Hydrogeomorphic Characteristics Research Articles

Food web structure in a double-basin ultra-oligotrophic lake in Northwest Patagonia, Argentina, using carbon and nitrogen stable isotopes

Fish, benthic macroinvertebrates, macrophytes, biofilm, plankton, and terrestrial material were analyzed for stable nitrogen (δ15N) and carbon isotopes (δ13C) to study the food web structure of a double-basined, ultra-oligotrophic lake in northwest Patagonia. The δ15N values of all biota were consistently higher in Moreno East basin, probably caused by a higher anthropogenic impact; however, the estimated trophic positions of fish showed no differences between basins, indicating that fish are feeding from food chains with different δ15N baselines. Fish δ13C values were higher in Moreno West basin but no pattern was observed for the rest of the organisms analyzed. The different hydrogeomorphic characteristics between the basins could lead to these differences in the C signatures of fish. SIAR (Stable Isotope Analysis in R) mixing model was used to study possible food sources for adult fish and the results were contrasted with published gut content analysis. According to the model, in both basins small size fish such as Small Puyen (Galaxias maculatus) and juvenile fish, had the highest relative isotopic contribution to introduced Rainbow Trout (Oncorhynchus mykiss) and Brook Trout (Salvelinus fontinalis), which had lower contributions from other sources such as insect larvae, decapods, and snails. On the contrary, decapods and insect larvae were isotopically more important for the native Creole Perch (Percichthys trucha) than small fish in both basins. An ontogenetic shift in the carbon source and trophic level was observed in Puyen Chico and Rainbow Trout from the West basin.

FLOOD INUNDATION MAPPING FOR INTEGRATED FLOODPLAIN MANAGEMENT: UPPER MISSISSIPPI RIVER SYSTEM

ABSTRACTNatural hydrogeomorphic characteristics and hydrologic alterations are important ecological drivers, and hydrology is also a common ecological, flood control and navigation system indicator. Hydrologic characteristics change dramatically from one end of the Upper Mississippi River System to the other, and hydraulic characteristics also differ spatially across the river channels and floodplain in response to dams, levees and diversions. Low flow surface water spatial change in response to navigation and flood control has been well known for many years, but little information was available on the spatial distribution of frequent floods. The flow frequency data presented here were developed to better estimate contemporary floods after historic flooding in 1993. Flood stage estimates are enhanced in GIS to help quantify and map potential floodplain inundation for more than 1000 river miles on the Upper Mississippi and Illinois Rivers. Potential flood inundation is mapped for the 50% to 0.2% annual exceedance probability flood stage (i.e. 2‐ to 500‐year expected recurrence interval flood) and also for alternative floodplain management scenarios within the existing flood protection infrastructure. Our analysis documents: (i) impoundment effects, (ii) a hydrologic gradient within the navigation pools that creates repeating patterns of riverine, backwater and impounded aquatic habitat conditions, (iii) potential floodplain inundation patterns for over 2 million acres and (iv) several integrated floodplain management scenarios. Extreme flood events are more common in recent decades, and they are expected to continue to occur at greater frequency in response to climate change. Floodplain managers can use the results presented here to help optimize land management and flood damage reduction on the Upper Mississippi River System. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.

Probabilistic flood inundation mapping of ungauged rivers: Linking GIS techniques and frequency analysis

This study presents an exhaustive methodology of floodplain mapping at ungauged rivers. To present our methodology, we selected the Halilrud basin and Jiroft city in southeastern Iran as an example of hazardous regions. To estimate flood quantiles in different return periods at ungauged reaches, we used regional flood frequency analysis. By using the well-known L-moments approach and related criteria, a homogeneous region was formed and the 3-parameter Log normal distribution was identified as the robust regional frequency distribution. The hydro-geomorphic characteristics and the land use properties of the catchments were then extracted using RS&GIS techniques to establish multivariate regional regression models between hydro-geomorphic characteristics and flood quantiles. After delineation of the catchments for the ungauged reaches, flood quantiles as an important factor in flood inundation at outlets of these reaches with different probabilities were estimated using the regional regression models. To delineate flood hazard maps and to enhance the accuracy of the hydraulic modeling, we applied satellite stereoscope images of Cartosat-1 along with the Rational Polynomial Coefficients to extract a high resolution DTM and detailed parameterization of the channel required by 1D hydraulic model HEC-RAS. The GIS-based HEC-Geo RAS pre- and post-processor were also used for careful optimization of the geometry features for real visualization of the flood prone areas. Information of some historical flood events was also used to evaluate the hydraulic model performance in predicting flood inundations. Finally, vulnerable areas were crossed with extracted land use mapping from IRS-P6 satellite images to differentiate the critical infrastructures and the valuable land use classes affected by floods in different return periods.

Delineation of groundwater potential zone in Chhatna Block, Bankura District, West Bengal, India using remote sensing and GIS techniques

Groundwater is one of the most valuable natural resources, which is an immensely important and dependable source of water supply in all climatic regions over the world. Groundwater is in demand in areas where surface water supply is inadequate and nonsexist in the Chhatna Block, Bankura district and is located on the eastern slope of Chotonagpur Plateau, which is mapped on 73 I/15, 73 I/16 and 73 M/3, and falls between latitude 23°10′–23°30′N and longitude 86°47′–87°02′E. It represents plain land and gentle slope, which is responsible for infiltration and groundwater recharge. The groundwater in this region is confined within the fracture zones and weathered residuum. The present investigation is, therefore, undertaken to delineate potential zones for groundwater development with the help of a remote-sensing study. IRS–LISS-III data along with other data sets, e.g., existing toposheets and field observation data, have been utilized to extract information on the hydrogeomorphic features which include valley fills, buried pediment moderate, buried pediment shallow and structural hills, lineament density contour and slope map of this hard rock terrain. The target of this study is to delineate the groundwater potential zones in Chhatna block, Bankura District, West Bengal. Satellite imagery, along with other data sets, has been utilized to extract information on the groundwater controlling features of this study area. Three features (hydrogeomorphology, slope, and lineaments) that influence groundwater occurrences were analyzed and integrated. All the information layers have been integrated through GIS analysis and the groundwater potential zones have been delineated. The weighted index overlay method has been followed to delineate groundwater potential zones. The results indicate that good to excellent groundwater potential zones are available in almost the entire block. The results show that there is good agreement between the predicted groundwater potential map and the existing groundwater borehole databases. The area is characterized by hard rock terrain—still due to the presence of planation surface along valley fills; it became the prospective zone. The area has been categorized into four distinct zones: excellent, good, fair and poor. Excellent groundwater potential zones constitute 30–35 % of the total block area; good groundwater potential zones occupy a majority of the block, covering approximately 55–60 % and the fair potential zones occupy about 10–15 % of the total block. Poor potential zones occupy a very insignificant portion (less than 1 %).

Exploring the influences of multiscale environmental factors on the American dipper Cinclus mexicanus

Aquatic organisms respond to the physical environmental across a range of spatial scales, but the precise nature of these relationships is often unclear. In order to forecast ecosystem responses to environmental alterations in watersheds, understanding how processes at different spatial scales affect the ecology of organisms is critical. We used the semi‐aquatic American dipper Cinclus mexicanus to evaluate how large‐scale, regional variables (e.g. climate); landscape‐scale, watershed variables (e.g. land use/cover); and local, reach‐level variables (e.g. stream geomorphology) influenced various descriptors of American dipper ecology, including productivity, stable nitrogen isotopes (δ15N), and individual condition. From 2005 to 2008, we collected data at 26 American dipper territories distributed throughout a 25 000 km2 region within Idaho, USA. We then used structural equation modeling to consider potential direct and indirect relationships among scalar factors on measures of American dipper ecology. We found that complex interactions among factors at all three spatial scales influenced dipper productivity, but that δ15N and individual condition were explained by characteristics at the regional and landscape scales only. In particular, model results demonstrate that precipitation was associated with notable variation in multiple dipper responses. Local factors, influencing only dipper productivity, were dominated by hydrogeomorphic characteristics. Our study underscores the simultaneous independent and synergistic roles of environmental factors across spatial scales on American dippers, and offers evidence that pathways influencing aquatic biota may not always conform to hierarchical spatial relationships in watersheds.

Multiscale landscape and wetland drivers of lake total phosphorus and water color

We quantified relationships between local wetland cover in the riparian lake buffer and lake total phosphorus (TP) and water color (color) using multilevel mixed‐effects models that also incorporate landscape features such as hydrogeomorphology and land use at broad regional scales to determine the following: (1) Within regions, are local wetland relationships with TP and color affected by interactions with local land use or hydrogeomorphic variables? (2) Across regions, are local wetland relationships with TP and color different? And if so, (3) Are differences in local wetland relationships with TP and color a result of cross‐scale interactions? We answered these questions by analyzing TP, color, and multiscaled landscape data for 1790 north temperate lakes. Local wetland‐TP and wetland‐color relationships were not affected by local‐scale interactions. However, these same relationships were different when compared across regions, and these differences were related to cross‐scale interactions with regional landscape characteristics. For example, regional human land use affected local wetland‐TP relationships such that in regions with high amounts of agriculture, local wetlands were associated with decreased lake TP. However, in regions with low amounts of agriculture, local wetlands were associated with increased lake TP. In contrast, regional hydrogeomorphic characteristics influenced local wetland‐color relationships such that in regions with high groundwater contribution, the strength of local wetland relationships were weak. Regional landscape setting influences local wetland relationships with TP and color through cross‐scale interactions, and lake TP and color are controlled by both local‐scale wetland extent and regional‐scale landscape variables.

Comparing Hydrogeomorphic Approaches to Lake Classification

A classification system is often used to reduce the number of different ecosystem types that governmental agencies are charged with monitoring and managing. We compare the ability of several different hydrogeomorphic (HGM)-based classifications to group lakes for water chemistry/clarity. We ask: (1) Which approach to lake classification is most successful at classifying lakes for similar water chemistry/clarity? (2) Which HGM features are most strongly related to the lake classes? and, (3) Can a single classification successfully classify lakes for all of the water chemistry/clarity variables examined? We use univariate and multivariate classification and regression tree (CART and MvCART) analysis of HGM features to classify alkalinity, water color, Secchi, total nitrogen, total phosphorus, and chlorophyll a from 151 minimally disturbed lakes in Michigan USA. We developed two MvCART models overall and two CART models for each water chemistry/clarity variable, in each case comparing: local HGM characteristics alone and local HGM characteristics combined with regionalizations and landscape position. The combined CART models had the highest strength of evidence (ω(i) range 0.92-1.00) and maximized within class homogeneity (ICC range 36-66%) for all water chemistry/clarity variables except water color and chlorophyll a. Because the most successful single classification was on average 20% less successful in classifying other water chemistry/clarity variables, we found that no single classification captures variability for all lake responses tested. Therefore, we suggest that the most successful classification (1) is specific to individual response variables, and (2) incorporates information from multiple spatial scales (regionalization and local HGM variables).

Estuary hydrogeomorphology affects carbon sources supporting aquatic consumers within and among ecological guilds

The relative importance of carbon sources supporting aquatic food webs within and among estuaries may be influenced by factors that affect relative availability of autotrophic carbon sources, as well as movement of individuals among marine, estuarine and freshwater zones. We used stable isotopes of carbon and nitrogen to examine (1) the relative importance of carbon sources supporting estuarine consumers among estuaries with different hydrogeomorphic characteristics, (2) stable isotope signatures of consumer ecological guilds defined by dependence on estuarine habitats and residence time, and (3) if patterns in stable isotope signatures of ecological guilds repeat across estuaries with distinct hydrogeomorphological features. At the assemblage level, consumer carbon isotope signatures reflected the consumption of locally abundant primary production sources and differed across estuary types (choked lagoon, coastal river). Consumer ecological guilds differed in δ13C within sites, and the same trend repeated across sites but with differing magnitudes. This variation is attributed to movement and residence patterns in addition to differences in the relative abundances of autotrophic sources across sites. Although within-estuary variation in consumer resource use is to be expected, estuarine food webs may be broadly classified according to landscape-scale hydrogeomorphic factors that allow an initial prediction of the relative importance of carbon sources to secondary production. Predictions may be refined at the species level using knowledge of habitat use and residence time. Such predictions are useful as a starting point for poorly studied regions such as ours in southern Brazil, as well as for global-scale analyses of patterns in estuarine food webs.

Flood seasonality‐based regionalization methods: a data‐based comparison

AbstractImproving techniques of flood frequency estimation at ungauged catchments is one of the major challenges for hydrologists, especially in arid and semi‐arid regions with insufficient information. Recently, popularity of flood seasonality‐based descriptors has increased among hydrologists for delineating of hydrologically homogenous regions.This study presents a data‐based comparison of three well‐known flood seasonality‐based regionalization methods in Halilrud basin in southeastern Iran. A Jack‐knife procedure is used to assess the performance of the methods for flood quantile estimation at ungauged sites. The results of these three seasonality‐based methods are compared to those results obtained from two alternative methods: a traditional regionalization method based on catchment's hydrogeomorphic characteristics similarity and a scenario that uses all available information without subdividing area.The results indicate that although peak over threshold (POT) approach which uses all flood events during year leads to better performance than other methods, but applying POT data series in a specific season (critical season) based on POT‐CS approach leads to better homogenous region and improves flood quantile estimation at ungauged sites. Copyright © 2011 John Wiley & Sons, Ltd.

Hydrogeomorphic features mediate the effects of land use/cover on reservoir productivity and food webs

Although effects of land use/cover on nutrient concentrations in aquatic systems are well known, half or more of the variation in nutrient concentration remains unexplained by land use/cover alone. Hydrogeomorphic (HGM) landscape features can explain much remaining variation and influence food web interactions. To explore complex linkages among land use/cover, HGM features, reservoir productivity, and food webs, we sampled 11 Ohio reservoirs, ranging broadly in agricultural catchment land use/cover, for 3 years. We hypothesized that HGM features mediate the bottom‐up effects of land use/cover on reservoir productivity, chlorophyll a, zooplankton, and recruitment of gizzard shad, an omnivorous fish species common throughout southeastern U.S. reservoirs and capable of exerting strong effects on food web and nutrient dynamics. We tested specific hypotheses using a model selection approach. Percent variation explained was highest for total nitrogen (R2 = 0.92), moderately high for total phosphorus, chlorophyll a, and rotifer biomass (R2 = 0.57 to 0.67), relatively low for crustacean zooplankton biomass and larval gizzard shad hatch abundance (R2 = 0.43 and 0.42), and high for larval gizzard shad survivor abundance (R2 = 0.79). The trophic status models included agricultural land use/cover and an HGM predictor, whereas the zooplankton models had few HGM predictors. The larval gizzard shad models had the highest complexity, including more than one HGM feature and food web components. We demonstrate the importance of integrating land use/cover, HGM features, and food web interactions to investigate critical interactions and feedbacks among physical, chemical, and biological components of linked land‐water ecosystems.

Stream fish occurrence in response to impervious cover, historic land use, and hydrogeomorphic factors

We evaluated competing models explaining the occurrence of five stream fishes in an urbanizing watershed to determine the relative importance of (a) impervious surface and other indicators of current land use, (b) historic land use (e.g., agriculture, impoundments), and (c) hydrogeomorphic characteristics (e.g., stream size, elevation, geology). For four of five species, the best-supported models were those that included both current effective impervious cover and historic land use predictor variables, although models with only effective impervious cover were equally well supported for two of those species. For the best-supported models for three species, occurrence probability was predicted to approach zero at levels of development equivalent to about 2%–4% effective impervious cover in the surrounding region. Data were drawn from 357 fish collections made in the Etowah River basin, Georgia, USA, between 1998 and 2003 and analyzed using hierarchical logistic regression accounting for imperfect species detection. This is the first study we know of to examine the response of individual fish species to both increasing impervious cover and historic land use. Such individual species assessments will be increasingly necessary to guide policies for managing urban effects and preventing extirpations of sensitive species.

Coping with hydrogeomorphic variations in a prairie river: resiliency in young‐of‐the‐year fishes

AbstractYoung‐of‐the‐year (YOY) fish in sand‐bed rivers of grassland ecoregions frequently encounter dynamic habitat conditions produced by highly variable flow and resulting changes in geomorphic complexity of the river. How these vulnerable life history stages cope with changes in habitat condition and location is largely unknown. Therefore, we examined biodiversity and abundance of YOY fish (larvae and juveniles) at two spatiotemporal scales in response to dynamic flow conditions in the Kansas River. During the summer of 2004, we collected and identified 13 745 YOY fish from various moderate to zero‐flow habitats. Patterns of community structure through time were compared with the river's hydrogeomorphic characteristics, as determined by aerial photographs and measurements of instream flow rate and other water quality characteristics.Our initial hypothesis was that species richness and total YOY abundance would be maximized in larger and longer‐lived slackwater habitats. In contrast, our data suggest that dominant fishes in these highly dynamic ecosystems have adapted to hydrological variations with a more generalist lifestyle by either: (i) temporarily using higher flow habitats (except possibly the thalweg) to cope with intermittent loss of prime habitat; or (ii) extending spawning through favourable and demanding conditions. In contrast to current theories, our results suggest that conditions for YOY success are optimized in dynamic prairie rivers during the intermediate flows that maximize habitat heterogeneity and availability. Copyright © 2007 John Wiley & Sons, Ltd.

Pattern and Process in Northern Rocky Mountain Headwaters: Ecological Linkages in the Headwaters of the Crown of the Continent1

Abstract: The Crown of the Continent is one of the premiere ecosystems in North America containing Waterton‐Glacier International Peace Park, the Bob Marshall‐Great Bear‐Scapegoat Wilderness Complex in Montana, various Provincial Parks in British Columbia and Alberta, several national and state forest lands in the USA, and Crown Lands in Canada. The region is also the headwater source for three of the continent’s great rivers: Columbia, Missouri and Saskatchewan that flow to the Pacific, Atlantic and Arctic Oceans, respectively. Headwaters originate in high elevation alpine environs characterized by high snow accumulations in winter and rainstorms in summer. Most headwaters of the region contain high quality waters with few ions in solution and extremely low nutrient concentrations. Alpine streams have few species of aquatic organisms; however, they often possess rare species and have hydrogeomorphic features that make them vulnerable to climatic change. Subalpine and valley bottom streams of the Crown of the Continent Ecosystem (CCE) flow through well forested watersheds. Along the elevation gradient, the streams and rivers of the CCE flow through series of confining and nonconfining valleys resulting in distinct canyon and floodplain reaches. The alluvial floodplains are characterized by high species diversity and bioproduction maintained by the hydrologic linkages of habitats. The streams and rivers of the CCE have low nutrient concentrations, but may be significantly affected by wildfire, various resource extraction activities, such as logging or mining and exurban encroachment. Wildfire has been shown to increase nutrient loading in streams, both during a fire and then following the fire for as much as 5 years. Logging practices increase nutrient loading and the algal productivity of stream periphyton. Logging and associated roads are also known to increase sediment transport into Crown of the Continent streams directly affecting spawning success of native trout. The CCE is one of the fastest growing regions in the USA because of the many recreational amenities of the region. And, while the region has many remarkably pristine headwater streams and receiving rivers, there are many pending threats to water quality and quantity. One of the most urgent threats comes from the coal and gas fields in the northern part of the Crown of the Continent, where coal deposits are proposed for mountain‐top removal and open‐pit mining operations. This will have significant effects on the waters of the region, its native plants and animals and quality of life of the people.

Effects of Channel Restoration on Water Velocity, Transient Storage, and Nutrient Uptake in a Channelized Stream

Channel design is an important component of stream restoration, but little is known of the interplay between hydrogeomorphic features and ecosystem processes within designed channels. Water velocity, transient storage, and nutrient uptake were measured in channelized (prerestoration) and naturalized (postrestoration) reaches of a 1-km segment of Wilson Creek (KY) to assess the effects of restoration on mechanisms of nutrient retention. Stream restoration decreased flow velocity and reduced the downstream transport of nutrients. Median travel time was 50% greater in the restored channel due to lower reach-scale water velocity and the longer length of the meandering channel. Transient storage and the influence of transient storage on travel time were largely unaffected except in segments where backwater areas were created. First-order uptake rate coefficients for N and P were 30- and 3-fold higher (respectively) within the restored channel relative to its channelized state. Changes in uptake velocities were comparatively small, suggesting that restoration had little effect on biochemical demand. Results from this study suggest that channel naturalization enhances nutrient uptake by slowing water velocity. Solute injection experiments revealed differences in the functional properties of channelized, restored, and reference streams and provided a means for quantifying benefits associated with restoration of ecosystem services.

Spatial pattern of water controlled wetland communities on the Sanjiang Floodplain, Northeast China

The study site is the Honghe National Nature Reserve, a Ramsar designated site on the Sanjiang Plain in Northeast China. We present results regarding the spatial pattern and structure of plant communities in these most important natural but continually diminishing freshwater wetlands of China to help promote both protection and restoration. By investigating three ecological levels (landscape, ecosystem and community), this paper quantifies the characteristics of spatial pattern with the aim to identify specific ecological correlations with different hydro-geomorphic features. Specifically, the research involves hierarchical mapping of vegetation types by use of remote sensed data, and the coupling of landscape indices with fluvial topographic zones that have been deduced by GIS from DEM. Statistics from historical survey data are also used to measure the degradation of marshes as well as the historical change of the hydrological regime. We found that dominant is the Calamagrostis angustifolia - Carex spp. community type, a wet meadow and marsh complex within the prevailing landscape mosaic of shrubland and meadow. The results suggest that the sites’ hydro-geomorphic character has decisive influence on plant community structure and composition. There is only limited direct human interference in the sites and, as a consequence, the spatial pattern of vegetation distribution is natural. However, changes to the hydrological regime as the result of extensive irrigation activity in the surrounding area has led to rapid degradation of marsh wetlands within the sites, which threatens the ecological status in this storehouse of “Natural Genes” in the reserve.

Aspects of the hydro-geomorphology of Illawarra streams: implications for planning and design of urbanising landscapes

Streams in the Illawarra region of New South Wales have dynamic hydro-geomorphic characteristics that are atypical of the broader Sydney Basin. These characteristics include: small, steep catchments subject to intense rainfall events that are capable of generating flood discharges comparable to world maximum rainfall-runoff events; high energy escarpment channels that debouch bedload sediment fans and bars onto a low energy coastal plain; well developed macro-channels that convey high magnitude flows through the middle catchment zone; rapid and prolific vegetation growth and downstream decreasing channel capacities within the lower catchment depositional zone. This paper outlines local examples of the dynamic interactions between flood hydrology, hydraulics and geomorphology of Illawarra streams. Appropriate planning to account for their dynamic nature is particularly important in the context of catchment management for Lake Illawarra as some 10,000 - 20,000 new dwellings are planned for future development in areas currently dominated by rural land uses.

MARSH DEVELOPMENT AT RESTORATION SITES ON THE WHITE MOUNTAIN APACHE RESERVATION, ARIZONA1

ABSTRACT: To prioritize sites for riparian restoration, resource managers need to understand how recovery processes vary within landscapes. Complex relationships between watershed conditions and riparian development make it difficult to predict the outcomes of restoration treatments in the semiarid Southwest. Large floods in 1993 scoured riparian areas in the Carrizo watershed on the White Mountain Apache Reservation in east‐central Arizona. We evaluated recovery at three of these sites using repeated photographs and measurements of channel cross sections and stream‐side vegetation along permanent transects. The sites were mapped as lying on the same soil type, had similar streamside vegetative communities, and were similarly treated through livestock exclusion and supplemental seeding. However, the sites and individual reaches within the sites followed strikingly different development paths. Dramatic recovery occurred at a perennial reach where cover of emergent wetland plants increased from 4.7 percent (standard error = 0.8 percent) in October 1995 to 55.5 percent (standard error = 2.7 percent) in September 2001. At several other reaches, geologic and hydro geomorphic characteristics of the sites limited inputs of fine sediment or surface water, resulting in modest or negligible increases in emergent cover. Recovery efforts for highly valued marshlands in this region should prioritize perennial reaches in low gradient valleys where salty sediments are abundant.

Geomorphic Influences on Large Wood Dam Loadings, Particulate Organic Matter and Dissolved Organic Carbon in an Old-Growth Northern Hardwood Watershed

ABSTRACT We quantified large wood loadings and seasonal concentrations of particulate organic matter (POM) and dissolved organic carbon (DOC) in three different geomorphic zones (each with unique hydrogeomorphic characteristics) of a pristine, old-growth northern hardwood watershed. The highest large wood dam loadings were in the high-gradient, bedrock controlled geomorphic type characterized by a cascading and step pool stream channel (19 dams km−1), while the lowest loadings were in the low-gradient, bedrock controlled geomorphic type (5 dams km−1). POM and DOC concentrations varied seasonally and were generally significantly correlated with discharge before and following leaf-off (mid to late September). The highest concentrations of POM were in the wetland dominated, low-gradient, bedrock controlled geomorphic type (3.74 mg L−1), while the highest DOC concentrations were in the high gradient, bedrock controlled geomorphic type following leaf-off (14.55 mg L−1). Our results suggest that organic matter dynamics vary both spatially and temporally in a watershed in response to changes in hydrogeomorphic conditions, and the processing of different types of organic matter may be intimately linked, resulting in the significant differences in how organic matter is processed and utilized in stream ecosystems flowing through forested watersheds.

Long-term changes of submerged macrophytes in the Lower Danube Wetland System

Transition towards hypertrophy has affected biodiversity and productivity of most aquatic and wetland systems in the Lower Danube Wetland System (LDWS) over the last two decades. The aquatic macrophytes have been deeply involved in ecosystem reorganization in these circumstances. Representative shallow lakes and channels located in the river floodplain and delta were studied in this period in terms of space distribution, diversity, species composition, primary production and main hydrogeomorphic features (morphometrical and physico-chemical parameters). Changes in submerged vegetation dynamics along two successive decades after 1980 included diminishing areas of about 50% in the Danube Delta, restructuring primary producers by suppressing aquatic weed in some lakes or parts of lakes and decreasing species richness to few populations with upright and floating growth strategy. Biomass production showed different trends, from severe reduction in some lakes and periods to marked increase in other ones, provided by a changed and simplified species structure, generally dominated by Ceratophyllum demersum L. and Potamogeton species. It was concluded that the eutrophication effects are maintaining, modulated by diverse response mechanisms developed by submerged macrophytes. Finally, the main lessons to be learned for the management of aquatic macrophyte-dominated systems in the framework of redesigning the LDWS structures are emphasized on the basis of a large scale and long-term prospect of the Danube River and Black Sea Basins.

Geomorphic issues associated with environmental flow assessment in alluvial non-tidal rivers

This paper explores the link between flow variability and stream morphology in the context of the geomorphic component of environmental flow assessment. The paper also attempts to bring some methodological order to the contribution by geomorphologists to environmental flow assessment. The geomorphological extension of the natural flow paradigm is the concept of alluvial river attributes. These are basic hydro-geomorphic characteristics of natural streams thought to be necessary for maintaining ecosystem integrity in alluvial rivers. It appears that the more variable is the flow regime, the more variable are these attributes, although observations indicate that many channels conform to basic relationships between overall channel shape and size and two or more groups of flows definable in terms of frequency and magnitude. There is evidence that some Australian streams are in a continual state of adjustment to cyclical changes in flood regime, so they do not adjust to a fixed discharge. Also, most of the classical literature on channel forming processes does not consider the role of boundary roughness and strength in any detail, and it appears that extensive modification of this aspect of many Australian rivers (mainly through desnagging and riparian vegetation clearance) has caused a fundamental shift in their geomorphic character. The first stage of any environmental flow assessment would be to place the significance of flow regulation as an agent of geomorphic change within this wider context. This will provide a realistic perspective on the potential for environmental flows to either maintain or improve channel functioning. In disturbed streams, or streams subject to a highly variable flow regime, the classical geomorphic concepts of bankfull discharge, effective discharge and channel maintenance discharge may not apply in the same way as described for intact and less hydrologically variable North American and European streams. Sediment transport formulae may be used with caution in circumstances where the process is not sediment supply limited – an uncommon situation in many Australian streams.Natural flow regimes are composed of numerous facets, or components, occurring as a complex time series, not discrete, predictable and independent events. Scaled-down flow regimes, or regimes with certain components culled from the regime, should not be expected to produce the same morphology as a natural flow regime. Environmental (regulated) flows will nearly always be simpler and less variable than natural flow regimes, so the resulting geomorphology will probably be less diverse. Many geomorphic problems in regulated rivers cannot be solved simply by flow intervention, and in unregulated rivers, increased water diversions will not necessarily be the main cause of future degradation. In heavily modified rivers, it may be preferable (or necessary) to use environmental flows to enhance the current geomorphic attributes, rather than seeking a return to some previous, or ideal state.