Lake Water Budget Research Articles

A 14,000-year diatom oxygen isotope record from the Romanian South Carpathians reflect changes in the seasonal distribution of precipitation and temperature

Oxygen isotope records from lacustrine sediments have the potential to reflect short-term and long-term changes in temperature, seasonal changes in the distribution of precipitation and changes in lake water budget determined by the evaporation to inflow ratio. This proxy has widely been used in the Alps and NW Europe to provide high-resolution temperature or evaporation records, but similar studies in the Carpathians are missing. Here we provide a continuous Lateglacial and Holocene record of diatom silica oxygen isotope changes (δ 18 O DIAT ) in a subalpine lake sediment sequence coming from the northern flank of the Retezat Mts (Taul dintre Brazi, TDB, 1740 m a.s.l.).

Fluxes of carbon and nutrients through the inflows and outflow of Lake Võrtsjärv, Estonia

We determined the incoming fluxes of total organic carbon (TOC), dissolved inorganic (DIC) and organic carbon (DOC), nitrogen, phosphorus, and silicon via four main inflows into Lake Vortsjarv and compared these with the outgoing fluxes from the lake during 2008-2009. The discharge and loads of the studied substances from the four main rivers alone were higher than the amounts carried out of the lake in 2008. In 2009, the outflow of water exceeded the inflows and this was the case with the amounts of TOC, DIC, and DOC as well. However, the incoming load of nutrients was continuously higher than the outgoing load. The lake accumulated nutrients (nitrogen, phosphorus, and silicon) irrespective of whether water retention was positive or negative, but the balance between carbon accumulation and carbon emission depended on the lake's water budget.

Uranium isotopes as proxies of the environmental history of the Lake Baikal watershed (East Siberia) during the past 150 ka

A new experimental method for the determination of the isotopic composition of authigenic uranium in Lake Baikal (Siberia) sediments has supplied a record of ( 234U/ 238U) aut ratios during the past 150 ka with a resolution of ca. 200 years. Reconstruction of the ( 234U/ 238U) aut activity ratio as a proxy for lake water composition shows that the uranium isotope disequilibrium has not stayed constant throughout this period: it varied greatly in response to regional climate. The 234U/ 238U activity ratio in Lake Baikal paleowaters was inferred to be high during interglacial time (∼ 1.85–2 during MIS 5.5 and the Holocene; ∼ 1.4–1.7 during MIS 5.1 and 5.3) and dropped to ∼ 1.16 ± 0.01 during glacial time. The variability in the deduced 234U/ 238U ratios of Lake Baikal waters of the past may have been caused by the climatically-modulated redistribution of contributions of riverine discharges from different provinces of the very large catchment of the lake. Aridity during ice ages was more pronounced in the south of eastern Siberia and in northern Mongolia relative to that in the northern regions of the Lake Baikal watershed. The southern contribution of riverine input into the lake was essentially absent during glacial periods. Records of some elements (Ca/K, Sr/Rb, Si/Al, La/Th, U/Th, CIW) from the bottom sediments of Lake Baikal during the last 0.5 Myr with a resolution of ∼ 2 kyr have also been obtained. Coupling these data with records of weathering indices shows that not only riverine waters but also terrigenous material delivered into Lake Baikal from different regions of the very large watershed during interglacial and glacial times. Glacial erosion delivered fine siliciclastic material (“glacial milk”) mainly from the nearest mountain glaciers situated in the northwestern region of Lake Baikal while during warmer periods terrigenous material was sourced from the surrounding river valleys. A conceptual model for the simulation of the fluvial discharge gradient between the northern and southern provinces of the Lake Baikal watershed is proposed and a first-order simulation of past changes in the contribution of the Selenga River to the lake water budget is given.

Water budget of Skærsø, a lake in south-east Jylland, Denmark: exchange between groundwater and lake water

The European Union’s Water Frame - work Directive aims to achieve a ‘good’ ecological status for groundwater bodies, for groundwater-dependent terrestrial ecosystems, and for aquatic surface water bodies by the year 2015. In Denmark, this goal will most likely not be fulfilled within such a short time frame due to the current poor ecological condition of Danish lakes (Søndergaard et al. 2008). However, public concern about the protection of aquatic environments has increased, and so has interest in improving lake water quality by reducing nutrient loading. Effective and sustainable lake restoration and conservation depend on the ability to (1) point out sensitive catchment areas for the lake, (2) estimate its total water and nutrient budgets and (3) relate observed differences in seepage rates to the abundance and distribution of macrophytes in the lake and to the topography and land-use of the surrounding terrain. In seepage lakes, i.e. lakes without inlets or outlets, the influence of the surrounding terrain, regional hydrogeology and lake geometry on the overall lake water budget has been studied in some detail (Krabbenhoft et al. 1990; Anderson & Cheng 1993; Cheng & Anderson, 1994; Kratz et al. 1997; Winter 1999; Townley & Trefry 2000). However, little efforthas been made to understand and quantify how riparian zones (wetlands) surrounding lakes may control the water flow and nutrient transport to the lakes. Although groundwater inflow to seepage lakes is suspected to be smaller than inflow from drainage ditches, it may still account for a significant nutrient influx.

Lake Hovsgol basin as a new study site for long continental paleoclimate records in continental interior Asia: General context and current status

Lacustrine sedimentary strata in the Lake Hovsgol rift basin, NW Mongolia, preserved an important regional archive with new powerful proxies for climate change in continental interior Asia. Two scientific drilling campaigns of the Hovsgol Drilling Project (HDP) recovered the most complete and best resolved mid-late Pleistocene paleoclimate archive in Mongolia. With the basal age of ca. 1 Ma, Lake Hovsgol drill core section complements those obtained previously in the neighboring Lake Baikal, and contains regional paleoclimate proxy records on a timescale comparable to that of marine sedimentary records and the longest Antarctic ice core record. Works in this volume discuss changes in lake chemistry, biota and environment, closely linked with drill core lithology and depositional trends apparent from sediment facies. The current collection of works illustrates the potential of proxy signals in the Hovsgol record and highlights new important constraints on their interpretation. Because of a nearly continuous record of endogenic carbonate accumulation in Lake Hovsgol, a wealth of paleoclimate proxy data is preserved in carbonate mineralogy, elemental geochemistry and stable isotope composition; such a unique long record was not previously available in this part of the world. The repetitive pattern of changes in the lake's water budget in response to the climatic cycles of the Pleistocene is established and constrained by absolute dating and the robust paleomagnetic event/reversal timescale. The new proxy records from the HDP sediment sections are both relevant and timely contributions to the discussion of the nature of paleoclimate changes in continental interior Asia during prior glacial and interglacial intervals of the Pleistocene. These records help establish the early timing of the post-glacial changes in atmospheric circulation and effective moisture budget in the region and resolve the previously proposed scenarios of extreme precipitation gradients during glacial periods. The key primary data presented in this volume make a compelling case for further in-depth studies of the available records and for future deeper drilling into the early Pleistocene and the Pliocene strata in this basin.

Climate signals in sediment mineralogy of Lake Baikal and Lake Hovsgol during the LGM-Holocene transition and the 1-Ma carbonate record from the HDP-04 drill core

Modeling the bulk sediment XRD patterns allows insight into the environmental and depositional histories of two neighboring rift lake basins within the Baikal watershed. Parallel 14C-dated LGM-Holocene records in Lakes Baikal and Hovsgol are used to discuss the mineralogical signatures of regional climate change. In both basins, it is possible to distinguish ‘glacial’ and ‘interglacial’ mineral associations. Clay minerals comprise in excess of 50% of layered silicates in bulk sediment. The abundance of smectite (expandable) layers in mixed-layer illite–smectites and the total illite abundance are the main paleoclimatic indices in the clay mineral assemblage. Both indices exhibit coherent responses to the Bølling–Allerød and the Younger Dryas. The smectite layer index is not equivalent to the abundance of illite–smectite, because illite–smectite tends to transform into illite. Repeated wetting–drying cycles in soils and high abundance of expandable layers in illite–smectites (>42%) favor the process of illitization. This relationship is clearly shown in both Baikal and Hovsgol records for the first time. The opposite late Holocene trends in illite abundance in Lake Baikal and Lake Hovsgol records suggest that a sensitive optimal regime may exist for illite formation in the Baikal watershed with regard to warmth and effective moisture. The Lake Hovsgol sediments of the last glacial contain carbonates, suggesting a positive trend in the lake's water budget. A progressive change towards lower Mg content in carbonates indicates lowering mineralization of lake waters. This trend is consistent with the lithologic evidence for lake-level rise in the Hovsgol basin. The pattern of mineralogical changes during the past 20 ka is used to interpret bulk sediment and carbonate mineralogy of the long 81-m Lake Hovsgol drill core (HDP-04) with a basal age of 1 Ma. The interglacial-type silicate mineral associations are confined to several thin intervals; most of the sediment record is calcareous. Carbonates are represented by six main mineral phases: calcite, low-Mg calcite, intermediate/high-Mg calcite, dolomite, excess-Ca dolomite and metastable monohydrocalcite. These mineral phases tend to form stratigraphic successions indicative of progressive changes in lake water chemistry. Five sediment layers with abundant Mg-calcites in the HDP-04 section suggest deposition in a low standing lake with high mineralization (salinity) and high Mg/Ca ratios of lake waters. Lake Hovsgol sediments contain the oldest known monohydrocalcite, found tens of meters below lake bottom in sediments as old as 800 ka. This unusual find is likely due to the conditions favorable to preservation of this metastable carbonate.

Heat budget estimates for Lake Ikeda, Japan

Summary Heat budget studies of lakes are essential components of efficient lake water management as they give direct information on evaporation and thus the lake water budget. A one-dimensional heat transfer model which includes vertical turbulent mixing in lake water and heat exchange between the lake and the atmosphere was developed and applied to estimate heat budget of Lake Ikeda from 1981 to 2005. The lake is in southern Japan, has a mean water depth of 125 m, and is an important water resource for agriculture, municipal water supply, and fisheries. The computed lake water temperatures were in good agreement with observed temperatures. The model reproduced both the thermal stratification characteristics and the uniform vertical 10 °C temperature profile that occurs in Lake Ikeda every February. When the storage heat was suitably quantified, the latent heat computed on a monthly basis by the model also agreed well with those calculated by both the Bowen ratio and Priestley–Taylor methods. Analysis of the heat budget for a 25-year period from 1981 to 2005 showed that the lake accumulates heat from March to August and releases it through latent and sensible heat under a small net radiation condition from September to February. Maximum latent heat occurs in October and minimum latent heat in April. The annual average evaporation is 938 mm and the autumn evaporation from September to November accounts for about 40% of the total annual evaporation.

Modeling the water budget in a deep caldera lake and its hydrologic assessment: Lake Ikeda, Japan

The hydrologic assessment of a lake water budget can be helpful in achieving proper water management and sustainable water use. A model to analyze a lake water budget was developed and verified for Lake Ikeda, Japan. Lake evaporation was estimated by numerical analyses of lake water temperature and the lake energy budget. Inflow from the lake catchment area and leakage from the lake bottom were estimated based on the tank model and Darcy's law, and the model parameters were optimized by the shuffled complex evolution method. The estimated monthly lake evaporation rate is consistent with the evaporation rate estimated by the energy budget Bowen ratio method based on in situ data from 2004 to 2005. Moreover, the calculated time series of daily lake levels agrees well with those of measured lake levels during 1983 to 1999. Thus, the model is useful for evaluating the lake water budget. Numerical analysis reveals seasonal and annual variation characteristics in the water budget components. Precipitation, inflow from the catchment area, and river water supply are generally high during the rainy season from June to July with substantial annual variation. Lake evaporation is greatest in October and least in April, but the annual variation is relatively small. Agricultural water use is relatively high from April to September. There are no marked seasonal changes in leakage and drinking water use. The lake level is generally highest in September and lowest in March, which is characterized by seasonal changes in water budget components. The model was also applied to 17-year simulations under hypothetical hydrologic conditions to examine the effect of water use and agricultural water management on the lake level. Results indicate that river water supply, provided under the agricultural water management system, effectively compensates for the decrease in lake water resulting from agricultural water use.

Isotopic variation in the lake water balance at the Yamdruk‐tso basin, southern Tibetan Plateau

AbstractThe use of stable isotopes is a practical tool in the study of the lake water budget. This is an one way to study the hydrological cycle in the large numbers of inland lakes on the Tibetan Plateau, in which the isotope record of the sediment is believed to reflect the climatic and environmental changes. The monitoring of stable isotopes of the precipitation, river and lake waters during 2004 in the inland Yamdruk‐tso basin, southern Tibetan Plateau, reveals the lake water δ18O is over 10‰ higher than the local precipitation. This high difference indicates strong isotope enrichment due to lake water evaporation. The simulation results based on the isotope technique show that the present lake water δ18O level corresponds to an average relative humidity of around 54–58% during evaporation, which is very close to the instrumental observation. The simulation results also show that the inland lakes on the Tibetan Plateau have a strong adjustability to the isotope shift of input water δ18O. On average, the isotope component in the inland lake water is to a large extent controlled by the local relative humidity, and can also be impacted by a shift of the local precipitation isotope component. This is probably responsible for the large consistence in the isotope component in the extensive inland lakes on the Tibetan Plateau. Copyright © 2008 John Wiley & Sons, Ltd.

Evaporation and energy budget in Lake Vegoritis, Greece

Evaporation is one of the main components in both the energy and water budgets of lakes and a primary process of water loss for most of them. A one-dimensional, eddy diffusion model of lake’s water temperature distribution is used to evaluate daily evaporation values as a residual of the energy budget in Lake Vegoritis in Northern Greece and for the year of 1993. Lake Vegoritis has been under a continuous deficit in the water balance for up to three decades. The water temperature model, calibrated with measured values from two different years, is used reversely to evaluate the evaporation through the energy budget. The equilibrium temperature approach for the surface boundary condition is used in the model, as well as the simplification of Bowen ratio in the energy budget. Evaporation values estimated by the model are used for determining a mass transfer-based evaporation equation for Lake Vegoritis. Estimated evaporation rates show a characteristic annual cycle with low values at spring and the highest values at summer. The energy stored in the lake at spring and early summer is released to the environment later in the year as sensible and mainly as latent heat.

Quantifying The Rainfall-Water Level Fluctuation Process in a Geologically Complex Lake Catchment

Simulating hydrologic processes in geologically complex environments is a difficult scientific task since it incorporates high level of uncertainty. Many studies have attempted to accurately quantify the rainfall-water level elevation relationship in freshwater bodies so as to predict flooding and drought events. For this purpose several types of models have been implemented including distributed, black box and conceptual models that often provide efficient results, depending on the availability of reliable data as well as on the level of understanding of the system. Nevertheless, in the particular effort, three different models have been used to describe the relationship between rainfall and water level elevation in Trichonis Lake during the period 1951-1997. A Transfer Function model, a Dynamic Linear Regression and a physically based model, consisting of the lake's water budget equation, its Digital Bathymetric Model and GIS algorithms. These models have been tested to assess their efficiency and applicability in a karstic environment and the aim of the study was to find the best modeling option for developing sustainable water management plans and establishing a flooding/drought warning system in the particular lake catchment. The results indicated that in areas with geologically complex conditions, simple, physically-based models operate better than mechanistic models which usually cannot describe adequately the complexity of the system.

Carbon burial and infill rates in small Western Boreal lakes: physical factors affecting carbon storage

Effects of depression depth (ZT), lake surface elevation (ES), catchment area:lake surface area (AT:AO), trophic status, and surficial geology on sediment burial rates in small Western Boreal Plain lakes were assessed using content and chronology of cores from a relatively large and small lake on each of moraine (M), glaciofluvial (GF), and glaciolacustrine (GL) deposits. Aquatic and terrestrial plant and sediment carbon:nitrogen (C:N) suggested most buried C was aquatic. The rate of long-term total C burial averaged 31 g·m–2·year–1 (range: 0–84 g·m–2·year–1); this was recently 79 g·m–2·year–1 (range: 40–180 g·m–2·year–1) (higher and more variable rates than previously reported for Boreal lakes). Long-term C accrual rate and sediment depth increased with increasing ZT. In each landform, a relatively low base elevation (EB = ES – ZT) lake began accumulating sediment thousands of years before a high EB lake. GF depressions were deeper and had accrued more C·m–2 (and infilled) faster than M and GL lakes; a large GF lake had no organic sediment, perhaps because of large groundwater inputs. Increasing AT:AO corresponded with increasing C accrual rates where precipitation and evaporation dominated (surface runoff infrequent) (M and GL) but not where groundwater dominated (GF lakes) lake water budgets, illustrating the importance of landform and depression characteristics in regionalizing lake-C burial estimates.

Effects of climate variability on lake evaporation: Results from a long-term energy budget study of Sparkling Lake, northern Wisconsin (USA)

Variations in lake evaporation have a significant impact on the energy and water budgets of lakes. Understanding these variations and the role of climate is important for water resource management as well as predicting future changes in lake hydrology as a result of climate change. This study presents a comprehensive, 10-year analysis of seasonal, intraseasonal, and interannual variations in lake evaporation for Sparkling Lake in northern Wisconsin (USA). Meteorological and lake temperature measurements are made at a raft on the lake and are supplemented by radiation measurements from a nearby airport. The data are analyzed over 14-day periods from 1989 to 1998 (during the ice-free season) to provide bi-weekly energy budget estimates of evaporation rate (along with uncertainty estimates). The mean evaporation rate for Sparkling Lake over the study period is 3.1 mm day −1, with a coefficient of variation of 25%. Considerable variability in evaporation rates is found on a wide range of timescales, with seasonal changes having the highest coefficient of variation (18%), followed by the intraseasonal (15%) and interannual timescales (12%; for summer means). Intraseasonal changes in evaporation are primarily associated with synoptic weather variations, with high evaporation events tending to occur during incursions of cold, dry air (due, in part, to the thermal lag between air and lake temperatures). Seasonal variations in evaporation are largely driven by temperature and net radiation, but are out-of-phase with changes in wind speed. This presents challenges when calculating evaporation rates by means of the simpler mass-transfer technique. On interannual timescales, changes in summer evaporation rates are strongly associated with changes in net radiation and show only moderate connections to variations in temperature or humidity. Nonetheless, we are able to identify a simple, empirical relationship for estimating interannual evaporation rates that is more accurate than the mass transfer technique.

A Screening-Level Laboratory Method to Estimate Pit Lake Chemistry

An analog pit lake (APL) test has been developed to predict pit lake water quality following closure of an equatorial copper-gold mine. The juvenile (0-9 years after closure) pit lake (JPL) water budget will comprise 10% rainfall; 26% surface runoff; 40% wallrock runoff, and 24% deep groundwater inflow. The mature (>65 years after closure) pit lake (MPL) will consist of 39% rainfall; 29% surface runoff; 15% wallrock runoff; 3% deep groundwater inflow, and 1% shallow groundwater inflow, with the balance (13%) contributed by the JPL. Wallrock runoff due to incident precipitation was replicated in humidity columns, subaqueous wallrock leachate by leaching columns of each rock type with groundwater, rainwater by addition of sea salt to deionized water, and surface runoff by a sample from a local creek. The solutions were combined in aquaria and the appropriate fraction evaporated, 7% for the JPL and 36% for the MPL. Electron microprobe analysis of precipitates identified clays and Al, Cu, and Zn adsorbed to ferrihydrite surfaces. A preliminary pit design resulted in an acidic (pH 3.3) JPL containing 7 mg/L Cu. However, by modifying the design to exclude a potentially acidgenerating andesite unit, the JPL water quality improves (e. g., pH 6.7; Cu 0.002 mg/L). The MPL pH with the andesite would be 6.1 (Cu = 2.2 mg/L), while the final design results in a pH of 7.1 and 0.22 mg/L Cu. The APL test can also be used to corroborate numerical models predictions and assess the efficacy of mitigation alternatives.

Variation interannuelle du bilan hydrique du lac Tanganyika (1932–1995): changement dans la relation précipitation-excédent lacustre / Interannual variation of the water budget of Lake Tanganyika (1932–1995): changes in the precipitation-lake water excess relationship

The data collected have allowed the evaluation of the variations in the water levels of Lake Tanganyika between 1932 and 1995, the discharge at the outlet, the excess of the lake budget (or “level without discharge”, ΔH*), and the precipitation on the drainage area. The evolution of the annual lake budget is related to the precipitation variability. However a marked increase in the excess after 1961 is shown, which corresponds to a change in the relationship between annual excess and precipitation, which further corresponds to a higher effectiveness of rainfall. This marked change in the lake water budget could partly correspond to wetter conditions at the beginning of the rainy season, but the man-induced changes in land use and in the surface runoff conditions appear partly responsible for the difference in the lake sensitivity to precipitation.

Factors contributing to the salinity of lakes, Riske Creek region, south-central British Columbia, Canada

The objective of this study was to determine the primary factors that contribute to the salinity of lakes located within the Riske Creek region of south-central British Columbia, Canada. The Riske Creek region contains numerous lakes with a salinity range of 0–10.8 ppt with high and low salinity lakes co-existing in close proximity to one another. The region is of extreme ecological importance because it is located on the Pacific flyway and serves as a major breeding ground for a number of waterfowl species. Water budgets, lake water chemistry and cation (Ca 2+, Mg 2+, Na + and K +) interstitial water composition were determine for 9 lakes, 3 oligosaline (0 ppt), 3 mesosaline (0.4–1.0 ppt) and 3 euryhaline (2.7–5.3 ppt) to determine if evapo-precipitive or saline groundwater inputs were the primary determinants of lake salinity. Lake water budgets indicated that meso and euryhaline lakes were in a close to zero or negative water balance whereas the 3 oligosaline lakes were in a positive water balance. Groundwater saline inputs, as measured by lake sediment interstitial water cation concentrations, indicated that groundwater made only minor contributions to lake salinity. Water budget calculations and sediment interstitial water chemistry suggest that lakes are saline largely due to evaporative processes.

Effects of nearshore recharge on groundwater interactions with a lake in mantled karst terrain

The recharge and discharge of groundwater were investigated for a lake basin in the mantled karst terrain of central Florida to determine the relative importance of transient groundwater inflow to the lake water budget. Variably saturated groundwater flow modeling simulated water table responses observed beneath two hillsides radiating outward from the groundwater flow‐through lake. Modeling results indicated that transient water table mounding and groundwater flow reversals in the nearshore region following large daily rainfall events generated most of the net groundwater inflow to the lake. Simulated daily groundwater inflow was greatest following water table mounding near the lake, not following subsequent peaks in the water level of upper basin wells. Transient mounding generated net groundwater inflow to the lake, that is, groundwater inflow in excess of the outflow occurring through the deeper lake bottom. The timing of the modeled net groundwater inflow agreed with an independent lake water budget; however, the quantity was considerably less than the budget‐derived value.

A multi-proxy study of Holocene environmental change in the Maya Lowlands of Peten, Guatemala

We used multiple variables in a sediment core from Lake Peten-Itza, Peten, Guatemala, to infer Holocene climate change and human influence on the regional environment. Multiple proxies including pollen, stable isotope geochemistry, elemental composition, and magnetic susceptibility in samples from the same core allow differentiation of natural versus anthropogenic environmental changes. Core chronology is based on AMS 14C measurement of terrestrial wood and charcoal and thus avoids the vagaries of hard-water-lake error. During the earliest Holocene, prior to ∼9000 14C yr BP, the coring site was not covered by water and all proxies suggest that climatic conditions were relatively dry. Water covered the coring site by ∼9000 14C yr BP, coinciding with filling of other lakes in Peten and farther north on the Yucatan Peninsula. During the early Holocene (∼9000 to ∼6800 14C yr BP), pollen data suggest moist conditions, but high δ 18O values are indicative of relatively high E/P. This apparent discrepancy may be due to a greater fractional loss of the lake's water budget to evaporation during the early stages of lake filling. Nonetheless, conditions were moist enough to support semi-deciduous lowland forest. Decrease in δ 18O values and associated change in ostracod species at ∼6800 14C yr BP suggest a transition to even moister conditions. Decline in lowland forest taxa beginning ∼5780 14C yr BP may indicate early human disturbance. By ∼2800 14C yr BP, Maya impact on the environment is documented by accelerated forest clearance and associated soil erosion. Multiple proxies indicate forest recovery and soil stabilization beginning ∼1100 to 1000 14C yr BP, following the collapse of Classic Maya civilization.

Lake Bonneville fluctuations and global climate change

Lake Bonneville, the largest late Pleistocene closed-basin lake in the North American Great Basin, fluctuated widely in response to changes in climate. The geochemistry and mineralogy of endogenic calcium carbonate deposited in deep water, and stratigraphic studies of shore-zone deposits, provide evidence of millennial-scale lake-level fluctuations that had amplitudes of about 50 m between 30 and 10 ka. Falling-lake events occurred at 21, 18.5–19, 17.5, 16–15.5, 14–13, and 10 ka (radiocarbon years) synchronously with the terminations of Heinrich events H1 and H2 and other smaller scale iceberg-rafting events (a, b, c, and Younger Dryas) in the North Atlantic Ocean. The Lake Bonneville results thus support other climate records that suggest that late Pleistocene millennial-scale climate change was global in extent. The size and shape of the Northern Hemisphere ice sheets, which determined the mean positions of storm tracks, may have been the primary control on late Pleistocene water budgets of Great Basin lakes.

Correlations of Climate and Streamflow in Three Minnesota Streams

Correlations between four climate parameters and streamflow in three Minnesota streams were investigated. Runoff values measured over periods of up to 37 years were correlated with precipitation, air temperature, wind, and dew point temperature. The overall objective was to examine if relationships can be obtained which require only readily available input parameters without calibration. Such relationships would be of great use, e.g. to compute future lake water budgets without recourse to more detailed and complex hydrologic runoff models. Monthly, seasonal, and annual time frames were investigated. A seasonal time frame using 3 month averages gave the closest fit for the linear regressions without time lag. Although the watershed sizes varied from 360 to 49,600 square kilometers, the 3 month period seemed sufficiently long to average long term hydrologic processes such as infiltration, evaporation, and groundwater flow. An equation was found for each season (3 months) for each of the rivers. Winter (December, January, February) regressions required only precipitation data; spring regressions required air temperature and precipitation; summer and fall regressions were found with precipitation, air temperature, dew point temperature, and wind speed. The coefficients in the regression equations were related to the watershed characteristics. The r2 values were highest for the Zumbro River in spring (0.69) and lowest for the Baptism River in winter (0.14). Root mean square error values ranged from 2.8 mm/mo for the Mississippi River in winter to 18 mm/mo for the Baptism River in spring. The coefficients of variability (CV) ranged from 0.24 to 0.52. Overall the results were disappointing but not all bad. Climate parameters without watershed parameters can characterize runoff only within limits. To project possible future runoff averages the GISS GCM-values for the 2 × CO2 climate scenario were applied to the seasonal runoff regression equations. The projections were that the spring runoff values would decrease by up to 35% while in the other seasons streamflows would increase by up to 50%. Annual runoff would not change significantly enough to be predictable. The results were in the range of changes predicted by other investigations using very different techniques. Since predictions were based on equations found with past records, it was implied that the land cover would remain unchanged in the 2 × CO2 environment. This may be unrealistic and needs further investigation.