River Research and Applications

The utility of hydrologic indices for describing various aspects of streamflow regimes has resulted in their increased application in riverine research. Consequently, researchers are now confronted with the task of having to choose among a large number of competing hydrologic indices to reduce computational effort and variable redundancy prior to statistical analyses, while still adequately representing the major facets of the flow regime. The present study addresses this concern by providing a comprehensive review of 171 currently available hydrologic indices (including the commonly used Indicators of Hydrologic Alteration) using long‐term flow records from 420 sites from across the continental USA. We highlight patterns of redundancy among these hydrologic indices and provide a number of statistically and ecologically based recommendations for the selection of a reduced set of indices that can simultaneously (1) explain a dominant proportion of statistical variation in the complete set of hydrologic indices and (2) minimize multicollinearity while still adequately representing recognized, critical attributes of the flow regime. In addition, we examine the transferability of hydrologic indices across ‘stream types’ by identifying indices that consistently explain dominant patterns of variance across streams in varying climatic and geologic environments. Together, our results provide a framework from which researchers can identify hydrologic indices that adequately characterize flow regimes in a non‐redundant manner. In combination with ecological knowledge, this framework can guide researchers in the parsimonious selection of hydrologic indices for future hydroecological studies. Copyright © 2003 John Wiley & Sons, Ltd.

Dissolved organic matter (DOM) in aquatic systems originates from a range of sources. Some is allochthonous, transported from the surrounding landscape to the water body, and is derived from and influenced by the geology, land use and hydrology of its origin. Some is created in situ through microbial activity, which may provide an independent source of organic matter, or a recycling mechanism for that which has been transported into the water body. The relative contribution of each source depends upon the location and environmental conditions within and without the water body. Human activity is also a source of DOM, much of which is believed to be labile, which can enter the aquatic system through direct point discharges, diffuse leaching and aerial dispersal. Fluorescence spectroscopy can provide an excellent tool to source DOM fractions, and to monitor and understand DOM transformations in aquatic systems, as much DOM has an intrinsic fluorescence. In particular, recent advances in optical technology, enabling rapid investigation of shorter wavelengths, have enabled more detailed characterization of organic material and its reactions in water. In this article, we review the use of fluorescence spectroscopic techniques to measure the intrinsic fluorescence of organic matter and the application of fluorescent DOM analysis in marine waters, freshwaters and wastewaters. Copyright © 2007 John Wiley & Sons, Ltd.

Việc sử dụng bền vững tài nguyên nước đòi hỏi có hướng dẫn rõ ràng về việc quản lý lượng ô nhiễm lan tỏa từ các nguồn nước vào sông. Nếu không có hướng dẫn thông tin, các quyết định quản lý sẽ ít khả năng mang lại những cải thiện hiệu quả về chi phí cho chất lượng nước sông như yêu cầu của chính sách nước hiện hành. Trong bài viết này, chúng tôi xem xét các bằng chứng có sẵn để đưa ra các hướng dẫn cải thiện về lượng trầm tích mịn vào các con sông dựa trên tác động đến động vật không xương sống lớn (macro‐invertebrates). Mối quan hệ giữa động vật không xương sống lớn và trầm tích mịn được định nghĩa chưa rõ ràng. Các nghiên cứu về tác động của trầm tích mịn lên động vật không xương sống lớn đã được tiến hành ở nhiều quy mô khác nhau, điều này ảnh hưởng đến các phản ứng được biểu hiện và độ tin cậy của các kết quả thu được; các kết quả từ các cuộc điều tra ở quy mô nhỏ hơn có thể không hiện rõ ở quy mô cần thiết để quản lý các dòng sông và ngược lại. Nhiều hiệu ứng đã được xác định của việc tăng cường lượng trầm tích mịn lên động vật không xương sống lớn xảy ra do sự lắng đọng trên đáy sông, nhưng nhiều hướng dẫn quản lý hiện tại dựa trên các mục tiêu trầm tích lơ lửng. Dựa trên cơ sở này, các hướng dẫn hiện có về chất lượng nước cho quản lý trầm tích khó có thể phù hợp. Bản quyền © 2011 John Wiley & Sons, Ltd.

Hydrogeomorphic processes within alluvial river systems create, maintain and degrade riparian habitat. The dynamic interactions between water, sediment, aquatic–terrestrial landforms and biotic elements control the functional processes and biodiversity patterns within the riparian zone and, thus, contribute directly to their ecological integrity and societal value. Numerous researchers from different disciplines publish work on the physical, biological, economic and societal functions of the riparian zone within various physiographic areas. The present paper aims to review the hydrogeomorphic processes of unconfined alluvial channel–floodplain rivers within the temperate zone. These processes and their interactions with the biotic environment provide the basis for understanding the physical as well as the ecological functioning of fluvial hydrosystems. The review focuses mainly on the European context, but major advances in riparian research from other continents are also considered. Rehabilitation and management strategies for the riparian zone are summarized and recommendations for further research conclude this review. Copyright © 2005 John Wiley & Sons, Ltd.

The paper promotes an emerging research area at the interfaces between aquatic ecology, biomechanics and environmental fluid mechanics. This new area,Hydrodynamics of Aquatic Ecosystems, bridges these disciplines together and is defined as a study of flow‐organism interactions at multiple scales with particular focus on relevant transport processes and mutual physical impacts. Being an important part of its mother disciplines,Hydrodynamics of Aquatic Ecosystemsdeals with two key interconnected issues: (i) physical interactions between flow and organisms (e.g. due to an interplay between flow‐induced forces and reaction forces generated by organisms) and (ii) ecologically relevant mass‐transfer‐uptake processes (e.g. due to molecular and turbulent diffusion). Key concepts and tools ofHydrodynamics of Aquatic Ecosystemsare outlined first and then a promising approach that may provide a unifying platform for coupling and integrating ecological, hydrodynamic and biomechanical processes, known as the double‐averaging methodology (DAM), is discussed. Copyright © 2009 John Wiley & Sons, Ltd.

Hydrologic metrics have been used extensively in ecology and hydrology to summarize the characteristics of riverine flow regimes at various temporal scales but there has been limited evaluation of the sources and magnitude of uncertainty involved in their computation. Variation in bias, precision and overall accuracy of these metrics influences the ability to correctly describe flow regimes, detect meaningful differences in hydrologic characteristics through time and space, and define flow‐ecological response relationships. Here, we examine the effects of two primary factors—discharge record length and time period of record—on uncertainty in the estimation of 120 separate hydrologic metrics commonly used by researchers to describe ecologically relevant components of the hydrologic regime. Metric bias rapidly decreased and precision and overall accuracy markedly increased with increasing record length, but tended to stabilize >15 years and did not change substantially >30 years. We found a strong positive relationship between the degree of overlap of discharge record and similarity in hydrologic metrics when based on 15‐ and 30‐year discharge periods calculated within a 36‐year temporal window (1965–2000), although hydrologic metrics calculated for a given stream gauge tended to vary only within a restricted range through time. Our study provides critical guidance for selecting an appropriate record length and temporal period of record given a degree of metric bias and precision deemed acceptable by a researcher. We conclude that: (1) estimation of hydrologic metrics based on at least 15 years of discharge record is suitable for use in hydrologic analyses that aim to detect important spatial variation in hydrologic characteristics; (2) metric estimation should be based on overlapping discharge records contained within a discrete temporal window (ideally >50% overlap among records); and (3) metric uncertainty varies greatly and should be accounted for in future analyses. Copyright © 2009 John Wiley & Sons, Ltd.

Sự tương tác giữa xói mòn và lắng đọng là những đặc điểm cơ bản của các lưu vực sông. Những quá trình này dẫn đến việc cung cấp, giữ lại và vận chuyển trầm tích qua các hệ thống sông. Mặc dù việc cung cấp trầm tích cho các sông là một hiện tượng tự nhiên, nhưng trong những năm gần đây, đã có sự lo ngại gia tăng về việc gia tăng tải lượng trầm tích do các hoạt động nhân tạo. Sự hiện diện của thực vật đại tràn trong các kênh sông có xu hướng tăng cường khả năng giữ lại trầm tích mịn dẫn đến những thay đổi trong thành phần đáy sông. Tuy nhiên, có một mối quan hệ phức tạp giữa thực vật đại tràn và trầm tích mịn: thực vật đại tràn ảnh hưởng đến việc vận chuyển trầm tích mịn và ngược lại, cũng bị ảnh hưởng bởi tải trọng trầm tích. Bài tổng quan này đề cập đến hai tác động tương hỗ này và đặc biệt tóm tắt các bằng chứng có sẵn về tác động của trầm tích mịn đến thực vật đại tràn. Việc gia tăng nồng độ trầm tích mịn dường như có cả tác động trực tiếp và gián tiếp đến cộng đồng thực vật đại tràn, làm thay đổi độ sẵn có ánh sáng, cấu trúc và chất lượng của đáy sông. Bản chất của những tác động này phụ thuộc chủ yếu vào tốc độ lắng đọng và bản chất của vật liệu được lắng đọng. Những thay đổi trong thành phần cộng đồng thực vật đại tràn có thể xảy ra khi vật liệu được lắng đọng có hàm lượng dinh dưỡng cao hơn so với đáy sông tự nhiên. Nhiều sự thay đổi trong thực vật đại tràn xảy ra với lượng trầm tích mịn gia tăng có khả năng giống như những gì xảy ra với sự gia tăng độ sẵn có của các chất dinh dưỡng hòa tan. Nếu những nỗ lực quản lý đầu vào chất dinh dưỡng cho các dòng sông muốn đạt được mục tiêu của chúng, thì điều quan trọng là phải xem xét động lực học và sự chuyển giao dinh dưỡng liên quan đến trầm tích mịn. Bản quyền © 2011 John Wiley & Sons, Ltd.

The importance of hydrologic variability in sustaining natural riverine ecosystems is now well accepted. Over the last 15 years or so, many typologies and assessment tools have been developed to assist ecologists and managers in describing natural flow regimes in quantitative terms. In the course of this recent progress, however, some critical questions have arisen concerning the degree to which generalizations about flow regime characteristics are geographically dependent both within and among regions, and the degree to which flow variability alone captures critical environmental variability. In this paper we address these issues in a hierarchical framework that allows comparative statements about hydrologic variability to be made a multiple spatial scales, from local to global.

First, we examined hydrologic variability among 463 readily available daily streamflow gauges from five continents/countries around the world: Australia, New Zealand, South Africa, Europe, and the United States. Using ordination and clustering techniques, we identified similarities and differences among these gauges. We found that the US gauges exhibited the greatest overall flow variability among a suite of 66 hydrologic indicators, whereas Australian streams showed the greatest influence by interannual variability in flow. Similarities in overall flow regime were greatest between Australia and the US, whereas New Zealand streams were most regionally distinctive. These results support the idea of intercontinental distinction in streamflow variability at a global scale; however, they also point to important similarities in flow characteristics among continents/countries.

Second, within the continental United States, we examined how hydrologic variability changes along river profiles as catchment area increases for five river basins arrayed across a gradient of hydroclimatic variation. Using historical streamflow records that precede river impoundment, we found that small ‘headwater’ streams exhibit the greatest similarity in flow characteristics across the basins, as compared to mid‐sized and larger river reaches, which often diverged among the rivers. These results reveal the importance of more carefully defining the spatial domain of allowable hydrologic extrapolation from individual stream gauges and emphasize the need to stratify within basins when considering hydrologic variability at regional scales.

Third, we used a modeling approach to illustrate how geomorphic setting provides a context for assessing the ecological consequences of flow variation at the local scale of stream reaches. For modeled channels having the same sediment size distribution but with either entrenched or floodplain morphology, we found that the effective regime of bed movement for three hydrologically distinct streams depended as much on geomorphic setting as on flow regime per se. These results emphasize the need to integrate hydrology with geomorphology to characterize ‘disturbance regimes’ at the channel reach scale to allow generation of spatially explicit mapping of flow‐mediated habitat dynamics for entire drainage networks within specific regions.

In sum, if riverine scientists wish to develop a general framework for comparing hydrologic variability across basins, regions, and continents, a hierarchical approach is advised. At very broad scales, intercontinental differences in flow regimes could allow a stratification of basins to identify similar hydroecological settings. Within continents or hydroclimatically similar regions, finer‐scale spatial analysis of flow regime types would further assist in hydrologic stratification, based only on the regionally‐relevant components of flow variability. Finally, within hydrologically homogeneous sub‐regions, geomorphic stratification could be applied to identify stream reaches or segments having similar hydrogeomorphic properties. Copyright © 2006 John Wiley & Sons, Ltd.