Hydrologic Inputs Research Articles

Stochastic description of water table fluctuations in wetlands

Wetlands are crucial ecosystems which provide several functions, beneficial both to human beings and to the environment. Despite such importance, quantitative approaches to many aspects of wetlands are far from being adequate, above all the interaction between rainfall, vegetation, soil moisture and groundwater depth. Starting from a previously developed model for below‐ground stochastic water level fluctuations, we extend it to consider the case of waterlogging. The extended model is now suitable for describing the long‐term probability distribution of water table depth in temporarily inundated wetland sites, whose hydrologic input is dominated by stochastic rainfall. The extended model performs well when compared to real data collected in the Everglades National Park (Florida, US), confirming its capability to capture the stochastic variability of wetland ecosystems.

The Effect of Municipal Wastewater Effluent on Nitrogen Levels in Onondaga Lake, a 36‐Year Record

This work presents a retrospective analysis of long-term trends in loading of forms of nitrogen (N) from the Metropolitan Syracuse Wastewater Treatment Plant (Metro), N concentrations in the receiving urban lake (Onondaga Lake, New York), and related water quality status for the period from 1972 to 2007. The history of the evolution of treatment and discharge at Metro, as it affected N loading, is reviewed and forms the basis for identification of five regimes during which unifying conditions of loading and in-lake conditions prevailed. Changes in industrial waste inputs have complicated the effects of upgrades in treatment at Metro from primary (until 1978) to advanced (starting in 2004). Current N loading from Metro is approximately 35% lower than the peak levels observed in the late 1980s to late 1990s, but the areal rate to the lake remains extremely high (approximately 97 g/m(2).y), representing approximately 75% of the overall N load. Implementation of year-round nitrification treatment has resulted in transformation of the composition of the N load from Metro from ammonia (T-NH3) to nitrate (NO3(-)) dominance. High N concentrations have prevailed in the upper waters of the lake throughout the study period with averages of total N ranging from 2.6 to 4.3 mg/L for the five regimes. Total N levels and partitioning among the forms in the lake generally have tracked Metro loading conditions for the five regimes. The effects of Metro loading on seasonal in-lake patterns are demonstrated to be modified by both hydrologic inputs from tributaries and in-lake operation of biochemical processes. Resolution of these effects is supported by application of both empirical and dynamic mass balance models. Water quality problems related to high concentrations of forms of N are documented, including (1) augmentation of dissolved oxygen depletion during fall mixing from in-lake nitrification events, enabled by high T-NH3 levels; (2) violations of ammonia toxicity limits; and (3) violations of nitrite toxicity standards. These problems were either greatly ameliorated or eliminated by Metro's most recent treatment upgrades. Prevailing conditions are considered in a management context, including (1) likelihood of exceedances of toxicity limits in the future and (2) potential role of elevated nitrate levels in preventing mobilization of methyl mercury from the lake's sediments.

Reverse engineered flood hazard mapping in Afghanistan: A parsimonious flood map model for developing countries

Most flood models are based on advanced algorithmic and multiple data requirements that are sometimes difficult to apply in developing countries. These feed-forward models cannot be applied to large areas and can lead to extreme over/under estimations in some developing countries due to extrapolation from inadequate datasets where each additional parameter adds further uncertainty. This study proposes to employ a parsimonious model that only relies on adequate available data reducing forward-uncertainty-propagation. A “reverse engineering” approach that relies on past inundation depths does provide a solution for flood hazard mapping where extracting the flood extent of extreme floods is the primary goal and where only inadequate hydrological input data are available. The feedback method was successfully deployed to create the nationwide Afghanistan Flood Hazard Map (AFG-FHM) at a scale of 1:100,000 using a high-resolution digital elevation model, sample measurements and Dartmouth Flood Observatory past flood data. This paper describes the parsimonious flood map model and general methodology employed to create the AFG-FHM, as it is a robust method to generate extreme inundation outlines, which can be utilised in other developing nations as well.

Lateglacial and Holocene paleoenvironmental changes recorded in lake sediments, Brock Plateau (Melville Hills), Northwest Territories, Canada

Sediments from South Lake, Brock Plateau (Melville Hills), Northwest Territories, provide one of the longest postglacial records from the mainland western Canadian Arctic, outside of eastern Beringia. Sedimentation commenced at least 13 900 cal. yr BP, and possibly as early as 16 000 cal. yr BP, in response to early deglaciation of the site. Pollen is present throughout the record, with an initial Artemisia-Salix assemblage indicative of very cold conditions, consistent with a locally severe Younger Dryas Stade or simply continued proximity of the Laurentide Ice Sheet margin ( c. 12 700 to 11 500 cal. yr BP). At c. 11 000 cal. yr BP, abiotic proxies signal a transition to warmer conditions, corroborated by a pollen assemblage dominated by Betula and Cyperaceae. Although South Lake was biologically productive during the early Holocene ( c. 11 000 to 7000 cal. yr BP), diatoms and other siliceous organisms are notably absent from the record, suggesting severe silica limitation. Rises in Alnus crispa and Picea mariana pollen at c. 7000 cal. yr BP suggest cooling and/or an increase in effective moisture. Wetter conditions and increased hydrological inputs and silica supply likely led to the establishment of a pioneering diatom community at c. 6500 cal. yr BP. Decreased organic sedimentation after c. 2000 cal. yr BP suggests cooler conditions. Additionally, changing niveo-eolian deposition of sand on lake ice varied with a c. 3000-year periodicity through the entire record. The South Lake multiproxy record supports the hypothesis that the Brock Plateau was one of the earliest deglaciated regions during the late Wisconsinan.

Inter‐ and intraspecific variation of stemflow production from Fagus grandifolia Ehrh. (American beech) and Liriodendron tulipifera L. (yellow poplar) in relation to bark microrelief in the eastern United States

AbstractStemflow is a spatially concentrated hydrologic input at the tree base. Prior work has documented the differential effects of stemflow from a wide range of plant species on ecohydrological processes, such as the alteration of soil pH and spatial patterning of understory vegetation. No known work has coupled stemflow yield with high resolution measurements of bark microrelief that definitively ascribe differential stemflow yield to bark microrelief. As such, our research objectives were to: (1) correlate inter‐ and intraspecific variation in stemflow yield to a quantitative bark microrelief scale and (2) compare and contrast stemflow for two co‐occurring deciduous species—Fagus grandifolia Ehrh. (American beech) and Liriodendron tulipifera L. (yellow poplar). Using a newly developed instrument to measure bark microrelief, namely the LaserBark™ automated tree measurement system, in combination with an 11‐month stemflow database for a broadleaved deciduous forest in eastern North America, it was found that bark microrelief values significantly differed between the two species [P = 0·000, F (1,19) = 49·32]. Funneling ratios [P = 0·000, H (1, 990) = 339·20] and stemflow generation [P = 0·000, H (1, 990) = 146·75] also significantly differed between the two species. Our results indicate that bark microrelief exerts a considerable effect on stemflow yield from F. grandifolia and L. tulipifera, possibly affecting water and solute flux to the forest floor. Copyright © 2009 John Wiley & Sons, Ltd.

A Streamflow Forecasting Framework using Multiple Climate and Hydrological Models1

Abstract: Water resources planning and management efficacy is subject to capturing inherent uncertainties stemming from climatic and hydrological inputs and models. Streamflow forecasts, critical in reservoir operation and water allocation decision making, fundamentally contain uncertainties arising from assumed initial conditions, model structure, and modeled processes. Accounting for these propagating uncertainties remains a formidable challenge. Recent enhancements in climate forecasting skill and hydrological modeling serve as an impetus for further pursuing models and model combinations capable of delivering improved streamflow forecasts. However, little consideration has been given to methodologies that include coupling both multiple climate and multiple hydrological models, increasing the pool of streamflow forecast ensemble members and accounting for cumulative sources of uncertainty. The framework presented here proposes integration and offline coupling of global climate models (GCMs), multiple regional climate models, and numerous water balance models to improve streamflow forecasting through generation of ensemble forecasts. For demonstration purposes, the framework is imposed on the Jaguaribe basin in northeastern Brazil for a hindcast of 1974‐1996 monthly streamflow. The ECHAM 4.5 and the NCEP/MRF9 GCMs and regional models, including dynamical and statistical models, are integrated with the ABCD and Soil Moisture Accounting Procedure water balance models. Precipitation hindcasts from the GCMs are downscaled via the regional models and fed into the water balance models, producing streamflow hindcasts. Multi‐model ensemble combination techniques include pooling, linear regression weighting, and a kernel density estimator to evaluate streamflow hindcasts; the latter technique exhibits superior skill compared with any single coupled model ensemble hindcast.

Mid‐Range Streamflow Forecasts Based on Climate Modeling – Statistical Correction and Evaluation1

Abstract: Mid‐range streamflow predictions are extremely important for managing water resources. The ability to provide mid‐range (three to six months) streamflow forecasts enables considerable improvements in water resources system operations. The skill and economic value of such forecasts are of great interest. In this research, output from a general circulation model (GCM) is used to generate hydrologic input for mid‐range streamflow forecasts. Statistical procedures including: (1) transformation, (2) correction, (3) observation of ensemble average, (4) improvement of forecast, and (5) forecast skill test are conducted to minimize the error associated with different spatial resolution between the large‐scale GCM and the finer‐scale hydrologic model and to improve forecast skills. The accuracy of a streamflow forecast generated using a hydrologic model forced with GCM output for the basin was evaluated by forecast skill scores associated with the set of streamflow forecast values in a categorical forecast. Despite the generally low forecast skill score exhibited by the climate forecasting approach, precipitation forecast skill clearly improves when a conditional forecast is performed during the East Asia summer monsoon, June through August.

Fog precipitation and rainfall interception in the natural forests of Madeira Island (Portugal)

Situated in the Atlantic Ocean, Madeira is a within-plate volcanic island, approximately 600 km northwest of the Western African coast. Cloud cover formed mainly of orographic origin persists on Madeira for more than 200 days per year between 800 m and 1600 m altitude. Since vegetation occupies 2/3 of the island's surface, fog precipitation, which occurs when fog droplets are filtered by the forest canopy and coalesce on the vegetation surfaces to form larger droplets that drip to the forest floor, is an important hydrological input. Rainfall interception and fog precipitation data were collected between 1996 and 2005 in the natural forests of Madeira. Six throughfall gauges were placed under the canopy of three different types of forest: high altitude tree heath forest (1580 m), secondary tree heath forest (1385 m) and humid laurisilva forest (1050 m). Fog precipitation is higher under high altitude heath forest (average canopy interception was −225% of gross precipitation) and dependent both on altitude and vegetation type, due to different tree architecture and leaf shape. Although results are conservative estimates of fog precipitation, they point towards the importance of fog-water as a source of groundwater recharge in the water balance of the main forest ecosystems of Madeira.

Intra-annual variation in the stable oxygen and carbon isotope ratios of cellulose in tree rings of coast redwood (Sequoia sempervirens)

Fog is a seasonally variable hydrologic input to coast redwood ( Sequoia sempervirens, D. Don) ecosystems with a stable isotopic composition (δ 18O, δ2H) that is distinct from rainfall. The intra-annual variation in tree ring cellulose δ18O of coast redwood was measured to determine what portion of the tree ring should be sampled to best target fog signals. Ten years of rings were subdivided into ten equal units for three trees at two sites in northern California. Intra-annual variation in cellulose δ18O was as high as 3‰ with a consistent pattern of enriched (in 18O) values from the annual ring boundary and depleted values from the central portion of the ring. These patterns show a strong coherence between replicate trees at the same site as well as significant correlations between individuals at sites over 250 km apart. Intra-annual variation in stable carbon isotope ratios (δ13C) was as high as 2‰ and produced a pattern with depleted (in 13C) values from the ring boundary and enriched values from the central portion of the ring. Although these δ13C patterns were not as strongly correlated between replicate trees as the patterns in δ18O variation, they did produce significant correlations with the variation in fog frequencies recorded at local airports. This study highlights the importance of quantifying intra-annual variation in tree ring stable isotope signals as a guide to further investigations on historic variability from long chronologies especially if the signal of interest is seasonally variable (eg, fog).

Hydrologic support of carbon dioxide flux revealed by whole‐lake carbon budgets

Freshwater lakes are an important component of the global carbon cycle through both organic carbon (OC) sequestration and carbon dioxide (CO2) emission. Most lakes have a net annual loss of CO2 to the atmosphere and substantial current evidence suggests thatbiologic mineralization of allochthonous OC maintains this flux. Because net CO2 flux to the atmosphere implies net mineralization of OC within the lake ecosystem, it is also commonly assumed that net annual CO2 emission indicates negative net ecosystem production (NEP). We explored the relationship between atmospheric CO2 emission and NEP in two lakes known to have contrasting hydrologic characteristics and net CO2 emission. We calculated NEP for calendar year 2004 using whole‐lake OC and inorganic carbon (IC) budgets, NEPOC and NEPIC, respectively, and compared the resulting values to measured annual CO2 flux from the lakes. In both lakes, NEPOC and NEPIC were positive, indicating net autotrophy. Therefore CO2 emission from these lakes was apparently not supported by mineralization of allochthonous organic material. In both lakes, hydrologic CO2 inputs, as well as CO2 evolved from net calcite precipitation, could account for the net CO2 emission. NEP calculated from diel CO2 measurements was also affected by hydrologic inputs of CO2. These results indicate that CO2 emission and positive NEP may coincide in lakes, especially in carbonate terrain, and that all potential geologic, biogeochemical, and hydrologic sources of CO2 need to be accounted for when using CO2 concentrations to infer lake NEP.

The association between climate teleconnection indices and Upper Klamath seasonal streamflow: Trans‐Niño Index

AbstractThis research investigates large‐scale climate features affecting inter‐annual hydrologic variability of streams flowing into Upper Klamath Lake (UKL), Oregon, USA. UKL is an arid, mountainous basin located in the rain shadow east of the crest of the Cascade Mountains in the northwestern United States. Developing accurate statistical models for predicting spring and summer seasonal streamflow volumes for UKL is difficult because the basin has complex hydrology and a high degree of topographic and climatologic variability. In an effort to reduce streamflow forecast uncertainty, six large‐scale climate indices—the Pacific North American Pattern, Southern Oscillation Index, Pacific Decadal Oscillation (PDO), Multivariate El Niño‐Southern Oscillation Index, Niño 3·4, and a revised Trans‐Niño Index (TNI)—were evaluated for their ability to explain inter‐annual variation of the major hydrologic inputs into UKL.The TNI is the only index to show significant correlations during the current warm phase of the PDO. During the warm PDO phase (1978–present), the averaged October through December TNI is strongly correlated with the subsequent April through September streamflow (r = 0·7) and 1 April snow water equivalent (r = 0·6). Regional analysis shows that this climate signal is not limited to UKL but is found throughout the northwestern United States.Incorporating the TNI variable into statistical streamflow prediction models results in standard errors of forecasts issued on the first of February and earlier that are 7–10% smaller than those for the models without the TNI. This, coupled with other enhancements to the statistical models, offers a significant increment of improvement in forecasts used by water managers. Copyright © 2009 John Wiley & Sons, Ltd.

Effects of DEM Source and Resolution on WEPP Hydrologic and Erosion Simulation: A Case Study of Two Forest Watersheds in Northern Idaho

The recent modification of the Water Erosion Prediction Project (WEPP) model has improved its applicability to hydrology and erosion modeling in forest watersheds. To generate reliable topographic and hydrologic inputs for the WEPP model, carefully selecting digital elevation models (DEMs) with appropriate resolution and accuracy is essential because topography is a major factor controlling water erosion. Light detection and ranging (LIDAR) provides an alternative technology to photogrammetry for generating fine-resolution and high-quality DEMs. In this study, WEPP (v2006.201) was applied to hydrological and erosion simulation for two small forest watersheds in northern Idaho. Data on stream flow and total suspended solids (TSS) in these watersheds were collected and processed. A total of six DEMs from the National Elevation Dataset (NED), Shuttle Radar Topography Mission (SRTM), and LIDAR at three resolutions (30 m, 10 m, and 4 m) were obtained and used to calculate topographic parameters as inputs to the WEPP model. WEPP-simulated hydrologic and erosion results using the six DEMs were contrasted and then compared with field observations. For the study watersheds, DEMs with different resolutions and sources generated varied topographic and hydrologic attributes, which in turn led to significantly different erosion simulations. WEPP v2006.201 using the 10 m LIDAR DEM (vs. using other DEMs) produced a total amount of as well as seasonal patterns of watershed discharge and sediment yield that were closest to field observations.

Sustainable water resource management under hydrological uncertainty

A proper understanding of the sources and effects of uncertainty is needed to achieve the goals of reliability and sustainability in water resource management and planning. Many studies have focused on uncertainties relating to climate inputs (e.g., precipitation and temperature), as well as those related to supply and demand relationships. In the end‐to‐end projection of the hydrological impacts of climate variability, however, hydrological uncertainties have often been ignored or addressed indirectly. In this paper, we demonstrate the importance of hydrological uncertainties for reliable water resources management. We assess the uncertainties associated with hydrological inputs, parameters, and model structural uncertainties using an integrated Bayesian uncertainty estimator framework. Subsequently, these uncertainties are propagated through a simple reservoir management model in order to evaluate how various operational rules impact the characteristics of the downstream uncertainties, such as the width of the uncertainty bounds. By considering different operational rules, we examine how hydrological uncertainties impact reliability, resilience, and vulnerability of the management system. The results of this study suggest that a combination of operational rules (i.e., an adaptive operational approach) is the most reliable and sustainable overall management strategy.

Conservation practice effectiveness in the irrigated Upper Snake River/Rock Creek watershed

The Upper Snake River/Rock Creek Conservation Effects Assessment Project was initiated in 2005 to determine the effectiveness of conservation practices in an irrigated watershed. Our objectives were to determine water and salt balances and water quality effects of using sprinkler rather than furrow irrigation in the Twin Falls irrigation tract in southern Idaho. Data from the current study were compared with earlier studies conducted from 1968 to 1971. Irrigation water diverted from the Snake River supplied 73% and 83% of the hydrologic input to this 82,000 ha (202,000 ac) watershed in 2005 and 2006, respectively, with approximately 40% flowing back to the Snake River through furrow irrigation runoff, unused irrigation water, and subsurface drainage. Net suspended sediment loss decreased from 460 kg ha -1 (400 lb ac -1 ) during the 1971 irrigation season to 220 kg ha -1 (190 lb ac -1 ) in 2005 and 10 kg ha -1 (9 lb ac -1 ) in 2006 by switching from furrow to sprinkler irrigation, applying polyacylamide, and installing sediment ponds. The relative amount of sprinkler irrigation in a subwatershed did not correlate with the total loss of suspended sediment for July 2005 and 2006 (r = 0.12). The lack of correlation was primarily due to extremely high sediment concentrations in two of the five subwatersheds, possibly due to furrow irrigation management. Two potential concerns identified during this initial analysis were an accumu- lation of total salts in the watershed and increased nitrate concentrations in four return flow streams compared to earlier studies. Future analyses will determine the effects of specific practices with this watershed.

Recent habitat degradation in karstic Lake Uluabat, western Turkey: A coupled limnological–palaeolimnological approach

The Ramsar site of Lake Uluabat, western Turkey, suffers from eutrophication, urban and industrial pollution and water abstraction, and its water levels are managed artificially. Here we combine monitoring and palaeolimnological techniques to investigate spatial and temporal limnological variability and ecosystem impact, using an ostracod and mollusc survey to strengthen interpretation of the fossil record. A combination of low invertebrate Biological Monitoring Working Party scores (<10) and the dominance of eutrophic diatoms in the modern lake confirms its poor ecological status. Palaeolimnological analysis of recent (last >200 yr) changes in organic and carbonate content, diatoms, stable isotopes, ostracods and molluscs in a lake sediment core (UL20A) indicates a 20th century trend towards increased sediment accumulation rates and eutrophication which was probably initiated by deforestation and agriculture. The most marked ecological shift occurs in the early 1960s, however. A subtle rise in diatom-inferred total phosphorus and an inferred reduction in submerged aquatic macrophyte cover accompanies a major increase in sediment accumulation rate. An associated marked shift in ostracod stable isotope data indicative of reduced seasonality and a change in hydrological input suggests major impact from artificial water management practices, all of which appears to have culminated in the sustained loss of submerged macrophytes since 2000. The study indicates it is vital to take both land-use and water management practices into account in devising restoration strategies. In a wider context, the results have important implications for the conservation of shallow karstic lakes, the functioning of which is still poorly understood.

Total mercury and methylmercury dynamics in upland–peatland watersheds during snowmelt

Wetlands, and peatlands in particular, are important sources of methylmercury (MeHg) to susceptible downstream ecosystems and organisms, but very little work has addressed MeHg production and export from peatland-dominated watersheds during the spring snowmelt. Through intensive sampling, hydrograph separation, and mass balance, this study investigated the total mercury (THg) and MeHg fluxes from two upland–peatland watersheds in Minnesota, USA during the 2005 spring snowmelt and proportionally attributed these fluxes to either peatland runoff or upland runoff. Between 26% and 39% of the annual THg flux and 22–23% of the annual MeHg flux occurred during the 12-days snowmelt study period, demonstrating the importance of large hydrological inputs to the annual mercury flux from these watersheds. Upland and peatland runoff were both important sources of THg in watershed export. In contrast to other research, our data show that peatland pore waters were the principal source of MeHg to watershed export during snowmelt. Thus, despite cold and mostly frozen surface conditions during the snowmelt period, peatland pore waters continued to be an important source of MeHg to downstream ecosystems.

Primary production, nutrient dynamics, and accretion of a coastal freshwater forested wetland assimilation system in Louisiana

This study reports on the response of a tidal, freshwater forested wetland ecosystem to long-term input of secondarily treated municipal effluent from the City of Mandeville, LA. Measurements of hydrology, nutrients, and aboveground net primary productivity were made from September 1998 through March 2002. Accretion measurements were made in October 2000 and October 2004. The major hydrologic inputs to the system were the effluent, precipitation, and back water flooding from Lake Pontchartrain. Nutrient levels were generally low except in the immediate vicinity of the outfall. Mean net primary production of the freshwater forest system was significantly higher downstream of the effluent discharge (1202 g m −2 yr −1) compared to the control site (799 g m −2 yr −1). Downstream of the outfall, accretion rates were double the rate of relative sea level rise in the area. Removal efficiencies of N and P were as high as 75% and 95%, respectively. The relatively constant flow of secondarily treated municipal effluent buffered the downstream area from salinity intrusion during a region-wide drought. Re-direction of nutrient-enhanced effluents from open water bodies to wetland ecosystems can maintain plant productivity, sequester carbon, and maintain coastal wetland elevations in response to sea-level rise in addition to improving overall surface water quality, reducing energy use, and increasing financial savings.

The Effect of River Pulsing on Sedimentation and Nutrients in Created Riparian Wetlands

Sedimentation under pulsed and steady-flow conditions was investigated in two created flow-through riparian wetlands in central Ohio over 2 yr. Hydrologic pulses of river water lasting for 6 to 8 d were imposed on each wetland from January through June during 2004. Mean inflow rates during pulses averaged 52 and 7 cm d(-1) between pulses. In 2005, the wetlands received a steady-flow regime of 11 cm d(-1) with no major hydrologic fluctuations. Thirty-two sediment traps were deployed and sampled once per month in April, May, June, and July for two consecutive years in each wetland. January through March were not sampled in either year due to frozen water surfaces in the wetlands. Gross sedimentation (sedimentation without normalizing for differences between years) was significantly greater in the pulsing study period (90 kg m(-2)) than in the steady-flow study period (64 kg m(-2)). When normalized for different hydrologic and total suspended solid inputs between years, sedimentation for April through July was not significantly different between pulsing and steady-flow study periods. Sedimentation for the 3 mo that received hydrologic pulses (April, May, and June) was significantly lower during pulsing months than in the corresponding steady-flow months. Large fractions of inorganic matter in collected sediments indicated that allochthonous inputs were the main contributor to sedimentation in these wetlands. Organic matter fractions of collected sediments were consistently greater in the steady-flow study period (1.8 g kg(-1)) than in the pulsed study period (1.5 g kg(-1)), consistent with greater primary productivity in the water column during steady-flow conditions.

Reconstructing hydrological variability in Lake Baikal during MIS 11: an application of oxygen isotope analysis of diatom silica

AbstractIn this paper we reconstruct hydrological variability in Lake Baikal during Marine Isotope Stage 11 (MIS 11) (427–362 ka BP) from oxygen isotope analysis of diatom silica. Highest δ18Odiatom values are found during MIS 11.3, highlighting the dominance of hydrological input from rivers flowing into the south and central basins of Lake Baikal, especially the Selenga River. Hydrological input from south basin rivers dominated for over 30 ka. However, there is evidence from both biogenic silica and δ18Odiatom records for an abrupt cooling event at ca. 390 ka BP. Stadial conditions at this time are coincident with an iceberg discharge event into the North Atlantic. The decline in δ18Odiatom values suggests increasing proportion of hydrological input from rivers to the north of Lake Baikal, due to greater influence of winter precipitation and snow‐melt. After a period of interstadial conditions during the early stages of MIS 11.1, biogenic silica and δ18Odiatom values decline, mirroring the slow growth in Northern Hemisphere ice sheets. Despite rigorous cleaning procedures, palaeoclimatic inferences need to be treated with caution due to contamination of the δ18Odiatom record; during stadial and glacial periods, contamination of the δ18Odiatom record is even more significant. © Natural Environment Research Council (NERC) copyright 2008. Reproduced with the permission of NERC. Published by John Wiley &amp; Sons, Ltd.

The effect of landscape processes upon gene flow and genetic diversity in an Australian freshwater fish, Neosilurus hyrtlii

Summary1. Flow regime and riverine architecture are two important landscape characteristics that influence genetic diversity and gene flow in riverine species.2. Using population genetic markers (mtDNA, microsatellites and allozymes), this study aimed to investigate genetic diversity and gene flow in the freshwater fish, Neosilurus hyrtlii, across two major drainage divisions in northern and central Australia (the Gulf of Carpentaria and Lake Eyre basins). These basins lie adjacent to each other and differ in their hydrological inputs and riverine structure, providing an ideal opportunity to identify the impact of landscape processes upon population dynamics of freshwater fish.3. Populations were strongly structured among basins, among catchments within basins and were weakly structured within catchments in the Lake Eyre Basin, providing support for the Stream Hierarchy Model.4. Interestingly, mtDNA and microsatellite diversity was much higher in the Gulf of Carpentaria Basin compared to the Lake Eyre Basin. It was concluded that this difference was due to the extreme hydrological variability in this basin and boom‐bust population cycles resulting in smaller effective population sizes in the Lake Eyre Basin.