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Lake Processes (lake + process)
Selected AbstractsTemporal coherence of two alpine lake basins of the Colorado Front Range, U.S.A.FRESHWATER BIOLOGY, Issue 3 2000J. I. L. L. S. Baron 1. Knowledge of synchrony in trends is important to determining regional responses of lakes to disturbances such as atmospheric deposition and climate change. We explored the temporal coherence of physical and chemical characteristics of two series of mostly alpine lakes in nearby basins of the Colorado Rocky Mountains. Using year-to-year variation over a 10-year period, we asked whether lakes more similar in exposure to the atmosphere be-haved more similarly than those with greater influence of catchment or in-lake processes. 2. The Green Lakes Valley and Loch Vale Watershed are steeply incised basins with strong altitudinal gradients. There are glaciers at the heads of each catchment. The eight lakes studied are small, shallow and typically ice-covered for more than half the year. Snowmelt is the dominant hydrological event each year, flushing about 70% of the annual discharge from each lake between April and mid-July. The lakes do not thermally stratify during the period of open water. Data from these lakes included surface water temper-ature, sulphate, nitrate, calcium, silica, bicarbonate alkalinity and conductivity. 3. Coherence was estimated by Pearson's correlation coefficient between lake pairs for each of the different variables. Despite close geographical proximity, there was not a strong direct signal from climatic or atmospheric conditions across all lakes in the study. Individual lake characteristics overwhelmed regional responses. Temporal coherence was higher for lakes within each basin than between basins and was highest for nearest neighbours. 4. Among the Green Lakes, conductivity, alkalinity and temperature were temporally coherent, suggesting that these lakes were sensitive to climate fluctuations. Water tem-perature is indicative of air temperature, and conductivity and alkalinity concentrations are indicative of dilution from the amount of precipitation flushed through by snowmelt. 5. In Loch Vale, calcium, conductivity, nitrate, sulphate and alkalinity were temporally coherent, while silica and temperature were not. This suggests that external influences are attenuated by internal catchment and lake processes in Loch Vale lakes. Calcium and sulphate are primarily weathering products, but sulphate derives both from deposition and from mineral weathering. Different proportions of snowmelt versus groundwater in different years could influence summer lake concentrations. Nitrate is elevated in lake waters from atmospheric deposition, but the internal dynamics of nitrate and silica may be controlled by lake food webs. Temperature is attenuated by inconsistently different climates across altitude and glacial meltwaters. 6. It appears that, while the lakes in the two basins are topographically close, geologically and morphologically similar, and often connected by streams, only some attributes are temporally coherent. Catchment and in-lake processes influenced temporal patterns, especially for temperature, alkalinity and silica. Montane lakes with high altitudinal gradients may be particularly prone to local controls compared to systems where coherence is more obvious. [source] Climatic effects on the phenology of lake processesGLOBAL CHANGE BIOLOGY, Issue 11 2004Monika Winder Abstract Populations living in seasonal environments are exposed to systematic changes in physical conditions that restrict the growth and reproduction of many species to only a short time window of the annual cycle. Several studies have shown that climate changes over the latter part of the 20th century affected the phenology and population dynamics of single species. However, the key limitation to forecasting the effects of changing climate on ecosystems lies in understanding how it will affect interactions among species. We investigated the effects of climatic and biotic drivers on physical and biological lake processes, using a historical dataset of 40 years from Lake Washington, USA, and dynamic time-series models to explain changes in the phenological patterns among physical and biological components of pelagic ecosystems. Long-term climate warming and variability because of large-scale climatic patterns like Pacific decadal oscillation (PDO) and El Niño,southern oscillation (ENSO) extended the duration of the stratification period by 25 days over the last 40 years. This change was due mainly to earlier spring stratification (16 days) and less to later stratification termination in fall (9 days). The phytoplankton spring bloom advanced roughly in parallel to stratification onset and in 2002 it occurred about 19 days earlier than it did in 1962, indicating the tight connection of spring phytoplankton growth to turbulent conditions. In contrast, the timing of the clear-water phase showed high variability and was mainly driven by biotic factors. Among the zooplankton species, the timing of spring peaks in the rotifer Keratella advanced strongly, whereas Leptodiaptomus and Daphnia showed slight or no changes. These changes have generated a growing time lag between the spring phytoplankton peak and zooplankton peak, which can be especially critical for the cladoceran Daphnia. Water temperature, PDO, and food availability affected the timing of the spring peak in zooplankton. Overall, the impact of PDO on the phenological processes were stronger compared with ENSO. Our results highlight that climate affects physical and biological processes differently, which can interrupt energy flow among trophic levels, making ecosystem responses to climate change difficult to forecast. [source] A Change of Climate Provokes a Change of Paradigm: Taking Leave of Two Tacit Assumptions about Physical Lake ForcingINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 4-5 2008David M. Livingstone Abstract Physically, lakes have traditionally been viewed as individual systems forced by statistically stationary local weather. This view implies that the physical response of a lake to external physical forcing is unique and stationary. Recent recognition of the importance of large-scale climatic forcing in driving physical lake processes, combined with the realisation that this forcing is undergoing a long-term trend as a result of climate change, has led to a shift in this paradigm. The new physical paradigm views lakes more in terms of a local response to large-scale climatic forcing modulated by the addition of local noise. A strong climate signal leads to large-scale spatial coherence in the physical lake response, while the existence of trends in large-scale climatic forcing associated with climate change means that both the forcing and the physical lake response are statistically non-stationary. Thus increasing realisation of the importance of climate and climate change is invalidating the tacit assumptions of individuality and stationarity that underlie the old conceptual framework, resulting in its gradual abandonment in favour of a new paradigm based on the concepts of spatial coherence and temporal non-stationarity. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Shoreline tufa and tufaglomerate from Pleistocene Lake Bonneville, Utah, USA: stable isotopic and mineralogical records of lake conditions, processes, and climate,JOURNAL OF QUATERNARY SCIENCE, Issue 1 2005Stephen T. Nelson Abstract Shoreline carbonate deposits of Pleistocene Lake Bonneville record the conditions and processes within the lake, including the evaporative balance as well as vertical and lateral chemical and isotopic gradients. Tufas (swash-zone) and tufaglomerates (cemented, subaqueous colluvium or beachrock) on multiple, well-developed shorelines near the Silver Island Range, Utah, also present an opportunity to examine physicochemical lake processes through time. Three shorelines are represented by carbonate deposits, including the 23,20,ka Stansbury stage, 15,14.5,ka Bonneville stage, and 14.5,14,ka Provo stage. Mean ,18OVSMOW values of all three shorelines are statistically indistinguishable (,,,27,±,1,), when a few Bonneville samples of unusual composition are neglected. However, differences in primary carbonate mineralogy indicate that the correspondence is an artefact of the different fractionation factors between calcite or aragonite and water. Second, in order to sustain a much smaller, shallower lake during the colder Stansbury stage, the climate must have also been relatively dry. Third, ,18O values in tufa are higher than tufaglomerate by ,,,0.5,, consistent with greater evaporative enrichment of lake water in the swash zone. Fourth, mean ,13C values for the Provo, Stansbury and Bonneville shorelines (4.4, 5.0 and 5.2,, respectively) show that carbon species were dominated by atmospheric exchange, with the variations produced by differences in the oxidation of organic matter. Comparisons of shoreline carbonates with deep-lake marls of the same approximate age indicate that shoreline carbonate was much higher in ,13C and ,18O values (both ,,2.5,) during Bonneville time, whereas isotopic differences were minor (both ,,1,) in Stansbury time. In particular, the Bonneville stage may have sustained large vertical or lateral isotopic gradients due to evaporative enrichment effects on ,18O values. In contrast, the lake during the much shallower Stansbury stage may have been well mixed. Differences in the primary mineralogy (Stansbury and Bonneville, aragonite,>,calcite; Provo, calcite,>,aragonite) reflect profound differences in lake chemistry in terms of open versus closed-basin lakes. The establishment of a continuous outlet during Provo time probably reduced the Mg2+/Ca2+ ratio of lake water. Curiously, regardless of primary mineralogy, tufaglomerate cements are enriched in Na+ and Cl, and depleted in Mg2+ relative to capping tufa of the same age. This probably reflects vital or kinetic effects in the swash zone (tufa). We suspect that ,abiotic' effects may have been important in the dark pore space of developing tufaglomerate, where the absence of light suppressed photosynthesis. Copyright © 2005 John Wiley & Sons, Ltd. [source] | ||||||||||