Wind River Research Articles

Grain size assisted thermal runaway as a nucleation mechanism for continental mantle earthquakes: Impact of complex rheologies

Thermal runaway has been proposed as a potential mechanism to initiate intermediate-depth earthquakes as well as lithospheric-scale shear zones at depths of 50–300km where brittle failure is inhibited due to the confining pressure. Microstructural analyses of mantle shear zones and pseudotachylites, experimental results as well as numerical models suggest that grain size reduction plays a significant role in this process and facilitates the initiation of thermal runaway and thus also the nucleation of intermediate-depth earthquakes as well as the formation of lithosphere-scale shear zones. Here I investigate the impact of complex composite rheologies on grain size assisted thermal runaway using numerical models.Results indicate that diffusion creep, dislocation accommodated grain boundary sliding as well as low-temperature plasticity do have a significant impact on the deformation of mantle rocks under lithospheric conditions and that peak stresses as well as the timing of grain size assisted thermal runaway. Ductile deformation in the shear zone leads to weakening of the rock due to grain size reduction and shear heating. Due to this weakening, the rheological contrasts between the shear zone and the surrounding rock are increased and the critical stress required to initiate thermal runaway is progressively decreased until the rock fails by self-localizing thermal runaway. However, dislocation accommodated grain boundary sliding reduces the temperatures at which this process is feasible, as it weakens the rock to such an extent that critical runaway stresses are never reached.Application of these numerical models to the 2013 Wind River earthquake (Wyoming) suggests that grain size assisted thermal runaway is a feasible mechanism for the nucleation of this earthquake.

Circulación residual en el fiordo Aysén, Chile, en condiciones de primavera

Time series of currents speed from 3 current meters moored at the mouth of Aysen Fjord, between October and November 1996, were analyze to estimate residual circulation and to relate surface flow to variations in salinity, wind and Aysen River runoff. Residual circulation and salinity at 6 m were determined by events of strong river discharge and relaxing of local wind. Periods of strong outflow and evident drop of salinity at the mouth of the fjord were preceded by a weakening of wind and in some cases were accompanied by an increase of Aysen river discharge. Moreover, the results confirm the 3-layer structure proposed for Aysen fjord, since seaward average currents were observed at 6 and 110 m depth, whereas weak transition average currents were observed at 50 m depth, representing a transition between an intermediate landward flow and the seaward bottom layer.

Structure of the buoyant plume formed by Ob and Yenisei river discharge in the southern part of the Kara Sea during summer and autumn

AbstractThis article focuses on the interaction between the Ob‐ and Yenisei‐dominated parts of the large Ob‐Yenisei buoyant plume formed in the southern part of the Kara Sea during ice‐free periods. It was shown that certain wind forcing and river discharge conditions cause the formation of a specific structure of the Ob‐Yenisei plume with significantly different properties of the Ob‐ and Yenisei‐dominated water masses. Under these conditions, the Yenisei runoff generates a narrow coastal current propagating northward from the Yenisei Gulf along the Taymyr Peninsula, which is isolated by the Ob‐dominated water mass from ambient sea water. As a result, the low‐salinity Yenisei‐dominated water mass occupies a relatively small area, while more saline Ob‐dominated water mass spreads over a wide area between the Gulf of Ob and the Taymyr Peninsula. The formation of the “isolation” configuration of the Ob‐Yenisei plume described above is presumed to be caused by the eastward Ekman transport and the resulting downwelling flow of the Ob‐dominated waters under the low‐saline and warm Yenisei‐dominated waters along the Taymyr Peninsula. Based on satellite imagery, wind reanalysis, and river discharge data collected and derived for the period of 2005–2011, it was estimated that the “isolation” configuration is regularly formed during late summer and autumn when the Ob discharge to the Kara Sea exceeds the Yenisei discharge and the local atmospheric circulation is dominated by the northerly wind regime. Assessment of the frequency and duration of the occurrence of the “isolation” configuration showed their synoptic time scale and significant interannual variability.

Historical Occurrence of White-Tailed Ptarmigan in Wyoming

We found 13 specimens (11 museum skins, 2 skeletons) of White-tailed Ptarmigan (Lagopus leucura) collected in Wyoming. All were collected in the 1911–1967 period: 12 from the Snowy Range (Albany County) and one from near Encampment (Carbon County). The last verifiable observations of White-tailed Ptarmigan in the Snowy Range were 2 separate reports in 1974, both of 4 individuals in the same location. A more recent report of 2 birds north of the Snowy Range on 15 October 2005 has also been verified. None of the verifiable observations or collection events was of more than 6 individuals. Most of the published observation records from areas other than in the Snowy Range were of single individuals and were likely Dusky Grouse (Dendragapus obscurus). Field investigations in the Beartooth Plateau, Bighorn Mountains, and Wind River Range outside of the Snowy Range revealed no ptarmigan or their sign. However, all unoccupied areas examined could potentially support White-tailed Ptarmigan populations, with the Wind River Range being most suitable, followed by the Bighorn Mountains and Beartooth Plateau. The lack of White-tailed Ptarmigan in alpine areas in Wyoming outside of the Snowy Range is most likely related to geologic events in the late Pleistocene period and not in the Holocene.

Complementarity of Hydro, Photovoltaic, and Wind Power in Rio de Janeiro State

Integrating renewable and intermittent energy sources into the electricity sector challenges traditional energy systems based on predictability and constant supply. Studies oncomplementarity between climate-related resources from different regions and countries are proving to be an efficient means to overcome the variability of single-source use. Although Rio de Janeiro State (Brazil) has set goals of increasing its use of clean and low carbon energy, there is no study to support the expansion process. Given that, this work aims to assess the complementarity potential of small hydropower plants, wind farms, and photovoltaic panels in the state. Power output estimates have been based on wind speeds, solar radiation and river flow data and without generation technologies assumptions. The Pearson correlation coefficient and linear programming have been used to comprehend and optimize the renewable mix. Daily complementarity has been observed among the energy sources considered, especially between hydro and solar resources. The optimization process showed an improvement of 61% in the total power standard deviation, from the worst—100% hydro power—to the best case—62% of photovoltaic, 21% of wind, and 17% of hydro power. The results highlight the benefits of appropriately joining the three sources and suggest investing in photovoltaic generation.

Estimation of occupancy, density, and abundance of larval lampreys in tributary river mouths upstream of dams on the Columbia River, Washington and Oregon

We estimated occupancy, density, and abundance of larval Pacific lamprey (Entosphenus tridentatus) and Lampetra spp. in tributary river mouths to impounded portions of the Columbia River, Washington and Oregon, using count data from deepwater electrofishing. Count data were analyzed by Bayesian methods using zero-inflated N-mixture models modified to include our experimentally derived estimate of capture probability of 0.70 (95% CI: 0.63–0.77). Lampetra spp. were only collected in river mouths in Bonneville Reservoir, while Pacific lamprey were also captured from river mouths in The Dalles and John Day reservoirs. In occupied river mouths, mean densities were commonly 0.2–0.3·m−2, but ranged from 0.18 to 1.72·m−2for Pacific lamprey and 0.24 to 1.72·m−2for Lampetra spp. Although there was spatial overlap, estimated density peaked in the Klickitat River mouth (556 600 larvae) for Pacific lamprey and in the Wind River mouth (544 800 larvae) for Lampetra spp. Our study demonstrates considerable larval rearing in river mouths to impounded portions of the Columbia River; however, information on survival is needed to evaluate the contribution of this production to population growth and conservation.

Video‐Based Electroshocking Platform to Identify Lamprey Ammocoete Habitats: Field Validation and New Discoveries in the Columbia River Basin

AbstractA deepwater electroshocking platform (DEP), developed to sample larval lampreys (ammocoetes) and associated habitat in depths up to 15 m, was recently tested in the field. Searches were conducted at a known rearing location (mouth of the Wind River, Washington) and at locations on the Cowlitz River, Washington, where ammocoetes had not previously been found. At the Wind River, video‐imaged ammocoetes ranged from 50 to 150 mm in water depths between 1.5 and 4.5 m, and were more common in sediments containing organic silt. Ammocoetes (n = 137) were detected at 61% (summer) and 50% (winter). Following the field verification, the DEP was used on the lower 11.7 km of the Cowlitz River. Ammocoetes (n = 41) were found at 26% specific search locations. Cowlitz River sediment containing ammocoetes was also dominated by silt with organic material, often downstream of alluvial bars in water depths from 0.8 to 1.7 m. Test results indicated the DEP was successful at detecting ammocoetes with little to no impact in relation to other sampling methods. The DEP can also be used to characterize lamprey ammocoete habitats.Received October 21, 2016; accepted March 17, 2017 Published online May 12, 2017

Sustainable Climate Change Adaptation in Indian Country

Abstract Much of the academic literature and policy discussions about sustainable development and climate change adaptation focus on poor and developing nations, yet many tribal communities inside the United States include marginalized peoples and developing nations who face structural barriers to effectively adapt to climate change. There is a need to critically examine diverse climate change risks for indigenous peoples in the United States and the many structural barriers that limit their ability to adapt to climate change. This paper uses a sustainable climate adaptation framework to outline the context and the relationships of power and authority, along with different ways of knowing and meaning, to illustrate the underpinnings of some tribes’ barriers to sustainable climate adaptation. The background of those structural barriers for tribes is traced, and then the case of water rights and management at the Wind River Reservation in Wyoming is used to illustrate the interplay of policy, culture, climate, justice, and limits to adaptation. Included is a discussion about how the rulings of the Big Horn general stream adjudication have hindered tribal climate change adaptation by limiting the quantity of tribal reserved water rights, tying those rights to the sole purposes of agriculture, which undermines social and cultural connections to the land and water, and failing to recognizing tribal rights to groundwater. Future climate projections suggest increasing temperatures, and changes in the amount and timing of snowpack, along with receding glaciers, all of which impact water availability downstream. Therefore, building capacity to take control of land and water resources and preparing for climate change and drought at Wind River Reservation is of critical importance.

Empirical estimation of recreational exploitation of burbot, Lota lota, in the Wind River drainage of Wyoming using a multistate capture–recapture model

AbstractBurbot, Lota lota (Linnaeus), is a regionally popular sportfish in the Wind River drainage of Wyoming, USA, at the southern boundary of the range of the species. Recent declines in burbot abundances were hypothesised to be caused by overexploitation, entrainment in irrigation canals and habitat loss. This study addressed the overexploitation hypothesis using tagging data to generate reliable exploitation, abundance and density estimates from a multistate capture–recapture model that accounted for incomplete angler reporting and tag loss. Exploitation rate μ was variable among the study lakes and inversely correlated with density. Exploitation thresholds μ40 associated with population densities remaining above 40% of carrying capacity were generated to characterise risk of overharvest using exploitation and density estimates from tagging data and a logistic surplus‐production model parameterised with data from other burbot populations. Bull Lake (μ = 0.06, 95% CI: 0.03–0.11; μ40 = 0.18) and Torrey Lake (μ = 0.02, 95% CI: 0.00–0.11; μ40 = 0.18) had a low risk of overfishing, Upper Dinwoody Lake had intermediate risk (μ = 0.08, 95% CI: 0.02–0.32; μ40 = 0.18) and Lower Dinwoody Lake had high risk (μ = 0.32, 95% CI: 0.10–0.67; μ40 = 0.08). These exploitation and density estimates can be used to guide sustainable management of the Wind River drainage recreational burbot fishery and inform management of other burbot fisheries elsewhere.

Detrital zircon geochronology of the Aycross Formation (Eocene) near Togwotee Pass, western Wind River Basin, Wyoming

The Aycross Formation is the basal unit of the Absaroka Volcanic Supergroup in the southern Absaroka Range and consists of volcanic sandstone, mudstone, breccia, tuff and conglomerate. The Aycross was deposited during the waning stages of the Laramide Orogeny and the earliest phases of volcanism in the Absaroka Range. U-Pb geo-chronology using laser ablation multicollector inductively coupled plasma mass spectrometry LA-ICP-MS was performed on detrital zircons collected from an Aycross sandstone bed at Falls Campground east of Togwotee Pass. The detrital zircon age spectrum ranged fom ca 47 to 2856 Ma. Peak ages, as indicated by the zircon age probability density plot are ca. 51, 61, and 72 Ma. Tertiary zircons were the most numerous (n = 32), accounting for 42% of the zircon ages spectrum. Of these 19 are Eocene, and 13 are Paleocene, which are unusual ages in the Wyoming-Idaho-Montana area. Mesozoic zircons (n = 21) comprise 27% of the age spectrum and range in age from 68–126 Ma; all but one being late Cretaceous in age. No Paleozoic zircons are present. Proterozoic zircons range in age from 1196–2483 Ma, and also consist of 27% of the age spectrum. The maximum depositional age of the Aycross Formation is estimated to be 50.05 +/− 0.65 Ma based on weighted mean of the eight youngest grains. The Aycross Formation detrital zircon age spectrum is distinct from that of other 49–50 Ma rocks in northwest Wyoming, which include the Hominy Peak and Wapiti Formations and Crandall Conglomerate. The Aycross must have been derived largely from distal westerly source areas, which include the late Cretaceous and Paleocene Bitteroot Lobe of the Idaho Batholith. In contrast, the middle Eocene units further to the north must have been derived from erosion of the Archean basement-cored uplift of the Laramide Foreland in southwest Montana.

Indigenous water histories II: water histories and the cultural politics of water for contemporary Indigenous groups

This is the second of two issues of Water History devoted to scholarship exploring water histories as experienced and understood by Indigenous peoples. The first special issue, published in December 2016, underscored the importance of oral histories, interpreted Indigenous perspectives, and, in doing so, revealed the complexity of waterscapes. Featured in the first special issue were water histories connected to: the Nuu Savi or Highland Mixtec peoples of Oaxaca, Mexico (Jimenez Osorio and Posselt Santoyo 2016); the Ojibwe around the Great Lakes of Michigan, U.S. (Gagnon 2016); Indigenous communities from the Harding, Ord, Roper, and Gilbert rivers areas of Western Australia, Northern Territory, and Queensland, Australia (Jackson and Barber 2016); Indigenous communities from the Baucau Viqueque zone of Timor Leste (Palmer 2016); and the northern Arapaho and eastern Shoshone peoples of the Wind River reservation in the inter-mountain West, U.S (Cavazos Cohn et al. 2016). This second special issue extends coverage to additional Indigenous groups and further examines water histories associated with: the Lumbee and Tuscarora Indians of North Carolina, U.S., as researched by William Maxwell; the Andean people of Tabacundo, Ecuador, as researched by Juan Pablo Hidalgo, Rutgerd Boelens, and Jeroen Vos; the Ngai Tahu (Maori) of the Waitaki River basin, South Island, New Zealand, as researched by Gail Tipa and Kyle Nelson; the Puyallup Tribe of the Pacific Northwest, U.S., as researched by Amory Ballantine; and the Yaqui people of Sonora, Mexico, as researched by Raquel Padilla Ramos and Jose Moctezuma Zamarron. While paying close attention to the significance of rivers, swamps, estuaries, irrigation, and other water systems for these Indigenous communities, each of the authors also stress the dynamics of settler colonialism within which conflicts over water arose and Indigenous resistance and re-appropriation took place. In other words, these articles examine the cultural politics of water from a historical perspective.

Influence of regional nighttime atmospheric regimes on canopy turbulence and gradients at a closed and open forest in mountain-valley terrain

Stable stratification of the nocturnal lower boundary layer inhibits convective turbulence, such that turbulent vertical transfer of ecosystem carbon dioxide (CO2), water vapor (H2O) and energy is driven by mechanically forced turbulence, either from frictional forces near the ground or top of a plant canopy, or from shear generated aloft. The significance of this last source of turbulence on canopy flow characteristics in a closed and open forest canopy is addressed in this paper. We present micrometeorological observations of the lower boundary layer and canopy air space collected on nearly 200 nights using a combination of atmospheric laser detection and ranging (lidar), eddy covariance (EC), and tower profiling instrumentation. Two AmeriFlux/Fluxnet sites in mountain-valley terrain in the Western U.S. are investigated: Wind River, a tall, dense conifer canopy, and Tonzi Ranch, a short, open oak canopy. On roughly 40% of nights lidar detected down-valley or downslope flows above the canopy at both sites. Nights with intermittent strong bursts of “top-down” forced turbulence were also observed above both canopies. The strongest of these bursts increased sub-canopy turbulence and reduced canopy virtual potential temperature (θv) gradient at Tonzi, but did not appear to change the flow characteristics within the dense Wind River canopy. At Tonzi we observed other times when high turbulence (via friction velocity, u*) was found just above the trees, yet CO2 and θv gradients remained large and suggested flow decoupling. These events were triggered by regional downslope flow. Lastly, a set of turbulence parameters is evaluated for estimating canopy turbulence mixing strength. The relationship between turbulence parameters and canopy θv gradients was found to be complex, although better agreement between the canopy θv gradient and turbulence was found for parameters based on the standard deviation of vertical velocity, or ratios of 3-D turbulence to mean flow, than for u*. These findings add evidence that the relationship between canopy turbulence, static stability, and canopy mixing is far from straightforward even within an open canopy.

Seems like I Hardly See Them Around Anymore: Historical Geographies of Riparian Change along the Wind River

Riparian areas—and the cottonwoods, water birch, bull berry, and currants that flourish within them—hold special significance for Tribes of the Intermountain American West. These species have served ceremonial and practical purposes for generations. Yet cottonwoods have experienced well-documented declines over the past several decades, and serve as indicators of overall riparian change. Research generally attributes this shift to the development of water control infrastructure, altered flood regimes, invasive species, and grazing, and rightfully so. Less attention has been paid to the cultural and historical geographies underlying these vectors of change. This research focuses on the Wind River as a case study to examine the cultural and historical factors related to riparian change. Using remote sensing, interviews and document analysis, we specifically examine boundaries between tribal/non-tribal lands along the Wind River and (1) heterogeneous patterns of riparian change, (2) significant differences in settlement patterns and the development of water infrastructure, and (3) distinct differences in water governance and its power relationships. We conclude that riparian change is heterogeneous; differs temporally, spatially, and between cultural boundaries; and relates to a socio-ecological interplay of values, practices, and policies that underlie water control, flood regime change, and proliferation of invasive species. Ultimately this research suggests that examinations of riparian change would benefit from additional in depth analyses of cultural and historical geographies, and their temporal and spatial relationships. Furthermore, tribal sovereignty over land and water may have significant impacts on overall landscape mosaics, particularly regarding the maintenance of species that support traditional lifeways.

Modeling the impact of river discharge and wind on the hypoxia off Yangtze Estuary

Abstract. The phenomenon of low dissolved oxygen (known as hypoxia) in a coastal ocean system is closely related to a combination of anthropogenic and natural factors. Marine hypoxia occurs in the Yangtze Estuary, China, with high frequency and long persistence. It is related primarily to organic and nutrient enrichment influenced by river discharges and physical factors, such as water mixing. In this paper, a three-dimensional hydrodynamic model was coupled to a biological model to simulate and analyze the ecological system of the East China Sea. By comparing with the observation data, the model results can reasonably capture the physical and biochemical dynamics of the Yangtze Estuary. In addition, the sensitive experiments were also used to examine the role of physical forcing (river discharge, wind speed, wind direction) in controlling hypoxia in waters adjacent to the Yangtze Estuary. The results showed that the wind field and river discharge have significant impact on the hypoxia off the Yangtze Estuary. The seasonal cycle of hypoxia was relatively insensitive to synoptic variability in the river discharge, but integrated hypoxic areas were sensitive to the whole magnitude of river discharge. Increasing the river discharge was shown to increase hypoxic areas, while decreasing the river discharge tended to decrease hypoxic areas. The variations of wind speed and direction had a great impact on the integrated hypoxic areas.

Indigenous water histories I: recovering oral histories, interpreting Indigenous perspectives, and revealing hybrid waterscapes

This special issue attempts to shed new light on salient but neglected aspects of water history, “Indigenous water histories.” In this first of two journal issues dedicated to this topic, we present five articles that are pertinent to three themes that Water History has not entirely or substantially dealt with before: the use of oral history, the interpretation of indigenous perspectives, and the emphasis on the hybrid/divergent aspects of waterscapes. Readers, however, will see that these new themes are largely complementary to the most popular topics this journal has explored before, such as the histories of reclamation projects, water distribution, management, pollution, and politics. Geographically, this collection offers a broad coverage of Indigenous water issues by encompassing cases from the United States (U.S.), Mesoamerica, eastern Timor Leste, and northern and western Australia. Valoree S. Gagnon traces the changes and continuity of Ojibwe Gichigami (Ojibwa’s Great Sea) water narratives and fishing rights among the Keweenaw Bay Indian Community in Michigan, the U.S. Teresa Cavazos Cohn and her coauthors discuss changes in riparian plants and landscapes in the Wind River watershed of Wyoming, the U.S., and the implications of these changes for the Eastern Shoshone and Northern Arapaho Tribes. The focus of these two articles on water history germane to fish and plants should be new for readers of Water History.

Nature Transformed: English Landscape Gardens and Theatrum Mundi

Nature Transformed: English Landscape Gardens and <i>Theatrum Mundi</i>

Long-term tectonothermal history of Laramide basement from zircon–He age-eU correlations

The long-term (>1 Ga) thermal histories of cratons are enigmatic, with geologic data providing only limited snapshots of their evolution. We use zircon (U–Th)/He (zircon He) thermochronology and age-composition correlations to understand the Proterozoic–Phanerozoic thermal history of Archean Wyoming province rocks exposed in the northern Laramide ranges of western North America. Zircon He ages from the Wind River Range (54 dates) and Bighorn Mountains (32 dates) show negative correlations with effective uranium (eU), a proxy for radiation damage. Zircon dates from the Bighorns are between 960 Ma (low-eU) and 20 Ma (high-eU) whereas samples from the Wind Rivers are between 582 Ma (low-eU) and 33 Ma (high-eU). We applied forward modeling using the zircon radiation damage and annealing model ZrDAAM to understand this highly variable dataset. A long-term t–T path that is consistent with the available geologic constraints successfully reproduced age-eU correlations. The best fit to the Wind Rivers data involves two phases of rapid cooling at 1800–1600 Ma and 900–700 Ma followed by slower cooling until 525 Ma. During the Phanerozoic, these samples were heated to maximum temperatures between 160 and 125 °C prior to Laramide cooling to 50 °C between 60 and 40 Ma. Data from the Bighorn Mountains were successfully reproduced with a similar thermal history involving cooler Phanerozoic temperatures of ∼115 °C and earlier Laramide cooling between 85 and 60 Ma. Our results indicate that age-eU correlations in zircon He datasets can be applied to extract long-term thermal histories that extend beyond the most recent cooling event. In addition, our results constrain the timing, magnitude and rates of cooling experienced by Archean Wyoming Province rocks between recognized deformation events, including the >1 Ga period represented by the regionally-extensive Great Unconformity.

Factors associated with crash severity on rural roadways in Wyoming

Abstract The ability to identify risk factors associated with crashes is critical to determine appropriate countermeasures for improving roadway safety. Many studies have identified risk factors for urban systems and intersections, but few have addressed crashes on rural roadways, and none have analyzed crashes on Indian Reservations. This study analyzes crash severity for rural highway systems in Wyoming. These rural systems include interstates, state highways, rural county local roads, and the roadway system on the Wind River Indian Reservation (WRIR). In alignment with the Wyoming strategic highway safety goal of reducing critical crashes (fatal and serious injury), crash severity was treated as a binary response in which crashes were classified as severe or not severe. Multiple logistic regression models were developed for each of the highway systems. Five effects were prevalent on all systems including animals, driver impairment, motorcycles, mean speed, and safety equipment use. With the exception of animal crashes, all of these effects increased the probability that a crash would be severe. Based upon these results, DOTs can pursue effective policies and targeted design decisions to reduce the severity of crashes on rural highways.

Late Pleistocene climate inferences from a water balance model of Jakes Valley, Nevada (USA)

Shorelines that formed in closed watershed–lake systems record past climate conditions. A simple monthly water balance model was used to explore the link between past climates, paleoclimate proxies, and the hydrologic system response of a closed watershed–lake system in the Great Basin, USA. The model was applied at a high spatial resolution and calibrated with available modern hydroclimate and watershed data and then used with existing paleolake shoreline estimates to investigate how climate and hydrologic conditions in the late Pleistocene differed from modern conditions. A range of climate conditions, ∆T (0 to −8 °C) and ∆P (1.9–2.4) from the modern climate, resulted in steady model simulations of the late Pleistocene lake highstand. Modeling results also indicate the watershed–lake system response is much more sensitive to changes in precipitation than to changes in temperature, and that the range of possible combinations of these variables can be reduced significantly when the results are compared with an independent modeling study that inferred paleoclimate conditions from glacial moraines in the Wind River Range near the eastern portion of the Great Basin. The modeling effort also revealed that physiographic heterogeneities and seasonality play a significant role in how the watershed–lake system responds to changes in precipitation and temperature, highlighting the importance of simulating the system behavior with an appropriate degree of spatial resolution. The significance of model calibration and performance evaluation over the modern period was demonstrated through a comparison of the calibrated model results with those obtained using default parameter values with the original model.

Aspects of fish conservation in the upper Patos Lagoon basin.

The Patos Lagoon basin is a large (201 626 km(2) ) and complex drainage system in southern Brazil. The lagoon is 250 km long and 60 km wide, covering an area of 10 360 km(2) . The exchange of water with the Atlantic Ocean occurs through a 0·8 km wide and 15 m deep inlet, fixed by 4 km long jetties, at the southernmost part of the Patos Lagoon. The estuarine area is restricted to its southern portion (10%), although the upper limit of saline waters migrates seasonally and year to year, influenced by the wind regime and river discharge. The known number of recorded limnetic fish species is 200, but this number is expected to increase. A higher endemism is observed in fish species occurring in upper tributaries. The basin suffers from the direct impact of almost 7 million inhabitants, concentrated in small to large cities, most with untreated domestic effluents. There are at least 16 non-native species recorded in natural habitats of the Patos Lagoon basin, about half of these being from other South American river basins. Concerning the fishery, although sport and commercial fisheries are widespread throughout the Patos Lagoon basin, the lagoon itself and the estuarine area are the main fishing areas. Landing statistics are not available on a regular basis or for the whole basin. The fishery in the northern Patos Lagoon captures 31 different species, nine of which are responsible for most of the commercial catches, but only three species are actually sustaining the artisanal fishery: the viola Loricariichthys anus: 455 kg per 10 000 m(2) gillnet per day, the mullet Mugil liza: 123 kg per 10 000 m(2) gillnet per day and the marine catfish Genidens barbus: 50 kg per 10 000 m(2) gillnet per day. A decline of the fish stocks can be attributed to inadequate fishery surveillance, which leads to overfishing and mortality of juveniles, or to decreasing water quality because of urban and industrial activities and power production. Global climatic changes also represent a major threat to the Patos system by changing the frequency of El Niño-La Niña-Southern Oscillation (ENSO).