitude of about 1220,m in the low-alpine zone, southern Norway, has a shore platform in calcitic and quartzitic muscovite-chlorite schists. The platform has recently been exposed by a fall in lake level due to upstream dam construction and exhibits micro-landforms ranging from pits and grooves to upstanding crenulate ridges produced by differential chemical weathering under relatively constant conditions over the last ca. 10,000 years. The maximum surface lowering rate of the calcitic layers estimated from differential weathering is 35,mm,ka,1, which is about an order of magnitude greater than most previous estimates from alpine and polar periglacial environments. Average bedrock surface lowering across the whole platform reached a maximum of 15.5,±,2.2,mm,ka,1 in a vertical zone corresponding with the former lake level, declining to negligible values around 0.7,m below lake level. Differential weathering and bedrock surface lowering were also negligible immediately above lake level. Correspondence of maximum surface lowering rates with the former lake level and a shoreline notch at the back of a platform suggest that the effects of solutional weathering of the calcite have been enhanced by water movement generated by small lake-surface waves. Copyright © 2006 John Wiley & Sons, Ltd. [source] Ecosystem CO2 exchange and plant biomass in the littoral zone of a boreal eutrophic lakeFRESHWATER BIOLOGY, Issue 8 2003T. Larmola Summary 1In order to study the dynamics of primary production and decomposition in the lake littoral, an interface zone between the pelagial, the catchment and the atmosphere, we measured ecosystem/atmosphere carbon dioxide (CO2) exchange in the littoral zone of an eutrophic boreal lake in Finland during two open water periods (1998,1999). We reconstructed the seasonal net CO2 exchange and identified the key factors controlling CO2 dynamics. The seasonal net ecosystem exchange (NEE) was related to the amount of carbon accumulated in plant biomass. 2In the continuously inundated zones, spatial and temporal variation in the density of aerial shoots controlled CO2 fluxes, but seasonal net exchange was in most cases close to zero. The lower flooded zone had a net CO2 uptake of 1.8,6.2 mol m,2 per open water period, but the upper flooded zone with the highest photosynthetic capacity and above-ground plant biomass, had a net CO2 loss of 1.1,7.1 mol m,2 per open water period as a result of the high respiration rate. The excess of respiration can be explained by decomposition of organic matter produced on site in previous years or leached from the catchment. 3Our results from the two study years suggest that changes in phenology and water level were the prime cause of the large interannual difference in NEE in the littoral zone. Thus, the littoral is a dynamic buffer and source for the load of allochthonous and autochthonous carbon to small lakes. [source] Redox control of N:P ratios in aquatic ecosystemsGEOBIOLOGY, Issue 2 2009T. M. QUAN ABSTRACT The ratio of dissolved fixed inorganic nitrogen to soluble inorganic phosphate (N:P) in the ocean interior is relatively constant, averaging ~16 : 1 by atoms. In contrast, the ratio of these two elements spans more than six orders of magnitude in lakes and other aquatic environments. To understand the factors influencing N:P ratios in aquatic environments, we analyzed 111 observational datasets derived from 35 water bodies, ranging from small lakes to ocean basins. Our results reveal that N:P ratios are highly correlated with the concentration of dissolved O2 below ~100 µmol L,1. At higher concentrations of O2, N:P ratios are highly variable and not correlated with O2; however, the coefficient of variation in N:P ratios is strongly related to the size of the water body. Hence, classical Redfield ratios observed in the ocean are anomalous; this specific elemental stoichiometry emerges not only as a consequence of the elemental ratio of the sinking flux of organic matter, but also as a result of the size of the basins and their ventilation. We propose that the link between N:P ratios, basin size and oxygen levels, along with the previously determined relationship between sedimentary ,15N and oxygen, can be used to infer historical N:P ratios for any water body. [source] Holocene carbon burial by lakes in SW GreenlandGLOBAL CHANGE BIOLOGY, Issue 11 2009N. J. ANDERSON Abstract The role of the Arctic in future global change processes is predicted to be important because of the large carbon (C) stocks contained in frozen soils and peatlands. Lakes are an important component of arctic landscapes although their role in storing C is not well prescribed. The area around Kangerlussuaq, SW Greenland (66,68°N, 49,54°W) has extremely high lake density, with ,20 000 lakes that cover about 14% of the land area. C accumulation rates and standing stock (kg C m,2), representing late- to mid-Holocene C burial, were calculated from AMS 14C-dated sediment cores from 11 lakes. Lake ages range from ,10 000 cal yr bp to ,5400 cal yr bp, and reflect the withdrawal of the ice sheet from west to east. Total standing stock of C accumulated in the studied lakes for the last ,8000 years ranged from 28 to 71 kg C m,2, (mean: ,42 kg C m,2). These standing stock determinations yield organic C accumulation rates of 3.5,11.5 g C m,2 yr,1 (mean: ,6 g C m,2 yr,1) for the last 4500 years. Mean C accumulation rates are not different for the periods 8,4.5 and 4.5,0 ka, despite cooling trends associated with the neoglacial period after 4.5 ka. We used the mean C standing stock to estimate the total C pool in small lakes (<100 ha) of the Kangerlussuaq region to be ,4.9 × 1013 g C. This C stock is about half of that estimated for the soil pool in this region (but in 5% of the land area) and indicates the importance of incorporating lakes into models of regional C balance at high latitudes. [source] Density-dependent mortality is mediated by foraging activity for prey fish in whole-lake experimentsJOURNAL OF ANIMAL ECOLOGY, Issue 4 2003Peter A. Biro Summary 1Whereas the effects of density-dependent growth and survival on population dynamics are well-known, mechanisms that give rise to density dependence in animal populations are not well understood. We tested the hypothesis that the trade-off between growth and mortality rates is mediated by foraging activity and habitat use. Thus, if depletion of food by prey is density-dependent, and leads to greater foraging activity and risky habitat use, then visibility and encounter rates with predators must also increase. 2We tested this hypothesis by experimentally manipulating the density of young rainbow trout (Oncorhynchus mykiss) at risk of cannibalism, in a replicated single-factor experiment using eight small lakes, during an entire growing season. 3We found no evidence for density-dependent depletion of daphnid food in the nearshore refuge where most age-0 trout resided. Nonetheless, the proportion of time spent moving by individual age-0 trout, the proportion of individuals continuously active, and use of deeper habitats was greater in high density populations than in low density populations. Differences in food abundance among lakes had no effect on measures of activity or habitat use. 4Mortality of age-0 trout over the growing season was higher in high density populations, and in lakes with lower daphnid food abundance. Therefore, population-level mortality of age-0 trout is linked to greater activity and use of risky habitats by individuals at high densities. We suspect that food resources were depleted at small spatial and temporal scales not detected by our plankton sampling in the high density treatment, because food-dependent activity and habitat use by age-0 trout occurs in our lakes when food abundance is experimentally manipulated (Biro, Post & Parkinson, in press). [source] Anguillicoloides crassus infection of European eel, Anguilla anguilla (L.), in inland waters of Estonia: history of introduction, prevalence and intensityJOURNAL OF APPLIED ICHTHYOLOGY, Issue 2010A. Kangur Summary Eel fishery in Estonian inland waters depends entirely on the stocking of glass eels or pre-grown (farmed) eels. Via importation of live eels of 20,30 cm length the non-indigenous swimbladder nematode Anguillicoloides crassus was probably introduced via Germany into Lake Võrtsjärv in 1988, and has since spread to many inland waters of Estonia. In 1992, the parasite was found in eel caught from Lake Võrtsjärv. Between 1992 and 2002 and additionally in 2008, we examined in total 870 eels from Lake Võrtsjärv (270 km2) and in 2008, 63 eels from three small lakes for adult A. crassus. The aim of the study was to obtain information on the variation of A. crassus infection in eels in Estonian lakes, to determine the temporal dynamics of prevalence and intensity of infection, and to establish a relationship between the length of host and intensity of infection in the eels in Lake Võrtsjärv. There appeared to be a pronounced variation in prevalences of infected eels (from 3.7% to 100%) between the four investigated lakes. However, in Lake Võrtsjärv, the prevalence of adult A. crassus infection remained stable (mean about 65%) for many years. The average number of nematode per infected eel (mean intensity) ranged from 12.6 ± 2.5 in 1993 to 4.0 ± 0.6 in 1999 in Lake Võrtsjärv, while it was significantly higher (P < 0.0001) in the period 1992,1998 compared to 1999,2002 and 2008. The mean number of parasites per swimbladder was not related to eel length and no statistical difference was found in the condition factor of infected and non-infected eels. Although under normal environmental conditions A. crassus has not caused serious disease problems to eels in the study area, high intensity of parasite infection may contribute to eel kills due to oxygen deficiency in winter under the ice in Lake Võrtsjärv. [source] | ||||||||||||||||