Inland Streams Research Articles

Spatial and temporal variability of movements among sympatric salmonids in an unfragmented inland watershed

AbstractObjectiveOur aim was to determine the movement patterns of three abundant salmonids—Brown Trout Salmo trutta, Mountain Whitefish Prosopium williamsoni, and Rainbow Trout Oncorhynchus mykiss—in the Smith River watershed of Montana.MethodsWe tagged 7172 fish with passive integrated transponder (PIT) tags, monitored their movements past 15 stationary PIT arrays over 4 years, and located tagged fish between arrays by conducting mobile surveys.ResultMovement patterns varied seasonally, among species, and among locations. Movement was greatest in the middle portion of the watershed, which included a pristine main‐stem canyon and lower reaches of major tributaries. Fish rarely left the canyon, but movement into the canyon from other regions was common. Mountain Whitefish were most likely to move, and Brown Trout were least likely to move. Most fish travelled less than 10 km, but some fish travelled over 100 km. Distinct movement patterns were not evident; rather, a continuous spectrum of movement behaviors was apparent. Movements by Mountain Whitefish and Rainbow Trout increased during their spawning periods. Movements peaked when mean daily water temperatures were between 11.3 and 17.1°C.ConclusionMovements were diverse and probably contributed to metapopulation dynamics, population resiliency, and species diversity. Fish movements along stream networks connect populations across diverse landscapes, and therefore, protecting and restoring stream connectivity along inland streams such as the Smith River is critical to maintaining productive fish assemblages.

Unveiling salinity-driven shifts in microbial community composition across compartments of naturally saline inland streams

Riverine environments host diverse microbial communities, exhibiting distinctive assemblies at both microscopic and macroscopic levels. Despite the complexity of microbial life in rivers, the underlying factors that shape the community structure across different compartments remain elusive. Herein, we characterized microbial community composition of biofilm and planktonic (water column) compartments in five naturally saline inland streams and a freshwater stream to examine changes in microbial communities following salinization via sequencing of the microbial 16S rRNA gene. Significant differences in specific conductivity, oxidation–reduction potential, dissolved oxygen, and pH among the sampled streams were measured, as were significant differences in the microbial community composition between the planktonic and biofilm. The bacterial families Bacillaceae, Vicinamibacterceae, and Micrococcaceae were significantly more abundant in the biofilm compartment, while Methylophilaceae, Alcaligenaceae, Spirosomaceae, Burkholderiaceae, and Comamonadaceae were more abundant in the planktonic compartment. In addition, salinity (based on specific conductivity) influenced the microbial community composition in both compartments, with higher sensitivity of the planktonic compartment. Increases in the bacterial families Shewanellaceae, Marinomonadaceae, and Saccharospirillaceae or loss of Anaeromyxobacteraceae could be indicative of increased salinity within inland streams. Our results suggest that monitoring of microbial assemblages of freshwater ecosystems could be used as early warning signs of increased salinization levels.

Agricultural Water Salinity of Reclaimed Tidelands in Southwestern Coastal Areas of South Korea

Monitoring of the salinity of agricultural soil and water is necessary for sustainable food production in salt-affected reclaimed tidelands (RTLs). Soil salinity has been extensively monitored; however, little attention has been given to water salinity. In this study, agricultural water salinity of five RTLs located in the southwestern coastal area of South Korea was monitored. A total of 215 water samples were collected from estuary lakes and inland streams in Bojeon (BJ), Goheung (GH), Gunnae (GN), Samsan (SS), and Youngsangang (YSG) RTLs in 2018, 2020, and 2022. Water samples were analyzed for electrical conductivity (ECw) and sodium adsorption ratio (SAR) to estimate the suitability of water salinity for agricultural uses based on the FAO guidelines. The ECw (average: 1.6 - 3.6 dS m-1) and SAR (5 - 8) were highly variable being dependent on RTL locations, water type (lake and stream), and sampling year and month. For rice cultivation, ECw of BJ, SS, and YSG RTLs was lower than the threshold ECw (2 dS m-1) for rice growth; whereas ECw of GN (2.1 ± 1.0 dS m-1) and GH (3.6 ± 1.2 dS m-1) RTLs were higher than the threshold ECw. For upland crops cultivation, both ECw and SAR of five RTLs were much higher than the FAO threshold values (ECw < 0.7 dS m-1 and SAR < 3). Therefore, our results suggest that agricultural water salinity of the study RTLs is not suitable for cultivation of upland crop. Therefore, long-term monitoring of water salinity as well as developments of advanced irrigation-drainage are necessary for diversification of agricultural uses of RTLs.Distribution of ECw and SAR of lake and inland stream of five RTLs. On the right side of the panels, FAO guideline for the degree of restriction on the use for irrigation water is depicted.

Recognizing a lost nesting ground: First unambiguous Testudines eggshells from the Eocene, associated with the pleurodiran Eocenochelus (Huesca, Northern Spain)

The Eocene record of turtle eggshells is scarce, with a single unconfirmed report from France. This scarcity contrasts with the great abundance of osteological remains, distributed over a wide palaeogeographical range as a result of climatic warmth. In this paper, we describe the first definitive Eocene Testudoolithidae eggshell fragments attributable to Testudines, most likely pleurodiran turtles, from the Eocene Sobrarbe Formation at the Castejón de Sobrarbe fossil site (CS-41) in northern Spain. The eggshells were found in association with osteological remains of at least four individuals of Eocenochelus eremberti (Pleurodira, Erymnochelyini) in an otherwise sirenian-dominated bonebed. Analysis of eggshell ultra- and microstructure allows comparison with eggshells from fossil and extant turtles. The eggshells are highly recrystallized but preserve relics of their original aragonitic radial ultrastructure as crystal phantoms. The barrel-shaped shell units, which are taller than wide, with compactituberculate ornamentation and funnel-shaped pore openings are similar to those of the Palaeocene ootaxon Haininchelys curiosa, whose holotype and paratype have been lost. The CS-41 eggshells are most similar to those of the pleurodiran Erymnochelys madagascariensis from Madagascar, the closest living relative to Eocenochelus, further supporting our attribution. Sedimentological and taphonomic analysis of the assemblage supports the hypothesis that the CS-41 fossil site was formed as the infilling of an abandoned tributary channel in the deltaic plain by an overbank or debris-flow deposit associated with a storm event. This storm resulted in the exhumation and subsequent re-sedimetation of the remains of a nesting ground of Eocenochelus eremberti, an otherwise coastal turtle, which would have entered inland streams to nest in the sand bars at the mouth of the Sobrarbe Deltaic Complex.

Quantifying thermal exposure for migratory riverine species: Phenology of Chinook salmon populations predicts thermal stress.

Migratory species are particularly vulnerable to climate change because habitat throughout their entire migration cycle must be suitable for the species to persist. For migratory species in rivers, predicting climate change impacts is especially difficult because there is a lack of spatially continuous and seasonally varying stream temperature data, habitat conditions can vary for an individual throughout its life cycle, and vulnerability can vary by life stage and season. To predict thermal impacts on migratory riverine populations, we first expanded a spatial stream network model to predict mean monthly temperature for 465,775 river km in the western U.S., and then applied simple yet plausible future stream temperature change scenarios. We then joined stream temperature predictions to 44,396 spatial observations and life-stage-specific phenology (timing) for 26 ecotypes (i.e., geographically distinct population groups expressing one of the four distinct seasonal migration patterns) of Chinook salmon (Oncorhynchus tshawytscha), a phenotypically diverse anadromous salmonid that is ecologically and economically important but declining throughout its range. Thermal stress, assessed for each life stage and ecotype based on federal criteria, was influenced by migration timing rather than latitude, elevation, or migration distance such that sympatric ecotypes often showed differential thermal exposure. Early-migration phenotypes were especially vulnerable due to prolonged residency in inland streams during the summer. We evaluated the thermal suitability of 31,699 stream km which are currently blocked by dams to explore reintroduction above dams as an option to mitigate the negative effects of our warmer stream temperature scenarios. Our results showed that negative impacts of stream temperature warming can be offset for almost all ecotypes if formerly occupied habitat above dams is made available. Our approach of combining spatial distribution and phenology data with spatially explicit and temporally explicit temperature predictions enables researchers to examine thermal exposure of migrating populations that use seasonally varying habitats.

A Review of Galaxias (Galaxiidae) Fossils from the Southern Hemisphere

The Galaxiidae is a Southern Hemisphere family of freshwater fish, considered to be of Gondwanan origin based on the current distribution of species in New Zealand, Australia (including Tasmania), New Caledonia, Africa, South America, and on some associated and subantarctic islands. The fossil record of galaxiids is extremely sparse and geographically restricted. The only galaxiid fossils currently known come from several Miocene lakes in southern New Zealand. They include more than 100 articulated fishes, some remarkably preserving soft parts such as eyes and skin, skulls and jaw components, and more than 200 isolated otoliths. Common coprolites and in situ preserved gut content at one site (Foulden Maar) indicate the different diets of larvae and adult fish. These discoveries reveal a diverse Galaxias fauna, the presence of lake-locked populations, ontogenetic diet shifts, and representatives of several non-migratory Galaxias lineages associated with inland streams and lakes. There are at least six Galaxias species based on macrofossils and six separate otolith-based species from varied volcanic and regional lacustrine environments. This diversity points to southern New Zealand as a centre of biodiversity and speciation in Galaxiidae in the early to late Miocene.

Development and Application of Predictive Models of Surface Water Extent to Identify Aquatic Refuges in Eastern Australian Temporary Stream Networks

AbstractMany organisms living in temporary streams rely on remnant surface water to survive during extended dry periods and recolonize newly established habitats when flow resumes. However, research on the spatiotemporal variations in surface water extent for entire river networks is scarce. In this study, we first present a new field method for rapid surface water assessment. Next, we develop predictive models relating observed water extent to environmental attributes at a large number of surveyed stream segments (n = 241) in eastern Australian coastal catchments. We use the models to predict daily variations in surface water dynamics throughout entire river networks over the period of 1911–2017, based on available long‐term environmental attributes influencing hydrological processes. We find descriptors of surface water extent can be accurately predicted based on robust internal and external validations. Environmental predictor variables representing water gaining processes were more important in predicting surface water extent than variables representing water losses. Simulated long‐term variations in surface water extent were highly dynamic through space and time, particularly in inland streams, which were predicted to be the driest on average. Total stream length with surface water ranged from 8,974 to 13,742 km across the study period. Our study presents a novel and practical approach to quantifying and predicting variations in surface water extent, with potential applicability to other parts of the world. The simulated surface water extent through space and time can be used to identify and prioritize potential aquatic refuge areas that sustain aquatic biodiversity in river networks during extended dry periods.

Vertical Distribution of Microplastics in the Water Column and Surficial Sediment from the Milwaukee River Basin to Lake Michigan.

Microplastic contamination was studied along a freshwater continuum from inland streams to the Milwaukee River estuary to Lake Michigan and vertically from the water surface, water subsurface, and sediment. Microplastics were detected in all 96 water samples and 9 sediment samples collected. Results indicated a gradient of polymer presence with depth: low-density particles decreased from the water surface to the subsurface to sediment, and high-density particles had the opposite result. Polymer identification results indicated that water surface and subsurface samples were dominated by low-density polypropylene particles, and sediment samples were dominated by more dense polyethylene terephthalate particles. Of the five particle-type categories (fragments, films, foams, pellets/beads, and fibers/lines), fibers/lines were the most common particle-type and were present in every water and sediment sample collected. Fibers represented 45% of all particles in water samples and were distributed vertically throughout the water column regardless of density. Sediment samples were dominated by black foams (66%, identified as styrene-butadiene rubber) and to a lesser extent fibers/lines (29%) with approximately 89% of all of the sediment particles coming from polymers with densities greater than 1.1 g cm-3. Results demonstrated that polymer density influenced partitioning between the water surface and subsurface and the underlying surficial sediment and the common practice of sampling only the water surface can result in substantial bias, especially in estuarine, harbor, and lake locations where water surface concentrations tend to overestimate mean water column concentrations.

Bones and Seeds: An Integrated Approach to Understanding the Spread of Farming across the Western Balkans

ABSTRACT Animals and plants, both farmed and hunted/collected, were an integrated part of the Neolithic food economy. When jointly analysed these can provide a holistic view of early food production systems which goes beyond individual descriptions of herd management and crop cultivation. Exhaustive surveys of both Neolithic zooarchaeological and archaeobotanical data were collected from the western Balkans and neighbouring regions (Croatia, Bosnia and Herzegovina, Serbia, southern Hungary, western Romania and eastern Italy). Here we combine both sets of data to explore the Neolithic food economy along the maritime and inland streams of Neolithisation. We demonstrate that, notwithstanding significant limitations, it is possible to compare and combine the datasets and present an integrated approach to the spread and development of farming within the western Balkans. Our research also evinces diachronic and spatial differences within the exploitation of domesticated and wild species, and the factors that may have influenced such practices.

Seasonal Loading and Concentration Patterns for Fecal Bacteroidales qPCR Markers and Relationships to Water Quality Parameters at Baseflow

Bacteria belonging to the Order Bacteroidales predominate the intestines of warm-blooded animals, and monitoring of these bacteria can indicate fecal pollution impacts to a waterbody. Differences in seasonal concentrations and loadings for Bacteroidales and their relationship with physicochemical water parameters were investigated in temperate, inland streams. Seasonal samples (n = 321) were collected during baseflow in three central Tennessee, USA, watersheds. To estimate total fecal bacteria in receiving streams, general Bacteroidales 16S rRNA gene targets were analyzed by quantitative PCR and reported as concentration and loadings for individual and combined watersheds. In most cases, Bacteroidales marker concentrations were highest during spring/summer and loading values were highest in the spring. Bacteroidales concentrations were positively correlated with temperature and total suspended solids and negatively with dissolved oxygen, while no consistent correlations were found between loadings and abiotic factors. Temperature, total suspended solids, and dissolved oxygen are likely drivers influencing seasonal patterns for Bacteroidales concentrations. Researchers and water quality stakeholders should carefully consider measurement type (concentration versus loading), season, and water quality parameters as elements that could impact results when developing fecal monitoring projects.

Chemical weathering across the western foreland of the Greenland Ice Sheet

Proglacial streams deliver melt water and chemical weathering products, including nutrients and radiogenic isotopes, from continental ice sheets to the ocean. Weathering products are also delivered to the ocean in non-glacial streams that form following ice sheet retreat and are disconnected from ice sheet meltwater by hydrologic divides. If weathering reactions differ in non-glacial and proglacial stream catchments, the streams could deliver different types and magnitudes of solutes to the ocean, depending on relative discharge volumes. Unlike proglacial streams, however, little is known of non-glacial stream solute compositions or discharge. Here we show specific discharges are similar from a proglacial stream draining the Greenland Ice Sheet (GrIS) with several streams disconnected from the ice sheet. We also evaluate weathering reactions across a 170-km transect in western Greenland that contains one proglacial stream draining the GrIS, and two coastal (ice distal) and three inland (ice proximal) areas with non-glacial streams. Non-glacial streams exhibit solute compositions and offsets between dissolved and bedload Sr isotope ratios that indicate weathering increases toward the coast with exposure age and precipitation. Major element mass balance calculations show weathering reactions shift from predominately carbonic acid weathering of carbonate minerals inland near the ice sheet to predominately sulfuric acid weathering of carbonate minerals near the coast. Strontium concentrations and isotopic ratios of the proglacial stream reflect mixing of at least two subglacial sources and minor in-stream weathering that consumes CO2. About 5 times less CO2 is consumed per liter in the proglacial than inland non-glacial streams; however, arid conditions inland suggest limited discharge from the ungauged inland streams leads to less total CO2 weathering than proglacial stream. One coastal area consumes less CO2 per liter than the proglacial stream and another coastal area exhibits net CO2 production. These results indicate estimates for glacial foreland solute fluxes and CO2 weathering consumption and production should include estimates from both non-glacial and proglacial streams. Understanding weathering fluxes from these two types of streams will be important for evaluations of past ice sheet retreat and predictions of future solute and CO2 fluxes associated with continued ice sheet retreat.

Reproductive potential of four freshwater prawn species in the Amazon region

The bioecology of freshwater prawns can be understood by studying their reproductive biology. Thus, the aim of this paper was to determine and compare the reproductive potential of four freshwater caridean prawns collected in the Amazon region. For two years, we captured females of Macrobrachium brasiliense, Palaemon carteri, Pseudopalaemon chryseus and Euryrhynchus amazoniensis from inland streams in the municipality of Itacoatiara (AM). At the laboratory, we measured the biometric variables total length, carapace length, abdomen length and total weight, and recorded the number of eggs (NE) by direct counting. There was a significant difference for all variables between the species. The females of M. brasiliense were the most abundant and had the largest sizes and NE. However, the fecundity index shows that P. carteri has the highest reproductive potential of the four species. Despite the differences in size and weight, all the species showed low fecundity, which is a characteristic of continental palemonidean K strategist prawns.

Water Management in the Urban Cultural Heritage of Myanmar

AbstractThis article assesses indigenous perceptions of water through a comparison of the water management strategies at three ancient sites located in different ecological zones of Myanmar. Two of our examples are in the high-rainfall regions of Lower Myanmar: Thagara in the Dawei River valley flanked by mountains on the east and west, and Kyaikkatha on delta lands at the egress of the Sittaung River. We contrast these adaptations with the micro-exploitation of the scarce water resources at Bagan (also spelled Pagan) in the arid zone of Upper Myanmar. In the southern wet regions, despite the different geographical setting of Thagara and Kyaikkatha, the focus was on drainage and control. Multiple ramparts and moats were used to conserve the scarce water in the dry months between December and April and control the heavy floods of the rainy months between May to November. At Bagan, sited directly on the broad Ayeyarwady River, water management of inland streams and seasonal lakes maximised the gentle slope of the plain while also coping with intermittent flash floods in the rainy months. The sites of Thagara, Kyaikkatha, and Bagan demanded specific adaptations but are alike in the absence of extensive transformation of the landscape. This balance of manmade and natural elements provides common ground despite their variable size and urbanised extent, ecological setting, and occupational sequence to highlight the shared significance of water management in their long-term urban success.

Regional wastewater treatment–an economical solution? Data from 40 years of operation gives the answer

Economic data from 40 years of operation of three regional wastewater treatment companies have been compiled and analysed. The transport systems consist mainly of gravity flow tunnels with lengths of 55–120 km. In spite of the heavy initial investments &amp;lt;20% of the cumulative total costs can be allocated to the transport systems. The treatment plants all remove 90% or more of the influent Biological Oxygen Demand (BOD) and phosphorus and 65–80% of the nitrogen. The wastewater treatment is responsible for about 90% of the cumulative operation costs while the transport system is responsible for 20–40% of the cumulative capital costs. Over time the cost of the transport systems has decreased considerably and is after 40 years of operation only 4–13% of the total costs. Although the main benefit of the regional solutions has been the transfer of wastewater from sensitive inland streams and lakes, the data presented give strong evidence that the regional solutions also has been advantageous from an economic point of view.

Sources and Transport of Phosphorus to Rivers in California and Adjacent States, U.S., as Determined by SPARROW Modeling

AbstractThe SPARROW (SPAtially Referenced Regression on Watershed attributes) model was used to simulate annual phosphorus loads and concentrations in unmonitored stream reaches in California, U.S., and portions of Nevada and Oregon. The model was calibrated using de‐trended streamflow and phosphorus concentration data at 80 locations. The model explained 91% of the variability in loads and 51% of the variability in yields for a base year of 2002. Point sources, geological background, and cultivated land were significant sources. Variables used to explain delivery of phosphorus from land to water were precipitation and soil clay content. Aquatic loss of phosphorus was significant in streams of all sizes, with the greatest decay predicted in small‐ and intermediate‐sized streams. Geological sources, including volcanic rocks and shales, were the principal control on concentrations and loads in many regions. Some localized formations such as the Monterey shale of southern California are important sources of phosphorus and may contribute to elevated stream concentrations. Many of the larger point source facilities were located in downstream areas, near the ocean, and do not affect inland streams except for a few locations. Large areas of cultivated land result in phosphorus load increases, but do not necessarily increase the loads above those of geological background in some cases because of local hydrology, which limits the potential of phosphorus transport from land to streams.

The sedimentary source, planform stability and shore normal morphological change of the Xichong beach on the southern coast of the Dapeng Peninsula of Shenzhen, Guangdong Province, China

The coast of the Dapeng Peninsula has been honored as one of “the eight most beautiful coasts in China”. The most precious tourism resource for the peninsula is headland bay beaches, among which the beach at Xichong on the southern coast of the peninsula is the longest and the most important one. The information of the stability, sedimentary source and shape change of the beach is very important for maintaining the beach in terms of sustainable development of the peninsula. Heavy minerals in the sand of the beach and the inland stream at Xichong are compared with those of a nearby beach on the same coast to determine the beach sand source; with help of a computer software, MEPBAY, the equilibrium planforms of the beaches on the peninsula are compared with those of an island without rivers to evaluate the stream’s effects on the beach stability; cross shore profiles along the Xichong beach are also surveyed in different seasons of a year to assess the annual shore normal beach changes affected by the stream input, and the relation between the equilibrium planform state and cross shore changes of the beach. It is shown that (1) stream is the main sedimentary source of the beach and the weathering materials of the rocky headlands on both sides of the bay transported by waves are the second source for the beach but it is limited, sand from an inner shelf is not the sedimentary source for the beach at present and was not even during the Holocene transgression; (2) the Xichong beach cannot reach static equilibrium around the entire bay shoreline, the segment of the shoreline where a stream outlet is located is in dynamic equilibrium, and the unstable section occurs in the wave shadow region in the lee of an offshore island; (3) no matter whether the section of the beach shoreline at Xichong is in an equilibrium state or not, it is eroded in the typhoon season and recovered after the season, the maximum change in erosion and accretion occurs in the unstable segment; (4) the Xichong beach can only have small sand body since it is supplied with sand mainly form inland streams, resulting in a possible danger in which sand loss induced by human activities or huge storms cannot be replenished naturally.

Sheltered coastal environments as archives of paleo-tsunami deposits: Observations from the 2004 Indian Ocean tsunami

The 2004 earthquake left several traces of coseismic land deformation and tsunami deposits, both on the islands along the plate boundary and distant shores of the Indian Ocean rim countries. Researchers are now exploring these sites to develop a chronology of past events. Where the coastal regions are also inundated by storm surges, there is an additional challenge to discriminate between the deposits formed by these two processes. Paleo-tsunami research relies largely on finding deposits where preservation potential is high and storm surge origin can be excluded. During the past decade of our work along the Andaman and Nicobar Islands and the east coast of India, we have observed that the 2004 tsunami deposits are best preserved in lagoons, inland streams and also on elevated terraces. Chronological evidence for older events obtained from such sites is better correlated with those from Thailand, Sri Lanka and Indonesia, reiterating their usefulness in tsunami geology studies.

Understanding Angler Preferences for Species and Water Bodies: Importance for New York's Future Fisheries Management

Classifications of recreational anglers have focused on factors that may not be easily influenced by fishery managers, such as fishing specialization, desired experiences, and fishing conditions. To provide managers with a more managerially relevant classification of angler groups, we used the 2007 New York statewide angler survey and hierarchical cluster analysis for binary data to describe seven groups based on their species and water body preferences. Angler groups ranged from those interested in fishing for trout on inland streams (16%) to those interested in fishing lakes for warm water species (37%). We compared groups using their preferences for certain management actions and found relationships that can aid managers in deciding how to target management efforts and deploy limited resources. Grouping anglers based on species and water body preferences provides managers with a different perspective that resonates more with their information needs than past research.

Lunar tidal influence on inland river streamflow across the conterminous United States

We employ a comprehensive (1900–2009) stream discharge gauge database to analyze the tidal impacts on inland streams. Our analysis reveals a strong lunar phase signal in stream gauge time series across the conterminous United States such that the largest tidal impact on inland rivers is evident at or just after the quarter moon (halfway between full and new moons). As an explanation, we examine precipitation using the Historical Climate Network precipitation dataset. Verifying early studies’ results, we find an equivalent well‐defined lunar phase relationship with precipitation such that the largest tidal impact on precipitation generally occurs just before the quarter moon. Our results imply that inland precipitation is influenced by lunar tides and forces the lagged runoff evident in stream gauges. The lunar‐induced periodicities in the stream gauge network, evident far from ocean‐induced tides, may also influence flooding, as well as water management and power generation.

Inland diatoms from the McMurdo Dry Valleys and James Ross Island, Antarctica

Diatom taxa present in the inland streams and lakes of the McMurdo Dry Valleys and James Ross Island, Antarctica, are presented in this paper. A total of nine taxa are illustrated, with descriptions of four new species ( Luticola austroatlantica sp. nov., Luticola dolia sp. nov., Luticola laeta sp. nov., Muelleria supra sp. nov.). In the perennially ice-covered lakes of the McMurdo Dry Valleys, diatoms are confined to benthic mats within the photic zone. In streams, diatoms are attached to benthic surfaces and within the microbial mat matrix. One species, L. austroatlantica, is found on James Ross Island, of the southern Atlantic archipelago, and the McMurdo Dry Valleys. The McMurdo Dry Valley populations are at the lower range of the size spectrum for the species. Streams flow for 6–10 weeks during the austral summer, when temperatures and solar radiation allow glacial ice to melt. The diatom flora of the region is characterized by species assemblages favored under harsh conditions, with naviculoid taxa as the dominant group and several major diatom groups conspicuously absent.